Time-frequency-based non-stationary interference suppression for noise radar systems

The problem addressed here is non-stationary interference suppression in noise radar systems. Towards this aim, two linear time ?frequency (TF) transforms, short-time Fourier transform and local polynomial Fourier transform are used as a means of signal representation and filtering. The noise radar return signal is a wideband random signal occupying the whole TF plane, whereas the interference signal is well concentrated in the TF plane. This implies that the filtering of the received signal can be performed by using a binary mask to excise only a portion of the TF plane corrupted by the interference. Simulations carried out on the radar return signal corrupted by extremely strong non-stationary interferences confirm the effectiveness of the proposed method.     

组网火控雷达低截获性研究

从火控雷达抗电子侦察的需求出发,研究通过组网技术降低雷达信号截获概率的方法。首先分析雷达侦察系统的前端截获概率以及影响雷达截获的因素,在此基础上,介绍基于交替间歇辐射的火控雷达组网理论,提出脉冲间隔自适应变化的辐射信号模型,并利用窗口函数对组网条件下的截获概率进行研究;最后设定参数,对三部火控雷达组网的效果进行仿真。实验结果证明:利用火控雷达组网的方法可以降低信号的截获概率,延长信号被反辐射武器截获的时间,从而获得良好的作战效能。     

Robustification of noise radar detection

A study of robust detection scheme for continuous wave noise radars is presented. The probability density function (PDF) of the noise at the input of the radar is not usually Gaussian and has heavy tails generated by impulse interferences. Although the PDF of interferences at the output of the noise radar correlator is Gaussian, impulse interferences increase the processing floor, and thus decrease the overall radar sensitivity. The proposed robustification applied to the correlator?s input signal increases the radar sensitivity in the presence of impulse interferences, and does not introduce any significant losses if the input noise is purely Gaussian.     

双基地声呐接收站散射波低截获技术

双基地声呐的接收站因散射主动信号存在暴露的风险,对此提出了基于发射声屏蔽的双基地声呐低截获技术。发射站采用垂直发射阵,利用屏蔽权对原始信号进行预处理,获得的低截获信号在接收站处被自动抵消,从而降低接收站散射信号的能量。仿真结果表明,发射声屏蔽技术能有效增加接收站散射信号到达目标处的能量衰减,而对到达接收站处的待测目标散射信号则无较大影响。该方法突破了以往低截获技术只是改变信号能量时频域分布的局限(在信号处理层面),利用多途结构真实降低了被截获信号能量(在物理层面),并适用于多种信号形式。     

Unsupervised estimation of speckle noise in radar images

Speckle in radar images has the characteristic of a multiplicative noise. In this article, two unsupervised methods are introduced to estimate the speckle noise statistics using the mean and the standard deviation of small image blocks (4 × 4, or 6 × 6 pixels). Since most radar images contain many small homogeneous areas, a scatter plot of the standard deviation versus the mean can reveal the characteristic of the noise. The blocks from inhomogeneous areas have higher values for the standard deviation, and they are scattered above the main cluster. They are considered as outliers, and should be excluded in the statistical estimation. These two methods are designed for obtaining a linear fit in the scatter plot by ignoring outliers. Several synthetic aperture radar(SAR) images are used for illustration.     

强干扰背景下的鱼雷辐射噪声信号检测方法

常规被动声纳利用宽带波束能量进行目标检测,在低信噪比、强目标干扰情况下,宽带能量检测的性能迅速降低。利用鱼雷辐射噪声信号中含有丰富线谱成分的特点,提出了一种针对鱼雷辐射噪声信号的窄带和宽带联合检测方法。通过对预成波束方向信号的窄带处理和线谱提取,利用特定频段的线谱能量对宽带波束输出进行加权,提高了线谱目标的检测能力。该方法能够有效地抑制非线谱强干扰目标,提高低信噪比信号的检测能力。仿真和海试数据处理结果验证了该方法的有效性。     

噪声干扰对被动声呐系统的影响及仿真分析

在从信号处理的角度,就干扰信号对被动声呐系统的目标信号检测、目标方位估计、接收系统饱和等方面的典型情况进行了仿真分析,定义了噪声掩盖比、方位偏离度、噪声阻塞级等参数,用以表征干扰信号对被动声呐系统的影响,并给出了典型的仿真结果。     

Hilbert-Huang transform analysis of human activities using through-wall noise and noise-like radar

Various parts of the human body have different movements when a person is performing different physical activities. There is a need to remotely detect and recognise specific human activities for applications involving anti-terrorism, hostage liberation and search-and-rescue. An ultrawideband noise radar system has been built to detect signatures of human activities. The Hilbert?Huang transform, which is used to extract the human-induced Doppler frequency shift from the received signal, facilitates the identification and recognition of various human activities. A non-stationary Doppler model is developed to describe various aspects of human motion, which compares well with measured data. The theoretical analysis and experimental results are discussed.     

Influence of noise on measurement errors in laser interference refractometers

The influence of noise in the optical and electronic channels of laser interference refractometers is subjected to a comparative analysis for several of the best-known methods used to measure the fractional part of an interference order.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 26–27, August, 1995.     

