Multipath mitigation in high precision GPS systems using Artificial Magnetic Conductors

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.