Joint Transmit and Reflect Beamforming Design for Active-RIS-Assisted Secure ISAC Systems

A secure integrated sensing and communication (ISAC) system enhanced by an active reconfigurable intelligent surface (RIS) is investigated in the letter. Unlike existing works, the proposed fairness-aware beamforming framework jointly ensures fair multi-target detection and secure multi-user communication. The objective is to maximize the minimum beampattern gain across target directions, subject to constraints on secure transmission, power budgets, active RIS reflection coefficients, and the noise introduced by the active RIS. To solve this non-convex problem, an alternating optimization (AO) algorithm that leverages penalty-enhanced successive convex approximation (SCA) is developed, which enhances beamforming gain and angular uniformity over standard semidefinite relaxation (SDR). Simulation results confirm the superior performance of the proposed design scheme compared to existing baseline schemes.