Investigation of circular waveguide with axially periodic thin metal disc inserts for wideband gyro-TWTs

Abstract

A circular waveguide with axially periodic thin metal disc inserts for its potential application in a gyro-TWT has been investigated for dispersion, form factor, power flowing through the structure, interaction impedance, and gain. The structure has been field analysed for its dispersion characteristics with due care to include the rigour of considering the effect of higher order space and modal harmonics. Dispersion characteristics reveal that the structure under study has like band-pass characteristics. Effect of variation of structure parameters on the dispersion characteristics has been observed in order to shape the waveguidemode curve for wideband operation of the device. With the help of form factor which decides the extent of coupling between beam and wave, optimum beam position has been decided where maximum interaction between beam and wave takes place. For the structure under study, the value of azimuthal interaction impedance increases with the introduction of metal discs in the waveguide except at higher frequencies, where it decreases rapidly to a value that is lower than that for a smooth-wall circular waveguide. Gain-frequency response observation shows that the dispersion characteristics are readily reflected in the gain-frequency response. It has been found that the disc-hole radius is more effective in controlling the device gain while it is disc-periodicity which is the most effective structure parameter in controlling the device bandwidth. Results have been verified against published results and found to be in very close agreement.