AN EFFICIENT REPRESENTATION FOR THE PLANAR MICROSTRIP GREEN'S FUNCTION

A relatively simple and accurate closed form asymptotic approximation for the electric current point source microstrip surface dyadic Green's function that remains accurate everywhere except in the very close vicinity of the point source is developed by a new approach in this dissertation. This closed form approximation of the surface microstrip Green's function includes the effects of the space wave, the surface wave and their coupling within the transition region near the source. The effect within the transition region is expressed in terms of an error function. The present approach developed in this work provides in this special microstrip problem a much simpler way for deriving both the surface wave and the space wave fields than the conventional saddle point integration method. However, the transition function which describes the coupling of the space and surface waves within the transition region near the source is partly heuristically based on the conventional saddle point integration method for the case when a simple pole singularity is near an isolated first order saddle point. The accuracy of the closed form approximation for the microstrip surface Green's function is shown to be valid even for observation points as near as 0.2(lamda) from the source point for a substrate thickness as large as 0.1(lamda), where (lamda) is the free space wavelength. As a result, the rigorous moment method analysis of the microstrip antenna arrays of arbitrarily shaped elements can be facilitated by replacing the conventional Sommerfeld integral form of the microstrip Green's function with the approximate closed form representation developed in this study when the observation point lies outside the immediate neighborhood of the source point.