Efficient closed-form Green's functions for layered stripline structures

In this article, simple and efficient closed-form Green's function representations for various inhomogeneously-filled (layered) stripline structures are derived in terms of cylindrical and spherical waves for a horizontal electric dipole source. The method is based on a two-level approximation of the spectral-domain Green's function. After using a fast pole-location method to extract the surface-wave modes that are guided by the dielectric slabs and the parallel-plate modes that are trapped by the two ground planes, we first use a method that is similar to the first step in the traditional two-level discrete complex image method (DCIM). This step provides a good approximation to the spectral-domain Green's function for large values of the spectral variable kρ, thus accounting for the fields at near and intermediate distances from the source. The remainder (smaller values of kρ) of the spectral-domain Green's function is approximated using a few poles and residues by using the total least squares algorithm, which requires much less computational resources as compared to the vector fitting method or DCIM. This portion of the Green's function accounts well for the fields that are further away from the source. Our proposed method provides an efficient and accurate means for representing Green's functions in layered stripline structures both near and far from the source. The results are verified by comparing with those obtained using the traditional two-level DCIM as well as direct numerical integration of the spectral-domain Green's function.