A Novel Design Method of RIS Element with A Wideband Varactor-Tuned Example

Reconfigurable intelligent surfaces (RISs) are developing rapidly nowadays and considered as a key technology for next-generation communications. However, when designing RISs with wideband feature, the traditional design method is complex and time-costly because the trial-and-error simulations lack clear design guidance. Here, we propose a radiation method to model, design and evaluate a RIS element, where the design goal is to match the element impedance to a pre-calculated impedance determined by the diode parameters. Using the novel method, a varactor-tuned RIS element is designed with a wide bandwidth of 20%, and the average loss is about 1.1 dB at 5.4 GHz, which significantly improves the performance of RIS elements.