Basic Researches On Applications Of Adaptive Beamforming Technique

From theories to applications, many practical issues also exist for adaptive beamforming technique. For example, the robustness performance of adaptive beamforming algorithm would be an immediate cause for the effectiveness in practice. Moreover, some jammings with special styles, like multipath coherent jamming, blinking jamming, smart jamming and so forth, also bring serious impacts on traditional adaptive beamforming. Therefore, the investigations of this dissertation are focused on the two issues of the robustness of algorithm and peculiar jamming suppression. The main research contents are summarized as follows.Several representive robust adaptive beamforming algorithms based on uncertainty set constraints are investigated. And the relationships between them are clarified. The performance of robust Capon beamforming based on spherical uncertainty set constraint is deeply analyzed, which show clear that several parameters how to influence the optimum diagonal loading factor of the adaptive weight vector and the performance of the algorithm.A modified robust minimum variance distortionless response(MVDR) beamforming algorithm is presented, which is on the basis of a novel spherical uncertainty set constraint whose center locates the estimated steering vector of the desired signal. The method not only overcomes the shortcoming of the output performance dependent on the upper limit of of the norm of steering vector error, but also can hold good robustness under serious mismatches of steering vector of the desired signal.For the sidelobe level of adaptive pattern of robust MVDR beamforming algorithm is relative high, a sidelobe control approach is presented. In the case of beam pointing error, the approach is able to control the arbitrary sidelobe areas of the adaptive pattern and attains perfect control effects, which realizes the effective combination of robust adaptive beamforming and low sidelobe level of the adaptive pattern.An approach of iterative Toeplitz based on the eigenspace-based beamforming is presented for eliminating the coherent jammings under beam pointing error. The iterative Toeplitz technic is firstly applied to conduct decorrelation for the coherent jammings. And then the adaptive beamforming based on eigenspace is used to mitigate the impact caused by the pointing error. Therefore, the approach has better robustness, especially has better capability for jamming suppression in the presence of small sample size.The jamming suppression issue under highly nonstationary circumstance is investigated. An optimized direct data domain least squares approach using single snapshot is presented, which increases the adaptive freedoms, ensures adaptive reception for the desired signal and suppression for the jamming signals, decreases the sidelobe level of adaptive pattern, and therefore obviously improves the output capability.The approaches against smart jamming are investigated. Combined with the idea of jamming samples recognition and collection, the time-space cascade adaptive sidelobe canceling method only confronting the smart jamming and the"canceling-recognizing-canceling"method simultaneously confronting the noise jamming and the smart jamming is put forward respectively. The two methods both take on favorable effects for jamming suppression.