Clutter Cancellation in Passive Bistatic Radar With Transmitter Nonlinearity

Passive bistatic radar (PBR) employs an ambient source of radio frequency (RF) energy, such as a television transmitter, as an illuminator. The continuous nature of such transmissions results in significant interference in the surveillance signal, as direct-path (DP) transmission and returns from clutter. These must be suppressed in order to make target returns detectable. Delay-Doppler processing can be enhanced by demodulating and reconstructing the captured reference signal. However, target detectability is known to be affected when a reconstructed signal is used in the zero-Doppler cancellation (ZDC) process. This study proposes transmitter nonlinearity as a reason for poor cancellation. Analysis of ambiguity peak-to-floor measures suggests that under certain conditions unmodeled nonlinearity will cause degradation in ZDC. Several methods of nonlinearity estimation and modeling are proposed. Simulation evaluates these methods with various levels of nonlinearity and sensor noise. The methods are applied to ambiguity processing of terrestrial digital video broadcast (DVB-T) real data in both single-channel and two-channel receiver configurations. The results are explained with reference to the earlier analysis.