Experimental wire grid modelling for antennas on structures

Theoretical wire grid modelling for antennas on structures involves the approximate solution of an approximate problem. By experimentally modelling the approximate problem of a wire grid replacing a continuous metal structure, it is shown that a wire grid with spacing ? ?/10 is a good approximation both for the far-field radiation pattern of the antenna and for its input impedance. Difficulties in providing accurate impedance predictions should therefore be ascribed to the approximate mathematical solution, rather than the wire grid model.     

Wire grid modeling of surfaces

When a surface is numerically modeled with a wire grid, results are sensitive to the wire diameter. It is shown that the best accuracy is obtained when the wire satisfies the "same surface area" rule of thumb, for the canonical problem of scattering (or radiation) from an infinite circular cylinder. It is important to note that wires that are too thick are just as bad as wires that are too thin. It is also shown that the boundary value match between wires is not a reliable check on the validity of farfield results. Finally, data are given on the effect of wire spacing. Results are obtained from exact solutions of both the true problem and the wire grid model, thus isolating the effects of wire grid modeling per se.     

周期性电抗加载介质结构电磁特性的等效分析

提出了一种周期性电抗加载介质结构传输特性的等效分析方法。在5～15GHz频率范围内,通过对A夹层介质结构中周期性加载金属丝网栅和金属条带网栅两种结构的电磁特性仿真分析,建立了金属条带宽度与金属丝直径之间的等效关系,并详细分析了电磁波入射方向、网栅加载位置、金属丝直径大小、网栅周期以及介质结构对等效的影响。仿真结果表明:电磁波任意方向入射,金属丝直径较小时等效条件为金属条带宽度为金属丝直径的π/2倍。因几何参数变化而导致的等效误差可以通过等效系数的经验公式予以修正。     

一种基于极化线栅的微波辐射计变温定标源研究

根据极化线栅的准光学的极化分离原理,设计了由极化线栅、人造黑体和冷空构成的新型线栅定标源.定标源通过极化线栅的旋转混合人造黑体和冷空的辐射能量,从而输出亮温变化可控的微波辐射,为微波辐射计外定标提供人造变温源,解决了低频段大口径天线辐射计的外定标难题.通过定标实验验证,极化线栅在L波段的透过率优于99.3%,反射率达到98.4%,线栅定标源的亮温呈正弦规律变化,变化范围为8~248K,实验结果与设计目标相吻合.     

Fabrication of wire-grid polarizers and dependence of submillimeter-wave optical performance on pitch uniformity

We describe a device for fabricating high-precision free-standing grids of fine wire, suitable for use as polarizing elements for radiation at millimeter and submillimeter wavelengths. Computer control of the winding process makes changing grid parameters particularly convenient and flexible. We present measurements of the mechanical uniformity and of the optical performance of wire grid polarizers made with 25 μm and 10 μm diameter wire. The flexibility of computer control is exploited to introduce a known degree of randomness in the grid pitch (center-to-center wire spacing), allowing the dependence of polarizer quality on uniformity to be quantified. This information allows prediction of the fabrication tolerances required for polarizers to be used at very high frequencies.     

A broad-band twist reflector

Polarization twisting reflectors, or twist reflectors, consisting of a wire grid spaced approximately3 lambda/8from a ground plane [1], [2] have a bandwidth of at most 30 percent. It is shown that the inclusion of an additional wire grid in front of the first grid makes bandwidths of 100 percent possible. Design formulas, theoretical performance in terms of cross polarization attenuation, and some experimental results for a twist reflector with two wire grids are given.     

The Impedance of a Wire Grid Parallel to a Dielectric Interface

Analysis is given for the problem of reflection of a plane wave at oblique incidence on a wire grid which is parallel to a plane interface between two homogeneous dielectrics. It is assumed that the wire grid is a periodic structure and consists of thin cylindrical wires of homogeneous material. The equivalent circuit is derived where it is shown that the space on either side of the interface can by a transmission line, and the grid itself is represented by a pure shunt element across one of the lines.     

The RCS of a metal plate with a resonant slot

A numerical method based on the thin-wire electric field integral equation is used to calculate the radar cross section (RCS) of a wire grid with a resonant slot. The numerical results are in good agreement with experimental data for a wire grid, where the antiresonance is found to occur at a slightly lower frequency than a similarly slotted plate.     

Transmission Characteristics of a Gaussian Electromagnetic Beam by a Cylindrcal Wire Grid

In this paper, the scattering formulae of a Gaussian electromagnetic beam by a cylindrical wire grid are derived. For the summation of Hankel functions, we adopt an integral form of lattice sums, which is developed by Yasumoto and Yoshitomi, to speed up convergence. The reflected and transmitted characteristics of a Gaussian beam by an actual wire grid are thoroughly investigated. Detailed simulation results are presented.     

