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.