【作者】 唐建生；

【导师】 孙超；

【作者基本信息】 西北工业大学 ， 水声工程， 2006， 博士

【摘要】 在较大的带宽上无失真地获取目标源的辐射噪声，能够给诸如信号检测、目标识别和定位等后续信号处理提供更为丰富的、完整的目标信息，对提高其性能至关重要，因此具有广泛的实际应用背景。本文结合水下军用目标特性国防重点实验室基金项目，针对能够无失真获取宽带运动源辐射噪声的波束形成技术，系统深入地开展了理论和实验研究。主要研究内容包括：1．建立了存在运动目标时阵列输出信号的数学模型，并从声场的角度对此模型进行了分析。给出了阵列接收到运动源辐射噪声的高精度模拟方法。从理论上论证了要无失真地估计处于主瓣区域宽带目标的辐射噪声，宽带波束形成器必须具有恒定束宽特征。2．给出了两种低旁瓣时域恒定束宽波束形成器(WCBB)的设计方法，即：通过设计低旁瓣期望波束的设计方法和直接优化的设计方法，并用仿真实验检验了它们的有效性。利用仿真实例指出了WCBB的子带设计方法的缺陷，即，无法保证非设计频率点上具有和设计频率点上相同的性能。利用湖上实验说明，使用实测阵元响应设计的WCBB能够改善波束形成器在实际环境中的性能。3．以时域波束输出无失真为准则，提出了WCBB的时域优化设计方法。与子带设计方法不同，此方法能够兼顾设计频段内更多频率点上的设计要求。设计中引入二维代价因子，通过调整代价因子，可以使设计得到的WCBB在期望的频率和方向上更满足设计指标。给出了代价因子的迭代寻优算法和加快实现期望旁瓣级的方法。通过设计实例验证了所提方法的有效性。4．提出了稳健的恒定束宽自适应波束形成方法。此方法通过设计线性约束，一方面使自适应波束形成对目标运动引起的方向矢量失配具有稳健性，另一方面使不同频率上的波束具有恒定束宽特征。通过奇异值分解得到约束矩阵的近似表达，以减小约束的个数。仿真实验表明，此方法能够稳健地形成恒定束宽波束，与非数据依赖的方法相比具有更强的干扰抑制能力，从而保证了存在强干扰时对运动目标源辐射噪声的准确获取。5．提出了基于频率不变波束形成(FIB)的稳健广义旁瓣对消器。为了稳健地实现对目标信号的阻塞，给出了两种具有扩展零陷的FIB的设计方法：直接施加线性约束的设计方法和施加虚拟干扰源的设计方法。仿真实验表明：此方法能够稳健地实现信号阻塞，具有较强的干扰抑制能力，并能够实时地给出目标辐射噪声的时间波形。6．把语音信号处理中的嵌套阵列波束形成方法与多采样率信号处理技术相结合，提出了嵌套阵列的多采样率波束形成方法。在实现中，把子阵设计和变采样率相结合，使不同子阵的波束形成器使用同一组滤波器系数而能得到相同的空间滤波特性，以简化设计和降低信号处理的复杂程度。给出了嵌套阵列的设计方法和实现方法。结合设计实例，利用仿真实验验证了此方法的正确性和有效性。7．利用水池和湖上实验数据，对本文所提方法在实际环境中的性能进行了检验。实验结果表明：利用低旁瓣的WCBB和基于FIB的广义旁瓣对消器均能够实现对宽带目标辐射噪声的无失真获取。更多还原

【Abstract】 Moving targets’ radiated noises often cover a wide bandwidth and how to acquire them distortionlessly has attracted many researches in the fields of SONAR, aeroacoustic measurement, and intelligent communication. It can provide more information for post processing techniques, such as target detection, classification and localization and thus is crucial for their performance improvements. Supported by the fund of the Key Laboratory of Military Targets’ Acoustic Characteristics, this dissertation systematically and deeply studied on the wideband array beamforming techniques to accurately acquire moving targets’ radiated noises. The main contributions are as follows:1. The model of signal received by the array for static sources is extended to the situation in presence of source motion and is further analyzed in acoustic field aspect. A method is then developed to precisely simulate the signal received by the array. Beamformer with constant beamwidth is theoretically demonstrated that it can distortionlessly estimate the moving targets’ radiated noise. Besides, it must have great capability of interference suppression to guarantee its performance.2. Two methods to design time domain wideband constant beamwidth beamformer (WCBB) with low sidelobe level are proposed, followed by two design examples to verify their correctness and effectiveness respectively. Through two simulation examples, the drawback of the classical sub-band decomposition based WCBB design method is pointed out. Lake-experiment is used to show the array mismatch errors in practical sonar systems will degrade the performance of WCBB. With measured array manifold, the performance can be improved.3. A time domain optimization method is derived to design time domain WCBB. Different from the sub-band decomposition based method, the derived one can take design results of the whole frequency band into consideration. A two dimensional cost function is introduced. By adjusting the cost function values, the beamformer will satisfy the design requests better at certain frequencies and directions. An iterative algorithm is further proposed to get the optimum cost functions. Via computer simulations, the effectiveness of the presented method is illustrated. 4. A robust adaptive beamforming method with constant beamwidth is presented. It is realized by linear constrained minimum variance adaptive beamforming method. A set of linear constrains are designed to assure the adaptive beampattern to be distortionless and the beamwidth constant over a certain frequency band. The low rank representation of the constraint matrix computed by the singular value decomposition is used to reduce the number of linear constraints. Simulation results show that the proposed method achieves greater interference reduction than data independent methods do, which ensures accurate estimation of the wideband signal.5. A robust generalized sidelobe canceller (GSC) employing frequency invariant beamformer (FIB) is proposed. In this method, the blocking matrix is replaced by a series of FIBs with nulls to block the signal. In order to block the signal reliably, two methods to design broadened nulls for FIBs are proposed. Simulation results show that the proposed method can effectively block the signal and reject interferences. Besides, the signal wave can be exhibited in real time through the proposed method.6. In order to conveniently process signal covering several octave bandwidths, the nested array is introduced and its multirate beamforming method is proposed. The effectiveness of the proposed method is illustrated by numerical examples.7. A tank-experiment and a reservoir-experiment are carried out respectively to verify the performance of the proposed methods in practical situations. Results of the tank experiment show that both WCBB and FIB based GSC can effectively reject interferences and accurately acquire moving targets’ radiated noise, the capability of interferences suppression of the former relies on sidelobe level, while the capability of the latter relies on FIB’s capability of blocking the signal. From the reservoir experiment, we illustrate frequency characteristics of the moving targets’ radiated noises acquired by time domain WCBB gets better than that by conventional delay-and-sum beamformer.更多还原