In-waveguide TE01-to-whispering gallery mode conversion using periodic wall perturbations

This paper reports numerical optimization calculations on mode converters to generate pure, rotating TE 1,2,3 (at 120 GHz) and TE 15,2 (at 140 GHz) whispering gallery modes (WGM) in oversized circular waveguides, for conversion efficiency optimization studies on high-power quasi-optical WGM gyrotron output mode transducers. Two-stage TE01-to-TEonto- TEm2 conversion sequences (n = 6 at 120 GHz, n = 7 at 140 GHz) using periodic radius and m-fold helical (corkscrew type) wall deformations, respectively, provide output mode purities of almost 99%.