Calculation of pulse wave propagation in a quasi-TEM line using mode expansion in time domain

The paper considers pulse propagation in a transverse inhomogeneous waveguide supporting a quasi-TEM wave. The calculation is based on presenting the sought fields in terms of mode expansion with mode amplitudes being functions of time and longitudinal coordinate (Mode Basis Method). In case of transverse inhomogeneous waveguide there is coupling between the modes. Meanwhile a very good convergence of such a mode series is shown here. The obtained solution was verified by direct FDTD calculation.