Standards, Methods and Issues of DESTRUCTIVE HIGH-POWER MICROWAVE TESTING (PART 2)
Tactical Consequences of Radio Spectrum Out-of-Band Properties
General overview of the Civilian and Military EMC norms
THE FIRST 10 YEARS OF EMC WORK FOR THE
JAS 39 GRIPEN FIGHTER AIRCRAFT CONFERENCES & EXHIBITIONS PAGE 4 • EYE ON… PAGE 6 >>>
Reflections
Welcome to this military applications theme WELCOME TO THIS special issue of
the Electronic Environment magazine, with a military applications theme. This theme brought penembers to several of our authors. EMC EUROPE 2015 took place in a
rainy Dresden in mid-August. The event, which ran parallel to the IEEE International Symposium on Electromagnetic Compatibility, attracted around 800 participants and many renowned exhibitors. In the next issue we will return with a more detailed report from there. DEADLINE FOR ABSTRACTS for the
Electronic Environment Conference has passed, and many very interesting suggestions on lectures have been submitted. Now the extensive work of planning lectures in thematic areas begins. These
areas are in turn divided into topical electronics areas to achieve an effect of a conference program in two dimensions. The biggest news for 2016 is, however, no doubt that the Electronic Environment Conference is this time arranged in parallel with the Nordic region’s largest meeting place for the professional electronics industry, SEE, 2016 at the Kista Expo, Stockholm. These two events running parallel gives an incredibly exciting venue for our electronics areas. The opportunities for interesting meetings for conference participants as well as exhibitors will be great. It will be a dynamic meeting place where you will find new knowledge, new contacts and new business opportunities. A first draft of the conference program will be presented at www.elec-
tronic.nu during the first week of November. THIS SPECIAL ISSUE with the mili-
tary applications theme, has indeed elicited pen-ember to several of our authors. Michel Mardiguian highlights the differences in EMC-operations between the military and civil EMC standards, KG Lövstrand gives us a great retrospect on the development of the JAS 39 Gripen, the first in a new generation of fighter aircrafts that was developed between 1979 and 1981. The government decided in 1982 to start production for the Swedish Air Force. Today JAS 39 Gripen is a very strong player in the global market for modern fighter aircraft. We also present part 2 of the article “Standards, Methods and
Issues of Destructive High-Power Microwave Testing”, as well as an extensive article about tactical communications for ground-based activities which require many colocated communication systems on combat vehicles; “Tactical Consequences of Radio Spectrum Out-of-Band Properties”. Pleasant reading!
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Shielded meeting rooms Turn key shielded and anechoic chambers Shielded rooms for data security Shielding materials for self-assembly: doors, windows, absorbers, ferrites, filters, gaskets and metallized textiles. • Shielded boxes for GSM, DECT and radio testing. • EMC testing services in our own lab. • EMC measurement equipment, amplifiers, antennas etc. Emp-tronic AB – HELSINGBORG Box 13060, SE-250 13 Helsingborg, Sweden, +46 42-23 50 60
Technical Editors: Peter Stenumgaard Miklos Steiner Michel Mardiguian
Advertising: Fredrik Johansson fredrik.johansson@justmedia.se
Our technical editors reach on: info@justmedia.se
Dave Harvett daveharvett@btconnect.com
Publisher: Dan Wallander dan.wallander@justmedia.se
Cover Photo: Thinkstock
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Print: Billes, Mölndal, 2015 Contents may not be reproduced in any form without the prior consent of the authors. While every attempt is made to provide accurate information, neither the publisher nor the authorsaccept any liability for errors or omissions.
Content, Electronic Environment 3.2015 Eng
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EE-Calender
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Eye On: The Ten Commandments For EMC, Part 2
Conferenser and courses
Zoning
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General overview of the Civilian and Military EMC norms Tactical Consequences of Radio Spectrum Out-of-Band Properties
18 The first 10 years of EMC work for the
JAS 39 GRIPEN FIGHTER AIRCRAFT
TECHNICAL EDITORS Peter Stenumgaard
Michel Mardiguian
M.Sc. In Applied Physics and Electrical Engineering, Linköping Institute of Technology, 1988. PhD in Radio Systems Technology, Royal Institute of Technology 2001. Until 1995, he worked as systems engineer at SAAB Military Aircraft with electromagnetic effects on Aircrafts. This included e.g. Lightning, Electromagnetic Pulse (EMP) and High Power Microwaves (HPM). He has been an adjunct professor both at the University of Gävle and at Linköping University. Today is a Research Director at the Swedish Defence Research Agency (FOI). He is specialized on electromagnetic interference on wireless communication systems. He was technical program chair for EMC Europe 2014 International Symposium on Electromagnetic Compatibility. Miklos Steiner Miklos has vocational high school education and training in mechanics and electronics, higher education in telecommunications and electronics, and an extensive experience from service and repair of consumer electronics, electronic design and project management of microprocessor-controlled printers, price labeling machines and dispensers, industrial control systems and installations. Miklos has since 1995 trained a large number of engineers in EMC and is also author of the popular EMC series “Eye On” in the magazine Electronic Environment. For many years, Miklos worked as EMC consultant, with EMC design and EMC testing for many customers. He has also been an instructor and led many EMC courses for electronics engineers, mechanical engineers and installers. Many years of experience in the development of EMC solutions in these missions have given Miklos basis, he credibly able to pass on in advice, courses and articles.
Michel Mardiguian, IEEE Senior Member, graduated electrical engineer BSEE, MSEE, born in Paris, 1941. Started his EMC career in 1974 as the local IBM EMC specialist, having close ties with his US counterparts at IBM/Kingston, USA. From 1976 to 80, he was also the French delegate to the CISPR. Working Grp on computer RFI, participating to what became CISPR 22, the root document for FCC 15-J and European EN55022. In 1980, he joined Don White Consultants (later re-named ICT) in Gainesville, Virginia, becoming Director of Training, then VP Engineering. He developed the market of EMC seminars, teaching himself more than 160 classes in the US and worldwide. Established since 1990 as a private consultant in France, teaching EMI / RFI / ESD classes and working on consulting tasks from EMC design to firefighting. One top involvment has been the EMC of the Channel Tunnel, with his British colleagues of Interference Technology International. He has authored 8 widely sold handbooks, two of them being translated in Japanese and Chinese, plus 2 books co-authored with Don White.
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EE-Calender
CONFERENCES & EXHIBITIONS
ANTENNA SYSTEMS 2015 November 5, Las Vegas, United States
PLASTIC ELECTRONICS October 6-8, Dresden, Germany
EMBEDDED SYSTEMS CONFERENCE November 4–5, Minneapolis, United States
IEEE CONFERENCE ON ENVIRONMENTAL AND ELECTRICAL ENGINEERING (EEEIC 2015) October 6, Rome, Italy ELKOM 2015 October 6–8, Helsinki, Finland IME CHINA 2015 October 28, Shanghai, China EMBEDDED CONFERENCE SCANDINAVIA November 3–4, Stockholm, Sweden
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PRODUCTRONICA November 10–13, Munich, Germany ELMIA SUBCONTRACTOR November 10–13, Jönköping, Sweden ESD DEVICE DESIGN ESSENTIALS November 11, Munich, Germany
EMBEDDED SYSTEMS CONFERENCE November 17–18, São Paulo, Brazil
SCANDINAVIAN ELECTRONICS EVENT April 19–21, 2016, Stockholm, Sweden
52ND ANNUAL AOC INTERNATIONAL SYMPOSIUM December 1, Washington, United States
INTERNATIONAL MICROWAVE SYMPOSIUM 2016 May 22, 2016, San Francisco, United States
ISQED 2016 March 14–16, 2016, Santa Clara, United States IOT SUMMIT March 17–18, 2016, Santa Clara, United States EDI CON CHINA 2016 April 19, 2016, Beijing, China
DVCON EUROPE November 11–12, Munich, Germany ADVANCED ESD CHARACTERIZATION AND TEST METHODS November 13, Munich, Germany
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Electronic Environment 3.2015 Eng
The Eye On Serie What everyone should know about EMC:
THE TEN COMMANDMENTS FOR EMC, PART 2
Zoning
One fundamental concept in EMC design is zoning. Zoning is easy to understand. It is used in the most varied contexts and situations. Situations covering everything from old communist dictatorships, such as for example the former East Germany (DDR), to city planners and the European Union. Zones are used in order to achieve various properties in demarcated geographic areas, or within volumes. Zoning with application in electronic engineering are also known as the Controlled Electromagnetic Topology. ZONING First, some definitions: EMC = Electromagnetic Compatibility, refers to a device’s ability to function satisfactorily in its intended electromagnetic environment without introducing unwanted EM interference to this environment. Electromagnetic environment = The sum of all electromagnetic phenomena which exist in a given volume. Electromagnetic environment zone = Volume, limited by a closed surface (real or imaginary), with a specific electromagnetic environment. The electromagnetic environment in one zone differ in some respect from adjacent zones. Zoning is a design tool used to achieve balanced EMC solutions. Zones, zoning and zone boundaries are described and illustrated with simple geometric figures (see Figures 1 and 2). 
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Coupling paths and coupling mechanisms are easily identified, as all coupling takes place through the zone boundary. Disturbance can be defined as unintentional energy leakage, from a source to a victim creating unwanted reactions, interference. Disturbance often links via parallel paths. There are three main coupling types of paths: field coupling (far field), cross talk (near field) and conducted coupling. The disturbing signal often change character and transforms from one type of path to another with multitude of combination possibilities in the chain. The boundary of a zone shall provide a reduction of the coupling for one or several electromagnetic phenomena and can be implemented in several ways (see Figure 3). 
Figure 3. Zone boundary represents coupling reduction. Coupling reduction may be treated as a generic shield, i. e. a measure that reduces coupling. The measures can be: • Insulation (for example by a transformer). • Separation by distance (field decreases with increasing distance). • Depolarization (for example two coils which lie in parallel couple more than those which lie perpendicular to each other). • Proximity to ground conductors, ground nets, ground planes. • More or less covering metal enclosure, a shield, (see the next article in the series). Filter (work only for wires and cables).
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To maintain the integrity of a zone boundary requires often several supplementary and simultaneous measures dealing with both conducted disturbance and EM-field disturbance. To reduce EM-field coupled disturbance different forms of shields are often used. To mitigate conducted interferences: use filters, surge protectors, optical couplers or transformers. The best way to deal with conducted coupling is by the use of fiber optics. A optical fiber (and all non-conducting material) may penetrate a shield (a zone boundary) without any measures! A filter or transformer must be located in the zone boundary (usually a shield) to be effective. A filter located on the middle of a cable, or a filter without a shield is often ineffective – and the other way around: a single conductor that passes unfiltered thru a shield can destroy the integrity of the zone boundary.
Figure 1. Zoning, Example 1.
One practical application of the zoning concept on a printed circuit board (PCB) is shown in Figure 4: Zone 3: Components with the highest operating frequencies are located at the furthest distance from the connectors. Zone 1: I/O circuits are placed next to the connectors. Zone 2: Circuits working at moderate operating frequencies are located between Zone 1 and Zone 3. The main zone border to the outer zone (Zone 0) is drawn in the middle of the filter array. All connecting wires must be filtered and, in applicable cases, protected against over-voltages. Connecting wires can be divided into additional zones depending of the mutual EM-susceptibility and EM-emission characteristics they have.
Figure 2. Zoning, Example 2.
Miklos Steiner miklos@justmedia.se
Figure 3. Zone boundary represents the coupling reduction.
Figure 4. Zoning for a circuit board.
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General overview of the Civilian and Military EMC norms (Rationale, Units/Limits, Test instrumentation and practical Test Set-ups) PREAMBLE As briefly described in our introductory Article N°1 (Issue #2-2015 of EE Magazine), ElectroMagnetic Compatibility is both a functional neccessity – equipments must operate in their intended environment without being disturbed nor causing disturbances to other devices- and a society requirement: interfering with radio/TV broadcast, radio-communications and other RF services is illegal and punishable by laws. Since consumers cannot be easily prosecuted as guilty for using an equipment that is causing interference, the most efficient way of controlling this EMC situation is to apply stringent limits to manufacturers, such as the products they put on market will "never" (exceptional situations accounted) cause interference. This latter aspect has been the driving force for all the civilian RFI regulations worldwide, since the 1950-60 era. Similarly, non-interference is a crtitical concern for military systems, as well as civilian aeronautics & automobiles, because of the severe issues at stake, like mission failure and flight or driving safety if a radio-communication or navigation device is jammed. All the same, it would be an unmanageable mess if too fragile (EMCwise) equipments were put on the market, causing a monumental number of litigations between unaware consumers and vendors / manufacturers, or cancellations of contracts in the military trade. Therefore, over the years, national and international bodies have devised complete series of emission and susceptibility EMC tests. The same was made in military domain by the various Departments of Defense. The fundamental difference is that Civilian Regulations are legally inforced, while compliance to Mil. Standards is a matter of contract fulfillment. In these Regulations & Standards, each one of the 4 facets of EMC domain (CE, RE, CS,RS) is covered by specific series of tests. Our twelve articles series is intended to be very practical, aimed for non-specialists and not heavy on theory. Yet, there are some basic definitions that must be covered right from the beginning, that will ease the understanding of the whole series. They will be addressed now.
