Compact Circularly Polarized Square Patch
Antennas
L. Lolit Kumar Singh1, Bhaskar Gupta2, Partha P Sarkar3
Department of Electronics and Communication Engineering, Mizoram University, Tanhril, Aizawl-796004, India1,
Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata-700032, India2,
Dept. of Engineering & Technological Studies, University of Kalyani, Nadia- 741235, West Bengal, India3
llksingh@yahoo.co.in1,
gupta_bh@yahoo.com2, parthabe91@yahoo.co.in3
Abstract— Two numbers of compact circularly polarized patch
antennas are developed by using slot loading techniques.
Compact circularly polarized (CP) operation of a pair of corner
truncated square microstrip antenna with slits on the patch and
ground plane is proposed and investigated. Compactness of the
proposed CP design is achieved due to the inserted slits on patch
and ground plane. These two different slot loaded compact
circular-polarized microstrip antennas are as follows :-Compact
CP microstrip antenna with slits on patch and ground plane ( Let
us say Antenna 1) and another Compact CP microstrip antenna
with four slits on patch (Let us say Antenna 2). At first a pair of
corner truncated square microstrip patch embedded with a pair
of slits in patch and four slits in the finite ground plane along the
directions of + 450 (Antenna 1) is developed to achieve compact
CP operation. These inserted slits in both patch and ground
plane can result in meandering of the excited fundamental-mode
patch surface current path, which effectively lowers the resonant
frequency of the modified square patch. The proposed compact
CP design can have an operating frequency reduction of about
21.95% as compared to the conventional corner-truncated
square microstrip antenna of same size without any slits in the
patch and ground plane. Another compact CP patch antenna
with a pair of corner truncated square microstrip patch with
embedding four slits of equal length and width in patch (Antenna
2) to achieve a simple compact CP operation. The proposed
compact CP design can have an operating frequency reduction of
about 23.16% as compared to the conventional corner-truncated
square microstrip antenna of same size without any slits on patch.
These inserted slits in both patch effectively lowers the resonant
frequency of the modified square patch.
I. INTRODUCTION
One of the many advantages of microstrip patches over
conventional antennas is their small size. However, there are
many present day applications where even these small
radiators are considered too large. To satisfy the requirement
of miniaturization of portable communications equipment,
studies of compact microstrip antennas have received much
attention, and several related designs with circularly polarised
radiation [1 – 4] have also been reported. By embedding
suitable slots or slits, such as a cross slot [1], four narrow slits
[2] and four bent slots [3] in the radiating patch of microstrip
antennas a compact circularly polarised microstrip antenna
can be obtained. The load of the slots or slits in the radiating
patch can cause meandering of the excited patch surface
current paths and result in lowering of the resonant frequency
of the antenna, which corresponds to a reduced antenna
size for such an antenna, compared to a conventional
circularly polarised microstrip antenna at the same operating
frequency. A compact circularly polarized microstrip antenna
with slotted ground plane is also reported [4]. In this paper at
first we presented a pair of corner truncated square microstrip
patch with embedding a pair of slit in patch and four slits in
the finite ground plane along the directions of + 450 to
achieve a compact CP operation (Antenna 1). The
compactness of the proposed CP design is achieved due to the
inserted slits at the square patch and finite ground plane. The
proposed compact CP design can have an operating frequency
reduction of about 21.95% as compared to the conventional
corner-truncated square microstrip antenna of same size
without any slits in the patch and ground plane. Also, the 3 dB
axial ratio (AR) centre frequency bandwidth is 0.43%.
Another, a pair of corner truncated square microstrip patch
with embedding four slits of equal length and width in patch
to achieve a simple compact CP operation (Antenna 2). The
compactness of the proposed CP design is achieved due to the
inserted slits at the square patch. The proposed compact CP
design can have an operating frequency reduction of about
23.16% as compared to the conventional corner-truncated
square microstrip antenna of same size without any slits on
patch. The 3 dB axial ratio (AR) centre frequency bandwidth
of 0.21% is obtained. These inserted slits can result in
meandering of the excited fundamental-mode patch surface
current path, which effectively lowers the resonant frequency
of the modified square patch. Details of the proposed compact
CP design are described, and simulated results are presented.
The IE3D simulation software based on Method of Moments
(MoM) is used for simulation and analysis.
