Transmissive RIS for 6G Communications: Design, Prototyping, and Experimental Demonstrations

TL;DR

This paper introduces a novel transmissive RIS design for 6G communications, demonstrating its prototype, experimental validation, and advantages in beamforming, data rate, and obstacle transmission.

Contribution

It presents the first transmissive RIS prototype with 2-bit phase control, validated through experiments, enhancing 6G communication capabilities.

Findings

Achieved a maximum gain of 22.0 dBi at 27 GHz.

Validated beam steering up to ±60°.

Demonstrated improved data rate and obstacle transmission.

Abstract

Reconfigurable intelligent surface (RIS) has been widely considered as a key technique to improve spectral efficiency for 6G communications. Compared with most existing research that only focuses on the reflective RIS, the design and prototyping of a novel transmissive RIS are presented in this paper, and its enhancement to the RIS-aided communication system is experimentally demonstrated. The 2-bit transmissive RIS element utilizes the penetration structure, which combines a 1-bit current reversible dipole and a 90{\deg} digital phase shifter based on a quadrature hybrid coupler. A transmissive RIS prototype with 16$\times$16 elements is designed, fabricated, and measured to verify the proposed design. The measured phase shift and insertion loss of the RIS element validate the 2-bit phase modulation capability. Being illuminated by a horn feed, the prototype achieves a maximum broadside gain of 22.0 dBi at 27 GHz, and the two-dimensional beamforming capability with scan angles up to $\pm$60{\deg} is validated. The experimental results of the RIS-aided communication system verify that by introducing the extra gain and beam steering capability, the transmissive RIS is able to achieve a higher data rate, reduce the transmit power, improve the transmission capability through obstacles, and dynamically adapt to the signal propagation direction.