RIS-aided Wireless Communications: Can RIS Beat Metal Plate?

TL;DR

This paper compares RIS and metal plates in wireless communications, showing RIS's superior performance in spherical wave scenarios through theoretical analysis and experimental validation.

Contribution

It provides a wave optics-based analysis and explicit scattering models demonstrating RIS's advantages over metal plates in specific conditions.

Findings

RIS outperforms metal plates with spherical waves

Metal plates have higher scattering efficiency but less effective in certain scenarios

Models validated by simulations and field measurements

Abstract

Reconfigurable Intelligent Surface (RIS) has recently been regarded as a paradigm-shifting technology beyond 5G, for its flexibility on smartly adjusting the response to the impinging electromagnetic (EM) waves. Usually, RIS can be implemented by properly reconfiguring the adjustable parameters of each RIS unit to align the signal phase on the receiver side. And it is believed that the phase alignment can be also mechanically achieved by a metal plate with the same physical size. However, we found in the prototype experiments that, a well-rotated metal plate can only approximately perform as well as RIS under limited conditions, although its scattering efficiency is relatively higher. When it comes to the case of spherical wave impinging, RIS outperforms the metal plate even beyond the receiving near-field regions. We analyze this phenomenon with wave optics theory and propose explicit scattering models for both the metal plate and RIS in general scenarios. Finally, the models are validated by simulations and field measurements.