Research On Wideband Beamforming Algorithm

Beamforming technology,an important research filed of array signal processing,is used to restrain interference signal and improve the signal-to-noise ratio in many applications such as signal's scout and reception,radar,sonar and geological survey and so on.Since the 1960 s,researchers have been studying the potential beamforming for the narrowband case.With the development of electronic technology,wideband signal is becoming more and more prominent in scientific research and practical use,the wideband beamforming has gradually become a hot area of research.In this paper,the beamforming algorithm based on wideband signal has been researched:Firstly,the model of array and signal is introduced,including narrowband signal and wideband signal.The model of the array receiving narrowband signal is established.According to correlation between narrowband and wideband,the model of the array receiving wideband signal is easy to get by expanding the model of broadband signal.Secondly,the classic beamforming algorithms based on narrowband signal and array pattern synthesis are studied.To solve the disadvantage of conventional beamforming algorithm,high sidelobe level and low angular resolution,the minimum variance distortionless response(MVDR)algorithm is researched to receive desired signal without distortion and improve the signal-to-noise ratio.In order to obtain a pattern performance with expected performance,the olen-compton method and convex optimization method is studied,first one reduces the sidelobe level via putting jamming in side lobe,which can adaptively adjust the power of jamming to get consistent sidelobe level,second one transforms the antenna pattern synthesis into a convex optimization problem and gets the result by convex optimization solution.the effectiveness of these algorithms is verified by computer simulation.Thirdly,the time-domain wideband beamforming algorithms are studied.To solve drift in conventional broadband beamforming algorithm,time delay processing is used to realize beamforming for the wideband case.Two kinds of fractional delay filter based on window function and maximally flat FD are mainly studied in this paper,the simulation results show that these two algorithms is useful.Finally,the frequency-domain wideband beamforming algorithms are studied.These kind of algorithms transform the signal from the time domain to the frequency domain,and use the narrowband beamforming algorithm at each frequency.ISM only uses the narrowband beamforming algorithm in each frequency bin,bringing no fruit in coherent signal,patterns of ISM differ at different frequencies.CSM focuses the signal subspaces at different frequencies to one single frequency,it is valid in coherent signal and cuts down the difference of patterns.The focusing matrix of CSM depends on DOA of wideband signal and the error of DOA effects the performance of CSM.Omnidirectional algorithm minimums focusing error in all angles,and this algorithm has strong robustness to the steering vector error.In order to suppress the mainlobe interference,a wideband beamforming algorithm which uses a blocking matrix to cancel the mainlobe interference based on EMP is studied.Simulation results verify the effectiveness of these algorithms.