Design and development of aperture coupled

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 02 Issue: 12 | Dec-2013, Available @ http://www.ijret.org 356
DESIGN AND DEVELOPMENT OF APERTURE COUPLED
RECTANGULAR MICROSTRIP ANTENNA FOR WIDE BAND
OPERATION
B. Suryakanth
Department of Electronics and Communication Engineering, Bheemanna Khandre Institute of Technology, Bhalki,
Karnataka 585328, India
Abstract
This paper presents the experimental investigations carried out for obtaining wide band operation of rectangular microstrip antenna
by using aperture coupled feeding technique. By incorporating U-slots with stubs on the radiating element, antenna resonates for
single wideband with an impedance bandwidth of 45.61%. The antenna has two resonant peaks f1 and f2 which occurs at 12.1 GHz
and 14.38 GHz with minimum return loss of −32.46 dB and −46.12 dB respectively. The lower resonant frequency f1 is closer to the
fundamental resonance of the rectangular patch. The second resonant frequency f2 is due to current along the edges of U-slots and
stubs of aperture coupled U-slot and stub rectangular microstrip antenna (AUSRMSA). This technique also enhances the gain to 9.96
dB which is 1.89 times more than the gain of conventional rectangular microstrip antenna (CRMA). The enhancement of impedance
bandwidth and gain does not affect the nature of broadside radiation characteristics. The design concepts of antennas are presented
and experimental results are discussed.
Keywords: Microstrip, wide band, Aperture coupled, Slots.
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1. INTRODUCTION
In the current communication systems, the use and significance
of microstrip antennas (MSAs) has become widespread due to
their attractive features such as light weight, low volume, ease
in fabrication and low cost [1]. However, the major limitations
associated with MSAs are narrow impedance bandwidth and
low gain. The conventional MSAs have typical impedance
bandwidth nearly 2 to 5% [1-2], which restricts their many
useful applications. Therefore, much work has been devoted to
increasing the impedance bandwidth of microstrip antennas,
such as adding an impedance matching network, stacked
patches, using parasitic patches, slots or by using additional
resonators [3–9] and gain [10-12]. In this presentation wide
band antenna is realized by using aperture coupled feeding
technique. Further the proposed antenna is also capable for the
enhancement of gain and reduction of cross polar power level
by placing U-slot & stubs on the patch and by feeding it
through aperture coupled technique. The enhancement of
bandwidth, gain and reduction of cross-polar power level does
not affect the nature of broadside radiation characteristics.
2. DESCRIPTION OF THE ANTENNA GEOMETRY
The art work of proposed antennas are developed using
computer software AutoCAD and are fabricated on low cost
glass epoxy substrate material of thickness h=1.6 mm and
permittivity εr=4.2. The CRMA has been designed using the
equations available in the literature [1]. Figure 1 show the
geometry of CRMA, which is designed for the resonant
frequency of 9.4 GHz. The antenna is fed by using
microstripline feeding. This feeding has been preferred because
of its simplicity and it can be simultaneously fabricated along
with the antenna element. Figure 1 consists of a radiating patch
of length L and width W, quarter wave transformer of length Lt
and width Wt used between the patch and 50 Ω microstripline
feed of length Lf and width Wf. At the tip of microstripline feed,
a 50 Ω coaxial SMA connector is used for feeding the
microwave power.
Fig 1 Geometry of CRMA

