Surface Wave Coupling and Penetration in Shadow Region by a Corner RIS

This paper proposes a method to penetrate the shadow region of a wedge-corner using passive Reflecting Intelligent Surfaces (RIS) placed on both faces of the corner. We refer to this configuration as a corner RIS (C-RIS). The study is framed within the concept of a smart radio environment (SRE), where efficient wave guidance and control around obstacles, such as corners, play a role in enhancing communication. We initially introduce two possible types of C-RIS: i) C-RIS using receiving and transmitting metasurface antennas based on cylindrical surface waves (SW), where the two metasurfaces are coupled at their feed points via a transmission line; ii) C-RIS based on planar SW coupling, where the transmission around the corner is ensured by the intrinsic properties of the metasurface impedance near the edge. The focus of the paper is on this second type of C-RIS, and in particular on the transmission coefficient across the corner. This is achieved using the exact solution of the impedance wedge problem, analytically extended to complex values of the incident plane wave parameters. The solution is validated through full-wave analysis even in presence of losses. The formulas presented in this work have significant implications for the design of surface-wave communication systems in SREs.