circularly polarized aperture coupled microstrip short backfire antenna with two rings
TRANSCRIPT
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International Journal of Electronics and Communication Engineering and Technology
(IJECET)
Volume 8, Issue 2, March - April 2017, pp. 13–25, Article ID: IJECET_08_02_003
Available online at
http://www.iaeme.com/IJECET/issues.asp?JType=IJECET&VType=8&IType=2
ISSN Print: 0976-6464 and ISSN Online: 0976-6472
© IAEME Publication
CIRCULARLY POLARIZED APERTURE
COUPLED MICROSTRIP SHORT BACKFIRE
ANTENNA WITH TWO RINGS
Kawa ABDOULA
Dept. of Communication Engineering,
Technical University of Varna,
Student SKA Str. 1, 9010 Varna, Bulgaria
ABSTRACT
A circularly polarized microstrip short back fire antenna (CPMSBA) with two ring
corrugated rim using aperture coupling feed method is proposed in this paper. The
antenna is designed to operate in KU-band. The simulation results verify the circular
polarization. The axial ratio bandwidth bwAR is 3.74%, gain is 10.43 dBi and
radiation efficiency is 89.7%. The antenna has a compact structure and high electrical
and mechanical characteristics.
Key words: Aperture Coupled Microstrip Antenna, Back Radiation, Circularly
Polarized Microstrip Antenna with Two Rings, Microstrip Short Backfire Antenna
(MSBA)
Cite this Article: Kawa ABDOULA, Circularly Polarized Aperture Coupled
Microstrip Short Backfire Antenna with Two Rings, International Journal of
Electronics and Communication Engineering and Technology, 8(2), 2017, pp. 13–25.
http://www.iaeme.com/IJECET/issues.asp?JType=IJECET&VType=8&IType=2
1. INTRODUCTION
The microstrip patch antennas have been used in many commercial and military applications
including radar, mobile communications, satellite communications and Wireless Local Area
networks (WLANs). The origin of microstrip antennas apparently dates back to 1953, when
Deschamps proposed the use of microstrip feed lines to feed an array of printed antenna
elements [1] - [ 2].
The microstrip patch antenna was first introduced by Munson in a symposium paper in
1972 [3]. Microstrip antennas are fed by one of four methods (a) microstrip line (b) coaxial
probe (c) aperture coupling and (d) proximity coupling. Microstrip patch antennas have
several well-known advantages over other antenna structures, including their low profile and
hence conformal nature, lightweight, low cost of production, robust nature, and compatibility
with microwave monolithic integrated circuits and optoelectronic integrated circuits
technologies [4]. Microstrip patch antennas suffer from several inherent disadvantage of this
technology in its pure form, namely, they have small bandwidth and relatively poor radiations
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efficiency resulting from surface wave excitations and conductor and dielectric losses. Many
specialized techniques have been developed to increase the bandwidth of a microstrip
antenna. These include either using thick foam substrates along with aperture coupled feeds to
avoid the probe reactance limitation, or using capacitive elements to compensate for the probe
inductance. Even further increases may be achieved by using configurations that exhibit dual
or multiple resonances, including stacked resonators or antennas surrounded by parasitically
coupled elements. [5]
The microstrip antennas (MSAs) may be designed for circular polarizations by adjusting
their physical dimensions so as to produce two degenerate orthogonal modes with in the
cavity region. This in turn results in the radiation of two orthogonally polarized waves near
the broadside direction. Thus circularly polarized radiation is obtained when two orthogonal
modes are excited with equal amplitude and in-phase quadrature [6].
2. RADIATION MECHANISM
The basic microstrip antenna is consisting of a radiating patch on one side of a dielectric
substrate, which has a ground plane of the other side. The microstrip patch and the ground
plane together form a resonant cavity (filled with the substrate material). The cavity is lossy,
due not only to the material (conductor and dielectric) loss, but also to the (desirable)
radiation into space [7].
In Figure 1. The electromagnetic energy provides by the feed microstrip line passes
though rectangular slot into the first resonator formed by patch element and the ground plane.
