Structure of frequency modulated and phase-shift keyed signals reflected from ionosphere at near-critical frequencies

The structure of frequency modulated and phase shift keyed radio signals distorted as the result of dispersion effects and leakage of spectral components through the ionospheric layer was investigated in the region of the critical frequency. Linear frequency modulated (LFM) signals reflected from an ionospheric maximum region and approximated by a symmetrical Epstein layer are examined. The dispersion distortions of LFM sounding signals reflected from the maximum region of an isotropic ionospheric layer are analyzed. The dispersion distortions of LFM signals reflected from a magnetoactive ionospheric layer are examined in a longitudinal propagation approximation. The dynamics of the development of distortions as the ratio omega sub o omega sub cr varies are traced. The LFM signal compression by the ionosphere is investigated. Conditions under which a maximally compressed reflected signal with the greatest amplification can be obtained are examined. The use of beam representations on the basis of the space-time geometric theory or diffraction makes it possible to predict and interpret distortions of complex signals.