Compound exponential distributions for undermoded reverberation chambers

Novel theoretical first-order probability density functions are derived for the energy density and magnitude of electromagnetic fields inside mode-tuned or mode-stirred reverberation chambers operated at relatively low frequencies. Deviations of physical characteristics for fields in undermoded chambers from those for ideal reverberation are quantified. These deviations are then used as parameters of the distributions. The distribution parameters can be easily and independently calculated from the measured tuner sweep data functions. The derivation is based on an eigenvalue decomposition of the 3/spl times/3 polarization matrix for the stir-averaged local field, followed by a polarization decomposition of the principal components. The theoretical distributions are compared with measured data, showing improved agreement and a significantly lower mismatch at lower frequencies compared to ideal /spl chi//sub 6//sup (2)/ distributions. The previously observed "flattening" of the cumulative distribution function is confirmed, resulting in a now calculable decrease of the mean value and an increase of the uncertainty for field statistics as frequency is lowered.     

EMC混响室电磁场模态研究

混响室谐振腔激励的三维电磁场的推导一般采用并矢格林函数的方法,物理意义不太明显。用本征函数迭加的方法推导混响室有源激励的电磁场分布公式,有利于正确建立混响室电磁结构模型,树立正确的物理概念。并根据公式及其推导过程,分析了混响室EMC电磁工作机理,以此将EMC混响室电磁工作状态按模式状况进行了系统地分类,为混响享研究设计提供理论指导。     

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.     

Reciprocity in reverberation chamber measurements

Even though reverberation chambers have been used primarily for radiated immunity testing, they are reciprocal devices that are equally applicable for radiated emissions testing. This short paper presents the theory for radiated emissions testing and uses electromagnetic reciprocity theory to demonstrate the link between radiated emissions and immunity testing.     

Statistical model for a mode-stirred chamber

The probability density functions for one- and three-dimensional fields in a mode-stirred chamber are derived and verified with chi-square goodness-of-fit tests on experimental data. Each of the three components of the field in the chamber is Rayleigh distributed, which is the same as chi distributed with six degrees of freedom. Each component of the power density is then exponentially distributed. Experimental data confirm these distributions, though unexpected high values, or outliers, were consistently found. Maximum-likelihood estimators of the functions' parameters are derived, and their accuracy is determined as a function of the amount of data. These results are applied to estimating chamber Q. The amount of data required for a given accuracy is determined     

Requirements for an effective reverberation chamber: unloaded or loaded

In this paper, we present two versions of a threshold metric for the purpose of accessing the effectiveness of a reverberation chamber. One metric is based on the chamber quality factor (Q), and the other is based on the volume of the loaded reverberation chamber. These metrics are baseline quantities that must be exceeded in order to have an effective reverberation chamber. These threshold metrics are obtained from two different approaches. The first approach is based on a free-space transmission formulation and the scalar mean power density associated with the "stirred energy" in the chamber and requires that the stirred energy exceeds the unstirred energy throughout most of the chamber volume. The second approach is obtained by requiring that the amplitude of the electric (or magnetic) field satisfies the expected Rayleigh probability density function throughout most of the chamber volume. We present an application of these metrics for the case of a reverberation chamber loaded with spheres composed of lossy materials.     

混响室设计与校准测试

给出了混响室测试系统的设计方法和基本性能的预测分析.根据设计建造了混响室,并且采用自动化测试软件完成了校准测试,分析了电场均匀性、品质因数等性能指标.测试表明建造的混响室性能完全符合测试标准的规定,多次测量重复性很好.最低可用频率200 MHz,电场均匀性小于3 dB.可以用来进行电磁兼容辐射发射和辐射抗扰度测试.     

相似原理应用于混响室缩比模型的验证分析

为了能够将缩比模型应用于混响室设计中,对电磁场相似原理在混响室金属谐振腔体中的适用性问题进行了验证。分析计算了混响室缩比前后的模式数目,证明其符合相似原理;对构造的模型进行了仿真分析,表明缩比前后混响室金属腔体中观察点的电场值具有相似性;通过混响室实物的场均匀性测试数据验证了仿真分析方法的正确性。理论推导和仿真分析结果均说明电磁场相似原理可应用于混响室缩比模型中。     

Increasing peak-field generation efficiency of reverberation chamber

The use of time-reversal techniques has been shown to allow focusing energy in a spot about half a wavelength wide. The fact of being able to concentrate energy into a reduced volume of space implies higher power densities and, ultimately, higher field levels. The use of this feature for improving the ability of a reverberation chamber in converting energy into high-intensity fields is investigated. Experimental results are compared to those predicted by a simple asymptotic model, revealing the role played by losses and frequency bandwidth and how the performance of time-reversal techniques depends on these parameters.     

