Wideband Circular TE21 and TE01 Mode Converters With Same Exciting Topologies

To accurately measure the performance of dielectric loaded circuits for gyrotron traveling wave tubes, a novel topological structure to generate the TE
₂₁
^O
or TE
₀₁
^O
(superscript represents circular waveguide) mode is proposed and verified in this paper. The topology is constituted by an overmoded TE
₁₀
^□
to TE
₂₀
^□
(superscript represents rectangular waveguide) mode converter with multiple matching steps and a taper from TE20
^□
to TE
₂₁
^O
or TE
₀₁
^O
mode. This topology allows the TE
₂₁
^O
or TE
₀₁
^O
mode to be excited by changing the taper dimensions. Simulation results reveal that the TE
₂₁
^O
and TE
₀₁
^O
mode converters, respectively, have a 1-dB bandwidth of 12.8 and 9.3 GHz with an excellent performance. Converters for the back-to-back millimeter-wave measurements were fabricated with computerized numerical control and wire cutting techniques. Vector network analyzer measurements are in good agreement with the simulations.