The problem of the deep fading of short-wave signals

The distribution of intensity fluctuations behind an arbitrarily shaped inhomogeneity which acts as a lens is formulated for low and high signal levels. This distribution and a distribution of fluctuations for a Poisson noise model are used as the basis for physical interpretation of the deep fading of short-wave signals using an example of two statistical models of the ionosphere (lens-type and scattering-type inhomogeneity models). The model of a statistical screen having a normal phase distribution and a Gaussian fluctuation-correlation function is compared to a model of lens-type Gaussian inhomogeneities whose focusing properties are not correlated along the coordinate axes.