搅拌器配置对混波室场影响的FDTD分析

混波室能提供统计均匀和各向同性的场,是一种用于辐射发射、屏蔽效能及敏感度测试等电磁兼容测试的小室。本文用FDTD方法分析混波室的场分布,分析了搅拌器不同大小及不同倾斜角度对混波室时间平均场分布的影响,为实际设计混波室的搅拌器提供参考。最后给出了与数值分析相一致的实验结果。     

声学散射体对混波室场均匀性的影响

为了改善混波室低频时的性能,文中提出了基于声学理论的Sehroeder散射体.通过FDTD数值仿真与实验相结合给出了不同频率散射体加入到装有搅拌器的混波室的前后场均匀性.分析了数值仿真与实验的结果,证明散射体能有效改善混波室中电场的均匀性尤其在较低频率下较为明显,拓展了给定混波室(由东南大学自主研发)最低使用频率(LUF)约100MHz,为改善混波室低频性能提供了思路.     

混波室场的直接耦合分量及其测量可重复性研究

通过实验验证了混波室内场的统计特性.给出了基于矢量网络分析仪的测量混波室可重复性的试验方法与配置.用矢量网络分析仪的方法对不同的发射天线方向进行了测试与比较.结果表明:发射天线的方向对混波室测量可重复性有较大的影响,对准混波室的角落和搅拌器时的测量可重复性较好.     

混波室测量中辐射信号与观测信号相关性研究

采用有限元方法研究二维混波室结构辐射电流和测量的辐射场平均值的关系,目的是了解混波室测量环境是否能够满足电磁兼容辐射测量的要求.从二维数值计算结果可以看到,观测场的平均值和辐射电流具有很好的线性关系,从而证明混波室可以作为电磁兼容辐射测量的一个有效测试设备.     

混波室中的信道测试仿真

随着混波室性能研究的深入,利用混波室提供的电磁环境进行信道研究成为一项热门课题。本文围绕混波室信 道研究时面临的建模仿真问题进行了一系列讨论,通过对比试验测量数据,对仿真计算模型进行简化和改进,达到了节 省计算时间且计算准确的目标,使仿真模型更贴近真实的测试环境,为接下来的混波室信道研究提供了可靠的支持。     

混波室测量技术

文章介绍了电磁兼容测量技术中的混波室测量技术.阐述了混波室的工作原理、理论分析模型、统计特性、混波室设计中的若干问题,以及混波室技术的现状和应用前景.     

混波室设计原理在微波炉性能改善中的应用

本文对家用平板微波炉和混波室的结构和应用进行了对比并提出在微波炉性能改善的工作中可以借鉴混波室的设计方法。在此基础上对多搅拌片和不规则形状的腔体进行了设计和验证。两种方法的验证结果相对传统的微波炉结构的微波加热均匀性都有明显的提升,表明混波室为形成统计均匀的电磁场的设计方法可应用于微波炉加热均匀性改善。     

大张角宽带对数周期天线的优化设计

文章运用矩量法对大张角对数周期天线的电性能进行了分析.经过优化设计制作的大张角宽带对数周期偶极子天线(LPDA,Log Periodic Dipole Antennas),经测试测量值与计算值吻合得较好,已用于混波室测试.     

TEM传输室多层介质支撑特性阻抗的数值分析

采用边界元法分析了芯板支撑对TEM传输室特性阻抗的影响.介绍了建模方法,以及边界元法计算多介质区域特性阻抗的基本思想.计算结果表明:芯板支撑对特性阻抗的影响比较显著,随材料介电常数的不同,影响值一般为2～5Ω左右.测量结果与计算结果基本吻合.提出的数值计算方法有助于TEM传输室的设计.     

不同回转半径搅拌器效率的仿真与研究

搅拌器是决定混响室场均匀性好坏的关键部件,而电场样本间的相关系数和归一化最大电场值又是衡量搅拌器效率高低的重要参数.通过采用有限元数值方法对混响室的电磁场分布进行仿真,并研究了采用不同回转半径的搅拌器时,混响室这两个参数的变化情况,结果发现,相对工作频率波长来说,高效率搅拌器的回转半径应该尽量大,但是当回转半径达到一定程度后,它对搅拌效率的改善变得不明显.     

