The effect of ionospheric refraction on the polar diagram of a short radio antenna

Abstract

Recently radioastronomers have used receivers in space vehicles in the upper part of the ionosphere to measure radio signals at frequencies which cannot penetrate the F region. When the results are interpreted, the effect of ionospheric refraction is important. This paper shows how to calculate the electric and magnetic field components at a point within the ionosphere when a plane unpolarized wave is incident from outside the Earth at a series of different angles. The anisotropy of the ionosphere, produced by the Earth’s magnetic field, has a profound effect on these fields. The received signal voltage across a small dipole or loop antenna can be found from these fields if the orientation of the aerial is known. Thus a given small antenna and the ionosphere together form a receiving system whose sensitivity varies with the direction of the incident wave. Diagrams showing this variation may be called polar diagrams by analogy with the diagrams often used for directive aerials. Some examples of the shapes of these diagrams are given.