Design and Prototyping of Wideband Transmissive RIS for Enhanced Wireless Communications

Reconfigurable intelligent surfaces (RISs) present significant potential for enhancing coverage and data rates in 6G wireless communication systems. While most research has focused on reflective RIS applications, studies on transmissive RIS (TRIS) have largely been limited to simulations or laboratory-scale prototypes. To evaluate the real-world performance of TRIS, we develop a 256-unit, 1-bit TRIS prototype operating at the 5.8 GHz frequency band. The design uses an antisymmetric configuration of two PIN diodes, achieving nearly uniform transmission amplitude with inverse phase states over a wide 20% bandwidth. A TRIS composed of 16 × 16 units is fabricated and validated through measurements, showing effective 1-bit phase tuning with minimal insertion loss and a 3 dB transmission bandwidth exceeding 1.2 GHz at the central frequency of 5.8 GHz. By dynamically modulating the quantized code distributions, ±90° scanning beams are achieved. We then integrate the TRIS into a wireless communication system and evaluate its performance in a real-world wall-penetration scenario. With directional antennas that are connected to the Universal Software Radio Peripheral (USRP) modules and are placed on either side of a 240 mm concrete wall, the TRIS provides a signal power gain of 19-23 dB within a ±90° beamforming range, significantly reducing path loss. Additionally, we assess its impact on a commercial Wi-Fi system, where the TRIS improves the average Signal-to-Noise Ratio (SNR) by 8 dB, with a maximum gain of 15 dB, across a 29 m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> indoor area. Downlink rates also increase, with a maximum improvement of 10.57 Mbps and an average gain of 8.01 Mbps. These results highlight TRIS’s effectiveness in reducing path loss, enhancing SNR, and improving Wi-Fi performance in challenging wall-penetration environments, leading to better user experiences.