Joint Active and Passive Beamforming for NLOS Target Detection in RIS-Assisted Mono-Static Radar

Reconfigurable intelligent surfaces (RIS) have gained widespread application in the field of communications and are gradually extending their utility to the radar domain. This paper focuses on a mono-static RIS-assisted radar system. The problem is to jointly design the active beamformer for the radar and passive beamformer for the RIS. We begin by introducing a general signal model. In order to enhance target illumination and echo reception, we maximize the received signal power through the optimization of both the radar beamformer and the phase-shift matrix for the RIS. We provide a closed-form solution for the resulting optimization problem. The proposed RIS-assisted radar is employed for non-line-of sight (NLOS) target detection, where the radar is obstructed from the target. A statistical analysis of the detection performance is presented. Simulation results underscore the significant impact of RIS size and radar-RIS distance on detection performance. Moreover, we demonstrate that RIS can offer a practical solution for NLOS target detection.