Combination of the complex images method and a new formulation of Green´s functions for a robust analysis of microstrip circuits

Printed circuits and antennas are accurately analysed by the integral equation technique solved by the method of moments. The numerical model obtained in this way provides good accuracy but the algorithm is quite time consuming. The main reasons for large computation time, when solving the integral equation by the method of moments, are the filling up of the matrix of moments and its inversion. In this paper, we propose a new expression of the Green´s functions which permits a gain of time in the computation of the elements of the matrix of moments for two reasons: first, the frequency and spatial dependence of the Green´s functions are computed separately. Thus, the geometrical coefficients are evaluated once only before the beginning of the matrix calculation independently of the number of frequencies. Second, the new formulation of Green´s functions present suitable properties for a simple application of the complex images method. The latter method removes the necessity of numerical and time consuming integration of the frequency coefficients. Furthermore, these coefficients present a smooth variation versus frequency. Therefore, the evaluation of the Green´s functions for a small number of frequencies and a simple interpolation allows the knowledge of Green´s functions in a large frequency band. A numerical model based on this new formulation of Green´s functions has been realized. It allows a faster filling up of the matrix of moments while maintaining accuracy