混响室\

在功率平衡法的网络化公式应用中, 精确预知腔内装载物的耦合截面积是关键, 这通常依赖于混响室的实验测定.文中使用平面波角谱概念和蒙特卡罗方法来数值模拟混响室中的电磁环境, 在此基础上, 首次应用基于互易定理的快速全波分析方法提取了理想混响室内靠近理想导电地平面的多导体传输线的平均耦合截面积, 验证了方法的正确性, 并计算了单根裸线传输线、带包层传输线、双绞传输线、传输线附近有导体挡板以及多导体传输线端口的平均耦合截面积.该方法具有计算精度高、仿真速度快、适用范围广的特点.     

Numerical and experimental analysis of the field to enclosure coupling in reverberation chamber and comparison with anechoic chamber

This paper presents a study of coupling between an external field and a metallic enclosure with a long aperture in the frequency range which includes several box resonances. A reverberation chamber (RC) and an anechoic chamber (AC) are considered as a field generation structure. In both cases, a customized FDTD code is used to calculate the current induced by the external field in a loop placed inside the enclosure. In order to simulate the AC facility, a single plane wave is used to represent the test field, whereas for the RC, the field is represented by a proper superposition of random plane waves. Numerical results are experimentally validated. The proposed method is useful to investigate the performance of the enclosure during its early design stage before the realization of a prototype.     

A Metrology Application of Reverberation Chambers: The Current Probe Calibration

This paper presents how it is possible to characterize a current probe in terms of its transfer impedance inside a reverberation chamber. The probe catches a floating wire placed inside the working volume of the chamber. The current on the wire is calculated from the knowledge of the total measured average field along the wire in the working volume. The current is calculated by representing the field in terms of a summation of random plane waves, where a finite-difference time-domain (FDTD) code is used to compute the current induced by each plane wave along the wire caught by the probe under test. Results for the current distribution along the wire are reported for several frequencies. Finally, the transfer impedance of commercial probes is recovered from the knowledge of the current and compared to the values given by the manufacturers and by an external laboratory     

时域有限差分法分析混晌室中场的均匀性

针对目前仿真分析混响室内的场分布过程中计算量大、耗费时间长和对计算机配置要求高的现状,用在一定的约束条件下随机分布于球面上的一组等效源辐射的平面电磁波叠加而成的一维推进的重叠平面渡模拟搅拌器搅拌过程中混响室内的电磁波,并采用时域有限差分法(FDTD)法对基于上述模型的混响室内的场分布进行了仿真计算,得出了使混响室内场分...     

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.     

Aperture excitation of electrically large, lossy cavities

We present a theory based on power balance for aperture excitation of electrically large, lossy cavities. The theory yields expressions for shielding effectiveness, cavity Q, and cavity time constant. In shielding effectiveness calculations, the incident field can be either a single plane wave or a uniformly random field to model reverberation chamber or random field illumination. The Q theory includes wall loss, absorption by lossy objects within the cavity, aperture leakage, and power received by antennas within the cavity. Extensive measurements of shielding effectiveness, cavity Q, and cavity time constant were made on a rectangular cavity, and good agreement with theory was obtained for frequencies from 1 to 18 GHz     

Plane wave integral representation for fields in reverberationchambers

A plane wave integral representation is presented for well-stirred fields in a reverberation chamber. The representation automatically satisfies Maxwell's equations in a source-free region and the statistical properties of the fields are introduced through the angular spectrum, which is taken to be a random variable. Starting with fairly simple and physically appropriate assumptions for the angular spectrum, a number of properties of the electric and magnetic fields and the power received by an antenna or a test object are derived. Many of these properties and test object responses are in agreement with other theories or with measured results. An important result for radiated immunity testing is that the ensemble (stirring) average of received power is equal to the average over plane wave incidence and polarization     

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。     

镜像对称结构对多馈源混响室场性能的影响

为解决混响室大体积与场性能高要求之间的矛盾,提出了一种基于镜像原理的多馈源混响室的设计思想,从原理上分析了镜像多馈源混响室的可行性和有效性,并通过仿真计算研究了镜像双馈源混响室的场性能.结果表明,在输入功率一定时,两个单混响室系统组合成镜像双馈源混响室后,在工作区域的场均匀性能不下降的基础上,不但可用于电磁兼容测试的工作区域体积大幅度增大,而且测试区域的电场强度也得到了提高.同时,对镜像多馈源混响室进行了进一步的扩展分析,得出了组成镜像多馈源混响室的单混响室系统数量的理论表达式.     

