GPS Microstrip Antenna Array on a Resistivity Tapered Ground Plane for Multipath Mitigation

GPS Carrier Multipath is a major source of error in Differential GPS that cannot be removed through signal processing in the receiver; it occurs from a variety of structural and ground reflections and is common to both land based and airborne GPS systems. In this paper we describe a new type of low profile, lightweight two-element microstrip antenna array used in combination with a resistivity tapered ground plane for reducing multipath in GPS systems. The concentric two-element array consists of an outer annular ring microstrip antenna enclosing a centrally located circular microstrip antenna. This antenna array is used as a polarization filter for adaptive cancellation of the cross polarized multipath signals; the function of the resistivity tapered ground plane is to reduce the back radiation lobes of the antenna by attenuating the signals that are either diffracted or reflected from the edges of the ground plane. A Proof of Concept (POC) version of this antenna that operates in the GPS L1 band has been built and tested to demonstrate feasibility of this concept. A dual band version that operates at both the GPS L1 and L2 frequency bands can be built by using stacked microstrip patch antenna elements. This new antenna offers significant advantages in terms of size, weight and cost over other multipath mitigation antennas such as the choke ring ground plane antenna or the three element vertical linear array. It is especially attractive for installation on airborne platforms because of its low profile, which is not possible with the much taller multi-element array. The microstrip antenna elements can be manufactured using printed circuit technology to reduce cost; the resistivity tapered ground plane can be made from different types of resistive material that are currently available such as textiles, composites, paints or thin films sputtered on thin plastic sheets. Since it does not need stamped or machined metallic parts like the choke ring ground plane, it is easier and less expensive to manufacture and also lighter in weight.