Beampattern synthesis for active RIS-assisted radar with sidelobe level minimization

Abstract

To enhance the performance, reconfigurable intelligent surface (RIS) is now employed in monostatic radars since it creates a new path between the radar and the target by artificially reflecting radar signals and thus provides novel degrees of freedom. This correspondence studies the transmit beampattern synthesis for an active RIS-assisted monostatic radar via minimizing the sidelobe levels. The proposed beampattern synthesis is coined as a nonconvex and nonlinear optimization problem which is solved by jointly optimizing the beamforming weights of the transmitter and the phase shift and amplification matrix of the active RIS. The auxiliary variables are first introduced to simplify the nonconvex constraints, and two variables are then alternatively optimized by the alternating direction method of multipliers (ADMM) where their close-form optimal solutions are derived. Numerical results show that the active RIS-assisted radar has a significantly lower sidelobe level than conventional monostatic radars.