Analysis and Experiment of a Low-Cost Multipanel Reconfigurable Intelligent Surface System for Signal Enhancement at mm-wave

This study presents a novel approach to enhance the power level at millimeter waves (mm-waves) with very low cost. Considering an mm-wave base station (BS) in a fixed location and the user equipment (UE) in the far-field (FF) region, a plane wave with a known direction of propagation reaches a specific region. A very large, predesigned fixed focal spot passive surface (S1) is designed and installed within the viewing angle of the plane wave to reflect and focus it in the near-field (NF) region on another wall. A small reconfigurable intelligent surface (RIS) device is installed on the other wall to be illuminated by the focused beam, and the RIS steers the beam dynamically inside the desired region toward the UE. By using this scheme, a large amount of power can be focused on the UEs to enhance the signal level. The components are modeled with full-wave electromagnetic simulation, and the best approach to design the mm-wave system is discussed. A prototype was fabricated and measured at 26 GHz to demonstrate the 2-D beam steering. The large passive fixed-beam surface is a single-layer printed circuit board (PCB) with$20\times 20$cm, and the RIS is$7\times 7$cm ($14\times 14$elements). For demonstration, 1-bit mechanical tuning elements are used for simplicity. Measurement results show$\approx \pm 50^{\circ }$of 2-D beam steering with around 10% gain bandwidth. The radiation characteristics of both surfaces are analyzed, and an expression for received power under the general condition is obtained. The entire system can be implemented at a very low cost due to its simple PCB design and small-scale RIS. Moreover, due to the large passive surface and small RIS, the power consumption can be significantly reduced compared to conventional RIS.