太赫兹雷达杂波背景中小目标检测研究北大核心CSCD

太赫兹雷达波长小于微波、毫米波，具有极大的信号带宽和很高的距离分辨力，适合在近距离的地杂波背景下实现目标的检测与识别。本文首先对典型的杂波概率统计模型如：Weibull模型、对数正态模型和Gamma模型进行理论分析，然后使用工作在0.36THz的太赫兹雷达系统进行杂波测量实验，获得了实际人行道路地杂波信号，并对实测数据进行了分析拟合，结果表明，Weibull分布对该太赫兹雷达系统的拟合度最优。根据杂波的概率统计模型，进一步采用基于小波多尺度阈值的杂波去除方法对实测数据处理，实现微小目标在杂波背景中的检测，实验验证了算法的有效性。     

太赫兹雷达目标HRRP特性分析

太赫兹由于其穿透性强、大带宽等优势,在雷达信号处理领域受到了广泛的关注。同时,高分辨率距离像（High Resolution Range Profiles, HRRP）在目标检测、识别以及成像等领域具有很高的应用价值,但是,针对太赫兹频段目标HRRP特性的研究却较少。本文首先从确定信号模型对太赫兹频段目标HRRP的方位角敏感性进行了研究,并利用协方差矩阵的主特征向量提取其平均HRRP,从而达到抑制目标HRRP方位角敏感性的目的。另外,根据距离单元中散射点的不同分布,对太赫兹雷达目标HRRP距离单元进行分类,并分别使用瑞利模型、赖斯模型以及混合分布模型进行统计建模。之后,使用对数积累量方法（Method of Log Cumulants, MoLC）和基于字典的随机最大期望（Dictionary based Stochastic Expectation Maximization, DSEM）算法对上述模型的参数进行估计。最后,利用研制的太赫兹高分辨率雷达系统开展了不同带宽下的复杂目标HRRP特性实验,实验结果表明,太赫兹频段下目标平均HRRP与HRRP帧内其他HRRP的相关系数高于单个HRRP,同时,对于高分辨率下的目标HRRP距离单元统计特性,可以使用混合分布模型对其进行建模。      

基于SIRV高分辨率雷达杂波建模与仿真

高分辨率雷达杂波建模与仿真是评估雷达性能的重要手段。广义复合概率密度通常用来描述高分辨率雷达杂波。在广义复合分布中,将散斑分量和调制分量均采用广义伽马(GΓ)分布来表示。采用球不变随机矢量(SIRV)进行杂波建模的优点在于能够独立控制其相关性和一维边缘概率密度。对广义复合分布和SIRV建模方法进行了讨论,在此基础上,给出了相干相关的广义复合分布的SIRV模型,利用计算机进行了广义复合分布的杂波仿真,并对杂波仿真的统计特性与理论值进行了比较。仿真结果与理论分析相吻合,说明了该模型的有效性和普适性。     

线性调频脉冲压缩雷达杂波统计模型分析

对线性调频脉压雷达杂波进行建模与仿真以及统计性分析,在雷达信号模拟领域中是非常重要的.给出了线性调频脉压雷达杂波模型以及仿真方法,并在以往对杂波特性研究的基础上,分析了杂波的分布特性、时间相关特性以及空间相关特性.对比常规脉冲雷达杂波,由于叠加效应,杂波统计特性有所不同.     

抛物面天线目标太赫兹雷达散射特性

抛物面天线目标在太赫兹波段下属于电大尺寸。基于电磁散射计算软件CST Microwave Studio来建立旋转对称抛物面天线目标的CAD模型,采用高频渐进法分别求解目标在太赫兹波段和X波段下的雷达散射截面,进而研究分析目标RCS特性,高分辨率一维距离像和逆合成孔径雷达像特性。     

太赫兹雷达RCS测量中的分时定标技术

太赫兹频段的目标散射特性测量技术是当前太赫兹雷达的重要研究方向,其中系统定标技术决定了雷达散射截面积(RCS)测量结果的准确性。使用基于微波倍频源的太赫兹宽带雷达目标散射特性测量系统,该系统由微波源经倍频后,中心频率达到440 GHz,带宽达25.6 GHz。利用光滑表面金属球为标准体,采用分时定标技术对太赫兹雷达系统进行定标,再对金属材质的战斗机模型和吉普车模型进行近场RCS测量实验,获得以上2种典型人造目标的近场RCS测量结果。测试结果与理论趋势符合良好,证明了太赫兹雷达系统RCS测量中分时定标技术的有效性。     

球载雷达地杂波建模与仿真分析

球载雷达由于平台的升高,易受到风的影响,其运动特性具有时变性,面临的强地杂波特性也会发生变化,地杂波不再是固定杂波,为了更好地处理地杂波,本文对球载雷达的地杂波进行建模。首先建立了球载雷达的空间模型和数学模型,重点分析了球载雷达平台受到风的影响对地杂波统计特性的影响,在此基础上考虑了地杂波的各种影响因素,利用零记忆非线性变换法产生随机的序列体现杂波统计特性。最后给出了球载雷达地杂波距离多普勒二维仿真并对仿真结果进行分析,进一步揭示了球载雷达地杂波特性,为下一步探讨球载雷达地杂波抑制方法提供了支撑。     

太赫兹波对抗等离子体隐身技术的探讨

等离子体隐身是隐身技术的一个新分支.在等离子体隐身机理分析中,重点探讨了等离子体折射隐身和吸收隐身特性.对太赫兹辐射具有的高穿透性、高分辨率和反隐身能力进行了研究.依据对等离子体隐身技术的局限性分析,提出了采用太赫兹雷达探测等离子体隐身飞行器的可行性及技术途径.     

