Harmonic injection effects in backed-off helix travelling-wave tubes. A study by Eulerian analysis

The problem of second harmonic generation in a helix travelling-wave tube w as studied by Eulerian hydrodynamical analysis. The correct regime of appli cability of the Eulerian analysis, with respect to the rf input power drive and the interaction length of the device, was found a priori by validating the analysis against the more accurate Lagrangian analysis. Within this re gime of applicability, which necessarily corresponds to the backed-off oper ation of the device, was studied the second harmonic generated in the devic e, with particular reference to its control by harmonic injection. In parti cular, the optimum values of the relative amplitude and phase of the additi onal second harmonic input signal relative to the main input signal were pr edicted for the minimum second harmonic output of the device.