GLOSSARY OF ESSENTIAL TERMS AND SYMBOLS BCI: Bulk Current Injection CE, CS, RE, RS: Conducted Emission, Susceptibility, Radiated Emission, Susceptibility DM , CM: Differential Mode (wire-to-wire), Common Mode (wires vs ground) currents or voltages CW: Continuous Wave (most generally sine wave, like a RF carrier) EUT: Equipment Under Test BB,NB: BroadBand, Narrow Band : when only one (NB) or many harmonics (BB) are seen by the receiver (N)EMP: (Nuclear ) Electro Magnetic Pulse VHF, UHF, SHF: Very High (30-300MHz), Ultra High (300-3000MHz) or Super High (3-30GHz) Frequencies λ : Wavelength. In air : λ (m) = 300 /F(MHz) ω : Angular frequency = 2 π F
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1. PRACTICAL EMC UNITS Traditionnally, voltage, current and fields are expressed in Volts, Amperes, Volt/meter (E-field) or Amp/meter (H-field). However, in EMC when dealing with sensitive receivers or with Emissions testing, these standard units are much too large. So submultiples are used instead, the most common ones being: MicroVolt (µV), Micro-Amp (µA), MicroVolt/m (µV/m), Micro-Amp/m (µA/m). Example: a good FM receiver tuned on a given station has a typical sensitivity of 0.5 to 1µV on its RF input (antenna socket). Given approximately 0.1Vper V/m for its rod antenna field conversion, the minimum discernable field by this radio set is: 1µV / 0.1=10µV/m. 2. WHY DECIBELS? The Decibel is widely used in EMC community for many reasons: - Specifications levels are most often imposed in dB - EMC hardware (filters, shields etc ..) performances are characterized in dB - Most measuring instruments are scaled in dB But why is this so ? Simply because an EMI situation is often facing a huge dynamic range: for instance a victim circuit having a sensitivity in the µV or mV range may be confronted with strong fields or a power transients having amplitudes of kV. This makes 6 to 9 orders of magnitude to the problem. A logarithmic scaling is much more convenient than a linear one in such cases. Also, the beauty of dBs is that, thanks to the properties of logarithms, all multiplications become additions and all divisions become substractions. By definition, the ratio of two powers is expressed by: dB= 10 Log (P1 /P2) where P1: power in Watts (or mW) of measured or computed phenomena P2: reference power in Watts (or mW) Power is not commonly used in EMC parlance, where amplitudes are more the rule. However, power is mentioned in RF applications where power amplifiers or Radio transmitters are used. The ratio of two amplitudes (Voltages, currents, E field or H field) is expressed by: dB= 20 Log10 (A1 /A 2) where A1: amplitude of measured or computed phenomena A2: reference amplitude
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AMPLITUDE RATIO
POWER RATIO
CORRESPONDING DB
2
4
+6
3.15
10
+10
10
100
+20
100
10 4
+40
1000
10 6
+60
0.5
0.25
-6
0.31
0.1
-10
0.1
0.01
-20
Table 1. Broad recap. of the essential Amplitude and Power ratios, and their dB equivalents.
Fig.1 Examples of some time-to-frequency representations.
But there is more to this. The Decibel is not just a dimensionless figure used for gain or attenuation. In EMC, we associate the dB to a unit, in order to express an amplitude. This way, voltages in µV can be also expressed in dB above 1 µV which writes dBµV, currents in dBµA and so forth.
Therefore, in many cases where signals are known by their time waveform, the EMC specialist will translate them in frequency domain, using Fourier conversion.  4. SUSCEPTIBILITY OR IMMUNITY? Although one term or the other are often used indistinctly, they are not synonymous. When testing the vulnerability of an equipment to CW or transients, the susceptibility threshold is the test level where the equipment is failing. Thus, a Susceptibility test is in fact a checking that the equipment is immune (not disturbed) for the prescribed level. Having successfully passed the test does not tell us what is our actual susceptibility level. A prudent practice during development or pre-qualification testing is to increase the conducted or radiated stimulus up to reach EUT malfunction (if it happens). Then, and only then can we know our EMC margin.
Examples: 1µV = 0dBµV 100µV = 40dBµV 200µA = 2 x 100 µA = ( 6dB + 40dB) above 1µA, that writes 46dBµA A 60dBµV RF noise, once passed through a 26dB filter will appear as : 60dBµV - 26dB = 34dBµV Notice that we have substracted dB (dimensionless ratio) to dBµV, therefore the result is dBµV. Speaking in linear terms, we'd have divided a voltage by a number (the filter attenuation), so the result is a voltage. When dealing with power, the Watt is often a too large unit, and the practice in radio, telecom and EMC has been to use the milliWatt, that expresses in dBm: 1mW = 0dBm 10mW= 10dBm 1000mW (or 1 Watt) = 30dBm
Example Assume our RS requirement is: the EUT must not fail for 10V/m. It passes all right; but raising the field amplitude, we find some some frequencies where malfunctions occur for 30V/m. This indicates our EMC margin: Margin = Actual Susceptibilty level / Required immunity = 30V/m / 10V/m = 3, that is a ≈ 10dB margin
Converting dBm into dBµV is possible if we know the impedance where this power is applied. For instance, into 50Ω (the most common impedance in the EMC instrumentation): 0 dBm (or 1mW) into 50Ω corresponds to 107dBµV (or 223mV) 3. WHY FREQUENCY DOMAIN? Except for transient pulses like Power line transients, lightning, ESD etc, EMC phenomena are most often treated in the frequency domain, because:
Practically, a 6-10dB immunity margin is a fair value for protecting the manufacturer against: - measurement uncertainties of the susceptibiliy tests - product aging during its actual life - variations in actual product installations at customers sites - maunfacturing variations due to process changes or components tolerances
- Most EMC Specifications levels are shown on frequency scales or curves - EMC hardware (filters, shields etc ..) performances are characterized in frequency domain - Most measuring instruments and sensors are scaled in frequency But why is this so ? - Many calculations ( field reflections, skin effect, transfer functions, resonances, Crosstalk etc ..) are simpler to perform in frequency domain - Many EMI emission problems or measurements end-up in measuring at some discrete frequencies - For estimating the coupling of a single impulse, simple, quick calculations can be carried using a sinewave at equivalent frequency (i.e. bandwidth) reciprocal to the pulse risetime Fig. 2 Organization tree of Mil-Std 461 ( Rev E or F).
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5. MILITARY EMC REQUIREMENTS Military and Civilian EMC requirements are built on similar principles. But significant differences exist in the severity of the limits and certain arrangements of the test set-ups. The applecore of Mil. EMC tests is the Mil-Standard 461 (currently at rev. F). It is one of the most widely used EMC tri-service standard, applied by Army, Navy and Air Force in the majority of nations. And the time-proven quality of its testing approach has convinced the civilian aircraft industry and the automobile industry to apply very similar EMC requirements. Per the classification principles explained in our former article (Issue 2-2015), the Mil-Std 461 follows the organization tree of Fig.2. One of the many advantages is that it is a fool-proof check list of all the Emission and Susceptibility tests that are normally performed. Yet, all the tests of Fig.2 are not necessarily carried, depending on the application of the equipment, and the service that will use it : Army, Air Force or Navy. Normally, the manufacturer must provide an EMC Control Plan describing how he will handle EMC during the design phasis, and an EMC test plan showing how he will validate his design. Therefore an equipment data sheet declaring the item as "compliant to Mil-Std 461" has little meaning as long as it is not said which tests have been done and at which levels.
CE 101 lim. Current
Bandwidth
100 Hz
CE 102 lim. Voltage
1 kHz
10 kHz
Fig. 4 Mil-Std.461-F CE101/102 limits, for the most severe categories, AC or DC power leads. For < 10kHz limits are given in current. Curve (1) is for < 1kVA, ships & submarines, (2) is for 28Vdc, Navy & Army aircrafts. For unclear reasons, the limit stops at 10MHz (former issues A,B,C had CE limits up to 50MHz, a much wiser frequency range).
EMISSION & SUSCEPTIBILITY TESTS SET-UP An interesting feature of Mil-461 is that practically a same test arrangement is kept for all the series of CE, CES, RE, RS tests, the changes being restricted to antenna types, receiver types and power generators for CW or Pulse excitation. Tests are carried in a shielded room (to avoid disturbances from or to the normal ambient environment). In addition, for avoiding parasitic reflections, the shielded room is made "anechoic" by covering walls and ceiling with RF absorbing materials like ferrite loaded pyramids or tiles, trying to re-create open field conditions. Since the early 2000s, an alternative started to develop for testing susceptibility and emissions in a reverberating chamber. As of today, the anechoic chamber remains the most widely used test site. The EUT is installed on a table with a copper foil top (Fig.3), such as to simulate a typical military mounting, in an aircraft, armored vehicle or ship, where cables are always laid not far from a conductive plane or structure. EUT cables are fixed on 5cm insulating blocks, that are forcing a fixed height above ground for all the tests to come. In practice, the measuring instruments are located in an adjacent chamber, such as the operators and the various peripherals used for the test control (PCs, printers, Video displays) do not interfere with the measurements. 5.1 MIL-STD 461 EMISSION TESTS Mil-461 Emission tests ascertain that equipments installed on a platform, sometimes in large quantities, will not interfere with radio services on the host system (aircraft, vehicle, ship etc ..) nor with other systems sharing the same platform or military site.
Shielded Room Wall LISN
2,4 or 4 Lines
EMI Receiver or Spectr. Analyser
EUT
Ground Plane
H= 50 mm Grounding Straps
Load 50 Ω Power Leads (AC or DC)
Fig 3. Mil Std set-up for emission tests. The EMI Receiver is generally located in an adjacent anteroom.
Fig. 5 Mil-Std 461 RE-102 limits for the most severe categories (Aircraft equipment).
CONDUCTED EMISSIONS LIMITS The EUT must demonstrate that it does not generate on its external cables (essentially power leads, but eventually signal cables in certain requirements) undesirable signals above the limits of Fig 4. Limits are given in voltage (dBµV) picked-up at the measurement port (Artificial Network). In some specific cases, a limit is given in current (dBµA), measured with an EMC current probe. Essential features of the test set-up are shown on Fig.3. Eventually EUT accessories and peripherals that are part of its normal operation are also installed on the test table. The artificial network (official name is LISN) is a very important device that simulates a standard, typical impedance of the power mains, for both CM (Phase + N vs ground) and DM (Phase-to-N) current paths. This prevents that a same EUT, tested in different places or labs could show different results because of different impedances of the local site power mains distribution.  RADIATED EMISSIONS LIMITS The EUT must demonstrate that it does not radiate, by its box and external cables, undesirable RF fields above the limits of Fig.5, showing the worst severity. The artficial network is still there, such as the set-up is about the same as for the CE test, except that a calibrated receiving antenna is installed at 1 meter distance (Fig. 6). The 1m test distance (a difference with the civilian tests that will be described later) is justified by many typical military applications where various equipments are packed closely in the carrier. RE-102 test is a severe constraint, since it
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Fig. 6 RE-102 Radiated Emission test set-up. The rod antenna (right) is used for E-field measurements < 30MHz
could require that at 1m distance the EUT does not radiate more than 15µV/m from 2 to 100MHz, a rather tough goal to reach. If required, a low frequency Magnetic Field emission (RE-101, 30 Hz-100kHz) is also carried with a loop antenna at short distance and various orientations from the EUT 5.2 MIL-STD 461 SUSCEPTIBILITY TESTS Mil-461 Susceptibility tests ascertain that equipment installed on a given platform will operate properly in the most adverse conditions of its applications, in the vicinity of its host system radio/radar transmitters (aircraft, vehicle, ship etc ..) or eventually in hostile environment related to its mission. This includes also immunity to severe transient phenomena like lightning and NEMP. CONDUCTED SUSCEPTIBILITY LIMITS The essential CS tests, in frequency domain (CW) or Transient Pulse (Time domain) are summarized in Fig.7. All these tests are carried with the EUT mounted on the table bench ground plane, with power sup-
plied through the LISNs, like for emission tests. For transient phenomena, the test plan must define what is an acceptable degree of EUT malfunction, if it is for instance a temporary, self-recoverable condition w/o critical consequences. RADIATED SUSCEPTIBILITY LIMITS The principal RS tests are RS103 and RS105. RS-103 is testing the EUT susceptibility to strong RF fields, as can be encountered in aircraft, military vehicle or ship environment. Besides the anechoic chamber, the test requires powerful amplifiers and antennas for creating RF fields values of 20 to 200V/m. In certain conditions, the procurement spec. may demand a special immunity to HIRF (High Intensity Radio Fields) as high as 2,000 or 5,000 V/m for pulsed radars. Normal RS-103 most severe levels for mission-critical equipments Equipment in non metallic aircrafts or Navy equipment above deck:
Airborne equipment in protected areas or Navy equipment under deck:
200V/m, 10kHz up to 40GHz if justified
20 to 50V/m, 10kHz up to 40GHz if justified
The RS-105 is a very specific test simulating a strong radiated pulse, like a NEMP. The set-up is different from all the former Mil-Std ones, with the EUT exposed in a parallel plate or TEM chamber, that is excited by a high voltage pulse to create a 50kV/m field with 3ns rise time and 30ns duration. 6. CIVILIAN EMC REQUIREMENTS EMC requirements for consumer and other civilian products are generally harmonized at International level, such a to avoid un-necessary multiplications of EMC tests when a product manufactured in country "A" is also exported for sales in countries X, Y, Z. These international standards are published under the IEC (International Electrotechnical Commission) authority, and studied/revised by comittees like CISPR (mostly devoted to RF interference) or specific IEC working groups, as for ESD, Lightning, RF immunity etc … The compliance of an equipment to its relevant EMC requirements is attested by a mandatory marking, like CE for conformity to European Norms (EN) or FCC for USA). We will only review the major requirements that a non-specialist should at least be aware of.
Fig. 7 Summary of Mil Std 461CS tests. The BCI tests are a substitution to an actual illumination of the entire system cables by very strong fields. The levels shown are generally those of the most severe category.
