Harmonic Radar Systems for Near-Ground In-Foliage Nonlinear Scatterers

The radar transmission equation for a harmonic radar operating over a planar, finite dielectric Earth through foliage is derived for an interesting class of nonlinear scatterers. The received power can typically depend on range to the (-14) power for small objects near the ground. The maximum detection range of a ground-based system is related to all major system parameters: it is most sensitive to polarization, transmit antenna height, and transmit wavelength; moderately sensitive to transmit power and transmit antenna area; and least sensitive to receive antenna area, harmonic scattering cross section, and mode of data processing. For example, there is seen to be a best apportionment of total available aperture area into disjoint transmit and receive apertures which can be well approximated by the equal gain condition. Also, there is seen to be a critical path distance through foliage; at distances less than this, small wavelengths are desirable and, conversely, the upper transmit frequency limit may be set by nonlinear scatterer response. Airborne synthetic aperture radar systems are discussed and quantification of harmonic noise and effects of scatterer fluctuation are made. A useful phenomenological model of a nonlinear scatterer is given that is consistent with some observations and predicts a frequency dependence. Nonlinear scatterer effects on range resolution are discussed.     

Bistatic Radar Cross Sections of Chaff

Bistatic cross sections applicable to scattering from a cloud of randomly positioned and randomly oriented resonant dipoles, or chaff, are found. The chaff cloud can have an arbitrary location relative to an illuminating radar and the radar antenna can have an arbitrarily specified polarization. The receiver can be located arbitrarily in relation to the radar and chaff cloud and can also have arbitrary polarization (different from the transmitter antenna). Average cross sections are found for a preferred receiver polarization and the corresponding orthogonal polarization. Results are reduced to simple, easily applied expressions, and several examples are developed to illustrate the ease with which the general results can be applied in practice.     

Bistatic Radar Cross Sections of Horizontally Oriented Chaff

Bistatic radar cross sections are determined for scattering from a cloud of randomly positioned resonant dipoles (chaff). Dipoles are assumed to be horizontally oriented with axes randomly oriented in the horizontal plane. The cloud is arbitrarily located relative to an illuminating source having an arbitrary (elliptical) polarization. Cloud cross section is found for an arbitrarily located receiver that views the cloud with an antenna of arbitrary polarization. Cross section applicable to the receiver's orthogonal polarization is also found.     

Cross Sections and Reaction Rates for Comparative Planetary Aeronomy

In this chapter we describe the current knowledge of a selection of collision processes and chemical reactions of importance to planetary aeronomy. Emphasis is placed on critical evaluation of what we know and what we wish we knew about fundamental processes required for interpretation, explanation, and modeling of atmospheric observations.     

A Model for the Radar Echo from a Random Collection of Rotating Dipole Scatterers

A theoretical model for the radar echo from a random collection of dipole scatterers is presented. The analysis of the model takes into account the effects of scatterer rotation which have been neglected in previous related work. It is shown that rotational motion of the scaterers can have significant effects upon the echo waveform. The fluctuating characteristics of clutter echoes are also investigated. The theory and some experimental results in the literature are shown to be in relatively good agreement.     

Monopulse Estimation of the Centroid of an Ensemble of Radar Scatterers

The use of data obtained by a monopulse radar to estimate the location of the radar cross-section centroid of an ensemble of scatterers is discussed. Both dish and phased-array antenna radars are treated. Expressions for the bias and variance of the centroid estimates are presented, including the effects of the radar receiver and beam pattern characteristics, receiver noise, and the video waveform sampling granularity, as well as the target properties. The monopulse tracking approach discussed here is contrasted with a raster scan approach presented previously.     

Radar Cross Section of Ships

A laboratory method to determine the magnitude and position of radar reflection sources on complex targets is described. In addition the method provides a way to measure the modification of the radar cross section (RCS) due to multipath. The method has application in modeling RCS for radar and electronic countermeasure (ECM) system performance analysis and in the study of the extent to which the signature of the target could be altered. The equipment described, termed MACROSCOPE, was developed for RCS studies by the U.S. Army and is described in limited distribution bution literature. The application to marine targets is new with this paper, as is the technique of measuring the RCS of parts of the target and analytically combining them to represent the whole. An illustration of the need for this type of laboratory equipment was illustrated by the extensive search for full scale data which could be compared to scale model data to validate the technique.     

直升机的RCS计算

RCS（Radar Cross Section）是反映目标雷达散射特性的一个重要参数。一般把雷达目标除质心平动之外的转动,小幅振动和其它高阶运动统称为微动。主要研究旋翼转动情况下的直升机RCS计算。通过对直升机模型进行可视化计算即一种将目标建模与散射特性计算合为一体的交互式计算,使用图形算法（GRECO）和三维造型软件UG相结合的方法,这种方法与传统的RCS计算方法相比具有实时性好,效率高的优点,计算出直升机主体的RCS,再通过其加入调制的方法,计算得到直升机在旋翼转动条件下的RCS。最后给出了微动直升机的在具体入射情况下的单站RCS值。     

The Jet Fighter Radar Cross Section

Two jet fighter models, 1/8th of original size, have been measured in the "radar range" installed in the anechoic chamber of the Armament Technology and Procurement Group in Berne. The measurements have been made at a frequency of 40 GHz (5 GHz for full scale), with an accuracy of ± 2 dB and a dynamic range of 80 dB. The statistical distribution of the radar cross section has been calculated with the help of a computer, based on the measured data. The detection probability has been calculated with the help of a correlation procedure. This procedure allows explanation of the symmetry relation between the detection probability and the cumulative distribution of the radar cross section, and of a well-known characteristic of the median value of the radar cross section. A statistical model is proposed for the distribution of the radar cross section of jet fighters, consisting of the distribution of a spheroid in which each element itself exhibits a Rayleigh fluctuation. This model presents a certain number of interesting characteristics, and there is an acceptable degree of coincidence with the measured values.     