Advanced method for estimating number of independent samples available with stirrer in reverberation chamber

A simple and efficient method for optimising the use of a stirrer in a reverberation chamber is presented. The maximum number of independent samples given by the stirrer is estimated using a regression model and central limit theorem in the case of dependent data. The predicted results are compared with measured data and good agreement is reported.     

Chaoticity of a Reverberation Chamber Assessed From the Analysis of Modal Distributions Obtained by FEM

Wave chaos theory is used to study a modeled reverberation chamber (RC). The first 200 modes at a given stirrer position are determined by the finite element method, and the Weyl formula is checked for various RC geometries, from integrable to chaotic. The eigenfrequency spacing distribution varies according to the degree of ray chaos in the RC related to its geometry. The eigenmode distributions are also analyzed and compared to the theoretical Gaussian distribution: close to the lower useable frequency, the modes of the studied chaotic RC fairly respect this asymptotic property. A general result of chaotic systems is illustrated: when perturbed by the stirrer rotation, the resonant frequencies of a chaotic RC avoid crossing. This implies that the frequency sweeps tend to vanish at high frequency.     

Comparison Between Different Criteria for Evaluating Reverberation Chamber Functioning Using a 3-D FDTD Algorithm

This paper is devoted to the comparison between different criteria used to evaluate the functioning of a mechanically stirred reverberation chamber. Usual criteria based on power or electric fields are considered, and we also propose a criterion based on the Kolmogorov-Smirnov test, called in this paper ldquosuccess ratio to Kolmogorov-Smirnov testrdquo (SRKS). The SRKS represents the acceptation ratio of this test applied at several points of the working volume, when considering a field component and its associated theoretical distribution. After a presentation of the criteria and of the studied chamber, data issued from 3-D finite-difference time-domain simulations and measurements are used to analyze the chamber functioning by the use of these criteria. This study is performed on a large frequency band, in the lossless case as well as with a lossy chamber, and for several stirrer shapes, to emphasize the influence of these parameters. The comparison of the usual criteria with the SRKS shows the SKRS is an accurate test to estimate the lowest usable frequency of a given reverberation chamber.     

On the FEM Modal Approach for a Reverberation Chamber Analysis

We review the difficulties linked to the modal approach when modeling a reverberation chamber by the finite element method (FEM). The numerical challenge is due to the large-scale problem involved by the overdimensioned cavity. Moreover, the field singularity on the stirrer has to be captured by the FEM. First, the following issues are discussed: existence of null-frequency solutions, convergence rate for h and p adaption, and formulation type in E or H field. The modal analysis is then compared to the classical harmonic one. Focus is put on the field singularity at the source point     

FDTD modelling of reverberation chamber

The finite-difference time-domain (FDTD) method is applied to the simulation of a reverberation chamber. The real losses of the reverberation chamber are taken into account in a post-treatment process. The predicted results are compared with measured data and good agreement is reported.     

Modeling of the Reverberation Chamber Method for Determining the Shielding Properties of a Coaxial Cable

The paper considers the reverberation chamber (RC) method for the measurement of the shielding effectiveness (SE) of coaxial cables with braided shields. In particular, the voltage at the cable termination is numerically computed and compared to that measured in an RC. The RC field is represented by a finite summation of random plane waves, and a finite-difference time-domain (FDTD) code is used to calculate the outer shield current induced by the RC field. The knowledge of the shield current distribution allows the determination of the voltage at the cable termination's internal circuit after a proper numerical averaging. It is then compared to the measured voltage averaged over stirrer rotations. The method is applied to a commercially available cable model RG58, and using the nominal value for the transfer impedance of this cable type gives results in a satisfactory agreement with the measurements. Finally, the possibility of recovering the transfer impedance from the measured SE of the RC is discussed.     

Experimental Investigation and Mathematical Modeling of Design Parameters for Efficient Stirrers in Mode-Stirred Reverberation Chambers

In this paper, we have investigated the design parameters for efficient stirring in reverberation chambers. We have measured the efficiency of the stirrer in terms of the lowest possible frequency for which it gives a certain number of uncorrelated samples. Rotating stirrers, when rotated about their axes, generate cylindrical volumes. The impact of a change of the stirrer diameter is approximately cubic compared with the change of the stirrer height. The efficiency of stirrers that are translated is proportional to the stepping increment and to the square root of the area of projection of the stirrer on a plane orthogonal to the direction of translation