Avibrating-Dipole Technique for Measuring Mlillimeter-Wave Fields in Free Space

EM field measuring techniques, based on the modulated-scattering principle, are well established at microwave frequencies. The main difficulty in extending measurements to the millimeter-wave region is that of scaling the scatterer for operation at these wavelengths. The technique of modulated scattering described in this paper overcomes this limitation. A thin metallic dipole, attached to a vibrating nylon cord, forms the modulated scatterer which interacts with the electric field and gives rise to a phase-modulated reflected wave. The reflected wave is then combined with preference wave in a coherent detection system. The detected signal contains information about the amplitude and phase of the field at the midpoint of the dipole's vibration. An analysis of the technique is presented and the factors affecting the accuracy of measurement are fully discussed. It is shown how the measurement errors can be minimized. Amplitude and phase measurements, taken at a wavelength of 4.8mm, verify the validity and accuracy of the technique.     

异轴角散射法中散射体几何模型的构建与优化

湿蒸汽参量测量对于保障汽轮机机组的高效安全运行具有重大意义。基于激光散射的异轴角散射法是湿蒸汽参数测量的光学方法之一。本文在分析异轴角散射法测量模型中激光散射的散射体几何建模存在问题的基础上,构建了CCD相机单个像元所对应的散射体的几何模型,并求解了散射体体积及与散射体相关的几何参数;并采用MATLAB软件进行了仿真计算,计算了水滴群质量中间半径r0.5、水滴数浓度N和尺寸分布系数K变化对散射光强的影响,并进行了误差分析。研究结果表明:采用新构建的散射体几何模型的异轴角散射法所得的仿真理论数据与实验数据间相对误差减小,且变化趋势更趋于一致,验证了几何模型优化的可行性和优越性,可为湿蒸汽参数测量提供更精确的数据。     

基于光散射技术的两种能见度探测方法的比较分析

为了提高大气能见度的仪器探测水平,并验证自行研制的车载式拉曼激光雷达探测大气水平能见度的可靠性,使用1种基于可见光波段的前向散射能见度仪,与基于后向散射原理的拉曼激光雷达进行了联合试验,对两者测量结果,进行了分析和讨论,结果表明这两种探测手段具有较高的相关性.同时,通过对前向散射原理的探讨,为能见度仪的国产化提供了参考,也检验了国内首台车载式拉曼激光雷达在测量能见度方面的可靠性,扩展了它的应用领域.     

Estimating the output field of a directly modulated laser diode

A method for estimating the chirp of the output light field of a directly modulated laser diode is presented and experimentally tested. This method is based upon simple measurements of the modulated output power and spectral lineshape. Using a method of best fit to the spectral lineshape, a good estimation of the field phase is easily evaluated. This information can then be used to determine the suitability of laser diodes in high-speed, high-dispersion intensity modulated direct detected optical systems     

A probe for making near-field measurements with minimaldisturbance: the optically modulated scatterer

We describe an optically modulated scatterer as an electric-field probe for measuring radio-frequency and microwave fields. It has a high spatial resolution and the ability to operate very close to conducting and dielectric objects without appreciable distortion of the field to be measured. Thus, it can scan close to antennas and diffracting metal structures. We describe how the electric field is deduced from the measurements and present gain measurements and far-field patterns deduced from near-field scans of antennas. The results are tested by comparing them with those obtained by established measurement techniques     

测量激光束横模结构的方法研究

分析了根据激光场强度相对分布计算激光束横模结构的方法,根据分析结果设计了利用光场分布测量激光束横模结构的实验方法。对所设计的方法进行了仿真验证,同时通过具体实验,对一款调Q激光二极管抽运固体激光器(DPL)的激光束横模结构进行了测量。实验中,在不知道谐振腔参数的情况下,根据设计的方法测量了激光束的各阶横模比例。以测量出的横模比例为基础,理论上重构出激光束,该光束和实际光束的空间传输过程基本吻合。     

Near-zone fields scattered by three-dimensional highly conductingpermeable objects in the field of an arbitrary loop

An efficient numerical technique is presented for electromagnetic scattering in the near-field zone by three-dimensional permeable conducting objects excited by a loop antenna. The impedance boundary conditions are used to simplify the formulation and reduce the computation time and memory. Numerical results are presented to illustrate the dependence of the scattered field on the physical characteristics of the scatterer and its location     

