Compact quasi-periodic and aperiodic TE/sub 0n/ mode converters in overmoded circular waveguides for use with gyrotrons

Designs of compact quasi-periodic and aperiodic TE/sub 0n/-TE/sub 0n-1/ circular waveguide converters for use with gyrotrons in an electron cyclotron heating (ECH) system are developed by analytically and numerically solving the coupled-mode differential equations. Quasi-periodic mode transducer designs which convert the TE/sub 02/ mode to the TE/sub 01/ mode, and in some cases also include a taper (waveguide radius reduction), are developed. A 60-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE/sub 02/-TE/sub 01/ mode converter. A 140-GHz aperiodic mode converter-taper combines a 6.35-cm-2.779-cm waveguide diameter taper and a TE/sub 03/-TE/sub 02/-TE/sub 01/ mode converter. The resulting designs are highly efficient (conversion efficiencies >or=99.4%), are shorter, have a broader bandwidth than previous designs, and have a waveguide radius greater than or equal to 1.389 cm over the entire length of the transducer to allow for high-power transmission. Experimental results consistent with theoretical calculations are presented.>