COUPLED-MODE ANALYSIS OF ELECTROMAGNETIC-WAVE PROPAGATION IN A LATERALLY NONUNIFORM DUCT IN ALTITUDE WITH AN EVEN POWER-N-PROFILE

This paper theoretically analyzes the effect of an inverted atmospheri c layer, nonuniform in the lateral direction, on wave propagation by m eans of the coupled mode theory. A grounded duct, an inverted atmosphe ric model, was employed in which a 2n power N profile (height) is loca ted under standard atmosphere and the lowest layer with a linear profi le. In terms of distance, the depth of the lowest layer is assumed to vary slowly with distance. The nonuniform atmosphere varying continuou sly in the distance is replaced by a staircase approximation. Numerica l examples are given for the coupling coefficient of the neighboring a tmospheres. The coupled mode becomes maximum immediately before the tr apping mode and the mode conversion is more conspicuous for a larger n . The spatial distributions of the propagation characteristics are sho wn in the nonuniform duct made of uniform, nonuniform, and uniform sec tions in the distance direction. It was found that the variation of th e received electric field changes significantly according to the chang e in duct height in the distance direction and that the effect of the order n is extremely significant.