Analysis of range dependence of clutter spectrum in bistatic STAP

Abstract

The range dependence of clutter spectrum is influenced by both the orientation of the receiver array axis and bistatic geometry. In order to mitigate the range dependence, there is a strong requirement of finding out the relationship between the Doppler frequency and the look direction of targets relative to the receiver array. The paper presents the analytical expressions of the clutter Doppler frequency and range for four types of bistatic radar system (the side looking and forward looking arrays with the vertical and horizontal baselines). According to these expressions the clutter spectrum can be compensated by the Doppler warping method. Analysis and simulations show that the clutter Doppler frequency trajectories exhibit a group of lines with different slopes for the side looking array with the vertical baseline, of which the clutter spectrum has a small dispersion in the main beam; the side looking array with the horizontal baseline has a wide clutter spectrum region in the main beam; there is a non-linear relation between Doppler and range for the forward looking array with the vertical or horizontal baseline wherein the Doppler frequency spread mainly depends on the orientation of the receiver array axis relative to the aircraft velocity vector; Doppler warping can mitigate the range-dependence effect on space-time adaptive signal processing (STAP) in four types of bistatic radars.