共查询到16条相似文献,搜索用时 93 毫秒
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在点目标回波模型基础上,通过对理想运动体目标的分析,引入了距离-速度联合分布密度和时延-时间伸缩联合分布密度函数的概念,详细推导了延展目标的宽带回波模型,解释了各密度函数和宽带扩展函数的物理意义及相互关系,最后给出了宽带回波模型的小波变换表示方法。 相似文献
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提出了一种基于广义边缘CWD—Hough(GMCWD—Hough)变换的宽带声成像方法。分析了基于时间伸缩-时延的宽带相关声成像的基本模型,介绍了广义边缘CWD—Hough变换。根据目标回波的时频分布特点,该方法基于时间一频率联合分析法,提取信号在时频域的分布特性参数进行时间伸缩时延的声成像。通过设计合理的广义边缘核函数,能有效避免常用的WVD方法产生的交叉项影响,检测性能优于常用的Wigner—ville分布方法。实验结果表明该声成像方法的有效性,不仅适合水声宽带成像,而且对于低信噪比条件下的其它成像方式也具有参考价值。 相似文献
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分析了宽带时延-时间伸缩声成像的基本理论,介绍了广义边缘CWD-Hough变换。根据目标回波的时频分布特点,提出了一种针对低速运动目标的基于广义边缘CWD-Hough变换的宽带时延一时间伸缩声成像方法。利用该方法能有效避免常用的WVD方法产生的交叉项影响,从而能对低速运动目标进行更好地检测及成像。计算机仿真结果表明了该声成像方法的有效性。 相似文献
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小波变换是近年来信号处理中的一个重要工具,由于其优良的时频局域性,在检测、估计以及识别等方面都得到了重视和研究,而将小波变换与传统的一些信号处理方法结合起来处理有关问题也是人们研究的一个方向,文章主要考虑到交互小波变换中的两参数(时延与尺度)与不同接收器目标回波间的时延及频率成对应关系,采用对两路LFM回波信号作小波交互相关,从而获得两回波的相对时延估计,继而得到方位估计。针对算法运算量较大的问题,文章采取先估计尺度与时延的大致范围,再将时延-尺度网格进一步细化得到精确结果,最后给出了部分计算机仿真结果。 相似文献
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建立了超声测距时延估计模型,由于窄带超声回波参考信号与接收信号的相关函数在极值点附近具有慢衰减高频振荡特性,所以有必要将搜索直接相关函数的极值点转化为搜索相关函数包络的极值点.针对相关峰常规插值方法在多倍插值的情况下存在计算复杂、时延估计精度不高等缺点,结合超声回波信号的窄带带通特性和相关峰细化(Fine Interpolation of Correlation Peak)原理,提出了直接提取相关函数包络及包络峰细化方法,并分析了其计算复杂度.仿真与实验研究表明,该方法能大大提高相关函数包络峰值分辨率,适用于类超声回波信号的带通信号精细时延估计问题. 相似文献
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在用超声脉冲回波法检测金属-非金属粘接结构的质量以及测量非金属层厚度时,需要提取出各界面回波间的延迟时间作为特征值.当非金属层较薄时,各回波信号间会产生严重混叠,难以准确获得时延估值.提出了一种多界面粘接结构的高分辨率时延估计方法,综合利用了维纳滤波解卷积技术和最大熵谱估计方法,从混叠信号中得到精确的时延估值,很好地解决了特征值提取困难的问题,并用模拟信号和实验信号验证了该方法. 相似文献
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传统的空时自适应处理(Space-Time Adaptive Processing,STAP)利用窄带混响和目标在空时平面的可分辨特征抑制窄带混响。对宽带混响和目标在空时平面分布特征进行研究,并通过理论推导,得出带宽对混响和目标空时分辨特征的影响公式。结果表明:宽带混响和目标在空时平面分布特征部分重叠,导致传统STAP效果不佳。在此基础上,借鉴STAP思想,并利用线性调频(Linear Frequency Modulation,LFM)信号在分数阶Fourier变换域上的聚焦性,分析了在空-分数阶Fourier域三维空间上抑制宽带LFM混响的可行性。 相似文献
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《IEEE transactions on instrumentation and measurement》1970,19(1):9-14
An accurate delay-time measuring equipment operating in the 50-GHz region has been developed. The equipment can measure wide-band delay-time characteristics of millimeter wave component and waveguide line. Sweep frequency range is variable from 0 to 1.5 GHz at any of the 46 to 52 GHz. The measurement method employs the usual comparison method and a newly developed rapid automatic switching method. The accuracy of the equipment is 0.1 ns at 20-dB insertion loss. Finally, some measured results are described. 相似文献
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Separation of overlapping linear frequency modulated (LFM) signals using the fractional fourier transform 总被引:1,自引:0,他引:1
Cowell DM Freear S 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2010,57(10):2324-2333
Linear frequency modulated (LFM) excitation combined with pulse compression provides an increase in SNR at the receiver. LFM signals are of longer duration than pulsed signals of the same bandwidth; consequently, in many practical situations, maintaining temporal separation between echoes is not possible. Where analysis is performed on individual LFM signals, a separation technique is required. Time windowing is unable to separate signals overlapping in time. Frequency domain filtering is unable to separate signals with overlapping spectra. This paper describes a method to separate time-overlapping LFM signals through the application of the fractional Fourier transform (FrFT), a transform operating in both time and frequency domains. A short introduction to the FrFT and its operation and calculation are presented. The proposed signal separation method is illustrated by application to a simulated ultrasound signal, created by the summation of multiple time-overlapping LFM signals and the component signals recovered with ±0.6% spectral error. The results of an experimental investigation are presented in which the proposed separation method is applied to time-overlapping LFM signals created by the transmission of a LFM signal through a stainless steel plate and water-filled pipe. 相似文献
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A model describing the time constant of a wide-band microwave differentiator is presented. The time constant combined with the amplitude response dictates the circuit behaviour of a microwave differentiator. By representing the formulations of differentiators in the discrete-time (or Z) domain, the authors implement the differentiators with equal-length transmission lines. The approach method consists of discrete signal processing techniques, transfer functions in the Z domain and optimisation algorithms. Three differentiators with different time constants and frequency bands are built and tested. The experimental results are in good agreement with theoretical values. 相似文献