Coupled mode analysis of electromagnetic wave propagation in a laterally nonuniform duct in altitude with an even power N profile

Abstract

This paper theoretically analyzes the effect of an inverted atmospheric layer, nonuniform in the lateral direction, on wave propagation by means of the coupled mode theory. A grounded duct, an inverted atmospheric model, was employed in which a 2n power N profile (height) is located under standard atmosphere and the lowest layer with a linear profile. In terms of distance, the depth of the lowest layer is assumed to vary slowly with distance. The nonuniform atmosphere varying continuously in the distance is replaced by a staircase approximation. Numerical examples are given for the coupling coefficient of the neighboring atmospheres. The coupled mode becomes maximum immediately before the trapping mode and the mode conversion is more conspicuous for a larger n. The spatial distributions of the propagation characteristics are shown in the nonuniform duct made of uniform, nonuniform, and uniform sections in the distance direction. It was found that the variation of the received electric field changes significantly according to the change in duct height in the distance direction and that the effect of the order n is extremely significant.