Propagation of radio waves in a model nonuniform terrestrial waveguide

The paper deals with propagation of radio waves in multimode waveguides of arbitrary height. In this work the boundaries are assumed to be perfectly reflecting. For the case when the height of the multimode waveguide increases monotonically in the direction of propagation, the required solution is obtained by a generalised quasioptical approach which assumes that the waveguide consists of an infinity of infinitesimal radial waveguides cascaded together. To extend the solution for both directions of propagation, the reciprocity theorem has been employed, thereby accounting for reflections. The results have been applied to the study of v.l.f. radio propagation when the effective height of reflection at the ionosphere varies along the path of propagation. Laboratory measurements obtained from a two-dimensional microwave model are compared with the theoretical solution to substantiate the analysis.