Broadband Resonance-Free Septum Circular Polarizer Operating Above 200 GHz

Abstract

In this paper, a broadband septum circular polarizer with double inline rectangular-to-semicircular waveguide transformers is proposed, which breaks through the theoretical single-mode bandwidth. Meanwhile, a novel waveguide splitting method is utilized, i.e., the common waveguide and inline waveguide transformers are integrally manufactured. This approach avoids the air gap introduced by the traditional split-block technology, and thus solves the problems of orthogonal-modes leakage and mode resonance caused by the waveguide discontinuity. Therefore, the proposed polarizer possesses the merits of broadband, resonance-free, high consistency of orthogonal modes and low insertion loss. In the polarizer measurement, a circular to rectangular waveguide converter is designed and fabricated. The measured insertion loss of the polarizer is found to be around 0.28 dB in the frequency range of 198~260 GHz, and the in-band return loss is better than 15 dB. Moreover, the isolation of left-hand and right-hand circular polarization ports exceeds 23 dB within 206~260 GHz. The proposed polarizer has widely potential applications in millimeter-wave and terahertz devices such as broadband antennas and radial power combiners.