球面波照明的同轴数字全息干涉图像模拟及应用研究

提出三次曲面拟合法表示到达CCD屏的照明物光与参考光位相差分布,并通过对CCD探测图像数据处理获得物光复振幅分布的方法。理论上讨论了球面波照明情况下实现同轴数字全息检测的可能性。     

Nonuniform currents on a wedge illuminated by a TE plane wave

Closed-form expressions for nonuniform currents on a perfectly conducting, infinite wedge illuminated by transverse electric (TE) plane wave are presented. These expressions are derived by requiring that they coincide with the current predicted by the asymptotic diffraction method far from the edge and, further, that they agree with the current predicted by the eigenfunction solution at the edge. The angle of incidence is arbitrary and our expressions remain valid even for glancing angles of incidence when either one or both faces of the wedge are in the vicinity of a geometric optic (GO) boundary. Formulas presented here are simple involving the well-known modified Fresnel functions but are not uniform. Exact expressions for nonuniform currents are available for the two special cases of half-plane and infinite plane. For these special cases, our solution reduces to the exact solution. Currents computed using the expressions developed here are compared with currents computed from the eigenfunction solution of the wedge. Good agreement is obtained throughout.     

Scattering from a turbulent rocket-exhaust jet illuminated by a plane wave

It has been found possible to describe the addition of noise to a microwave carrier by a rocket-exhaust jet in terms of a simple quantitative model of incoherent volume scattering by the turbulent discontinuities in the jet. The power scattered is spread throughout the noise spectrum by the variation with position in the jet of the magnitude of the mean gas-velocity vector. Comparison between computer calculation and experimentally determined amplitude and phase noise data is found to be excellent.     

The currents on a cylinder illuminated by a generalobliquely-incident plane wave

A relation is presented that determines the total current induced by a general plane wave obliquely incident or a perfectly electrically conducting cylinder of arbitrary cross section from the total current induced by a normally incident plane wave. Remarkably, this same relation ran also be used to determine the physical optics (PO) and nonuniform (NU) currents for oblique incidence directly from the PO and NU currents, respectively, for normal incidence     

一种改善球形目标RAM优化速度的方法

采用遗传算法设计球形目标雷达吸波材料时，由于适应度函数是以级数形式给出，且随物体尺寸的增大，级数收敛减慢，优化时间成倍增长，为提高设计效率，依物体电尺寸的大小分段使用不同的方法进行优化设计，其次，采用浮点数编码，可以节省计算机内存，简化优化过程，从而大大缩短优化设计的时间，为避免算法陷入局部最优，采用分段变参数遗传算法，提高进化的效率，最后，用Matlab设计算法，通过算例证明方法的快捷、有效。     

Transient currents on a cylinder illuminated by an impulsive plane wave

An analytical and numerical study of the transient current density induced on a perfectly conducting circular cylinder has been carried out. Both TE and TM incident plane waves with impulsive time dependence are considered. Complete closed form expressions for the TE and TM current density at all points on the cylinder and for all time values are obtained by a functional interpolation of both large and small time asymptotic solutions. The complete expressions should he useful in future transient radar scattering problems for approximating the transient current behavior on portions of a complex scatterer. The numerical results are presented in the form of "snapshots" of the current density at specific instants of time. The results are interpreted in terms of specular reflection and creeping waves. The creeping wave pulses are seen to be a continuation of pulses generated on the illuminated surface; their propagation into the shadow region is a highly dispersive phenomenon. The natural mode spectrum is seen to have both discrete and continuous components with the response at very large times determined by the latter.     

NONUNIFORM CURRENTS ON A CONDUCTING WEDGE ILLUMINATED BY A TM PLANE WAVE

Closed-form expressions for nonuniform currents induced on a perfectly conductinginfinite wedge illuminated by a TM plane wave are presented.Results computed by using theseexpressions are in good agreement with ones of the eigenfunction solution of the wedge.     

Scattering of a beam wave by a spherical object

The theoretical analysis of the scattering of a beam wave by a small spherical object, which exists at the neighborhood of the beam waist on the propagation axis, is treated. In this analysis, the property of a spherical object is generalized so as to have anr-dependent dielectric constant. Through numerical calculations for the case of the conducting sphere, the difference between the scattering of a beam wave and that of a plane wave are discussed.     

Measurements of surface currents on a finite circular tube illuminated by electromagnetic wave

An experiment is designed to confirm a rigorous theory on the three-dimensional electromagnetic scattering from a circular tube of finite length. Both axial and transverse components of the outside total current for the case ofEpolarization have been measured for two finite tubes withka = 1.895andkh = 0.4827piand0.724pi, both as a function ofzortheta. Special care was taken to preserve the continuity of the transverse current after each change in the position of the probe. The measured results are in good agreement with the theoretically computed data. Theoretical curves for the corresponding infinite cylinder are also included to show the limitations of using them as approximations to the currents on finite cylinders.     

多站制CW雷达目标动态模拟器设计

针对多站制连续波（CW）雷达工作特点,设计了一种CW雷达目标动态模拟器,满足多站连续 波测 量系统动态模拟联试的需求。采用高性能CPCI工控机作为模拟器硬件平台,信号处理单元 以CPCI板卡为载体,模拟控制信息依据弹道数据生成。模拟器通过控制测距信号的时间延迟 ,实现目标距离变化的模拟;通过载波频移控制,实现目标速度的模拟;通过数控衰减器控 制模拟信号的幅度,实现目标信号强弱的模拟。通过多站制测量系统动态模拟联试,验证了 模拟器的有效性和距离与速度的相关性。     

GTD analysis of near-field and far-field patterns of a parabolic subreflector illuminated by a plane wave

A geometrical theory of diffraction (GTD) analysis of the principal plane far-field and near-field patterns of a near-field Cassegrainian subreflector is presented. The uniform geometrical theory of diffraction (UGTD) [1] that drastically reduces the computation time has been utilized to analyze the subreflector in the form of a paraboloid illuminated by a plane wave. The numerical computations of the far-field amplitude and phase patterns of a typical paraboloidal subreflector based on the above technique correlate well with the results obtained by physical optics current integration, justifying the validity of the analysis presented. The GTD near-field analysis presented here is an improvement over that published earlier [2] and removes some of its limitations.     

