Download - A Compact Dual-Band GPS Antenna Design
-
5/26/2018 A Compact Dual-Band GPS Antenna Design
1/4
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013 245
A Compact Dual-Band GPS Antenna DesignMing Chen, Student Member, IEEE, and Chi-Chih Chen, Senior Member, IEEE
AbstractThis letter discusses a small slot-loaded, prox-
imity-fed patch antenna designed for GPS operation at L1(1575 MHz) and L2 (1227 MHz) bands. High-dielectric substrate
and meandered slotsare employed to reduce theantenna size downto 25.4 mm in diameter and 11.27 mm in thickness. The thicknessis important for achieving the wide bandwidth ( MHz) insupport of modern GPS coding schemes. The dual-band coverageis achieved by utilizing the patch mode in L2 band and slotmode in L1 band. This design features additional slot stubs for
independently tuning the L1 frequency. The right-hand circularlypolarized (RHCP) field property is achieved by connecting twoproximity probes to a small surface-mount 0 90 hybrid chip.Simulated and measured antenna performance will be presented.This compact GPS antenna design is suitable for small GPS
antenna arrays and portable GPS devices.
Index TermsCircular polarization, dual-band, GPS, patchantenna, proximity feeding.
I. INTRODUCTION
W ITH the deployment of several major global navigationsatellite systems (GNSS) such as GPS, GLONASS,Galileo, and Beidou [1], [2], many more frequency bands will
be available for global positioning applications. In addition,
the clustering of many neighboring GNSS channels requires
better coding schemes for these satellite signals [3], [4]. These
advanced coding schemes often need a wider bandwidth.
Therefore, future GNSS and GPS antennas will need to be able
to receive more GNSS channels and have wider channel band-
widths. Most existing commercial small L1/L2 GNSS/GPS
antennas have relative narrow bandwidth (10 MHz), and thus
are not adequate for supporting advanced GPS codes. Some
GNSS/GPS antennas adopting wideband designs such as
bowtie dipoles or spiral antennas have good bandwidth, but are
relatively large in size [5], [6]. Dual-band GPS antennas not
only can operate in two frequency bands, but can also provide
more reliable and accurate positions when used with proper
GPS receivers that combine information received at both fre-
quencies [7][9]. Therefore, the dual-band GPS antenna design
presented in this letter attempts to address size, bandwidth,
manufacturability, and scalability, i.e., easily redesigned forother frequencies.
Manuscript received October 11, 2012; revised November 28, 2012 and Jan-uary 28, 2013; accepted February 06, 2013. Date of publication February 20,2013; date of current version March 14, 2013. This work was performed undera subcontract from Applied EM, supported by the US Air Force under SBIRTopic A073-72, Miniature GPS Antenna Arrays Using Novel Materials. Dis-tribution is unlimited for public release (Air Force Public Release ApprovalNumber: 88ABW-2013-0727).
The authors are with the ElectroScience Laboratory, Electrical and ComputerEngineering Department, The Ohio State University, Columbus, OH 43212USA (e-mail: [email protected]).
Color versions of one or more of the figures in this letter are available onlineat http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LAWP.2013.2247972
Fig. 1. Geometry of the new compact L1/L2 GPS antenna.
Existing compact dual-band circularly polarized (CP) patch
antennas include stacked-patch designs [10], [11], specially
shaped patches [12], and slot-loaded patch [13]. However,these designs are still not small enough ( mm). In addition,
the stacked-patch design is not easy to manufacture due to its
internal probe and bonding issue at the metaldielectric and di-
electricdielectric interfaces. Zhou et al. proposed a proximity
probe design that requires only external probes conveniently
located on the side of the antenna [14].
In this letter, we present a compact dual-band (L1: 1575 MHz,
and L2: 1227 MHz) GPS antenna design (see Fig. 1, patent
pending) that is only 25.4 mm in diameter and 11.27 mm in
thickness [15]. The size of the antenna is only about in
L2 band. Unlike conventional stacked-patch designs, this de-
sign does not have an internal conducting patch. The dual-bandcoverage is achieved by operating the patch mode in L2 band
and slot mode in L1 band. The low-loss, high-dielectric sub-
strate and the meandered-slot designs are employed to increase
the antennas electrical size. This design also adopts external
proximity probes [14]. The combination of the above features
greatly improves its manufacturability and reliability. In addi-
tion, this design utilizes a small 0 90 hybrid chip (Mini-cir-
cuit QCN-19) to reduce the size of the feeding network and
achieve good right-hand CP (RHCP) performance over a wider
frequency range. Later, the application of this new GPS antenna
design in a four-element array without suffering performance
degradation due to mutual coupling will also be demonstrated.
