EIGENSTRUCTURE TECHNIQUES FOR 2-D ANGLE ESTIMATION WITH UNIFORM CIRCULAR ARRAYS

The problem of 2-D angle estimation (azimuth and elevation) of multiple plane waves incident on a uniform circular array (UCA) of antennas is considered in this paper. Two eigenstructure-based estimation algorithms that operate in beamspace and employ phase mode excitation-based beamformers have been developed. The first, UCA-RB-MUSIC, is a beamspace version of MUSIC that offers numerous advantages over element space operation, including reduced computation, as subspace estimates are obtained via real-valued eigendecompositions, enhanced performance in correlated source scenarios due to the attendant forward-backward averaging effect, and the applicability of Root-MUSIC. The second, UCA-ESPRIT, represents a significant advance in the area of 2-D angle estimation. It is a novel closed-form algorithm that provides automatically paired source azimuth and elevation estimates. With UCA-ESPRIT, the eigenvalues of a matrix have the form mu(i) = sin theta(i)e(jphii) where theta(i) and phi(i) are the elevation and azimuth angles, respectively. Expensive search procedures being thus avoided, UCA-ESPRIT is superior to existing 2-D angle estimation algorithms with respect to computational complexity. Finally, asymptotic expressions for the variances of the element space MUSIC and UCA-RB-MUSIC estimators for the 2-D scenario have been derived. Results of simulations that compare UCA-RB-MUSIC and UCA-ESPRIT and also validate the theoretical performance expressions are presented.