A closer look at reverberation Chambers - 3-D Simulation and experimental verification

This paper presents three-dimensional (3-D) full-wave simulations of the electromagnetic field inside a medium-sized reverberation chamber. A frequency-domain method-of-moments approach based on the electric field integral equation is used. A synopsis of the computational challenges particular for reverberation chambers is described and a detailed overview on the chamber modeling procedure is given. The electric field inside the chamber is computed and the influence of small geometric details and asymmetries is investigated as well as the effect of different excitations and stirrers. It is demonstrated that a statistics-based validation of reverberation chamber simulations is insufficient. To validate simulation results, therefore extensive near-field measurements inside the prototype reverberation chamber are performed. The complete 3-D reverberation chamber simulation, considering stirrers, door, and various practical excitations, accurately predicts the fields within the chamber in the important lower-to-medium frequency range and thus represents a reliable tool facilitating reverberation chamber optimization.     

双发射天线对混响室场性能影响的数值分析

提出了双天线激励混响室的方法,研究了双天线激励对混响室场性能的影响。分析了双天线改善混响室场均匀性的原理,对单天线激励下的混响室模型以及处于不同位置的双天线激励下的混响室模型进行了仿真计算,从场均匀性和场强两个方面研究了双天线对混响室场性能的影响,对双天线影响场强的机理进行了分析。研究表明:采用双天线激励改善了混响室工作区域的场均匀性;采用双天线可以降低对功率放大器的要求,降低大型混响室测试成本。最后对双发射天线在大型混响室中的应用进行了探讨和展望。     

Validation of a Three-Dimensional Transmission Line Matrix (TLM) Model Implementation of a Mode-Stirred Reverberation Chamber

Reverberation chambers are attractive electromagnetic compatibility test facilities, both economically and technically. Careful design and analysis of these facilities are important, if the results obtained are to be treated with a high level of confidence. Numerical modeling is an important part of the process of reverberation chamber design and analysis. Hence, it is important that the modeling techniques to be used are appropriately validated. Much of the published work to date takes either a statistical or a deterministic view of validation. This paper provides validation evidence for a low-resolution transmission line matrix (TLM) model of a reverberation chamber in a manner approximating the way in which the chamber is used, i.e., validating based on the effects of a simple device under test. A variety of statistical and heuristic approaches have been used to quantify the level of agreement, intending to set the likely lower bound for the quality of comparisons between simulations and measurements. While not drawing any "universal" conclusions about the veracity of the TLM technique, the paper concludes that a relatively simple model of a reverberation chamber provides a useful analysis of the chamber with close comparisons between modeled and measured data.     

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.     

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.     

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。     

Study of antennas in reverberation chamber using method of moments with cavity Green's function calculated by Ewald summation

A numerical model of wires in rectangular metal cavities is introduced for computing antennas in a simplified theoretical reverberation chamber. The code is based on the method of moments, and it uses the Ewald summation for efficient calculation of the cavity Green's function. The Q-value of the chamber is accounted for in the model by a homogeneous material filling the chamber. The S-parameters of two dipoles placed in many random positions in the cavity are computed and averaged to provide the average transfer function of the chamber. This represents mode stirring by moving the antennas, referred to as position stirring. The computed results are compared with theoretical statistical values as well as experimental results. The discrepancies are discussed.     

Efficiency measurement of UWB antennas using time reversal in reverberation chambers

Using the reverberation chamber to obtain antenna radiation efficiency is considered. The reverberation chamber, which has for many years been used for electromagnetic compatibility measurements, can also be used with great advantage for antenna measurements since it simulates effectively a uniform multipath propagation environment. How a reverberation chamber can be used to measure the ultra-wideband (UWB) antenna efficiency in a very short time is described. The procedure based on time domain is described and some experimental results are given and compared to measurements obtained by the Wheeler cap method extended by Schantz to UWB antennas.     

混响室校准与辐射抗扰度测试

在对混响室的基本原理进行简要介绍的基础上,依据标准IEC61000-4-21中的规定,对混响室的校准方法及操作过程进行了详细介绍和分析,并对在混响室内进行辐射抗扰度测试的方法及步骤进行了介绍。     

A surrogate model to assess the whole body SAR induced by multiple plane waves at 2.4?GHz

The assessment of the exposure to electromagnetic waves is nowadays a key question. Dealing with the relationship between exposure and incident field, most of previous investigations have been performed with a single plane wave. Realistic exposure in the far field can be modeled as multiple plane waves with random direction of arrival, random amplitude, and random phase. This paper, based on numerical investigations, studies the whole body specific absorption rate (SAR) linked to the exposure induced by five random plane waves having uniformly distributed angles of arrival in the horizontal plane, log-normal distributed amplitudes, and uniformly distributed phases. A first result shows that this random heterogeneous exposure generates maximal variations of ??25% for the whole body specific absorption. An important observation is that the exposure to a single plane wave arriving face to the body, used for the guidelines, does not constitute the worst case. We propose a surrogate model to assess the distribution of the whole body SAR in the case of an exposure to multiple plane waves. For a sample of 30 values of whole body SAR induced by five plane waves at 2.4?GHz, this simple approach, considering the resulting SAR as the sum of the SAR induced by each isolated plane wave, leads to an estimated distribution of whole body SAR following the real distribution with a p value of 76% according to the Kolmogorov statistical test.