Spoofer Bearing Estimation Using Weighted C/N0 Measurements of a Directional Antenna

This paper extends previous research on determining the direction and location of radio frequency interference sources by evaluating whether a dual-antenna Global Navigation Satellite System (GNSS) setup equipped with a directional antenna can also be used for spoofing localization. Building on earlier jamming localization work, this study investigates whether the same measurement architecture, consisting of a dual-antenna GNSS receiver, a directional antenna, and an Inertial Measurement Unit (IMU)-based heading determination, can reliably detect the bearing of spoofed GNSS signals while remaining portable, cost-efficient, and deployable by non-experts. The system processes signals from a main omnidirectional GNSS antenna through the primary port and either a combined omni / directional antenna signal or a solely directional antenna signal through the auxiliary port. Because GNSS-based heading could not be obtained inside the aircraft hangar where two measurement campaigns were conducted, an IMU was used to provide continuous heading estimates. Two measurement campaigns were performed using a GNSS repeater as a local spoofing source. For each campaign, two antenna configurations were tested. In the first configuration, where the auxiliary input received a combined omnidirectional and directional signal, no consistent Carrier-to-Noise density ratio (C/N0 ) behavior corresponding to the spoofing source direction could be identified. In contrast, the second configuration, which used only the directional antenna on the auxiliary port, showed a clear peak in C/N0 values and a corresponding minimum in antenna gain values when the antenna was pointed toward the spoofing source. Across both campaigns, the bearing estimated with the second configuration using a weighted C/N0 averaging method differed only slightly from the reference bearing, demonstrating its suitability for spoofing direction-of-arrival estimation. Using two such bearing measurements from different positions, a qualitative localization of the spoofing source was illustrated. The study concludes with recommendations for future work, including outdoor testing with an actual spoofer, improved heading initialization, and the use of GNSS-optimized directional antennas to enhance directional sensitivity.