Conformal Polarization Conversion Metasurface for Omni-Directional Circular Polarization Antenna Application

In this article, conformal linear-to-circular (LTC) polarization conversion metasurface (MS) in transmission mode is engineered and fabricated. The conformal MS is cylinder-shaped with curved elements bent on the cylinder wall. First, the anisotropic element with the capability of LTC polarization conversion in high transmission efficiency is designed and simulated, and the electromagnetic response on the variation of the curvature radius of the conformal element is discussed. Second, the cylinder conformal polarization conversion MS is engineered based on the anisotropic element. Then by launching a monopole antenna at the center of the cylindrical axis as the feed source, the omni-directional circular polarization antenna is implemented. More importantly, the height, radius, and element number along the longitudinal direction of the MS are optimized to obtain an optimized performance of the antenna. Finally, the antenna system is fabricated, assembled, and measured. The device can operate in 9.9-10.1 GHz with an axial ratio lower than 3 dB along the circumferential direction and at 10 GHz the radiation fluctuation along the circumference is less than 1 dB. This study opens up a new way to design conformal MS on a curved surface and affords an efficient alternative for circular polarization antenna design.