不同海况下雷达目标检测性能分析

海杂波是海表面电磁散射的回波,其产生机理复杂且强度较高,会对雷达探测目标信息造成不利影响。为了评估实际应用场景中海杂波对雷达目标检测的影响,该文基于现有雷达参数及TSC后向散射系数模型设定信号检测门限,对不同海况下雷达信杂噪比进行分析和评估。根据分析结果可以预测不同海况下雷达的工作性能,为后续设计雷达信号处理方法抑制杂波提供参考。     

地杂波与杂波对消技术

现代雷达一般在强电磁干扰环境下工作，但是由于雷达天线波束比较窄，在任一时刻相当于定向辐射，因此对雷达产生实质性影响的信号主要是雷达的泄漏信号和近物反射的信号。特别在雷达低仰角工作时，回波信号远大于有用目标的回波信号，其差别可大干80dR。如此巨大的杂波信号要求接收机信道要具有很大的动态范围，强信号使得数字化信道无法实现。本文分析了固定杂波和目标回波，总结出了它们之间的异同点。根据固定杂波和目标回波的特点上设计出了杂波对消器，并可以用数模混合电路和模拟电路分别实现。     

野战型雷达接收机噪声系数测试仪

本文阐述了野战型雷达接收机噪声系数测试仪的设计思想、结构特点、工作原理测试仪的使用方法。重点介绍应用新器件、新技术实现对雷达接收机噪声系数的测试。     

野战型雷达接收机器噪声系数测试仪

本文阐述了野战型雷达接收机噪声系数测试仪的设计思想、结构特点，工作原理、测试仪的使用方法，重点介绍应用新器件、新技术实现对雷达接收机噪声系数的测试。     

软件化雷达信号检测系统的设计与实现

雷达回波经接收机转化为视频后,形成的大容量的数据对系统的实时性和可靠性要求较高,为此,本文给出了一种在实时操作系统VxWorks平台下建立某雷达信号检测系统的设计方案,描述了雷达信号检测在VxWorks中的多任务架构设计和实现。     

基于FSE序列的MRI设备性能测试的探讨

本文对国家新制定的《医用磁共振系统校准规范(征求意见稿)》进行验证;分析并探讨快速自旋回波序列(FSE)代替自旋回波序列(SE),对磁共振设备性能测试的可行性;依据征求意见稿的测试条件与计算方法,对该设备进行性能测试,并分别采用自旋回波序列(SE)和快速自旋回波序列(FSE)扫描SMR-170模体,对成像参数进行对比分析。实验证明：在征求意见稿指定的性能测试参数条件下,SE序列对设备的性能测试具有可行性。     

基于火箭橇弹道的北斗接收机动态仿真测试

针对北斗接收机动态测试的问题,提出基于火箭橇弹道的北斗接收机动态仿真测试技术。该方法主要研究如何在火箭橇运动的加速度曲线的基础上通过多项式滤波、辛普森分段复化积分及坐标转换建立导航信号模拟器可输入的弹道仿真模型,并利用模拟器对两款可接收不同卫星信号的接收机开展仿真测试。通过对比仿真模型数据和接收机的解算数据计算动态定位、速度误差。误差结果反映接收机的动态性能,说明这种方法可以作为对北斗接收机动态测试的有效手段。     

岸基雷达的海杂波特性分析及抑制方法研究

介绍岸基雷达的海杂波幅度分布、相关性、海杂谱和与海杂波反射面积相关的参数等特性,针对这些特性提出与岸器雷达系统设计相应的海杂波抑制措施,并重点研究基于雷达回波相关特征的海杂波抑制方法,仅作参考。     

一种AFS接收机的设计

文中对AFS接收机主要技术指标进行较详细的分析,给出一种AFS接收机的设计方法:采用接收通道、频率控制电路、对数放大电路、干扰分析组件来分析和处理干扰信号,电路简捷,且具有动态大、快速捷变频等特点.该AFS接收机在阵列多波束雷达、机载相控阵雷达中得到广泛应用.     

