Aperture Coupled Fan Blade Shaped Slotted Microstrip Antenna for
Circular Polarization
Ajay Kurnar ~harrna',A shok ~ i t t a l 'a nd B.V.R ~ e d d ~ ~
University School of Information & Communication Technology GGSIPU, Sector 16-C Dwarka Delhi - 110 078
Ambedkar Institute of Advanced Communication Technologies and Research, Geeta Colony, Delhi - 110 031
DESCRIPTION
Microstrip antennas with circular polarization are extensively used in navigation, radar, satellite
and wireless communication systems. As compared to linearly polarized antennas, the circularly
polarized antennas give greater flexibility in terms of transmitter and receiver orientations. Singly
fed microstrip patch antennas are most popular geometries for circular polarization operation
because of their various merits like reduced weight, less complexity and freedom from use of
external hybrids and couplers. However, singly fed microstrip antennas suffers from low 3 dB axial
ratio bandwidth. A lot of research is underway nowadays to achieve wide axial ratio bandwidth
using single feed.
Aperture coupled microstrip patch antennas are the most popular configuration to improve upon the
impedance bandwidth. The aperture coupled microstrip antennas has numerous advantages over
conventional probe fed microstrip antennas. In aperture coupled antennas, separate substrate can be
used for the feed circuit and the antenna element to isolate spurious feed radiation from the antenna
element by use of a common ground plane. Further, the input impedance can be controlled by the
position and size of the aperture. Any excess reactance generated by the coupling aperture can be
tuned out by the use of tuning stubs in the feed line. The shape of the aperture can be chosen
appropriately to improve coupling with the feed line and the patch.
FIELD OF INVENTION
The field of invention is "Circularly Polarized Microstrip Patch Antennas using single feed. The
concept of generating circularly polarized radiation in a single band by cutting different asymmetric
shape slot geometries like U-shaped slot, C-shaped slot, F-shaped slot etc into the radiating patch
have been attempted and reported in the past.
For the first time a symmetric 'Fan Blade' shaped slot is used to obtain wideband circularly polarized
radiation along with wide impedance bandwidth characteristics. A symmetric 'Fan Blade' shaped
slot has been cut into a nearly square radiating patch singly fed in aperture coupled configuration.
This has resulted in perturbation of patch currents in a manner so as to excite two orthogonal modes
with 90 degree phase difference thereby generating circularly polarized radiation over a wide
frequency band.
The coupling aperture is rectangular in shape and is matched to the radiating patch with a unique
oval shaped stub in feed line. A foam layer with a conducting plane is used as a back shield to
suppress the unwanted backside antenna radiation. The shield is positioned at a distance of
approximately 0.16 h from the aperture plane. This has resulted in gain enhancement of the antenna.
Page 1 of 9
It has been investigated through simulation and proved experimentally that a symmetric 'Fan blade'
shaped slot generates circularly polarized radiation in a wide band. Measured results show that the
proposed structure exhibits a 2: 1 VSWR bandwidth of 24.08 % with respect to mid-band frequency
of 2.45 GHz. The 3 dB axial ratio bandwidth is 2.89 % with respect to measured minimum axial
ratio frequency of 2.42 GHz. This makes the antenna suitable for Wireless and Satellite
Communication applications.
DESIGN DETAILS AND RESULTS
Aperture Coupled 'Fan blade' sha~edsl otted Microstrip Antenna
A nearly square radiating patch is designed at a frequency of 2.45 GHz. The patch dimensions are
calculated to be 39.0 mm x 38.0 mm and aspect ratio of 1.026. Top view of the patch geometry is
shown in Fig. 2 while view of the aperture side and feed side of the substrate is shown in Fig 3. The
patch and the feed substrates used are Roger Corporation's RT Duroid (5880) having E, = 2.2, tan 6
= 0.0009 and thickness, t = 3 1 mil. A foam layer of thickness 10.0 mm with E, = 1.07, tan 6 = 0.0002
is used to increase height between patch and the ground plane. The length and width of the
rectangular coupling aperture cut in the feed ground plane are L, = 33.3 mm and W, = 2.9 mm
respectively. An oval shaped stub with length L, = 8.6 mm, width W, = 3.2 mm is used to match the
coupling aperture to the radiating patch by tuning out the excess reactance. A symmetric 'Fan blade'
shaped slot is cut into the patch area with dimensions as per Table I, with details shown in Fig 1. The
antenna specifications are tabulated in Table-11.
