Efficiency Improvement of Broadband Helix Traveling Wave Tubes Using Hybrid Phase Velocity Tapering Model

A hybrid phase tapering model is proposed for a wideband (two-octave) vane-loaded helix traveling wave tube, of which the dispersion characteristic is anomalous over the operating frequency band. The small signal gain and electron efficiency is studied by using a novel nonlinear one-dimensional beam-wave interaction theory. Compared with a conventional helix traveling wave tube, of which the helix pitch is held constant in the output section, this hybrid phase velocity tapering model, which can be realized by changing the helix pitch, can provide a wideband efficiency improvement, especially in the lower or higher frequency band. It is concluded from our results that in order to effectively improve the electron efficiency, dispersion shaping and helix pitch tapering should be taken into account simultaneously.