数字域谱估计的GNSS系统信号带宽测试方法

针对传统的单载波扫频法不适于GNSS（全球导航卫星系统）信号生成通道的带宽测量的问题,提出了采用数字信号处理的信号带宽方法.对实际导航信号进行高速采样,在数字域对采样的导航信号和本地数字生成的理想导航信号进行频谱估计和计算,从而得到GNSS信号带宽.分别使用周期图法和Welch法谱估计,对提出的测试方法进行仿真.仿真结果表明,采用Welch法进行理想信号和实际信号谱估计,对谱估计后的结果进行计算,可以完成GNSS信号带宽精密测量,在Welch法估计参数设置合理的情况下,GNSS信号带宽估计的准确度可以达到99.9％以上.     

民用航空发动机传感器信号重构方法及其应用

以转速传感器为例,研究了基于信号合成的航空发动机高精度的传感器信号重构方法.针对民用大涵道比涡扇发动机,分析选取了用于转速传感器信号合成的参数,完成了传感器信号全包线稳态合成和动态补偿的原理分析及设计.利用发动机控制系统全数字仿真平台,对信号合成的结果进行了仿真测试.结果显示:转速合成信号的稳态误差不超过1%,动态误差不超过3%,表明该传感器信号重构方法具有高精度.      

一种利用非线性预报的动力学降噪法

建立在背景信号能够用低维动力学系统建模的基础上,利用待分离信号与干扰背景的频谱差异,通过连续拟合的两层RBF网来构造非线性逆滤波器分离信号与背景噪声.文中给出了以仿真混沌信号为背景与单频、调频脉冲信号相分离的示例,证明了该算法实现信号分离的可行性.     

雷达信号的模糊聚类分选方法

随着现代电子战的激烈对抗,复杂体制雷达迅速增加并逐渐占居主导地位,侦察接收机接收到的雷达信号更加复杂和密集.为克服传统信号分选算法的局限性,采用基于模糊聚类分析的雷达脉冲信号分选方法,此方法能利用雷达信号的特征参数有效地分选出非常规和常规雷达信号.首先介绍模糊聚类的基本原理,并进行信号分选仿真实验.仿真结果证明分选结果较理想,验证了此方法的有效性和可行性.该方法易编程实现,适用于处理大量数据,是一种解决密集复杂脉冲信号分选问题的新途径.     

硬车削过程中声发射和振动信号的监测及分析

为了对硬车削过程进行监测和分析,本课题建立了一套基于虚拟仪器的信号采集系统,采集模具钢硬车削加工过程中的声发射和振动信号.对声发射和振动信号进行小渡变换并重构后,发现硬车削过程中的声发射和振动信号都与转速密切相关.随着转速的增高,淬硬钢的声发射信号也随着增大,但振动信号却随之减小.     

虚拟仪器在导弹测试发控系统中的应用

设计的基于PC/104嵌入式计算机系统的虚拟仪器,具有测量各种电学信号和时频信号功能;同时具有输出各种模拟信号、不同频率和幅值的脉冲信号及各种波形信号的信号源功能.其测量精度高,输出信号精度高,可用于导弹测试发控系统对其进行各种测试和控制.     

基于可编程逻辑器件的增量式编码器信号 去抖方法的实现

在伺服系统中,实时、准确地获得编码器反馈信号对伺服闭环控制至关重要.从增量式编码器的结构原理出发,分析引起其输出信号抖动的可能原因.根据D触发器逻辑功能,设计了一种基于可编程逻辑器件的增量式编码器信号去抖方法.实验结果表明,该方法能有效滤除信号的边沿抖动和干扰毛刺.     

滚动轴承故障诊断的品质因子可调小波重构方法

针对轴承早期故障诊断困难的问题,提出了基于信号共振稀疏分解与品质因子可调小波重构的滚动轴承故障诊断方法.该诊断方法首先对轴承故障信号进行共振稀疏分解获得高共振分量和低共振分量;然后对低共振分量进行品质因子可调小波重构,并结合峭度分析,筛选出最佳分析信号;最后对最佳分析信号进行希尔伯特解调分析,从而提取滚动轴承故障特征信息.通过对仿真信号和实际故障信号进行分析,该方法能有效提取轴承故障信号中的冲击成分,凸显故障特征.      

