Small-signal model for inhomogeneous helix traveling-wave tubes using transfer matrices

• DOI: 10.1063/5.0218729
• Publication Date: 2024-12-06T19:00:00Z
• Authors: Robert Marosi; Kasra Rouhi; Tarek Mealy; Alexander Figotin; Filippo Capolino
• Keywords: Traveling-wave tube; Helix (gastropod); SIGNAL (programming language)

We introduce a practical method for modeling the small-signal behavior of frequency-dispersive and inhomogeneous helix-type traveling-wave tube (TWT) amplifiers based on generalization one-dimensional (1D) Pierce model. Our model is applicable to both single-stage multi-stage TWTs. Like model, we assume that electrons flow linearly in one direction, parallel proximity slow-wave structure (SWS) guides single dominant electromagnetic mode. Realistic helix TWTs are modeled with position-dependent frequency-dependent SWS characteristics, such as loss, phase velocity, plasma frequency reduction factor, interaction impedance, coupling factor relates modal characteristic impedance impedance. For TWTs, provide simple lumped element circuit combining stages separated by sever, or gap, which attenuates guided mode while allowing space-charge wave beam pass freely next stage. The dispersive characteristics accounted using full-wave eigenmode simulations realistic supported dielectric rods metal barrel, all contribute distributed loss. compare our computed gain vs frequency, transfer matrices, results found through particle-in-cell 1D TWT code LATTE demonstrate accuracy Furthermore, ability reproduce ripple due mismatches at input output ports TWT.