Propagation prediction for the Navy Extremely Low Frequency (ELF) program

This paper examines the extremely low frequency (ELF) radiation from a horizontal antenna in the earth-ionosphere waveguide. Attention is focused on the application to field predictions in the Navy´s ELF program. The field expressions in the presence of an anisotropic ground are obtained by a heuristic approach based upon a linear relationship between the horizontal electric and magnetic field components. Phasing anomalies at the Wisconsin Test Facility (WTF) have been observed since 1974. A theoretical model of this phenomenon is derived on the basis of a mutual coupling mechanism between the two WTF antenna elements and characteristics observed in measured field strength data. The diurnal variation of the radiated field is studied in terms of the attenuation rate, phase velocity, and height of the ionospheric reflecting layers. The diffusivity characteristics of realistic ionosphere are analytically modeled. A comparison of the predicted field strength/phase with the measured data yields excellent agreement.