电波暗室性能指标的测试方法

介绍了评估电波暗室性能的方法,包括屏蔽效能、归一化场地衰减、传输损耗、场均匀性的详细测试过程,并对可能影响测试结果的因素和需要注意的问题进行了分析.     

Modeling semi-anechoic electromagnetic measurement chambers

Previous studies developed a model to predict theoretically the low-frequency plane-wave reflection coefficient of an array of pyramid cone absorbers such as those used to line anechoic electromagnetic measurement chambers. The present authors apply this model in a geometrical optics approach to predict the electromagnetic field in a chamber lined with cone absorbers in the frequency range of 30-300 MHz. The results are compared with site attenuation measurements for two actual semi-anechoic chambers     

Coexistence Between Ultra-Wideband Radio and Narrow-Band Wireless LAN Communication Systems—Part I: Modeling and Measurement of UWB Radio Signals in Frequency and Time

The correct modeling and measurement of ultra-wideband (UWB) radio signal are a critical issue to evaluate the electromagnetic (EM) emission of any communication system based on this technology. In this paper (Part I), UWB radio communication systems based on impulse radio (IR) and multiband orthogonal frequency division multiplex (MB-OFDM) technologies are characterized by simulations and experiments in both frequency and time domains. The EM characteristics of UWB radio are measured by different methods (conducted and radiative) and in different environments (anechoic and reverberation chambers).      

Reverberating chambers as sources of stochastic electromagneticfields

Reverberating chambers are of recognized relevance in many EMC applications since they allow us to generate a reference electromagnetic statistical field. This paper investigates the electromagnetic field in reverberating chambers. Reverberating chambers are large overmoded cavities wherein a nonstationary electromagnetic field is present. This electromagnetic field is stochastic in nature; therefore, proper analytical tools need to be considered in order to characterize it. We deal with the theoretical aspects related to the characterization of the electromagnetic field inside the chamber and with the application to the case of the reverberating chamber of the Istituto Universitario Navale     

Design Criteria for Cost-Effective Broad-Band Absorber-Lined Chambers for EMS Measurements

The problem considered here concerns simulating the electromagnetic environment for electromagnetic susceptibility (EMS) measurements over a wide frequency range. Means of bridging the existing gap between low-and high-frequency techniques are suggested by extending the use of anechoic-type chambers downward in frequency. Results of measurements over a wide frequency range are presented to demonstrate the behavior of such absorber-lined chambers (ALC's). Basic criteria and guidelines for the design of ALC's are proposed.     

The effects of intrinsic test fixture isolation on materialshielding effectiveness measurements using nested mode-stirred chambers

The paper evaluates the effects of test fixture isolation when using nested mode-stir chambers for conducting electromagnetic shielding measurements. The nested chamber technique is used by both government and industry to evaluate the electromagnetic attenuating properties of materials as varied as infrared sensor windows to the composites used in the hulls of new ships. Two cases are considered: (1) the test aperture provides little inherent isolation between the two chambers, and (2) the aperture provides reasonably good isolation. It is shown that in the former case, data taken in this fashion can exhibit significant deviation from the latter. A correction factor for the former case is developed     

A low-frequency model for wedge or pyramid absorber arrays-I:theory

The interaction of electromagnetic waves with an array of absorbing wedges or pyramid cones is studied in the low-frequency limit; i.e., when the period of the array is small compared with wavelength. A theoretical model is obtained using the method of homogenization, which replaces the transversely periodic structure with a transversely uniform medium possessing a certain (generally anisotropic) effective permittivity and permeability. Plane-wave reflection from such structures can then be modeled using well-known techniques for one-dimensionally inhomogeneous media; a Riccati equation for the reflection coefficient is used in this work. This model is appropriate for use with absorbers found in anechoic chambers used for electromagnetic compatibility and electromagnetic interference (EMC/EMI) measurements over the frequency range of 30-1000 MHz     

Optoelectronically-pulsed antennas: characterization andapplications

A brief tutorial on the picosecond photoconductive effect is given. The use of picosecond optoelectronics for the characterization of broadband antennas is described. In particular, the transient radiation properties of equiangular-spiral and exponentially tapered coplanar-strip antennas are discussed. The transient radiation behavior and the polarization and radiation patterns of these antennas are easily determined with this measurement technique, without the need for anechoic chambers. Applications of picosecond-duration transient electromagnetic radiation to filter measurements, materials measurements, and scattering studies are discussed     

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.     