求解非线性方程及方程组的模拟退火算法

探讨了用模拟退火算法求解非线性方程及方程组的方法,该方法把方程组求解问题转化为函数优化问题.计算中不需要使用目标函数的导数信息,在Matlab环境下实现了该算法,数值实验结果表明了该算法的有效性.     

Some Aspects of Swerling Models for Fluctuating Radar Cross Section

The structure of Swerling's 1957 model for fluctuating radar cross section and signal amplitude is examined prinwrily in terms of mixture representations. The authors also show the relationship of Nakagami's m distrubution to Swerling's amplitude distribution, and Nakagami's q distribution (Hoyt vector density) is reduced to the Swerling distribution. Nonuniform phase distributions associated with Swerling's functions are also derived. Results are given when Swerling's amplitude density is used as a prior distribution with Bennett's (Rice's) distribution for the amplitude of a sine wave plus narrowband Gaussian noise.     

舰艇雷达散射截面的计算公式

通过引入雷达散射截面的概念,采用物理光学积分、几何建模等电磁散射方法,给出舰艇目标有效散射截面的精确计算模型;介绍了舰艇有效散射截面的经验估算公式并提出了修正方法;基于实际测量数据与理论计算结果的比较分析,对算法的可信度和工程应用价值给出了评价。     

Nonlinear Estimation with Radar Observations

The nonlinearities of the radar measurement model equation are examined and their influence upon the accuracy of filtering and smoothing is determined. A simple algorithm by which the effects from these nonlinearities can be significantly reduced is derived. It consists of processing the radar observations in this order: azimuth, elevation, and range, using the azimuth residual to evaluate the elevation residual, and then using this combined result to evaluate the range residual. The accuracy of estimates obtained via the algorithm is compared with and shown to be superior to that of the extended Kalman filter (EKF). Furthermore, use of the algorithm does not increase the computational complexity of estimation beyond that of the EKF.     

异型截面轻体构件内高压成形技术

介绍近年来在内高压成形机理、工艺、设备和应用方面的进展情况.针对大截面差管件、弯曲轴线异型截面构件和枝杈管3类工艺给出典型零件缺陷形式、形状精度、壁厚分布及工艺参数对它们的影响.介绍了航空航天器铝合金异型截面件研制和热介质内高压成形探索成果,以及哈尔滨工业大学最新研制的三轴数控内高压成形机,并给出了研制的典型零件及其在航空航天中的应用情况.     

直升机雷达散射截面计算与试验验证

采用高频预估法,建立了一套基于“面元边缘”的直升机RCS计算方法,然后对某型直升机进行了RCS计算分析以及RCS测试.最后,对比分析直升机机身雷达散射试验和理论计算结果,得出了一些减缩直升机RCS的外形设计特征.结果表明:在设计要求许可的情况下,改变武器挂架长度比改变后掠角缩减RCS效果要明显;直升机头部鼻锥部位使用锥形结构,可以减小头向方位RCS;直升机主桨榖采用圆台形代替圆柱形,可以减缩头向和侧向方位的RCS.     

雷达散射截面计算方法综述

对目标雷达散射截面（RCS）计算方法进行了总结，指出了各种方法的适用范围。以具有复杂外形特征的军用战斗机为例，用物理光学法进行了全机的RCS计算，验证了该方法在飞机设计中的实用性。     

Estimating the Radar Cross Section of a Cavity

The radar cross section (RCS) characteristics of cavities are considered. Experimental data on simplified models obtained in 1966, but which heretofore have not received very wide dissemination, are reviewed and the results are compared with predictions based on a simplified (and semiempirical) theory for the end-on aspect case combined with a ray tracing procedure for other aspects. This theoretical method for estimation purposes is seen to provide quite adequate results.     

四阶常微分方程两点边值问题解的存在性

利用上下解的方法,讨论了非线性四阶常微分方程y(4)=f(t,y,y',y″,y)满足条件g0(y(a),y'(a))=0,g1(y'(a),y″(a))=0,g2(y″(a),y(a))=0h(y(c),y'(c),y″(c),y(c))=0的非线性两点边值问题解的存在性,其中函数f,gi和h是具有一定单调性质的连续函数。     

Atmospheric Lens Effect; Another Loss for the Radar Range Equation

A small additional loss for radar range calculations at low grazing angles is described. This loss results because the variation in atmospheric refraction versus altitude makes the atmosphere act like a lens, causing thinning of radar signal energy to and from the target, independent of frequency. The magnitude of loss is derived and is plotted versus grazing angle and range. The maximum two-way loss, occurring at zero degrees grazing angle and a range well beyond the atmosphere, is 2.9 dB.     

雷达散射截面并行计算中的MPI实现技术研究

基于MPI（Message Passing Interface）并行计算平台,开发了高效的并行多层快速多极子算法程序,可用于飞行器等目标RCS计算分析。为提高通信效率、增加程序的鲁棒性,提出了优化的通信措施,分析了点对点通信、阻塞通信、非阻塞通信的使用优缺点,针对RCS计算,组建了完整的通信方法,从而有效防止死锁的发生。算例证明,程序能胜任于电大尺寸的RCS散射计算,具有较高的精确度。