Due to the polarization diversity (PD) of element patterns caused by the varying curvature of the conformal carrier, the conventional direction-of-arrival (DOA) estimation algorithms could not be applied to the conformal array. In order to describe the PD of conformal array, the polarization parameter is considered in the snapshot data model. The paramount difficulty for DOA estimation is the coupling between the angle information and polarization parameter. Based on the characteristic of the cylindrical conformal array, the decoupling between the polarization parameter and DOA can be realized with a specially designed array structure. 2D-DOA estimation of the cylindrical conformal array is accomplished via parallel factor analysis (PARAFAC) theory. To avoid parameter pairing problem, the algorithm forms a PARAFAC model of the covariance matrices in the covariance domain. The proposed algorithm can also be generalized to other conformal array structures and nonuniform noise scenario. Cramer-Rao bound (CRB) is derived and simulation results with the cylindrical conformal array are presented to verify the performance of the proposed algorithm. 1. Introduction Conformal arrays mounted on curved surfaces are commonly applied in various areas such as radar, sonar, and wireless communication [1]. The conformal antennas could fulfill specific aerodynamics, space-saving, elimination of random-induced bore-sight error, potential increase in available aperture, and so on [2, 3]. Most researches focus on the design of antenna configuration [4–6], the transform between the local and global coordinate [7–10], and the pattern synthesis of conformal array [11–15]. The conventional direction-of-arrival (DOA) estimation algorithms, for example, the multiple signal classification (MUSIC) [16] and the estimation of signal parameters via rotational invariance techniques (ESPRIT) [17], are not applicable due to the varying curvature of the conformal array. The “shadow effect” of the conformal array is caused by the metallic shelter, leading to the condition that not all elements have the ability to receive the signal. As a result of the incomplete steering vector, common DOA estimation algorithms cannot be used for conformal array. Recently, DOA estimation algorithms for conformal array have been proposed for high resolution [18–22]. With the help of fourth-order cumulant and ESPRIT algorithm, a blind DOA estimation algorithm is proposed in [18]. Based on the mathematical technique of geometric algebra, 2D-DOA and polarization parameter estimations are completed by
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