Reflectivity level of radio anechoic chambers

A comparison between the antenna-pattern comparison technique and the free-space voltage standing-wave ratio technique for evaluating the reflectivity level of radio anechoic chambers is presented. Based on an analysis of the two techniques, it is pointed out which parameters influence the measured value of the reflectivity level. The comparison is illustrated with experimental results and it is explained why inconsistent and uncorrelated results may be found when the two methods are used. Furthermore, it is demonstrated, by introducing improvements in a chamber, how the reflectivity level can be used to measure the improvements. This work is inspired by the current discussion of finding a figure of merit for anechoic chambers. Based on the results, an evaluation procedure for anechoic chambers is indicated. However, it is pointed out and illustrated by examples that further investigations are necessary before a satisfactory procedure can be outlined.     

无线电吸波暗室的反射电平（上）

给出了天线方向图比较法和自由空间电压驻波比法两者的对照,这2种方法可用于评估无线电吸波暗室的反射电平。在分析这2种方法之后,指出了哪些参数会影响反射电平的测量值。通过实验结果的对照,揭示了为什么在采用这2种方法时会得到不尽一致和不相关联的结果,进而还表明当吸波暗室性能获得改进之后,如何利用反射电平来衡量这种改进。基于目前的研究成果,描述了吸波暗室性能的评估步骤。同时,还通过举例指出有必要开展进一步的研究,以便归纳出满意的评估步骤。     

Reflections in anechoic chambers in 100-200 GHz range

Three anechoic chambers have been tested at 110 and 183 GHz. Typical sidewall reflectivity levels are about -60 dB at 110 GHz and -50 dB at 183 GHz measured with pyramidal horns which have a gain of 20 dB. Backwall reflectivity levels are about -35 dB at 110 GHz and -25 dB at 183 GHz.<>     

无线电吸波暗室的反射电平（下）

给出了天线方向图比较法和自由空间电压驻波比法两者的对照,这2种方法可用于评估无线电吸波暗室的反射电平。在分析这2种方法之后,指出了哪些参数会影响反射电平的测量值。通过实验结果的对照,揭示了为什么在采用这2种方法时会得到不尽一致和不相关联的结果,进而还表明当吸波暗室性能获得改进之后,如何利用反射电平来衡量这种改进。基于目前的研究成果,描述了吸波暗室性能的评估步骤。同时,还通过举例指出有必要开展进一步的研究,以便归纳出满意的评估步骤。     

Comparison of electromagnetic absorber used in anechoic andsemi-anechoic chambers for emissions and immunity testing of digitaldevices

The absorber used in anechoic and semi-anechoic chambers employed for emissions and immunity testing of digital devices is examined. Using reflectivities obtained by the method of homogenization, the advantages and disadvantages of urethane pyramids, twisted-pyramids, wedges, as well as ferrite tiles, ferrite grids, and “hybrid” combinations of urethanes and ferrites, are determined. General reflectivity guidelines are also presented for comparing absorber used for the electromagnetic compatibility (EMC) testing of digital devices from 30 to 1000 MHz     

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     

基于镜像射线跟踪法的电波暗室仿真设计

为提升暗室吸波工程的设计能力,运用镜像射线跟踪法对10 m 法电波暗室进行仿真设计,通过合理布置吸波材料,考虑一次反射和二次反射对静区的影响,计算了不同极化方式下静区的反射电平、归一化场地衰减和场均匀性。结果表明垂直极化和水平极化时,场地电压驻波比仿真与测试偏差小于2.3 dB;归一化场地衰减仿真与测试误差小于3 dB,场均匀性误差小于2 dB。仿真与测试结果吻合较好,各项指标均满足设计要求,验证了吸波材料布局的合理性及算法的可靠性。该仿真方法可应用于暗室静区性能评估,优化吸波材料布局,进而有效缩短设计周期。     

电波暗室吸波墙壁反射电平测试技术

介绍了测试电波暗室墙壁反射电平的两种方法,既电压驻波比法（VSWR）和基于矢量网络分析仪的改进电压驻波比法（AVSWR）,并对这两种方法进行了比较,给出了每种方法的优缺点。     

AXB型吸波材料及微波暗室

介绍AXB型吸波材料的性能.用AXB型吸波材料建造的天线近、远场测量微波暗室,10m半电波暗室和RCS测量微波暗室的技术指标都符合相关标准的要求.     

