Analysis of HF pulse reflection from a randomly varying ionosphere

The reflection of high-frequency (HF) pulses by a randomly inhomogeneous, dispersive, and absorbing ionosphere is considered. The distortion of the transmitted pulses due to the intrinsic ionosphere dispersion, multipath effects, and frequency incoherence is related to the spatial, temporal, and frequency dependent characteristics of both the ionosphere and the troposphere. The envelope broadening of a constant-carrier pulse due to the dispersion (delay distortion) and randomness of the media (diffuse multipath) is seen to be small compared to the discrete mulfipath spread resulting from variations of the ionosphere´s index of refraction with height. In the case of chirp-pulse transmission, pulse compression in the range of 20-30 dB may be achieved provided the frequency sweep of the transmitted pulse is matched to the slope of the delay of the channel and the bandwidth of the chirp pulse is large enough (0.1-10% of the center frequency).