Table I: Design parameters of Fan blade shaped slotted microstrip antenna
Page 2 of 9
Parameter Description Value Parameter Description
Patch Radiator (Square)
Value
Symmetric Fan blade shaped slot
39.0 mm
38.0 mm
1.026
LP
WP
LP/WP
5.0 mm
12.0 mm
8.0 mm
13.5 mm
7.9 mm
2.0 mm
2.0 mm
Patch length
Patch width
Aspect ratio
s 1
s2
s3
s4
ss
SW
sw
As per Fig 1
As per Fig 1
As per Fig 1
As per Fig 1
As per Fig 1
As per Fig 1
Slot Width
Coupling Aperture (Rectangular)
La
Wa
Aperture length
Aperture Width
33.3 mm
2.9 mm
Matching Stub (Oval Shaped)
Ls
Ws
Stub length
Stub Width
8.4 mm
3.2 mm
LP
Fig. 1 Dimensions of the Fan blade shaped slot in radiating patch
Fig. 2 Top view of the aperture coupled Fan blade shaped slotted microstrip antenna
Page 3 of 9
Rectangular
Aperture
Oval
Shaped
Matching
Stub
- Feed line
Fig. 3 (a) View of Coupling Aperture Fig. 3 (b) View of Feed line with Oval Stub
(a) Return Loss
The antenna return loss is measured using Agilent Technologies PNA-X Network Analyzer
model N5244A. The 2:l impedance bandwidth exhibited by the antenna is 0.59 GHz which is
24.08% with respect to the mid-band frequency of 2.45 GHz. The return loss plot is shown in Fig 4.0
below.
Fig. 4 Return Loss
Page 4 of 9
a
(b) Axial Ratio
The boresight axial ratio of the fabricated antenna is measured using an Orbit MiDAS planar antenna
test system and plotted in the bore sight direction. The axial ratio bandwidth is defined in the range
where the axial ratio is below 3 dB. The plot of axial ratio vs. frequency for measured and simulated
case is shown in Fig 5. The measured 3 dB axial ratio bandwidth is 2.89 % with respect to measured
minimum axial ratio frequency of 2.42 GHz.
I (c) Gain
The simulated and measured boresight Gain of the circularly polarized Fan blade shaped slotted
microstrip antenna is shown in Fig. 6. A nominal gain of greater than 8.5 dBi in the circularly
polarized band is obtained with the proposed geometry.
2.6
Frequency, GHz
Fig. 5 Axial Ratio in boresight direction
Simulated
Measured
2 2.2 2.4 2.6 2.8 3
Frequency, GHz
Fig. 6 Gain in boresight direction
Page 5 of 9
(d) Power Pattern
The Azimuth and Elevation power pattern measured using an Orbit MiDAS planar antenna test
system is shown in Fig. 7 and Fig 8 at the circularly polarized resonating frequency of 2.42 GHz.
The measured 3 dB Azimuth & Elevation beamwidth at 2.42 GHz are 48" & 43" respectively.
Fig. 7 Radiation pattern of antenna in Azimuth Plane at 2.42 GHz
Page 6 of 9
Fig. 8 Radiation pattern of antenna in Elevation Plane at 2.42 GHz
Table I1 Specifications of the Aperture Coupled Fan blade Shaped Slotted
Microstrip Antenna
(Based on Experimental results)
Page 7 of 9
Antenna Parameter
Frequency Range
2:l Impedance
Bandwidth
Gain
3 dB Axial Ratio
Bandwidth
Specification
2.15 - 2.74 GHz
0.59 GHz (24.08% @ 2.45
GHz)
> 8.5 dBi
2.38-2.45 GHz
2.89% @ 2.42 GHz
Simulated using IE3D from
Zealand, Inc
2.17-2.75 GHz
0.58 GHz (23.67 % @ 2.45
GHz)
> 8.0 dBi
2.41-2.485 GHz
3.06% @ 2.45 GHz
Measured Results
2.15 - 2.74 GHz
0.59 GHz (24.08% @ 2.45
GHz)
> 8.5 dBi
2.38-2.45 GHz
2.89% @ 2.42 GHz
CLAIM
A novel ~eometrvw ith a symmetric slot {"Fan Blade" shaped) cut into a nearly square radiating
patch is designed for wide band circular polarization and wide impedance characteristic using single
feed and aperture coupled configuration. The coupling aperture is matched to the patch with a
uniaue oval shaped stub incorporated in the feed line.