新型微波暗室吸波材料——AXB型吸波材料

介绍了新型微波暗室吸波材料--AXB型吸波材料,该材料同常规吸波材料相比吸波性能相当,同时,具有功率承载能力强、安全环保、洁净卫生、结构稳定等显著特点。自1999年定型以来已成功建造各类微波暗室70多座,被广泛应用于雷达、卫星、无线通信、天线测量和EMC测试领域。     

应用于卫星导航与对抗的穹形满天星暗室的仿真设计

针对当前信息化战争背景下卫星导航装备对无线测试环境的应用需求,结合现阶段国内外暗室发展现状,对矩形、穹形两种暗室进行选型分析,从静区特性、应用性能等方面进行系统仿真分析,最终采用穹形暗室作为暗室选型方案。通过满天星天线布局,模拟真实环境中的卫星轨迹和信号,构建与真实环境高度逼真的无线测试环境,能够有效支撑卫星导航装备尤其是波束成形抗干扰终端的测试,填补了国内在穹形满天星暗室方面的设计空白,可指导工程实践应用。     

Efficient detection of resonances in anechoic chambers using thematrix pencil method

In a previous paper we have presented a method for evaluating the performance of anechoic chambers by analyzing the S-parameters of a system comprising two antennas facing each other in an anechoic chamber using the matrix pencil method. In this work, we present an improvement of this resonance detection technique using only the transmission parameter S₂₁. The propagating components of the transmission parameter S₂₁ are derived over small frequency intervals using the matrix pencil method and then removed from S₂₁ in a two-level decomposition procedure. The resonances are clearly identified from the residual signal. Two examples of resonance detection in two different anechoic chambers illustrate the proposed method     

电磁兼容测试用暗室的性能设计

作为电磁兼容测试场地,半电波暗室越来越显示出其重要性.介绍了半电波暗室的基本设计方法,并举例介绍了射线法技术,给出了10m法半电波暗室的设计结果.     

A review of electromagnetic compatibility/interference measurement methodologies

This paper presents a review summary of radiated emission and susceptibility measurement methodologies currently used for assessing the electromagnetic compatibility/interference (EMC/EMI) characteristics of electronic devices and systems. In particular, measurement methods using open sites, transverse electromagnetic (TEM) cells, reverberating chambers, and anechoic chambers are discussed, in light of their technical justifications and bases, their strengths and limitations, and interpretation of the measured results.     

电波暗室用吸波材料的工艺和性能

详细介绍了电波暗室用吸波材料的种类、制造工艺,以及电波暗室用吸波材料的反射率、阻燃性、耐功率等性能指标,为暗室建造企业在选择吸波材料时提供参考.     

暗室工程的概念设计

从暗室使用者的角度,结合暗室的测试功能、无反射特性、屏蔽效能、测量设备和测量方法等方面,以举例的方式,介绍一些暗室概念设计的思路和方法,以期暗室建成后的性能能达到初始期望的要求。     

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     

Correlate measurements at different test sites

A new method for systematic correlation of measurements in semi-anechoic and anechoic chambers is presented. A signal measured in a semi-anechoic chamber is first processed using the matrix-pencil method which is applied sequentially on small frequency intervals. On each interval the measured signal is decomposed into its propagating wave components. The component corresponding to the wave reflected from the ground is identified and removed to fully retrieve the signal measured in an anechoic chamber. Three examples using log-periodic and Vivaldi antennas in different anechoic and semi-anechoic chambers for varying frequency ranges illustrate the method. The proposed decomposition algorithm can be utilized to characterize measurement test site imperfections     

Measurement of electrically large array antennas in small anechoic chambers [Measurements Corner]

A post-processing procedure that yields accurate array-antenna radiation-pattern estimations is described. By resorting to this strategy, measurements of large array antennas inside small anechoic chambers become feasible. The method employs an adequate phase-correction derived from an optical ray approach, under the assumption that the elementary radiators themselves are electrically small and can be measured under far-field conditions inside the relevant anechoic chamber. The effectiveness of the proposed technique is demonstrated by examining the case of a nonuniform linear array antenna.     

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).