Use of the optimum/adaptive beamforming (so called, Capon method) in bearing estimation of closely located sources has become very popular due to its superresolution properties [1–4]. It has been shown that this method is capable of resolving two independent sources which are separated by an angle which is of the order of one standard beamwidth (SBW) and sometimes less. However, when some sources are fully or highly correlated (coherent), i.e. when one source is a scaled and delayed replica of another source, this method encounters significant difficulties concerning with signal cancellation effect [2, 3, 6, 7]. Note that coherent sources appear frequently in practical problems. A well-known example is the phenomenon of multipath propagation.

The purpose of this paper is to obtain analytical estimation of the potential capability for adaptive beamforming in the presence of correlation between the sources as a function of coherence coefficient, signal power and the parameters of the optimum processor. Our resolution analysis is based on the assumption that the covariance matrix of the received signal will be determined rigorously by averaging over an infinite period of time, thus enabling us to obtain an estimate of the limiting ability of resolution.