High-performance broadband circular polarizer using self-similar patterns

We propose a high-performance broadband circular polarizer which could effectively convert linear-polarized electromagnetic wave into circular-polarized states with a wide fractional bandwidth of 62.1%. The broadband circular polarizer is essentially a reflective metasurfaces composed of two self-similar copper patterns etched on a grounded F4B substrate. The reflection properties of the metasurface were studied numerically by finite element method using COMSOL Multiphysics. Circular conversion efficiency of the metasurface was then calculated from the simulated reflection spectra, and it is found that in a very wide frequency band 10.0–18.6 GHz, the circular conversion efficiency is larger than 90%, confirming that it could work as a high-performance broadband circular polarizer. For comparison, we also calculated the circular conversion efficiency of metasurfaces containing only one part of the self-similar patterns. There is only one peak in the circular conversion efficiency when there is only pattern Part 1 on the metasurface, and there is no effective conversion when there is only pattern Part 2. It is hence believed that this wideband linear-to-circular polarization conversion arises from an extra resonance mode introduced by the interactions between the two self-similar patterns, which superposes with the resonance mode of pattern level 1 and leads to the wideband circular polarization conversion effect. Near field maps at specific frequencies are extracted from the simulations to confirm the different modes of their interactions. This circular polarizer could have many promising applications in telecommunications as it could work satisfactorily in the whole Ku band (12–18 GHz) of the microwave spectrum.