Single-feed, compact, GPS patch antenna using metasurface

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Single-Feed, Compact, GPS Patch Antenna Using
Metasurface
Son Xuat Ta, Dao Ngoc Chien
National Center for Research and Development of Open
Technologies, Ha Noi, Vietnam
E-mail: tasonxuat@yahoo.com
Khac Kiem Nguyen, Hien Doan Thi Ngoc
School of Electronics and Telecommunications, Hanoi
University of Science and Technology, Ha Noi, Viet Nam
Abstract—This paper proposes a single-feed, compact,
metasurface-based antenna with circularly-polarized (CP)
radiation for the Global Positioning System (GPS) receivers. The
antenna consists of a square patch on the metasurface, which is a
periodic lattice of 4 × 4 square metallic patches arranged on a
grounded dielectric substrate. The CP radiation is obtained by
truncating corners of the patch radiator. The truncated-corner
square patch on the metasurface structure is used to achieve an
antenna miniaturization. The final design, with a size of 60  60 
4.0 mm3 (0.315λo  0.315λo  0.021λo at the GPS L1 frequency)
yields a bandwidth for |S11| < –10 dB of 1.562 – 1.733 GHz (171
MHz) and 3-dB axial ratio (AR) bandwidth of 1.570 – 1.592 GHz
(22 MHz). At 1.58 GHz, the proposed antenna yielded a gain of
2.75 dBic and a 3 dB AR beamwidth of 138º and 144º in the x-z
and y-z planes, respectively.
Keywords—square patch, truncated corner, metasurface,
circular polarization, antenna miniaturization, Global Positioning
System.
I. INTRODUCTION
Nowadays, the Global positioning system (GPS) is a most
popular member of Global Satellite Navigation Systems, which
can be used for providing position and navigation or tracking
the position of something with a receiver [1]. In order to
mitigate the Faraday rotation effects caused by the ionosphere,
the circularly polarized (CP) radiation was adopted for the GPS
applications. Moreover, antennas for the GPS receivers require
to have right-hand circular polarization (RHCP), a 3-dB axial
ratio (AR) beamwidth greater than 120º facing the sky, and a
small back-radiation to avoid interference from the ground [2].
Microstrip patch antennas have been always the most popular
choice as a beginning configuration for addressing the demands
of the GPS receiver antenna, e.g. see [3], [4], due to their
features of compact size, planar configuration, low cost, easy
fabrication, as well as easily integrated with other components.
On the other hand, the patch antennas incorporated with
metasurface structures [5] have been recently introduced as an
antenna engineering innovation for enhancing their
performances. The metasurface refers a kind of sheet material
typically engineered with novel or artificial structures to
produce electromagnetic properties that are unusual or difficult
to obtain in nature. Several features of metasurfaces have been
intensely exploited for antenna applications. They include, for
instance, artificial magnetic conductor surface, electromagnetic
bandgap surface, high-impedance surface, uniplanar compact
photonic band-gap surface, and reactive impedance surface.
Antenna minimization is one of the main purposes on physical
and performance enhancement of the patch antennas using
metasurface [6]. Several works [7] – [11] have demonstrated
on this purpose. Most of these antennas have achieved a small
electrically sizes, good impedance match to a 50-Ω source,
good CP radiation, as well as high radiation efficiency.
In this paper, a low-cost, compact, single-feed, CP antenna
using a metasurface is presented for the GPS applications. The
antenna utilizes a truncated corner patch radiator to produce the
CP radiation [11]. The patch is loaded with the metasurface of
4 × 4 square metallic patches to shift the resonance forward the
lower frequency. The antenna has been characterized
numerically using the ANSYS High-Frequency Structure
Simulator (HFSS) and validated by the measurements.
II. ANTENNA DESIGN AND CHARACTERISTICS
A. Antenna Geometry
The antenna geometry is shown in Fig. 1. It consists of a
patch radiator, a metasurface, a ground plane, a 50-Ω
subminiature version A (SMA) connector, and two FR4
substrates (εr = 4.4 and tanδ = 0.02). The metasurface was a
periodic structure including 4 × 4 square metallic patches
printed on the top side of the substrate #1 with. The patch
radiator is a truncated corners square patch with a dimension of
Wp × Wp and the truncation of Lc, which was designed to excite
two orthogonal modes with a 90º phase difference [12], and
consequently, produce the CP radiation. The patch radiator was
arranged on the top side of the substrate #2. The outer part of
the SMA connector is connected to the ground plane, while its
inner part extends through the metasurface and substrates and
connects to the patch radiator at Fy away from the center. The
antenna was optimized via the Ansoft HFSS for a compact size,
a nearly completed impedance match to the 50-Ω SMA
connector, and a good CP radiation at the GPS L1 frequency.
