A Novel Design of Varactor-Based RIS: Achieving Low-Profile, Wideband, and Continuous Phase Control

This letter presents a novel Reconfigurable Intelligent Surface (RIS) that features a low-profile structure, wide operating bandwidth, and continuous phase control. By incorporating a middle patch layer without introducing an additional air gap, the proposed design maintains a low-profile property, while achieving a smooth <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$360^{\circ }$</tex-math></inline-formula> phase shift over 10% bandwidth at 6 GHz with excellent reflection. A fabricated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10\times 10$</tex-math></inline-formula> RIS array exhibits stable performance, enabling precise beam control across a 600 MHz bandwidth. These results highlight the potential of the proposed low-profile, wideband RIS with continuous phase tuning for next-generation wireless communication systems.