Beampattern Design for Transmit Architectures Based on Reconfigurable Intelligent Surfaces

In this work, we consider a transmit architecture where few active antennas (sources), each equipped with a dedicated radio frequency chain, illuminate a reconfigurable intelligent surface (RIS) that control the beam-steering capability of the whole system. In this framework, we tackle the beampattern design problem, where the waveform emitted by the sources and the phase shifts introduced by the RIS are designed so that the realized beampattern matches, in a least-square sense, the desired one. The design of this architecture can be useful in many areas, such as radar detection and tracking, millimeter wave, sub-THz, and THz communications, and integrated sensing and communications. We provide a sub-optimum solution to the beampattern design problem, and we report an example to show that this RIS-based transmit architecture can be competitive with respect to fully-digital MIMO systems, especially if constant-modulus waveforms are required.