Localization of Mixed Near-Field and Far-Field Sources Using Symmetric Double Nested Arrays

Nested arrays have recently attracted a growing concern owing to their ability of achieving extended aperture and enhanced degrees of freedom (DOFs) compared to conventional uniform linear arrays (ULAs). In this paper, we devise a source localization scheme under the simultaneous existence of near-field (NF) and far-field (FF) sources using a symmetric double-nested array (SDNA). First, the direction-of-arrivals (DOAs) of FF sources are estimated using 1-D MUSIC spectrum. Then, the NF components can be extracted by applying the oblique projection technique. By constructing a special NF cumulant matrix and performing vectorization to generate the virtual array signal, the DOAs of NF sources can be estimated by the spatial smoothing MUSIC (SS-MUSIC) algorithm. Finally, with the NF DOA estimates, the range estimates of NF sources are obtained via 1-D peak searching. We also derive the consecutive range of the difference coarray and optimum array configurations for the SDNA, under a given number of sensors. The proposed algorithm exploits the large coarray aperture to enhance the localization performance and can distinguish correctly the types of the sources. The numerical results demonstrate that our proposed method significantly outperforms the existing methods for both DOA and range estimations.