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6.1 CIVILIAN EMISSION STANDARDS Civilian emission standards are a guarantee that equipments sold and installed for public use, sometimes in mass quantities, will not interfere with radio services. The most widely applied requirements are those of CISPR 14 (Household appliances) and 22 (data processing equipment,
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soon to be replaced by CISPR 32 covering data processing and also radio, TV and video devices). Very similar limits are required by FCC part15-B "Low Power, unlicensed devices" in USA. These conducted and radiated limits, which apply to all equipment using functional frequencies > 9kHz,are deemed sufficently severe for radio protection in most critical conditions: - close proximity of the RF souce and victim receivers - low attenuation of surrounding walls - RFI sources / victims sharing the same power mains More precisely, two classes were defined to control the above user's installation conditions: Class B: a situation where source and victim can be as close (but no less) as 3 meters, with only one separation wall in-between. They may share the same power distribution branch (Ph and Neutral) with only two power metering devices between them. That is the two equipments belong to different users, but one can be the next door's neighbour in a same building, typical of urban residential situation. This is regarded as a worst case for both Conduction and Radiation couplings. Class A: a situation where source equipment is always located in industrial or large commercial sites, with no private dwellings at less than 30m distance. The facility is powered by a dedicated step-down transformer that is not shared with private houses. Accordingly, two corresponding severity levels are assigned for CE (dBµV) and RE (dBµV/m) limits. Class B limits are the most severe, since this configration carries the highest risk of interference. As a result, an equipment that meets Class B limits can be used anywhere, w/o restrictions. Conversely, Class A limits are 10dB more permissive, but an equipment labelled "Class A" should not be used in residential areas. A note on the equipment case or the user's guide must state clearly that "using it in a residential area could cause interferences, for which the user would be responsible". CONDUCTED EMISSIONS( CIVILIAN) The EUT must demonstrate that it does not generate on its external cables (essentially power leads, but also signal cables in certain applications) undesirable signals above the limits of Fig 8. In contrast to Mil-Std 461 CE test, the limit is imposed up to 30MHz, a safe practice. Essential features of the set-up are shown on Fig.9. The EUT is installed in manner representative of its normal use (table or floor-standing), with eventually its accessories and peripherals. Like for Mil-Std testing, an artficial network (LISN) is inserted on the EUT power leads for both CM (Phase + N vs. ground) and DM (Phase-to-N) current paths. RADIATED EMISSIONS (CIVILIAN) The EUT must demonstrate that it does not radiate, by its box and its external cables undesirable RF fields above the limits of Fig 9. The essential features of the test set-up are shown on Fig.10. Like for the former test, the EUT is installed in manner representative of its normal use (table or floor-standing). The EUT set-up is about the same as for
Fig. 8 Limits for EN 55022 Conducted Emissions. The red line captioned QP (quasi-Peak) is a relaxed limit authorized for those EUT emissions that are BroadBand (spurious noise with low repetiton rate).
the conducted test, including the artficial network. While in theory it is supposed to be done on a free-field open test site, the test is generally performed in a shielded anechoic room. The calibrated antenna is either at a fixed height (for certain tests), but more generally on a mast that allows a variable height scanning to find the worst case emissions. For a same reason, the EUT is on a rotating platform, allowing a 360° scan for searching the maximum radiation pattern . REMARK ABOUT CISPR / FCC RADIATED EMISSIONS LIMITS Most civilian requirements have RE limits that start only at 30MHz. The rationale for not measuring radiated emissions < 30 MHz is two-fold:
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Electronic Environment 3.2015 Eng
onstrate that it does not exhibit failures or malfunctions when exposed to these tests levels. The severity levels, required by the European Directive and corresponding European Norms (EN) of the CENELEC are depending on the class of equipment and its application, varying from ordinary consumer appliance up to industrial or medical equipment, where failures and malfunction could have disastrous consequences.  CONCLUDING REMARKS A few interesting comments can be made when comparing civilian vs Mil-Std EMC limits. While deemed more severe than civilian limits, the Mil-Std limits are: - for CE tests, practically the same as the class A (less severe) civilian ones
Fig. 9 EN 55022 Radiated Emissions limits. Both limits are oficially given at 10m. For practical reasons, they are often measured at 3m, for which a +10dB adjustment is made to the "B" limit. For EUT with clock frequencies >108MHz, limits are extended as follows: 1- 3GHz , Class A: 56dBµV/m / Class B: 50dBµV/m. 3 - 6GHz, Class A: 60dBµV/m / Class B: 54dBµV/m
- for RE tests, they could appear much more severe (limit about 20dB more stringent than CISPR 22 class B, and measured at only 1 meter). But the fact that the cables are laid 5cm above a gnd plane is almost offsetting this difference up to about a few hundred MHz. Because of this, a commercial off-the-shelf item that passes Class B with a fair margin (≥ 6dB) may be expected to meet the most severe RE-102. Of course, this does not exonerate of an actual testing. - for susceptibilty, the Mil-Std tests are generally more severe than the civilian ones, however some IEC tests like Fast Transient Bursts (61000-4-4) or ESD (61-000-4-2) that are very severe in the industrial category have no real equivalent in the Mil-461 arsenal.
Fig. 10 Test set-up for EN 55022 Radiated Emissions in a shielded, anechoic room, with EUT on a turntable. The antenna (wideband,log periodic) is adjusted in height by an automated sliding support (mast visible on the right) that allows horiz. /vertical polarization. Photo by R.Swanberg, courtesy of DLS Electronic Systems. www.dlsemc.com
a) below 30MHz (corresponding wavelength is ≥ 10m), the radiation from the EUT box itself is minimal, due to the small size – typically < meter, of its internal elements. The remaining contributors are the I/O cables, but their length, too, is limited ( ≈ 1.50m) by the set-up, so they will not radiate efficently in such set-up. b) Measuring radiated emissions at 3 or 10m in a limited test space for frequencies < 30MHz complicates the test, because of a mediocre efficiency of available antennas, the near-field Radiation conditions of the test etc … Both a), b) difficulties are solved by the Conducted Emission measurement: the CE limit is assumed severe enough to grant that the equipment will not interfere with nearby victims, not only through conduction on power mains, but also because the corresponding cable currents will not radiate an objectionable field. 6.2 CIVILIAN IMMUNITY STANDARDS The immunity (sometimes quoted as "susceptibility") standards are a guarantee that equipments sold to consumers or industry will not suffer from unexpected failures or malfunctions from their intended electromagnetic environment. These could result in direct or indirect prejudices for the users, eventually with harmful consequences, not to mention a maze of litigations to decide who's fault it was. The conducted and radiated immunity tests of the most common civilian standards (IEC 61.000-4 series) are summarized on Fig.10. The EUT must dem-
Fig. 11 Summary of Civilian Conducted and Radiated Immunity tests.
Now, having reviewed the essentials of Civilian and Military testing, readers may wonder "Now, what to do if we fail the test?". This will be the subject of another article, but before addressing this topic, several forthcoming articles will explain and demystify the basics of EMI conducted and radiated coupling mechanisms. This is a necessary stop-over for designing an EMC-compliant product, or eventually understand what went wrong and what to do….. Michel Mardiguian, EMC Consultant, France m.mardiguian@orange.fr
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Notices
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An Editor’s Reflections
Who has the current lead in EMC?
T
he EMC area has evolved in different directions since it was born about hundred years ago. From the beginning, the driving force was concerns about unintentional interference from electronics and how such interference might affect the new public radio broadcasting services.
D
uring the cold war, the interest of EMC issues increased in the military area when platforms, such as aircraft and ships, become more dependent on advanced electronic systems on board. As a result of the nuclear threat, the protection against nucelar electromagnetic pulse (NEMP) become of major concern, both for military platforms and critical infrastructure in the society.
D
uring the cold war, lots of large investements were done in test facilities, computational electromagnetics, and design rules within all subareas of EMC. Today, the largest interest for EMC issues seems to have shifted to another area once again. Even if the military area is still concerned about EMC issues, the automotive area seems to have taken the lead in the further development of the EMC area.
T
he strong competition within the automotive area, togehter with the increased use of digital technologies and wireless services, has made EMC issues of critical concern for succesful development of new car models. Due to the high requirements on reliability and trust in the automotive area, lots of EMC subareas have to be handled with great concern. Examples are shielding, grounding, antenna design, intersystem interference, crosstalk, and ESD.
T
he last year, it has been a clear trend at EMC conferences that the publications from automotive applications deal with several of the most challenging EMC problems right now and several automotive companies are investing in their own large EMC test facililites. Thus, in the post cold war era, it looks like the automotive area has taken over the leading role from the military side. The automotive area is therefore an example where EMC issues are one of the necessary enablers for succesful business.
PETER STENUMGAARD info@justmedia.se
Satel is on its way to becoming the market leader in the area of mission-critical radio communication At Intergeo from 15 - 17 September 2015 the Finnish radio data communication specialist Satel present innovative new products, a step toward establishing itself as the market leader in mission-critical radio data networks. In Germany, radio data communication solutions from Satel are distributed exclusively by the full-range and systems provider Welotec. At the trade fair in Stuttgart the partners will present their products at adjacent stands. By 2020 Satel intends to be the world’s number one provider of mission-critical data connections. This goal also includes becoming the technology leader, which the company will achieve through intensified research and development. That these measures are already producing results will be evident at this year’s Intergeo, where Satel will present its latest products. For example, visitors will be able to see the OEM modules Satelline-M3-TR1 and Satelline-M3-TR4. These modules allow use of the frequencies requiring a license (330 - 473 MHz) as well as the European license-free frequency ranges (433.05 434.79 MHz and 869.400 - 869.650 MHz). The newly developed Satelline-M3TR4 is currently the smallest available data transceiver module in its class. The Satel Compact-Proof is a portable radio data modem with a rechargeable battery and a flexible tuning range (403 - 473 MHz). The robust Satelline EASy Pro 25W, likewise with a broad tuning range (403 - 473 MHz), allows radio communication up to a range of 50 km, which makes it quite versatile. At the world’s leading trade fair for geodesy, geoinformation and land management, Satel will present its products directly adjacent to the company’s exclusive German partner, Welotec GmbH. Both Satel as a radio data communication specialist and Welotec as a full-range and systems provider have a strong portfolio for the core market of RTK/GNSS, UAV and RPAS applications. Welotec offers a large range of antennas, for example, which more than optimally supplement the Satel radio data modems: the antennas cover a large frequency range from 68 MHz to 6000 MHz, indoor and outdoor applications, MIMO technology and also antennas with an operating range from -40 °C to +80 °C for use in harsh environments. At the trade fair in Stuttgart visitors will also be impressed by innovative solutions from Welotec in the area of industrial communication - for example the industrial UMTS, LTE and WLAN routers of the TK800 series or the high-performance Industrial-WLAN access point DM500. For measuring tasks Welotec offers the laser distance sensor OWTB V2.1, which features an extremely high resolution and ranges of up to 500 metres, making it ideal for industrial applications.
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THE FIRST 10 YEARS OF EMC WORK FOR THE
JAS 39 GRIPEN FIGHTER AIRCRAFT
THE GRIPEN SYSTEM WAS THE FIRST OF A NEW GENERATION FIGHTER AIRCRAFT Copyright Saab AB.
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torate of the Defence Materiel Administration, FMV T&E. The EMC group at FMV T&E represented the defence customer for the EMC quality control of the Gripen project. Several major EME test systems were acquired by FMV for the Gripen testing (Government Furnished Services, GFS). FMV T&E also supported SAAB and the IG JAS at the EMC design work. The first flight of a Gripen test aircraft took was made in 1988 but the design and system test programs for the production aircraft continued. The detailed EMC requirements and technical design of Gripen can for natural reasons not be presented here as such information is classified for commercial and defence reasons. THE GRIPEN PROJECT STRUCTURE The Gripen project was formed by more than 20 sub-system projects, Figure 1. The JAS 39 Gripen fighter aircraft
THE JAS39 GRIPEN FIGHTER AIRCRAFT PROJECT. The new version of the JAS39 Gripen fighter is now a strong competitor in the fighter aircraft world market and the aircraft operates in several countries. A historical review of the early EMC work for the Gripen project may be of interest. The JAS 39 Gripen fighter aircraft project was outlined and presented in 1979-1981 by SAAB Military Aircraft & The Industry Group JAS also including the Ericsson Microwave Co. and Volvo Flygmotor. The development of the Gripen system and a production of 30 aircraft for the Swedish Air Force was decided by the Government in 1982. The decision was made after an intense debate in the media whether Sweden had the competence and capability to continue the independent fighter aircraft development although such projects had become extremely complex and costly. The Gripen system was the first of a new generation fighter aircraft. It was designed with extensive use of carbon fibre composites, CFC. The supersonic very agile and instable aircraft was controlled by a full authority digital fly-by-wire system. A multitude of conventional aircraft instruments were replaced by three multi-mode electronic displays. The engine was controlled by a high authority Digital Engine Control unit. Gripen had a new tactical radio system, old and new weapons and other tactical systems should be integrated and controlled via data-buses by the central computer. Gripen’s integrated advanced Radar and Electronic Warfare suit with many sensors and transmitters communicated via multiplexed data-buses. The Gripen system formed a new very complex and unexplored technology for Sweden. It was named ‘The first 3rd generation fighter aircraft’. Many companies in Sweden and other western countries were involved in the multi-national ‘Swedish’ project!  The avionics technology had seen a dramatic development during the 1970s’ and 80s’. SAAB was one of the leading companies and had already in the 1960s’ formed the Datasaab Co. where computers were designed and produced for general needs, for the design work at SAAB and for the avionics of the SAAB 37 Viggen fighters forming the backbone of the Swedish Air Force in the 1980s’. Its predecessor the SAAB 35 Draken with the first version developed in the early 1950s’ had been designed with the slide-ruler as the tool for calculations! In 1980 many of the system engineers at SAAB had a high competence from several aircraft projects including the Draken and the Viggen projects. Late editions of the Draken aircraft were still in service during the first years of the Gripen project. The capability of the EMC group at SAAB had followed the general avionics development. The group had developed new requirements, methods, instrumentation and tools that formed a valuable base for the EMC work at the Gripen development. The review of the 10 first years of EMC work for the Gripen project illustrates the design challenges at the development of a new advanced fighter aircraft system 30 years ago. The author gives an insight in the EMC work of the project from his position in the EMC group at SAAB Military Aircraft during the first 5 years of the project and thereafter from his position as manager of the EMC group of the Testing Direc-
Figure 2. The JAS39 Gripen affair was an important issue for the western avionics industry.
e.g. aircraft structure, engine system, flight control, navigation etc. The sub-system projects were coordinated by the Gripen System Design Manager. Although not being a hardware system, the EMC design was one of the sub-system projects and the group reported weekly at the joint system design meetings. The tight communication among the subsystem projects was essential at the very fast and complex design work. Misunderstandings were avoided, any mistakes could be corrected immediately and design compromises were agreed together. Unavoidable project delays were communicated continuously and extra efforts were spent on the time schedule. The formal structure and documentation of the project work was well organised by coordinated time-schedule and activity plans. EMC had a dedicated position in all documents and at all sub-system activities. General design parameters were identified for the weight and cost of all components. A specific project cost including project ‘time consumption’, was defined for each parameter. Such aspects had to be considered also for the EMC design as well as any project delay risks. Risk management has traditionally been in focus at aircraft design. The SAAB EMC-group managed the integrated EME-design and coordinated the EMC work within the Industry Group IG JAS. The group got a strong position in the project and were well supported by the management and the customer. That was essential for the EMC work. The SAAB-Fairchild 340 commuter aircraft project was initiated in parallel with the Gripen project. That imposed a heavy workload on the small EMC group. The civil SF 340 project met a very hard commercial competition with an extremely tight time-schedule. In the 1980s’ the Viggen aircraft built by SAAB formed the backbone of the Swedish Air Force. Several versions, both the older ‘analogue’ versions and the modern JA37 having a digital flight control system, would be in service for more than 10 years. Signs of ageing due to many flight- hours caused minor EMC problems such as fly-by-voice, transmitter cross-talk and P-static noise. Some up-gradings were still made.
