In the context of coherent signal classification, a spatial smoothing scheme first suggested by Evans et al., and subsequently studied by Shan et al., is further investigated. It is proved here that by making use of a set of forward and complex conjugated backward subarrays simultaneously, it is always possible to estimate any K directions of arrival using at most 3 K / 2 sensor elements. This is achieved by creating a smoothed array output covariance matrix that is structurally identical to a covariance matrix in some noncoherent situation. By incorporating the eigenstructure-based techniques on this smoothed covariance matrix, it then becomes possible to correctly identify all directions of arrival irrespective of their correlation.

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A b s t r a c t This paper presents new results for resolving three uncorrelated lcoherent plane wave sources in presence of white noise, when subspace based high resolution estimators are used to estimate the directions of arrival of incoming signals. The signal to noise ratio required to resolve three closely spaced sources is derived here for two distinct source scenes and the results and compared with that corresponding to a two uncorrelatedlcoherent source scene. In this context, parametric expressions for signal subspace eigenparameters in three source scenes consisting of uncorrelated as well as coherent situations are deueloped here.