Packaging and Antenna Design for a 46-element Dual-surface mmWave Active STAR-RIS built with CMOS RFICs

This paper presents a compact, fully integrated packaging–antenna solution for a programmable active STAR-RIS capable of simultaneous transmission and reflection. Through co-design of a multilayer organic package, dual-sided mmWave arrays, and active RF front-end modules, the architecture enables independent, continuous control of transmitted and reflected wavefronts. A 60-GHz prototype implemented on a 14-layer laminate incorporates 46 CMOS ICs, each providing power-efficient amplification, wide-range phase shifting, and high-isolation interlayer transitions for low-loss routing and robust thermal behavior. The dual-side radiating structure is optimized for high-gain, wide-scan beams while suppressing cross-coupling to ensure independent STAR operation. Measurements confirm dual-sided beam steering, generating simultaneous transmitting and reflecting beams at 45° and 180° with over 17-dBi on/off gain per side and precise programmability across ±60°. The results demonstrate a scalable platform for next-generation software-defined mmWave intelligent radio environments.