714CD型天气雷达回波关联故障浅析

回波作为714CD型天气雷达性能的最直观表现之一,往往能够成为故障判断的切入口,本文从雷达的运行原理、信号流程着手,通过对雷达各分系统的功能剖析,结合赤峰市新一代天气雷达历史故障实例,浅析雷达分系统与回波故障的关系。     

A Novel Method of Distance Measurement Based on Pulse Position Modulation and Synchronization of Chaotic Signals Using Ultrasonic Radar Systems

This paper deals with a novel method of transmission and receipt of a signal based on both the property of two chaotic systems generating the same chaotic signal when they are synchronized and the property of pulse position modulation (PPM) to be insensitive to the distortions of the transmission channel. The method is discussed in the context of ultrasonic radar systems, in which the transmitter and receiver, which consist of ultrasonic sensors, are near each other, and the received signal consists of the transmitted signal reflected by an obstacle. A reference sinusoidal signal is superimposed to a chaotic signal generated by a master chaotic system, and the whole signal is modulated according to the PPM method and transmitted by the sensor. The received signal is demodulated, and the demodulated signal forces a slave chaotic system to generate the chaotic signal embedded in it, which allows recovery of the sinusoidal signal by subtracting this chaotic signal from the demodulated echo. The difference of the phases of the reference sinusoidal signal and the recovered sinusoidal signal allows computation of the time of flight of the signal and, consequently, the distance of the radar system from the obstacle. The novel method is illustrated and tested by both simulation and experiments. The interference problem between the considered radar system and other radar systems ( crosstalk) is also addressed, and a solution is proposed to avoid it.     

基于经验模态分解的管道超声回波信号噪声消除

在管道超声无损检测中,超声回波信号往往受到电子噪声、结构噪声等噪声的影响,所以在分析缺陷回波信号时,必须对回波信号进行去噪处理.本文提出了一种新型的基于经验模态分解的方法对超声回波信号进行了良好的消噪处理.通过计算,超声回波信号的信噪比大约提高了11 dB.     

基于超声相控技术的船舶吃水测量方法

为了解决内河船舶因超吃水引起的通航阻塞以及船舶安全问题,提出一种基于超声相控技术的船舶吃水测量方法。以超声相控技术为理论基础,通过控制一维线型超声相控阵列换能器发射聚焦声波,实现对目标船舶的相控扫描,获取各扫描点的回波信号;利用匹配滤波算法对回波信号进行滤波,改善信噪比;利用阈值法提取回波信号的时延;利用渡越时间法,计算出扫描点到各发射振元中心的距离,利用双曲交汇法计算出扫描点的空间坐标;分析回波信号幅值和扫描点位置坐标即可得到船舶吃水深度。为验证方法的可靠性,搭建了小比尺船模吃水测量实验系统,分析了110~140 mm不同吃水深度下的实验结果,计算了实际吃水与测量吃水间的相对误差。实验结果表明,使用匹配滤波法处理后的回波信号信噪比从15.26 dB提高至36.39 dB,实验时,最大相对误差出现在船舶实际吃水130 mm时,绝对误差为2.3 mm,相对误差为1.7%。     

齿轮焊缝超声检测信号降噪方法研究

汽车变速箱齿轮焊缝的超声检测过程中,超声回波信号存在信噪比较低导致误检率较高的问题.该文根据齿轮焊缝超声检测信号中噪声的特点,提出利用经验模态分解进行滤波的方法.针对经验模态分解过程中出现的虚假频率现象,提出镜像扩展的解决算法,把镜内信号映射成一个周期性的信号,抑制端点效应,避免虚假频率现象.仿真结果表明该方法可有效提...     

Quality enhancement of image generated with bistatic ground based noise waveform SAR

A new method for quality enhancement in a noise synthetic aperture radar (SAR) image and the first results of its application to the SAR image generated with the use of a bistatic Ka-band ground-based noise waveform SAR (GB NW-SAR) are presented. A SAR image generated with a noise SAR suffers from the masking effect which is tied to residual random fluctuations in noise radar response from bright scatterers in the scene. This is similar to the masking effect present in the deterministic waveform SAR when the signal sidelobes of echoes from bright scatterers may mask the main response from a weaker target. The procedure presented is a variation of the CLEAN algorithm. Knowing precisely the emitted signal and finding positions of the strongest scatterers one may model the echo signal originated from a selected scatterer. Extraction of the modelled signal from the received one reduces the residual fluctuations and makes it possible to clean the image and increase its dynamic range. The final image is constructed from the cleaned signal and the previously removed strongest scatterers. A theoretical background is provided to the proposed procedure and its application to enhance the SAR image using simulated data as well as data generated by the Ka-band bistatic GB NW-SAR is demonstrated. The GB NW-SAR, recently developed and tested in LNDES IRE NASU, may operate in CW and pulse random signal regimes for short range applications.     

