Joint Transmit and Receive Beamforming for Hybrid Active–Passive Radar

We consider a new hybrid radar paradigm consisting of an active array and a passive array. In this hybrid system, the radar transmits a probing signal from its active array and receives two types of echoes: One is the return from the cooperative active transmission and the other is the target return due to transmission from noncooperative illuminators of opportunity. The motivation for this approach is to exploit not only the active signal but also any passive signals that are present in the surveillance area, thereby maximizing the signal-to-interference-plus-noise ratio (SINR). Numerical results demonstrate that the proposed concept can achieve a significant improvement of the output SINR, compared with conventional methods for active-only or passive-only radar systems.