International Journal of Electronics, Communication & Instrumentation Engineering Research and Development (IJECIERD) ISSN 2249-684X Vol.2, Issue 3 Sep 2012 45-55 Š TJPRC Pvt. Ltd.,
STUDY ON COMPACT ULTRAWIDEBAND MONOPOLE ANTENNA NAVEEN S. M.1, VANI. R. M.2 & P. V. HUNAGUND1 1 2
Department of Applied Electronics, Gulbarga University, Gulbarga-585106, India
University Science Instrumentation Centre, Gulbarga University, Gulbarga-585 106, India
ABSTRACT In this paper, design and analysis of planar printed monopole antenna for Ultra Wide Band applications is presented and discussed. To obtain the wide band response the length, width of patch, slit in ground plane and L-shaped notches on the patch are varied. This parametric study is carried out by using IE3D simulation software. The antenna is fed via a microstrip line matched at 50â„Ś impedance. Good return loss, radiation characteristics and gain are obtained in the frequency band of interest.
KEY WORDS: Microstrip fed monopole antenna, Impedance bandwidth, Frequency band, Ultrawideband.
INTRODUCTION UWB is a technology in which information is transmitted in the form of very narrow pulses or other spread spectrum transmissions. The global interest in UWB is increasing rapidly into numerous applications such as medical imaging, indoor positioning, sensor applications and wireless communication for which a compact and cheap UWB antennas are required. One of the serious limitations of conventional microstrip antennas is their narrow bandwidth. This is normally only a few percent of the centre frequency. Therefore, printed planar monopole antennas may provide the best candidate for this application [1, 2]. Since UWB adoption by US-FCC in 2002, there has been a remarkable research interest both in academia and industry in the development of ultra wideband (UWB) technology. Due to its inherent attributes, UWB is capable of bringing significant advances not only to wireless communications (delivery of high data rate transmission in the presence of existing communication systems) but also to other areas such as microwave imaging. For these applications, the assigned frequency spectrum is 3.110.6 GHz. The challenging part of UWB concerns the design and development of compact, low-profile, low-cost front-ends including antennas with wideband performance and an appropriate radiation pattern [3-6]. In this paper, a compact printed rectangular monopole antenna (PRMA) is studied which provides an impedance bandwidth from 3.09GHz to 13.89GHz. Our goal is to obtain a UWB antenna with a small size, simple configuration and low fabrication cost. The proposed antenna consists of a
46
Naveen S. M., Vani. R. M. & P. V. Hunagund
rectangular slit in the ground plane along with L-shaped notches in the radiating patch as one of the method to optimize the bandwidth. Various design parameters of the PRMA are varied such as patch length, patch width, feed gap, slit in the ground plane, L-shaped notches in the radiating patch. During these parametric studies, the behavior of the lower start frequency (fL) of the bandwidth and higher end frequency (fH) of the bandwidth, radiation pattern, gain, radiation efficiency is studied.
ANTENNA DESIGN The geometry of the proposed Printed Rectangular Monopole Antenna (PRMA) with slit in the ground plane & L-shaped notch fed by 50Ω microstrip line is shown in fig. 1. The rectangular Printed Monopole Antenna is printed on one side of the glass epoxy substrate & the ground plane is located on the other side of the substrate. The dimensions of the substrate are width ‘Wsub‘ & length ‘Lsub’. The dimensions of the ground plane width ‘Wg’ and length ‘Lg’. The dimensions of rectangular printed patch are ‘Lp’ and ‘Wp’. The antenna plate is fed by microstrip line of characteristic impedance 50Ω having the width ‘Wf’ and length ‘Lf’. The printed plate is located at a feed gap ‘g’ from the ground plane. The glass epoxy substrate is h=1.6mm thick with permittivity εr=4.4. The two L-shaped notches of dimensions ‘a’ & ‘b’ are introduced at the lower edges of microstrip patch, which affect the electromagnetic coupling between radiator and the ground plane. Also a slit of width ‘Wgs’ & length ‘Lgs’ is placed in the ground plane to control the impedance bandwidth of PRMA.
