Active Reconfigurable Intelligent Surface for mmWave

Description

Reconfigurable intelligent surfaces (RISs) will play a key role to establish reliable low-latency millimeter wave (mmWave) communication links for indoor automation and control applications. In case of a blocked line-of-sight between the base station (BS) and the user equipment (UE), a RIS mounted on a wall or on a ceiling enables a bypass for the radio communication link. In this work, we present an active RIS for the mmWave frequency band. Each RIS element uses a field effect transistor (FET) to amplify the reflected signal and an orthogonal polarization transformation to increase the isolation between impinging and reflected radio wave. By switching the bias voltage at gate and drain of the FET we can establish four states for each RIS element: two reflection states with different phase shifts, an active amplification and an off state.
We present measurement results of the active RIS in an anechoic chamber as well as in a lab environment, the 127 antenna elements are arranged in a hexagonal grid operating at 23 - 25 GHz. The RIS field patterns obtained by numerical simulations and by empirical measurements in both scenarios show an excellent match. The active RIS provides an improved SNR by at least 4 dB compared to the reflective mode. A first outlook to results of the digital twin for reflective environments will conclude the presentation.

Period	14 Feb 2024
Event title	The 6G series workshop by Hexa-X-II
Event type	Conference
Degree of Recognition	International