It has been investigated through simulation and proved experimentally that the symmetric "Fan
Blade" shaped slot cut into the patch area of a nearly square geometry generates circularly polarized
radiation over a wide frequency band.
We Claim that:
1. Circularly polarized radiation in a wide band can be achieved by cutting a symmetric "Fan
Blade" shaped slot into a radiating patch of a nearly square geometry.
2. The symmetric "Fan Blade" shaped slot perturbs the patch currents in a manner so as to
excite the two orthogonal modes with a 90 degree phase shift required for circular
polarization operation.
3. By varying the line lengths S4 of the "Fan Blade" shaped slot, the operating frequency of
circularly polarized band can be adjusted.
4. The aperture can be matched to the radiating patch over a wide bandwidth by incorporating
an oval shaped stub in the feed line.
Page 8 of 9
ABSTRACT
Microstrip antennas with circular polarization are extensively used in navigation, radar, satellite
and wireless communication systems. As compared to linearly polarized antennas, the circularly
polarized antennas give greater flexibility in terms of transmitter and receiver orientations. Singly
fed microstrip patch antennas are most popular geometries for circular polarization operation
because of their various merits like reduced weight, less complexity and freedom from use of
external hybrids and couplers. However, singly fed microstrip antennas suffer from low 3 dB axial
ratio bandwidth. A lot of research is underway nowadays to achieve wide axial ratio bandwidth
using single feed.
A unique geometry of nearly square patch antenna (aspect ratio=1.026) with an embedded
symmetrical Fan blade-shaped slot for circular polarization is investigated. The proposed structure
has aperture coupled feed which is matched over a very wide frequency band. This is accomplished
by incorporating a novel, oval shaped stub at the end of the single microstrip feed-line. The antenna
exhibits a measured 3 dB axial ratio bandwidth of 2.89% (2.38-2.45 GHz) with respect to the
measured minimum axial ratio frequency of 2.42 GHz. The measured 2:l VSWR (or 9.6 dB return
loss) bandwidth obtained is 24.08% (2.15-2.74 GHz) with respect to the mid-band of 2.45 GHz. The
measured gain is greater than 8.5 dBi over the circular polarization band. The antenna is well suited
for Wireless and Satellite Communication applications.
Ajay Kumar Sharma Ashok Mittal k- .V.R. Reddy
Page 9 of 9

Aperture Coupled Fan Blade Shaped Slotted Microstrip Antenna for
Circular Polarization
Ajay Kumar ~harma',A shok ~ i t t aaln~d B.V.R ~ e d d ~ ~
"University School of Information & Communication Technology GGSIPU, Sector 16-C Dwarka Delhi - 110 078
Ambedkar Institute of Advanced Communication Technologies and Research, Geeta Colony, Delhi - 110 03 1
CLAIM
A novel geometry with a symmetric slot ("Fan Blade" shaped} cut into a nearly square radiating
patch is designed for wide band circular polarization and wide impedance characteristic using single
feed and aperture coupled configuration. The coupling aperture is matched to the patch with a
uniaue oval shaped stub incorporated in the feed line.
It has been investigated through simulation and proved experimentally that the symmetric "Fan
Blade" shaped slot cut into the patch area of a nearly square geometry generates circularly polarized
radiation over a wide frequency band.
We Claim that:
1. Circularly polarized radiation in a wide band can be achieved by cutting a symmetric "Fan
Blade" shaped slot into a radiating patch of a nearly square geometry.
2. The symmetric "Fan Blade" shaped slot perturbs the patch currents in a manner so as to
excite the two orthogonal modes with a 90 degree phase shift required for circular
polarization operation.
3. By varying the line lengths S4 of the "Fan Blade" shaped slot, the operating frequency of
circularly polarized band can be adjusted.
4. The aperture can be matched to the radiating patch over a wide bandwidth by incorporating
an oval shaped stub in the feed line.
Ajay e umar Sharma Ashok Mittal b-- B.V.R. Reddy