Analytical approaches to a disc-loaded cylindrical waveguide for potential application in wide-band gyro-TWTs

An all-metal disc-loaded cylindrical waveguide excited in TE modes was cold-analyzed in the fast-wave regime for dispersion characteristics, keeping in view of its potential application as an interaction structure for wide-band gyro-traveling-wave tubes (TWTs). The analysis was carried out considering the standing and propagating waves in the disc-occupied and disc-free regions, respectively, using three approaches which differ from one another with respect to how they process the boundary conditions at the interface between these two regions. One such approach is capable of including higher order harmonics in both the structure regions. An adequate number of harmonics with reference to the two regions was taken in the calculation to ensure the convergence of results. The results have been validated against available published results based on different other approaches. The passband and shape of the dispersion characteristics both depend on the disc-hole radius and periodicity, being more sensitive to the latter. The adjustment of disc parameters led to the widening of the straight-line portion of ω-β dispersion characteristics, for wide-band coalescence between the beam-mode and waveguide-mode dispersion characteristics of a gyro-TWT as required for wide-band device performance.