1-D Time-Dependent Nonlinear Analysis Model for Folded-Waveguide Traveling-Wave Tube

This article presents a novel 1-D active transmission matrix-based time-dependent (ATM-TD) model for the beam-wave interaction analysis of folded-waveguide (FWG) traveling-wave tubes (TWTs). The slow wave structure (SWS) is modeled as a series of coupled resonant cavities, with each cavity modeled by a three-port network represented by an active transmission matrix. The voltage and current of each port alternate with time for the purpose of the time-dependent analysis. The circuit field in each cavity is obtained by the voltage of the interaction gap and can be approximated with a Gaussian profile. The space charge field is derived from the Green function. The motion of the beam electron is represented by utilizing the leap-frog algorithm in the particle-in-cell (PIC) method. The alternating beam current obtained by the Fourier transform method acts as a current source, generating the electromagnetic wave along the chain of cavities. To verify the proposed model, a 1-D code has been developed and applied in an E-band FWG TWT example, and the results obtained from the ATM-TD model demonstrate good consistency with the PIC simulated results. This model offers more convenience in depicting real-time interactions between the electron beam and the electromagnetic wave in FWG TWTs. It enables the performance analysis of devices driven by multisignal and complex digital modulation signals, thus facilitating the design of FWG TWT.