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The Viggen system generated most of the workload for the small EMC group at SAAB. The initial EMC work for the Gripen program had to be squeezed into the almost full calendar of the EMC-group. Several new engineers were soon included in the group. MURPHY’S LAW APPLIED The overall design strategy of the Gripen project stated that Murphy’s law applies - All that can go wrong will do so. The implication was that every design, equipment and integration detail should be kept under tight control. The high quality control ambition was somewhat modified by a message from the EMC project manager to the EMC design team that ‘Our design and quality control work has been over-ambitious if we don’t find any problem at the final system verification tests’. The conclusion was that a very stringent and well controlled primary design and quality control work was needed that might result in a limited number of manageable EMC problems. NEW CHALLENGES FOR THE EMC WORK ON THE 3RD GENERATION FIGHTER The aircraft and avionics technologies had seen a period of dramatic development during the 1960s’ and 70s’. In USA Rockwell had developed the B1 Lancer bomber in the 1970s’. In Sweden the Viggen system was upgraded with the JA37 having first generation digital avionics. BAe in the U.K. had developed the Tornado aircraft and in the USA new editions of the General Dynamics’ F16 were developed with upgraded features similar to those of Gripen. The Lockheed F-117 Nighthawk stealth aircraft with an exotic airframe had been developed in the same period. However, the Nighthawk was very secret and it was not revealed to the world. The development of new generations of air systems had also stimulated the development of new EMC hardware components and design tools. Still, one major challenge for the early Gripen design was the lag-
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ging status of several EMC technologies and standards needed for the new fighter. The engineering tools, competences and EMC standards were adapted to electromechanical and analogue electronics and the analogue HF-UHF radio transmitters of the 1960s’ and 70s’. No defence standards were available for integrated air systems EME testing. The political debate concerning Sweden’s capability to develop the Gripen had created a strong attention on the engineering capability and efforts. The project got a very strong support from the Government and the Defence HQ. The focus was put on quality control, safety, aircraft performance, less on the economic aspects. The attention and support from the top management at SAAB on the engineering work and resources, included EMC, throughout the design and production work. This was invaluable for the EMC group. In 1980 the office computer power at SAAB was not useful for detailed EM calculations. Much of the early Gripen EMC work during the 1980s’ was spent on exploration of the new Cray-1 supercomputer capabilities for CEM calculations and on the development of the EMC standards, test tools and methods for the high performance and safety requirements of the Gripen system. THE INFORMATION EXCHANGE HANDICAP – INTERNET AND E-MAIL WERE NOT YET INVENTED A handicap that can hardly be realised today was the lack of the Internet and e-mail that were not invented in 1980. There were no ways to communicate except telephone, facsimile and slow letters. Participation in expert communities and particularly being an active speaker at conferences were the best ways to form contacts with experts from other nations. That opened for an exchange of many unpublished technical reports and documents from foreign authorities and companies. Reports in technical magazines and printed books could be searched and ordered via the SAAB library but that was a slow process. Conference proceedings and their reference lists formed one major source of information. Many publications of potential great value were not detected in time for the Gripen design work. One example is the very comprehensive ‘Design Principles and Practices for controlling Hazards of EM radiation to Ordnance (Hero Design Guide), NAVSEA OD 30393.The document published in the 1970s’ is very useful both for weapon systems and for air platforms design. It was obtained by SAAB a few years too late in the mid 1980s’. It presents many of the design principles and the background physics that were applied for the Gripen but had to be explored independently by SAAB for the Gripen design. Similar publications particularly devoted to aircraft design appeared soon after that. The SAAB group - like other engineering groups at that time - had to do extensive advanced in-house technical R&D work for their project needs. The accumulated and structured collection of paper documents at the SAAB EMC office formed a valuable source of information for the project. THE EME AWARENESS FORMED BY SEVERAL ACCIDENTS Several severe EME-related accidents in Europe and USA were related to HIRF, HERO and lightning e.g. the tragic HERO related fire on the USS Forrestal in 1967 and HIRF accidents of several Black Hawks,
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Lighning Antenna - antenna NEMP RF HERO Mobile transmitters TEMPEST
EM signature
Figure 3. Illustration of the EMC requirements on JAS 39 Gripen
F16s and a Tornado. Lightning strikes to aircraft had caused several fuel tank explosions. Two lightning strikes in Viggen aircraft had caused one accident and one severe incident in 1978. The accidents had formed a broad awareness of the EME risks and had clearly illuminated the need for a thorough EMC design work for complex air systems and airborne weapons and a need for refined EME protection methods. THE NEMP AND LIGHTNING COMMUNITIES WERE SEPARATED FROM THE EMC COMMUNITY Nuclear EMP interaction was a sensitive subject related to nuclear weapons. The NEMP community and their conferences were only partly open and NEMP protection was separated from regular EMC work. European lightning scientists were very traditional and organised their own conferences. Few studies were reported in Europe on aircraft lightning effects. The main source of information on lightning and electrostatic effects on air systems was the annual International Aerospace and Ground Conference on Static Electricity and Lightning, sponsored by the FAA, NOAA and the US Defense. At these conferences SAAB could report and discuss technical experiments and design issues concerning aircraft lightning and P-static. However, not many general EMC experts participated in these meetings. SAAB decided that an integrated EMC system design work by one group of engineers including all EM effects was essential for the Gripen project. Initially that required contacts with three EM communities. The situation was soon improved when other projects followed the SAAB example.
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INTERPRETATION OF THE OPERATIONAL REQUIREMENTS FOR THE EMC REQUIREMENTS ON THE GRIPEN The Air Force had defined the Operational Requirements of the Gripen system, e.g. tactical functions, all weather operability, system availability, maintainability etc. These requirements had been translated into a System Specification for the Gripen contract by The Defence Materiel Administration, FMV. The EM effects chapter included all relevant EME factors with eference to defined standards and requirement levels. Some effects allowed for an acceptable degradation of the aircraft performance and some maintenance after an exposure. The JAS39 Gripen System Specification formed the baseline for the EM effects design work . It included all EME components, HIRF (radio- and radar transmitters), TEMPEST (RÖS), ESD (P-static) HERO, EMI, EM signature, antenna-antenna coupling, lightning effects and NEMP. In 1981 it was not conventional to include NEMP, TEMPEST and EM signature in EMC specifications. Several EMC groups of the sub-system suppliers were unfamiliar with such requirements. The EMC requirements as expressed in the System Specification and the Equipment Requirements were based on the known character of the EM environment and the response to it by equipment of the 1970s’. Such specifications were not fully adequate for the Gripen technology. New parameters were needed. One reference in the System Specification was the first edition of MIL-STD-1757 for lightning strikes. It did not include repetitive lightning current pulses. Such stress might impair digital signal sequences. The definition of a lightning strike in the System Specification had to be refined after an agreement between FMV and IG JAS. That had a consequence on several sub-system requirements. In 1985 the US Federal Aviation Authority, FAA, summoned the international aircraft community to a meeting regarding the HIRF environment. The FAA message was that the very severe HIRF environment near various RF-transmitters had been neglected for aircraft design and verification. The problem applied to the Gripen project and the Gripen HIRF specification had to be revised. The requirement concerning pulsed microwave radiation had to be increased by almost 60 dB in one frequency band! That had a concrete consequence not only on the equipment requirements but also on the overall platform design and on the planned system tests. The alarm from FAA and the improved HIRF specification created a basic HPM protection of the Gripen. A few years later the extra efforts paid off when the HPM vulnerability of the system was questioned in public media. SAAB could then claim a basic HPM system hardness of Gripen as the potential HPM threat was met by the Gripen HIRF design with its design margin to the HIRF environment. THE INTERNATIONAL INTEREST AND ENGAGEMENT IN THE EMC DESIGN WORK The Gripen project was of great interest to other western nations. SAAB had formed a cooperation with Rockwell at an early phase of the project. They had recent experience from the design the B1 Lancer bomber. The
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contacts with Rockwell also included aircraft EMC but they were soon replaced by Figure 500-1 Risk Assessment of COTS / MOTS Procurement Main Flow Chart 500-A2 a cooperation with BAe in the U.K. for the Figure 500-2 Define Environment Flow Chart 500-A3 design and production of the carbon comFigure 500-3 Evaluate EMC Specification Flow Chart 500-A4 posite main wing. SAAB and FMV mainFigure 500-4 Assess Risk against Functional Criticality Flow Chart 500-A7 tained a close cooperation with The U.K. Defence Research Agency at Farnborough. Figure 500-5 Mitigate Risk Through Design and / or Retest Flow Chart 500-A9 SAAB were members of the Culham Lightning Club that organised lightning research Table 501-1 Default Performance Criteria Guide 500-14 for their members from the aircraft industry Table 500-1 EMC GAP Analysis Factors Affecting Test Severity 500-A6 and several authorities. Table 500-2 Guide to Minimum Acceptable Risk Resulting from EMC Gap Analysis 500-A8 The interest by U.K. and BAe in the Gripen work partly originated from their early work on the Eurofighter aircraft, Typhoon. The Typhoon concept included similar Table 1. Figures and tables in the NATO AECTP 500, ed 4. illustrating a system EMC program. EMC technology challenges as those of Gripen. A first Typhoon demonstrator, EFA lagged a few years behind the Gripen. Also the US Air Force were supportive and arranged several meetings at their main EMC test ranges at Wright-Patterson AFB in Dayton, the Naval Surface Warfare Center at Dahlgren and the US Navy Patauxent River Test Base where a very advanced EM effects system test capability is located. The NEMP protection design and testing was discussed at the Kirtland AFB and Sandia Labs in Albuquerque where Sweden had good NEMP research contacts via the Defence Research Agency, FOA (FOI). Some of the equipment at the Swedish NEMP test centre was used at the Gripen tests including B-dot and D-dot probes, 1GHz bandwidth transient digitizers with fibre optic Figure 4. Geometry for HIRF exposure analysis of an aircraft passing a pulsed radar. links. The equipment design originated from the US Nuclear protection research activities in Albuquerque. So did the Finite Difference computer codes ment at some high power HF transmitter sites in Sweden. The measand the major NEMP test facility at FMV T&E in Linköping. urements were supported by DRA, Farnborough, with their helicopter borne field measuring equipment. THE GRIPEN EMC DESIGN PROCEDURE The HIRF hardness of the test aircraft had only been proved to limA procedure was defined for the transformation of the Gripen System ited levels and some restrictions were imposed on the flight envelop. The Specification into detailed EM requirements on the aircraft platform, mapping of the HIRF environment was very useful at the early flights of on its avionics and on the tactical functions. The very same procedure the prototype Gripen aircraft in Sweden and abroad. is defined in the present NATO document ‘ALLIED ENVIRONMENTAL CONDITIONS AND TESTS PUBLICATION, ‘ELECTROMAGCOMPUTATIONAL ELECTROMAGNETICS, CEM – COMPUTER NETIC ENVIRONMENTAL EFFECTS TEST AND VERIFICACAPABILITY AND EM DESIGN TOOLS TION’, AECTP 500 ed. 4. The AECTP document specifies the steps for SAAB got the CRAY-1 super-computer in 1983. Going from punchanalysis of the EM environment of the system, how requirements can be card and Fortran 4 to Cray-1 was a real challenge. The initial everyday tailored against the functional and safety criticality of individual subtool for calculations in 1981 was the ABC 800 table top computer. It systems and what margins should be applied for each design step. In the had a very limited capability and was not suitable for EM analysis. Earchapter ‘Category 505’ the AECTP document defines the verification ly support was hired from Messerschmitt Böhlkow Blohm in Münich procedure for air systems and refers to the MIL-STD 464C standard for analysis of the external EM coupling to the aircraft. However, the for the detailed EME system requirements. stick model algoritm used was not suitable for EM analyses of deltaThe high quality of the Gripen work procedure from 1983 that even winged aircraft like Gripen. The market was surveyed and a few anameets today’s specifications from NATO, was partly a result of the close lytical tools were identified that had been developed for the US nuclear dialogue with several influential EMC groups in USA and the U.K. The program. The Finite Difference EM tool, FDEM, that had been develGripen EMC engineers contributed to the NATO procedures with sevoped by the EM Applications Co. (EMA) in Albuquerque and Denver eral elements from the Gripen project by participation in the aircraft was the best code available. It could be implemented in the new Cray1 community’s standardisation work. computer at SAAB. A long term close cooperation was established with EMA in 1983. The FDEM-code had been developed for Nuclear EMP DEFINITION OF THE EME ENVIRONMENT COMPONENTS FOR protection analysis. That made them sensitive. The export license from GRIPEN the US Dept. of Energy required much diplomatic efforts. The work Much work was spent on the definition of the EM operational environwas delayed by almost one year. In the meantime the many potential ment of the Gripen. No up to date data were available concerning the applications of the FDEM-tool were identified. EMA could begin their HIRF environment near powerful Swedish and foreign radio and raprogramming work including several sub-routines and optimization of dar transmitters. Swedish fixed, land-, sea- and ground-mobile stations the code to the Cray1 and the JAS39 dimensions. Many improvements were analyzed from available transmitter data as a consequence of the were made of the code during the several years of joint work by the alarm from FAA. Several European countries were contacted and their SAAB and EMA CEM experts. data were also analyzed for the HIRF environment near high power The initial CRAY 1 memory capacity, 1MB, limited the analyzed transmitters. The HIRF environment was mapped for many European volume to about 20x30x30 elements which resulted in a poor time and transmitters. The radar stations close to airfields was of particular imspace resolution. The CAD technology was not yet available and data portance. A detailed mapping was made of the near-field RF environinput was made manually from paper drawings. Any mistake resulted
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Figure 5. Top view of early FDEM drawing of Gripen and a 3D plastic model visualization.
