A 90° Oversized Broadband TE₀₁-to-TM₁₁ Mode Converter for High-Power Transmission Line

This article proposes a novel method to design a 90° oversized TE01-to-TM11 mode converter for high-power transmission line. In order to obtain a full power conversion at 90° bend angle rather than an acute angle, the mode coupling process inside the oversized circular waveguide bend is analyzed, and a phase rematching method is deduced. Based on the analysis results, a phase rematching structure, consisting of two identical circular-to-elliptical transitions and a uniform circular waveguide which can transform the phase difference from $-\pi $ /2 into $\pi $ /2, is introduced. Two mode converters with the input/output radius of 14 mm are designed at the center frequency of 34 GHz to validate the proposed method. The results show that the mode converter with a limited height has a bandwidth of 4.6 GHz, while the mode converter with a limited width has 4.3 GHz with conversion efficiency over 95%. The mode converter with a limited height is manufactured and measured, and the high-purity outputs are validated by the obtained radiation field patterns at the output port of the mode converter from 32 to 36 GHz. The proposed mode converter provides a new approach for developing a compact, high-efficiency, and broadband high-power millimeter-wave transmission line.