Its optimized design parameters are follows: g = 0.6 mm, P =
15 mm, h1 = 3.2 mm, h2 = 0.8 mm, Wp = 35 mm, Lc = 5 mm,
and Fy = 13 mm.
B. Antenna Miniaturization
As mentioned above, the patch antenna is incorporated with
the metasurface structure to further decreasing the resonance
frequency. This feature is confirmed in Fig. 2, which shows a
comparison of |S11| and AR values for the truncated corner
square patch antenna without and with the metasurface. For a
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Wp
g
P
x
y
z
Wp
Lc
Fy
(a)
Metasurface
SMA
Patch h2
h1
GND
x
z
y
(b)
Fig.1. Geometry of the proposed antenna: (a) top view and (b) cross
sectional view.
-20
-15
-10
-5
0
|S11| (dB)
Frequency (GHz)
1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2
With metasurface
W/o metasurface
(a)
0
3
6
9
12
Axial ratio (dB)
Frequency (GHz)
1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2
With metasurface
W/o metasurface
(b)
Fig. 2. Simulated results of the patch antenna in without and with the
presence of metasureface: (a) |S11| and (b) AR values.
fair comparison, the antenna without metasurface has the same
parameters as those of the proposed structure. As shown in Fig.
2, the antenna without metasurface operates near a frequency
of 2.0 GHz. Since it was not fully optimized, its impedance
matching bandwidth for |S11| < –10 dB was 1.950 – 2.045 GHz,
whereas it yielded zero 3-dB AR bandwidth with a CP center
frequency at 1.925 GHz (AR = 4.8 dB). Due to the presence of
the metasurface, the resonance frequency of the antenna shifted
toward the lower frequency. As shown in Fig. 2, the
metasurface-based antenna yielded a |S11| < –10 dB bandwidth
of 1.555 – 1.655 GHz and a 3-dB AR bandwidth of 1.570 –
1.592 GHz (22 MHz) with a CP center frequency of 1.580 GHz
(AR = 1.54 dB). This result indicates that an antenna
miniaturization was obtained by using the metasurface.
C. Loss Tangent of Substrate Material
It is well known that the loss-tangent of the substrate is one
of the key parameters, which mainly determine the radiation
efficiency of the patch antenna. The substrate loss-tangent also
affects the efficiency of the metasurface-based patch antenna
significantly. For better understanding this issue, a parametric
study of the substrate loss-tangent for the proposed antenna
was carried out and given in Fig. 3. As the loss-tangent
decreased, the impedance matching and AR characteristic of
the antenna degraded, whereas the radiation efficiency was
increased significantly. With the real value of tanδ = 0.02, the
antenna yielded a radiation efficiency of 50%, while with tanδ
= 0.005, the efficiency achieved ~80%. The impedance
matching and CP radiation can be easily improved by changing
the design parameters of the antenna, while the antenna
efficiency can be improved by using the substrate with a low
loss-tangent. However, the use of better substrate is usually
accompanied with increasing cost.
III. RESULTS AND DISCUSSIONS
For verification, the patch antenna using metasurface was
realized and tested. The patch radiator and the metasurface
were realized on FR-4 substrates with 0.035-μm metallic
thickness via a standard wet-etching technology. Fig. 4 shows a
fabricated sample of the antenna. It has an overall size of 60 
60  4.0 mm3 (0.315λo  0.315λo  0.021λo at the GPS L1
frequency). For a simple fabrication, the two substrates were
fastened together by thin tapes, and consequently, there was an
undesired air-gap between them. Fig. 5 shows a comparison of
measured and simulated |S11| values of the fabricated prototype.
The measured bandwidth is broader than the simulated one; i.e.,
the measurement resulted in a |S11| < –10 dB bandwidth of
1.562–1.733 GHz (171 MHz), whereas the simulated value was
1.555–1.655 GHz (100 MHz). This difference could be
attributed to the undesired air-gap in the fabricated prototype.
The simulated radiation characteristics of the proposed
antenna are shown in Figs. 6 – 8. It is observed that the antenna
radiated a good right-hand CP at the GPS L1 frequency. As
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1.50 1.55 1.60 1.65 1.70
-20
-15
-10
-5
0
|S11| (dB)
Frequency (GHz)
tanδ = 0.01
tanδ = 0.02
tanδ = 0.005
(a)
1.50 1.55 1.60 1.65 1.70
0
3
6
9
12
Axial ratio (dB)
Frequency (GHz)
tanδ = 0.01
tanδ = 0.02
tanδ = 0.005
(b)
1.50 1.55 1.60 1.65 1.70
Radiation efficiency
Frequency (GHz)
tanδ = 0.01
tanδ = 0.02
tanδ = 0.005
0.0
0.2
0.4
0.6
0.8
1.0
(c)
Fig. 3. Simulated (a) |S11|, (b) AR, and (c) radiation efficiency values of
the proposed antenna for different loss-tangents of the substrate.