基于小波收缩策略的一种新阈值去噪方法研究

分析了信号处理中相干噪声的特点,针对小波变换标准软阈值去噪法处理相干噪声能力相对差的弱点,介绍了一种基于SURERisk理论建立的自适应阈值去噪法,但其数字计算能力较差。基于同样理论,提出一种新的阈值函数,具有二阶导数和实际应用数字特性。并在此基础上确定了自适应阈值计算方法,建立了新的阈值去噪法,可用于去除相干噪声。计算机仿真表明,对于受相干噪声干扰的数字信号,该方法能较大提高信噪比,较好恢复信号。     

基于小波变换的反卷积技术

为了提高薄层复合材料超声无损检测(UNDT)中A扫描信号时域分辨率,提出一种基于小波变换多分辨率分析的反卷积技术新方法。针对传统反卷积技术在信噪比(SNR)降低时提高时域分辨率能力有限以及稳定性较差的缺点,将小波变换应用到反卷积技术中,对超声脉冲回波信号进行不同频带内分解,选取其中一个低频带内信号单支重建后,将传统反卷积技术应用到所选信号进行处理。计算机模拟和实验结果表明,与传统反卷积技术相比,该方法在提高时域分辨率（特别是低信噪比时）能力方面有较大改观。     

基于小波变换的裂谱分析法

 为了提高超声无损检测（UNDT）和无损评价（UNDE）中基础数据的信噪比（SNR）,提出了一种基于小波变换多分辨率分析的裂谱分析新方法．该方法在分析传统裂谱分析（SSP）方法原理及其局限性的基础上,通过采用小波变换多分辨率分析能力将原始超声回波信号进行等Q子带分解,然后按照一定的信噪分离规则来消除噪声,达到提高信噪比的目的．实验结果表明,与传统裂谱分析方法相比,该方法提高了消噪性能的稳定性,增强了湮没晶粒(或其他散射体)散射中的缺陷回波信号能力．     

Signal matching wavelet for ultrasonic flaw detection in high background noise

The wavelet transform (WT) is widely used in ultrasonic flaw detection (UFD) systems because of its property of multiresolution time-frequency analysis. Those traditional WT-based methods for UFD use a wavelet basis with limited types to match various echo signals (called wavelet matching signals), so it is difficult for those methods to achieve the optimal match between echo signal and wavelet basis. This results in limited detection ability in high background noise for those WT-based methods. In this paper, we propose a signal matching wavelet (SMW) method for UFD to solve this problem. Unlike traditional UFD systems, in the proposed SMW, the transmitted signal is designed to be a wavelet function for matching a wavelet basis. This makes it possible to obtain the optimal match between the echo signal and the wavelet basis. To achieve the optimal match from the aspect of energy, we derive three rules for designing the transmitted signal and selecting the wavelet basis. Further, the parameter selection in applying the proposed SMW method to a practical UFD system is analyzed. In addition, a low-rate discrete WT structure is designed to decrease the hardware cost, which facilitates the practical application of the proposed SMW. The simulation results show that the proposed SMW can efficiently detect flaws in high background noise even with SNR lower than -20 dB, outperforming the existing methods by 5 dB.     

基于经验模态分解的超声波管外测压信号去噪

在超声波管外测压中,回波信号往往受到噪声的干扰,所以在提取信号特征时,需对回波信号进行去噪。提出了一种基于经验模态分解（EMD）的超声波信号去噪方法,首先利用EMD求出信号的本征模态函数（IMF）,然后通过对比分析,利用反映信号主要特征的模态分量对信号进行重构以实现去噪。实验结果表明,该方法能够有效地去除噪声,提高超声回波信号的信噪比。