Single Antenna GPS Spoof Detection that is Simple, Static, Instantaneous and Backwards Compatible for Aerial Applications

Despite the antenna’s privileged position as the first line of defense against interferers, jammers and spoofers, most detection and mitigation techniques are realized in the receiver’s backend signal processing blocks. Nonetheless, these solutions often require considerable additional hardware added to the receiver’s frontend and antenna design. For example, multi-antenna arrays replace a single antenna design for the purpose of detection/mitigation of interference, jamming [1] and spoofing [2] [3]. Among the single antenna detection/mitigation designs, some form of antenna movement over time is required. For example, the use of a synthetic aperture [4] and the generation of high frequency antenna motion [5] has been proposed for spoof detection/mitigation. All of the aforementioned innovations utilize additional signal processing blocks in the backend, in conjunction with the supplemented frontend hardware, to achieve their intended goals. A primary technique for achieving this type of adaptability in sub-wavelength single antenna systems is the use of discrete circuit components on or near the antenna element [6]. Circuit components manipulating signals in the RF domain can achieve analog “signal processing” directly on the antenna, essentially eliminating additional computational complexity. However, signal processing in the digital domain often affords far more flexibility and applicability. The primary limitation of this design is that the spoofdetection technique is most effective when spoofed signals are originating from a source below the antenna, thus limiting its applicability to predominantly aerial implementations. Nonetheless, we feel this solution is well suited to the form-factor and payload constraints that aerial applications such as commercial aviation and UAVs demand. Additionally, we introduce some techniques for extending the applicability of this design. In our design we simply add an electronic switch inside the radome of the antenna that permits high speed switching from the default radiation pattern that is predominantly right-hand circularly polarized (RHCP) to one that is predominantly left-hand circularly polarized (LHCP), in the upper hemisphere of the antenna. However, at very low angles of elevation and generally below the antenna, the radiation pattern is neither predominantly RHCP or LHCP [7], so the switching has little effect on the radiation pattern at all. We can exploit this expected telltale drop in the received SNR or C/N0 to identify if the signal is originating from above the antenna or from below it, and thus, if the signal is genuine or spoofed.