Phase Characteristics of Radio Signals received via the Ionosphere

Abstract

A RADIO wave after reflexion from the ionosphere may be considered to consist of a specular component and a varying diffracted component¹, the latter being the result of random scattering from a large number of moving irregularities. If the effect at a point on the ground is considered, the diffracted component may be regarded as a cone of radiation having its apex at the point on the ground and its base spread over a large area of the ionosphere. The specular component appears as a coherent wave the arrival path of which is assumed to be along the axis of the diffraction cone and changes direction slowly compared with the fading rate of the signal². Information concerning the amplitudes of the specular and diffracted components of a radio wave and of the angular spread of the cone of rays forming the diffracted component is an important factor in the design of some types of receiving aerials. This information may be obtained from the probability distribution of the phase-difference between the two signals which result from the reception of the radio wave at two aerials spaced apart by a known distance.