Localized growth rates of intermodulation products in a multitone traveling wave tube amplifier

Summary form only given, as follows. Recently developed ultrawideband (UWB) TWTAs (bandwidth exceeds one octave) present new possibilities for simultaneous amplification of multiple carrier signals (multitone operation). However, additional aspects of nonlinearity (giving rise to unwanted intermodulation products or IMPs) are also introduced, due to the fact that carrier harmonics and IMPs are now included within the broader gain bandwidth of the amplifier. By modifying a perturbational technique previously developed for FELs and gyrotrons we are able to predict local growth rates of these deleterious signals in the presence of two driving tones, and hence estimate their levels at the tube output. The technique represents an IMP or harmonic as a perturbation about a nonlinear numerical solution of a Hamiltonian TWTA model with two driving tones. A dispersion relation and hence growth rate as a function of frequency and distance along the tube is attained. The technique allows us to examine the dependence of the IMP growth rate on the frequencies and amplitudes of the drive signals.