Experimental demonstration of reflected beamforming and interference nulling at sub6GHz thanks to varactor-based reconfigurable intelligent surface

Reconfigurable intelligent surface (RIS) is a promising solution to boost coverage sustainably by reflecting waves from a transmitter to a receiver and acting as a low-power and passive relay. In this paper, for the first time, we demonstrate experimentally that a reconfigurable intelligent surface designed for sub6GHz, and using varactor technology, can perform three-dimensional reflective beamforming and interference nulling. This result is achieved with a RIS prototype of 984 unit-cells, thanks to a compact control circuit individually addressing and configuring the voltage of each unit-cell, with a distinct voltage. To our knowledge, this prototype configures 17 to 70 times more distinct voltages than in the state-of-the-art. The experimental results in an indoor environment show a 10-dB gain. They also show, for the first time, that producing such a new prototype is feasible with minimal energy footprint and environmental impact, thanks to refurbishing. Indeed, a reflectarray antenna originally designed for three-dimensional beamforming has been turned into a RIS.