A new technique based on the Galerkin Method of Moments (MoM) is presented to analyze discontinuities in microwave planar circuits. The technique is formulated to compute the admittance matrix of N -port-discontinuities. Each port is connected via a line to an excitation source. To assure the adaptation source-line, the normalized fundamental mode is used as a source. An integral equation is derived by applying the boundary conditions of the electromagnetic fields of the sources and of the circuit. The admittance matrix is obtained from the solution of the integral equation using the Galerkin method. This technique is implemented to compute a number of discontinuities in coplanar wave guides and finlines. Computed results show good agreement with the published data.