After multiple reflections between the inner walls of the first resonator, a part of this energy
radiated directly into the space and other part of this
Figure 1 Geometry of the antenna Cross section (b) Front view
Circularly Polarized Aperture Coupled Microstrip Short Backfire Antenna with Two Rings
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Electromagnetic energy penetrates via the short sides of the patch element to the second
resonator, formed by the small reflector and ground plane. After multiple reflections between
the inner walls of the second resonator, the electromagnetic energy radiated between the short
sides of the small reflector and the rim in the broadside of the antenna. The rims reduce the
back and side radiations of the proposed antenna.
3. DESCRIPTION OF THE ANTENNA
Figure 1. shows the geometry of the aperture coupled microstrip short backfire
antenna(ACMSSBFA) The antenna consists of the following elements:
1. Screen 2. Screen Substrate 3. Feed line 4. Feed substrate 5. Ground (D2) 6. Rim 7.
Rectangle Cross-Slot 8. Patch 9. Patch substrate 10. Small Reflector (D1) 11. Additional
substrate. 12.Small reflector Substrate 13. Additional ring and five substrates as follows:
additional substrate AS (Taconic TLX-7: "εrt = 2.6, tan _t = 0.0019); small reflector substrate
SRS (Arlon AD 410: "εrq = 4.1, tan _q = 0.0030, the small reflector substrate is realized by
two layers with standard thickness of 3.175 mm); patch substrate PS (Arlon AD 600: "εrp =
6.15, tan _P =0.0030); feed substrate FS (Arlon AD 600: "εrf = 6.15, tan _f = 0.0030) and
screen substrate SS (Taconic TLX-7: "εrs=2.6, tan_S=0.0019).
4. EFFECT OF THE DIMENSION OF THE ANTENNA ON ITS
ELECTRICAL CHARACTERISTICS
The simulation of the CP antenna model is done by the software package CST Microwave
Studio 2010. The final results are verified with several others software packages.
Seven antenna electrical characteristics such as module of reflections coefficient |S11|
(return loss), axial ratio AR, gain G, back radiations level BRL, radiations efficiency ηeff and
radiations pattern are investigated in this paper.
Nine CP antenna dimension and constructive parameters such as length of patch LP, patch
size coefficient KP= LP/WP, average length of the cross slot La. Cross size coefficient
KS=La1/La2, length of the small reflector Lsr, small reflector size coefficient K1=Lsr/Wsr, width
of the first ring W1, width of the second ring W2 and length of the matching stub LS are chosen
as independent variables in the optimization.
Their influence of the return loss, axial ratio and gain behavior are shown in figures 2-10.
figures 2-10 shows strong influences of the all 9 dimensions and constructive parameters on
the return loss and axial ratio, while the same parameters and dimensions have low influence
on the antenna gain behavior. Co- and cross polar radiation patterns in φ = 45º-plane at three
frequencies (fmin=11.175 GHz, f0 = 0.5(fmin +fmax) =11.388 GHz and fmax = 11.602 GHz) are
shown in figure 11.
Figure 11 shows small changes of the radiations characteristics over the whole operating
frequency range. Figure 12 shows the return loss, axial ratio and gain of the proposed CP
antenna calculated by two different software packages- CST Microwave Studio 2010 and
HFSS version 11.1.
The both curves in the figure 12. (a) have similar behavior and their values close to each
other. CST Microwave gives the following results: central frequency f0=11.709 GHz and
impedance bandwidth bwS11 = 10.83%, while the HFSS Product is f0=11.560 GHz and bwS11 =
9.69% respectively, i.e. the above results differ only by 1.3% with respect to central frequency
and by 10,5% regarding the impedance bandwidth, which indicate a good agreement of the
obtained simulated results.
Figure 12. (b) shows the axial ratio. CST MWS gives the following results: central
frequency f0=11.388 GHz and axial ratio bandwidth bwAR =3.74%, while the HFSS Product is
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f0=11.42 GHz axial ratio bandwidth bwAR= 3.39% the results differ by 0.3% with respect to
central frequencies and by 9,35% regarding the axial ratio bandwidths bwAR.