中红外量子级联激光器偏振合束实验研究

合束是实现量子级联激光器高功率输出的关键技术,基于激光的偏振特性,研究了偏振合束的实验原理及实验方法。使用线栅偏振片和中波半波片组成偏振合束装置,对两路4.05 μm量子级联激光器进行偏振合束,测试了中波半波片对4.05 μm激光的透过率以及中波线栅偏振片对4.05 μm激光透射率和反射率与入射角的关系,通过实验研究,当透射路光束和反射路光束与线栅偏振片的夹角为30°时,透射路的透射率为81%,反射路反射率为91%,其光束合束效率达到约86%,并使用光束质量分析仪对合束之后的光束质量进行测试分析。结果表明:两路光束通过该合束装置合束之后,在保证合束效率的条件下,具有较好的光束质量。     

采用前置栅网滤波的天基红外成像点目标探测技术

天基红外成像预警大多属于点目标探测,如何在复杂背景及随机点噪声条件下实现点目标的有效探测和跟踪是天基红外预警技术重点研究内容。研究了新型前置栅网滤波热成像理论,分析了基于前置栅网滤波形成特定衍射斑对天基红外成像点目标探测的影响,利用Matlab对栅网的滤波效果进行了模拟仿真,所得仿真图像与实验图像的衍射强度分布具有较好的一致性;并在相同点目标能量条件下,对点目标及其前置栅网滤波衍射图案进行了人眼视觉探测实验,初步分析表明了其对于点目标探测和跟踪的有效性,为进一步研究和发展高性能的天基红外成像技术提供了一种新途径。     

基于遗传算法的栅格天线阵旁瓣电平优化方法

在推导出栅格天线阵列方向图的基础上,提出一种基于遗传算法的栅格天线阵旁瓣电平优化的方法。此方法首先简化栅格天线阵物理模型,给出等效模型下的阵列方向图,然后以栅格天线阵的短边电流幅度为优化参量,以阵列天线方位面的副瓣电平为适应度函数,利用遗传算法的最优化搜索得到满足副瓣要求的电流幅度,再通过电流幅度计算辐射单元阻抗,最终设计出满足要求的低旁瓣栅格天线阵。为了验证该方法的有效性,对一种频扫微带栅格天线进行了优化,在电磁仿真软件中对优化后的天线进行了仿真,根据设计结果加工制作了原型天线并进行了测试,测试结果显示优化后天线阵的副瓣电平降低了5dB,优化效果明显。     

The near field of a wire grid model

The extreme near-field behavior of the wire grid model of a conducting surface is examined. Using a wire grid model of an infinite transverse magnetic circular cylinder, it is verified that the best accuracy for the E-field is obtained when the wire satisfies the `same surface area' rule of thumb. Two excitations are considered: a uniform surface current and plane wave incidence. In the first case, although the boundary value match between the wires is poor the extreme near field is still quite accurate. In the second case, the near field is also accurate, however, the largest errors occur not between the wires, but in the interior of the scatterer. In both cases, the boundary match between the wires as a check on the accuracy of the solution is misleading     

采用前置栅网滤波的红外点目标探测方法

根据红外热成像系统前置栅网的衍射效应,分析其应用于点目标探测领域的可行性;提出了一种基于前置栅网滤波的红外点目标探测方法,详细介绍了算法处理流程,该算法通过背景抑制、图像分割、图形匹配有效地实现了对前置栅网滤波后的点目标像探测;最后,将其与传统的TBD探测方法进行比较。实验结果表明:该方法由于使点目标实现了特定形状的扩展,能更好地区分真实目标和噪声,同时降低算法复杂度,能够实现实时处理,具有很好的应用前景。     

Note on the impedance of a wire grid parallel to homogeneousinterface

Numerical data are provided for the correction factor that is used to calculate the impedance of a planar wire grid parallel to the interface between two dielectric half-spaces. Comparisons with earlier investigations clarify, extend, and supersede previous computations. The authors show more clearly the significant influence of the interface on the equivalent grid impedance     

Optical properties of F.I.R. metallic grids: Reflection phase shift measurements

Utilization of metallic grids stacks for F.I.R filters needs a good knowledge of optical properties of each grid. We study here an experimental method in order to determine the wave's change of phase by reflection on a wire grid. We use a Perot-Fabry interferometer constituted by these grids.     

电线电缆维护技术及管理措施研究

我国经济的飞速提升,造就了我国电力事业的进步.其中电线电线电缆作为电网建设发展的核心内容之一,可以直接影响着社会居民的用电安全和用电正常情况.这就需要国家以及社会各阶层提高对电线电缆维护以及管理工作的重视,相关工作人员对自己的岗位充分负起责任,共同提高电线电缆的应用质量问题.     

Modeling of thin wires in a lossy medium for FDTD simulations

An equivalent radius of a thin wire in a lossy medium, represented by the finite-difference time-domain method, is derived using the concept that was proposed to derive an equivalent radius of a thin wire in air. Then, a simple technique to specify an arbitrary radius of a thin wire in a lossy medium is proposed. The proposed technique does not employ locally fine or nonuniform subgrids, but is based on an orthogonal and uniform-spacing Cartesian grid. The validity of the proposed technique is investigated in a transient state, as well as in a quasisteady state, and shown to be satisfactory.