Bistatic Detection of Weak Targets in the Presence of a Strong Direct-Path Signal

Bistatic radar target detection is often complicated by a direct-path signal from the bistatic transmitter to the bistatic receiver. This direct-path signal can be much stronger than the signal scattered by the target of interest. In order to detect targets in the presence of the direct-path signal, it must be attenuated or cancelled. In this paper, we determine the detectability of weak targets in the presence of a direct-path in the presence of additive white Gaussian noise (AWGN) in the clairvoyant case, in which the target amplitude, direct-path amplitude, and the AWGN variance is known. This results in a detection problem in which the likelihood ratio is not in general a monotonic function of the matched filter output. This means that the most powerful test with a fixed false-alarm rate is not a threshold test on the matched filter output. We analyze the ability of a radar with phased array and delay-Doppler matched filter processor to exploit differences in the direct target direction, delay, and Doppler to attenuate the direct-path and optimally detect the target. This performance analysis is useful as a benchmark in developing direct-path cancellation algorithms.