Multimode scattering matrix optimisation for the mitigation of harmonics in anomalous reflection metasurfaces

We propose a method to reduce the level of parasitic Floquet harmonics for anomalous reflection metasurfaces. A linear array that discretises a phase law using phase shifting unit cells is designed to perform anomalous reflection. The level of parasitic radiations is lowered by optimising the dimensions of the periodic pattern constituting the array : the supercell. The goal of the supercell optimisation is defined through its multimode scattering matrix elements.