II. COMPACTL1/L2 GPS ANTENNADESIGN
A. Antenna Structure and Operational Principles
As shown in Fig. 1, the proposed antenna is composed of
a single slot-loaded conducting patch design on top of two
stackeddielectric layers. The top layer includes the slot-loaded
patch design that is fabricated on a Rogers TMM10i board
( mm, ) using standard
printed circuit board (PCB) fabrication processes. The bottom
substrate is a high-dielectric ceramic puck ( mm,
). The two substrates are bonded
together using ECCOSTOCK dielectric paste to
1536-1225/$31.00 2013 IEEE
-
5/26/2018 A Compact Dual-Band GPS Antenna Design
2/4
246 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013
Fig. 2. Equivalent current magnitude on slotted patch at L1 (1575 MHz) andL2 (1227 MHz) bands.
avoid air gaps and low-dielectric bonding layer formed by
common glues, both causing detuning of resonant frequencies.
This new design is also mechanically superior to conventional
stacked-patch designs where the presence of the middle con-
ducting patch weakens the bonding between the top and bottom
layers when the patch size is relative compared to the diameter
of the dielectric layers. Two conducting strips (width mm,height mm) on the side serve as proximity feeds for the
new design. The bottom ends of these strips are connected to
the outputs of a 0 90 hybrid to obtain RHCP property. These
two feeding strips are located in the middle of two adjacent
longer meandered slots at 90 azimuth angle from each other.
Fig. 2 shows the computed magnitude of equivalent currents
on the patch at 1227 MHz (left) and 1575 MHz (right). It shows
that resonant current distribution occupies the entire patch in L2
mode and is mostly concentrated around the meandered slots in
L1 mode. The meandered slots, the center circular hole, and the
high-dielectric substrate help to establish L2 mode resonance
within the physically small antenna volume. The concentrationoffields only around slots in L1 band also makes it possible to
tune the L1 frequency independently by adjusting the length
of the inner tuning stubs, as will be discussed shortly.
B. Design Procedures
The design procedure of the proposed compact dual-band
patch antenna begins with selecting the diameter based on
physical constraints and the two desired resonant frequencies of
a specific application such as GPS. The three-step design pro-
cedure is discussed as follows.
Step 1: The first step is to determine the dielectric constant
and thickness of the two stacked dielectric materials according
to the desired lower resonant frequency. The effective dielectric
constant of two stacked dielectric layers can be estimated
using a double-layer parallel-plate capacitor model that gives
(1)
where are the dielectric constant and thickness
of top and bottom dielectric layers, respectively. The resonant
frequency of the lowest mode can then be estimated from [16]
(2)
Note that, in practice, and are limited by available PCB
materials. By properly choosing , and , one canfirst
Fig. 3. Input impedance curves for the antenna in Fig. 1 as the meandering slotlength varied from 9 to 10 mm.
Fig. 4. Input impedance curves for the antenna in Fig. 1 as the meandering slotwidth varied from 0.5 to 0.7 mm.
Fig. 5. Input impedance curves for the antenna in Fig. 1 as the tuning stublength varied from 0.2 to 1.5 mm.
produce the patch-mode resonance close to the desired lower
frequency band. The total thickness can be deter-
mined according to the bandwidth requirement of the specific
application.
Step 2: The second step is to design the length and width
of the meandering slots (see Fig. 1) to tune the resonant fre-
quency of the lower mode. Figs. 3 and 4 plot simulated input
impedance as a function of slot length and width , respec-
tively. Fig. 3 shows that increasing the slot length from 9 to
10 mm effectively lowers the resonant frequency of both low-
and high-frequency modes. As is shown in Fig. 4, changing the
slot width from 0.51 to 0.76 mm shifts the higher resonant
frequency from 1.48 to 1.6 GHz, but only shifts the lower reso-
nant frequency slightly. Therefore, the low-frequency mode can
-
5/26/2018 A Compact Dual-Band GPS Antenna Design
3/4
CHEN AND CHEN: COMPACT DUAL-BAND GPS ANTENNA DESIGN 247
Fig. 6. (a) Feeding circuit and (b) the GPS antenna element.
Fig. 7. (a) Measured return loss ( ) and insertion loss ( ) and(b) phase difference of the testing board.
be first tuned to the desire frequency by changing slot length and
width.
