Augmented Quaternion ESPRIT-Type DOA Estimation With a Crossed-Dipole Array

In this letter, a quaternion-based ESPRIT-type algorithm called augmented quaternion ESPRIT (AQ-ESPRIT) is proposed for direction of arrival (DOA) estimation with a co-located crossed-dipole array. Firstly, two quaternion models are constructed by judiciously arranging the observed signals, and then concatenated to form a new AQ model. Secondly, the AQ signal subspace is estimated by applying the quaternionic eigenvalue decomposition to the resultant AQ covariance matrix. Finally, the derived AQ signal subspaces of different subarrays are employed to form the rotational invariance equation, which is then used to obtain the ultimate DOA estimates. Numerical results show that the proposed AQ-ESPRIT has a better performance in low signal-to-noise ratio scenarios.