Linear dipole response in a reverberation chamber

A new spatial correlation function is derived for the axial electric field and is compared with the previously known spatial correlation function for the total electric field. The new correlation function is used to determine the average power received by a linear dipole antenna in a reverberation chamber. The result for the average received power agrees with the previous result for an arbitrary impedance-matched antenna derived by the angular spectrum method     

基于平面波叠加模型的混响室莱斯场环境模拟

从经典混响室的平面波叠加模型出发,针对已有的概率统计模型不能模拟莱斯分布场环境的情况,建立了改进型的平面波叠加模型。为了验证该模型的有效性,用蒙特卡洛方法仿真了不同K因子下的各场量的概率密度函数(PDF),并用理想PDF进行拟合。并进一步验证了当莱斯K因子为零时,莱斯分布场模型退化为经典混响室的场模型。最后考虑了模型的抽样参数(平面波叠加数和搅拌器位置数)对仿真结果的影响,确定最佳的抽样样本,从而获得稳定的PDF曲线。     

混响室条件下的辐射敏感度测试新方法

提出了一种基于统计平均思想的新的辐射敏感度测试方法,在大量实验的基础上验证其可靠性。两种工作模式分别采用位于测试区域内的接收天线在统计平均时间内接收环境场的平均值和所有步进位置测试结果的平均值作为最终测试结果。实验结果表明该方法测试过程简单,能够得到给定设备在任意敏感频点的辐射敏感度阈值,且具有良好的测试可重复性。将国际电工委员会(IEC)颁布的IEC61000-4-21第二版新标准与旧版本中关于步进模式最少独立采样位置的数量做了简要对比,通过实验数据验证了新版本的测试结果。     

Optimization of stirrer designs in a reverberation chamber

This paper describes an investigation into the key factors which contribute to an effective mode stirrer. The work concentrates on the lower frequency range, since all stirrers have poorer performance at low frequencies. The stirrer's shapes and sizes have been investigated, together with an optimization of the finer details in the stirrer's shape. The modeling of the mode stirred chamber has been performed using the transmission-line matrix (TLM) method. Software has been developed which, for each position of the rotating stirrer, builds the shape of the stirrer using thin, perfectly conducting boundaries. Results indicate that the design of the stirrer's basic shape has a small but significant impact on its performance. A genetic algorithm has been used to optimize certain parameters in the shape of the stirrer, and a fitness factor based on a free space model of the stirrer has been used. The free space model runs 1500 times faster than the model in the chamber. The optimization is shown to improve the stirrer's performance in three different sizes of chamber. Computer modeling has been verified by measurements performed in the chamber at the University of York.     

Power transfer characteristics of a microwave reverberation chamber

Power transfer through a microwave reverberation chamber is studied theoretically and experimentally. Two configurations are employed as follows. In the first, the chamber contains a transmitting antenna and a receiving antenna; in the second, it contains a transmitting antenna and a receiving D-dot sensor. For each configuration a theoretical model is derived and laboratory measurements are carried out for the power gain of the chamber as a function of frequency. The models prove useful in predicting the observed variation of gain with frequency, and they provide insight into the importance of power flow to the chamber walls and to the receiving antenna/sensor     

Delay spread and coherence bandwidth in reverberation chamber

The reverberation chamber becomes an attractive tool for simulating a multipath environment. Starting from the definition of the delay spread and of the coherence bandwidth, analytical expressions in terms of the Q-factov of the room are determined and compared with those of the power density decay factor and of the mode bandwidth, allowing a better insight into the chamber characterisation.     

Analytical angular correlation function in mode-stirred reverberation chamber

A new closed-form expression for the autocorrelation function of the electric field as a function of the rotation angle of the stirrer is proposed. It allows the quantification of the influence of the stirrer radius on the stirring efficiency. A comparison between theoretical and experimental results is also given.     

Theoretical investigation of the field conditions in a vibrating reverberation chamber with an unstirred component

In this paper, we examine the use of a vibrating reverberation chamber in which an equipment under test (EUT) is directly illuminated by a source antenna. A three-dimensional theoretical model, based on a simplified ray tracing method has been applied on a reverberation chamber whose dimensions were varied. The field distribution together with the field homogeneity was investigated, introducing the Rice distribution due to the presence of the line-of-sight component between the antenna and the EUT.     

Some remarks on antenna response in a reverberation chamber

The simple formula, 〈P_r〉=(E₀² /η)(λ²/8π), for the received power of an antenna with a matched load in an over-moded cavity actually holds for an antenna of any shape and size. This can be seen from the close connection between the correlation tensor of the cavity field at two different points and the imaginary part of the free-space dyadic Green's function