Figure 12. (c) shows the antenna gain. CST MWS gives the Gmax=10.43 dBic while the
HFSS gives the Gmax=10.904 dBic, the results differ by 4.54%.
The dimensions of the proposed CP antenna are listed in Table 1, the optimized
parameters of the antenna structure are listed in Table 2, and the e electrical parameters of the
antenna are shown in the Table 3.
Table 1 Dimension of the antenna
Dimensions [ mm] Description
D 2 24 Big Reflectors inner diameter
tg 0.0175 Big reflector& ground thickness
L 13.155 Antenna length
Wsr 3.30 Small reflector width
W 7.6825 Rim width
tt 0.035 Small reflector thickness
tw 0.5 Rim thickness
Wp 2.38 Patch width
tp 0.035 Patch thinness
Wa1 0.45 Slot1 width= 0.1La1
Wa2 0.40 Slot2 width = 0.1 La2
l 11.9 Microstrip feed line length
Ls 1.0 Stub length
Wf 0.98 Microstrip feed line width
tf 0.0175 Microstrip feed line thickness
Ds 24 Screen diameter
ts 0.035 Screen thickness
ht 1.58 Additional substrate thickness
hq 6.35 Small reflector substrate thickness
hp 1.27 Patch substrate thickness
hf 0.635 Feed substrate thickness
hs 3.175 Screen substrate thickness
t1 0.5 Ring thickness
h1, h2 0.4 Distance between the upper edge of the peripheral
screen and the upper edge of the first and second ring
Circularly Polarized Aperture Coupled Microstrip Short Backfire Antenna with Two Rings
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Table 2 Optimized parameters of the antenna
Name Value [ mm] Description
LP 2.7 Patch length
K1 1.12 Small reflector ratio Lsw/Wsr
KP 1.13 Patch Ratio LP/WP
KS 1.10 Slot Ratio La1/La2
La 4.3 Slot Length
La1 (2*La*Ks)/(Ks+1) Aperture 1 Length
La2 2*La/(Ks+1) Aperture 2 Length
Ls 1.0 Stub Length
Lsr 3.7 small reflector Length
Wa1 La1/10 Aperture 1 Width
Wa2 La2/10 Aperture 2 Width
WP LP/KP Patch Width
Wsr Lsr/K1 (W1) Small Reflector Width
W1 3.0 First ring Width
W2 3.0 Second ring Width
Table 3 Electrical parameters of the antenna
Impedance Bandwidth
Minimum frequency fmin , GHz 11.075
Maximum frequency fmax , GHz 12.343
Central frequency f0 , GHz 11.709
Relative bandwidth bw,% 10.83%
Frequency bandwidth BW, GHz 1.27
Axial Ratio bandwidth, Back Radiation, Gain and
efficiency
Minimum frequency fmin AR , GHz 11.175
Maximum frequency fmax AR , GHz 11.602
Central frequency f0 AR , GHz 11.388
Frequency bandwidth BWAR, GHz 0.427
Relative bandwidth bwAR, % 3.74
Gmin, dBi 10.17
Gmax, dBi 10.43
BRmin, dB -17.84
BRmax, dB -16.091
Efficiency ηmax, % 89.74%
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(a) (b)
(b) (b)
(c) (c)
Fig 2. Effect of the patch length LP (LP = 2.4 Fig. 3. Effect of the coefficient KP = LP/WP
mm –blue dashed line, LP = 2.7 mm – red solid line (KP = 1.03 – blue dashed line, KP = 1.13 – red
and LP = 3.0 mm – green dotted line) on the solid line and KP = 1.23 –green dotted line) on
electrical characteristics of the antenna: (a) the electrical characteristics of the antenna: (a)
return loss, (b) axial ratio, (c) gain return loss, (b) axial ratio, (c) gain.
