A Microfabricated PCM-Switched Reconfigurable Intelligent Surface for Wideband Millimeter-Wave Beam Steering

TL;DR

This paper introduces a microfabricated, PCM-based reconfigurable intelligent surface for wideband millimeter-wave beam steering, demonstrating scalable design, experimental validation, and significant gain enhancement at 33 GHz.

Contribution

It presents a novel monolithically integrated VO2 switch-based RIS architecture with scalable microfabrication for high-frequency beam steering applications.

Findings

Achieved 10-20 dB gain enhancement over 18% bandwidth at 33 GHz.

Demonstrated programmable beam steering up to 60 degrees.

Validated phase and amplitude responses through experiments and simulations.

Abstract

This paper presents the design, fabrication, and experimental validation of a reconfigurable intelligent surface (RIS) employing electrically actuated vanadium dioxide (VO2) switches for millimeter wave beam steering. The proposed RIS is realized using a multilayer microfabrication process on an alumina substrate, enabling monolithic integration of hundreds of sub-4 micrometer VO2 switching elements within deeply subwavelength unit cells, approximately one-fifth of the wavelength. The switching-induced modulation of surface impedance is analyzed through full-wave simulations, and the resulting phase and amplitude responses are experimentally characterized using a custom WR-28 waveguide measurement setup. Based on the validated unit-cell design, a 10 x 20 RIS array integrating 200 VO2 switches is fabricated. The switches within each column are serially biased using integrated routing lines, allowing programmable control of the spatial phase distribution across the surface. Synthesized phase profiles enable dynamic beam steering, resulting in measured far-field gain enhancement of 10-20 dB over an 18 percent fractional bandwidth centered at 33 GHz, with steering angles up to 60 degrees. The measured radiation patterns are in good agreement with semi-numerical channel modeling predictions. By combining thin-film PCM switching with an integration-aware unit-cell design, this work demonstrates a scalable RIS architecture that mitigates packaging parasitics and footprint limitations inherent to conventional semiconductor-based implementations, providing a practical pathway toward higher-frequency reconfigurable surfaces.