Fig. 1 Geometry of Printed Rectangular Monopole Antenna (PRMA)
RESULTS AND DISCUSSIONS The PRMA was simulated by using IE3D simulation software. The effects of varying the different parameters on performance of the antenna are described in the following sections. Effect of Patch Length (Lp) The patch length is varied starting from 13mm to 18 mm and the feed gap is fixed at g=2mm and the simulations were carried out. From the results it is clear that as the length of patch Lp increases from 13mm to 18mm, the lower start frequency of the bandwidth (fL) decreases from 5.15 GHz to 3.1 GHz and the upper end frequency (fH) decreases from 14.15 to 12.38 GHz. This can be due to the increase in current path with the increase of the Lp. From the simulation data, the lower starting
47
Study on Compact Ultrawideband Monopole Antenna
frequency of the bandwidth (fL), higher end frequency bandwidth (fH) and bandwidths are recorded as shown in fig. 2 & tabulated in table 1. So, for UWB range we have selected the length 17.5mm which gives fL=3.16GHz & fH=12.57GHz with dual bands. To achieve impedance matching, other parameters are varied and further study has been made.
Return Loss (dB)
0 -1 0 -2 0 PL=13m m PL=14m m PL=15m m PL=16m m PL=17m m P L = 1 7 .5 m m PL=18m m
-3 0 -4 0 4
6
8 10 12 F re q u e n c y (G H z )
14
Fig. 3 Return Loss characteristic of PRMA for variation in Patch length Table 1. Results of variation in patch length Patch Length
fL (GHz)
fH GHz)
Bandwidth (GHz)
(mm) 13 14 15 16 17 17.5 18
4.68
7.77
3.08
10.75
14.15
3.4
3.78
7.36
3.57
10.28
13.97
3.69
3.54
6.97
3.43
9.9
13.55
3.64
3.36
6.64
3.27
9.52
13.15
3.62
3.22
6.35
3.13
9.15
12.77
3.61
3.16
6.21
3.05
9
12.57
3.57
3.11
6.07
2.95
8.82
12.38
3.56
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Naveen S. M., Vani. R. M. & P. V. Hunagund
Effect of Patch Width (Wp) The patch width is (Wp) is varied from 8mm to 13mm and feed gap is fixed at g=2mm and simulations were carried out. From the simulation data, the lower start frequency fL, higher end frequency fH and the bandwidths are recorded in the table 2. The Return Loss characteristics with respect to the patch width variation is shown in fig 3. From this it is quite clear that as the patch width increases the lower start frequency of the bandwidth slightly increases, but the variation of patch width has much impact on the higher end frequency (fH). The fH decreases with a increase in the Wp. The operation band is maximum for Wp=10mm but by again increase in the patch width, the higher end frequency decreases & antenna performance degrades to that of dual band antenna. 0
Return Loss (dB)
-5 -10 -15 -20 W W W W W W
-25 -30 -35
p=8m m p=9m m p=10m m p=11m m p=12m m p=13m m
-40 2
4
6
8
10
12
14
F re q u e n cy (G H z )
Fig 3. Return Loss characteristic of PRMA for variation in Patch width Table 2. Results of variation in patch width Patch width
fL
fH
Bandwidth
Wp (mm)
(GHz)
(GHz)
(GHz)
8mm
3.19
6.12
2.92
9.17
12.16
2.99
3.22
5.99
2.76
9.39
11.78
2.38
3.27
5.85
2.57
9.73
11.25
1.52
11mm
3.3
5.7
2.4
12mm
3.36
5.53
2.16
13mm
3.4
5.35
1.92
9mm
10mm
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Study on Compact Ultrawideband Monopole Antenna
Effect of Slit in the Ground Plane: To get compact size for the proposed UWB antenna and to increase the impedance bandwidth, a slit is introduced in to ground plane to alter the input impedance characteristics. The size of the slit is optimized by IE3D and the selected size is LgsXWgs = (2 mm X 4 mm) along with other parameters to get wide bandwidth. The data is shown in table 3 & return loss characteristics are shown in fig. 4.