II. ANTENNA DESIGN
Analysis is performed for single layer single feed square patch
antenna with finite ground plane. The substrate dielectric
constant (εr = 4.4) and height (h =1.6 mm) of substrate from
ground plane is used. Figs. 1(a-c) show the proposed Antenna
1 single-feed square microstrip antenna for compact CP
operation. The square microstrip patch has a side length L =
28 mm and finite ground plane length LG = 50 mm. The slits
are of equal length 8 mm and width 1 mm and are inserted in
the patch. A pair of truncated corners is of equal side length
∆L= 2.5 mm. The four numbers slits of equal length (L S) and
width (WS) are also inserted in the ground plane along the
directions of + 450. The single probe feed is placed at point
along Y- axis, a left- hand CP operation is obtained.
Figs. 2 (a, b) show the proposed Antenna 2 single-feed square
microstrip antenna for compact CP operation. The square
microstrip patch has a side length L = 28 mm, four numbers
slits of equal length (LS) and width (WS) are inserted in the
patch along the directions of + 450. A pair of truncated
corners is of equal side length ∆L= 2.5 mm. The single probe
feed is placed at point along Y- axis, a right- hand CP
operation is obtained.
a.
a.
b.
b.
Fig. 2 Antenna 2 a. Geometry of the compact circularly polarized square
microstrip antenna b. Side view.
III. ANALYSIS AND RESULTS
For running simulations in IE3D Zeland Software, finite
ground plane is considered for Antenna 1 and infinite ground
for Antenna 2.
c.
Fig. 1 Antenna 1 a. Geometry of the compact circularly polarized square
microstrip antenna b. Side view c. Geometry of ground plane. (All the
dimensions are in mm).
Antenna 1: Several designs with the feed point position along
Y-axis and slit length (LS) on ground plane for left- hand CP
operation were studied. Figs. 3 (a-b) shows return loss, axial
ratio (AR) against frequency for case 1 of Ls = 15 mm, WS=
1mm, XS = YS = + 6.5 mm. The axial ratio bandwidth of
0.43% at centre frequency, total gain of 2.51 dBi and total
directivity of 5.42 dBi are obtained at 1.966 GHz.
a.
a.
b.
Fig. 3 a. Return loss Vs Frequency b. Axial Ratio (AR) Vs Frequency .
b.
Fig. 4. a. Radiation patterns (E-total) at 1.966 GHz b. Radiation Patterns (Eleft and E-right) at 1.966GHz.
The Simulated radiation characteristics at 1.966 GHz are
shown in Figs. 4 (a, b) for the case 1. The corresponding gains
of E-left and E-right are 2.24 dBi and -10.06 dBi respectively
at phi = 0 (degree).
The performances of the proposed CP microstrip antenna with
different parameters are shown in Table 1.
TABLE 1: Performance of the proposed CP microstrip antenna (Antenna 1)
∆L= 2.5 mm, L=28 mm, LG= 50mm, εr = 4.4 , h =1.6 mm
Antenna
Parameter (dimensions are in
mm)
Feed
point
YF (mm)
Frequency
(GHz)
Gain(dBi),
Directivity
(dBi)
Main ,
Back Lobe
(dBi)
Reference
Square patch with pair of
truncated corner
-7
2.519
5.25/6.66
15.31
Case 1
Slits on patch
( X=-5,Y=10, l=1,w=8)
(X=10,Y=-5, l=8, w=1) Slits on
ground plane
(XS=YS= + 6.5, LS=15,WS=1)
-4
1.966
2.51/5.42
5.03
Percentage
of frequency
reduction %
3 dB
BWAR %
0.55
21.95
0.43
Fig. 5 a. Return loss Vs Frequency b. Axial Ratio (AR) Vs Frequency .
The back lobe size increases as slits are introduced in ground
plane and simultaneously radiation efficiency decreases to
46.3%, operating frequency also decreases from 2.519 GHz to
1.966 GHz (case 1).
Antenna 2: Two different designs with the feed point position
along Y-axis and slit length (LS) in patch for right- hand CP
operation were studied. Figs. 6(a-b) shows return loss, axial
ratio (AR), against frequency for case 1 of Ls = 15.4 mm, WS=
1mm, XS = YS = + 6 mm. The 3 dB axial ratio bandwidth of
0.21% obtained at 1.921 GHz.
The Simulated radiation characteristics at 1.921 GHz are
shown in Figs. 6 (a, b) for the case 1. The corresponding gains
of E-left and E-right are -25.59 dBi and -0.021 dBi
respectively at phi = 0 (degree).
a.
a.
b.
Fig. 6. a. Radiation patterns (E-total) at 1.921 GHz b. Radiation Patterns (Eleft and E-right) at 1.921 GHz.
b.
