Wideband and Wide-Angle Single-Layered-Substrate Linear-to-Circular Polarization Metasurface Converter

A wideband and wide-angle linear-to-circular polarization converter (LCPC) based on a single-layer dielectric substrate is proposed. The converter element consists of a metal strip cross backed by a strip horizontally and centrically located on the other metallic layer. The vertical arm of the strip across the whole surface performs as a high- pass filter with a wide passband above a low cutoff frequency. Meanwhile, the horizontal strip resonates at a high out-of-band frequency and also offers a wideband response below the resonant frequency. Another two short strips vertically and horizontally placed around the crosses increase the phase shift caused by the crosses and improve both the passbands. Using equivalent circuit models and ANSOFT HFSS, an example of LCPC is designed with the overall element size of only $0.11\lambda _{0}\times 0.21\lambda _{0}$ for a 90 degrees phase difference and wide-angle stability over the wide operation band. The prototype shows the simulated / measured axial ratios (ARs) below 3 dB over the bandwidth of 69%/74% for a normal incidence wave and 54% for the oblique incident angle of 55 degrees in yz plane, respectively. With the insertion loss of less than 3 and 2 dB, the measured 3 dB AR bandwidth keeps 70% and 55%, respectively.