We present the first experimental prototype of a reflective beyond-diagonal reconfigurable intelligent surface (BD-RIS), i.e., a RIS with reconfigurable inter-element connections. Our BD-RIS consists of an antenna array whose ports are terminated by a tunable load network. The latter can terminate each antenna port with three distinct individual loads or connect it to an adjacent antenna port. Extensive performance evaluations in a rich-scattering environment validate that inter-element connections are beneficial. Moreover, we observe that our tunable load network's mentioned hardware constraints significantly influence, first, the achievable performance, second, the benefits of having inter-element connections, and, third, the importance of mutual-coupling awareness during optimization.
@article{arxiv.2505.13392,
title = {Beyond-Diagonal RIS Prototype and Performance Evaluation},
author = {Jean Tapie and Matteo Nerini and Bruno Clerckx and Philipp del Hougne},
journal= {arXiv preprint arXiv:2505.13392},
year = {2025}
}