Compact Design of a Transmission-Type Reconfigurable Intelligent Surface System for Beam-Steering Applications

Although reconfigurable intelligent surfaces (RISs) have attracted broad attention, they usually require a large scale of elements and hundreds of tunable components, particularly for beam-steering applications. Herein, a methodology is proposed for the compact design of a transmission-type RIS system for beam steering. The approach leverages a customized horn feed equipped with a gradient refractive index metalens to tailor the electromagnetic fields over the horn aperture, resulting in focused amplitude and uniform phase distributions. This enables us to reduce the feed-RIS distance and significantly decrease the RIS scale using only a small number of components while still achieving acceptable beam-steering performance. The investigations are carried out through theoretical studies, simulations, and experiments. A prototype system is fabricated as an exemplary demonstration, which occupies a volume of 3.3 & lambda;(0) x 2.6 & lambda;(0) x 3.5 & lambda;(0), including the feed, and contains only 3 x 5 RIS elements and 60 varactors. With every single element being controlled individually by a simple network, beam-scanning ranges of & PLUSMN;30 & DEG; are measured on the E-, H-, and 45 & DEG;-planes, respectively. With the above intriguing properties, the proposal can find potential applications where miniaturization, high portability, and low cost are required for beam-steering functions.