Capacitances of a Shielded Balanced-Pair Transmission Line

The exact formulae (calculable to any accuracy) for mutual and conductor-to-ground capacitance (Cm, and Cg) for a shielded balanced pair are expressed as infinite determinants. Convergence of these determinants is rapid except as the conductors of the pair approach each other or the shield. Approximate expressions developed by Philips Research, though not extremely accurate, are simple and in closed form thereby allowing capacitance surfaces to be plotted. These surfaces show qualitatively the variation of capacitance with dimensions.