Return Loss (dB)
0 -5 -1 0 -1 5 S lit S lit S lit S lit S lit S lit
-2 0 -2 5
1 /2 1 /3 1 /4 2 /2 2 /3 2 /4
-3 0 4
6
8
10
12
14
F re q u e n c y (G H z )
Fig. 4 Return Loss characteristics for variation of slit in the ground plane
Table 3. Results for effect of slit in ground plane
Effect of Feed Gap (g)
Ground slot length (Lgs, Wgs)
fL (GHz)
fH (GHz)
Bandwidth (GHz)
1,2
3.38
5.61
2.22
1,3
3.37
5.62
2.25
1,4
3.36
5.63
2.27
2,2
3.36
5.53
2.17
2,3
3.37
5.55
2.18
2,4
3.36
5.54
2.18
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Naveen S. M., Vani. R. M. & P. V. Hunagund
All the parameters of the Printed Rectangular Monopole Antenna (PRMA) as described earlier is kept the same, only the feed gap is varied starting from 0 to 4 mm and simulations were carried out. From the simulation data, the lower start frequency (fL), higher end frequency (fH) and the bandwidths are recorded and shown in the fig 5. All the data are tabulated in the table 4. From the fig. 5 it is quite clear that as the feed gap between the ground plane and the printed plate increases, the lower start frequency of bandwidth (fL) decreases. But in case of higher end frequency of bandwidth (fH) with the increase of the feed gap, the value of fH increases sharply and reaches the maximum at feed gap of 2mm and then decreases.
0 Return Loss (dB)
-4 -8 -1 2 -1 6 -2 0
g a p -0 m m g a p -1 m m g a p -2 m m g a p -3 m m g a p -4 m m
-2 4 -2 8 -3 2
4
6
8 10 12 F re q u e n c y ( G H z )
14
Fig. 5 Return Loss characteristic of PRMA for variation in feed gap Table 4. Results of variation in feed gap Feed Gap
fL
fH
Bandwidth
(mm)
(GHz)
(GHz)
(GHz)
0
5.3
6.5
1.2
1
4.9
7.5
2.6
2
4.6
11.7
7.1
3
4.3
10.8
6.5
4
3.9
4.5
0.6
6.7
9.5
2.8
Effect of L-shaped notches in the radiating patch (aXb)
51
Study on Compact Ultrawideband Monopole Antenna
In the present design, the L-shaped notches at the lower edges of PRMA as well as ground plane with slit are responsible for the impedance matching. By inserting L-shaped notches and carefully adjusting their parameters (a and b in fig 1) additional resonances can be excited and hence much enhanced bandwidth may be achieved. It has been observed that without L-shaped notch, the bandwidth obtained is 3.4 to 5.5 GHz. But after putting the L-shaped notches with dimensions a & b and by varying the a & b the performance of the antenna is studied. The variation of fL, fH & bandwidth are shown in fig. 6 and the obtained data is tabulated in table 5. With increase in a & b the lower start frequency (fL) decreases and the higher end frequency (fH) increases. So, the optimized value of aXb is selected as 3mmX4mm.
Return Loss (dB)
0 -5 -1 0 -1 5 -2 0 -2 5
1 /1 2 /2 3 /3 3 /4
-3 0 -3 5 4
6
8 10 12 F r e q u e n c y (G H z )
14
Fig 6. Return Loss characteristic for variation of L-shaped notches in lower corner of radiating Patch Table 5. Results for variation of L-shaped notches in the radiating patch Notches (a & b)
fL (GHz)
fH (GHz)
Bandwidth (GHz)
1, 1
3.3
5.7
2.4
2, 2
3.3
6
2.7
6.1
13.1
7
3, 3
3.2 8.4
6.7 15
3.5 6.6
3, 4
3.09
13.8
10.71
Finally after optimization, the obtained different parameters for the PRMA shown in fig.1 are: Wsub=16mm, Lsub=25mm, Wg=16mm, Lg=4mm, Lp=17.5mm, Wp=12mm, Wf=2mm, Lf=6mm,
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Naveen S. M., Vani. R. M. & P. V. Hunagund
g=2mm,Wgs=4mm, Lgs=2mm, a=3mm & b=4mm. With these values the PRMA is fabricated and tested using ‘Rohde and Schwarz, German make ZVK model No.8651 Vector Network Analyzer’. With the said parameters the overall size of antenna is (16X25) mm2 only. Experimentally measured results are plotted along with simulated results as shown in fig.7 and are found to be in good agreement. The simulated bandwidth is from 3.09 GHz to 13.84 GHz and measured bandwidth is from 3.1GHz to 14.15 GHz which covers the FCC’s UWB requirements.
Return Loss (GHz)
-5 -1 0 -1 5 -2 0 -2 5 -3 0 -3 5
S im u la te d M e a su re d
-4 0 4
6
8
10
12
14
F re q u e n c y (G H z )
Fig 7. Return Loss characteristics of PRMA Further the antenna impedance versus frequency is studied and it is shown in fig 8. This tells us that “the real part of antenna impedance’ is exactly 50Ω at 3.1GHz & 13.65 GHz, where the imaginary part of the antenna impedance equals zero. Throughout the bandwidth of the antenna, the real part of the optimized antenna impedance varies from 40Ω to 90Ω, whereas the imaginary part of the antenna impedance is in the range of -30Ω to +30Ω, which is not a major variation of the antenna impedance.
