Inherent limitations in the localization of a coherently scattered source

This paper addresses the problem of localizing a single coherently scattered, far-field, narrowband source emitting a Gaussian signal and observed in additive, Gaussian noise. An explicit expression for the Cramer-Rao bound (CRB) of the unknown spatial and spectral (i.e., source and noise power level) parameters of the source is presented for arbitrary array geometry. The CRB is used to study the inherent limitations in the estimation of the mean angle of a scattered source in comparison to the case of a point source at the same mean angle.