FDTD analysis of S-parameters for a multi-mode waveguide with CW excitation

In this paper, a new algorithm to obtain S-parameters using the FDTD for a multi-mode waveguide is presented. In the proposed method, the complex electric field expression is calculated in different two virtual planes, and weighting coefficients for incident and reflected waves can be obtained by solving two equations corresponding to the two virtual planes together with modal decomposition. As an example of the analysis, the vacuum window of a unit-cell for a slotted waveguide array for plasma excitation is analyzed. The frequency characteristic of reflection coefficients calculated by the FDTD method agrees well with that by the generalized scattering matrix (GSM)-method of moments (MoM) hybridization analysis.