Measured Properties of Small Self-Resonant Helical Antennas at Low Frequencies for Application in Dissipative Media

摘要

The behavior is described of small, self-resonant helical antennas in the frequency-region between 3 kHz and several MHz. Measured quantities are the input impedance and the current distribution; at first in a laboratory and then in a cavity in an old Tyrolian mine near Innsbruck. The cavity contained once air and once fresh water, whose electrical properties were measured separately. In the mine the magnetic near field and transition zone have also been measured for both cases, antenna in air and in water. The measured data are in good agreement with the theory of a network model (with the exception of the dielectric losses which can only be measured) and of a combination of an electric and a magnetic dipole, respectively. Some criteria are given for an optimum construction or application of these antennas. Fundamental problems are discussed which occur when comparing antennas in a dissipative medium. (Author)