High Resolution Direction-of-arrival Estimation Of Wideband Array Signals

Wideband signals possess the characteristics of high resolution, large information quantity, weak correlation with background noise, low probability of intercept and anti-interference, which benefit target detection, precision parameter estimation and target feature extraction. Therefore wideband signals are widely used in radar, sonar, communication, seismic exploration, radio astronomy, medical imaging and other fields, such as ultra-wideband synthetic aperture radar, UAV synthetic aperture radar, high range resolution (HRR) radar, wideband LPI radar and ultra-wideband communication.For wideband signals, the phase difference between sensor outputs is no longer just dependent on the DOA alone, but also depends on the temporal frequency, which has a wide range. The difference brings a large deviation, or even failure, to the narrowband DOA estimation algorithms from the true parameters. Therefore, in passive reconnaissance, effective wideband array processing methods should be proposed. Meanwhile, in order to meet the need of reconnoitering signals of complex modulation types or of large time-bandwidth product, wideband array processing techniques should cope with the problems of existing array processing techniques, such as the weak adaptation to large signal bandwidth, tremendous amount of computation and incompatibility with existing equipments.Supported by the Natural Science Fund of China, this dissertation carries on the following research into the problems above: the formation of focusing matrix with and without preliminary DOA estimation, test of orthogonality of subspace, fast wideband DOA estimation algorithms and beam-space wideband DOA estimation algorithms.Some basic problems are discussed in Chapter 2. The influence of bandwidth on narrowband sources' number detection and MUSIC algorithm is studied. Some ways of modeling the signals received by wideband array are developed.Wideband DOA estimation algorithms based on preliminary DOA estimation are studied in Chapter 3. A new wideband CSSM algorithm based on signal subspace decomposition is developed, the new algorithm has the same performance as that of TCT algorithm, but has less computation burden. A new method of forming focusing matrix, basing on SVD of the array manifold, is proposed. In addition to that, a new ISSM method, which bases on the synthesis of preliminary DOA estimation and ISSM method, is developed through the replacement of array manifold.Wideband DOA estimation algorithms without preliminary DOA estimation are studied in Chapter 4. The CSSM method based on Bessel function expansion is studied; the frequency and DOA are separated through the expansion of the array manifold, the part related to frequency is used to form the focusing matrix. A new CSSM method based on cubic spline interpolation is developed, the virtual array outputs are formed by cubic spline interpolation and are allied at the reference frequency, thus narrowband DOA estimation can be used. The consistent focusing method is improved, in which unitary matrix constrain is added to the focusing matrix to gain better performance.The algorithm of subspace's orthogonality testing is studied in Chapter 5. A new algorithm is proposed basing on the frequency domain subspace's orthogonality testing. The new algorithm avoids the estimation of signal subspace at the reference frequency and has better performance and lower computation burden compared with TOPS.The fast algorithms in wideband DOA estimation are studied in Chapter 6. The multi-stage Wiener filter, propagator method, fast signal subspace decomposition and Householder QR decomposition are introduced into wideband DOA estimation. The proper focusing matrices are proposed according to the characteristics of the above fast algorithms. The proposed methods are in the form of multiply-accumulator, so they are real-time realizable in hardware.The wideband beam-space DOA estimation algorithms are studied in Chapter 7. The narrowband beam-space DOA estimation algorithms are summarized and developed to wideband scenario. The wideband DOA estimation based on frequency invariant beamforming is summarized. Two new methods that construct frequency invariant beamforming are developed. These methods are used in the wideband DOA estimation, and the performance is verified through simulations.