Enhanced formulation for polynomial-based surrogate modeling of microwave structures in frequency domain

Practical formulations for EM-based modeling of microwave structures using simple polynomial surrogate functionals are described in this paper. A new polynomial surrogate formulation is proposed and compared against a previously published formulation. Both formulations calculate the surrogate model weighting factors in closed form, yielding global optimal values in the least squares sense. These formulations are suitable for EM-based design problems with no equivalent circuital models available. Our new formulation exhibits smaller learning errors and better generalization performance than the original formulation. Both methodologies are illustrated by the EM-based modeling a SIW interconnect with microstrip transitions on a standard FR4-based substrate implemented in a 3D full-wave FEM simulator.