Because of the weak signal power of Global Positioning System (GPS), GPS receivers are vulnerable to intentional and unintentional radio frequency interferences (RFI), which can prevent the acquisition and tracking of GPS signals or cause a significant degradation of navigation accuracy. In order to mitigate the impact of GPS RFI, various antenna array processing techniques have been studied. Since an antenna array is able to mitigate jamming signals and simultaneously preserve Signals of Interest (SOI), it has greater interference suppression capability than a single-element antenna. It is known that an N-element Right Hand Circularly Polarized (RHCP) antenna array has N-1 degrees of freedom in the sense that the array can form up to N-1 beams and nulls. If a dual-polarized (i.e., RHCP and Left Hand Circularly Polarized, LHCP) antenna array is used instead of a typical RHCP antenna array, the degrees of freedom of the array increases to 2N-1. Thus, the maximum number of beams and nulls which can be formed by the dual-polarized antenna array also increases 2N-1. In this work, the null-steering using a dual-polarized antenna array is studied. The calculation of optimal weight is based on the Minimum Variance Distortionless Response (MVDR) algorithm to which the modified steering vector is applied. As a result, the dual-polarized antenna array can place spatial nulls in directions of interferences. For simplicity, it is assumed that each antenna element has uniform antenna gain in all directions and perfectly cancels the signal components of opposite polarization Simulation were performed under various interference scenarios, where different number of narrowband RHCP interferences is considered. For each scenario, the array pattern is presented to demonstrate interference suppression capability and the array pattern of a single-polarized array is also presented for comparison.

Keywords: global positioning system (GPS), radio frequency interference (RFI), dual-polarized antenna Array, minimum variance distortionless Response (MVDR)