Guided propagation of HF radio waves in the ionosphere

A review is given of the work done in the field of ionospheric guided propagation of HF radio signals from artificial satellites. The possible theoretical approaches to the problem are summarized with more details on the analysis in terms of ray-tracing based on a geometric-optics treatment.A survey is done of the experimental observations performed through satellite transmissions, with particular emphasis on the results obtained through three ad hoc developed experiments: Orbis, S. Marco and OV 4.