GPS Multipath Mitigation Using a Three Dimensional Phased Array

Digital beam steering with a phased array has previously been demonstrated to improve the Signal/Multipath (S/M) level for precision applications by providing gain in the direction of the GPS satellites. A disadvantage of using horizontal planar antenna arrays is that the beam pattern is symmetric in the Up/Down directions. This means that only the phased array ground plane affects the antenna array Up/Down ratio, which defines the relative gain between the satellite and a horizontally reflected multipath signal. By including both horizontal and vertical antenna element separation in an array design, multipath can be rejected, improving both the Up/Down gain ratio (for horizontal multipath sources) and also rejecting multipath from other directions. In this paper the relative advantages of some alternative 3-D antenna array designs are shown, compared with conventional planar or vertical arrays. Simulation results are shown of the alternative antenna array properties and a 3-D antenna array that has been built and tested using our in-house digital beam-steering GPS receiver is presented.