Ultrathin Dual-band Metasurface Polarization Converter

Metamaterials offer great freedom to manipulate the polarization states of light at the subwavelength scale. However, previous designs generally made use of single resonance and hence only function for one specific incident polarization within a single frequency band. In this paper, we present a dual-band metasurface based on a concentric rectangular arrangement to control the polarizations of both linearly and circularly polarized electromagnetic waves. We show that, on the one hand, the proposed metasurface structure can convert the polarization of linearly polarized waves to the cross direction in two broad frequency bands 4.40-5.30 GHz and 9.45-13.60 GHz. On the other hand, this design can also reflect circularly polarized waves without changing the handedness in two frequency bands 4.47-5.35 GHz and 9.57-13.57 GHz. For both cases, average polarization conversion efficiency larger than 86% was obtained in our experiment. Numerical simulations reveal that the dual-band cross-polarization coupling results from the strong electric and magnetic resonances between the top and bottom layers. The ultrathin polarization converter experimentally realized in this work provides an important stepping stone for future design of other dual-band metasurface devices and is believed extendable to higher frequency regimes.