FSK/PSK雷达杂波的建模与仿真

本文基于常规脉冲雷达杂波的产生原理,分析了FSK/PSK信号的特性,并对FSK/PSK雷达杂波模型进行了研究.用零记忆非线性(ZMNL)法,仿真出雷达杂波回波信号,并对其进行概率密度特性、功率谱特性和空间相关特性分析.由于子脉冲回波的叠加效应,FSK/PSK雷达杂波的统计特性与常规脉冲雷达杂波有所不同.     

FSK/PSK雷达杂波的建模与仿真

本文基于常规脉冲雷达杂波的产生原理,分析了FSK/PSK信号的特性,并对FSK/PSK雷达杂波模型进行了研究.用零记忆非线性(ZMNL)法,仿真出雷达杂波回波信号,并对其进行概率密度特性、功率谱特性和空间相关特性分析.由于子脉冲回波的叠加效应,FSK/PSK雷达杂波的统计特性与常规脉冲雷达杂波有所不同.     

See-through Detection and 3D Reconstruction Using Terahertz Leaky-Wave Radar Based on Sparse Signal Processing

We experimentally demonstrate see-through detection and 3D reconstruction using terahertz leaky-wave radar based on sparse signal processing. The application of terahertz waves to radar has received increasing attention in recent years for its potential to high-resolution and see-through detection. Among others, the implementation using a leaky-wave antenna is promising for compact system integration with beam steering capability based on frequency sweep. However, the use of a leaky-wave antenna poses a challenge on signal processing. Since a leaky-wave antenna combines the entire signal captured by each part of the aperture into a single output, the conventional array signal processing assuming access to a respective antenna element is not applicable. In this paper, we apply an iterative recovery algorithm “CoSaMP” to signals acquired with terahertz leaky-wave radar for clutter mitigation and aperture synthesis. We firstly demonstrate see-through detection of target location even when the radar is covered with an opaque screen, and therefore, the radar signal is disturbed by clutter. Furthermore, leveraging the robustness of the algorithm against noise, we also demonstrate 3D reconstruction of distributed targets by synthesizing signals collected from different orientations. The proposed approach will contribute to the smart implementation of terahertz leaky-wave radar.     

Influence of high-resolution processing on background noise distribution in ship-borne radar

When a high-resolution algorithm is applied in a ship-borne radar, its non-linearity and distributional characteristics before high-resolution processing determine the distributional characteristics of background clutter after high resolution and detector design afterwards. Because background noise before high-resolution has physical significance, the statistical model of first-order Bragg lines and second-order components of sea clutter is put forward. Then, by using higher order cumulative quantity's statistical verification of actual measured data, it is concluded that the background noise before high resolution conforms to normal distribution in a ship-borne radar. The non-linearity of the high-resolution algorithm means that the background noise after high-resolution processing conforms to non-normal distribution. Non-normal-distributed clutter mainly includes Weibull, lognormal, and K-clutter. Rayleigh clutter can be seen as a special case of Weibull clutter. These clutter types have different statistical characteristics and can be discriminated by recognition of clutter characteristics. The numerical domain's distribution after high-resolution processing is determined by an improved, minimum entropy, clutter characteristics recognition method based on the AIC rule, namely, a two-parameter domain-scanning method. This identification method has a higher recognition rate. It is verified that the background noise after high-resolution by pre-whitened-constrained-MUSIC conforms to lognormal distribution.     

基于卷积神经网络的天基预警雷达杂波抑制方法

利用天基预警雷达实现动目标指示具有重要的军事应用价值。对于天基预警雷达,其平台高速运动及受地球自转影响导致杂波复杂非平稳性,更大的波束照射区域带来更严重的杂波非均匀性,从而导致适用于机载预警雷达的传统空时自适应处理(STAP)方法无法直接应用。针对上述问题,该文分析了天基预警雷达杂波分布特性,并构建了基于卷积神经网络(CNN)超分辨谱估计的STAP处理框架。首先,利用雷达系统和卫星轨道参数,仿真随机生成不同纬度、距离门、阵元误差、杂波起伏和地貌散射系数的回波数据集;然后,设计并调优了含5个权重层的二维CNN,实现由小样本所估低分辨杂波谱到高分辨谱的非线性映射;最后,基于高分辨空时谱构造空时滤波器实现杂波抑制和目标检测。仿真实验验证所提方法在小样本条件下可实现次最优杂波抑制性能,同时所需在线运算量远低于现有稀疏超分辨类方法,因此适用于天基预警雷达实际应用。      

