Abstract
A technique is developed, based on the microwave antenna theory of Schelkunoff, which provides an additional degree of control over the beampattem of linear microphone arrays. The technique uses a far field array formulation, by which the sensitivity of a commensurately spaced linear array can be represented by an n* order polynomial, where n is the number of array elements. The roots of this polynomial correspond to the minima of the sensitivity pattern, and so, by appropriate choice of roots, a polynomial can be generated, the coefficients of which are the weights which must be applied to the array elements in order to achieve a prespecified set of sidelobe positions. The technique is used in the application of a linear microphone array to the measurement of high speed propeller noise. It is further shown how the cross-spectral matrix must be treated, before array weighting is attempted, to ensure that the weighting function is not contaminated by the intrinsic element weighting which can occur as a result of the directional nature of aeroacoustic systems.
Published Version
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