Wideband linear-to-circular polarization conversion realized by a transmissive anisotropic metasurface

We propose a metasurface which consists of three conductive layers separated by two dielectric layers. Each conductive layer consists of a square array of square loop apertures, however, a pair of corners of each square metal patch surrounded by the square loop apertures have been truncated, so it becomes an orthotropic structure with a pair of mutually perpendicular symmetric axes u and v. The simulated results show that the metasurface can be used as a wideband transmission-type polarization converter to realize linear-to-circular polarization conversion in the frequency range from 12.21 GHz to 18.39 GHz, which is corresponding to a 40.4% fractional bandwidth. Moreover, its transmission coefficients at x- and y-polarized incidences are completely equal. We have analyzed the cause of the polarization conversion, and derived several formulas which can be used to calculate the magnitudes of cross- and co-polarization transmission coefficients at y-polarized incidence, together with the phase difference between them, based on the two independent transmission coefficients at u- and v-polarized incidences. Finally, one experiment was carried out, and the experiment and simulated results are in good agreement with each other.