Radar target identification of aircraft using polarization-diversefeatures

The characteristics and target identification potential of a representation of the information from two polarization-diverse measurements of the radar backscatter of an unknown target are considered. The locus of these two polarization-diverse waveforms, termed the transient polarization response (TPR), has been shown to be closely related to the geometry of the scattering centers of the target. The polarization-related components of features derived from the TPR concur well with the shape and orientation of the major scattering centers distributed in the downrange profile of the object. This illustrates the intuitively appealing result that the polarization of the backscatter, as represented by the TPR and mapped onto the modified polarization chart, is determined by target geometry. It is shown that both polarization-related and amplitude-related features derived from the TPR are useful for target identification. By using distance measures that depend on various components, the elliptical parametrization information alone is sufficient to allow satisfactory target identification at SNRs of 0 dB and above. The significance of this result is that the absolute amplitudes of the received horizontally polarized and vertically polarized channels need not be known. However, if amplitude information is known, target identification percentages improve     

Doppler imaging based on radar target precession

A unique form of target motion reminiscent of the precession of a rotating top is investigated. Images are generated with the radar looking either along the precession axis or orthogonally to it. Features of the two methods are discussed and demonstrated by imaging simulated point target scenes     

Raindrop Shape Limitations on Clutter Cancellation Ratio Using Circular Polarization

Cancellation ratio limitations from raindrop properties in a perfectly circularly polarized radar system were found using a new raindrop size distribution which has an improved fit to the existing empirical data. Winds and multiple reflections between raindrops were not considered.     

基于双频微片激光器回馈效应的多普勒测速技术研究

多普勒测速是激光回馈研究领域中最主要和最活跃的分支之一。本文介绍了激光回馈多普勒测速的基本原理,回顾了该领域的研究进展。重点介绍了基于正交偏振双频激光器回馈效应的多普勒测速方法,并在此基础上设计了一种基于双频Nd：YAG微片激光器的回馈多普勒测速方案,分析了其装置原理和影响因素,讨论了其可行性。     

一种极化雷达极点特征抽取算法

在建立雷达目标的单频多极化幅度响应方程的基础上,提出了运用极化分集技术和线性化最小二乘法提取目标极化本征系数的方法,此组系数是与目标的姿态角无关的绝对极化不变量,亦即目标的极点。最后以哑铃型目标为模型进行计算机仿真研究,结果表明这种极化雷达极点特征抽取算法是有效可行的。     

High resolution exponential modeling of fully polarized radarreturns

A method for modeling full polarization radar target is considered. The approach taken is to estimate a set of target features which describes the target as a set of attributed scattering centers. Each scattering center is characterized by its range, amplitude, and a polarization ellipse. An exponential model for the fully polarized radar return is described, and an algorithm for estimating the parameters in this model is developed. The modeling procedure is applied to compact range measurements of model aircraft     

极化滤波反射面隐身天线研究

介绍了一种极化滤波反射面天线,将天线工程中的周期结构反射面技术应用于解决飞行器天线的RCS问题,采用由金属丝栅网构成的周期结构作为天线主反射面,使其对正交极化的来波具有良好的透射性,从而降低了天线的RCS。给出了此天线辐射方向图和雷达散射截面(RCS)的实测结果,并与普通金属反射面天线的结果进行了比较。     

直升机翼面类部件雷达目标特性分析及评估

基于准静态原理,采用电磁高频法开展直升机翼面类部件的雷达目标特性分析及评估.首先,为获得翼面类部件对直升机散射特性的影响规律,并考虑旋翼高速旋转的动态效应,着重分析了装配不同翼面类部件后机身雷达散射截面（RCS）的变化趋势、强散射分布和回波信号的时频域谱特征,揭示了翼面类部件雷达散射影响机理;然后,在评估直升机强散射源分布特征和多元响应特性的基础上,比较装配不同翼面类部件后机身的雷达探测距离,提出并建立了方位、俯仰与滚转姿态下直升机的雷达4级预警机制和角域范围,并针对性的给出对抗雷达探测的方案.研究发现:装配平尾、短翼及平尾和短翼组合的直升机相比孤立机身的雷达暴露距离分别增加11.54%,14.88%和18.06%,综合隐身能力下降.      

