Backscatter, Reconfigurable Intelligent Surfaces and MIMO Communications with a Multipurpose Antenna Array

Multiple input multiple output (MIMO) systems exploit multiple antenna arrays to boost the performance of wireless communications. However, they rely on energy-greedy arrays of transmit and receive radio-frequency (RF) chains. Recent advancements in low-power communications have introduced two novel approaches, avoiding the use of RF transmit chains. The first one consists in using electronically tunable mirrors called Reconfigurable Intelligent Surfaces (RIS) to improve the wireless propagation channel between a transmitter and a receiver, instead of using active repeaters with transmit RF chains. The second one consists in backscattering ambient waves and modulating the propagation channel to implement ultra-low power communication, instead of transmitting with an RF chain. While a MIMO device is obviously made up of an antenna array, this can also be the case for RIS and backscattering ones when connected to reconfigurable loads. To exploit this synergy, we propose a Multipurpose Antenna Array (MAA) capable of managing all three operating modes. In this paper, we present a model of the MAA based on S-matrix analysis, which highlights the link between the 3 modes. It also allows a fast but accurate simulation of MAA. Furthermore, we have build and successfully tested the three modes over a first real-time prototype made of 8 patch antennas operating at 3.7 GHz.