2010 New Method for Back Lobe Suppression Of
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Transcript of 2010 New Method for Back Lobe Suppression Of
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New Method for Back Lobe Suppression of
Microstrip Patch Antenna for GPS
Won-Gyu Lim #1, Hyeong-seok Jang 2, Jong-Won Yu 3
#Korea Aerospace Research Institute (KARI)
Daejeon, 305-333, [email protected]
Department of Electrical Engineering and Computer Science, Korea Advanced Institute of Science and Technology
Daejeon, [email protected]
Abstract A new method for back lobe suppression of mi-crostrip patch antenna with a small ground is proposed andinvestigated for GPS receiver at 1.575 GHz. To reduce back loberadiation, we use the slotted ground choke by etching slots on
the corner of the ground plane. Experiment results show thatthe back lobe radiation is reduced lower than -35 dBi and thefront-to-back ratio more than 40 dB.
I. INTRODUCTION
Global Positioning System (GPS) is a global navigation
satellite system (GNSS) to determine the instantaneous loca-
tion, the time and the velocity information almost anywhere
on or above the surface of the earth at any time. Despite
continuing improvements in GPS receivers, multipath signal
propagation has remained a dominant cause of error in differ-
ential positioning. Multipath refers to the existence of signals
reflected from objects in the vicinity of a receivers antenna
that corrupt the direct line-of-sight signals from the GPSsatellites, thus degrading the accuracy of both code-based and
carrier phase-based measurements. The multipath signals can
be mitigated by using a low back lobe antenna. A conventional
approach to mitigate the multipath interference is to use a
choke ring ground plane [1]. Choke ring ground plane consists
of multiple concentric ring shorted at the bottom and open
at the top. The choke ring ground plane effectively reduces
the multipath signals; however it significantly increases the
antenna size, making its adoption difficult in applications that
need small form factor antennas. Alternative technologies have
been pursued using the Electromagnetic Band Gap (EBG)
structures [2], artificial magnetic conductor [3] and vertical
choke ring [4].
In this paper, we present a new compact structure, the
slotted ground choke, to reduce the back lobe of the microstrip
patch antenna. The slotted ground choke is as effective as a
conventional choke ring ground plane and the increase of the
antenna size is kept minimal.
II . ANTENNA DESIGN
Circular polarization is required for GPS applications. Cir-
cularly polarized patch antennas can be constructed using var-
ious structures and configurations such as slot-loaded patches,
Fig. 1. The geometry of the proposed microstrip patch antenna with slottedground choke in (a), side view in (b) and top view in (c)
near-square patches, square patches with orthogonal feeding,
etc. In this study, in order to get circular polarization, a double
feed is used which allows to excite two orthogonal TM01mode on the square patch by feeding the two inputs
90o out of phase. Fig.1 shows the geometry and dimensions
28-30 September 2010, Paris, France
Proceedings of the 40th European Microwave Conference
978-2-87487-016-3 2010 EuMA 679
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Fig. 2. The simulated radiation patterns of microstrip patch antenna on thefinite ground plane with/without slots (Wg=Lg=90mm, Wa=La=82.4mm,Ha
=5mm, Ls
=30mm,Ws
=5.8mm)
s
of the proposed patch antenna with slotted ground choke. A
rectangular patch is designed to operate at frequency f =
1.575GHz and is fabricated with copper plate ( t=1mm and
Wa=La=82.4mm). It is fed directly by using copper wire with
1mm diameter and height Ha=5mm above the
FR4 substrate (Hd=0.6mm,Wg=Lg=90mm and relative per-
mittivity 4.6). The slotted ground choke is created by etching
four slots at the corner of the ground plane of the FR4
substrate and the quadrature hybrid coupler is designed on
the other side of the ground plane. Backward radiation isgenerated at microstrip patch antenna on the finite ground
plane due to the ground plane edge diffraction. To reduce
backward radiation, we insert four slots in the corner of the
ground plane with Ls=30mm and Ws=5.8mm. Fig. 2 shows
the simulated radiation patterns of the microstrip patch antenna
on the finite ground with slots and without slots. It shows that
the backward radiation from the microstrip patch antenna with
slotted ground choke can be dramatically reduced about 45dB
more than without slots. The simulations are performed using
the CST Microwave Studio Package which utilizes the finite
integration technique for electromagnetic computation. Fig. 3
shows the simulated radiation patterns for different length (Ls)and different width (Ws) of the slotted ground choke. IfLs is
30mm and Ws is 5.8mm, the backward radiation is decreased
considerably about -45dBi at =180o.