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Figure 2 shows the geometry of AUSRMSA. The radiating
element is etched on the top surface of substrate S1 as shown in
Fig. 2 (a). The two open circuited stubs of length LT and width
WT are placed at a distance D1 on the radiating element. The
dimensions of LT and WT are taken as λ0/6.30 and λ0/63.83
respectively. The distance D1 is chosen as λ0/63.83 from the
non-radiating edges of the rectangular patch. The U-slot is
placed at the centre of the patch, which is symmetrical to its
centre axis along the width. The distance between the vertical
arms of the U-slot and open circuit stub D2 is λ0/16.38. The
length and width of the U-slot are same as that of the open
circuit stubs. The distance between the inner sides of the U slots
Ua is taken as λ0/10.64. The copper layer on the bottom
surface of S1 is removed. The H-coupling aperture is etched
on top surface of substrate S2 which is the ground plane as
shown in Fig. 2 (b). The length L1 of vertical arm in H-slot is
λ0/10.64 and width W2 is λ0/63.83. The length and width of
horizontal arm namely L2 and W1 of this slot are λ0/15.95 and
λ0/63.83 respectively as shown in Fig. 3.
(a) Radiating element of AUSRMSA (b) Coupling slot on the ground plane (c) Microstrip line feed etched on the top surface of S1
Fig. 2 Geometry of AUSRMSA
In the aperture coupled feed configuration, the field is coupled
from the microstripline feed to the radiating patch through an
electrically small aperture or slot cut in the ground plane as
shown in Fig. 2 (b). The coupling aperture is usually centered
under the patch, leading to lower cross-polarization due to
symmetry of the configuration. The shape, size and location of
the aperture decide the amount of power to be coupled from the
feed line to the patch. The expanded geometry of the coupling
H-slot is as shown in Fig. 3. This aperture has been preferred
because it is more effective in coupling the power to the patch
etched on the top surface of S1 when compared to any other
aperture [13]. The length of each vertical arm in H-slot is L1
and width W2. The length and width of horizontal arm of this
slot are L2 and W1 respectively as shown in Fig. 3. Table1 and
Table 2 show the design parameters of the proposed antennas in
mm.
Fig. 3 Expanded geometry of H-coupling slot
Table 1 Design parameters of CRMA
Antenna
Parameters
L W Lt Wt Lf Wf h N M
Dimensions
(mm)
7.10 9.89 4.18 0.48 4.10 2.50 16 25 25

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Table 2: Design Parameters of Adusrmsa
Antenna
Parameters
L′f W′f L1 L2 W1& W2 LT WT Ua D1 D2
Dimensions
(mm)
13.00 2.50 3.00 2.00 0.50 7.06 0.5 2.99 0.50 1.95
3. EXPERIMENTAL RESULTS
The CRMA is designed and fabricated for 9.4 GHz of
frequency which is standard or test frequency of X-band. The
impedance bandwidth over return loss less than −10 dB is
measured from 8 to 12 GHz of frequencies. The variation of
return loss versus frequency of CRMA is as shown in Fig. 4.
Fig 4 Variation of return loss versus frequency of CRMA
From this figure, it is seen that the antenna resonates at 9.11
GHz of frequency with minimum return loss of −16.79 dB. The
impedance bandwidth (BW1) of CRMA is calculated by
using equation (1) and is found to be 4.40 %.
BW = 




 −
C
LH
f
ff
× 100% (1)
Where, fH and fL are the upper and lower cut-off frequency of
the band respectively when its return loss becomes -10dB and fc
is the centre frequency between fH and fL. The variation of
return loss versus frequency of AUSRMSA of Fig. 2 is as
shown in Fig. 5. From this figure, it is seen that, the antenna
resonates for single band BW. The impedance bandwidth of
BW is found to be 45.61 %. From the Fig. 5, it is observed that,
two resonant peaks f1 and f2 occurs at 12.1 GHz and 14.38 GHz
respectively with minimum return loss of −32.46 dB and
−46.12 dB respectively. The use of U-slots with stubs in this
antenna resonates very close to the patch resonance.
Fig 5 Variation of return loss versus frequency of AUSRMSA
The co-polar and cross-polar radiation patterns of CRMA are
measured in its operating band. The typical radiation patterns
measured at 9.11 GHz are as shown in Fig. 6. From this figure,
it is seen that, the pattern is broadsided and linearly polarized.
The half power beam width (HPBW) measured from Fig.6 is
found to be 760
. The cross-polar power level is −10.14 dB down
compared to co-polar power level. The cross polar power level
usually -10 dB down or below with respect to co-polar power
level normally indicates the broadside nature of radiation. The
gain of CRMA is found to be 5.26 dB.
Fig 6 Co-polar and cross polar radiation patterns of CRMA
measured at 9.11 GHz.
The co-polar and cross-polar radiation pattern of AUSRMSA is
measured in its operating band BW. A typical radiation pattern
measured at 12.1 GHz is as shown in Fig. 7. From this figure, it
is seen that, the pattern is broadsided and linearly polarized.
The HPBW measured from Fig 7 is found to be 94.84°. The