in very odd results. Computer graphics was not yet available in 1983. Primitive matrix printer illustrations (2D-layers) of the FDEM model of aircraft were visualized by a 3D plastic model.  The original code was developed for EM coupling of a short transient plane wave. Analysis of lightning strikes required a thorough refinement and new codes were developed for lightning strikes and field diffusion through CFC walls. Some lightning strike analyses including field diffusion through CFC walls required a calculated time span of 1ns - > 10 µ (> 10.000 time steps) with an extremely stabile code and perfectly absorbing boundaries of the analyzed volume. Each of such calculations required many hours of Cray-1 data processing. Examples of early FDEM analyses for the JAS39 EME project: • Plane wave NEMP and HIRF coupling to the aircraft. Local fields and skin currents on the external aircraft structure. • EM coupling to external stores (weapons) and sensors. • Comparison between alternative lightning test generator designs. • Lightning current distribution for several lightning attachment points. • Comparisons between the current distribution for real lightning strike attachments and for various test configurations. • Correction factors for local skin currents on aircraft in the air compared to aircraft on a ground plane at HF HIRF testing with the current injection - return conductor test set-up. • Lightning current diffusion through CFC wing walls and the induced local voltages and currents inside a CFC wing and a CFC wing box for testing. • EM coupling through points-of-entry of various geometries. The CEM capability of the project has been developed continuously. The group of CEM experts at SAAB has grown since the first years of
the JAS39 project. The computer capability has improved and many new codes and applications have been developed. CEM can now replace much of the experimental EMC work. The early code development and later achievements have been presented in many technical reports. THE OVERALL AIRCRAFT EMC DESIGN - ZONING The Gripen aircraft structure should provide a controlled internal EM environment for all installations. The EMC equipment requirements should if possible be kept at ‘conventional’ levels preferably those recommended nominally in the equipment standard of the project, MILSTD 461B. The amount of internal cable shielding bringing extra weight should be kept to a minimum. A zoning concept was established for the project while not yet commonly accepted n the early 80s’. Four zones were defined; zone S a shielded EM environment, providing high attenuation of external effects, zone I an environment inside the conventional metal aircraft providing the attenuation of a normal metal skin, zone C an environment internal of Carbon Fibre walls, zone O an open environment where the external structure did not provide any significant shielding e.g. on the exterior of the aircraft, inside radomes and in the cock-pit area. The SICO-concept was thus formed for the EMC project work. All structural design measures, installation principles and sub-system/ equipment requirements were guided by the SICO-principle. A well shielding compartment forming zone S was enclosing the vast majority of the avionic equipment. All cabling inside the S-zone could go without external shielding as the S-zone structure provided a > 40 dB shielding to the external environment. That required thorough design
Figure 6. Side view of the Gripen and the original drawing of the SICO zoning concept.
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measures. Particularly all equipment bay doors had to be designed with conducting gaskets. Frequently opened service doors were provided with extra reliable and enduring shielding measures. Any compromise of the shielding by external surface mounted components such as air-sensors and electric lights were controlled by EM pointof-entry requirements named RS/RE and RS/CE. The p-o-e quality requirements were uniquely defined for the Gripen project. The related test method was a combination of MIL-STD 462 emission and susceptibility testing i.e. radiated and conducted emission from internal cabling with the test item illuminated on the external side with RS- requirement levels. The strict RS/RE - RS/CE requirements controlled all local pointsof-entry for EM fields. Extra design measures had to be taken for some components in order to meet the p-o-e requirements e.g. metal mesh on some external lamp housings and extra shielding of the connectors in the wing pylons. The shielding continuity between the S- and I-zones was achieved by closed metal walls. All cable ‘feed-throughs’ into the S-zone had connectors with shielding back-cap connectors on the shielded cable bundles in the I- and C-zones. The cable bundle shielding quality was defined for an internal cable environment comparable to that in the Szone. The resistivity and mutual inductance per meter of braided shields were defined according to the location in the I- and C-zones. Some cables were installed with ‘lossy-line’ cable jackets. The C-zone was characterized by a high shielding quality at high frequencies that did not diffuse through the continuous CFC wing and fin skins. At low frequencies < 10 MHz, EM fields could diffuse through the several mm thick CFC walls making the C-zone shielding less effective. LIGHTNING PROTECTION Experiments were made at the High Voltage Research Institute in Uppsala on a Gripen scale model in order to define the primary lightning attachment zones. The results were supported by the FAA recommendations for civil aircraft. One consequence of the very agile Gripen performance was that the avionics and flight control systems had to continuously maintain their full function during and after a lightning strike. A criticality analysis indicated what functions had to sustain induced transients from lightning strikes, their required functionality after a strike and any acceptable consequences for the remaining functions. The refined definition of a lightning strike according to later editions of MIL-STD 1757 included multiple strikes and current burst having a > 1 second duration. All critical functions were tested according to the improved lightning standard. The fin, the canard wings and the Gripen main wings were designed with CFC outer skins. The wings had a hybrid structure with a CFC outer skin, internal CFC spars, metal ribs, metal tubes for cables and several metallic fuel pipes. The wings also had metallic wing tip rails for EW sensors and weapon pylons and under-wing pylons for tactical loads. The lightning protection of the main wings formed a particular problem as the wings formed fuel tanks, so called ‘wet wing’ tanks, without rubber lining. One engine fuel alternative was JP4 (MC77) that is highly inflammable. No sparks were allowed inside the tanks and the very complex wing structure had to be lightning protected. The spark free design required very large efforts, basic research work and an extensive technical development work. An aircraft lightning expert, J.A. Plumer, Lightning Technologies Inc., was consulted for the lightning protection of CFC wing structure. A number of design alternatives were proposed by LTI. Somewhat later SAAB got the excellent NASA Reference Publication 1008, ‘Lightning Protection of Aircraft’ with J.A. Plumer as co-author. BAe was contracted for the main CFC wing design and production. The lightning protection of the wings was worked out by SAAB in cooperation with BAe engineers. The protection techniques could also be used for the EFA design and the engineers at BAe learned the lightning protection technique from the Gripen and became aircraft lightning experts in the U.K. Many FDEM analyses and experiments were made by SAAB for the lightning protection design. Experiments were made at the Culham Lightning Labs. in U.K. on a large ‘wing-box’ sample with realistic CFC walls containing all critical internal wing components. Incendiary sparking was initially detected with fibre optic sensors in the wing box at threat level lightning experiments. After several refinements such
Figure 7. The author at an inspection of the central equipment bay of the JAS39 Gripen (photo Pia Ericson FMV T&E)
Figure 7. The author at an inspection of the central equipment bay of the JAS39 Gripen. (Photo Pia Ericson FMV T&E)
Figure 8. Model experiment for determination of the lightning attachment points on the Gripen. (Photo SAAB Aeronautics)
Metal strips
Metal end ribs
CFC rib CFC spars
Metal rib Lower CFC skin
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Figure 9. FDEM model of the wing box for lightning tests with the top CFC skin removed.
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Figure 10. Overview of suppliers to the Gripen system. (photo Saab Aeronautics)
sparking was fully suppressed. Detailed production instructions provided the spark-free lightning protection of the wing tanks. It was found experimentally that direct lightning attachment to metal fasteners in the CFC wall of the fuel tanks could produce heavy thermal sparking. Fuel ignitions were demonstrated when a simulated tank with an inflammable gas mixture was tested. Several alternative protection measures were tested until a spark-free solution was found. The local hot-spot formation on the resistive CFC wing walls at direct lightning strikes might induce thermal ignition of fuel vapours in the wing tanks. Lightning strike experiments were made at the High Voltage Research Institute in Uppsala with real time measurements of the internal skin temperature at full threat lightning strikes. A first generation Thermovision camera was used. It showed that cooling the wing surface with a realistic external air-flow limited the internal hot-spot formation well below dangerous temperatures (> 200C) for fuel ignition. The lightning protection design of the aircraft nose radome was made according to the experience from the lightning protection of the similar Viggen nose radome. That protection had been worked out after the accidents in 1978 that were caused by a poor lightning protection of the pitot-tube heating wires in the nose radome. The lightning protection of the Gripen cockpit canopy was another challenge. The large Perspex canopy has an internal metalized layer for signature purposes. It is provided with an explosive strip along the top for the pilot emergency ejection. A lightning strike is not allowed to affect the rescue function nor the metallisation. The lightning hardness of the canopy was verified by several lightning strike tests. The protection of many other details were tested against direct lightning strikes e.g. the landing gear and several antenna elements. STATIC ELECTRICITY – ‘P-STATIC’ A well known problem from the Viggen and other aircraft is electrostatic charging when flying in air containing frozen snow particles, called P-static. The voltage generated may be > 100 kV such high voltages produce corona- and streamer discharges from pointed details on the aircraft surface. The generated EM noise may severely disturb transmitters and sensors. This problem is worst for signals < 10 MHz but also signals at higher frequencies could be disturbed. The Gripen was protected from any P-static problem by eliminating all external isolated metallic details inch and by anti-static paint on dielectric surfaces e.g. the antenna elements. Experiments showed that the aircraft could do without the P-static dischargers that are common on many aircraft. The static free design was proved by testing with a static particle spray gun that could create heavy charging of insulated objects and dielectric surfaces.
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NEMP The response of Gripen to Nuclear EMP radiation was analysed with the FDEM tool. The induced coupling from NEMP into any apertures was added to the composite EME stress envelop for aircraft cables and equipment. The extra contribution to the composite stress envelop from NEMP was marginal to that from lightning strikes and HIRF. Aircraft components in zone O were tested for direct NEMP effects. SUB-SYSTEM AND EQUIPMENT SUPPLIERS TO THE GRIPEN SYSTEM One challenge was to identify and evaluate sub-system suppliers having the capability to design and supply equipment according to the strict quality requirements. The Gripen design work included about 20 sub-system suppliers from USA, UK, France and Germany. After the contracting of the suppliers the next step was to create an efficient cooperation for the detailed, tightly controlled, EMC procedures and to get acceptance from some non-US sub-system suppliers of the requirements specified according to the US MIL-STD 461B with some tailoring for the Gripen design. Several sub-systems were supplied by Swedish companies. A standardized equipment design concept had been worked out for the Swedish equipment. The standard design included strict rules for the EMC design of equipment casings, grounding of boxes and circuits, external connector installations, filtering and transient protection of power units, signal filtering, the internal box lay-out and a general PCB design. The standard concept saved many efforts for the project. The EMC design work by the IG JAS partners was reviewed by SAAB. The integration of the radar and the EW suite with the air platform required much joint work. The missile systems to be integrated were government property (GFE). They were not designed according to the Gripen standards and some EMC data were missing. That required extra work and complimentary testing. No modifications were allowed on the missiles and the aircraft interface had to be adapted to their properties. Many coordination meetings were held at the suppliers of the subsystems. Formal Preliminary Design Reviews (PDRs) and Critical Design Reviews (CDRs) were made before all sub-system tests. The test plans were reviewed and accepted and the EMC tests were witnessed in the labs by SAAB EMC engineers. Some test set-ups were very elaborate with simulators for testing of active equipment. The tests sometimes continued for a long time. The testing by Lear Siegler of the very extensive flight control system lasted several months at the Genesco Lab near Long Beach. The digital engine control system, DEC, was produced by the original
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engine designer, General Electric for Volvo Flygmotor. The DEC was installed on the hot side of the engine. Because of the severe environment at the engine it had a very unconventional and seemingly primitive design that confused the SAAB engineers. The DEC technology was considered to be sensitive by GE and US DoD. Little information of its EMC design was provided and the equipment box could only be inspected very briefly. However, no EMC problems were ever caused by the DEC. The fast electronics revolution during the 1980s’ formed a particular problem. Successive upgrading of TTL-technology equipment
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Figure 11. Flow chart showing the air systems E3 verification procedure in AECTP 500.
with C-MOS components and re-designed PCBs should formally have required re-testing in all cases when the compliance tests had been performed on first generation TTL-equipped functions. Many compromises had to be made and in several cases re-testing could be replaced by analysis of the design documents. THE EMC VERIFICATION OF THE GRIPEN SYSTEM The verification of the Gripen system was managed by a separate department at SAAB. The verification activities were followed and supported by FMV T&E. The EMC testing was performed with close contacts with the EMC design group at SAAB. The group also supported many test activities. A general strategy was not to accept any system requirements until realistic verification tools and methods were identified. Particularly three EM components, lightning, HIRF and NEMP required extra efforts. The tight project time schedule required a fully available full threat level lightning test system. It was decided that a lightning test system was needed. It had to be tailored to the needs of the Gripen project. The design was supported by FDEM analysis and the Swiss Co Haefely supplied the test system. The Gripen EMC certification plan followed a procedure very close to that defined in the present AECTP 500 ed. 4, Category 505. The alternative verification paths shown in figure 11 were followed for verification of the various EM effects. In several cases complementary testing was performed according to both the high level and the coupling measurements verification alternatives.
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Figure 12. The Microwave Test Facility and some data of the test system.
The many challenges of the project resulted in a significant improvement of the Swedish EMC engineering competence including many technical and analytical tools. GENERAL PRINCIPLES FOR EM ASSESSMENT OF THE INTEGRATED GRIPEN SYSTEM One test approach for system level assessment of the avionics and other electronic functions was to measure the coupling of EM effects into the aircraft S-, I- and C-zones at external exposure. The Gripen system was put in a simulated ‘in-the-air’ status at the coupling tests in order to have the proper signal and power leads connected. The aircraft skin shielding according to the SICO zoning concept was controlled at the system tests. The internal coupling was measured for many cables and the shielding and installation hardness was demonstrated statistically. That approach was applied for the RF HIRF testing < 1 GHz, the NEMP- and the lightning tests. Measured internal EM signals were corrected for any scaling factors and compared to the MIL-STD 461B / MIL-STD 462 sub-system requirements and laboratory verifications. The lightning coupling tests were performed at the threat level to allow for any non-linear effects. The threat level MTF system was used at go/no-go testing for assessment of HIRF effects at frequencies > 1 GHz. The tests were made with the Gripen equipment put in an in-the-air mode with the engine running and the aircraft tied in the test position. A pilot in the cock-pit observed the instrumentation for any disturbances. He had to wear a metalized suite for protection against the very intense radiation. The first Gripen test aircraft was tested primarily for its air-worthiness clearance and for a basic functionality for the flight tests. The production aircraft were thoroughly tested for assessment of the EMC hardness quality of the aircraft to be delivered to the Swedish Air Force.
