Invariant Target Detection in Multiband FM-Based Passive Bistatic Radar

FM-based passive bistatic radars (PBRs) exploiting a single broadcasted channel suffer from time-varying detection performance due to the time-varying program content of the transmitted signal as well as the propagation condition of that channel. To circumvent this matter, it is a viable idea to exploit multiple broadcasted channels from a single transmitter for detection. In this case, we formulate the problem of detecting a target in the presence of interference signals such as receiver noise, direct signal, multipath/clutter echoes and interfering targets as a composite hypothesis test. To address this, we derive a multiband uniformly most powerful invariant (UMPI) test as an optimal invariant detector. Closed-form expressions for calculating false alarm probability and detection probability for the target models of Swerling 0 and Swerling 1 are derived. A thorough performance assessment is also given, and the results show the robustness of the proposed multiband detector against the time-varying program content of FM radio channels. In addition to the reliable detection performance, a multiband PBR system offers advantages in terms of combined diversity gain and frequency diversity gain as compared with a single band PBR system. The former happens due to the joint exploitation of multiple broadcasted channels for detection, while the latter occurs when independent returns are received from one target over different frequency channels.