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gain of AUSRMSA is found to be 9.96 dB which is 1.89 times
more than the gain of CRMSA.
Fig 7 Co-polar and cross polar radiation patterns of AUSRMSA
measured at 12.1 GHz.
The variation of input impedance of AUSRMSA is measured
on VNA which is as shown in Fig. 8. In this figure the multiple
loci appears around the centre of the Smith chart. This validates
its wide band nature.
Fig 8 Variation of input impedance of AUSRMSA
The minimum input impedance of this antenna is 49.24−ј78.33
Ω found from Smith chart which is very close to the
characteristic impedance of 50 Ω. This shows excellent
impedance matching.
CONCLUSIONS
From the detailed experimental study it is concluded that the
use of aperture coupled technique is effective in enhancing the
impedance bandwidth of CRMA. The impedance bandwidth of
BW of AUSRMSA is found to be 45.61 %. This technique also
enhances the gain to 9.96 dB which is 1.89 times more than the
gain of CRMA. The enhancement of impedance bandwidth,
gain and reduction of cross-polar power level does not affect
the nature of broadside radiation characteristics. The proposed
antennas are simple in design and fabrication and they use low
cost substrate material. The wideband broadside nature of
radiation of AUSRMSA may find applications in radar
communication systems operating from X to Ku-band of
frequencies.
ACKNOWLEDGEMENTS
The author would like to thank Dept. of Science & Technology
(DST), Govt. of India, New Delhi, for sanctioning Vector
Network Analyser to the department of P.G. Studies and
Research in Applied Electronics, GulbargaUniversity, Gulbarga,
Karnataka 585 106, India under FIST project.
REFERENCES
[1] I. J. Bahl and P. Bhartia, Microstrip antennas. Artech
House, New Delhi, 1981.
[2] D. M. Pozar, “Microstrip antennas,” proceedings of the
IEEE., vol. 80, no. 1, pp. 79-91, Jan. 1992.
[3] H. F. Pues and A. R. Van de Capelle, “An impedance
matching technique for increasing the bandwidth of
microstrip antennas,” IEEE Trans. Antennas Propagat.,
vol. 37, no. 11, pp. 1345-1354, 2002.
[4] K. Oh., et al. “Design of dual and wideband aperture
stacked patch antenna with double-sided notches,”
Electron. Lett., vol. 40, no. 11, pp. 643-645, 2004.
[5] J. Y. Sze and K. L. Wong, “Slotted rectangular
microstrip antenna for bandwidth enhancement,” IEEE
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1152, 2000.
[6] Jeun-Wen Wu and Jui-Han Lu, “Slotted circular
microstrip antenna for bandwidth enhancement”, IEEE
Int. Symp., vol. 2, pp. 272-275, June 2003.
[7] G. Kumar and K. P. Ray, “Broadband Microstrip
Antennas”, Artech House, Norwood, 2003.
[8] D. M. Pozar and B. Kaufman, “Increasing bandwidth of
a microstrip antenna by proximity coupling”, Elect. Lett.,
vol. 23, no. 8, pp. 368-369, April 1987.
[9] G. Kumar and K. C. Gupta, “Broad-band microstrip
Antennas using additional resonators gap-coupled to the
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[10] R. David Jackson and G. Nicolaos Alexopoulos, “Gain
enhancement method for printed circuit antennas,” IEEE
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[11] E. Nishiyama and M. Aikawa., “Wide-band and High
Gain Microstrip Antenna with Thick Parasitic Patch
Substrate,” IEEE Trans. Antennas Propagat., vol. 32, pp.
1375-1379.

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[12] David R. Jackson and Nicolaos G. Alexopoulos, “Gain
enhancement method for printed circuit antennas,” IEEE
Trans. Antennas Propagat., vol. 33, No. 9, 976-987,
2002.
[13] X. H. Yang and L. Shafai, “Multi frequency operation
technique for aperture coupled microstrip antennas”,
IEEE, Society Int. Symp. Digest, vol. 2, pp. 1198-1201,
1994.
BIOGRAPHIE
Dr. B. Suryakanth received the M.E degree in
Power Electronics from Poojya Doddappa Appa
College of Engineering, Gulbarga, Karnataka in
the year 2004 & Ph. D degree in the field of
Microwave Electronics in the Department of P.
G. Studies & Research in Applied Electronics, Gulbarga
University, Gulbarga, Karnataka in the year 2013. His research
interest involves design, development and parametric
performance study of microstrip antennas.

Design and development of aperture coupled

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Design and development of aperture coupled