Methodology and Design of Absorptive Filtering Reconfigurable Intelligent Surfaces

Reconfigurable intelligent surface (RIS) is regarded as a potentially critical technology for 6G wireless communications. However, suppressing interference from wireless systems in RIS applications remains a challenge that needs to be overcome. In this communication, the methodology and design of the absorptive filtering RIS are presented. First, the ideal reflection responses of the absorptive filtering RIS are modeled and characterized. Second, the theoretical conditions that achieve the ideal reflection response for the absorptive filtering RIS are analyzed and derived. Third, following the guidance of the theoretical conditions, the equivalent circuit model and the element are developed and simulated, and the simulated results show that both a tunable phase shift and a good bandpass-like magnitude response are achieved. Finally, an absorptive filtering RIS prototype is fabricated and measured to verify the filtering property. The measured results coincide well with that in simulations, showing that the 1-dB working bandwidth ranges from 4.9 to 5.28 GHz, and the 10-dB rejection band ranges from 3 to 4.32 GHz and from 5.68 to 7 GHz. To the best of the authors’ knowledge, the RIS with absorptive filtering capability is first proposed. Besides, the main beam can be scanned within 0°–60°. Benefiting from the merits of the filtering feature and good in-band performance, our work has potential applications in enhancing the communication quality of RIS-assisted wireless systems.