Passive Transmissive Reconfigurable Intelligent Surface

Reconfigurable intelligent surfaces (RISs) have been extensively studied as a key technology for advanced 6G communications. Although active RIS systems present innovative opportunities for wave manipulation and communication, they are hindered by their complex structures and high costs due to the extensive use of active elements. In this paper, we introduce the concept, design, and validation of a transmissive RIS, consisting of two passive metasurfaces with pre-engineered phase distributions. This system enables the modulation of electromagnetic waves from a source antenna into a directional beam, with the beam's direction dynamically controlled by adjusting the relative positions of the passive metasurfaces. The performance of the passive transmissive RIS is validated through both numerical simulations and experimental results. This proposed design avoids the reliance on numerous active elements, thereby significantly reducing the complexity and cost associated with RIS implementation.