A Reconfigurable Intelligent Surface at mmWave Based on a Binary Phase Tunable Metasurface

TLDR

Reconfigurable intelligent surfaces (RIS) enable smart environments by controlling electromagnetic reflections, attracting attention as a green, scalable technology for future 6G networks. This work designs, models, and experimentally demonstrates a millimeter‑wave RIS using a binary‑phase tunable metasurface. The authors numerically design a PIN‑diode unit cell achieving wide‑band phase shift and low return loss at 28.5 GHz, then fabricate and characterize the 10 cm × 10 cm surface and provide analytical models for near‑field reflectarray and far‑field access‑point extension. Experimental tests confirm that the binary‑phase RIS achieves efficient millimeter‑wave beamforming in both near‑ and far‑field scenarios, with high control efficiency limited only by the PIN‑diode power dissipation.

Abstract

Originally introduced in the early 2010's, the idea of smart environments through reconfigurable intelligent surfaces (RIS) controlling the reflections of the electromagnetic waves has attracted much attention in recent years in preparation for the future 6G. Since reconfigurable intelligent surfaces are not based on increasing the number of sources, they could indeed pave the way to greener and potentially limitless wireless communications. In this paper, we design, model and demonstrate experimentally a millimeter wave reconfigurable intelligent surface based on an electronically tunable metasurface with binary phase modulation. We first study numerically the unit cell of the metasurface, based on a PIN diode, and obtain a good phase shift and return loss for both polarizations, over a wide frequency range around 28.5 GHz. We then fabricate and characterize the unit cell and verify its properties, before fabricating the whole 10 cm ×10 cm reconfigurable intelligent surface. We propose an analytical description of the use that can be done of the binary phase RIS, both in the near field (reflectarray configuration) and in the far field (access point extender). We finally verify experimentally that the designed RIS works as expected, performing laboratory experiments of millimeter wave beamforming both in the near field and far field configuration. Our experimental results demonstrate the high efficiency of our binary phase RIS to control millimeter waves in any kind of scenario and this at the sole cost of the energy dissipated by the PIN diodes used in our design.