Ultra-wideband and high-efficiency reflective polarization converter for both linear and circular polarized waves

In this work, an ultra-wideband and high-efficiency reflective polarization converter is proposed based on an orthotropic anisotropic metasurface for both linear and circular polarized waves, which is a symmetric structure with a pair of mutually perpendicular symmetric axes. Both the simulated and measured results show that the polarization converter can realize linear polarization conversion at x- and y-polarized incidences in the frequency range from 8.77 to 24.71 GHz, which is corresponding to a 95.2% relative bandwidth; moreover, it can keep the handedness of the reflected wave the same as that of the incident wave in this band and realize reflection-type circular polarization conversion at circular polarized (CP) incidence. We have explained the root cause of these polarization conversions, and made it clear that it is just the symmetry of the metasurface structure which makes the magnitude of co-polarized reflection coefficient at CP incidence equal to that of the cross-polarized reflection coefficient at x- and y-polarized incidences, thus it is shown that the previously proposed various reflective linear polarization converters based on orthotropic anisotropic metasurfaces can all realize reflection-type circular polarization conversion.