Automated Full-Sphere Measurement Methodology for Reconfigurable Intelligent Surface Beam Steering in an Anechoic Chamber

Abstract

Reconfigurable intelligent surfaces (RISs) need measurement methodologies that quantify the three-dimensional scattering response of a programmed surface, not only the received power of one bistatic link. This paper presents an automated anechoic-chamber methodology for full-sphere characterization of a varactor-based RIS around 5 GHz. The developed platform combines a state-of-the-art spherical near-field scanner with a near-field-to-far-field transformation, which is suitable for antenna measurements, with a common, low-scattering mount for the RIS and the excitation antenna. It enables programming of several independent DC voltages for remote RIS beam steering configuration via a control unit integrated into the chamber, which features a multichannel digital-to-analog converter. The RIS states are synthesized from a pre-measured phase-voltage characteristic and evaluated against an unbiased-RIS reference using local angular power averages. Measurements at 5.3 GHz serve as a proof of operation: the workflow programs one-dimensional and two-dimensional anomalous-reflection states, localizes the resulting beams over the sphere, and extracts target-window gain, maximum-window gain, and pointing error from the same dataset. For five measured RIS beam-steering states, the prescribed target windows show relative beam-steering gains up to 8.8 dB, while the locally detected main-lobe windows show relative gains up to 14.0 dB with an average of 11.3 dB. The reported gain is not active amplification by the RIS; it is a reference-normalized local power ratio for a fixed measurement configuration.