A Dual-Band Metasheet for Asymmetric Microwave Transmission With Polarization Conversion

A metamaterial-based planar polarization conversion screen is designed by exploiting the mutual interactions between two distinct types of resonators. The design starts from a unit cell comprising a subwavelength T-type resonator and a rectangular split-ring resonator (RSRR). In order to enhance the cross-polarization conversion, the unit cell is rotated by 90° to obtain a chiral geometry and the right diagonal elements are scaled down to construct a rotationally asymmetric $2\,\times \,2$ supercell. The supercells are arranged periodically on either side of the substrate. In the bottom layer, each element is rotated by 90° with respect to the corresponding element in the top layer to achieve the asymmetric transmission property and to introduce the desired phase difference between the two orthogonal linear vector components of the transmitted wave. The proposed design exhibits very good circular polarization efficiency, which is primarily achieved by transverse magnetic dipole-magnetic dipole coupling. The polarizer has an ellipticity of 44.4° and a polarization extinction ratio of 37.30 dB at 14.79 GHz. Furthermore, the polarization conversion ratio for both linear orthogonal components is identical at this frequency. At 9.15 GHz, strong orthogonal polarization rotation is observed. The electrical size of the unit cell is $0.25\lambda _{0} \times 0.25\lambda _{0} \times 0.077\lambda _{0}$ . Simulation and measurement results are presented to verify the performance of the polarization converter.