Adaptivity of a real-symmetric array by DOA estimation and null steering

An efficient two-step adaptive algorithm is presented for a uniformly spaced linear array using symmetric amplitude only control (SAOC). In the first step of the algorithm, the directions of arrival (DOAs) of the interfering signals are estimated using the noise-subspace eigenvectors of a real-symmetric covariance matrix, which has a dimension half that of the array. As the dimension of the problem is halved, and only real numbers are involved, the computation time is significantly reduced as compared with conventional subspace methods. Owing to the symmetry property of the direction vector, image directions arise from the DOA estimation process. However, with the SAOC null-steering method applied in the second step, it is not necessary to identify the true DOAs before suppressing the interfering signals. This greatly simplifies the design and improves the adaptive response. Moreover. The SAOC null-steering method is computational efficient and allows the implementation of a monopulse technique for tracking the DOA of the desired signal. Computer simulation results are presented to demonstrate the effectiveness of the proposed adaptive algorithm and monopulse technique