Repeated tests were performed when major changes had been made on the aircraft. Many R&D activities supported the EMC system tests: • Interpretation of EME factors for modern digital systems, e.g. multiple strike/burst & long duration lightning effects • Adaption of MIL-STD 462 test methods for the technology of the 1980’s. • The development of many FDEM algoritms in co-operation EMA • Design of the lightning test system + FDEM analysis • HF & HEMP Skin current testing with FDEM support • EM properties of Carbon fiber composites. EM diffusion through an-isotropic materials • Ignition hazards test techniques for direct lightning testing including the risks of thermal sparking, electric sparking and hot-spots • EMC components and cavity resonance suppression techniques for the avionics compartments • Exploration of the Mode Stirred Chamber test technique for high intensity HIRF testing of external components and missiles (long time before it was standardized): - General validity of MSC testing (was it hocus pocus??) - Statistical comparison between MSC and plain wave testing, - Number of frequency steps required at MSC testing, - Feeder horn geometry - Q-value of test chamber - Test set-up geometry for MSC testing e.t.c. EMC The intra-system EM compatibility verification of the early test aircraft as well as the production version of the Gripen was based on the equipment verifications and the equipment integration controls. System level EMC controls were made on the ground for the air-worthiness clearance. The general system functionality including any EMC influences was controlled at the ordinary detailed flight testing of each produced aircraft before its delivery.
Figure 13. The JAS 39 Gripen at HIRF testing with the MTF test system (photo Saab Aeronautics).
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HIRF RF HIRF testing. HF-band hardness testing was performed with a current injection test set-up similar to the system lightning tests but with the lightning impulse generator replaced by a powerful CW current injection generator. The HF test configuration had an about 70 Ω input impedance that approximately matched the generator. FDEM calculations were made of the local current density for an exposed aircraft in the air compared to that for the HF test configuration. Correction factors were applied on any measured values when needed. The aircraft was illuminated locally for RF testing in the VHF and
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UHF frequency bands. The testing was performed with ordinary generators, power amplifiers and antennas from the SAAB EMC test lab. The coupling into the S- I- and C-zones was determined at several locations for each geometry of illumination. Microwave HIRF Testing The HIRF protection of the first prototype aircraft was demonstrated for its air worthiness cearance by illumination with a Viggen nose radar and together with several mobile radar stations that were brought to SAAB for the testing with several radar technicians. That test exercise required unrealistic efforts and a dedicated Microwave Test Facility had to be acquired for the planned recurring HIRF tests. Several potential suppliers were contacted for a proposal on the very powerful HIRF test system. The US Titan Beta Co was chosen for the MTF system design with the EM Design Company as subcontractor for the advanced very high intensity illumination antenFigure 14. Illustration of the nas. Gripen lightning test set-up The overall requirement on the system was to generate the worst case HIRF environment for Swedish fighter aircraft. The capability of the system was limcurrent were of concern and the ca 30 kHz dominating frequency of ited to microwave sources of five fixed frequencies covering the L, S, C, the injected test current was in focus. However, strong and very fast X and Ku radar bands. They could generate radiation with varying sigsecondary transients were noted initially in many recordings of internal parameters such as PRF, pulse length, burst length and intensity. The nal cable currents. A thorough analysis revealed the importance of the generator output peak power was 25, 20, 5, 1 and 0,2 MW respectively. high frequency content of the test current pulses. The findings were The maximum pulse length is 5 μs. reported internationally and the lightning community agreed that the The diagonal horn antenna patterns were decided for a test object high frequency content at real lightning strikes as well as of the injected distance of 15-25 m. The radiation footprint at the test distance should lightning current at testing, were of great importance. have at least 10 wavelengths diameter and should well cover any access The planning of the flight worthiness lightning test was a real chaldoor of an aircraft. This implied a radiation footprint of at least ca 2.5-3 lenge. The unique first test aircraft had to be lightning tested at full threat m diameter. Horn antennas with dielectric lenses were designed to meet level in a simulated flying mode. The test was not allowed to damage the the required antenna pattern. The near field limit of the antennas is 12 system or impair its flight worthiness. The test generator was designed m or less. in cooperation with the Haefely Co. who supplied and produced the test The threat level microwave HIRF tests were performed only at the system according the the SAAB requirements. The generator had a very five frequencies, one each for the L, S, C, X and Ku radar bands. No frecompact and fast ‘peaking capacitor’ for generation of a fast current quency adjustable generator was available for the extreme output power impulse and proved to be very efficient for the tests. needed for the testing. Swept frequency coupling experiments on Gripen The testing was made with injected current pulses having an early full equipment bays showed a strong frequency dependence. The variations threat peak current derivative, di/dt = 1011 A/s. The peak current was limwere partly due to a directivity factor and partly due to internal resoited to ca 30 kA. Also the charge and energy transferred at each injected nances of cavities, structural elements and cables. The uncertainty cretest pulse were limited in order to eliminate the risks for equipment and ated by spot frequency testing could partly be diminished by illuminastructural damage. A return conductor system was designed for the ‘intion with several angles of incidence. The uncertainty due to any internal direct’ lightning effects testing. It formed an about 70Ω coaxial geometry resonances was covered by a good test margin to the external HIRF with the aircraft with the current injection point at the nose pitot tube. environment requirement. The geometry was similar to the test set-up for the Viggen tests (fig 14). The Microwave Test Facility, MTF, was designed for the Gripen HIRF The impedance matching and distribution of the return conductors along testing. It is still in use and has been extensively used by Swedish groups the fuselage of the aircraft was refined for high frequency performance of and by other nations for experimental HPM research work. the test set-up while the Viggen test configuration had neglected the high frequency current components. The importance of such effects were not NEMP realised until the evaluation of the Viggen tests. The Nuclear EMP requirements on Gripen included full system threat level testing. In 1980 Sweden decided to establish a large NEMP test HERO TESTING centre in Linköping. Its capability should enable NEMP testing of the The Gripen missiles were government supplied equipment GFE). FMV new fighter aircraft. The Gripen contract did not specify a hardness veriwas responsible for the EME hardness assessment of each missile. Comfication at the planned test facility. The centre was not operable until sevplimentary EMC tests were performed at the FMV T&E EMC lab for eral years after the formal NEMP verification of the Gripen. The NEMP some missing data including the new RS/RE and RS/CE requirements. hardness was assessed by a combination of FDEM analysis, components The aircraft gun was an integral part of the aircraft. Its hardness was testing and a threat level skin current injection test on the full aircraft assessed at the sub-system level. according to the ‘SCIT’ method. The aircraft missile installations were tested for HIRF coupling by use of simulated missiles with a detector installed in each of the ignition LIGHTNING SYSTEM TESTS circuits of the missile engines. The detector was a non-contact bridgeA full threat level lightning test was required for air-worthiness of the wire thermal sensor with the output signal coupled via a Fibre Optic test aircraft. The focus of the test was to prove the flight safety and the Link to the measurement system. The sensor and FOL system had been integrity of the basic aircraft functions. The testing of the production explored and the test method refined by Bofors Co for testing with both aircraft should assess the hardness of all funtions. CW and pulsed HIRF exposures. The sensor system was just barely A threat level system test had been performed by the Viggen aircraft in sensitive enough for the Gripen HERO assessment including the extra 1981. The testing was supported by the Culham Lightning Lab. At that design margin required for ordnance systems. time only the thermal effects and the high voltages of the direct lightning
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ANTENNA – ANTENNA COUPLING Swept frequency coupling measurements were made for each antennaantenna coupling path. The measured coupling combined with the measured out of band transmitter emission and susceptibility data from the MIL-STD 462 testing could assess the disturbance free antenna – antenna system design. All transmitter and antenna data were put into a transmitter/antenna database with data for the > 20 antenna elements on the aircraft. The database supported the continued management of the transmitters and sensors development of the Gripen. TEMPEST AND EM SIGNATURE The Swedish TEMPEST (RÖS) performance of Gripen and the EM noise emission from the aircraft were controlled in parallel with the EME work. The RÖS and EM signature requirements and the test methods are classified as well as the protection measures. Therefore, no information about the RÖS and EM signature design is included in this survey. THE SYSTEM REPORT The entire EMC design work on the aircraft platform at the sub-system and integrated system levels including all design reviews, analyses and tests were summarised in a Gripen EM System Report for each version of the aircraft. The System Reports list all the design and analysis measures and assessment details with the relevant reports as references. The number of references varied for each version of the aircraft but was about 500. The System Reports summarized the facts that demonstrated that the airworthiness and performance requirements were met and how that was assessed. Any limitations were clearly stated as well as what influence they had on the aircraft performance.
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CONCLUSIONS The Gripen project formed a huge challenge for the EMC group at SAAB. That challenge could be met with the strong competence formed at SAAB together with a close cooperation and support from several Swedish and international technical experts and scientists. The EMC design resulted in an aircraft system that met the ambition goal of the manager of the EMC group at SAAB. Several deviations were found at the EMC system tests but they could all be corrected. The first version of the Gripen formed a good baseline for the continued Gripen work beyond the first 10 years. The very stringent methods used at the EMC design work proved to be successful. The technical integration work of the very complex aircraft system could be made without any severe EMC problems. The Gripen system has been developed with several new versions and the EMC group has grown and been transformed with the system. The pre-computer/IT-age of the early project has been replaced by new high performance IT-systems and instruments supporting the EMC work at the present major system development and for the future versions of the Gripen. The many challenges of the project resulted in a significant improvement of the Swedish EMC engineering competence including many technical and analytical tools. The procedures and many technical methods used at the Gripen EMC design have been included in many EMC courses and EMC guidelines e.g the EMMA manual for defence EMC work. K G Lövstrand Techn. Director (ret.) FMV T&E, Linköping
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Electronic Environment 3.2015 Eng
Yokogawa launches enhanced version of the world’s best-selling power meter WT300E Series features higher accuracy, new measurement functionality and improved connectivity Yokogawa has introduced an enhanced version of its best-selling WT300 Series of compact 5th generation digital power meters featuring higher accuracy, new measurement functionality and improved connectivity including Modbus/TCP capability to aid integration into production environments. The new WT300E Series has a basic power accuracy of ±0.15% at 50/60 Hz on all measurement ranges - the highest level of accuracy available in any compact power meter – along with a bandwidth of DC and 0.1 Hz to 100 kHz. The influence of power factor is also greatly reduced: at low power factor the accuracy is twice that of the previous models (±0.1% of apparent power S). The WT300E series covers a broad range of input currents from a few mil-
liamperes up to 40 A RMS, making it equally suitable for measuring low currents in standby power testing to the high currents encountered in induction cookers. It can also measure waveforms with both AC and DC content. The WT300E Series contains four models: the WT310E single phase (including extremely low-current measurement capability down to 50 µA); WT310EH single phase high current; WT332E two-element; and WT333E three-element. For the engineer doing standby power measurements, Energy Star®, SPECpower and IEC62301/EN50564 testing as well as battery-charger and other low level power measurements, the WT310E is the ideal solution. The WT310EH is a single-phase high-current version with current ranges from 1 A to 40 A RMS. The bandwidth on this model is DC and 0.1 Hz to 20 kHz. The WT332E is a two-element meter for use on split-phase and threephase/three-wire circuits. The WT333E is a three element meter for use on three-phase/three-wire or three-phase/four-wire circuits. These models have current ranges of 0.5 A to 20 A RMS, with low-current measurements down to 5 mA. All models have voltage ranges from 15 to 600 V RMS, and low voltage measurement capability to 150 mV. The new instruments are particularly suited to measurements on today’s power conversion circuits using energy-saving switching techniques, which can cause highly distorted voltage or current waveforms with high harmonic content. They also have a new enhanced low-frequency measurement capability of 0.1 Hz in addition to the upper bandwidth limit of 100 kHz. An optional harmonic analysis function is available which provides simultaneous measurement of both the normal power parameters and harmonic data for faster and more accurate power analysis. Harmonic analysis and total harmonic distortion calculations can be made up to the 50th order from a 50 or 60 Hz fundamental frequency. An integration function measures ampere-hour and watt-hour parameters: tests that are especially important for standby power measurements. In the standby mode the current can be very low, but it can increase substantially when the device goes into operational mode. The new auto range feature will optimise the range setting for maximum accuracy measurements. Yokogawa’s “average active power” function makes it possible to measure power consumption under conditions where the power fluctuates greatly. With this system, watt-hours are measured over a time period, and the time is divided out to give an average power reading. A new feature has been added to the data update rate. The WT300E series can follow fluctuating input frequencies, which typically occur in motor applications, by changing the data update rate automatically. Starting from the lowest 0.1 Hz input, this function can will detect cycles of the input signal automatically and measure it correctly.
