Massive Metasurface-Assisted Multidirectional Beam Shaping: Prototyping and Outdoor Experimental Results in Millimeter-Wave Band

Metasurface reflectors and reconfigurable intelligent surfaces (RISs), which are key technologies for robust, high-speed, and high-capacity communications in millimeter-wave bands, can eliminate shadowed areas caused by buildings and moving objects by artificially shaping the propagation environment. Metasurface reflectors are passive devices that can generate reflected waves in desired directions and are expected to be installed on buildings and windows as low-cost, power-free solutions. However, since their reflection angles cannot be adjusted after installation, the improvement in coverage area may be limited. To address this limitation, we propose the concept of building a multipath environment by deploying a massive number of metasurface reflectors on windows and building surfaces. When scaling up such deployments, each metasurface reflector must be individually designed due to variations in the distance and angle relative to the base station and the user equipment, leading to increased design and manufacturing costs. To mitigate this issue, we also propose a method for simplifying the design of the incident and reflection angles for metasurface reflectors. We fabricated prototype metasurface reflectors, each measuring one square meter, and designed them to exhibit specific incident and reflection angle characteristics. These metasurface reflectors were deployed continuously to form a ten-meter-long array, and we experimentally evaluated their angle-of-arrival characteristics in a large-scale setting. We confirmed that the reflected waves arrived from the designed reflection angle at each point within the measurement area.