Edge boundary conditions derived from specific modes of microstrip line in planar circuits two-dimensional analysis

The fullwave analysis of the specific modes of microstrip lines is shown to provide an edge boundary condition for the two-dimensional analysis of planar circuits. This edge line boundary condition accounts for the dispersive behavior of the fringe fields all around the original open structure and relates the normal derivative of the electric field to the tangential one. Applied to a microstrip line, this edge line boundary condition gives an approximated dispersion equation consistent with the fullwave one. The first step will be to discuss specific modes in fullwave analysis in the spectral domain. The second step substitutes the edge line boundary condition for the usual Neuman´s boundary condition in the integral Green´s equation applied to planar discontinuities. Application to a symmetrical patch shows computed results that concord with experimental data in the whole frequency range