Broadband electromagnetic absorber with ferrite/ferrite hybridstructure

A new broadband electromagnetic absorber has been constructed by using the NiZn/NiZn ferrite hybrid structure and analysed using the FEM (finite element method). The structure is only 55.5 mm high, and has a reflection loss of <-20 dB in the frequency range 30 MHz-3 GHz. These characteristics are superior to those of conventional absorbers which have been used in anechoic chambers     

低频/甚低频电磁脉冲测量系统研究

为了准确地测量电磁脉冲（electromagnetic pulse,EMP）的波形,开展低频/甚低频（low-frequency/very low-frequency,LF/VLF）EMP的形成和传播机理研究,识别不同EMP的特征,并以此为依据来识别、确认雷电及核爆炸等现象,提出了一种高分辨率的EMP原始波形测量系统方案,同时针对LF/VLF这一较低的频段提出了一套有效的系统标校方法,实现了对EMP的连续、准确测量和快速有效判别,并能通过网络实时上传数据.系统采用正交环磁场天线和平板电容电场天线实现信号的接收,设计了低噪声高保真的信道调理电路和高速数据采集电路来实现信号的采集,利用高精度的授时模块为EMP信号标记时间戳,最后结合多点监测波形实现EMP定位估计.实测结果表明:该系统能够给出高分辨率、高精度的LF/VLF EMP波形;利用该系统组网可以实现远距离EMP源的定位,定位精度与目前近距离的定位手段相当.通过长期的运行,验证了该系统具有高可靠、低失真、判别准确、实时性强等特点.     

Standard antennas for electromagnetic interference measurements andmethods to calibrate them

This tutorial paper discusses various standard antennas for measuring radio-frequency electric and magnetic fields. A theoretical analysis of each antenna's receiving characteristics is summarized and referenced. The antennas described are an electrically short dipole, a resistively loaded short dipole and halfwave dipole, an electrically small loop, a resistively loaded loop, photonic probes, and a single-turn loop designed for simultaneous measurement of the electric and magnetic components of nearfields and other complex electromagnetic environments. Each type demonstrates a different compromise between broadband responses and sensitivity. This paper also discusses the calibration techniques for these probes using standard EM fields established in TEM cells, waveguide cells, anechoic chambers, and open-field sites     

New method for assessing EED susceptibility to electromagneticradiation

An infrared fiber optical temperature sensor (IFOTS) used for the measurement of induced electric currents caused by electromagnetic radiation in electroexplosive devices (EEDs) is presented. Features of the sensor include an infrared optical fiber that is immune to electromagnetic radiation, a probe assembly that eliminates any appreciable thermal and electrical loading of the EEDs bridgeware, a signal processing technique that enhances signals in the presence of noise, and a means of providing continuous and/or pulsed measurement of bridgeware temperature caused by induced electric currents     

Low-frequency reflectivity approximation for two- andthree-dimensional EM absorbers

Large-size electromagnetic absorbers are mainly used in anechoic and semi-anechoic chambers for electromagnetic compatibility testing. Therefore, the determination of the reflectivities in the low-frequency range (30-300 MHz) are of paramount importance in the performance evaluation of the absorber and, finally, in a “dark room” design. We here present a low-frequency approximation of the reflectivity based on a boundary and surface integral equation technique. This approach makes it possible to compare the approximation to the rigorous integral equation approach and to other approximations in the literature. The validity of the new low-frequency approximation is discussed based on reflectivity calculations of representative two- (2-D) and three-dimensional (3-D) absorber structures     

