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We present a 1-bit reconfigurable intelligent surface (RIS) operating at millimeter-wave frequencies that suppresses the undesired grating lobes encountered in binary phase modulation schemes and achieves high resolution beam steering. We incorporate fixed, random phase delays at each unit cell of the surface which breaks the periodicity of the phase quantization error and suppresses side lobes. Additionally, the random phase delays reduce the beam pointing error – a limitation of binary RISs - which can be beneficial in applications that require high resolution beam steering. The proposed topology allows for scalable RIS apertures that are compatible with printed circuit board (PCB) fabrication technology. It consists of four metasurface tiles of 256 radiating elements ( $16\times 16$ ) connected on a separate control board that houses the control unit and power supply. The prototype is designed to operate at 27.2 GHz and perform electronic beam steering in ±60° in both azimuth and elevations planes. A quantization lobe reduction of more than 10 dB is achieved with the proposed technique and the surface is well suited for mmWave 5G communication scenarios to enhance signal coverage and signal-to-noise ratio.

We present a method for the mitigation of quantization lobes in single-bit reconfigurable reflective surfaces (RRSs). Typically, RRSs are planar beamforming structures consisting of hundreds or thousands of antennas with integrated tunable switches. Under plane-wave illumination, single-bit RRSs suffer from undesired side lobes or quantization lobes, which are caused by the periodicity of the errors due to the limited number of bits used in phase quantization. In this article, we present a topology that suppresses the quantization lobes using single-layer, 1-bit RRSs, by implementing a fixed but random phase delay in every unit-cell. The introduction of phase randomization breaks the periodicity of the quantization errors, thus reducing the quantization lobe level (QLL). We carry out a theoretical analysis to demonstrate the effect of phase randomization in RRSs, and for the first time, provide the condition for choosing the range of randomization required to achieve the lowest sidelobe level (SLL). Leveraging this condition, we design a single-layer, 1-bit 30 × 30 randomized RRS at 222.5 GHz. The reflective surface is fabricated on a thin, low-loss alumina ribbon ceramic wafer from Corning Inc. using a simplified fabrication technique suitable for large-scale production of mmWave/THz RRSs. Finally, we present the radar cross-section (RCS) characterization results obtained from a quasi-optical measurement setup validating the mitigation of quantization lobes using the proposed randomization technique.