Numerical-asymptotic synergic approach for speeding up the filling time in a MoM/mode matching code for large SIW structures

A novel spectral formulation is proposed for the efficient computation of coupling integrals between a cylindrical wave with arbitrary radial wavenumber and azimuthal dependence and a slot. The coupling is originally expressed through a two-fold spatial integration. It is then transformed into an equivalent one-fold spectral integral, whose integration path is deformed in order to cross a steepest-descent point and obtain a Gaussian decay of the integrand. Numerical comparisons against the standard spatial approach will be shown to validate the new formulation, and its advantage in terms of computation cost will be investigated in depth.