Designing, Building, and Characterizing RF Switch-based Reconfigurable Intelligent Surfaces Marco Rossanese NEC Laboratories Europe marco.rossanese@neclab.eu Placido Mursia NEC Laboratories Europe placido.mursia@neclab.eu Andres Garcia-Saavedra NEC Laboratories Europe andres.garcia.saavedra@neclab.eu Vincenzo Sciancalepore NEC Laboratories Europe vincenzo.sciancalepore@neclab.eu Arash Asadi TU Darmstadt, Germany aasadi@wise.tu-darmstadt.de Xavier Costa-Perez i2cat, NEC Labs Europe, ICREA xavier.costa@neclab.eu ABSTRACT In this poster, we present the Reconfigurable Intelligent Surface (RIS) that we designed, built, and tested. At first, the RIS technology is briefly discussed, subsequently, our prototype details are explained, and finally, we conclude by showing the obtained test results. Our RIS design comprises arrays of patch antennas, delay lines, and pro- grammable radio-frequency (RF) switches that enable almost-passive 3D beamforming, i.e., without active RF components. 1 INTRODUCTION Reconfigurable Intelligent Surfaces (RISs) are well per- ceived as a key technology for next-generation mobile systems [2]. A RIS can be seen as a planar structure able to manipulate the electromagnetic response of the impinging RF signals. A typical RIS can programmatically re-focus the re- ceived signal towards selected directions by changing the phase shifts of its antennas/reflectors. This ability of the RIS opens a new paradigm of wireless environment: traditionally it has been treated as an optimization con- straint, but now it plays an active role in the system, creating the so called Smart Radio Environment [1]. For instance, the presence of a RIS can be beneficial when the line of sight between the base station and the user is obstructed; the user can rely on the RIS, which still has a direct channel with the base station and can beamform the signal to the user. This scenario is depicted in Fig. 1. Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for third-party components of this work must be honored. For all other uses, contact the owner/author(s). ACM MobiCom ’22, October 17–21, 2022, Sydney, NSW, Australia © 2022 Copyright held by the owner/author(s). ACM ISBN 978-1-4503-9181-8/22/10...$15.00 https://doi.org/10.1145/3495243.3558256 RIS TX RX Figure 1: Scenario with blocked RX. Figure 2: Example of RIS beamforming. Beamforming is a technique that exploits the phe- nomenon of interference: in the RIS case, the signals are received by the antennas, forwarded to the phase shifters, and finally retransmitted. If the phase shift for each antenna is correctly applied, then the signals will constructively interfere towards the desired direction and destructively interfere with the rest. Therefore, the signal is reinforced and the power channeled where it is needed, as represented in Fig. 2. In addition, RISs are supposed to be cheap and low consuming devices, hence they must satisfy the follow- ing requirements: (𝑖) RISs shall (re-)steer RF signals with minimal power loss; (𝑖𝑖) RISs must not use active RF com- ponents; (𝑖𝑖𝑖) RISs must minimize the energy required to re-configure their reflective cells; (𝑖𝑣) RISs shall be re- configurable in real-time; and (𝑣) RISs must be amenable to low-cost production at scale. 2 OUR RIS PROTOTYPE Our prototype [3] is built in PCB technology with a thickness of 0.6mm, it contains 100 patch antennas dis- posed in a 10x10 grid and all the necessary electronic components; the RIS prototype can be seen in Fig. 4. The working frequency of the antennas is 5.3 GHz with a bandwidth of 100 MHz and the antennas are separated by an inter-element distance between antennas of 𝜆/2. The RIS is designed with a 3bit phase shift granularity; the phase shifting procedure is the me