基于位势函数的欠定盲源分离识别诊断方法

对观测器数目小于源信号数目的欠定盲源分离进行了研究,提出了一种基于位势函数的稀疏信号欠定盲源分离方法,该方法从能量的观点出发,通过构造位势函数,将寻找混合信号在直线方向上的聚类问题转化为寻找累积位势函数的局部极大值问题,从而准确的估计出源信号数目和混合矩阵,克服了通常的基于k-means聚类的混合矩阵估计法需预先给定源信号数目的缺点.利用仿真信号检验了该方法的有效性.基于信号频域稀疏性假设,将该方法应用于欠定条件下的滚动轴承振动故障信号的盲分离,较好地分离出了故障信号.      

基于Doppler估计的弹载接收机抗欺骗干扰研究

GNSS接收机在军用方面尤其是高精度制导武器中的应用日益增强.针对卫星信号易受敌方欺骗信号干扰的问题,设计一种基于Doppler频率估计的弹载接收机抗欺骗干扰的方法.首先分析了欺骗干扰和真实信号的Doppler变化特点;然后在捕获阶段利用残留信号检测存在欺骗干扰的卫星编号;最后根据弹载的高动态特性,在跟踪阶段采取扩展 Kalman 滤波器(EKF)进行载波Doppler频率估计,并根据Doppler变化的相似性提取出欺骗信号.通过仿真实验验证,该方法可以有效排除欺骗信号的干扰.     

Noise factor and antenna gains in the signal/noise equation for over-the-horizon radar

A recommended form of the signal-to-noise equation that includes both internal and external system noise and signal/noise processing losses is discussed. The recommended form conforms to the internationally accepted definition of system operating noise factor but is extended to include signal/noise processing. The predetection signal-to-noise ratio (SNR) of a radar or communication system is proportional to the power gain of the transmit antenna and the directive gain of the receive antenna, and is inversely proportional to the operating noise factor of the receiving system. The operating noise factor is approximately equal to the product of the external noise factor and the signal/noise processing factor when the system is external noise limited, as is usually the case for over-the-horizon (OTH) radar.<>     

多区聚焦技术在粉末高温合金微缺陷检测中的应用

针对大厚度粉末高温合金材料中微缺陷的检测难题,采用多区聚焦检测技术,对粉末高温合金微缺陷试样进行了检测灵敏度、信噪比和C扫描成像试验,并与普通单一探头聚焦检测结果进行比较.试验结果表明,多区聚焦技术检测灵敏度高,信噪比好,对于厚度75mm粉末高温合金材料中的微缺陷具有较好的检测效果.     

一种提高单片机内嵌式A/D分辨力的方法

单片机内嵌式Ａ／Ｄ的使用要比外置式Ａ／Ｄ简单、方便，且容易获得更高的信噪比，但其分辨力相对比较低，难以满足精密测量的使用要求。本文介绍了一种提高单片机内嵌式Ａ／Ｄ转换器分辨力有效实用法，简单外转电路和单片机内部软件计算可以将原分辨力将提高１￣３倍。     

Spectrum Distortion Due to Frequency Instabilities in a Two-Way Coherent Doppler Radar

The power spectral density of the intermediate frequency signal in a coherent Doppler navigation radar is derived. The effects of antenna parameters, periodic frequency instabilities, signal two-way transit time, and transmitter frequency modulation noise are considered Several examples based on the measured frequency modulation noise of a solid-state source transmitter are presented. The results indicate the degree of loss in signal-to-noise ratio, and spectrum broadening due to an increase in signal transit time and/or frequency modulation noise.     

