Abstract: A new excitation source model is proposed in this paper, which can successfully solve the problem that the feed source can’t be set at the junction between antennas and sphere. By adding and subtracting Green’s function in the infinite homogenous media the convergence speed of Green’s function is increased when the source point and the field point are close each other or lie on the surface of the metal sphere. The calculated result of the monopole in the presence of the metal sphere shows the validity and effectiveness of the analysis way. Finally, probe-fed patch antenna is calculated, the calculated result is in good agreement with the one simulated by FEKO.