Millimeter-Wave Active STAR-RIS with Programmable Reflect and Transmit Operation and Channel Sensing for Secure ISAC

This paper presents the design and experimental validation of the first millimeter-wave (mmWave) active simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) for secure integrated sensing and communication (ISAC). A programmable 60-GHz STAR-RIS prototype with embedded amplification, phase shifting, and independent dual-side control enables high-gain, flexible beamforming in both transmission and reflection. The STAR-RIS allows the base station (BS) to maintain reliable indoor communication while sensing line-of-sight blockers on both BS and user sides via on-surface modulation. Comprising 23 custom 60-GHz CMOS ICs per side, the panel supports programmable amplification and multi-beamforming. Measurements demonstrate robust 0.5 Gbps 16-QAM communication over 2.6 m, alongside effective detection of obstacles and eavesdroppers, confirming the STAR-RIS as a promising platform for next-generation ISAC systems.