Design and Analysis of Linear to Circular Polarization Converter With Third-Order Meta-Frequency Selective Surfaces

This article introduces a novel ultrathin linear-to-circular polarization converter based on third-order meta-frequency selective surfaces (meta-FSS) that operates at the
$X$
-band. The meta-FSS unit cell is composed of three metal layers and is separated by two dielectric substrates with a thickness of
$\lambda _{0}$
/20 (
$\lambda _{0}$
is the free space wavelength at 9.8 GHz). The transmission coefficients at two orthogonal directions are equal, while a 90° transmission phase difference is introduced between them over a wide bandwidth. A detailed procedure of equivalent circuit design has been developed for a better understanding of the operating principles. A horn antenna is employed as a linear source to verify the performance of the proposed structure. The measured results show that the designed meta-FSS can effectively convert a linear polarized (LP) wave to a left-hand circular polarized (LHCP) wave in the frequency range 9.1–10.82 GHz (approximately 17.5%) and to a right-hand circular polarized (RHCP) wave in the range 8.8–10.9 GHz (approximately 21.4%).