A GPS receiver based system, with associated antenna array design, will provide continuous information for attitude determination. This system supports L1/L2 and SAASM functions under both GPS jamming, and spoofing attack, to maintain navigation in contested environments. The approach utilizes two orthogonal, beam steered arrays which point a minimum of four beams at a priori known satellite locations relative to the platform orientation. Three of these coherent sub-arrays are arranged to form orthogonal baselines aligned on the platform and interferometric signal processing is used to compute the azimuth and elevation vectors to the signals tracked. The measured azimuth and elevation for each signal is compared to the expected angle of arrival of the GPS satellite signals, as computed from the ephemeris. Agreement between measured angle of arrival and computed angle of arrival indicates legitimacy. If the measured angles of arrival of do not match the expected angles, a spoofed signal is indicated. So long as the signals are legitimate, differential carrier phase across the orthogonal baselines is used by the system to calculate platform attitude (pitch and roll). When signals are not legitimate, the differential phase information is not used calculate attitude and a bearing to the threat is reported.
