Circularly Polarized Folded Metasurface Array with High Aperture Efficiency and Ultra-Low h/D Ratio

In this letter, a design method of an ultra-low h/D (where h is profile height and D is the diameter of the metasurface array) ratio circularly polarized folded metasurface array is proposed. This research has a more flexible and complete phase adjustment method and highlights that the selection of the focal points and the constant phase can be used for optimization of the aperture efficiency (AE). A novel folded architecture and optimizing method are proposed to optimize AE while maintaining an ultra-low h/D. To validate the proposed design method, highly efficient, compact unit cells are designed to form the transmission and reflection arrays. A folded metasurface array with h/D of 0.105 is optimized and experimentally tested. The measured peak gain is 25 dBic at 30.2 GHz (maximum AE of 43%). The effectiveness of the proposed folding design theory and optimization methods is validated.