Variationally computed antenna impedances and accuracy of resulting current distributions

The difference between a stationary and a nonstationary impedance formulation is shown to become zero if a complex current distribution produces zero tangential electric field along the metallic surface of the antenna. This difference between the two impedances is used as a criterion for establishing the accuracy for a given approximate current distribution. Illustrative examples consider dielectric-coated antennas in free space and insulated antennas in a magnetoionic medium.