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This article describes a new fast method that yields an S-parameter's description for a structure immediately after solving the method of moments (MoM) matrix. A virtual elongation is added to the line without extra coupling calculations. The line can be excited by imposing traveling waves with the correct propagation constant and current profile on this elongation. The elongation is also used to modify the line's self-coupling matrix (without changing its size) to make it appear as though it is terminated in a matched load at its fed end. The described method allows a close integration between the method of moments and S-parameter circuit solvers.

In this article a new fast method for the calculation of mutual coupling in planar microwave circuits is described. The circuit is divided into three component classes: lines, small discontinuities and larger, meshed, structures. Modules are proposed to calculate the intra-and inter class couplings. The first two models take full advantage of the specific properties of lines and small discontinuities to speed up calculations. For lines, this means using the traveling waves and for small discontinuities the radiation behavior is approximated by that of an elementary dipole. The third module is the regular method of moments (MoM), which has been altered in such a way that solving the integral equation matrix immediately yields the S-parameters on the lines that feed the structure. The new method uses far less unknowns and needs far less CPU time than the traditional MoM. The advantage over other circuit simulators such as Advanced Design System (ADS) and Microwave Design System (MDS) is that the new method includes the parasitical coupling effects in the entire circuit that are ignored in these commercial packages. These parasitical couplings can sometimes have a large effect upon the circuit.