Multipath Mitigation in High Precision GPS Systems Using Artificial Magnetic Conductors

Haider R. Khaleel Department of Engineering Science

Sonoma State University Rohnert Park, California, USA

khaleel@sonoma.edu

Hussain Al-Rizzo, Ayman Isaac, Ayad Bihnam Department of Systems Engineering

University of Arkansas at Little Rock Little Rock, Arkansas, USA

axabbosh@ualr.edu

Abstract— A low profile circularly polarized antenna based on Artificial Magnetic Conductor (AMC) ground plane is presented in this paper. The AMC ground plane is utilized to reduce the effects of multipath by blocking the propagation of surface waves. Hence, the proposed antenna is suitable for high precision GPS systems which require sub centimeter level of precision. Typically, choke ring antennas are used to efficiently reduce the effects of multipath interference. However, they are bulky, heavy and expensive. The antenna presented here consists of a microstrip antenna resonating at the L1 band (1.575 GHz) based on an 8x8 unit cells AMC structure; the result is an antenna showing good multipath rejection and a low axial ratio over a wide angular range. The advantage of the integrated AMC ground plane is the low cost of manufacturing, light weight, and a relatively low profile solution.

I. INTRODUCTION

The performance of high accuracy GPS is compromised by a major source of error known as multipath, which is the interference of multiple reflections with the direct GPS signal. Multipath signals, coming from reflections of the receiver’s surroundings would significantly affect its performance [1]. Choke ring based antennas are typically used to improve multipath rejection at the receiver’s level. In general, these antennas are bulky, heavy (about 5 kg) and expensive. With the advent of new microwave technologies like Electromagnetic Bandgap (EBG), AMC and metamaterials, it is now possible to design light, compact and cheaper solutions. In [2], a metallo-dielectric EBG surface based on Sievenpiper’s mushroom structures has been utilized to improve the interference mitigation of a GPS antenna in the L2 and L1 bands. Drawbacks of this system are: large dimensions, and fabrication complexity (including vias). In [3], a low profile antenna for geodesic applications is presented. The design consists of a rigid low temperature co-fired ceramic (LTCC) patch antenna embedded in an EBG based substrate; though efficient, the antenna lacks conformability and involve vias which complicates the manufacturing process. In [4], a crossed dipole antenna integrated on a wideband AMC is proposed. This design demonstrates a good performance; however, it consists of four PCB layers. In this paper, a simple low profile and cost effective solution is proposed. The antenna exhibits an improved gain, polarization

purity, low back radiation, and similar performance to the choke ring antenna.

II. ANTENNA DESIGN

A simple circularly polarized microstrip square patch antenna (47mm x 47mm) positioned over a 85mm x 85mm substrate with a dielectric constant of 3.6 and 4mm thickness is designed to resonate at 1.575 GHz (L1 band). Two feeds were located 10 mm in x and 10 mm in y axes from the center of the patch to achieve an optimized circularly polarized impedance matching. Next, an 8 x 8 unit cells AMC structure (total size is 286 mm x 286 mm) is designed to have a zero reflection phase at the same frequency. The antenna is placed over the AMC structure which is utilized to obtain a low back radiation and good axial ratio performance (< 3 dB), which is essential for the considered applications [5]. The proposed antenna-AMC design is shown in Fig.1.

Fig.1. GPS antennas with AMC (right) and without AMC (left) showing dimensions in millimeter. The return loss for the antenna is shown in Fig.2, while the reflection phase of the AMC unit cell is shown in Fig.3. The proposed design is compared with an antenna with the same dimensions but without the AMC structure, improvements in performance in terms of gain and polarization purity are observed and depicted in figures 4 and 5, respectively.

432978-1-4799-3540-6/14/$31.00 ©2014 IEEE AP-S 2014

Fig.2. Return loss for the proposed GPS antenna.

Fig.3. Reflection phase for the AMC unit cell for the GPS antenna.

Fig.4. Right and left polarization for the antenna with and without AMC structure.

Fig.5. Axial ratio for the antenna with and without AMC structure.

III. CONCLUSION

A low profile microstrip antenna on an AMC ground plane has been designed and simulated. The improved gain, polarization purity, and low back radiation make this antenna a promising candidate. The proposed system is more than five times thinner than the choke ring antenna with a comparable performance; it is also lighter in weight and more cost effective.

REFERENCES [1] E. D. Kaplan, Understanding GPS Principles and Applications. Norwood,

MA, USA, Artech House, 1996.

[2] J. M. Tranquilla, ‘The experimental study of global positioning satellite antenna hack plane configurations,” Contract Rep. NASNJet Propulsion Lab, Contract 957959, Radiating Syst. Res. Lab., Univ. New Brunswick, Fredericton, Canada, 1988.

[3] R. Baggen, J. M. Martinez-Vasquez, J. Leiss, S. Holzwarth, L. Drioli, and P. de Maagt; “Low Profile GALILEO Antenna Using EBG Technology,” IEEE Trans. On Antennas and Propagation, vol.56, no.3, pp. 667–674, March 2008.

[4] J.-M, Baracco, L. Salghetti-Drioli, and P. de Maagt, "AMC Low Profile Wideband Reference Antenna for GPS and GALILEO Systems," IEEE Trans. On Antennas and Propagation, vol.56, no.8, pp. 2540–2547, August 2008.

[5] Raad, H.R., Abbosh A. I., Al-Rizzo, H. M., and Rucker, D. G., “Flexible and Compact AMC Based Antenna for Telemedicine Applications,” IEEE Trans. On Antennas and Propagation, vol. 61, pp. 524–531, February 2013.

[6] H. R. Khaleel, H. Al-Rizzo, D. Rucker, S. Mohan, "A Compact Polyimide Based UWB Antenna for Flexible Electronics," IEEE Antennas and Wireless Propagation Letters, vol.11, no., pp. 564–567, May 2012.

[7] H.R. Khaleel, H. Al-Rizzo, D. Rucker, "Compact Polyimide-Based Antennas for Flexible Displays," IEEE Journal of Display Technology, vol.8, no.2, pp.91–97, February 2012.

[8] H. R. Khaleel, H. Al-Rizzo, D. Rucker, Y. Al-Naiemy, "Flexible printed monopole antennas for WLAN applications," Antennas and Propagation (APSURSI), 2011 IEEE International Symposium on , vol., no., pp.1334–1337, July 2011.

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