Two-dimensional direction-of-arrival estimation for cylindrical nested conformal arrays

Recently, nested arrays have received considerable interest because such array configurations can be systematically designed and their degrees of freedom (DOFs) can be expressed in closed form. Compared with uniform linear arrays, they have obvious advantages in array aperture and DOFs. In this paper, we introduce nested subarray structure to cylindrical conformal array to form a nested conformal array, and develop a corresponding algorithm for two-dimensional (2-D) direction-of-arrival (DOA) estimation. By vectorizing the covariance matrices of the nested subarray outputs, we firstly generate the three-parallel difference coarray signal and derive the rotational invariance structures between three coarray manifolds. An augmented covariance matrix of the coarray outputs is then constructed via three-dimensional spatial smoothing processing. Finally, the 2-D DOAs of the sources are estimated by the total least squares (TLS)-ESPRIT method. Compared with the traditional schemes with uniform conformal arrays, our algorithm fully exploits the extended aperture of the nested subarrays, and thus enhances the DOA estimation accuracy. Numerical results demonstrate the superiority of the proposed algorithm in comparison to the existing methods.