Yang T C
Naval Research Laboratory, Washington, DC 20375, USA.
J Acoust Soc Am. 2003 Mar;113(3):1342-52. doi: 10.1121/1.1534604.
The single-element spectrogram for a continuous broadband signal, plotted as a function of range, has been shown to exhibit striated bands of intensity maxima and minima. The slope of the striations is an invariant of the modal interference and is described by a waveguide invariant parameter "beta." The striation pattern is analyzed and modeled in this paper for the beam outputs of a horizontal line array obtained by conventional beamforming. Array beamforming makes it possible to measure the waveguide invariant parameter for weak signals due to the enhancement of signal levels by the array gain over that of a single element. It is shown that the signal beam spectrogram as a function of range exhibits the same striation pattern as that (predicted) for a single element. Specifically, for a broadside signal, the beam striation is identical to that of a single-element plus a constant signal gain. For a nonbroadside target, the signal beam intensity will be modified by a frequency-bearing dependent signal gain due to the signal spread over multiple beams, nevertheless the beam spectrogram retains the same striation pattern (slope) as for a single element. The sidelobe beams (outside the canonical cones containing the signal arrivals) exhibit an entirely different striation pattern as a function of frequency and range. For array processing, it is shown that a fast range-rate, close range target and a distant, slow range-rate interference source will have a different striation pattern (slope) in the corresponding beam spectrograms as a function of time, assuming no prior knowledge of the source ranges. The difference in the striations between the beam spectrograms can be used in array processing to suppress the interference contribution. A 5-7 dB interference suppression is demonstrated using simulated data.
连续宽带信号的单元素频谱图，作为距离的函数绘制，已显示出强度最大值和最小值的条纹带。条纹的斜率是模态干涉的一个不变量，由波导不变参数“β”描述。本文对通过传统波束形成获得的水平线阵的波束输出的条纹图案进行了分析和建模。阵列波束形成使得能够测量弱信号的波导不变参数，因为阵列增益相对于单个元素增强了信号电平。结果表明，作为距离函数的信号波束频谱图呈现出与单个元素（预测）相同的条纹图案。具体而言，对于正侧信号，波束条纹与单个元素的条纹相同，再加上一个恒定的信号增益。对于非正侧目标，由于信号在多个波束上传播，信号波束强度将因频率相关的信号增益而改变，不过波束频谱图仍保留与单个元素相同的条纹图案（斜率）。旁瓣波束（在包含信号到达的标准锥之外）呈现出作为频率和距离函数的完全不同的条纹图案。对于阵列处理，结果表明，假设对源距离没有先验知识，快速距离变化率、近距离目标和远距离、缓慢距离变化率干扰源在相应的波束频谱图中作为时间函数将具有不同的条纹图案（斜率）。波束频谱图之间条纹的差异可用于阵列处理以抑制干扰贡献。使用模拟数据展示了5 - 7 dB的干扰抑制效果。
