单脉冲前视成像多目标分辨算法

单脉冲前视成像技术通过单脉冲测角来提高角分辨率。但是当多个目标处于同一分辨单元时,单脉冲测角只能得到等效散射中心的角度,从而导致目标无法分辨,成像质量变差。针对该问题本文建立了关于多目标到达角的似然函数,通过求解似然函数极值来估计多目标的到达角,实现对目标的准确定位,从而进行准确能量投影。最后,通过仿真实验验证了该方法估计同一距离单元多目标到达角的有效性,实现了不同方位目标角度分辨,并将估计结果应用于前视成像仿真实验,有效改善了图像的质量。      

The Multitarget Monopulse CRLB for Matched Filter Samples

It has recently been found that by jointly processing multiple (sum, azimuth-, and elevation-difference) matched filter samples, it is possible to extract and localize several (more than two) targets spaced more closely than the classical interpretation of radar resolution. This paper derives the Cramer-Rao lower bound (CRLB) for sampled monopulse radar data. It is worthwhile to know the limits of such procedures; and in addition to its role in delivering the measurement accuracies required by a target tracker, the CRLB reveals an estimator's efficiency. We interrogate the CRLB expressions for cases of interest. Of particular interest are the CRLB's implications on the number of targets localizable: assuming a sampling-period equal to a rectangular pulse's length, five targets can be isolated between two matched filter samples given that the target's signal-to-noise ratios (SNRs) are known. This reduced to three targets when the SNRs are not known, but the number of targets increases back to five (and beyond) when a dithered boresight strategy is used. Further insight to the impact of pulse shape and of the benefits of oversampling are given.     

基于对角差信号的单脉冲雷达二维角估计新方法

传统单脉冲雷达具有方位、俯仰二维角度的测量能力,其角度分辨率取决于天线波束宽度,对主波束宽度内的双/多目标不具备分辨能力。为了提高传统单脉冲雷达测角分辨能力,提出一种新的单脉冲雷达系统结构,巧妙地提取和利用了雷达对角线差通道的接收信号,通过建立新的雷达观测方程,提出了四通道单脉冲联合测角新方法,一次脉冲测量即可同时获得两个目标的角度信息,推导了二维单脉冲角估计的解析表达式。新方法计算量少,工程易实现,可使单脉冲雷达的角度分辨率至少达到波束宽度的三分之一,显著提高了单脉冲雷达的角度分辨能力。在不同信噪比和两目标回波功率比条件下,对新方法进行了仿真分析,验证了方法的有效性。     

数字阵列雷达方位超分辨角度估计的仿真

基于幅度比较单脉冲方法的测角局限性,采用先进的阵列超分辨测向技术MUSIC算法,对处于同一距离门和频率门的2个目标,在纯噪声背景和杂波背景下进行了波达方向(DOA)估计,对不同的信噪比和目标进入角度,仿真了目标的分辨情况并计算了DOA角度估计的精度,证明了机载雷达方位超分辨角度估计可以较好地实现落入清晰区或者副瓣杂波区目标的角度分辨与精度估计,但是对目标的信噪比和进入角度有一定的要求.     

Radar signal design for target resolution

Target resolution involves the recognition of a particular target in an arbitrary target environment. While pulse compression methods have solved the problem of separating two closely spaced targets of about the same cross section, this separation is usually accomplished at the expense of introducing "sidelobes" in the matched filter response, which may mask weak targets and prevent their detection altogether. The paper investigates the nature of the constraints on combined range and range rate resolution in a matched filter radar and establishes a clear tie between the uncertainty relation and the practical limitations on the resolution performance of radar. It is found that, in general, an optimum radar waveform for target resolution cannot exist. Radar signal design for target resolution consists of matching the waveform to the characteristics of the target environment, and a signal can be optimum only in that it achieves the best match. These findings are illustrated by examples of matching the radar waveform to a given target environment.     

