Ultra-broad band and dual-band highly efficient polarization conversion based on the three-layered chiral structure

• We proposed and investigated a novel multi-layered structure.
• Numerical simulations based on different algorithm prove the related results.
• The design achieves highly efficient asymmetric effect with extremely broad bandwidth.
• The structure also realizes the multi-band dispersionless 90° polarization angle.
• The reason of high amplitude is analyzed based on the Fabry-perot like resonance.

In the paper, a novel three-layered chiral structure is proposed and investigated, which consists of a split-ring resonator sandwiched between two layers of sub-wavelength gratings. This designed structure can achieve simultaneously asymmetric transmission with an extremely broad bandwidth and high amplitude as well as multi-band 90° polarization rotator with very low dispersion. Numerical simulations adopted two kinds of softwares with different algorithms demonstrate that asymmetric parameter can reach a maximum of 0.99 and over than 0.8 from 4.6 to 16.8 GHz, which exhibit magnitude and bandwidth improvement over previous chiral metamaterials in microwave bands (S, C, X and Ku bands). Specifically, the reason of high amplitude is analyzed in detail based on the Fabry-perot like resonance. Subsequently, the highly efficient polarization conversion with very low dispersion between two orthogonal linearly polarized waves is also analyzed by the optical activity and ellipticity. Finally, the electric fields are also investigated and further demonstrate the correctness of the simulated and calculated results.