Researches And Designs On Broadband Beamformer

The array signal processing technique has been widely used in defense technical and national economy applications including radar, sonar, modern communication, geologic exploration, radio astronomy, medical imaging and so on. As an important approach of array signal processing, the beamforming technique is mainly to realize two functions: 1) obtaining spatial processing gain of signals of interest against noises, interferences or reverberations, and 2)achieving high spatial resolution for more accurate target detection and localization. While broadband signal processing has become an important research topic, because of the fact that broadband signal has many merits,The essence of this paper can be concluded as follows. Firstly, introduce the underwater multipath channels and its propagating loss, the generation of underwater target radioactive noise and its characteristics. Build the theory foundation of modeling and simulation through the acoustic spectrum of underwater targets radioactive noise.Secondly, study on several methods of narrowband beamforming, including CBF method, ESPRIT method, ROOT-MUSIC method. Analyze carefully both advantages and disadvantages of each method by experiments and simulation.Thirdly, study some approaching methods for broadband beamformer, including the frequency-domain beamforming, time-domain beamforming. After the analysis of the defects in classical time-domain broadband beam former, consequently obtain two ways to realize constant band of beam forming, which means change the array elements interval or its number with respect to frequency, and change the weighted coefficient with variation of frequency.Fourthly, in basis of Sub-band division method, explore the beamformer of constant band based on time domain FIR filters. Investigate respectfully the LMS self-adaptive filter and another filer based on BP neural network formation. Discuss the impact of approximation effect from the filter’s order and cost factor.Finally, an FPGA implementation of broadband beamformer based onuniform linear arry is shown.