Source: Yokogawa
Roxtec launches new fibre cable seal for telecoms market Manchester cable seal manufacturer Roxtec has developed a new product aimed at the telecoms market which protects fibre cables as they enter buildings. Developed in conjunction with a leading telecoms company, the Roxtec End User Inlet is a quick and easy-to-install plug for both new and existing cables. Roxtec UK managing director Graham O’Hare said the watertight seal prevents dust and rodents from interfering with fibre cables, which are now widely used to transmit telephone signals, Internet communication and cable television signals. “The Roxtec End User Inlet is designed to be used wherever fibre or hybrid cables are being installed into existing buildings,” he said. “Specifically manufactured with the telecoms market in mind, the product provides a high level of protection and is IP 68-rated. The End User Inlet can be installed into drilled holes in brick or concrete walls or floors to prevent dust and rodents from entering the building and, crucially, provides water ingress protection too. “The product has been rigorously tested for constant pressure, has a 2mm tolerance level, is available in a range of sizes for cables from 4 to 16mm in diameter and can be used below ground to a maximum depth of 3m. Like other Roxtec products, the End User Inlet ensures safety, efficiency and operational reliability and has been manufactured to stand the test of time.” For flexibility, the flange can be removed to enable installation into angled holes. Re-installation is also possible with existing seals. Roxtec develop and manufacture complete sealing solutions for cable and pipe penetrations. The firm’s modular-based seals are its foundation, but its
growth is primarily built on committed personnel, strong values and a clear customer focus. Graham O’Hare said the company’s close co-operation with customers has created an innovative environment which enables Roxtec to tailor new solutions such as the End User Inlet and target new markets. “This new product fits perfectly with Roxtec’s ethos of delivering highquality sealing solutions that are easy to fit,” he said. “All of our seals protect against multiple hazards and, as the creation of the End User Inlet shows, our specialist staff have the knowledge and experience to tailor bespoke designs which ensure that our customers’ needs are met.”
www.electronic.nu – Electronic Environment online
Source: Roxtec
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Notices
Electronic Environment 3.2015 Eng
Pasternack Expands Portfolio of In-Stock and Ready to Ship GaN Power Amplifiers Diverse Offering of GaNPower Amplifiers Boast High Power & High Gain over Wide Bands Up to 7.5 GHz Pasternack, a leading manufacturer and supplier of RF, microwave and millimeter wave products, announces their expanded offering of gallium nitride (GaN) coaxial power amplifiers. GaN has emerged as the technology of choice in power amplifier designs. The high power density of gallium nitride semiconductor technology dissipates heat more effectively which results in amplifier designs that have significantly higher output power levels over broadband and narrowband frequencies. These rugged connectorized designs have the advantage of high output load impedance that offers easier impedance matching over wider bandwidths using lower loss components. Applications include commercial and military radar, jamming systems, medical imaging, communications and electronic warfare. Pasternack’s offering of RF amplifiers includes GaN-based models that feature very high gain levels from 43 to 60 dB across mostly broad frequency bands ranging from 30 MHz to 7.5 GHz. Saturated output power levels range from 10 watts to 100 watts with 20 to 35% Power Added Efficiency (PAE). The thermal efficiency of GaN technology enables these assemblies to be integrated into smaller more compact coaxial packages with the same level of high reliability. All of the high power GaN amplifiers from Pasternack have single voltage supplies which are internally regulated. The 50 ohm input/output matched designs are adaptable to a range of power and modulation requirements. These PAs also show impressive harmonic response (-15 to -20 dBc) under worst case conditions. These GaN amplifiers are designed to withstand environmental conditions such as humidity, altitude, shock and vibration. Some models are also equipped with integrated heat sinks and cooling fans. Most designs are EAR99. “Pasternack’s broad selection of in-stock GaN power amplifiers sets a new standard in offering leading-edge technology for the availability market,” explains Tim Galla, Active RF Components Product Manager at Pasternack. “These highly efficient PAs cover broad and narrowband frequencies with high levels of gain and power in small coaxial packages.”
Fairview Microwave Expands Waveguide Portfolio with New Family of Waveguide Directional Couplers New Millimeter Wave Waveguide Directional Couplers Operating Up to 110 GHz Now In-Stock at Fairview Fairview Microwave Inc., a supplier of on-demand microwave and RF components, introduces their new family of precision waveguide directional couplers. This release consists of 28 models covering a frequency range from 18 GHz to 110 GHz in seven popular frequency bands including K, Ka, Q, U, V, E and W bands. Fairview Microwave’s waveguide couplers are available in waveguide sizes from WR-42 up to 18 GHz all the way to WR-10 up to 110 GHz. These directional couplers are offered with 10 dB or 20 dB coupling values and have high directivity of 30 dB typical with insertion loss is as low as 0.6 dB in certain models. Fairview’s new waveguide couplers are available in both standard and split block configurations and are also available in both E-Bend and HBend designs. They utilize a multi-hole design that provides optimal power reflection measurements and consistent performance. Fairview’s new millimeter wave waveguide directional couplers are widely used in applications such as on-the-bench testing scenarios, radar systems, satellite communications, point-to-point backhaul, signal sampling and other general purpose applications in wireless transceivers. These waveguide couplers are constructed using high quality brass copper and are gold plated for added precision and accuracy. “Our newest portfolio of waveguide directional couplers provide designers a comprehensive selection for millimeter wave signal sampling and testing components when coaxial solutions are not possible,” explains Brian McCutcheon, Vice President and General Manager at Fairview Microwave. “We are committed to expanding our waveguide product lines to ensure we have the components needed by engineers as the industry continues to push towards higher and higher frequency applications.”
Source: Fairview Microwave
Source: Pasternack
Frankonia present SAC-10 Plus Triton Class After 2 years of intense research and development Frankonia is proud to present its newest product in the field of EMC Testing Chambers: The SAC-10 Plus Triton Class. The SAC-10 Plus Triton Class is Frankonia’s new fully compliant EMC testing solution. It’s a semi-anechoic chamber designed for measuring distances of 10.0 and 3.0 meters on a Quiet Zone of Ø 3.0 m. The highlight of this chamber is its triple test axis. The innovative shape with its optimized absorber layout allows a simultaneous use of three axes for emission and immunity tests and superior minimized reflections. The SAC-10 Plus Triton Class for EMC testing is a revolution in its class.
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The benefits of its triple test axes allow our customers to measure all required EMI/EMS procedures without the need to modify the test environment or the test setup. This also includes the test equipment and instruments that can remain connected in the chamber. The antenna and absorber area for each procedure specifically moves to the test scenario either in manual, semi-automatized or full-automatized mode controlled by Frankonia software. Thus, the quality of EMC testing remains at a constant high level, the testing time decreases, and malfunction and damage is almost impossible. The frequency range of the all-new SAC-10 Plus is from 30 MHz to 18 GHz (optional 40 GHz) and offers outstanding performance for NSA, SVSWR and FU. By simplifying the testing procedures the SAC-10 Plus addresses in particular the everyday problems of test engineers and laboratories. They can benefit from an efficient usage, reduced time of set-up and measurement, reduced cost and a stable quality level which are derived from its optimized layout and arrangement of absorbers and antennas. Therefore, this chamber guarantees a future-proofed solution for any kind of EMI/EMS testing at the highest performance level.
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Source: Frankonia
Fully anechoic chamber for radio and EMC tests.
In our fully anechoic chamber we perform radio and EMC measurements up to 26 GHz. Ideal for products with e.g. WLAN, Bluetooth, Zigbee, 868 MHz, RFID etc.
Electrical safety lab with climate testing equipment.
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Our semi-anechoic chamber for most types of EMC tests.
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Electronic Environment 3.2015 Eng
Tactical Consequences
of Radio Spectrum Out-of-Band Properties
Tactical communications for ground-based operations requires many co-located communication systems on combat vehicles. Typical frequency bands for such communications are the 30–88 MHz band for army combat radio and the harmonized NATO band 225–400 MHz. As a result of increasing demands of different communication services and larger bandwidth, the amount of co-located communication systems in these bands is continuously increasing. A consequence of this is that the used frequencies will be less separated, meaning that out-of-band properties will be of severe importance for the performance of the individual systems.
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F
urthermore, another practical consequence is that the possible co-location distance between different combat vehicles is directly dependent on the out-of-band properties of in-going systems. In this paper, we present examples of how these co-location distances can be affected of out-of-band properties and how this in turn will affect the possible separation distances between combat vehicles, the possible communication range and the service available on the radio links. We show the importance of making tactical considerations already in the specification of requirements for out-of-band properties of tactical communication systems. Keywords: Intersystem interference, tactical wireless communications, electromagnetic interference, frequency hopping, co-location, out-ofband emissions INTRODUCTION Tactical communications for ground-based operations requires lots of co-located communication systems on the combat vehicles. Typical frequency bands for such communications are the 30 – 88 MHz band for army combat radio and the harmonized NATO band 225 – 400 MHz. In these frequency bands different types of communication systems must co-exist e.g. frequency-hopping (FH) and fixed-frequency systems. Systems for tactical communications designed to be used for larger communication distances are mixed with short-range systems for internal communication in- and between combat vehicles. Furthermore, in Europe the lower and upper part of the 225-400 MHz band is planned to be used for civilian services e.g. 225-240 MHz for DAB and DVB-T2 and 380-400 MHz for TETRA. This means a reduction of the available frequency range for tactical communications. As a result of increasing demands of different communication services and larger bandwidth, the amount of co-located communication systems in these bands is continuously increasing. Moreover, unintentional electromagnetic interference from electric equipment in the vehicles can also affect communication performance. All electronic devices produce radiated electromagnetic interference that can cause severe interference problems for co-located wireless systems. Several interference accidents in military applications have been reported the last decades which highlight the need of controlling this interference in every military operation and platform. Civilian electronic systems are in general allowed to produce considerably higher levels of radiated electromagnetic interference than military specified equipment. This means that an increased amount of so called Commercial off the Shelf (COTS) products in military applications therefore automatically increase the intersystem-interference levels. A consequence of the increasing amount of wireless systems on the platforms is that the communication frequencies used will be less separated, meaning that out-of-band properties will be of high importance for the performance of the individual systems and for the overall wireless network. The increasing amount of radio systems leads to a larger number of antennas on each vehicle. Together with all other practical requirements on a combat platform, optimal antenna locations are not always possible to achieve, which in turn degrades communication performance. Furthermore, another practical consequence is that the possible co-location distance between different combat vehicles will be directly dependent on the out-of-band properties of in-going systems. Altogether, considering the different requirements above, the integration of tactical communications on combat vehicles is a really challenging work that needs careful attention in the early design phases of a military platform. One fundamental way of reducing intersystem-interference on a platform is to reduce the interference from out-of-band emissions from wireless transmitters. Out-of-band properties for radio systems can be either specified for a certain application or by referring to a standard requirement. In order to determine what requirement that is necessary, dedicated analyses must be done and often a trade-off between the desired properties, possible technical solutions and the economic cost must be done. Typically such analyses are done in the integration work for a certain platform. However, including possible co-location distance between combat vehicles in such analyses is also necessary since there is a direct connection between spectrum properties and co-location consequences. The latter is not so often done to the knowledge of the authors and no open publications have been found on this matter.
Intersystem interference can affect wireless communication systems in different ways: • communication disruptions, • reduced communication range, • increased time delay of data, • reduced data rate; reduction of possible wireless services on the link, • increased range for hostile jammers. The most difficult interference problems to handle are those that do not give obvious communication problems such as disrupted links. If a communication link is disrupted, the operator recognizes this immediately and can prepare counteractions. However, if the interference gives a more gradual degradation, it is considerably more difficult for the operator to be aware of an interference problem. It is also important to note that every intersystem-interference problem gives a hostile jammer an advantage since the jammer can obtain the same impact on a larger distance than in the case with no interference present at the victim receiver.
Electromagnetic interference gives a gradual degradation of communication performance and can therefore be difficult to discover by the user
Thus, out-of-band interference can degrade the communication performance without a clear warning to the user. In this paper we present examples of how possible co-location distances between combat vehicles can be affected by out-of-band properties and how this in turn will affect the possible separation distances in a vehicle convoy, the possible communication range and the service available on the radio links. We show the importance of making tactical considerations already in the setting of requirements for out-of-band properties of tactical communication systems. The paper is organized as follows. In the next section, requirements on out-of-band properties are discussed. Furthermore, the concept of orthogonal frequency hopping sequences is introduced as a technique to avoid frequency collisions when several FH systems are present. Also, the properties of the two frequency bands are summarized. This section is followed by examples of the impact of different out-of-band properties on communication performance for a group of combat vehicles. We show the tactical consequences of out-of-band emissions in terms of necessary separation distances between vehicles, available services or a reduced communication range. Finally, the paper is concluded. FREQUENCY MEASURES FOR CO-LOCATION REQUIREMENTS ON OUT-OF-BAND PROPERTIES In general, the out-of-band domain is defined to start at a frequency offset of 0.5 times the necessary bandwidth and extends up to 2.5 times the necessary bandwidth. However, for very narrowband and wideband emissions, there may be exceptions for the upper boundary. For these cases the upper boundary is defined in ITU-R SM.1539 [5]. Here, we use an extended definition since performance will be affected by emissions further above/beyond the carrier frequency. This will be shown later in the paper. Out-of-band properties for radio systems can be either directly customized and specified for a certain application or by referring to a standard requirement. For military radio systems, one typical standard requirement of out-of-band properties is the RE103 (Radiated Emission) in MILSTD-461F [1]. The requirement says: “Harmonics, except the second and third, and all other spurious emissions shall be at least 80 dB down from the level at the fundamental. The second and third harmonics shall be suppressed to a level of -20 dBm or 80 dB below the fundamental, whichever requires less suppression.” The requirement is not applicable within the bandwidth of the transmitted signal or within ±5 percent of the fundamental frequency, whichever is larger.
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For civilian systems, ITU-R SM.1541 [2] covers definitions of various terms used in the context of unwanted emissions, general out-of-band limits for many services and principally describes ways to measure conformance with the limits. However, Out-of-band limits for some modern digital systems are not always given in general, e. g. digital cellular systems, short range devices (SRD), personal communication systems (PCS). ITU-R SM.329 [3] covers unwanted emissions in the spurious domain. It describes measurement methods and contains general limits. Examples of measures to reduce out-of-band emissions are • spectral efficient modulation schemes, • sharper transmitter filters, • linear amplifiers. Furthermore, measures for improved interference performance can also be done in the receiving system e.g. • sharper receiver filters, • co-location filters, • active interference cancellation [6], • hybrid spread-spectrum methods [7]. For example, to prevent that the out-of-band transmission of JTIDS/ MIDS terminals interfere with air navigation and flight safety, the system out-of-band emission is strictly specified and the terminals are equipped with an interference protection feature to monitor their terminal transmissions. Reduction of out-of-band emissions is costly so there is always a trade-off between requirements, the choice of measures and economy. The typical way of creating specifications for the out-of-band emissions is by analyzing the impact on co-located systems within a platform or at a certain separation distance. For digital communication systems, the bit error probability (BEP) required for a certain quality of service (QoS) determines the maximum tolerable amount of out-of-band emissions. For instance, if the BEP is larger than, say 10-3, voice may still be unaffected but data transfer is impossible. Furthermore, the relation between the signal-to-interference ratio (SIR) in a receiver and the availability of a certain service is not linear but has a threshold behaviour and typical maximum limits of BEP for some services may be e.g.
Figure 1: The resulting BEP of two co-located FH-systems, using the same frequency band, will result in a threshold behaviour. Dashed line represents the BEP when only the fundamental frequency in the transmitted spectrum is considered.
