Investigation of Reverberation Chamber Measurements Through High-Power Goodness-of-Fit Tests

This paper aims to improve the analysis of distribution functions of a rectangular component of the electric field (E_R) and the power received in an overmoded reverberation chamber. All data and analysis were achieved in the Institute of Electronics and Telecommunications of Rennes (IETR) mode-stirred chamber. For the power received on a large antenna, tests are consistent with the exponential probability density function assumption. However, high-power goodness-of-fit tests modify the determination of the lowest frequency from which the ideal underlying theoretical distributions can be associated with measurements. For the electric field in an overmoded regime, a Weibull distribution is proposed to model E_R measurements, instead of the Rayleigh distribution hypothesis, which is rejected by statistical tests. Furthermore, Weibull distribution provides better agreement with standard deviation of samples. An additional experiment with a monopole-like antenna illustrates that the exponential distribution is rejected when the monopole is small with respect to the wavelength, but is accepted when the antenna length is roughly over lambda/4. Experimental results are provided by a large number of goodness-of-fit tests. The paper highlights that the use of adapted critical values is necessary for testing a distribution function whose parameters are estimated.     

应用新型混响室技术进行电磁辐射和抗干扰检测

混响室能模拟较复杂的电磁环境,产生较均匀的电磁场,是一种经济有效的新型辐射和抗干扰检测技术.文章介绍了混响室的原理和结构,对混响室的校准步骤和抗干扰性测量方法作了详细论述.     

混响室条件下雷达电磁辐照效应研究*

选择一小型雷达作为受试设备,在混响室内进行了微波辐照效应研究。结果表明:一定场强条件下,雷达产生显示延迟,甚至丧失了探测能力。确定了混响室内雷达的辐射损伤阈值低于20V/ m。结合雷达工作原理分析可知,雷达显示结果滞后于实际目标物,是由于辐射干扰延长了雷达回波延迟时间,从而使其与参考码延迟时间不符引起的。     

Scattering Cross Section Measurement in Reverberation Chamber

Reverberation chambers are now common test facilities used in electromagnetic compatibility. Objects loaded in the chambers, such as antennas and reflectors, can affect the measurement because they absorb and scatter the diffuse field. Thus, it is important to know the scattering and absorbing cross sections of these objects. In this paper, we propose a new technique to measure the scattering cross sections averaged over all angles of incidence and both polarizations in a reverberation chamber. It is based on stacking time-dependent fields generated by a repetitive pulsed source while the objects are moving. The fields recorded by wire antennas are averaged over the object positions. The square of the averaged field is shown to decrease exponentially with the time spent by the wave in the chamber. The cross section is deduced from the exponential factor. The technique has been experimentally validated in a 1 m³ reverberation chamber at 2.45 GHz with metallic spheres of several radii. The experimental cross sections are found to be in agreement with the theoretical ones.     

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     

混响室搅拌器位置优化的数值分析

为研究混响室搅拌器位置对测试区域场均匀性影响,采用基于矩量法的电磁仿真软件FEKO对混响室仿真模型进行数值计算,通过与遗传算法相结合对混响室搅拌器位置进行优化,得到了搅拌器位置的最优解以及相应的表征混响室测试区域场均匀性的电场标准偏差值.研究表明:搅拌器位置影响测试区域场均匀性,当搅拌器位置处于最优配置时,测试区域各轴向电场标准偏差较初始状态分别下降了47.4%、20.1%、57.1%,总标准偏差下降了44.0%,测试区域场均匀性较优化前有所提高,提高了混响室用于电磁兼容测试时的准确度.     

顶角设置QRD散射体的混响室内场均匀性分析

提出了混响室内设置散射体的一种新方法。用FDTD方法对该结构混响室内的场进行了仿真分析,并与无搅拌器及散射体结构的混响室内的场均匀性、散射体位于混响室内6个壁面时混响室内的场均匀性进行了分析比较。结果表明:本文所提出的8个顶角处均设置QRD散射体的方法可有效提高混响室内的场均匀性,实现了进一步提高混响室内场均匀性的目的。     

混响室条件下失真信号消噪技术研究

为研究混响室条件下失真信号消噪恢复技术,采用Mallat算法和预失真技术的失真数据补偿方法,首先,利用蒙特卡洛方法 (Monte Carlo)模拟混响室内电磁环境,获得全向辐照电磁环境和接收系统的联合传递函数;再将联合传递函数的反函数置于预失真器中,用于补偿信号通过混响室内全向辐照电磁环境和接收系统后产生的误差和畸变。利用验证信号进行验证,结果表明该方法可有效消除系统带来的误差,较好地恢复和保持了接收信号信息。     

Evaluation of Transmit Antenna Position in Reverberation Chamber

The position of the transmit antenna is analyzed and evaluated according to the measurement data in our developed reverberation chamber. Nine calibrations are measured carefully. The key parameters such as field uniformity, quality factor, the average normalized electric field, and the receive antenna calibration factor are analyzed in detail. It is indicated that the position of the transmit antenna has insignificant influence on the test repeatability of calibrations     

A Theoretical Feasibility Study of a Source Stirring Reverberation Chamber

A novel theoretical feasibility study to reverberate a large metallic chamber is proposed. The method is based on the displacement of a radiating antenna inside the chamber, and the reverberating effect is obtained by coupling the antenna current in different ways with the cavity modes. This technique eliminates mechanical rotating paddles inside the chamber and offers the advantage of a continuous-wave operation compared with the frequency stirring method. The reverberating characteristics of the proposed technique are evaluated by calculating the field statistics. The analyzed situation concerns a real antenna, and its radiation into the reverberation chamber is modeled using Green's function of cavity. The numerical problem is solved by the method of moment. The model has been tested and is able to rigorously characterize the reverberating environment for the design and optimization of antenna configurations to be addressed in future studies.      

