Subharmonic Mixing Using a Reflective Spatio-Temporally Modulated Metasurface

A reflective, dual-polarized, space-time metasurface with subwavelength unit cells (d0 = λ0/5) is reported. Each column of unit cells on the metasurface can be independently, temporally modulated, allowing space-time modulation along one axis. The time-modulation of adjacent columns is staggered to establish a desired modulation wavenumber. A homogenized model of the metasurface is proposed that includes the discretization of the spatial modulation. Compared to the continuous spatial modulation commonly assumed in earlier works, the discretized modulation allows new phenomena such as subharmonic mixing. Specifically, when the reflection phase is a sawtooth function in time, subharmonic frequency translation can be achieved without additional filtering and mixing circuitry. Measurement results validating the theoretical findings are presented at 10 GHz.