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声波信号作为系统测速的载体,直接影响测速性能,是多普勒测速技术的关键。研究 了不同发射信号的频谱特性及基于复协方差法的多普勒频移测量误差。一般假设二相编码信号频谱关于载频对称,但实际上其频谱为不关于载频对称的双边谱,不对称程度由不对称系数量化。不对称系数越小,测频偏差、标准差均越小,即测频性能更佳。仿真实验表明,在不考虑波束开角的点回波模型下,差分重复伪随机Blackman码元幅度调制编码信号与常用的非差分重复伪随机二相编码信号相比:不对称系数低3个数量级;信号频带同带宽内信噪比在0~-10 dB范围内测频标准差约下降2%~20%;信噪比高于10 dB时相对测频偏差约小5‰~6‰。 相似文献
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研究了复协方差频移估计测速下相关时延及接收信号频谱幅值不对称对声学多普勒测速偏差的影响。不考虑测速公式简化误差,复协方差频移估计测速偏差可以简化为多普勒频移测量偏差。经推导,不考虑发射信号波束开角的窄带测频无偏、宽带测频有偏;考虑波束开角的窄带测频和宽带测频均有偏。相关时延不准确且频谱不对称是该偏差的重要来源。仿真分析表明,点回波模型下,消除时延不准确或频谱不对称影响,测频偏差可趋于0。基于上述发现,建立底跟踪多普勒测速声呐的相位、幅度双重加权的椭圆网格测频模型;给出相同脉冲长度下窄带与宽带测频偏差存在差异的理论解释。利用所建宽带测频模型仿真出真实频移与估计频偏的拟合曲线,进而对实际数据进行修正,水槽实验场景速度测量相对偏差从1.14%降至0.78%,最大绝对值从2.83%降至1.83%;海试场景速度测量相对偏差从4.79%降至3.82%。 相似文献
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刘建新 《工程物理研究院科技年报》2004,(1):228-228
脉问二相编码信号不仅满足脉冲多普勒雷达高度表的要求,而且在频域和时域具有较高的分辨率和测量精度,同时能够解决测距和测速模糊。除此之外,距离旁瓣和多普勒旁瓣亦可有效抑制。然而,脉间二相编码和传统的二相编码信号一样,该信号仍属于多普勒敏感信号。要实现对该类信号的匹配处理必须进行多普勒补偿。基于频域滤波、相干积累与相位补偿的一致性原理可采用图1的处理方法。 相似文献
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以脉冲半导体激光器为例,对3种测量激光脉冲时基抖动技术进行了对比实验。这3种测量技术分别是:基于宽带取样示波器的时基抖动测量技术;基于相位比较检相器的相位噪声测量技术和基于频谱仪的谐波频谱分析技术。对比研究发现:基于宽带取样示波器的时基抖动测量技术适用于脉冲宽带及脉冲抖动较大的光脉冲;基于频谱仪的谐波频谱分析技术适用于低重复频率光脉冲的抖动测量;基于相位比较检相器的相位噪声技术测量精度高、动态范围大、结果可靠,对于高重复频率的超短光脉冲,建议选用相位噪声测量技术测量激光脉冲的时基抖动。 相似文献
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利用掺镱双包层光纤放大器对百皮秒单脉冲(重复频率1 Hz)进行了放大实验,分析了其放大过程中自相位调制对脉冲时域和频域特性的影响.采用小芯径(纤芯直径6.5 μm)掺镱双包层光纤作为增益介质,研究了放大器中从小信号增益到增益深度饱和整个变化过程中自相位调制引起的频谱展宽效应,并分析了SPM引起的脉冲波形和频谱光强分布的变化.采用布喇格光纤光栅扫描方法观察了其光谱的变化,解决了单脉冲光谱不易测量的问题.结果表明:区别于无源光纤中的自相位调制效应,随着抽运功率的增加,百皮秒脉冲放大过程中增益饱和效应和自相位调制效应的共同作用,使脉冲频谱分裂成不对称双峰结构,且光强分布先向短波后逐渐向长波集中. 相似文献
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合成孔径激光雷达具有成像分辨率与探测距离无关的特点。与微波相比,激光波长至少小3个数量级,因此能实现更高分辨率的成像,但是波长更短时成像更容易受系统自身引入的相位误差的影响,从而导致成像模糊。为了消除该误差对成像的影响,提出采用光学锁相环(OPLL)技术抑制编码合成孔径激光雷达的系统随机相位噪声。在发射端,激光信号经编码信号驱动的电光调制器调制后用于探测目标;在接收端,对接收到的回波信号与本振光进行正交解调。所提出的基于OPLL的编码合成孔径激光雷达工作在1550 nm波段,调制带宽为1.25 GHz,脉冲重复频率最高可达1.2 MHz/s。实验结果表明,在没有OPLL时,系统随机相位波动大于100 rad,采用OPLL后,系统内部相位稳定度优于0.1 rad,大幅度提高了系统自身的相位稳定度和方位向合成成像精度。 相似文献
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Blind parameter estimation of pseudo-random binary code-linear frequency modulation signal based on Duffing oscillator at low SNR 下载免费PDF全文
《中国物理 B》2021,30(5):50708-050708
Conventional parameter estimation methods for pseudo-random binary code-linear frequency modulation(PRBCLFM) signals require prior knowledge, are computationally complex, and exhibit poor performance at low signal-to-noise ratios(SNRs). To overcome these problems, a blind parameter estimation method based on a Duffing oscillator array is proposed. A new relationship formula among the state of the Duffing oscillator, the pseudo-random sequence of the PRBC-LFM signal, and the frequency difference between the PRBC-LFM signal and the periodic driving force signal of the Duffing oscillator is derived, providing the theoretical basis for blind parameter estimation. Methods based on amplitude method, short-time Fourier transform method, and power spectrum entropy method are used to binarize the output of the Duffing oscillator array, and their performance is compared. The pseudo-random sequence is estimated using Duffing oscillator array synchronization, and the carrier frequency parameters are obtained by the relational expressions and characteristics of the difference frequency. Simulation results show that this blind estimation method overcomes limitations in prior knowledge and maintains good parameter estimation performance up to an SNR of-35 d B. 相似文献
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Localization mechanisms and location methods of the disturbance sensor based on phase-sensitive OTDR
