A Reconfigurable Intelligent Surface With Surface-Wave Assisted Beamforming Capabilities

The integration of tunability mechanisms in the metasurface design has unleashed a tremendous potential for wireless communications. In particular, reconfigurable intelligent surfaces (RISs) can manipulate the reflections of an incident electromagnetic wave at will, based on the real-time conditions, with the aim of enhancing communication links. In this article, we develop an RIS at C band that operates with a transverse-electric (TE) polarization and can shape the radiation pattern at a single plane with high accuracy, in addition to the more conventional beamsteering functionalities. The beamforming is facilitated by subwavelength unit cells that allow the excitation of auxiliary surface waves in the vicinity of the RIS. Importantly, these evanescent fields are predicted and harnessed through an integral-equation framework used for the analysis and optimization of the RIS. A fabricated prototype demonstrates beamsteering up to ±60° with an average illumination efficiency of 95% and sector patterns with a varying beamwidth (ranging from 30° to 60°) that verify the full-wave simulations. Finally, losses are predicted and constrained during the optimization stage leading to solutions with relatively high power efficiency.