AbstractNumerical results relating off‐diagonal elements of the impedance matrix [Z] for a two‐port waveguide junction are derived based on a general waveguide circuit theory [1] and a rigorous space‐domain approach. The junction between a coaxial line and a lossy shielded microstrip line is considered. Data indicate that even when the waveguides are composed of reciprocal media, the forward and reverse transmission coefficients are not necessarily equal. © 1995 John Wiley & Sons, Inc.