Surface Impedance and the Efficiency of Horizontal-Dipole Extremely Low Frequency (ELF) Antenna Arrays

The effective conductivity of a potential antenna site is a measure of the field strength that an antenna built on the site would radiate. Only in special cases, however, is this same measure suitable for characterizing the power that the antenna would dissipate. It is shown that in the case of a current-sheet antenna built on a horizontally stratified half-space, a measure that characterizes both the radiation and dissipation properties of the site is the complex surface impedance. This same measure remains substantially valid for an antenna composed of separate cables and for inhomogeneous half-spaces of not too great lateral variation. The most reliable methods of measuring the surface impedance are the E/H and H/I methods, provided both include the measurement of the phase of the ratio.