Design and Test of Broadband Rectangular Waveguide TE10 to Circular Waveguide TE21 and TE01 Mode Converters

In this paper, converters of TE10 square-TE21 degrees mode and TE10 square-TE01 degrees mode with similar exciting topologic structures are designed and verified for a cold test of gyroTWT. Both the proposed converters are composed of three sections, including TE10 square to TE20 square mode converterwith ridged twist waveguide, TE20 square to TE22+ mode converter with variable cross-shaped waveguide, and the last section TE22+ to TE21 degrees or TE01 degrees mode converter ((square) represents the rectangular waveguide,(+) represents the cross-shapedwaveguide, and (square) represents the circular waveguide). The mode converters can be designed step-by-step and exhibit excellent wideband performance and high conversion efficiency. Simulation results reveal that the proposed TE21 degrees mode and TE10 square mode converters have less than 0.04 and 0.03 dB loss over 13.5-and 12-GHz bandwidths, respectively, while the return loss is below -25 dB. Prototype TE21 degrees and TE10 square mode converters were fabricated and back-to-back millimeter-wave measurements were performed to verify the design.