Demonstrating and Improving the Performance of a GNSS Dual Polarization Antenna (DPA) for Spoof Detection in Flight

Abstract

Dual polarization antennas (DPAs) are being developed to provide robust GNSS spoof detection and interference mitigation. These antennas show great potential in determining the azimuthal direction of arrival (DOA) of incoming GNSS signals with just a single GNSS patch antenna. With satellite signal DOA, we can test for and detect non-genuine or spoofed signal. Under nominal conditions, it can provide static heading with as few as one GNSS satellite. The Stanford DPA prototypes have demonstrated an ability to find DOA from both genuine and spoofed signals [1][2][3]. The DPA provides right hand circularly polarized (RHCP) and left hand circularly polarized (LHCP) signal components that can be used to determine signal DOA, detect spoofing, or mitigate interference through directional nulls. Improved versions of the Stanford DPA have the ability to support high rate measurements, operate in dynamic situations and improved spoof detection algorithm that can utilize other detection metrics. In this paper, we examine several means to improve performance and spoof detection with a DPA. It first discusses the design of the improved Stanford printed circuit board (PCB) based DPA [1] [4] to make is suitable flight trials. The design was modified to support high dynamics which means supporting a faster DOA determination capability than our first generation PCB DPA. Additionally, this DPA PCB supports a processing chains using a commercial off the shelf (COTS) GNSS receiver. Next, the paper examines the dynamic performance of the COTS GNSS DPA in flight test. It quantifies the factors that affect DOA performance such as satellite used, elevation angle and other factors. Accurate knowledge and incorporation of these factors can improve our DOA based spoof detection algorithm. It also examines performance in different flights conditions such as nominal and interfered. We will examine the resulting performance of the signal for spoof detection using algorithms developed to utilize DOA along with other detection metrics, specifically pseudo range residuals (prr). Finally, we examine the improvement in spoof detection if we are able to resolve the 180-degree ambiguity of DPA DOA measurements. Our analysis shows that resolving the ambiguity can greatly strengthen our confidence of spoof detection.