A covariance approximation method for near-field direction-finding using a uniform linear array

Most narrowband high-resolution bearing estimation algorithms were proposed based on the assumption of a far-field source environment. When this assumption is violated, i.e. some sources are in the near field, these algorithms generally provide unsatisfactory performances. A new algorithm is proposed to handle this near-field problem using a uniform linear array. The received signal covariance matrix for near-field sources is viewed as a corrupted measurement of the ideal signal covariance matrix for far-field sources located at the same bearings. Taking this viewpoint, the authors reconstruct a far-field approximation (FFA) covariance matrix from the received covariance matrix to reduce the corruptions. Therefore, existing high-resolution bearing estimation techniques can be directly applied to estimate the bearings of the near-field sources. The properties of the proposed approach are investigated in detail. Simulation results demonstrating the effectiveness of this approach are included