MIMO雷达三维干涉诊断成像方法

2维合成孔径雷达(Synthetic Aperture Radar, SAR)和逆合成孔径雷达(Inverse Synthetic Aperture Radar, ISAR)成像是目标散射机理高分辨率分析和散射诊断测量的重要手段,现有被广泛采用的技术主要包括转台ISAR和导轨SAR成像技术。相比于传统的2维成像,3维成像可以提供目标局部散射中心在空间的3维位置和散射强度信息。因此,探索新的、可工程化实现与应用的目标3维成像技术是一项极具吸引力的工作。该文提出一种基于多输入多输出(Multiple-Input Multiple-Output, MIMO)阵列技术的3维干涉成像方法。首先,设计并试验了一种具有高孔径利用率和通过虚拟孔径实现干涉成像功能的MIMO阵列;其次,分析了MIMO阵列合成的两组虚拟孔径所成两幅2维雷达像的干涉相位与目标散射中心高度之间的关系,发展了MIMO雷达3维干涉成像算法;最后,通过数值仿真和原理样机实验验证了所提方法在目标散射机理分析和诊断测量应用中的可行性和有效性。      

Velocity/field characteristic measurement using a high-frequency modulated solid-state laser diode

A new experimental method to determine a velocity/field characteristic in semiconductor material is reported. This is a time-of-flight technique based on the phase-shift measurement between the photocurrent created by the output modulated light beam of a laser solid-state diode and the high-frequency signal which modulates the laser. First results concerning hole velocity in silicon and electron velocity in gallium arsenide are presented.     

基于单片机的激光远场光斑直接测量系统

激光远场光斑测量对描述激光束的远场性能,评价激光器以及系统的实际工作性能具有重要意义,通过比较激光光斑远场直接测量与间接测量的优缺点,提出使用单片机控制的探测器阵列进行远场光斑直接测量．描述了系统结构,分析了关键技术,给出了主要程序的框图．该系统能够测量激光光斑大小、形状、总能量、能量分布、重心、束散角等参数,可适用于多种重复频率的激光器,测量面积大、精度高,实时性好,为激光束绝对空间能量分布的测量提供了有效手段。     

电吸收调制器和DFB激光器集成器件的测量

提出了一种测量电吸收调制器和激光器集成器件芯片散射参数的新方法.根据电吸收调制器和封装寄生参数的等效电路模型,对测量的反射系数进行拟合,得到封装寄生参数和电吸收调制器的等效电路元件的参数值.通过分析发现测试封装寄生参数对电吸收调制器的测试结果有很大影响.去除了封装寄生参数的影响后,得到了调制器的反射和传输参数的真实频响特性     

Reduction of the number of unknowns in large stacked planarstructures by a fringe aperture formulation

For scattering problems comprising a combination of planar structures, the total number of unknowns may be significantly reduced if an aperture formulation is employed rather than a patch formulation. The rationale behind using the aperture formulation is based on the recognition that the decay rate of the scattered aperture field is independent of the size of the scatterer. Therefore, any scatterer may be surrounded by an aperture of fixed width over which an integral equation is formulated. The area of this aperture is proportional to the perimeter of the scatterer rather than its area, and it becomes much smaller compared with the entire scatterer area as the size of the scatterer increases, hence the reduction in the number of independent unknowns. A truncation criterion for the finite aperture is determined via a numerical study of the aperture field behavior for various angles of incidence. In addition, the a priori knowledge of the physical optics component is also taken into account, reducing the unknown function to an aperture field component that is the outcome of the remaining fringe current only. The total current distribution can be subsequently derived from this field by adding the known physical optics field and invoking the inverse of the Green's function in the spectral domain. This analysis of isolated planar scatterers results in a spectral scattering matrix representation that is subsequently used for cascading of stacked structures     

基于激光散射原理的表面粗糙度测量方法研究

文章基于Beckmann散射模型,提出一种表面粗糙度的在线测量方法。以半导体激光器为光源构成远心光路,通过线阵CCD记录粗糙物体表面的散射光场。计算机分析处理得到表面粗糙度特征值Sn,在较大的范围内表面粗糙度Ra和Sn有很好的对应关系。该测量方法结构简单、精度高、速度快,可以对不同加工方法的工件表面粗糙度实现非接触实时检测,在工件的在线检测方面有很好的发展前景。     

Moment method with isoparametric elements for three-dimensionalanisotropic scatterers

A new method for computing the frequency-domain electromagnetic fields scattered from, and penetrating into, arbitrarily shaped, three-dimensional, lossy, inhomogeneous anisotropic scatterers is presented. The method is based on a general volume integro-differential formulation of the scattering problem, and consists of the numerical solution of the coupled integral equations by the moment method and point matching. A particularly powerful feature of this method is that the numerical model of the scatterer is obtained by parametric volume elements and the basis functions used to represent the field within each element are the same used in the finite-element method. Element integration problems due to the singular kernel of the integral equations are treated in some detail. Numerical results for both the isotropic and the anisotropic spherical scatterer are presented, including comparisons with results obtained by different numerical methods for the isotropic cases considered. The capability of the numerical code presented here to deal with cases where the material parameters of the scatterer are given by singular matrices is discussed for two particular examples     

