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This paper presents a wideband high‐gain dual‐circularly‐polarized (CP) antenna with a simple configuration. Instead of improving the gain using the dual‐CP element array, the Fabry‐Perot resonator antenna concept is applied in this work. By designing a dual‐linearly‐polarized Fabry‐Perot resonator antenna and a linear‐to‐circular polarization (LP‐CP) metasurface polarizer separately and combining them, a wideband high‐gain dual‐CP antenna can be achieved. Structural simplicity and less design difficulty are advantages of the antenna design. Experimental results validate the design concept. It exhibits 3‐dB axial‐ratio bandwidths of over 12% for both LHCP and RHCP performance, a high polarization isolation of over 25 dB, and peak gains of 12.78 dBi and 12.89 dBi for LHCP and RHCP radiations respectively.

Most high‐efficiency polarization converters in literatures are based on reflective structures. Here we report the designs and experiments of high‐efficiency transmissive polarization converters using novel compact frequency‐selective surfaces (FSSs). By combining the common dipole and square ring based band‐pass FSSs, a novel FSS can be generated, whose high‐efficiency pass bands and transmissive phases for two orthogonal polarizations can be tuned by changing the dimensions of the FSS structure. As demonstrations of the concept, a transmissive cross polarization converter (a half‐wave plate) and a transmissive linear‐to‐circular polarization (LP‐CP) converter (a quarter‐wave plate) are designed and tested, respectively. Simulated results show that the polarization conversion ratio over 90% for the transmissive cross‐polarization converter is from 18.5 to 23.5 GHz, about 23.8%, and the 3‐dB LP‐CP conversion bandwidth is 19.6%. Experiments are carried out to validate both designs.