Derivation of common impedance coupling from the transmission-line equations

Impedance of the return path common to two circuits can produce a component of crosstalk that is referred to as common impedance coupling. The current of one circuit flowing in this impedance induces a contribution to the crosstalk voltages in the other circuit. This is usually derived on intuitive grounds. The incorporation of the return conductor impedance into the transmission-line equations provides a solution which does not rely on intuition