Design and Measurement of a Subarray Element Reconfigurable Intelligent Surface

A reconfigurable intelligent surface (RIS), which can electrically control the direction of radio wave reflections other than specular reflection, is expected to improve the area to coverage holes in non-line-of-sight (NLOS) environments. An RIS is produced by arranging reflective elements with control elements in an array. Because no amplifiers or other devices are used, it can be achieved with lower power consumption and cost than other methods, such as relays. However, because a large area of the RIS is required for area improvement, the number of control elements increases, and power consumption and cost may not decrease. Therefore, in this article, we propose a subarray element type RIS in which two reflective elements are controlled by a single control component to achieve low power consumption. We show that a staggered arrangement is an efficient arrangement of reflective elements that can suppress the reduction of the reflection angle range by subarraying and that a specific design method for a subarray element. We show the measurement results of a prototype based on this design and demonstrate that the number of control elements in the RIS can be reduced by 25% compared with the conventional design without degrading the high-frequency characteristics.