Preliminary study of 0.14 THz water surface clutter reflectivity at near vertical incidence angle

As the development of radar systems developed for the terahertz and higher millimeter region continues to grow, the interest in the water surface and land clutter at terahertz and higher millimeter frequencies continues to increase. An empirical model of sea clutter reflectivity is described firstly, which is valid at near vertical incidence and has small average absolute deviation compared to other empirical models. Simulated results of 0.14 THz sea clutter at near vertical incidence with this model are shown. An indoor test-bed is constructed in order to measure 0.14 THz water surface clutter reflectivity and an experiment is carried out. Initial experimental results are presented and compared to the simulation results, which partially verifies that the empirical sea clutter model still works at 0.14 THz.     

Texture and speckle in high resolution synthetic aperture radarclutter

A theoretical model of high-resolution synthetic aperture radar (SAR) clutter that is able to predict the statistical effects of spatial averaging upon homogeneous clutter that is speckled and spatially correlated is discussed. The predictions of this model, when the texture correlation was assumed to be Gaussian-shaped, were found to be in excellent agreement with experimental results using grass clutter seen through a high-resolution radar. The predictions of this model, when the texture correlation was assumed to be exponential-shaped with a slant-range cosine factor, were found to be in excellent agreement with experimental results using tree clutter seen through a high-resolution radar. The use of an exponential shape, rather than a Gaussian shape, was necessary in order to achieve the more gradual decay in spatial correlations observed with tree clutter. The use of a slant-range cosine factor was necessary in order to achieve the negative correlations that were observed with tree clutter in the slant-range, but not the cross-range, dimension     

实测海尖峰特性分析及抑制方法

在高分辨率、低擦地角、高海况以及HH极化工作方式下,雷达回波强度会明显增强,容易产生海尖峰,使得海杂波具有高幅值、非平稳和非高斯等特点,严重影响雷达对海面微弱动目标的检测.为此,该文提出一种海尖峰抑制方法,首先,给出了海尖峰判别和筛选方法,在此基础上,分析了海尖峰的幅值特性、时间相关性、多普勒谱和分数阶功率谱特性;其次,通过剔除背景中的海尖峰并选取最小平均功率水平的背景杂波作为待检测数据,能够抑制海杂波,改善SCR;最后,实测数据的实验结果验证了该方法的有效性.      

空基双基地雷达地杂波建模及特性分析

在充分考虑双基地工作和机载工作特点的条件下 ,首先建立空基双基地雷达地杂波的等椭圆几何关系模型 ,然后计算分析了空基双基地雷达的地面反射率 ,最后提出一种通用的空基双基地雷达地杂波模型。在该模型的基础上分析了空基双基地雷达地杂波特性 ,并仿真分析了不同几何配置和运动配置下空基双基地雷达地杂波的多普勒特性和地杂波脊特性 ,结果表明地杂波特性敏感于空基双基地雷达的几何和运动配置 ,合理的配置可以降低信号处理中地杂波的影响     

一种改进的球载雷达气象杂波建模方法

球载雷达由于雷达平台的升高并采用下视工作,面临着强的地海杂波和气象杂波。针对径向速度较小的目标落在气象杂波区会降低雷达检测性能这个问题,为了更好地抑制气象杂波,本文提出了一种球载雷达气象杂波建模方法。首先建立了气象杂波的空间模型和数学模型,然后分析了气象杂波的分辨特性和幅度频率特性,基本完成了球载雷达杂波建模。最后通过对杂波建模仿真及其MTD结果的分析,进一步揭示了气象杂波的特性,为下一步探讨球载雷达杂波抑制方法提供了支撑。     

基于球不变随机过程的高分辨率雷达杂波仿真

球不变随机过程（SIRP）是对高分辨率雷达的检测性能进行仿真分析时广泛采用的杂波模型。在总结SIRP主要理论结果的基础上，详细分析了Rangaswamy M等学者给出的仿真方法对长“拖尾”的“尖”杂波仿真效率低的原因，提出了对杂波包络的概率密度函数（PDF）进行分割，用分割点上的PDF值来构造上界函数的新的仿真方法，仿真算例表明改进的方法显著地提高了仿真的效率。     

某雷达杂波数据分析及杂波图技术研究

强地物、海浪杂波严重影响目标检测概率。频域杂波抑制手段是雷达信号处理常用的杂波抑制方法。但是,杂波的时空分布特性复杂多变,所以对杂波的幅度、频谱等特性的研究有助于选择合适的杂波抑制方案。结合某雷达实际工程采集数据分析了地杂波和海杂波的时域和频域分布特性,提出了一种基于雷达杂波环境特性自适应选择遗忘因子的杂波图方法,具体分析了该杂波图检测概率。实测数据实验结果证明了该方法的正确性和有效性。