Design and Prototyping of Transmissive RIS-Aided Wireless Communication

TL;DR

This work addresses coverage limitations of reflective RIS by proposing a transmissive RIS with 1-bit phase control achieved through antisymmetric placement of two PIN diodes. A four-layer metasurface unit cell is designed and simulated, and a 16×16 prototype (512 PIN diodes) is fabricated with a PCB-based bias network to enable independent element control. Experimental results demonstrate a $>20\%$ transmission bandwidth around $5.8$ GHz with a $\approx180^{\circ}$ phase difference between the two states and a measured $\sim0$ dB transmission loss at peak, validating the concept. A RIS-aided wireless prototype shows an average gain increase of about $7$ dB in a through-wall scenario, underscoring the practical viability of transmissive RIS for filling coverage gaps and enabling dynamic beam scanning in beyond-5G networks.

Abstract

Reconfigurable Intelligent Surfaces (RISs) exhibit promising enhancements in coverage and data rates for wireless communication systems, particularly in the context of 5G and beyond. This paper introduces a novel approach by focusing on the design and prototyping of a transmissive RIS, contrasting with existing research predominantly centered on reflective RIS. The achievement of 1-bit transmissive RIS through the antisymmetry configuration of the two PIN diodes, nearly uniform transmission magnitudes but inversed phase states in a wide band can be obtained. A transmissive RIS prototype consisting of 16 $\times$ 16 elements is meticulously designed, fabricated, and subjected to measurement to validate the proposed design. The results demonstrate that the proposed RIS unit cell achieves effective 1-bit phase tuning with minimal insertion loss and a transmission bandwidth of 3 dB exceeding $20\%$ at 5.8GHz. By dynamically modulating the quantized code distributions on the RIS, it becomes possible to construct scanning beams. The experimental outcomes of the RIS-assisted communication system validate that, in comparison to scenarios without RIS, the signal receiving power experiences an increase of approximately 7dB when RIS is deployed to overcome obstacles. This underscores the potential applicability of mobile RIS in practical communication.

Figures (9)

• Figure 1: Geometry of the designed metasurface element, (a) schematic and side view, (b) Radiating layer and (c) Receiving layer
• Figure 2: Current distribution on the unit cell, (a) 0-state, (b) 1-state
• Figure 3: Simulated results of unit-cell in different states
• Figure 4: a) The bias layer network layout. b) Schematic diagram of the steering-logic board circuit design. (c) the fabricated transmissive RIS prototype.
• Figure 5: S21 test environment