A comparison of spread and point-source multiple-direction estimation techniques for high latitude HF direction finding / by Robert W. Jenkins. : Co24-3/8-1998-2E-PDF

"Previous simulation studies were conducted to determine the direction-finding performance of four different antenna array geometries with and without antenna pattern errors, operating with the deterministic maximum-likelihood (ML) algorithm. Here they are extended to a new DF algorithm, 'spread maximum likelihood' (SML), which assumes distributions of signal directions, rather than single directions, to approximate the signal information seen by the array. The SML algorithm is thought to be more appropriate to the high-latitude HF radio environment, where signals often arrive from a spread set of directions due to multiple reflections or scattering from irregularities in the ionosphere and, at the same time, from a single great-circle direction as a result of sporadic-E propagation. Using a performance criterion of 'point-source visibility' in the presence of a stronger spread source, the simulation shows the SML technique to yield substantially better performance than ML, for all arrays and levels of error, and array apertures of four wavelengths or more. The SML technique extended the useful range of array apertures upwards to 10 wavelengths in most cases. As was seen previously for the ML algorithm, the three-pronged star configuration was found to be best of the array geometries tested"--Abstract, page iii.

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