Scattering analysis of conducting bodies of revolution usingfictitious currents and point-matching

In this paper, a fictitious current model using point-matching is introduced for the electromagnetic scattering problem of a conducting body of revolution. To take advantage of the rotational symmetry of a scatterer, test points and source points are assumed to have φ-dependence of e^jnφ and are grouped into test loops and source loops, respectively. The number of sample points in each loop is determined in proportion to the length of the loop. Thus, the range of orders to be considered in each loop is dependent on the length of the loop. The field components of higher order modes which can arise due to aliasing are removed using appropriate approximations. Since the current sources and the boundary condition testing are of point-form, the numerical evaluation of the matrix elements is simple and fast. Numerical results are compared with other methods, and the numerical efficiencies obtained with this method are discussed     

基于分形结构的植被高阶相干散射模型研究

电磁波低频入射情况下,植被中散射体独立不相关的假设无效,此时应考虑散射体之间的相干效应以及近场互作用。该文提出一种基于分形结构的植被高阶相干散射模型,该模型利用分形理论生成近乎真实植被的3维几何结构,根据每个散射体的空间位置信息考虑了相干效应,应用互易定理计算了相邻散射体间高阶互作用,结合非相干的分层模型中后向散射机制划分方式,给出了各项散射机制的表达式。与机载合成孔径雷达实验数据对比,验证了模型的准确性。在针叶林仿真参数下,分析了各项散射机制对总散射效应的贡献与入射频率、角度、植被结构的关系,结果表明,低频入射条件下,稀疏植被散射模型可进一步简化从而应用于参数反演中。     

单脉冲寻向天线和目标的一体化仿真及测角误差分析

本文通过矩量法及其高效数值方法（MLFMA）对近距离目标--单脉冲收发天线的电磁互作用进行一体化数值仿真,定量研究了单脉冲天线的近场角度测量特性.在该近场模型中,目标散射近场的幅、相分布和同轴探针激励的喇叭单脉冲天线的辐射场（对应远场和波束）、接收端响应（对应远场差波束）均采用全波数值模拟获得.首先,计算单脉冲天线的辐射场并将其作为对目标照射的激励条件;接着,计算目标散射近场的空间分布;并计算出单脉冲天线所接收到的目标散射场;最后,使用幅值法和相位法计算出单脉冲天线近场测角角度,并在此基础上对近距离测角误差进行研究.在导弹目标算例中,将天线--目标一体化建模和天线口径面上散射近场的幅、相分布计算结果用于近距离条件下单脉冲天线测角误差的研究,并通过频率、距离的变化对测角精度做了对比分析;发现目标近场散射幅、相分布的非均匀性,是导致单脉冲天线近距离角度测量产生较显著的测角误差的主要原因;而频率较低时,测角误差较小.文中给出了物理解释,并提出近距离测向时借助于较低频信号的校正以降低测角误差的建议.     

FINITE DIFFERENCE METHOD FOR ELECTROMAGNETIC SCATTERING FROM PERFECTLY CONDUCTING CYLINDER

A numerical method of solving electromagnetic wave scattering problem is described.Radiation boundary condition(RBC)is applied to confine EM scattering problem in unboundedregion into problem in finite region.Combined with RBC and scatterer surface boundary condi-tion,Helmholtz equation in the finite region is solved numerically by the finite difference method.Thus the distribution of induced surface current on conducting cylinder and near field can beobtained.Computational results for both polarizations for circular,elliptic and square cylindersare presented.These results are in excellent agreement with those obtained by the eigenfunctionexpansion method or moment method and much better then the results of OSRC method.     

Improvements to an electromagnetic near-field sensor forsimultaneous electric and magnetic field measurement

A sensor for simultaneous electric and magnetic field measurement has been described by M. Kanda (see ibid., vol.EMC-26, no.3, p.102-10, 1984). It relies upon measuring the voltage across precisely matched loads at opposite sides of a loop antenna. A modification to the theory is presented to account for unmatched loading of the loop. Measured results of wave impedance over a 10-400-MHz range demonstrate the accuracy of the modified theory as well as highlighting a novel calibration technique     

All Automatic System for Simultaneous Measurement of Amplitude and Phase of Millimeter-Wave Fields (Short Papers)

A measuring system for the simultaneous determination of amplitude and phase distributions of EM fields is described. The system employs the vibrating-dipole technique, which is based on the principle of modulated scattering. The phase-modulated wave scattered by the vibrating dipole contains information about the amplitude and phase of the EM field at the midpoint of the dipole's vibration. The system has been made automatic by the inclusion of a servo loop. The measured free-space distributions compare well with those calculated from theory.