On Determining the Capacitances of Shielded Multiconductor Transmission Lines

A numerical method for computing the capacitances of n conductors located inside a grounded rectangle is presented. The method is based on an integral equation for the charge densities on the conductors with a Green´s function as kernel. The integral equation is solved numerically by replacing the integral with a finite sum, using a Gaussian quadrature formula. The feasibility of the method depends on each conductor having a simple analytical description (circle, ellipsoid, straight line, etc.). As an illustration, graphs are shown giving the dimensions of an offset pair of zero-thickness strips versus coupling coefficient for a 50-ohm transmission line for various sizes of the grounded rectangle.