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

In this paper, converters of TE $^{\Box }_{{10}}$ –TE $^{\circ }_{{21}}$ mode and TE $^{\Box }_{{10}}$ –TE $^{\circ }_{{01}}$ mode with similar exciting topologic structures are designed and verified for a cold test of gyro-TWT. Both the proposed converters are composed of three sections, including TE $^{\Box }_{{10}}$ to TE $^{\Box }_{{20}}$ mode converter with ridged twist waveguide, TE $^{\Box }_{{20}}$ to TE+22 mode converter with variable cross-shaped waveguide, and the last section TE+22 to TE $^{\circ }_{{21}}$ or TE $^{\circ }_{{01}}$ mode converter ($^{\Box }$ represents the rectangular waveguide, + represents the cross-shaped waveguide, and ° 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 TE $^{\circ }_{{21}}$ mode and TE $^{\circ }_{{01}}$ 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 TE $^{\circ }_{{21}}$ and TE $^{\circ }_{{01}}$ mode converters were fabricated and back-to-back millimeter-wave measurements were performed to verify the design. [ABSTRACT FROM AUTHOR]