Impedance
100 90 80 70 60 50 40 30 20 10 0 -1 0 -2 0 -3 0
Im a g in a ry R eal
4
6 8 10 F re q u e n c y (G H z )
12
14
Fig. 8 Antenna impedance versus frequency
53
Study on Compact Ultrawideband Monopole Antenna
The simulated 2D radiation patterns along E-plane and H-plane of the optimized antenna at 3.1, 5.8 and 10.6 GHz are shown in fig.9 & 10. It can be observed that the E-plane radiation pattern is in the shape of figure ‘8’ at 3GHz & at the higher frequencies. The H-plane radiation pattern on the other hand is purely omni-directional pattern throughout the ultrawideband.
Fig 9. a) E- Plane radiation pattern
Fig 10. a) H-plane radiation pattern
at 3.1 GHz
at 3.1 GHz
Fig 9.b) E- Plane radiation pattern at 5.8 GHz
Fig 10. b) H-plane radiation pattern at 5.8 GHz
54
Naveen S. M., Vani. R. M. & P. V. Hunagund
Fig 9 c) E- Plane radiation pattern
Fig 10. c) H-plane radiation pattern
at 10.6 GHz
at 10.6 GHz
2
Gain (dBi)
1 0 -1 -2 -3 4
6
8
10
12
14
F re q u e n c y (G H z )
Fig. 11 Gain of the proposed antenna
Fig. 12 Current distribution of the proposed antenna.
Fig.11 shows frequency versus gain for PRMA. The antenna has maximum gain of 1.83dBi and it is almost uniform throughout the UWB band. Fig.12 shows the current distribution of the PRMA at 5.8GHz. This shows that the current is maximum at corners of the feed and corners of the L-shaped notch of the radiating patch. The antenna has very less reflections and maximum radiation efficiency due to proper impedance matching.
CONCLUSIONS In this paper, we have studied a printed rectangular monopole antenna (PRMA) with slit in the ground plane and L-shaped notches on the radiating patch. The various antenna parameters have been
Study on Compact Ultrawideband Monopole Antenna
55
optimized and the optimized antenna exhibits ultrawideband ranging from 3.1GHz to 14.2GHz. This covers the FCC’s UWB requirements. The proposed antenna features compact size, wide impedance bandwidth and consistent radiation patterns over the ultra wideband frequency spectrum. The gain is almost uniform over the entire band of UWB. It provides omnidirectional radiation pattern in H-plane and they are bidirectional in E-plane over its whole frequency band. So, the proposed antenna satisfies most of the features required for UWB communication systems.
ACKNOWLEDGEMENTS The authors acknowledge their thanks to UGC, New Delhi for sanctioning the Mentor Graphic’s IE3D simulation software under major research project, which is most useful and reliable for designing of microstrip antennas.
REFERENCES 1) Jyoti Ranjan Panda, Rakhesh Singh K shetrimayum, “Parametric Study of Printed
Rectangular
Monopole Antennas”, International Journal of Recent Trends in Engineering, Vol. 1, No. 3, May 2009. 2) Ramu Pillalamarri, G. Sasi Bhushana Rao, S. Srinivasa Kumar, “Novel Printed Rectangular Patch Monopole Antennas with Slit Ground Plane for UWB Applications”, The NEHU Journal, Vol VIII, No. 1, January 2010. 3) Marek Bialkowski, Amin Abbosh and Hing kan, “Design of Compact Components for Ultra Wideband Communication front ends”. 4) M. Akbari, M. Koohestani, Ch. Ghobadi, J. Nourinia, “A New Compact Planar UWB Monopole Antenna”, Internation Journal of RF and Microwave Computer- Aided Engineering , Vol. 21, No. 2, march 2011. 5) Jihak Jung, Wooyoung Choi, Jaehoon Choi, “A Compact Broadband Antenna with an L-shaped Notch”, The Institute of Electronics, Information and Communication Engineers, Vol. E89-B, No. 6, June-2006. 6) K.C. Kong, K.M. Luk and K.L. Lau, “Compact Ultrawideband Wide-slot antenna”, Microwave and optical technology letters, Vol. 49, No. 4, April 2007.