Joint DOA, Range, and Polarization Estimation in the Fresnel Region

A new algorithm of joint direction-of-arrival (DOA), range, and polarization estimation is proposed to localize multiple polarized sources in the Fresnel region. The algorithm is based on a sparse linear array composed of dual-polarization sensors with symmetric subarray partition. By the symmetric property of sparse linear array, the steering vector of the polarized array can be expressed as the product of a complex matrix with the signal's DOA and a complex matrix with the signal's range and a complex vector with the signal's polarization. A spectral rank reduction (RARE) algorithm is presented to estimate the DOA independent from the range and polarization. With each estimated DOA, the range of each source is accordingly estimated by defining the 1-D range RARE function. For each DOA and range of source, a MUSIC algorithm is finally adopted for the signal's polarization. The DOA and range identifiability of the proposed algorithm are discussed, and the range ambiguity issues caused by sparse linear array are analyzed. The proposed algorithm employs only second-order statistics and 1-D search so that its computational burden is reduced. The limitation of inter-element spacing ( d ≤ λ/4) is overcome. By numerical examples, it is shown that the proposed algorithm can enhance the angle resolution even with the limited number of sensors.