Step 3: The last step is to tune the resonant frequency of
the higher mode independently by adjusting the length of the
inner tuning stubs. Fig. 5 shows that changing the length ofthe inner stub from 0.2 to 1.5 mm shifts the higher resonant
frequency from 1.57 to 1.51 GHz without affecting the lower
resonant mode.
C. Compact RHCP Feeding Network
The feeding circuitry for the new miniature GPS antenna ele-
ment is shown in Fig. 6(a) on a 1.27-mm-thick FR4 board
. Fig. 6(b) shows that the antenna is inserted into a tightlyfit
circular hole that is cut out of the FR4 board. The bottom of
the antenna and feeding circuitry shares the same ground. Two
equal-length microstrip lines with characteristic impedance of
50 connect the outputs of a commercial broadband 0 90
chip hybrid to the bottom of the two antenna probes. The hybrid
performance was verified usinga separate test board as shown in
Fig. 8. (a) Single-element GPS antenna configuration. (b) Four-element GPSantenna array configuration.
Fig. 9. Comparison between the measured and simulated broadside RHCP andLHCP gain.
TABLE I
PATCHANTENNA DESIGN PARAMETERS
Fig. 7(a). The measured reflection coefficient shows less
than 20 dB from 1.1 to 1.7 GHz, and the transmission coeffi-
cients ( ) are approximately 3.2 dB, very close to the
desired 3 dB from a half-power divider, within the frequency
range of interest. The measured phase difference between thetwo output ports varies monotonically from 88 at 1.227 GHz
to 90 at 1.575 GHz [Fig. 7(b)], which is very acceptable for CP
operation.
III. MEASUREMENTRESULTS
Table I summarizes the optimized design parameters
of the final L1/L2 GPS antenna element design. Fig. 8(a)
shows a fabricated antenna element was then mounted on a
117.2 117.2 mm FR4 board containing the feeding circuitry.
The simulated and measured broadside gain for the
Fig. 8(a) configuration are plotted in Fig. 9, which shows
an excellent agreement. The RHCP antenna gain is around
3.2 dBi at 1.227 GHz and 3.5 dBi at 1.575 GHz. The
RHCP-to-left-hand-CP (LHCP) isolation is 20 dB at L2
-
5/26/2018 A Compact Dual-Band GPS Antenna Design
4/4
248 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013
Fig. 10. Radiation pattern comparison between four-element array and singleelementat L2 andL1 band: (a) four-element pattern at L2 band; (b)four-elementpattern at L1 band; (c) single-element pattern at L2 band; (d) single-elementpattern at L1 band.
band and 15 dB at L1 band. The axial ratio is found to be 1.3 dB
at 1.227 GHz and 1.9 dB at 1.575 GHz. The 3-dB bandwidth of
lower mode is 45 MHz from 1200 to 1245 MHz, and high modeis 50 MHz from 1545 to 1595 MHz at zenith. Such bandwidths
are sufficient to support modern coding schemes such as P/Y
and M code [3], [4].
It is well known that mutual coupling between closely spaced
antenna array elements often affects impedance matching condi-
tion, resonant frequency, and radiation pattern of the element. To
examine these effects, a four-element GPS array was assembled
as shown in Fig. 8(b).The distance between adjacent elementsis
62.5 mm. The measured elevation patterns at center frequencies
of L1 and L2 bands are shown in Fig. 10(a) and (b) by operating
the Element 1 only with other three elements terminated with
50- loads. For comparison, the measured patterns for the pre-vious single-element configuration shown in Fig. 8(a) are also
included in Fig. 10 (c) and (d). These comparisons show that the
sky coverage and broadside gain level between the single-el-
ement and four-element configurations are quite similar. The
maximum gain for the four-element array is 3.3 dBi at L2 and
3.9 dBi at L1, which is fairly close to the single-element gain
performance. Notice that these patterns are slightly tilted and not
completely symmetric due to the finite ground-plane scattering
effect. Reasonable RHCP-to-LHCP isolation is also preserved
in the four-element array. Therefore, we concluded that the mu-
tual coupling impact on antenna performance is not significant
compared to a single element for this antenna design. Also, the
measurement data are in good agreement with the simulation
data.
