Design and Prototyping of Filtering Active STAR-RIS With Adjustable Power Splitting

This article proposes a novel filtering active simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) operating in the 2.58–2.63-GHz band to overcome the limitations of conventional passive RIS in complex propagation environments. The proposed design incorporates power amplifiers (PAs) to enable active gain, achieving up to 15 dB improvement over traditional passive RISs. It supports independent 1-bit phase control of transmission and reflection modes and enables dynamic power splitting between transmitted and reflected signals, providing a controllable range of up to 7 dB. The prototype demonstrates effective out-of-band harmonic suppression and maintains stable beam steering performance within a ±50° scanning range, with minimal gain fluctuation. Moreover, we extend the traditional radar cross section (RCS)-based path loss model to active STAR-RISs systems, experimentally validating its accuracy through measurements consistent with simulation results. The experimental results further demonstrate the feasibility and practicality of the proposed system in real-world applications.