Theory and Field Trial Results for Aerial Applications of Anti-Jam and Spoof Detection

S E P T E M B E R / O C T O B E R 2 0 1 5 www.insidegnss.com A GNSS single-antenna system can be compared to a singlepixel camera. Electromagnetic waves traveling 20,000 kilometers from every overhead direction can reach us. Yet once at the antenna, this diverse set of information is collapsed into a single magnitude and phase value, then sent off to the receiver so that value can be extracted. Antennas can redeem themselves by adding some features, but generally at the cost of greatly increased complexity. Most antenna systems that provide additional functionality rely on multiple antenna elements and multiple analogto-digital converters (ADCs). This extra hardware and processing is often used for the simultaneous reception of a single-incident waveform at multiple phase fronts, as is done for example, in a multi-antenna array system. The simultaneously received signals are phase coherent components of the incident waveform: similar in magnitude but shifted in phase. Functionality, such as beam/null steering, can be accomplished by phase shifting and then combining the signals to obtain constructive and destructive interference. This article introduces a low complexity mechanism for generating radiation pattern nulls and beams without requiring any additional hardware or signal processing blocks beyond those already inherent to GPS receiver systems. It describes the mathematical model that underlies this mechanism, including simulation results, as well as two applications: single-antenna jam mitigation and single-antenna spoof detection. Results of several field trials are presented based on a prototype implemented in off-the-shelf components and using a standard GPS receiver. Single Antenna, Dual Use Theory and Field Trial Results for Aerial Applications of Anti-Jam and Spoof Detection