Mixed Near-Field and Far-field Source Localization Using COLD Arrays

Many mixed near-field (NF) and far-field (FF) source localization algorithms in the open literature are developed based on the Fresnel approximation model, which is a simplified model of the exact source-array spatial geometry. Unlike these algorithms, in this paper, a new algorithm is derived to localize a mixture of NF and FF electromagnetic sources based on the exact spatial model with the use of a linear cocentered orthogonal loop and dipole (COLD) array. The summation of the dipole covariance matrix and the loop covariance matrix is shown to be independent of the source polarization parameters. Using this property, a multiple signal classification (MUSIC) pseudo-spectrum is defined for joint angle and range estimation. To facilitate the computational efficiency of the algorithm, a set of coarse angle and range estimates are derived using the estimating signal parameter via rotational invariance techniques (ESPRIT) philosophy to initiate the MUSIC searching. The major advantage of the proposed algorithm over the existing algorithms is that it does not introduce the systematic errors caused by the mismatch between the exact model and the Fresnel approximation model.