HBAR-Based 3.6 GHz oscillator with low power consumption and low phase noise

We have designed and built 2 oscillators at 1.2 and 3.6 GHz based on high-overtone bulk acoustic resonators (HBARs) for application in chip-scale atomic clocks (CSACs). The measured phase noise of the 3.6 GHz oscillator is -67 dBc/Hz at 300 Hz offset and -100 dBc/Hz at 10 kHz offset. The Allan deviation of the free-running oscillator is 1.5 × 10^-9 at one second integration time and the power consumption is 3.2 mW. The low phase noise allows the oscillator to be locked to a CSAC physics package without significantly degrading the clock performance.     

RF领域的SOI器件及低噪声放大器电路研究

从两种不同结构形式的部分耗尽器件性能研究入手,以０．６μｍ ＮＭＯＳ工艺为基础,设计并研制了在芯片内部具有高Ｑ值折平面电感的ＳＯＩ低噪声放大器电路。电路在１．５Ｖ电压下,中心频率１．８ＢＧＨｚ时峰值增益为２４ｄＢ,浮体ＳＯＩ器件结构的ＬＮＡ电路比体接触结构的ＬＮＡ电路有更高的增益和较低的噪声。     

Use of precision low noise monolithic instrumentation amplifiers at low temperatures

The FET analogue devices AD524AD and AD624AD, precision instrumentation amplifiers, have been successfully used at 77 K. The devices ceased to function when immersed in liquid helium but recovered, without damage, after warming. The gain, set by internal resistors on the chips, was almost independnet of temperature, but a small temperature dependent offset voltage was a standard feature. A pre-amplifier operating down to nitrogen temperatures can thus be implemented by a single low power integrated circuit device with minimal external components for use in cryogenics, metrology and space physics.     

Influence of noise on the noise-immunity indices of laser interference refractometers

The influence of noise on the resultant error probabilities in the detection of integral interference orders by various methods of the kind most frequently used in laser refractometry is investigated. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 46–49, March, 1996.     

The phenomenology of low noise charge sensitive amplifiers

The equations describing the noise performance of charge sensitive amplifiers have been reported in several papers. In this article, these equations are evaluated for several practical sets of amplifier parameters under a wide variety of operational conditions. These data are presented as a series of plots of noise versus amplifier shaping time. The results are compared with measurements made upon several versions of the LeCroy HQV810 amplifier hybrids.     

拖船噪声对拖线阵声呐的干扰特性分析

针对拖船自噪声影响线列阵探测性能的问题,文章研究了浅海和深海环境下线列阵对拖船自噪声的波束响应。仿真结果表明,浅海环境下拖船自噪声会在0°~20°的方位区间内产生干扰,深海环境下会在0°~20°和60°~90°两个方位区间内产生干扰,并给出了最大波束响应偏离端射方向和深海环境下远离端射方向干扰出现的主要原因。海试数据处理结果证明,深海环境下拖船自噪声确实会在相应的方位区间内产生干扰。拖船干扰在不同环境下特性分析的结果有望应用于拖船自噪声抑制算法的研究。     

利用自适应噪声抵消消除工频脉冲干扰仿真

介绍一种将自适应噪声抵消算法应用于消除周期性工频脉冲干扰的方法。该方法利用周期sinc函数仿真工频脉冲干扰信号,与白噪声叠加作为参考输入,利用最小均方(Least Mean Square,LMS)算法与归一化最小均方(Normalized Least Mean Square,NLMS)算法进行自适应噪声抵消滤波仿真实验。MATLAB仿真处理结果显示,在无增益、增益饱和、增益过饱和这三种情况下,当信噪比为3 d B时,分别用LMS算法与NLMS算法滤波后可以清晰地分辨多次回波。     

高效低噪的二维翼型优化设计

针对传统的气动优化设计未考虑气动噪声影响的局限性,开展了基于噪声预测模型的气动优化设计方法在二维翼型中的应用研究。建立了由几何外形参数化方法、径向基函数(Radial Basis Function,RBF)动网格技术、改进粒子群优化算法、气动分析方法、气动噪声预测方法等五大模块构成的优化设计系统,且各模块均采用标模算例进行验证。通过对二维SC(2)-0714超临界翼型进行了单点多目标优化设计。通过对比翼型几何形状、压力系数分布以及在不同迎角下的气动力系数曲线与总声压级的关系可得,翼型头部半径、厚度影响其头部压力峰值、压力恢复、逆压梯度等特性,从而影响升阻比和总声压级,逆压梯度越小,翼型的总声压级越小。优化结果表明,在设计状态下显著提高了升阻比、降低气动噪声,考虑气动噪声的二维翼型优化设计系统可在实际的工程设计中进行应用。     

超宽带SiGe HBT低噪声放大器的设计和分析

设计了一款具有电阻反馈的新型超宽带(UWB)SiGe HBT低噪声放大器(LNA).因为摒弃了使用占片面积大的电感,所以极大节省了放大器的芯片面积和制作成本.在新型放大器的反馈支路中,使用了复合分布式电阻和隔直流电容,代替了传统的单一电阻.用这种方式设计的LNA,仅通过调整与电容串联的电阻就可以极大地改善放大器的端口匹...