Investigation of the effect of trapped modes in circular waveguide mode converters

Abstract

TE/sub 0n/-TE/sub 0q/ circular waveguide mode converters such as the TE/sub 02/-TE/sub 01/ type typically have radius variations which increase and then decrease again. This provides the possibility for trapped higher order modes which can exist between the uptaper and the downtaper, but cannot escape the region of enlarged radius. Trapped modes can sometimes have a catastrophic effect on device transmission at certain resonant frequencies. The effect of trapped modes are considered in a few simple cases in this paper using the computer simulation programs HFSS and Cascade.