Mutual coupling in phased arrays of randomly spaced antennas

Abstract
Mutual coupling effects in phased arrays with randomly located elements are studied. The network formulation of antenna arrays is found to be a convenient and useful approximation. Two main effects of coupling are separately considered. The first is the increase in the sidelobe level. A new solution for the distribution of sidelobe level has been obtained which is applicable even for small arrays. It is found that the increase in sidelobe level is noticeable only for small average spacing (e.g., less than 2.5 wavelengths). The second effect of coupling is that it causes the fluctuation of main-beam amplitude as a function of the scan angle. The probabilistic properties of these fluctuations are studied. In the uniformly spaced arrays the accumulation of coupling effects may cause "blind angles". In random arrays this accumulation is highly improbable. This method of removing blind angles is further illustrated by an experiment on diffraction gratings where Wood's anomalies and blind angles are recognized as identical phenomena. Finally, an important contribution of this investigation is the analysis by various methods of the radiation pattern of random array. The results obtained by these methods agree remarkably well with the Monte Carlo simulations.

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