Circularly Polarized Aperture Coupled Microstrip Short Backfire Antenna with Two Rings
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(a) (a)
(b) (b)
(c) (c)
Fig 4. Effect of the average length of the cross Fig 5. Effect of the coefficient KS = La1/La2
slot La (La = 4.0 mm – Blue dashed line, La = 4.3 (KS = 1.05 –blue dashed line, KS = 1.10 – red
mm – red solid line and La = 4.6 mm –green dotted solid line and KS = 1.15 – green dotted line) on
line) on the electrical ratio, characteristics of the the electrical characteristics of the antenna: (a)
antenna: (a) return loss, (b) axial ratio, (c) gain return loss, (b) axial ratio, (c) gain
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(a) (a)
(b) (b)
(c) (c)
Fig 6. Effect of the small reflector length Lsr Fig 7. Effect of the coefficient K1 = Lsr/Wsr
(Lsr = 3.1 mm –blue dashed line, Lsr = 3.7 mm – (K1 = 1.02 –blue dashed line, K1 = 1.12 –red
red solid line and Lsr = 4.3 mm –green dotted solid line and K1 = 1.22 – green dotted line) on
line) on the electrical characteristics of the the electrical characteristics of the antenna: (a)
antenna: (a) return loss, (b) axial ratio, (c) gain. return loss, (b) axial ratio, (c) gain.
Circularly Polarized Aperture Coupled Microstrip Short Backfire Antenna with Two Rings
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(a) (a)
(b) (b)
(c) (c)
Fig 8. Effect of the first ring width W1 (W 1= 2.0 Fig 9. Effect of the second ring width W2 (W 2=1.0
mm –blue dashed line, W1 = 3.0 mm – red solid mm –blue dashed line, W2 = 3.0 mm – red solid
line and W1 = 4.0 mm – green dotted line) on the line and W2 = 5.0 mm – green dotted line) on the
electrical characteristics of the antenna: electrical characteristics of the antenna:
(a) return loss, (b) axial ratio, (c) gain. (a) return loss, (b) axial ratio, (c) gain.
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(a) (a)
(b) (b)
(c) (c)
Fig 10. Effect of the stub length LS (LS = Fig 11. Radiation patterns of the antenna (co-
0.5mm –blue dashed line, LS = 1.0 mm – red polar, RHCP –red solid line and cross-polar,
solid line and LS = 1.5 mm –green dotted line) LHCP –green dashed line), plane φ = 45º: (a) f
on the electrical characteristics of the antenna: = fmin = 11.175 GHz, (b) f = f0 = 11.388 GHz,
(a) return loss, (b) axial ratio, (c) gain. (c) f = fmax = 11.602 GHz
Circularly Polarized Aperture Coupled Microstrip Short Backfire Antenna with Two Rings
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(a) (b)
(c)
Fig 12. (a) Return loss, (b) AR and (c) Gain of the antenna calculated by means of two different
software’s: CST MWS 2010 –red solid line, HFSS v.11.1 –blue dashed line.
5. DISCUSSION AND NUMERICAL RESULTS
In this study an aperture coupled microstrip short backfire antenna was designed and
investigated. The following features of the proposed antenna design need discussion.
Advantages of the antenna
The impedance bandwidth bwS11 of the CP antenna is 10.83% while its polarization
bandwidth bwAR is equal to 3.74% this is good bandwidth compared with the conventional
microstrip antenna. The bandwidth enhancement in this case is due basically to the type of
chosen feed, suitable choice of the values of substrate dielectric constants and thicknesses,
optimization of antenna dimensions and insertion of two resonances in the antenna impedance
characteristic. The first of these resonances (the patch resonance) is at lower frequency while
the second resonance (the backfire resonance) is at higher frequency.
The CP antenna gain ranges from 10.17 dBic to 10.43 dBic within the antenna bandwidth,
at the central frequency f0 = 11.388 GHz the antenna has gain G0 =10.40 dBic, radiation
efficiency ηeff0 = 89.74%. The presence of corrugated rim improves the antenna gain by
approximately 0.5 dBic compared to the antenna with conventional rim.
The back radiation level of the CP antenna varies between -16 dB and -17.84 dB across
the antenna bandwidth. The basic contribution to this good result is due to the presence of the
screen and rim.
