Low-Complexity Phase-Transition-Based VO₂ Transmissive Reconfigurable Intelligent Surface for Indoor Millimeter-Wave...

This paper presents a low-complexity and low-cost transmissive reconfigurable intelligent surface (TRIS) based on the phase-change material vanadium dioxide (VO₂) for indoor millimeter-wave (mm-wave) communications. Although mm-wave systems enable ultra-high data rates and low latency, their performance is limited by severe path loss and non-line-of-sight propagation. RISs offer a promising solution by dynamically controlling electromagnetic wave propagation. In particular, TRISs provide greater deployment flexibility than reflective RISs in indoor environments where transmitter-receiver links are blocked by walls, windows, or other barriers. However, wide phase tunability in TRISs typically requires complex circuit architectures. Moreover, conventional active components such as PIN and varactor diodes suffer from significant parasitic effects at mm-wave frequencies, which degrade performance and increase design complexity. To address these limitations, the proposed TRIS exploits the metal-insulator phase transition of VO₂ and geometrically engineered VO₂ switch patterns to achieve flexible phase reconfiguration without complex biasing networks or lossy lumped components. The design is validated through theoretical analysis, full-wave simulations, and measurements. The prototype steers transmitted waves from 0° to ± 20° at 65 GHz and achieves up to approximately 15 dB transmission enhancement between the programmed and reference states across 64-66 GHz, demonstrating its potential for indoor mm-wave and WiGig applications.