Application of spatial filters to DOA estimation of coherent sources

Problems associated with spatial smoothing which relate to the rate of decorrelation of correlated sources are discussed. Although a small improvement is attained, if sources have small differences in their directions-of-arrival (DOAs), they will remain highly correlated and the problem is not significantly diminished. A method which is based on the spatial filtering of an array vector is proposed. A procedure is developed that significantly reduces the correlations among sources and results in a nearly diagonal source covariance matrix. The design of the proposed spatial filters requires preliminary estimates of DOAs. This requirement, however, is not a drawback to this method, as is shown. Simulation studies are carried out for a 12-element linear array with quarter-wavelength element spacing. In all cases, 100 snapshots are used to estimate the array covariance matrix. In each case, 10 different simulations, with different noise sequences, are performed to present the variability of the resultant spectrum. The number of sources is set to 3 with -60°, 30°, and 40° DOAs