低频噪声源的测试方法

介绍了针对低频噪声源三种参数的测试方法.讨论了低频噪声源的最大输出功率、噪声输出幅度以及噪声带宽测试的实现途径.     

基于梳状谱发生器的毫米波相参脉压模拟器

研制了一种基于梳状谱发生器的全相参脉冲压缩毫米波雷达目标射频回波模拟器。通过与被测雷达共用基准频率参考信号,结合梳状谱发生器及DDS,保证了输出信号和雷达发射信号的相参性和快速频率跳变,实现较好的相位噪声性能和杂散抑制。该系统输出为Ka波段,带宽2GHz,步进100kHz,相位噪声小于一80dBc@1kHz,跳频时间小于2μs。     

Comments on "Optimum Bandwidth of a Low-Pass Filter for Detection of a Pulse in Nonstationary Noise"

In a recent correspondence1 a calculation of the optimum bandwidth of a low-pass RC filter for the detection of a pulse signal in nonstationary noise was presented. The purpose of this correspondence is: 1) to point out additional references to the work which has been conducted in the stationary noise case, and 2) to present an interesting alternate derivation of the expected output noise power for the nonstationary noise case.     

一种低相位噪声频标分配放大器的设计实现

随着测控试验系统对低相位噪声频标指标要求的不断提高,国内市场上的绝大部分相关产品已无法满足要求。本文给出一种低相位噪声频标分配放大器的设计实例,实例采用基于MAX4104增益放大和LMH6609分配放大的2级放大电路结构,充分利用MAX4104的低相位噪声放大特性和LMH6609的大电流驱动分配特性,同时采用先进的PCB（印制电路板）设计技术和有效的电路噪声抑制手段,实现了频标的低相位噪声分配放大输出。最后对实例设计进行了验证分析。本设计相关产品已广泛应用于卫星地面测控系统的时频分系统中,实践证明设计指标满足航天测控和武器试验用户的要求。     

数字闭环光纤陀螺的调制串扰误差

 通过分析数字闭环光纤陀螺的阶梯波调制信号与输出死区、周期噪声干扰及小角速度漂移的关系,提出了调制串扰误差的概念。指出调制信号与探测器输出信号之间的电交叉耦合及调制信号产生的调制误差是产生调制串扰误差的干扰源。将调制串扰通道模型简化为比例环节和部分积分环节,并和光纤陀螺理想模型结合,建立了光纤陀螺调制串扰误差模型,利用该模型推导出了产生死区的条件及周期噪声干扰和小角速度漂移造成的输出偏差表达式,并对周期噪声的幅值、频率与陀螺输出量级、带宽之间的关系进行了定量分析。调制串扰误差的仿真和实验结果与理论分析结果基本一致,验证了调制串扰误差模型的正确性。     

Operational modal parameter identification with colored noise excitation

Operational Modal Analysis (OMA) refers to the modal analysis of a structure in its operating state. The advantage of OMA is that only the output vibration signal of a system is used in the analysis process. Classic OMA is based on the white noise excitation assumption and many identification methods have been developed in both time domain and frequency domain. But in reality, many environmental excitations are not compliance with the white noise assumption. In this paper, a method of half power bandwidth analysis is applied to power spectrum analysis to deal with the colored noise and trapezoidal spectral excitation. The modal frequencies and modal damping ratios are derived and the error caused by trapezoidal spectral and colored noise excitation are analyzed. It is proved that the OMA algorithm based on the white noise assumption can be extended to the colored noise environments under certain conditions. Finally, a simulation example with a cantilever beam and a vibration test with four kinds of colored noise and trapezoidal spectrum base excitation are carried out and the results support the proposed method.     

基于DDS驱动PLL结构的X波段雷达信号频率综合器

给出了一种基于DDS驱动PLL的频率综合器结构。该结构采用AD9854DDS芯片产生低频的参考信号,然后驱动锁相环和VCO产生X波段射频信号。实验和测量结果表明,该频率综合器具有较宽的工作带宽和较低的相位噪声,可以用来产生连续波、线性调频信号和频率捷变信号用于X波段雷达信号的仿真。     

FM Laser Noise Effects on Optical Doppler Radar Systems

A detailed analytical study is made of the effect of FM noise on a laser carrier frequency which is used in a Doppler radar. Both long-term drift and short-term FM noise are considered. The case of high modulation index of the noise is permitted by the theory. Forward as well as slanted beams are examined. Curves have been calculated for each case to allow rapid estimates of the bandwidth requirements to accomodate the laser noise. This, in turn, will give the resolution limit of the radar caused by that noise. A summary of the results is given.     

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...     

超流体物质波干涉陀螺仪的噪声研究

 陀螺仪的精度与其噪声密切相关,为开发新型高精度的超流体物质波干涉陀螺仪,必须对其噪声进行系统研究。根据超流体陀螺噪声产生的机理,分析了该陀螺噪声的来源,并把超流体陀螺的噪声类型归纳为:热、锁定值波动、温度波动、频率波动和检测元件等。在建立了各噪声数学模型的基础上,利用超流体陀螺通用的参数,对其噪声进行了分析。分析结果表明:热噪声与陀螺的结构参数和工作参数相关,与被测角速度无关;锁定值波动噪声只与结构参数相关;其他噪声与结构参数、工作参数和被测角速度都相关;检测元件、频率波动和锁定值波动噪声是构成超流体陀螺输出噪声的主要因素;在角速度变化量的范围内,超流体陀螺的输出噪声非线性变化,在1 Hz的带宽下,其变化范围为-7到-6次方的数量级。     