基于协方差矩阵双层重构的稳健自适应单脉冲测角

常规自适应单脉冲方法在主瓣干扰下会引起自适应波束形成性能恶化并导致其单脉冲比曲线严重失真,影响被动雷达的测角精度与跟踪性能。针对此问题,提出了一种适用于平面阵的基于协方差矩阵双层重构的稳健自适应单脉冲测角方法。首先,利用Capon功率谱通过稀疏重构法初步估计出干扰加噪声协方差矩阵,通过干扰导向矢量估计完成对协方差矩阵的优化校正以提高自适应波束形成性能;然后,基于线性约束最小方差(Linearly Constrained Minimum Variance, LCMV)准则对方位角和俯仰角进行联合线性约束以避免单脉冲比曲线在主瓣干扰下严重失真;最后,根据自适应单脉冲比值求出目标与波束指向之间的偏转角以实现目标测角。与常规方法相比,所提方法在干扰抑制能力与测角精度上都有显著提升。     

基于线性约束的空时自适应单脉冲技术

机载雷达平台的空时自适应处理(Space-Time Adaptive Processing,STAP)通常用于对地面运动目标的检测,但无法实现对相应目标的空时参数估计。该文基于线性约束自适应单脉冲技术,提出一种运动目标空时参数估计新方法。该方法通过对差波束进行零点约束、鉴角率约束及去耦约束,有效地克服了主瓣内杂波对差波束形状的影响,保持了单脉冲特性,提高了目标空时参数的估计性能。仿真结果表明,与同类方法相比,该方法具有优异的空时参数估计性能。     

一种基于Gibbs抽样的多信号源分辨方法

对落在同一距离单元、同一波束内且多卜勒参数相近的多个目标回波,常规单冲雷达是难以区分的。本文提出一种分辨多个信号源的新方法,即采用Gibbs抽样方法对多信号源进行角估计,利用最小描述长度(MDL)准则检测信号源数目。仿真结果证实所提方法对多信号源的分辨是有效的,如当目标信噪比为20dB、目标数为2个时,可达100%的分辨。     

非相干干扰下导弹的命中误差

非相干干扰对单脉冲雷达导引头具有很强的干扰效果。介绍非相干干扰的实施方法及分类,建立了单脉冲雷达导引头对同一波束内两目标的测角特性模型,分析了干扰条件下导弹命中误差形成原理。通过计算机仿真研究了雷达分辨目标的原理,给出了闪烁干扰和非闪烁干扰下导弹命中误差的计算方法。计算机仿真结果表明,对于非闪烁干扰,当能量比近似为1时,初始误差等于目标距离的50%;当能量比较大时,初始误差等于0;对于闪烁干扰,初始误差等于0。     

Time-delay estimation of multiple targets with wavelet based phase-only matched filter

As a well-known variation of the conventional matched filter (MF), the phase-only matched filter (POMF) shows superior range resolution over the MF and thus is widely used in image and radar signal processing. However, performance of the POMF degrades considerably if the input signal-to-noise ratio falls below a certain threshold value. In this paper, a novel time-delay estimator, wavelet based phase-only matched filter (WPOMF) is proposed to provide accurate time-delay estimation for narrow-band radar systems in the presence of multiple targets and high-level noise. Both the theoretical analysis and simulation results illustrate that the proposed method yields superior performance in terms of the estimation accuracy of multiple targets over the conventional or modified MF based time-delay estimators. The simulation results also illustrate that the proposed method has a low computational cost and low SNR threshold close to the estimation accuracy of the maximum-likelihood method.     

宽带单脉冲跟踪雷达的最大熵测角新方法

为抑制单脉冲雷达的测角闪烁,本文提出宽带单脉冲跟踪雷达的最大熵测角新方法.文中分析了由于差波束方向图调制引起的回波谱展宽现象,证明了目标角运动中心与谱展宽程度和波形熵之间的关系,提出基于最大波形熵搜索的目标角度估计方法,并给出了改进的最大熵测角步骤以降低计算量.与现有的高分辨体制下的角度估计方法相比,本方法具有更强的角闪烁抑制能力.仿真结果说明了本方法的有效性.     

Angular jitter in an amplitude comparison monopulse radar due to turbulence

Calculations are presented of the bias and spread of the angle estimator of an amplitude comparison monopulse radar caused by propagation through a layer that contains random index of refraction fluctuations. These fluctuations, caused by irregularities between a target and a receiver, bias the angle estimator towards boresight and cause a spread in the measurements of both on- and off-boresight angles. To illustrate the general results simplified expressions are given for Gaussian antenna patterns, targets near boresight, and a simple power-law irregularity spectrum. Comparisons with other models of angular jitter show that the mean square angular fluctuation observed with an amplitude comparison monopulse radar is closely related to the angular fluctuation, which is predicted when the averaging effect of a radar aperture is considered.     

