Single-buried-layer reflection-mode metasurfaces for dual-band linear to circular polarization conversion

In this paper, analysis, design and simulation of dual-band metasurfaces as the reflection-mode linear to circular polarization converters (RMCPs) consisting of single-buried-layer rectangular patches are carried out. The proposed structure for RMCPs can be realized for all frequency ranges from microwave to optical frequencies. However, two far-infrared frequencies, 2 THz and 10 THz, are considered for the design. Dimensions of the dual-band RMCP are obtained using equivalent transmission line circuit and defining a circular polarization (CP) indicator factor (RLI), which should be about +/- 1 for CP. An advantage of the proposed RMCP is the wide permitted angle of incidence (theta) in both operating frequencies. Simulation results of the proposed RMCP indicate 41.2% and 39.1% bandwidths for 3-dB axial ratio (AR) at 2 THz and 10 THz, respectively with theta(min) = 25 degrees and theta(max) = 50 degrees. In addition, higher quality of CP can be obtained by reducing the incident angle difference. For example, 2-dB AR bandwidths of the proposed metasurface are 28.4% and 42.1% at 2 THz and 10 THz, respectively, with theta(min) = 25 degrees and theta(max)= 45 degrees.