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 3.3λ0 × 2.6λ0 × 3.5λ0, including the feed, and contains only 3 × 5 RIS elements and 60 varactors. With every single element being controlled individually by a simple network, beam‐scanning ranges of ±30° are measured on the E‐, H‐, and 45°‐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.