Multi-mode Simulation for An Output Window of Gyrotron Based on Transfinite Element Method

In this paper, a fast algorithm to obtain S parameters and mode field using the transfinite element element(TFE) method for a multi-mode output window is presented. In the proposed method, the eigenmodes of uniform electromagnetic waveguides have been regarded as a basis function. The coefficients for incident and reflected waves can be obtained quickly by solving finite element matrix equation. As an example of the analysis, the double disks output window for a gyrotron traveling-wave tube is analyzed. The reflection coefficients of
$\mathbf{TE}_{\mathbf{11}}$
mode and
$\mathbf{TE}_{\mathbf{01}}$
mode calculated by the TFE method agree well with the results simulated by HFSS.