Harmonic Characteristics of the Multipactor for an Impedance Transformer

In this study, the multipactor process of an impedance transformer is simulated by a 3-D electromagnetic (EM) particle-in-cell (PIC) method to research the generation mechanism of the harmonics during the secondary electron avalanche. The position of the seed electron sources is changed to achieve different secondary electron distributions. Then, the frequency spectra of the reflected signals for different electron distributions are obtained by the fast Fourier transform (FFT). The simulation results show that for this impedance transformer, the different distributions of the secondary electrons have a significant influence on the characteristics of the harmonics caused by the multipactor. Different electron spatial distributions can lead to different harmonic characteristics of the port signal. Subsequently, finite-difference time-domain (FDTD) simulation and microwave network theory are used to verify the rationality of this conclusion.