Measurement of the angular spread of HF signals reflected from the high latitude ionosphere by means of super-resolution direction finding

Observations of the direction of arrival of a narrow band pulsed channel sounding signal propagated over a high latitude path have been made with a multi-channel receiver system connected to a wide aperture antenna array. The signals received on each antenna were processed to provide a measure of the relative times of flight of the propagating modes and their associated Doppler spectra. In this way, the signal was split into complex amplitude components distinguished by antenna position, time of flight and Doppler frequency. A direction finding algorithm was then applied to each of the signal components in turn in order to determine the directional characteristics of the received signal