A i r Defence
Photographs: Rheinmetall
Detect, Identify & Destroy
Skyshield Radar
The combination of radar and computers revolutionised the fire control systems for air defence LT GENERAL (RETD) NARESH CHAND
M
anually calculating an effective trajectory, for the firing of air defence (AD) guns or missiles to destroy a moving target, is an uphill task. The problem becomes more complex when the target is a fighter aircraft that can zoom past at supersonic speed in all the three dimensions simultaneously. Before the invention of radars, AD guns were fired by manually calculating the lead angles. Search lights were used for engagements at night. With the invention of radar, detection of aerial targets became easier but the problem of calculating the accurate trajectory still remained. This was partially overcome with mechanical predictors, where the radar indicated the current position and the predictor predicted the future position based on target speed and direction of movement. Next came the mechanical computers which did not automatically train the gun towards the target, but moved a dot on a disc which was then followed by the gun layers. The earlier mechanical computers were humongous in size, weighing as much as a three-tonne lorry. The story goes that when one such system was to be moved to Devlali (where the School of Artillery is located) from Mumbai, its tyres had to be deflated in order for it to pass through the tunnels on the Western Ghats without getting obstructed by the roof. The mechanical prediction system was known as ‘mechanical devices’ as it had a number of moving rods and cylinders; later, capacitors were also incorporated. Solving a mathematical problem mechanically was an act of sheer genius. Ballistic problems became easier and faster to solve with the development of analogue computers. The size of the computer also became smaller and smaller. Analogue computers were followed by digital computers which were even more accurate, faster and smaller. These were primarily weapon computers which were dedicated to a specific weapon system. Thus, the combination of radar and computers revolutionised the fire control systems for AD.
Fire-control radars
A fire control consists of a radar and a weapon computer. The radar is designed
specifically to provide information regarding the target with respect to target bearing, elevation, range and velocity to the weapon computer for computing the firing trajectory to the target. This trajectory is then passed on to the guns or missiles for firing. This process is continuous and automatic as long as the target is within range of the radar. Fire control radars have a very narrow intense beam (X band and below) to ensure accurate tracking of the target. One of the first modern fire control radars was Contraves’ Superfledermaus which had a pencil shaped beam in X band. It could perform the functions of surveillance by mechanically moving its beam to cover a larger area. After detection of the target, it started tracking it with the help of its analogue computer. This process caused some delay, and being a narrow beam, the surveillance had wide gaps in its coverage. It had a range of 40 km for detection and tracking started at 9.5 km when the computer started functioning. It had an optical laying system as a back up and could control two guns, but it was possible to control more guns or missiles with a tailor made computer. It could also be provided target detection from a surveillance radar. Autonomous Systems: With the flying profile of fighter aircraft dipping lower and lower to avoid radar detection, long range for surveillance became redundant as the pickup ranges came to about 20 to 25 km, depending upon the height of the antenna. This also resulted in lowering of reaction timings, thereby necessitating an autonomous surveillance and fire control radar located on a common platform with the target being passed electronically within the system. Skyguard was one such system developed to replace the Superfledermaus. It is has two radars, one each for search and track. It also uses a digital computer instead of the earlier analog system. The search radar is a fully coherent pulse doppler system. It utilises a common transmitter in tandem with the acquisition radar, works in I, J and K band and has a range between 17 km and 25 km. Skyshield is the latest version of Skyguard. Both these are developed by Oerlikon Contraves (now a subsidiary of Rheinmetall). Track-while-scan: Some modern radars
come equipped with a TWS capability that allow for simultaneously operation as a fire-control radar and a search radar. This works either by having the radar switch between sweeping the search sector and sending directed pulses at the target to be
tracked, or by using a phased-array antenna to generate two or more radar beams and dividing them between both the roles. In the TWS mode, the radar has a possibility to acquire additional targets, as well as providing an overall view of the airspace. Track-while-scan radars became possible with the introduction of two new technologies: phased-array radars and computer memory devices. The development of tunable high-power coherent radio frequency oscillators and digital computers enabled TWS radars. By effecting a slight phase shift between a series of antennas, the resulting signal could be steered and focused electronically, and superior memory of digital computers to retain the radar data from scan to scan, permitted the dual function of track and scan simultaneously. Defence
One of the first modern fire control radars was Contraves’ Superfledermaus which had a pencil shaped beam in X band Research and Development Organisation has also developed an effective phased array radar called Rajindra for Akash Missile System. All current fire control radars are normally autonomous or TWS. Autonomous systems can be mounted on tanks, vehicles or can be towed thus are more suitable for mobile weapon systems. They are also less costly. TWS are more suitable for medium and long range missile systems—and also more costly. SP
Skyguard
Latest & Best Flycatcher Mk 2 (HSA Signaal now taken over by Thales) Flycatcher Mk 2 is an autonomous, all-weather, hybrid weapon control centre that has an I-band radar and a K-band radar/Electro-Optical (E-O) tracking suite employed with short range and very short range AD Systems. It can be integrated with a variety of guns and missile systems. Its search radar is a 3-D sensor that covers up to 70° in elevation on every scan. It can be operated in AD and Command Centre (CC) modes, with the former being the radar’s basic operational mode. In the CC function Flycatcher Mk 2 acts as the co-ordination centre for a group of systems within a short range AD network. Accurate 3-D target tracking during an engagement is performed by either the system’s K-band radar or by its E-O subsystem. Raytheon’s AN/MPQ-53 and AN/MPQ-65 Radar Set The AN/MPQ-53/65 Radar is a passive electronically scanned array radar which is equipped with IFF, electronic counter-countermeasure and track-via-missile (TVM) guidance sub systems. The AN/MPQ-53 Radar Set supports PAC-2 and older units, and the AN/MPQ-65 Radar Set supports PAC-3 units. The main difference between these two radars is the addition of a second traveling wave tube which gives the AN/MPQ-65 Radar increased search, detection, and tracking capability. The radar’s antenna array consists of over 5,000 elements which “flash” the radar’s beam many times per second. Additionally, the radar’s antenna array contains an IFF interrogator subsystem and a TVM array. Patriot’s radar is somewhat unique in that it is a “detection-to-kill” system, implying that a single unit performs all functions of search, identification, track, and engagement. Normally, separate radars are required for performing each function. The beam created by the Patriot’s flat phased array radar is comparatively narrow and highly agile compared to a moving dish. This gives the radar an unmatched ability to detect small, fast targets like ballistic missiles or low radar cross section targets such as stealth aircraft or cruise missiles.
3/2009 SP’S LAND FORCES
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