非相干干扰目标分辨的计算机仿真

分辨角是非相干干扰的重要性能指标之一。在介绍单脉冲雷达角跟踪系统工作原理的基础上,建立了单脉冲雷达对同一波束内两目标测角特性的模型。通过计算机仿真,分析了雷达分辨目标的原理,给出了分辨角的计算方法。计算机仿真结果表明,当能量比为1时,分辨角约等于波束半功率宽度。当能量比不为1时,没有明显的目标分辨时刻,天线逐渐向能量大的目标偏转并对准目标。     

主被动雷达复合导引头信息融合技术研究

针对主被动雷达复合导引头,研究了基于序贯扩展Kalman滤波的信息融合算法。利用主被动雷达复合导引头对目标角误差进行观测,将匹配后的测量角度进行最优加权,进而以角度信息作为量测,估计目标的运动信息。通过试验验证,基于主被动雷达信息融合状态估计比仅依赖主动雷达观测量的状态估计稳态误差小,且滤波器收敛速度更快。     

单脉冲雷达多目标分辨技术研究

常规单脉冲雷达对落在同一距离单元、同一波束内的多个目标是难以区分的。本文提出一种基于单脉冲雷达进行多目标分辨的方法,即利用改进的遗传算法对多目标参数进行估计,利用最小描述长度(MDL)准则进行目标数确定。仿真实验证明了该算法的有效性。     

四通道单脉冲抗雷达诱饵干扰技术研究

在常规单脉冲角跟踪雷达技术的基础上,增加一个在方位向、俯仰向均含有零深的差接收波束,将为单脉冲角跟踪雷达对抗波束主瓣干扰提供一种可能途径。文中首先介绍了利用四通道单脉冲技术对抗有源雷达诱饵干扰方法的工作原理,并进行了可行性分析。然后,重点探讨了利用不同差通道接收信号间的相位差信息对雷达诱饵进行角度跟踪的方法以及可能达到的角度跟踪性能。初步研究结果表明：该对抗诱饵干扰的方法不仅理论上是可行的,也具有较好的工程可实现性,而且在诱饵的雷达回波信号不可忽略的情况下仍然有效,因此,不失为雷达导引头对抗有源、无源雷达诱饵干扰的一种有效途径。     

毫米波频率步进单脉冲雷达角跟踪技术研究

在毫米波雷达目标跟踪中,角闪烁的非高斯特性将使得经典的卡尔曼滤波器失效。研究了非线性度函数方法在毫米波频率步进单脉冲雷达目标跟踪中的应用,采用非线性度函数方法对高分辨距离像测角数据进一步处理,仿真表明该算法性能优于经典的卡尔曼滤波。     

Study on monopulse angle measurement method based on virtual polarization matching

A monopulse angle measurement method for polarization array radar is studied in this paper. The receiving signal model is established and then a monopulse angle measurement method based on virtual polarization matching is proposed. To analyze the estimation performance, the Cramer-Rao Lower Bound （CRLB） of angle estimation is derived. Both theoretical analysis and simulation show that： firstly, the proposed method is superior to the traditional angle measurement methods based on the single polarization. Secondly, the performance of the new method is unrelated to the echo polarization. Thirdly, angle estimation of this method is asymptotically optimal. The results show that this method has great potential to be used in polarization array radar.     

The probability density function of the monopulse ratio for n looks at a combination of constant and Rayleigh targets

The exact probability density function for the "monopulse ratio, of an amplitude-comparison monopulse radar is presented in closed form. The analysis is valid for multiple looks at any combination of fixed targets, pulse-to-pulse independently fluctuating targets, and receiver noise. The average receiver noise powers in the difference and sum channels need not be equal. Arbitrary signal-to-noise ratio, arbitrary monopulse ratio versus angle characteristic, and arbitrary locations of the targets and jammers in the beam are accommodated. Plots of the density function for various signal-to-noise ratios and off-axis location of the targets are included. A linear approximation is introduced, and the exact results are compared to the linear theory when the signal-to-noise ratio is "small."     

Radar separation of closely spaced targets

The capability of a hypothetical radar against attacks by closely spaced aircraft may be examined in geometric terms and the results can be plotted graphically. It is seen that a pulse Doppler type radar, which provides information about target velocity as well as range and angle, is essential in this kind of environment. When the targets are so closely spaced that all else fails, then separation or at least knowledge of the number of targets present is still possible if sufficient Doppler resolution is available to permit the measurement of the small changes in velocity that will be required for the aircraft to maintain formation.