高功率脉冲电源超大电流检测技术研究

随着高功率脉冲电源(Pulse Power Supply)在电磁轨道炮、电磁弹射器及电磁推射装置中的广泛应用,对其产生的脉冲大电流的精确测量显得尤为重要,但目前电流测试领域常用的测试方法由于稳定性不足、量程有限、测量精度不高等缺陷,无法满足具有兆安级放电电流的高功率脉冲电源的测试需求。因此,提出了一种基于罗氏线圈和积分器的超大电流测试技术。首先通过COMSOL有限元分析软件的AC/DC磁场模块建立模型对该电磁环境进行仿真分析,以确定采集系统在该电磁环境中的安全测试距离,并对罗氏线圈和积分器的测试原理做了具体说明,最后搭建硬件平台在实际的试验中证明该方案能够实现对兆安级脉冲大电流的测试,论证了该测试方法的可行性。     

Generalized stochastic field model for reverberating chambers

In this paper, we present a new stochastic model to characterize the electromagnetic field in reverberating chambers. The model is physically based and is capable to embody as special cases the reference thermodynamic limit (perfectly stirred case) and the Rician case (presence of unstirred component). The stochastic field model is characterized by the generalized K distribution, i.e., a three parameters probability density function (pdf) that ensures a continuous and physically consistent transition among very different scattering scenarios. Theoretical modeling is supported by means of an experimental study based on measurements made at the Universita/spl grave/ di Napoli Parthenope, Naples, Italy, formerly Istituto Universitario Navale (IUN), mode-stirred reverberating chamber.     

强脉冲电场测量技术研究

强脉冲电场测量技术在强流加速器系统电磁兼容设计、核电磁脉冲（NEMP）测量、雷电电磁脉冲（LEMP）效应研究以及高压输电线、大功率开关的电磁辐射澳0量中起着关键的作用,测量结果的有效性直接影响到理论研究和系统设计的正确性。本文系统地回顾了强脉冲电场测量技术的发展,对有源电光调制法和基于Pockels效应的无源电光调制法两种常用方法进行了详细的分析比较,说明测量系统的研究正朝着提高稳定性、探头微小化、探头无源化、提高带宽、提升灵敏度、后端信号处理便捷、系统维护方便、容易实施标准化测量等方向发展;文章还对测量实践中的屏蔽、信号区分以及获取特征量等具体方法和技巧作了研究,为强脉冲电场的准确测量打下基础。     

GTEM cell facility use during project development phases for automotive

The purpose of this paper is to present the results obtained with a gigahertz transverse electromagnetic mode (GTEM) cell for each phase of the project development, which consists of measuring and quantifying the integrated circuit's emissions and immunity compliance with automotive standards. These standards are defined using half anechoic chambers (HAC). Studies have already been conducted to compare trans electromagnetic (TEM) cell and HAC, or far-field emissions, and the test results show a limited correlation between TEM cells and the free space field or HAC. In this paper, it is shown that the correlation between the measurements made in a GTEM cell and HAC can be good enough in allowing us to use the GTEM facility during the research and development (R&D) phase (considering the facts that the HAC facility is often quite overloaded and of a high cost), that knowledge of the electromagnetic compatibility behavior of the integrated circuit is important for predicting the whole system's results as well as how to use an integrated circuit electromagnetic model to make the prediction of emissions.     

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.     

Reflectivity measurements in anechoic chambers in the microwave to millimeter range

A voltage standing-wave ratio (VSWR) measurement method and ensuing reflectivity characteristics are presented for anechoic chambers in the range 1-76.5 GHz. The free space VSWR measurements are performed using a composite antenna technique. By making use of two different anechoic chambers, the dependency of the reflectivity characteristics upon direction in the horizontal plane and absorber's height is analyzed.