Spiky sea clutter at high range resolutions and very low grazingangles

X-band (9.5-10.0 GHz) backscatter at near grazing incidence (0.2 deg) from the sea off the coast of Kauai, Hawaii, was measured with a radar characterized by a high spatial resolution in range (0.3 m) and a high temporal resolution (2000 Hz pulse repetition frequency (PRF)). Extensive amounts (over 20 min per measurement) of vertically and horizontally polarized sea clutter data were taken with upwind (UP) and crosswind (CR) transmit geometries during the collection campaign. Specific but representative examples of the clutter were statistically and phenomenologically analyzed over time scales varying from long (200 s), to intermediate (5 s), to short (50 ms), and over range swaths varying from full (160 m), to partial (30 m), to a single range cell (0.3 m). All analyses and results presented here are noncoherent, involving only the clutter amplitudes. Each type of clutter exhibited the characteristic spiky behavior which has come to be expected from microwave sea backscatter observed at low grazing angles and high range resolutions, while showing, between themselves, marked transmit geometry and polarization dependent contrasts, with the horizontally polarized clutter, measured with an UP transmit geometry, being especially notable for its frequently occurring, significant high frequency spectral content. Within the same clutter type, differences were observed in the probability distributions of radar cross sections (RCS) of spatially and temporally extended spiking events     

High Resolution in Azimuth for Radar Targets Moving on a Straight Line

Target classification is sometimes desired together with airspace surveillance. To some extent this is possible by observing the flight track resulting from typical radar plots. A possibility for measuring the lateral variation of the radar cross section for single targets is described in the following. This method assumes a straight unaccelerated flight path, at least for a few seconds, with tangential components. This restriction is mitigated by prevailing straight flight paths and by observation of targets with radar nets, so there is always a tangential component. This method is especially suitable for electronic steerable radar application.     

Velocity Estimation from Position Outputs of a Three-Dimensional Radar

Kalman filtering equations to obtain estimates of velocity from radar position information are defined. In a track-while-scan operation, a three-dimensional radar sensor measures range, bearing, and elevation (r, ?, ?) of an airborne target at uniform sampling intervals of time T. The noisy position measurements are converted to x, y, z coordinates and put through a Kalman filter to obtain x, y, z velocity components. The filtering equations together with steady-state error estimates are given.     

Multiradar Tracking System Using Radial Velocity Measurements

Multiradar tracking using both position and radial velocity measurements is discussed. The measurement of two or more different radial velocity components allows the calculation of rectangular velocity components. The measurement noise of the velocity components is filtered using a Kalman filter in the same way as the Cartesian position components. Before the conversion of velocity components from radial to Cartesian coordinates, the radial velocities are aligned on a time scale to account for the time shift of the radar measurements. In order to compare multiradar tracking system performance with and without radial velocity, some simulation tests have been performed for typical paths. The simulation results show a significant improvement when radial velocity is used for tracking.     

Statistical Characteristics ics of the Polarization Power Ratio for Radar Return with Circular Polarization

In this paper, the radar return from a clutter target illuminated by acircularly polarized wave is investigated statistically. The ratio of theenvelope of the left circular component to that of the right circularcomponent of the return signal is formed, and the probability densityfunctions and cumulative distributions of this ratio are found forlinear, square, and logarithmic law detectors. Plots of all densities anddistributions are given for several statistically modeled clutter-typetargets with typical depolarizing and back-scattering characteristics.The probability density functions for the ratio signal from a logaritmicic detector are compared for the cases of circularly and linearlypolarized waves incident on the same clutter-type target. Linearpolarization produces the worst case of spreading of the probabilitydensity function from its median value. Plots are given which indicatethat changes in the amount of depolarization by the clutter cause moresignificant changes in the median value of the polarizationration forlinear than for circular polarization.     

