Application of frequency-dependent absorber and diminishing phase velocity under it to improve parameters of ultra broadband TWT

The method of broadening the operation frequency range to the long-wave edge of powerful broadband helix TWT is suggested. It consists in the use of frequency-dependent absorbers. And, the absorber attenuation is significantly less at the lower frequency than at the upper one. Computations for ultra broadband TWT are carried out. It is shown, that due to this method an electronic efficiency at lower frequencies is increased, and the level of the second harmonics is decreased. Further improvements of the parameters can be achieved by decreasing helix pitch under the absorber.