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The antenna construction is compact, robust and with a low volume. The volume and the
aperture area of the antenna, for example are 3.4 times less than the corresponding dimensions
of the CP SBFA with an air cavity.
Disadvantages of the antenna
The antenna gain is lower compared to the conventional CP SBFA with an air cavity due to
the reduced dimension.
6. CONCLUSION
A broadband circularly polarized aperture coupled microstrip short backfire antenna with two
ring corrugated rim has been designed and numerically examined.
The bandwidth widening of the antenna is achieved by use of two resonances: a patch
resonance and a backfire resonance, it has maximum gain 10.43 dBi, maximum back radiation
-16.091 dB, efficiency 89,74% and axial ratio bandwidth 3.74%, this is good bandwidth
compared with conventional microstrip antenna. The antenna is designed to operate within
KU-band. The antenna has a compact construction and high electrical and mechanical
characteristics. It can be used as a single antenna or as an element of microstrip antenna arrays
with various applications in the various communication systems including Radar, Mobile
communications, satellite communications and wireless local area network.
7. ACKNOWLEDGEMENTS
The authors wish to acknowledge associate professor Georgi Kirov and associate professor
Georgi Chervenkov at the Technical University of Varna, Bulgaria to their support during my
study and investigation of the microstrip short backfire antenna (MSBA).
REFERENCES
[1] G. Deschamps, W. Sichak, Microstrip microwave antennas, Proc. of Third Symp. on
USAF Antenna Research and Development Program. October 1953, 18–22,
[2] J. T. Bernhard, E. Mayes, D. Schaubert, and R.J. Mailloux, A Commemoration of
Deschamps ’and Sichak’ s ‘Microstrip Microwave Antennas’ 50 Years of Development,
Divergence, and New Directions, Proc. of the 2003 Antenna Applications Symp.
(September 2003) 189–230.
[3] R. E Munson, Microstrip phased array Antennas, Proc. of Twenty-Second Symp. on
USAF Antenna Research and Development Program. October 1972.
[4] K. F. Lee, Ed. Advances in Microstrip and Printed Antennas. John Wiley, 1997.
[5] J. L. Volakis, Antenna Engineering Handbook, 4. Edition 2007 chapters 7.1.
[6] S.D. Tragonski, D. M. Pozar, Design of wideband circularly polarized aperture-coupled
microstrip antennas. IEEE Transactions antennas and propagation. 1993, Vol 41, no 2.
[7] Rashmi A. Pandhare and Prasanna L. Zade. Dual Band Compact Microstrip Patch
Antenna with Defected Ground Structure, International Journal of Electronics and
Communication Engineering & Technology, 6(9), 2015, pp. 75-81.
[8] Jolis Gupta and Deshraj Shakya. Design of Microstrip Diplexer Using Lowpass Filter and
Hybrid Bandpass Filter. International Journal of Electronics and Communication
Engineering & Technology, 6(12), 2015, pp. 07-12.
[9] Sudhina H. K, Dr. Jagadeesha S, Dr. N. M. Shetti and Dr.Girish Attimarad, Sierpinski
Carpet Fractal Microstrip Antenna For Improved Bandwidth Using Stacking Technique
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& Technology, 6(1), 2015, pp. 8-16
Circularly Polarized Aperture Coupled Microstrip Short Backfire Antenna with Two Rings
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[10] D. M. Pozar, D., H. Schaubert, The Analysis and Design of Microstrip Antennas and
Arrays, University of Massachusetts at Amherst, a selected Reprint Volume, IEEE
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ABOUT AUTHOR
Kawa ABDOULA was born in Sulaimaniyah, Iraq in 1962; he received his MSc degree in
radio and television engineering from the Technical University of Varna, Bulgaria in 1988.
He worked between 1988 and 1990 as engineer at the Technical University of Varna. Since
1990 he lives in Sweden. He worked at Ericsson Energy System 3 years, Emerson Energy
System 2 years, Ericsson Mobile Communications 2 years, and 14 years as system engineer at
Itron AB in Stockholm, Sweden, (current job). He is Ph.D. student by distance at Technical
University of Varna.