A closed-form expression of the nonsymmetrical components of Green's function for multilayered media

The Green's function for multilayered media is expressed in terms of Sommerfeld integrals. The discrete complex image method is an appealing technique in handling such integrals. However, the results of the nonsymmetrical components lacks sufficient accuracy in the near-field region. This is due to the fact that these components have slowly varying spectral-domain behavior. In this work, the quasi-dynamic contribution is explicitly extracted. The remaining part has fast decaying behavior. The generalized pencil-of-function method is used to recast this part into a set of exponentials. Using a special identity, a closed-form expression is obtained that is valid in the near-field region. The method is demonstrated to yield accurate results for microstrip structures.