SRAR-RISs: Simultaneous Reflecting and Refracting Reconfigurable Intelligent Surfaces

In this letter, simultaneous reflecting and refracting reconfigurable intelligent surfaces (SRAR-RISs) are studied. Compared with RISs that only operate in the reflection mode, the coverage area of SRAR-RISs is extended via simultaneous reflection and refraction. We separately present a hardware model and channel models for the near-field region and the far-field region. The proposed channel models give closed-form expressions of the channel gains in terms of physical parameters of the SRAR-RIS and the geometrical information of the receivers. The differences between the far-field and the near-field channel models are revealed by analytical results and simulations.