A closed form spatial Green´s function for the microstrip structure using the Gaussian expansion

The spatial Green´s function of the open microstrip structure is usually represented by the time-consuming and computationally inefficient spectral integral. This paper introduces a new closed form Green´s function for the open microstrip structure by applying the GGF method. Therefore, the numerical integration of the spectral integral can be avoided entirely, leading to a considerable decrease of calculating time. Owing to the remarkable resemblances between the CI and GGF methods, for improvement of approximation especially in large distances, some useful techniques such as extraction of the surface wave poles can be carried out. Even though only an open microstrip structure with one substrate is studied, the method of this paper can be correspondingly applicable to the microstrip structures with multiple su.bstrates.