IV. CONCLUSION
A novel compact GPS antenna design was presented for
operating at 1.227 GHz with 45-MHz 3-dB bandwidth and
1.575 GHz with 50-MHz 3-dB bandwidth at zenith. High-di-
electric substrate and meandering slots were shown to be able
to miniaturize the antenna size down to 25.4 mm in diameter
without the feeding network. The footprint of a single elementwith the feeding network is about 25.4 40.6 mm . Simulation
results indicated that 90% radiation efficiency is achieved
by using the low-loss dielectric materials in this design. A
three-step design procedure of this new antenna design was
discussed and can be used to design for different operating
frequencies. The RHCP feeding circuitry was implemented
using a small 0 90 hybrid chip that provides desired power
splitting and stable quadrature phase difference at its two out-
puts. The measured gain and pattern data validated simulated
performance and showed wide RHCP sky coverage and more
than 15 dB of RHCP-to-LHCP isolation at both L1 and L2
bands. We also demonstrated an application of this antennadesign in a compact four-element array configuration.
REFERENCES
[1] P. Misra and P. Enge, Global Positioning System: Signals, Measure-ments, and Performance. Lincoln, MA, USA: Ganga-Jamuna Press,
2010.[2] N. Samama, Global Positioning: Technologies and Performance.
New York, NY, USA: Wiley, 2008.
[3] B. C. Barker, J. W. Betz, J. E. Clark, J. T. Correia, J. T. Gillis, S.Lazar, K. A. Rehborn, and J. R. Stration, Overview of the GPS Mcode signal, inProc. ION Nat. Tech. Meeting, 2000, pp. 542549.
[4] J. W. Betz, Binary offset carrier modulation for radio navigation,ION J. N avig., vol. 48, pp. 227246, 2001.
[5] F. Scire-Scappuzzo and S. N. Makarov, A low-multipath widebandGPS antenna with cutoff or non-cutoff corrugated ground plane,IEEE
Trans. Antennas Propag., vol. 57, no. 1, pp. 3346, Jan. 2009.[6] J. J. Kasemodel, C.-C. Chen, I. J. Gupta, and J. L. Volakis, Minia-
ture continuous coverage antenna array for GNSS receivers,IEEE An-tennas Wireless Propag. Lett., vol. 7, pp. 592595, 2008.
[7] L. I. Basilio, R. L. Chen, J. T. Williams, and D. R. Jackson, A newplanar dual-band GPS antenna designed for reduced susceptibility to
low-angle multipath,IEEE Trans. Antennas Propag., vol. 55, no. 8,pp. 23582366, Aug. 2007.
[8] X. F. Peng, S. S. Zhong, S. Q. Xu, and Q. Wu, Compact dual-bandGPS microstrip antenna, Microw. Opt. Technol. Lett., vol. 44, pp.5861, 2005.
[9] X. L. Bao and M. J. Ammann, Dual-frequency circularly-polarizedpatch antenna with compact size and small frequency ratio, IEEETrans. Antennas Propag., vol. 55, no. 7, pp. 21042107, Jul. 2007.
[10] Z. Wang, S. Fang, S. Fu, and S. L, Dual-band probe-fed stackedpatch antenna for GNSS applications, IEEE Antennas WirelessPropag. Lett., vol. 8, pp. 100103, 2009.
[11] X. Sun, Z. Zhang, andZ. Feng, Dual-band circularly polarized stackedannular-ring patch antenna for GPS application,IEEE Antennas Wire-less Propag. Lett., vol. 10, pp. 4952, 2011.
[12] L. Boccia, G. Amendola, and G. Di Massa, A dual frequency mi-crostrip patch antenna for high-precision GPS applications, IEEE An-
tennas Wireless Propag. Lett., vol. 3, pp. 157160, 2004.
[13] Nasimuddin, Z. N. Chen,and X. Qing, Dual-bandcircularly polarizedS-shpaed slotted patch antenna with a small frequency ratio, IEEETrans. Antennas Propag., vol. 58, no. 6, pp. 21122115, Jun. 2007.
[14] Y. Zhou, C.-C. Chen, and J. L. Volakis, Dual band proximity-fedstacked patch antenna for tri-band GPS applications, IEEE Trans. An-tennas Propag., vol. 55, no. 1, pp. 220223, Jan. 2007.
[15] M. Chen and C.-C. Chen, A compact dual-band (L1/L2) GPS antenna
design, inProc. IEEE Antennas Propag. Int. Symp., Jul. 2012, pp.12.[16] C. A. Balanis, Antenna Theory: Analysis and Design. New York, NY,
USA: Wiley, 2005, pp. 844846.