Surface Wave-based Metasurfaces for Smart Radio Environment

This thesis investigates the design and application of metasurfaces (MTSs) to enhance electromagnetic wave manipulation for smart radio environments (SREs). Metasurfaces, as planar equivalent of metamaterials, provide efficient, low-cost solutions for wave control, making them ideal for next-generation wireless communication. A key focus of this work is transitioning from traditional reflecting intelligent surfaces (RIS), which rely on anomalous reflection, to surface wave (SW)-based RIS (SW-RIS) leveraging a double conversion process: converting space waves (SPWs) into guided SWs and back into SPWs. This novel approach offers superior reliability, reduced losses, and enhanced control over beamforming in challenging environments and at millimeter-wave (mmWave) frequencies. The research begins with a comprehensive analytical framework for designing modulated MTSs capable of efficiently coupling SPWs and SWs. A systematic synthesis process based on a penetrable impedance boundary condition (PIBC) model is introduced to achieve high conversion efficiency and precise control over aperture fields. This approach enables the realization of MTS devices with smooth impedance modulation profiles, ensuring practical feasibility. Subsequently, advanced design techniques are proposed to overcome limitations of canonical sinusoidal modulation, such as the open-stopband issue and inefficiencies at broadside and forward radiation angles. By incorporating higher-order harmonics into the impedance modulation, the study demonstrates improved control over desired radiation modes and suppression of unwanted higher-order modes, achieving superior performance in SW-SPW conversion. Building on these theoretical foundations, the thesis develops MTS configurations tailored for broadband and frequency-scanning applications. A three-section MTS design— comprising receiver, transition, and transmitter sections— demonstrates effective SW propagation, dispersion management, and frequency-dependent beam steering. The proposed designs are validated through extensive full-wave simulations, showcasing their efficiency and broad angular and frequency operation ranges. Additionally, the performance of SW-based MTS is benchmarked against conventional reflector-based designs, highlighting its advantages in addressing frequency dispersion and reducing radio blind spots. The investigation also includes the impact of SW dispersion on diffraction losses in bent transition sections, further advancing the understanding of SW-based devices. The final phase of the study explores reconfigurable MTS-based leaky wave antennas (LWAs) for continuous beam scanning at mmWave frequencies. By integrating mushroom structures with voltage-controlled varactors, the proposed LWAs achieve tunability and suppression of open-stopband effects. A detailed analysis of opaque and transparent impedance models provides insights into their accuracy in capturing the electromagnetic behavior of the mushroom structure, guiding the design of high-performance reconfigurable antennas. This work establishes a solid foundation for the design and deployment of MTS-based SW-RIS and reconfigurable LWAs, addressing key challenges in beamforming, dispersion management, and energy efficiency. The findings have significant implications for SREs, offering scalable solutions for enhanced wireless communication in urban and broadband environments.