Design of Wideband Quad-Ridge Waveguide Polarizer

In modern satellite communication antenna, circular polarizer is one of the key components of feed network. The relative bandwidth of traditional circular polarizers, whether metallic iris circular polarizer, circular waveguide polarizer with a dielectric septum inserted or septum circular polarizer, can not exceed 40% under the condition of ensuring a low axial ratio, which can no longer meet the requirements of modern satellite communication. In this paper, based on the broadband characteristics of ridge waveguide, the phase constants of two orthogonal main modes in square waveguide are adjusted by loading horizontal ridge and vertical ridge on the four walls of waveguide, so as to realize circular polarization. On this basis, two groups of metal ridges are designed respectively, which broadens the relative bandwidth of circular polarizer. According to this method, a broadband K-band circular polarizer is designed, with an operating bandwidth of
$\mathbf{15}\sim \mathbf{25}\mathbf{GHz}$
and a relative bandwidth of 50%. The results show that the reflection coefficients of two orthogonal polarizations of the circular polarizer are less than -24dB and the phase difference is
$\mathbf{90}^{\circ} \pm \mathbf{3.9}^{\circ}$
. The corresponding axial ratio is less than 0.6dB.