Pulse propagation through a plane stratified ionosphere

Abstract

The paper concerns the propagation of pulses or wave packets through an ionospheric plasma. The rise time, which appears in the ionospheric weighting function, is shown to be a realistic measure of the magnitude of the pulse shape distortion and the shortest usable pulse length in single-path, single-mode communication. Although rather general, smooth models of the medium can be dealt with, we consider in particular the case of a horizontally stratified, unmagnetized and collisionless ionosphere. Two such simple models are studied, which describe the lower part of the layer and the region of the maximum of electron density, respectively. These models allow a completely analytic treatment, and hence one may obtain explicit expressions, in terms of the parameters of the profiles, for the rise time. The illustrations show that the rise time may be less than 1 μs for a steep profile typical for sporadic E-layers, but in the range of one to a few tens of μs for propagation through a normal layer. Results of preliminary estimates indicate, however, that pulse mixing due to the differences in group path between the O- and X-mode rays dominates over pulse shape distortion in many cases.