The effects of antenna array geometry and element pattern uncertainty on high-latitude HF direction finding / by Robert W. Jenkins. : Co24-3/7-97-006E-PDF

"Simulation studies are described which model the performance of a sampled-aperture HF direction-finding (DF) system operating with specified array geometries in the presence of both single-reflection (point-source) and multiple reflection/scattering (extended-source) ionospheric radio propagation typical of observed high-latitude nighttime conditions. A multiple-direction estimator was used to obtain direction estimates; the deterministic maximum-likelihood algorithm was selected for this, following a comparison between it and the MUSIC algorithm. Array pattern errors, based on previous phase and amplitude pattern measurements and numerical modelling, were included in the simulation. The performance is characterised in terms of the ability of the DF system to see a weaker point source in the presence of the extended source. The array apertures in wavelengths (or alternatively operating frequencies for a fixed-size array) over which good performance was obtained was limited at the low end by the resolving power of the array, and at the high end by the narrow array beamwidth and the limited number of directions available to the DF algorithm to describe the situation. Pattern errors reduced performance significantly; much more at small array apertures (2.5 wavelengths or less) than at larger apertures (5 wave-lengths or more). Of the four 12-element array geometries tested, the 'star' array, consisting of three arms with its smallest spacings at its extremities, performed best over the widest range of aperture sizes (or alternatively, operating frequencies)"--Abstract.

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