Small-Signal Model for Inhomogeneous Helix Traveling-Wave Tubes using Transfer Matrices
arxiv(2024)
摘要
We introduce a practical method for modeling the small-signal behavior of
dispersive and inhomogeneous helix-type traveling-wave tube (TWT) amplifiers
based on a generalization of the one-dimensional Pierce model. Our model is
applicable to both single-stage and multi-stage TWTs. Like the Pierce model, we
assume that electrons flow linearly in one direction, parallel and in proximity
to a slow-wave structure (SWS) which guides a single dominant electromagnetic
mode. Realistic helix TWTs are modeled with position dependent and
frequency-dependent SWS characteristics, such as loss, phase velocity, plasma
frequency reduction factor, and interaction impedance. For the multi-stage
helix TWT, we provide a simple lumped element circuit model for combining the
stages separated by a sever, or gap, which attenuates the guided circuit mode
while allowing the space-charge wave on the beam to pass freely to the next
stage. The dispersive SWS characteristics are accounted for using full-wave
eigenmode simulations for a realistic helix SWS supported by dielectric rods in
a metal barrel, all of which contribute to the distributed circuit loss. We
compare our computed gain vs frequency, computed using transfer matrices, to
results found through particle-in-cell (PIC) simulations and the 1D TWT code
LATTE to demonstrate the accuracy of our model. Furthermore, we demonstrate the
ability of our model to reproduce gain ripple due to mismatches at the input
and output ports of the TWT.
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