Wideband (2:1) Phase Shifter for Reconfigurable Intelligent Surfaces With Linear Phase Control

This paper presents a novel wideband phase shifter that utilizes an elliptically shaped slot-based topology for millimeter wave (mm-Wave) Reconfigurable Intelligent Surfaces (RIS). The proposed design is implemented on a multi-layer PCB and operates across 15 GHz to 30 GHz with minimal phase error. The phase shifter employs umbrella-loaded elliptical slots and patches to achieve a stable differential phase shift across 2:1 bandwidth. At the same time, the ellipsoidal elements maintain a low-loss response. Moreover, the proposed miniature phase shifter (5 mm x 5 mm) can be readily incorporated into the limited space of the RIS unit element. The proposed concept is validated via fabrication and characterization of a prototype. Specifically, the measurements demonstrated a stable 2:1 bandwidth operation with phase errors of less than 7 ∘ across the entire band. The proposed phase shifter maximizes gain and minimizes beam-steering errors across large bandwidth, using a 1-bit RIS. To the best of the author’s knowledge, this is the first design to monstrate 2:1 bandwidth with stable phase for RIS applications.