地球球面和大气折射对气象雷达目标探测的影响

介绍等效地球半径、地球曲率和大气折射指数的概念,讨论地球球面和大气折射对机载气象雷达最大探测距离和测高的影响,并做出定量分析。在此基础上,用Matlab软件提供的可视化工具Simulink建立系统仿真模型,给出仿真结果。用于修正和完善机载气象雷达的目标探测仿真模型,使其能够更准确、合理地反映实战条件下各种背景因素对气象雷达探测性能的影响。     

Micro-motion target sensing by stepped-frequency continuous-wave radar

Mechanical micro-vibration of a target may induce phase modulations on the radar echo, and the vibration can be detected to identify micro-motion target. In this paper, a new method to detect a mi-cro-motion target and obtain its range and micro-motion frequency is proposed in which multiple periods stepped-frequency continuous-wave signal and Moving Target Indication (MTI) filter are adopted. The simulation results illustrate the validity of this method and present the detection of the target range and the vibration frequency. The experiment gives promising results.     

Reduction of radar image artifacts caused by target inlets

The standard radar weak-scatterer model is inappropriate to targets with inlets and cavities and range-resolved images created using this model often display artifacts associated with these structures. Since inlets and cavities (typically) make a strong contribution to the radar field scattered from aircraft targets, these artifacts can confound the image interpretation process. Many of the more complete and accurate scattering models require extensive knowledge about the cavity/inlet shape and size and, moreover, are numerically intensive-features that make them unsuitable for many imaging applications. We examine an older (first-order) model based on a weak-scattering modal expansion of the structure which appears to be well suited to radar imaging     

基于车载毫米波雷达的目标检测CFAR算法研究

汽车雷达信号处理的一个重要任务是可靠地探测汽车前方及周边的目标,通过比较雷达反射信号的频谱来判断频谱信号是否达到特定的检测门限值,使用恒定的门限值会导致大量虚警目标被检测,如果虚警目标太多,会使计算机的处理能力达到饱和,势必影响正常目标的检测。因此,一种自适应噪声阈值的恒虚警率(CFAR)算法被广泛的应用在雷达信号处理中。本文针对汽车FMCW雷达常用的两种CFAR算法,从原理上对算法进行阐述,并通过仿真软件和实验数据对算法性能进行分析比较。     

雷达目标信号模拟器的设计与实现

为满足雷达数据处理系统目标跟踪算法的测试需求,介绍了一种基于USB和FPGA技术的雷达目标信号模拟器设计方案。文中重点讨论了模拟器的结构和目标数据形成、传输、存储、信号波形产生等主要技术。该模拟器具有成本低、灵活性高的特点。实际应用表明该模拟器具有良好的性能,可以作为雷达数据处理系统的调试设备。     

Analytical aspects of plane wave illuminated thin wires and slits

The paper deals with simple elementary approximations for the current and charge response on different straight wire structures, dipoles and short slits in the receiving case. After proof that transmission line equations are also valid for single wires without discontinuities, these equations are formulated including the incoming wave. They turn out have simple particular solutions that could be expected for the case, when the electric field is parallel to the wire, but holds true for the general case too. Satisfying the boundary condition at discontinuities (wire ends, lumped elements) gives rise to additional waves appearing as solutions of the homogeneous wave equation. The formulation of currents along and voltages across a slit, including an illuminating magnetic field at one side of the screen, leads again to transmission-line type equations and, consequently, to the inhomogeneous wave equation. As slits in screens are usually small in terms of wavelength, an approximative solution for the short slit will do. For this case, even closed-form expressions are possible for the magnetic near field     

Radiation characteristics of a spherical array of circularly polarized elements

The radiation properties of a spherical phased-array antenna with circularly polarized elements are studied. Each antenna element is assumed to have a cosine type of field pattern. It is found that such an array is capable of providing complete hemispherical coverage without appreciable loss of gain. The radiation produced by the array stays circularly polarized in all directions, and the state of polarization is independent of beam steering. A special distribution of elements on a spherical surface is developed. This considerably suppresses the grating lobes in the pattern and thereby makes the antenna array broadband. Numerical calculations are made to determine the directivity and half-power beamwidth for the radiation patterns produced under various situations.     

光电雷达对目标参数被动测量的方法研究

根据光电雷达测量到的目标方位信息,运用自适应修正增益扩展卡尔曼滤波理论。可以估计出空中目标相对载机的位置和速度参数。文章首先推导了坐标系的转换矩阵,建立数学模型后推导对应的自适应修正增益扩展卡尔曼滤波方程,通过对所得的算法进行仿真验证,表明该算法具有较好的实用性,能够满足载机对目标参数被动探测的要求。     

雷达目标一维距离像识别中的非训练目标判别

针对雷达目标一维距离像识别中的特征子空间法不能判别训练目标的缺点，提出一种非训练目标判别门限，在特征子空间法的分类阶段对非训练目标进行判别。仿真实验结果表明：在特征子空间法中引入该门限，既能有效地对非训练目标予以判别，同时对训练目标又能保持较高的正确识别率。