Structure of the near zone electric field and the power radiated from a VLF antenna in the ionosphere

Abstract

In this paper we examine the electric field and radiated power produced in the near zone of a ring VLF antenna whose loop plane is aligned parallel to the external magnetic field. In this case there exist two resonance surfaces, one inside the other, which can be given in parametric form. The electric field singularity on the resonance surfaces is of a logarithmic type, but there are also curves and points (focuses) where the field displays a more severe singularity (branch pole type). The asymptotes of the field close to the resonance surfaces are given. Using the expression for the Fourier component of the antenna generated magnetic current, the radiated power and the percentage of the power that goes into the whistler mode are calculated for different values of the angle between the antenna loop and the external magnetic field. The results show that only a small portion of the radiated power is transferred to the whistler mode. Suggestions as to how to increase the portion of the radiated power that goes into whistler waves are discussed.