Design of metasurface-based polarization modulators by using Smith chart method

Abstract

Polarization modulation (PoM) provides an additional degree of freedom for the modulation of carrier waves and may be an alternative to conventional wireless communication techniques that use amplitude, frequency, and phase modulations. Metasurfaces have provided unprecedented freedom for modulating the polarization state of electromagnetic waves. In this study, we introduce the Smith chart method to guide the design of metasurface-based modulator that transforms a linearly polarized wave into a circularly polarized wave. The proposed method bridges the metasurface pattern and its equivalent circuit impedance. We show that the parameter changes in the pattern can be directly displayed in the Smith chart, which provides clear physical image guidance to designers. According to the Smith chart analysis, we obtained a single-layer modulator with 50% efficiency and a three-layer modulator with 100% efficiency, all of which are verified using the full-wave simulation method. The Smith chart method will also be helpful in the design of other metasurface-based devices, such as metasurface absorbers.