高频振荡器噪声分析

 本文将高频振荡器视为具有深度正反馈噪声放大器。对它分析,给出正弦波信号的谱、等效带宽及相位噪声谱;同时还提出诸如高频振荡器内部产生的随机游走噪声形成机理等新看法。     

A noise insensitive solution to an ambiguity problem in spectralestimation

The instantaneous frequency measurement (IFM) receiver is capable of measuring the center frequency of single frequency pulses over a wide range (bandwidth) of center frequencies. Because of various constraints, the frequency resolution requirement results in long correlator delay times that reduce the single correlator bandwidth. A large bandwidth can be achieved only if two or more correlators are used. The problem of estimating frequency is then reduced to the simultaneous congruence problem of number theory. A design procedure is presented for solving the congruence problem for a given amount of noise protection, a stated frequency resolution, a minimum bandwidth, and a fixed level of precision (bits) in the IFM receiver     

宽带信号角跟踪和四通道单脉冲方案

分析了宽带信号角跟踪的特殊问题及其实现方案。基于互相关函数的角误差检测方法,推导出了在非相关噪声及相关噪声背景下差路信号的输出信噪比及其角度随机误差的数学表达式,进而给出了带宽增益和最佳带宽的概念,以及提高输出信噪比的方法。为了在低载噪比（C/N）时获得角捕获所需要的和路信号以及差路的归一化信号,提出了四通道单脉冲方案。最后归纳出了低C/N时宽带信号角捕获和角跟踪的几种方法并提出了建议。     

The Effect of Hard Limiting an Angle-Modulated Signal Plus Noise

The effect of hard limiting an angle-modulated signal plus narrow-band Gaussian noise is analyzed. Several examples are considered?sinusoidal angle modulation, Gaussian angle modulation, and biphase angle modulation. The general conclusion is that when a zonal band-pass filter is used, which rejects dc and second harmonics, an angle-modulated signal plus Gaussian noise provides the same output signal-to-noise ratio as shown by Davenport for a CW signal plus Gaussian noise. However, when a narrow bandpass filter is used, which has a bandwidth approximately equal to the input angle-modulated signal, an angle-modulated signal plus Gaussian noise has a better output signal-to-noise ratio than a CW signal plus Gaussian noise.     

Theory of LDV Tracking Systems

The application of frequency-tracking systems to the analysis of laser doppler velocimeter (LDV) signals degraded by background noise has been studied both theoretically and experimentally. Expressions are derived for both the correlation function and the expected value of the phase derivative in the general case of noise off center from the Doppler frequency, and these results are specialized to specific cases of practical interest. Laboratory measurements of output signal-to-noise ratio (SNR) and dc error, for varying input SNR and noise center frequency offset, show good agreement with the theoretical predictions.     

对旋轴流风机降噪措施的实验研究

针对一台自行设计的高效对旋轴流风机噪声高的缺点, 分析了主要噪声源及噪声的频率特征;并用消声声衬及适当增加管道长度的方法进行了大量的实验研究, 取得了良好的效果。总声压级由101dB(A)降至88dB(A)。      

Detection of Known Signals in Nonstationary Noise

The basic design of a nonlinear, time-invariant filter is postulated for detecting signal pulses of known shape imbedded in nonstationary noise. The noise is a sample function of a Gaussian random process whose statistics are approximately constant during the length of a signal pulse. The parameters of the filter are optimized to maximize the output signal-to-noise ratio (SNR). The resulting nonlinear filter has the interesting property of approximating the performance of an adaptive filter in that it weights each frequency band of each input pulse by a factor that depends on the instantaneous noise power spectrum present at that time. The SNR at the output of the nonlinear filter is compared to that at the output of a matched filter. The relative performance of the nonlinear system is good when the signal pulses have large time-bandwidth products and the instantaneous noise power spectrum is colored in the signal pass band.     

Mismatched Filtering of Sonar Signals

A replica correlator (matched filter) is an optimum processor for a receiver employing a pulse of continuous wave (CW) signal in a white Gaussian noise background. In an active sonar, however, when the target of interest has low Doppler shift and is embedded in a high reverberation background, this is not so. High sidelobes of the correlator frequency response pass a significant portion of the signal contained in the mainlobe of the reverberation spectrum. In order to reduce the sidelobes of the correlator output spectrum and at the same time keep the increase in its 3 dB bandwidth to a small amount, we propose lengthening of the replica of the transmitted signal and weighting it by a Kaiser window. It is demonstrated that by extending the weighted replica by 50 percent compared with the transmitted signal, it is possible to reduce the sidelobe levels to at least 40 dB below the mainlobe peak, with the concomitant increase of the 3 dB band-width by less than 5 percent. The degradation in signal-to-noise ratio (SNR) performance for such a ?mismatched? filter receiver with respect to the matched filter is less than 1.5 dB.     

低速风洞的消声降噪改造设计研究

对搬迁改造中的西北工业大学低（变）湍流度风洞进行了降噪设计研究。根据低速风洞噪声的机理及频率特性和该风洞的结构形式及风扇转速,采用两种降噪方法——主动降噪和被动降噪,对风洞进行降噪设计。主动降噪设计方法包括风扇动力段的气动、结构及振动的声学优化设计,被动降噪设计则采用在风洞洞体上安装微穿孔板,利用共振吸声技术进行降噪。结果表明：结合上述措施,55m/s风速下,相同测点和相同运行条件下,风洞噪声值下降约30%;76m/s最大设计风速下,风洞环境噪声被控制在78dB以下。