A Compact Low-Cost Reconfigurable Intelligent Surface for Wide-Angle Beam Steering

Abstract

This letter presents a 2-bit reconfigurable intelligent surface (RIS) implemented on a low-cost FR4 substrate for wide-angle beam steering applications in 5G and beyond. The proposed RIS employs a varactor diode-based unit cell design combined with an air spacer that achieves four discrete reflection states (−165°, −75°, 15°, and 105°) over an aperture size of 4.4λ0 × 4.4λ0, λ0 being the wavelength at 4 GHz. With the dynamic regulation of reflection phases, the design exhibits the beam steering operation covering an angular range of −50° to +50° under normal incidence, further extending to ±70° for an incident angle of ±60°. A detailed analysis is carried out to illustrate the steering operation, which is further confirmed by experimental measurements conducted in both indoor and outdoor environment. A comparative analysis with existing designs reveals significant improvements in the beam steering performance, thereby demonstrating the potential of the proposed RIS in advanced wireless communication systems. © 2026 Wiley Periodicals LLC.