Beamforming Algorithm for Digital Coding Metasurface and its Verification

As an emerging technology, digital coding metasurfaces have attracted wide attention due to their remarkable capabilities in controlling electromagnetic waves. Since the transmissive/reflective phases of digital-coding metasurfaces have finite states, the quantization effect must be considered in determining the coding strategies. In traditional approach, one directly optimizes continuous phases and then quantizes the results, obtaining the discrete codes that are impressed on the metasurfaces. The quantization errors of such a two-step approach inevitably increase the highest side lobe level (HSLL) of beam patterns produced by the digital coding metasurfaces. To tackle the problem, we use phase sensitivity analysis and descent algorithm to reduce the HSLL. An exemplary application of the algorithm is presented, wherein the phase coding of an 8×8 2-bit metasurface in the Ku band is optimized. Good results are achieved in numerical calculations, full-wave simulations, and experimental measurements, showing the validity of the proposed approach. The approach will promote the development of analysis and design technology of the digital coding metasurfaces.