Secure Beamforming for Pinching-Antenna Systems

Recently, pinching-antenna systems (PASS) have demonstrated pronounced advantages in mitigating large-scale path loss. This paper investigates their performance advantages in downlink secure transmission. We consider a scenario with multiple waveguides, one legitimate user, and one eavesdropper. The goal is to maximize the secrecy rate by jointly designing the baseband beamformer and the positions of pinching antennas (PAs). To handle the coupled optimization problem, we first exploit a generalized Rayleigh quotient structure to derive the optimal baseband beamformer. This step converts the coupled problem into a single-variable optimization over PAs' positions. Then, an efficient gradient-based method is proposed to achieve PA position updates. Finally, simulation results demonstrate that the proposed algorithm converges rapidly and stably, and that PASS achieve substantial secrecy rate gains over the fixed-antenna baselines.