Fig. 4 shows the simulated surface current distribution on
the slotted ground plane at 1.575GHz. We can see more
and stronger surface current is concentrated around the edge
of slots and is oppositely directed between the interior and
exterior of the slot. This causes the slotted ground to operate
in a transmission-line-like mode, which transforms the nearly
zero impedance (short circuit) at the edge of the slot to nearly
high impedance(open circuit) at the edge of the ground plane.
Fig. 3. The simulated radiation patterns for different length (Ls) andWs=5.8mm in (a) and for different width (Ws) and Ls=30mm in (b)
Fig. 4. The simulated surface current distribution on the slotted ground planeat 1.575GHz
The high impedance leads to the desired high attenuation of
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Fig. 5. A photograph of the fabricated antenna
Fig. 6. The measured return loss of the proposed antenna
edge diffraction and cut off backward radiation.
III. MEASUREMENTS
Fig.5 shows a photograph of the fabricated microstrip patch
antenna with slotted ground choke. Fig. 6 shows the measured
return loss of proposed antenna. The impedance bandwidth
defined by -10 dB return loss about 400 MHz centered at about
1.575 GHz is observed, which is due to the wide bandwidth
characteristic of the feed network . The measured peak gain
and axial ratio are shown in Fig. 7. The proposed antenna has
a good axial ratio under 0.5 dB and peak gain about 6dBi at
1.575 GHz. Fig. 8 shows the measured radiation pattern. We
can see that forward and backward gain are 6dBi and -35dBi,
respectively. By using the slotted ground choke, we can get
the high front-to-back ratio about 41dB.
i
Fig. 7. The measured peak gain and axial ratio of the proposed antenna
Fig. 8. The measured radiation pattern of the proposed antenna at 1.575GHz
IV. CONCLUSION
The slotted ground choke is proposed to reduce the back-
ward radiation of microstrip patch antenna with finite and
small ground plane. The simulated and experimental results
show that the back lobe can be successfully reduced below
-45dBi and -35dBi, respectively. The proposed antenna offersgood circular polarization and uniform hemispherical gain
pattern for the operating band, and provides an excellent
multipath rejection characteristic. The new structure effectively
suppresses back lobe without an increase in the size of the
ground plane.
REFERENCES
[1] Tranquilla, J.M., Carr, J.P. and Al-Rizzo, H.M. Analysis of a chokering groundplane for multipath control in Global Positioning System(GPS) applications IEEE Transcations on Antennas and Propaga-tion,vol.42,no.7,pp. 905 - 911, July, 1994.
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[2] Baggen, R., Martinez-Vazquez, M., Leiss, J., Holzwarth, S., Drioli,L.S. and de Maagt, P., Low Profile GALILEO Antenna Using EBGTechnology,IEEE Transactions on Antennas and Propagation, vol. 56,no.3, pp. 667-674, March, 2008. Page(s):667 - 674
[3] McKinzie, W.E., III, Hurtado, R.B., Klimczak, B.K. and Dutton, J.D.,Mitigation of multipath through the use of an artificial magneticconductor for precision GPS surveying antennas, IEEE InternationalSymposium on Antennas and Propagation, vol.4, pp. 16-21, June, 2002.
[4] Yoonjae Lee, Ganguly, S. and Mittra, R., Multi-band L5-capable GPSantenna with reduced backlobes, IEEE International Symposium on
Antennas and Propagation, vol. 1A, pp. 3-8, July, 2005.
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