The mathematic models of the disturbance sensor based on phase-sensitive optical time-domain reflectometry (OTDR) are established. On the basis of the models, the localization mechanisms of the conventional location techniques for phase-sensitive OTDR are simulated. The simulation results indicate that the frequency characteristics of the backscattered signal at disturbance region are different from other regions. According to the results, a novel location method relied on power spectrum analysis is described. The experiment is then conducted over a monitored length of 9 km with a spatial resolution of 100 m, which demonstrates that the described location approach can significantly enhanced signal-to-noise ratio (SNR) to 19.4 dB. 相似文献
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针对窄带光纤参量放大(FOPA),区别于以往增益谱的大增益斜率区域,研究了FOPA增益谱边带脉冲信号的快慢光特性.首先从理论上推导出了小信号增益条件下信号延时量的解析表达式;其次,在低抽运功率条件下(1 W),实验研究了10 Gb/s伪随机二进制序列脉冲信号在FOPA增益谱边带的延时特性,实验结果与理论计算基本符合;最后,通过分析研究抽运光功率、光纤色散及非线性系数等参数对信号延时量的影响规律,可以为FOPA增益谱边带的快慢光延迟线的设计提供参考. 相似文献
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A. V. Gostev S. A. Ditsman V. V. Zabrodskii N. V. Zabrodskaya F. A. Luk’yanov E. I. Rau R. A. Sennov V. L. Sukhanov 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(11):1456-1461
Semiconductor detectors of backscattered electrons are basic elements of all modern scanning electron microscopes. Their quality is determined by the properties of planar p-n junctions and the parameters of the protective layer on the detector surface. The main characteristics of semiconductor detectors are considered, their response functions are calculated, and the threshold signal cutoff energies are found both for a monoenergetic electron beam and for detection of the total energy spectrum of backscattered electrons. The experimental results are in good agreement with the computational model data. 相似文献
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Numerical simulation methods are described for the spectral characteristics of an acoustic signal scattered by multiscale surface waves. The methods include the algorithms for calculating the scattered field by the Kirchhoff method and with the use of an integral equation, as well as the algorithms of surface waves generation with allowance for nonlinear hydrodynamic effects. The paper focuses on studying the spectrum of Bragg scattering caused by surface waves whose frequency exceeds the fundamental low-frequency component of the surface waves by several octaves. The spectrum broadening of the backscattered signal is estimated. The possibility of extending the range of applicability of the computing method developed under small perturbation conditions to cases characterized by a Rayleigh parameter of ≥1 is estimated. 相似文献
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All-fiber digital heterodyne interferometry is a laser metrology technique employing pseudo-random codes phase modulated onto
an optical carrier signal. In this heterodyne interferometer system, the optical signal includes signal reflected and transmitted
from the sample, respectively. Compared with the conventional heterodyne interferometry, this enhanced optical system has
much higher measurement sensitivity, and can distinguish the signal which reflected from the front and the rear surface of
the sample. Analysis and simulation for the digital heterodyne interferometry are presented. It takes approximately 4 s to
scan the whole surface with the diameter of 300 mm. The thickness profile of the sample is obtained in the experiment. The
discussion about the experiment is given finally. 相似文献
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由于探测光脉冲宽度受到限制,布里渊光时域反射仪(BOTDR)在对光纤上的应变进行分布式测量时,空间分辨力只能达到1 m。针对布里渊光时域反射仪单次采样接收背向布里渊散射信号(BBS)需要一定的时间,提出了基于等效脉冲光的多洛仑兹拟合法以提高其应变测量的空间分辨力。该方法将探测光脉冲在布里渊光时域反射仪完成单次采样所需的时间上进行积分,将积分函数作为等效脉冲光的表达式,再根据等效脉冲光的形状将布里渊光时域反射仪接收到的背向布里渊散射谱(BBS)细分,并对它进行多洛仑兹迭代拟合,准确求得每个细分布里渊散射谱的中心频率,进而利用光纤中布里渊频移与应变的对应关系,得到光纤中与细分布里渊散射谱对应的细分光纤单元上的应变情况。实验结果表明,利用这种方法,可使布里渊光时域反射仪应变测量的空间分辨力提高至0.05 m。 相似文献
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为了减小通信信息对一体化波形模糊函数的影响,以连续波信号为基础,提出了一种基于扩频的多OFDM符号调制的雷达通信一体化信号模型,并分别从波形以及雷达模糊函数的角度对其进行分析。通过对通信信息预扩频后采用OFDM调制的方法,可显著改善一体化信号的模糊函数性能,降低距离维旁瓣。理论分析表明,一体化信号的距离旁瓣由所用伪随机编码序列的自相关、互相关特性及调制的通信信息共同决定,为波形的性能改进提供了指导方向。仿真结果表明扩频因子、子载波数目、数据长度的不同取值对雷达通信一体化信号的距离维模糊函数的旁瓣的影响,为优化一体化信号的性能提供依据。设计的雷达通信一体化信号模型可有效改善对通信信息和多普勒频移的敏感性,满足雷达探测波形要求。 相似文献