A Subwavelength Element for Broadband Circularly Polarized Reflectarrays

A subwavelength element is presented for designing a circularly polarized (CP) reflectarray that converts the linearly polarized incident field of the feed into an outgoing circularly polarized field. To evaluate the performance of the designed element, a parametric study is carried out using Ansoft HFSS. Compared to the conventional near-resonant patch, the subwavelength one can realize a more similar behavior for the phase curves at different frequencies, leading to broader bandwidth. The phase shifts for both linear polarizations can be controlled by varying the x- and y-dimension of the element. Aprime-focus reflectarray with this type of element has been designed and implemented, and a superior bandwidth performance has been verified, compared to a reflectarray with conventional lambda/2 elements. The measured results show that the obtained 1-dB gain and 3-dB axial ratio bandwidths of the reflectarray with subwavelength elements can reach as large as 17% and 11%, respectively.