An X-Band Linear-to-Circular Polarizer With High Refractive-Index Metamaterials

This paper presents a novel wideband low-profile linear-to-circular polarizer based on high refractive-index metamaterials in the X band. The proposed design is a multilayer structure that is built from two kinds of metamaterial unit cells consisting of 4-H-shaped strips and 1-H-shaped strips. Combining the two unit cells realizes the flexible and independent control of the refractive index difference between two orthogonal E-field components and thus achieves a consistent 90-degree phase delay over a wide bandwidth. Moreover, the proposed unit cell shows a high refractive index, which contributes to lowering the height of the LP-CP polarizer. In order to improve the axial ratio (AR) bandwidth, two impedance-matching layers are introduced to combat the reflection loss on the metamaterial-air boundary. Nevertheless, the proposed design can provide a wide 3 dB AR bandwidth of 37.7% and a low insertion loss of 0.5 dB with a thin profile of
$0.21~{\lambda }_{0}$
. The prototype was fabricated and measured, while the experimental results agree well with the simulated ones, thus validating the working mechanism and its practical feasibility.