Yu. B. Nechaev, E. S. Makarov

In this paper problem of high-resolution UHF direction-finding with four-element antenna array with radii 0,1 wavelength on frequency 31,5 MHz is considered. Large amount of real-world signals emanating from far-field test generator placed at different DOAs was recorded and than processed off-line to define performance of DOA estimation. Firstly it was discovered by authors that direction-finding errors mostly depend on array manifold perturbations through bias in angle-of-arrival estimates rather than on signal-to-noise ratio. So it seems obviously to estimate antenna array manifold over entire field of view using sources at known positions. However, in UHF such approach becomes complicated and time-consuming as wavelength is large and far-field condition is fulfilled on sufficiently large distances. So, in this paper optimal number of calibration points in sense of resolution probability and minimum variance of estimates is defined empirically to minimize time to define real array manifold. Another discovered fact is increasing of phase shifts between array elements due to mutual coupling. Rely on this fact it is possible to estimate factor of such increasing via 1-3 measurements and than use this factor in estimation of real array manifold. Thirdly, iterative extension of Pierre-Kaveh calibration method is proposed in which calibration matrix is calculated in predefined sector of view instead of full space calculation. Size and location of sector are defined from results of initial direction-finding subject to estimated factor of shifts in-creasing. Performance of MUSIC-based radio direction-finder is investigated under application of examined calibration techniques and resolution about 25° is achieved with reasonable accuracy of AOA estimates for antenna array radii of 0,1 wavelength on frequency 31,5 MHz.