Small-Signal 1-D Model of Multistage Serpentine Waveguide Traveling Wave Tubes With Severs

We present a model for calculating the small-signal gain of a multistage serpentine waveguide traveling wave tube (TWT) with one or more severs. To mitigate the occurrence of self-oscillations, the TWT stages are separated by a sever to stop RF wave propagation while the modulated electron beam (e-beam) is free to pass and is modeled by the electrons’ motion equations. Our small-signal model is an advancement of the Pierce model, assuming 1-D electron flow along a slow wave structure (SWS), accounting for SWS dispersion, the space-charge effect, and a frequency-dependent coupling strength coefficient relating the characteristic impedance to the interaction impedance. We compute the theoretical gain versus frequency for the multistage TWT and compare our results with particle-in-cell (PIC) simulations. The good agreement demonstrates the accuracy of our analytical model for the multistage serpentine waveguide TWT with one or more severs. Here, we focus on showing the performance of our model as an effective tool for designers rather than proposing an optimal design strategy.