• < 10-2 for voice, • < 10-5 for data with moderate requirements, • < 10-7 for data with high requirements. If, for example, frequency-hopping systems with overlapping frequency bands are co-located, the resulting BEP will show a threshold behaviour with respect to SIR, see Fig. 1. In Fig. 1 the resulting BEP caused by co-location of two FH-systems within the 30-88 MHz band is shown, and is calculated according to [9]. The solid line in Fig. 1 represents the BEP when the all out-of-band products are considered, for out-of-band emissions shown in Fig. 2. The dashed line (fundamental only) in Fig. 1 represents the case when only the main spectrum lobe is considered. Each step in the BEP is caused by one of the spectrum lobes so that the lowest step (around SIR~0 dB) is caused by direct collisions of the carriers. The second lowest step (around SIR ~ -5 dB) is caused by the largest out-of-band components up to 100 kHz (approx.) colliding with the centre frequency of the receiver. The step related to the highest BEP value (around SIR~-40 dB) is caused by the out-of-band components above 100 kHz in the transmitter spectrum. Hence, an improvement of the out-of-band characteristics may not always improve the QoS for a system, since the BEP is affected in steps and the maximum permitted BEP for a certain service must be fulfilled. Thus, an improvement of the out-of band characteristics must be large enough to pass the threshold in BEP for a specific service. Finally, it is also important to notice that even if a certain limit of the bit error probability is achieved, the maximum communication range will also be affected. We will therefore include such analyses in our scenario examples in the next section and show that a large reduction in communication range can appear. 
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 Figure 2: Example of out-of-band emission spectra for a transmitter used in the analysis.
FREQUENCY-HOPPING SEQUENCES Co-located frequency-hopping systems often use the same frequency band and are separated by different FH sequences, i.e. stacked nets. The benefits of that all systems use the whole band is that it is harder for a hostile jammer to disrupt the communications if a large band is used. A drawback of using the same band is the interference from other FH transmitters. Hence, for a frequency hopping system, it is beneficial to avoid that several users use the same frequency at the same time. To handle this, the frequency hopping sequences may be designed in a certain way. For sequences of a specific length and number of frequency hopping channels a bound exist of the autocorrelation of a sequence [10] and sequences fulfilling the criterion are called optimal or orthogonal frequency-hopping sequences. Examples of optimal frequency hopping sequences can be found in [11], [12]. However, in reality, the system’s out-of-band properties may aggravate the possibility to obtain negligible interference from other users. Since the transmission spectrum often has a decaying emission power from the carrier frequency and outwards, a possible approach is to put restrictions on how close the used simultaneous carrier frequencies may be located. That is, the carrier frequency used by a user must be at least
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Electronic Environment 3.2015 Eng
Object palette, with radio systems, interference sources, platforms, compounded objects
Scenario 3D view
Result presentation
Figure 3: A snapshot of the operators view in GENESIS. In [4], GENESIS is used to determine necessary co-location between medical electrical equipment and tactical radio systems at military camps, not to cause interference. Object attribute settings
∆ f from all other used carrier frequencies at a certain moment, in the network. This approach may handle carrier frequency collision and avoid considerable interference from other user’s out-of-band emission in your own network. Other radio networks, however, cannot be coordinated in this way. Such situations stress the need for error correction that is implemented over several frequency hops. The problem with stacked nets is acknowledged in [8], where it is highlighted that the number of concurrent hopping patterns is limited to 20 before error rates produce significant impact in JTIDS/MIDS. If additional interference appears, the number of nets needs to be reduced further. MILITARY FREQUENCY BANDS The military band 30-88 MHz is typically used for frequency-hopping, military army combat, radios. Such systems usually have 25 kHz channels and a relatively large number of frequency channels to hop between. The equipment is often mounted on military vehicles or in masts and the co-location issues may arise when several antennas are grouped together. In co-operation involving collaboration between nations or when several nations are sharing the same camp, interference issues is likely to appear. Another demanding situation is several vehicles moving in convoy. The harmonized military frequency band at 225-400 MHz is used by a large number of different military radio systems. The bandwidth of the systems are usually wider than in the 30-88 MHz band and for FH systems, bandwidths in the order of 1 MHz is not unusual, with the consequence that the number of frequency channels becomes less. This band accommodates FH systems (Saturn, HQI/II with future versions, national versions of army combat radios), as well as fixed frequency systems (Marlin, national versions of hand held radios). In addition, in some countries also other systems are allocated in parts of this band, such as Tetra systems. There is also a great pressure from completely civilian services to be able to use parts of this band and, for example, in the lower part of the band radio and/or television transmissions are already in use in some countries. In general, the 225-400 MHz band involves more different actors in the same frequency band than in the
Information window, e.g. interference spectrum
30-88 MHz band, with actors from the army, the air force and the navy, as well as civilian actors. In these bands, emission from unintentional interferers is very common. It can for example be interference from engines, electronic devices, in particular civilian computers and other transmitting devices, such as radar systems and electronic warfare equipment. The frequency utilization of the radio systems is often preplanned and coordinated. Nevertheless, due to out-of-band properties of other radio systems, unintentional interference and unexpected co-location situations, interference from other radio systems cannot be avoided and interference issues appear. Altogether, radio systems in these bands will be exposed to sever interference problems, which may even increase in the future.
Out-of-band emission will not only affect the BEP on co-located systems but also the necessary separation distance between combat vehicles, the communication range and availability of different services TACTICAL CONSEQUENCES A. ANALYSIS TOOL GENESIS For the analyses of the impact from spectrum properties on co-location distances, communication range and service availability, the research tool GENESIS is used. GENESIS is a software research tool developed for intersystem interference analyses of military camps and mobile platforms. The main features of GENESIS are very briefly summarized below. • Analysis methods dedicated for modern digital telecommunication systems have been developed to prevent intersystem-interference problems in military and homeland-security applications.
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• Parameter-reduced calculation models for fast analysis. Such models are used both for electromagnetic modeling and modeling of interference impact on digital radio receivers. • Interaction with the network analysis tool OPNET Modeler in order to analyze the intersystem-interference impact on large communication networks. In GENESIS, the operator works in an advanced 3D graphic environment, see Figure 3. All objects are stored in a data base with all relevant parameters (object attributes) connected to every object. If one wish to alter any parameters that can be done directly in the object. The objects consist of radio systems, antennas, vehicles, containers etc and with all relevant parameters specified. GENESIS has been tested and evaluated by military officers and military engineers and is now used for education and intersystem-interference analyses. In GENESIS, the quality of the communication is visualized by different colors, such as good, poor or failing (green, yellow or red) communications. The acceptable BEP for a system depends on the supported service; e.g. voice communications can often tolerate a higher BEP than data communications. For each system and service, two BEP levels are set in GENESIS and used to show the link quality by different colors. In GENESIS, calculations of BEP can be performed over an area. The results can show resulting BEP for different placements of a receiver or of an interfering equipment. The former can be used for example when evaluating suitable places for a receiver at a camp with many interfering equipment. The latter is often used when analyzing which distances between a receiver and certain equipment that are needed to fulfill a certain requirement. CO-LOCATION DISTANCES FOR COMBAT VEHICLES Two fundamental scenarios are used 1. Three combat vehicles containing frequency-hopping systems for communication in three different networks in the 30-88 MHz band. 2. Two combat vehicles containing frequency-hopping systems for communication in two different networks in the 300 MHz band.
For each scenario, the necessary co-location distance to achieve the required BEP is determined as well as the reduction of communication range. The transmitter spectrum in Fig. 2 is used in the evaluation of the convoy radio performance when the 30-88 MHz band is used. In this scenario, the instantaneous bandwidth is 25 kHz. The out-of-band emission is evident in several channels outside the intended frequency band; 400 kHz consists of 16 separate frequency hopping channels. In Fig. 4, a convoy of three vehicles is shown and the analyzed receiver is in the middle vehicle. The communication system is a FH system with 2320 hopping frequencies in the band 30-88 MHz. Without any co-located vehicles, the BEP is 6∙10-20 and the quality of the communication is excellent. However, when two radio systems are co-located with the receiver the BEP increases and the communication is disrupted.
Figure 4: Co-location of three VHF radio systems analyzed in GENESIS.
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CONCLUSIONS We have shown that possible co-location distances between combat vehicles can be heavily affected by out-of-band properties of the wireless communication systems on board. We have also shown how the co-location will affect the possible communication range and the service available on the radio links. The results show the importance of making tactical considerations already in the specification of requirements for out-of-band properties for tactical communication systems. The paper shows that there can be a significant impact of the radio transmitter’s out-of-band emission and that, without coordination of the used frequency patterns for frequency hopping systems, the intersystem interference between the radio networks can be crucial. This is a consequence of the fact that the number of frequency channels is in practice limited. This raises the need for:
Figure 5: Co-location of two UHF radio systems analyzed in GENESIS.
Both the transmitters have transmission spectra shown in Fig 2 that fulfills RE103 in MIL-STD-461F. All systems are using the same frequency band and can accidentally use the same hopping frequency at the same time. This is expected, since the co-location is close and the out-of-band emission levels are high. Moreover, since the number of FH-channels is limited, the probability is relatively high for collisions. This results in a large number of disturbed frequency channels. Orthogonal frequency hopping patterns can improve the performance by separating the hopping patterns by a number of channels. Here, the patterns are separated by 8 channels, with the result that the BEP decreases to 8∙10-3, and communications are possible but with degraded performance. However, the communication range for the system with good communication quality is severely degraded; only 6% of the range for the original link is obtained. A way to further improve the performance is to attenuate the transmitter spectra. If the spectrum is modelled for the same frequencies but with a level of -80 dB, the BEP is
One fundamental way of reducing intersystem-interference on a platform is to reduce the interference from out-of-band emissions from wireless transmitters reduced slightly to 6∙10-3 in the receiver if orthogonal hopping patterns are used. However, a larger improvement is obtained on the range of the communication link, which now is 25 % of the maximum range. The reduction in range is large since a large improvement in SIR is needed to achieve the BEP; this is also illustrated by the BEP performance for a FH system shown in Fig. 1. The area in which the communication link quality is degraded is shown in Figure 4. The necessary distance between the interfering transmitters and the receiver is about 40 meter. In the UHF band, the number of available frequencies is more limited. Here, it is assumed that the frequency hopping systems use a frequency band of 100 MHz, i.e. 80 different channels for a bandwidth of 1.25 MHz. The transmitter spectrum is modelled as an attenuation of 80 dB at the 2 nearest channels at both sides of the fundamental. The co-location results in a BEP of 6∙10-3 and negligible communication range for the communication system. When orthogonal frequency hopping is used and the direct collisions are avoided the BEP is 9∙10-5 and the range is 40% of the maximal range for a system without interference, see Fig. 5.. The necessary separation between the systems is shown in Fig. 5, showing that a separation of about 40 meter is needed. The impact of intersystem interference is more severe for the UHF system than for the VHF system, since the UHF system have fewer FH channels. This illustrates the need of a fair amount of frequencies to perform frequency hopping on if the performance should not be severely degraded.
• coordination of the frequency hopping sequences, including optimal sequences, coordination between systems and frequency separation of used frequency channels of frequency hopping systems. • strict limits on the out-of-band emission of the transmitter, which can be controlled by proper radio design and filters. Here, relevant design and spectrum requirements are important, taking tactical scenarios and the possible platform configuration with other systems into account. These challenges need to be considered in the design phase of the development of the radio system. This will be increasingly important since the number of co-located systems is expected to increase at the same time as the available frequency bands are strictly limited. REFERENCES [1] MIL-STD-461F, “REQUIREMENTS FOR THE CONTROL OF ELECTROMAGNETIC INTERFERENCE CHARACTERISTICS OF SUBSYSTEMS AND EQUIPMENT”, 10 December 2007. [2] ITU-R SM.1541, Unwanted emissions in the out-of-band domain, 2001 [3] ITU-R SM.329, Unwanted emissions in the spurious domain, 2012 [4] Peter Stenumgaard, Karina Fors, Kia Wiklundh, Sara Linder “Interference on Tactical Radio Systems from Collocated Medical Equipment on Military Camps” IEEE Communications Magazine, Vol 50, no 10, pp, 63-69, October 2012. [5] ITU-R SM.1539, Variation of the boundary between the out-ofband and spurious domains required for the application of Recommendations ITU-R SM.1541 and ITU-R SM.329, 2002 [6] Zahedi-Ghasabeh, A.; Tarighat, A.; Daneshrad, B., “Active Interference Cancelation for user coexistence in the presence of I/Q imbalance,” Proceedings of IEEE MILITARY COMMUNICATIONS CONFERENCE, 2010 - MILCOM 2010, pp.261,265, Oct. 31 2010Nov. 3 2010. [7] Olama, M.M.; Killough, S.M.; Kuruganti, T.; Carroll, T.E., “Design, Implementation, and Evaluation of a Hybrid DS/FFH SpreadSpectrum Radio Transceiver,” Proceedings of IEEE Military Communications Conference (MILCOM), 2014, pp.1368-1373, 6-8 Oct. 2014 [8] C. Kopp, “NCW101: An introduction of network centric warfare, part 3”, Strike Publication, Air Power Australia, 2008. [9] Sara Linder, Karina Fors, Kia Wiklundh, Peter Stenumgaard,” Intersystem interference model for frequency hopping systems”, Proceedings of EMC Europe 2012 International Symposium on Electromagnetic Compatibility, Rome, Italy 17-21 September 2012, pp. 1-4. [10] A. Lempel and H. Greenberger, “Families of sequences with op timal hamming-correlation properties,” Information Theory, IEEE Transactions on, vol. 20, no. 1, pp. 90–94, Jan 1974. [11] R. Fuji-Hara, Y. Miao, and M. Mishima, “Optimal frequency hopping sequences: a combinatorial approach,” Information Theory, IEEE Transactions on, vol. 50, no. 10, pp. 2408–2420, Oct 2004. [12] W. Chu and C. Colbourn, “Optimal frequency-hopping sequences via cyclotomy,” Information Theory, IEEE Transactions on, vol. 51, no. 3, pp. 1139–1141, March 2005. Peter Stenumgaard, Karina Fors, Kia Wiklundh, Sara Linder Swedish Defence Research Agency, FOI Dept. of Robust Telecommunications, Sweden
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