A Scalable, Binary Phase, Millimeter-Wave Reconfigurable Intelligent Surface

We present a 1-bit reconfigurable intelligent surface (RIS) operating at millimeter-waves (mmWaves) that employs a 2.5D integration topology for size scalability and a randomized phase delay pattern to suppress quantization lobes. As opposed to fixed beam metasurfaces, RISs require a biasing and control circuitry to excite the necessary phase shift distribution across the aperture. Additionally, binary phase RISs result in coarse phase modulation and require additional transmission lines within every unit cell to mitigate the quantization lobes. The proposed RIS topology features a tiled topology that includes the radiating elements, phase shifters, delay lines, shift registers, and necessary connectors to interface with the control board. We present a RIS tile comprising 64 elements arranged in a 16×16 array and a control board to house the control unit, RIS tiles, and power supply. The prototype tile is designed to operate at 28 GHz with electronic beam-steering in both azimuth and elevation planes. It is fabricated using printed circuit board (PCB) technology and characterized using a mmWave radar cross section (RCS) measurement setup. The proposed architecture can be utilized to realize arbitrary large apertures and helps achieve quantization lobe reduction of more than 10 dB.