The performances of the proposed CP microstrip antenna with
different parameters are shown in Table 2.
TABLE 2: Performance of the proposed CP microstrip antenna (Antenna 2)
∆L= 2.5 mm, L=28 mm, εr = 4.4, h =1.6 mm
Antenna
Referenc
e
Case 1
Parameter (dimensions are in mm)
Feed
point
YF (mm)
Frequency
(GHz)
Gain(dBi),
Directivity
(dBi)
Main lobe
(dBi)
Square patch with pair of truncated
corner
-7
2.5
4.98/6.355
4.98
Four Slits on patch along + 450
XS=YS= + 6, LS=15.4,WS=1)
-2.5
1.921
-1.91/6.15
-1.91
IV. CONCLUSION
The compactness of the proposed CP design is achieved due
to the inserted slits at the square patch and finite ground plane.
These inserted slits result in meandering of the excited
fundamental-mode patch surface current path, which
effectively lowers the resonant frequency of the modified
square patch. The proposed compact CP (Antenna 1) design
can obtained an operating frequency reduction of about
21.95% as compared to the conventional corner-truncated
square microstrip antenna of same size without any slits on
patch and ground plane. The radiation efficiency of the
proposed CP microstrip antenna is about 46.3 %. The 3 dB
axial ratio (AR) centre frequency bandwidth is 0.43%.
Another, compact CP (Antenna 2) design can obtained an
operating frequency reduction of about 23.16% as compared
to the conventional corner-truncated square microstrip antenna
of same size without any slits on patch. The 3 dB axial ratio
(AR) bandwidth of 0.21% is obtained.
REFERENCES
[1]
[2]
[3]
H. Iwasaki, “A circularly polarized small-size microstrip antenna
with a cross slot,” IEEE Transactions on Antennas &
Propagation, vol. 44, no. 10 pp. 1399-1401, 1996.
W.S. Chen, C. K. Wu, and K. L. Wong, “Novel Compact
circularly polarized square microstrip
antenna,” IEEE
Transactions on Antennas & Propagation, vol.49, no.3, pp. 340342, March, 2001.
W.S. Chen, C. K. Wu, and K. L. Wong, “Compact circularly
polarized microstrip antenna with bent slots,” Electronics Letters,
vol. 34, no. 13, pp. 1278-1279, June, 1998.
3 dB
AR
BW %
0.57
23.16
0.21
H. D. Chen,“ Compact circularly ploarised microstrip antenna with
slotted ground plane,” Electronics Letters, vol. 38, no.13, June
2002.
[5] Chih-Chiang Chen, Chow-Yen-Desmond Sim, and Fu-Syuan Chen,
“ A Novel Compact Quad-Band Narrow Strip-Loaded Printed
Monopole Antenna”, IEEE Antennas and Wireless Propagation
Letters, Vol. 8, 2009, pp. 974-976.
[6] T. Debogovic, and J. Bartolic, “ Pattern Reconfigurable Compact
Antenna”, IEEE MTT-S International Microwave Workshop on
wireless sensing, Local Positioning, and RFID (IMWS 2009Croatia), 2009.
[7] Yipeng Fan, Guang Fu, Qiyi Lu, and Rui Zhang “ A compact
microstrip antenna by a finite U-shaped ground plane”, 9th
International Symposium on antennas Propagation and EM
Theory (ISAPE), 2010, pp. 229 – 231.
[8] A. Hassan, F. Elhefnawi, A.Z. Elsherbeni, M. Hendi, and S.
Elramly, “
Compact dual circularly-polarized microstrip
antennas”, IEEE Antennas and Propagation Society International
Symposium (APSURSI), 2010.
[9] Wen-Shan Chen, Bau-Yi Lee, and Po-Yuan Chang, “ A compact
and small printed monopole antenna for WLAN applications”,
Microwave and Optical Technology Letters, Vol. 53, No. 7, Jul.,
2011, pp. 1518-1522.
[10] Nasimuddin, Xianming Qing, and Zhi Ning Chen, “ Compact
Asymmetric-Slit Microstrip Antennas for Circular Polarization”,
IEEE Transactions on Antennas and Propagation, Vol. 59,No. 1,
Jan., 2011, pp. 285-288.
[4]
As slits size in ground plane increases gain decreases,
simultaneously radiation efficiency decreases, operating
frequency also decreases from 2.5 GHz to 1.921 GHz (case 1).
The antenna gain and 3dB axial ratio bandwidth for such
compact circular polarization (CP) designs are also
decreased.
Percentage
of frequency
reduction %