基于预估-反馈联合处理的射频噪声干扰抑制算法

针对强射频（RF）噪声干扰下脉压雷达目标检测概率较低的问题,提出了一种基于预估-反馈联合处理的射频噪声干扰抑制算法。首先,对回波信号进行盲源分离预处理,并利用分数阶傅里叶变换（FRFT）的特性对目标回波信号进行参数估计以及窄带滤波处理,滤除大部分干扰和噪声的能量;然后,在数据层运用M/N逻辑法进行点迹处理,并结合径向速度方向判决,实现对目标航迹的预估检测;最后,利用数据层对航迹状态的反馈实时修正滤波器参数,从而在信号层更好地滤除干扰能量,并对中断航迹进行剔除,完成射频噪声干扰的抑制。仿真结果表明：与现有射频噪声干扰抑制技术相比,所提算法具有更优的干扰抑制效果。     

Analysis of a Signal Processor for an Antenna Array

A signal processor that provides ratio-squared predetection combining, has been investigated for application in an adaptive antenna array. The analysis and experimental data presented here pertain to the signal processing gain when the antenna array is illuminated by a coherent signal source and a partially coherent noise source. For a noise source which is coherent, the processing gain depends on relative strength of the signal and noise, relative directions of arrival, and the usual "array factor." The array exhibits capturing effects much as in an FM receiver. The effective antenna pattern is a superposition of two beams of different magnitudes, one directed to the signal source and the other to the noise source. When the noise is partially coherent, the behavior of the signal processor is quite complex. Analytical prediction and experimental simulation measurement on a four-channel system indicate that the partially coherent noise may be regarded as the source of an incoherent noise component plus a coherent noise component with the magnitude of the latter determined by the coherence coefficient for the noise source.     

航空声学风洞3/4开口试验平台地板对远场噪声测量的影响

利用Kirchhoff-Helmholtz声学理论建立了地板声波反射问题的时域理论模型,推导了地板面上反射波的幅值函数和延迟时间的表达式,并引入了恰当的数值方法对反射声场进行求解,理论方法的正确性得到了实验结果的验证。以典型的高斯调制正弦波脉冲和连续正弦波为例,用建立的理论方法对噪声信号的传播过程和平台地板对远场噪声测量的影响进行了数值模拟研究,结果表明：地板的存在将使得远场接收到的噪声信号中出现直达波和反射波,反射波包含了中心波和边缘波。在低频段,地板宽度增加,远场噪声声压级增大;在高频段,地板宽度增加对远场总噪声级影响不明显。对于高速列车（HST）模型,车底位置的声源比车顶位置的声源在高频段受到地板反射的影响更大。     

Now You See It, Now You Don't

The signal enhancement properties of a single-loop delayline integrator (DLI) are derived for operation in the presence of correlated noise. The signal is assumed periodic with a period equal to the delay of the DLI and present only for a finite time interval. The noise is assumed additive, zero mean, statistically independent from the signal, and present for an infinite time. The noise also is assumed covariance stationary with a specified auto correlation function. Enhancement is defined as the ratio of the increase in average signal power to the increase in average noise power due to integration. The results are general in that the enhancement is derived in terms of the autocorrelation coefficients of the input noise. Plots of enhancement versus number of signal observations and feedback gain are shown for uncorrelated and exponentially correlated noise. The plots show graphically the optimum choices of feedback gain and number of signal observations for a specified auto correlation function and signal observation time. When strongly correlated noise, characteristic of 10-GHz backscatter from salt flats at low incidence angles, rather than uncorrelated noise is assumed present at the input of the DLI, an example, using DLI parameters typical of modern airborne radars, shows a degradation in the maximum achievable enhancement of 9 dB.     

噪声调制连续波雷达信号波形射频隐身特性

雷达信号波形的射频(RF)隐身性能是雷达系统能否适应现代战场环境的重要因素,雷达射频隐身信号波形设计是现代雷达系统设计中的重要课题.首先,在介绍随机噪声信号雷达原理的基础上,基于Schleher截获因子阐述了噪声调制连续波雷达信号波形的射频隐身特性.然后,分析了高斯噪声相位和频率调制连续波雷达输出自相关函数和高斯噪声相...     

Locally optimal and suboptimal signal detection in transformationnoise

The efficacy of the optimal detector of a known vanishingly small signal in additive nonwhite transformation noise is compared with that of some eleven structurally simpler suboptimal detectors. Simulation is done under various signal choices, marginal densities, and correlation functions. The block g_lo and the block combination g followed by R_v^-1 in the optimal detector structure are found to be important for good performance in constant and oscillating signals, respectively. Two suboptimal detectors with these block structures, D₈ and D₁₀, are found to perform well consistently in all situations considered. A structurally simple suboptimal detector D₂ is found to be good in the cases with less correlated noise