Propagating quasi-TE modes in a vacuum axisymmetric corrugated-wall waveguide

The nonaxisymmetric quasi-TE modes in an axisymmetric corrugated-wall metal slow-wave structure are analyzed numerically and confirmed to coincide with test measurement. In our experiment of high-power backward-wave oscillators (BWOs), the oscillation of TE/sub 11/ mode was observed below the starting condition of the conventional axisymmetric TM/sub 01/ mode that has been mostly assumed in previous reports. The existence of nonaxisymmetric TE/sub 11/ mode must not be ignored for improved performance with a single frequency operation of high-power BWOs.