Bayesian gamma mixture model approach to radar target recognition

This paper develops a Bayesian gamma mixture model approach to automatic target recognition (ATR). The specific problem considered is the classification of radar range profiles (RRPs) of military ships. However, the approach developed is relevant to the generic discrimination problem. We model the radar returns (data measurements) from each target as a gamma mixture distribution. Several different motivations for the use of mixture models are put forward, with gamma components being chosen through a physical consideration of radar returns. Bayesian formalism is adopted and we obtain posterior distributions for the parameters of our mixture models. The distributions obtained are too complicated for direct analytical use in a classifier, so Markov chain Monte Carlo (MCMC) techniques are used to provide samples from the distributions. The classification results on the ship data compare favorably with those obtained from two previously published techniques, namely a self-organizing map and a maximum likelihood gamma mixture model classifier.     

F-22机载火控雷达系统研究

通过有源相控阵技术、低噪声接收部件、紧凑布局和高级模态开发 ,F - 2 2雷达系统实现了在性能、可靠性和低可探测性方面的大幅提升。本文基于载机综合航电系统概念 ,在分析APG - 77雷达系统硬软件体系结构的基础上 ,探讨了F - 2 2雷达在生存性、杀伤性、可靠性和保障性等方面的独特优势 ,讨论了有源相控阵技术在低雷达散射截面战斗机上应用的折衷考虑。     

Target motion compensation in synthetic aperture radar

In a synthetic aperture radar (SAR) targets on the ground that are moving become smeared as a result of velocity components parallel to the motion of the radar and are moved to radically different angular positions if they have velocity components perpendicular to the motion of the radar. Methods for restoring moving targets to their correct size and position are described. The samples collected for SAR processing are frequency-modulated RF pulses. Mathematically this leads to spectra that are described by Fresnel integrals. For stationary targets, the spectrum is symmetrical around the origin. If there is a moving target in a range cell, its Doppler spectrum will be displaced from the origin and may undergo other changes as a result of its nonzero velocity. Proper compensation to locate the target at the correct position requires that the spectrum be translated to a position dependent on the along-track velocity rather than to the origin. From the central frequency, the along-range velocity component can be estimated and the length of the translation can then be found. After translation, the spectrum is converted back to the time domain and the customary SAR processing is performed     

Doppler Return from a Random Rough Surface

A theoretical analysis of the Doppler return from a random rough surface ace shows that the Doppler spectrum is composed of three distinct components. The methods of analysis for determining the average power return for the static case and an application of the ergodic hypothesis for a stationary surface show that the assumption of a single Doppler component is based on a smooth surface. In addition to this coherent component, the incoherent components of the random rough surface produce two additional frequency components. The amplitudes of these latter components depend on the variance of the surfaceand the antenna beamwidth averaging. Radar measurements were made, utilizing a scatterometer, in order to measure the surface characteristics. s. Simultaneous measurements from a Doppler radar system were analysed to identify the additional frequency components.     

Optimal polarimetric detection of radar target in a slowlyfluctuating environment of clutter

It is shown that in a situation where a radar target is distant enough from the radar and is included in a natural or artificial clutter environment in such a manner that the conventional detection methods fail, it is possible to improve the radar detection performance by using appropriate signal processing on two orthogonal polarization states. A CFAR (constant false alarm rate) polarimetric detection system based on the study of the polarization difference between clutter and target is proposed. Since the polarization state of the clutter echoes fluctuates slowly from cell to cell, an autoregressive model can be applied to the components of the polarization vector to predict the detection thresholds needed to follow the polarization state variation. The detection thresholds are determined to maintain a false alarm probability equal to 10^-6. The presence of a target registers as a significant variation of the estimation error of the polarization vector. Results obtained from measurements of simple and canonical targets with artificial clutter are presented, and these results validate the principle of polarimetric detection     

IPIX雷达海尖峰统计特性研究

根据雷达海尖峰构成原理，以K分布为模型，提出了海尖峰的统计特性分析方法，并使用该方法对IPIX雷达实测海杂波数据进行了统计特性分析，分析结果证明了该方法的有效性。