Theoretical power output and bandwidth of traveling-wave amplifiers

Expressions are developed to calculate the theoretical power output of traveling-wave amplifiers using any type of RF structure. Calculations are made for helix-type tubes and it is shown how to calculate the power output of tubes using more dispersive structures in terms of calculations made for helix tubes. The principal factors accounting for higher power output of dispersive structures are presented and discussed. The gain and bandwidth of forward-wave helix amplifiers are derived from the small-signal theory as functions of frequency and it is shown that the gain in db times the frequency bandwidth is a constant as a function of helix length for high
\gamma_{0}a'
and the gain times the bandwidth squared is a constant for low
\gamma_{0}a'
.