混响室的空间相关特性测量

主要研究混响室内场分布的统计模型,对空间相关函数SCF进行了测量研究,并将测量结果与理论模型进行对比分析,得出一个低频限制的临界频率点。研究结果是在一定频率范围内观察得到的,即从不理想、欠模状态到理想、过模状态的操作。从这些实验结果中可以得到混响室操作的低频限制标准。     

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。     

On the Measurement of the Absorption Cross Section and Material Reflectivity in a Reverberation Chamber

In this paper, all losses in a reverberation chamber (RC) are represented by equivalent absorption cross sections (ACSs), both those due to the power dissipated and those due to the power lost through leakage. This representation enables us to define an absorption cross section of the RC, so that we can easily measure and compare the losses of different natures in an RC directly in terms of ACS. Additionally, this representation of the losses leads to equal measurements of the attendant ACS in relation to two different methods to represent the electromagnetic radiation in an RC suggested by Corona and Hill. As a specific applicative example, an effective method to measure the reflectivity of materials based only on ACS measurements is shown. Finally, its validity will be presented, applying the same principle of the reflectivity measurement to a nested reverberation chamber system.      

集成电路辐射敏感度混响室测试方法

介绍了混响室测试法的工作原理,并通过对GTEM法与混响室法的测试方法和测试结果的对比分析,表明混响室测试方法在1 GHz以上的高频范围测量集成电路(IC)的辐射敏感度更有优势.     

混响室内电磁场统计特性的理论分析

基于混响室内沿各方向来波参数的随机分布等若干基本前提假设,利用"最大熵法"推导了电场强度幅度所满足的概率密度,给出了完整的推导过程。通过和相关文献对比,该分析结果和目前混响室统计特性的相关结论完全一致。     

Maximum Field Inside a Reverberation Chamber Modeled by the Generalized Extreme Value Distribution

Classically, the statistical model of the maximum field inside a reverberation chamber (RC) is derived from the field magnitude model that is only known for the overmoded RC. We propose in this paper to model the maximum field by the generalized extreme value (GEV) distribution, as an application of the Fisher-Tippett theorem that formulates the asymptotic distributions of sample maximum. As the knowledge of the parent distribution (field magnitude) is not required, the GEV distribution is suitable for both overmoded and undermoded regimes (few modes excited). A Monte Carlo simulation illustrates the use of the GEV distribution for the overmoded RC. Modal FEM analysis of the RC extends the application to the undermoded regime. Special attention is brought to the issue of GEV parameter estimation: The so-called L-moments technique is advantageously employed to estimate the parameters from the small data sample. Dispersion of the estimated parameters is approximated and reduced by averaging uncorrelated values obtained from a narrow frequency band     

Numerical Study of Position Stirring and Frequency Stirring in a Loaded Reverberation Chamber

A numerical model of a loaded reverberation chamber is used to study the effectiveness of 3-D position stirring and frequency stirring. The numerical model is based on thin wires, the moment method, and a cavity Green's function. The average power transfer level between two dipole antennas is compared to the average power transfer level between a dipole antenna and a loop antenna. The two transmission levels should ideally be the same, as both the dipole and the loop are treated as being lossless and impedance matched. The standard deviation of the level differences is a measure of the accuracy of the chamber, and this is used to estimate the stirring effectiveness. It is shown that frequency stirring must be done over a larger bandwidth than the average mode bandwidth to be effective. The 3-D position stirring is also shown to be much more efficient than expected.      

混响室条件下无线电引信敏感度测试方法研究

针对国内各类标准及实验中提出的开阔场环境下敏感度测试方法无法满足线度较大弹体及高场强测试需要的问题,利用混响室在测试空间和强场模拟等方面的优势,提出了混响室条件下无线电引信敏感度测试方法.这种测试方法也可以为其他大型装备的敏感度测试提供方法借鉴.该方法基于混响室步进工作模式,测量受试引信在测试频点不同采样点处的临界发火场强.试验证明,取各测试频点在不同采样点处测量值的最小值作为混响室条件下无线电引信的敏感度阈值,不仅在数值上接近于开阔场条件下的测量结果,而且两种实验环境的测试结果保持了很好的相关性,体现了这种测试方法的可行性.     

Errors in Dielectric Measurements Due to a Sample Insertion Hole in a Cavity

The measurement of complex permittivities of isotropic media at microwave frequencies is performed with high precision by means of cylindrical cavity resonators. However, a hole in the cavity wall, for inserting the sample causes a frequency pulling of the resonator, which in turn introduces an error in the measured dielectric constant. These effects are measured, and with perturbation theory as a guide, correction factors are developed.     

利用多天线源搅拌改善混响室场均匀性的分析

通过在混响室的简化三维模型中随机设置激励天线的位置和姿态实现多天线源搅拌因素的引入.与其他方法的对比验证确定利用矩形腔体的电并矢格林函数来仿真电偶极子激励下的电场分布.研究和分析了多天线源搅拌技术对传统混响室工作区域内场分布均匀性的改善作用,结果和理论分析吻合,其性能的提升会受到天线极化和工作频率的影响.