(a) (b) (c)
Fig. 4. Photograph of fabricated antenna: (a) top view, (b) metasurface,
and (c) back view with SMA connector.
Measurement
Simulation
|S11| (dB)
Frequency (GHz)
-30
-20
-10
0
1.50 1.55 1.60 1.65 1.70 1.75 1.80
Fig. 5. Simulation and measurement |S11| values of the antenna.
1.50 1.55 1.60 1.65 1.70
0
3
6
9
12
Axial ratio (dB)
Frequency (GHz)
-2
0
2
4
6
Broadside gain (dBic)
AR
Gain
Fig. 6. Simulated AR and broadside gain values of the antenna.
shown in Fig. 6, its AR < 3 dB bandwidth was 1.570–1.592
GHz (22 MHz) with a CP center frequency of 1.580 GHz (AR
= 1.54 dB), and a broadside gain was excess 2.5 dBic across
the operational bandwidth. Fig. 7 shows that the antenna
resulted in widebeam and highly symmetric radiation profile in
both the x-z and y-z plane. At 1.58 GHz, the antenna resulted
in a gain of 2.75 dBic and half-power beamwidths (HPBWs) of
97º in both x-z and y-z planes. As shown in Fig. 8, the antenna
yielded a very wide CP radiation; its 3 dB AR beamwidth was
138º and 144º in the x-z and y-z planes, respectively.
A performance comparison between the proposed antenna
and the recent single-feed CP patch designs [8]–[11] are
presented in Table I. It is observed that although the proposed
antenna was designed with a low-cost substrate material of
FR4, its performances are comparable with the priors.
IV. CONCLUSION
A single-feed, compact, GPS antenna using a metasurface
has been proposed. The antenna employs a truncated corner
square patch to produce a CP radiation, which is incorporated
with a metasurface of 4 × 4 square metallic plates to achieve an
antenna miniaturization. The final design, with an overall size
of 60  60  4.0 mm3 (0.315λo  0.315λo  0.021λo at the GPS
L1 frequency) yielded a |S11| < –10 dB bandwidth of 1.562 –
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TABLE I. COMPARISON OF THE PROPOSED ANTENNA AND THE RECENT
COMPACT CP ANTENNAS USING METASURFACE
Antenna
structures
Size (λ03)
Substrate
(loss tangent)
–10
dB
|S11|
BW
(%)
3-dB
AR
BW
(%)
Gain
(dBic)
Proposed
0.315  0.315
 0.021
FR4 (0.02)
10.4
1.4
2.75
Ref. [8]
0.177 × 0.181
× 0.025
MEGTRON 6
(0.009)
4.62
1.46
2.98
Ref. [9]
0.327 × 0.327
× 0.028
MEGTRON 6
(0.009)
4.9
1.68
3.0
Ref. [10]
0.292 × 0.292
× 0.031
FR4 (0.02)
5.2
1.6
3.41
Ref. [11]
0.262 × 0.262
× 0.020
F4B (0.001)
4.7
1.05
4.15
λ0 is a free space wavelength referring to the operational frequency.
-10
-5
0
5
-15
-10
-5
0
5
270
300
330
0
30
60
90
120
150
210
240
(dBic) RHCP
LHCP
x-z plane
-10
-5
0
5
-15
-10
-5
0
5
270
300
330
0
30
60
90
120
150
210
240
(dBic) RHCP
LHCP
y-z plane
Fig. 7. Simulated radiation patterns of the antenna at 1.580 GHz.
-100 -50 0 50 100
0
3
6
9
12
Axial ratio (dB)
Theta (°)
x-z plane
y-z plane
Fig. 8. Simulated AR vs. theta angle of the antenna at 1.580 GHz.
1.733 GHz (171 MHz), 3-dB AR bandwidth of 1.570 – 1.592
GHz (22 MHz), and a 3 dB AR beamwidth of 138º and 144º in
the x-z and y-z planes, respectively. With the features of
compact size, planar structure, good impedance matching, good
CP radiation, and wide 3-dB AR beamwidth, the patch antenna
using metasurface can be widely applied to GPS purposes, as
well as to satellite communications.
ACKNOWLEDGMENT
This research is funded by Vietnam National Foundation
for Science and Technology Development (NAFOSTED)
under grant number 102.04-2016.02.
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