Broadband Beamforming Optimization Of Sonar Arrays

Modern sonar systems generally use hydrophone arrays and advanced signal processing techniques to improve their detection and localization abilities, whereas beamforming plays an important role. Wideband array signal processing has been an active research area during the past years, In this thesis, optimization design techniques of wideband beamforming are studied systematically.In this thesis, we first introduce optimization design methods of narrowband beamforming for arbitrary arrays, and analyze various broadband beamforming methods systematically. Based on these two points, the main works are as follows:1. Broadband low sidelobe beamforming in time domain is studied thoroughly in conjunction with a practical sonar volumetric array. It is shown that, due to array mismatch errors, the practical beam patterns are distorted greatly. This thesis develops the robust beamforming optimization method of narrowband systems to broadband systems. The problem that we face in broadband systems is pointed out. An approach of designing FIR filters based on expected response interpolation is presented to solve this problem. Analysis results of the experiment verified the correctness and effectiveness of the approach.2. Methods of broadband constant beamwidth beamforming for arbitrary geometry arrays are studied. The approache of directly designing the FIR filter fan to realize broadband constant beamwidth beamforming is introduced and applied to an arc array. Simulation results of two kinds of optimization methods are compared and imply that the beampatterns obtained by the second kind of methods satisfy the desired performance better.3. Beamforming for signal sources located in the nearfield of an array is studied. A nearfield compensation method for nearfield beamforming is outlined. A constrained least-square optimizing method using the nearfield signal model to design nearfield beamformers is proposed for arbitrary geometry arrays. Simulation results show the effectiveness of the proposed method. Broadband nearfield beamforming problems are discussed, the optimizing method using semi-definite programming is presented to design broadband nearfield beamformers and the simulation results are satisfactory.