Low-Profile Circularly Polarized Transmitarray for Wide-Angle Beam Control With a Third-Order Meta-FSS

In this article, we develop a low-profile high-gain transmitarray antenna (TA) with a meta-frequency-selective surface (FSS) operating in the
$X$
-band. The employed meta-FSS element is designed to realize a third-order bandpass filter, which has a high transmission and wide angular stability. A phase difference of 180° can be introduced between the two orthogonal directions with optimized parameters. Based on element rotation theory, the meta-FSS elements are arranged with the desired rotation angles to convert the incident quasi-spherical wave to the outgoing plane wave with the reverse polarization, e.g., a left-hand circularly polarized (LHCP) wave to a right-hand circularly polarized (RHCP) wave. To experimentally validate the focusing ability and wide-angle beam control ability of the proposed structure, principle prototypes are designed, fabricated, and measured. The experimental results show that the full transmitarray can achieve a 1 dB gain bandwidth of 13.0%, an aperture efficiency of 40.2%, and a 3 dB axial ratio bandwidth of 24.0% in the broadside direction. In addition, good circular polarization radiation performance can be successfully realized with the proposed structure at beam tilt angles from
$\theta = 0^{\circ }$
to 60°.