Effects of Elevation and Ground Conductivity on Horizontal Dipole Excitation of the Earth-Ionosphere Waveguide


  • Richard A. Pappert


Horizontal electric dipole excitation of vertical E at the ground for 19.8-kHz radiation beneath a hypothetical daytime ionosphere and beneath a highly anisotropic ionosphere has been numerically investigated as a function of ground conductivity and source elevation. East to west propagation is considered with a magnetic dip angle of 50°, and full allowance is made for earth curvature and ionospheric anisotropy. In horizontal dipole excitation between a highly anisotropic ionosphere and a good conducting ground, broadside launching, except for sources very close to the ground, is to be preferred to end-on launching. Since TE waves are launched broadside, this is a direct consequence of mode coupling in the ionosphere. For source elevations comparable to or greater than a wavelength, the horizontal and vertical electric dipole excitations can become comparable. In excitation by a horizontal electric dipole beneath a daytime ionosphere, end-on launching is to be preferred to broadside launching for a ground-based horizontal dipole exciter. However, for an elevated horizontal dipole source, the preferred direction of launch depends upon the ground conductivity as well as transmitter-receiver distance. Thus, even with weak ionospheric anisotropy, mode coupling can be significant. Up to elevations of 40 km (the highest considered in this paper), the elevated vertical dipole is a more efficient source of vertical E at the ground than is the elevated horizontal dipole.