Design of Coding Metasurface Units Based on a New Deep Deterministic Policy Gradient Algorithm

In this letter, a design method of broadband digital coding metasurface units based on a novel deep deterministic policy gradient (DDPG) algorithm is proposed. And a reflective-coded metasurface unit with a surface structure randomly arranged by discrete micro digital patterns is proposed. Its structure is optimized based on the DDPG algorithm, which achieve constant phase difference in the broadband. The units designed in this work achieve a 1 bit phase shift with a bandwidth of 1.54 GHz within 170 degree to 190 degree from 9.26 to 10.8 GHz and a 2 bit phase shift with a bandwidth of 0.5 GHz within 80 degree to 100 degree from 11.04 to 11.54 GHz.