Miniature anechoic chamber for chronic exposure of small animals to plane-wave microwave fields.

A system of miniature anechoic chambers for chronically exposing a sizeable number of animals to microwave radiation was developed in which each animal can be individually exposed to microwaves or sham-exposed under controlled environmental conditions. Each animal is supplied with food and water by means designed to eliminate undesirable perturbations of the field. Field patterns in each chamber correspond closely to those made in large anechoic chambers; measurements indicate that a power density of 169 microW/cm2 per watt of input power can be provided, which results in peak SAR levels of 0.37 W/kg in cadavers of exposed rats.     

Experimental study on direction dependency of reflectioncoefficients of microwave electromagnetic anechoic chamber

For measurements of reflection coefficients in an anechoic chamber by the free-space voltage standing wave ratio (VSWR) method, the composite antenna technique, using a combination of two antennas, is proposed. Reliable data on reflection coefficients can be obtained by this technique, with respect to reflected waves from arbitrary directions. Using the measurement results, the direction dependency of reflection coefficients is studied in relation to specular reflection and to the directivity of a transmitting antenna     

EMC电波暗室及发展方向

介绍了EMC电波暗室的性能、材料和应用的发展方向.     

Characteristics of a tapered anechoic chamber

The characteristic features of a tapered anechoic chamber are described. The smooth illumination amplitude in the chamber makes it usable as an indoor range for antenna pattern measurements, even at low frequencies. Variations in the transmission attenuation in the chamber as compared to free space require careful interpretation of absolute gain and cross section data.     

3m法电波暗室的构建

电磁兼容性（EMC）是指设备或系统在其电磁环境中符合要求运行并不对其环境中的任何设备产生无法忍受的电磁干扰的能力。EMC检测包括测试方法、测量仪器和检测场所。电波暗室的建设是EMC实验室建设的重要内容,也是决定EMC检测质量的关键。EMC实验室按照暗室尺寸来分常见的有3种：3m法、5m法、10m法。本文介绍如何建设一个标准的电波暗室（3m法）,并提出具体方案和验收结果。     

经济型消声室介绍

随着中国加入WTO,把产品推向世界势在必行。因而对产品的检测方法和手段,也就必须和世界接轨。     

Ignitability of anechoic chamber foam by electric currents

Anechoic chamber foams are easily ignited by passage of current through them. Two distinct ignition processes can be observed. The first is a contact fire that results when two sharp points which are at a potential difference of more than 100 V touch the conducting foam. The second is an I²R heating of the interior of the foam which begins with smoldering, then a glowing chunk of foam inside the material which grows and usually ignites. An unexpected by-product of burning carbon-impregnated foam is the voluminous release of dense toxic smoke (Tatem and Williams [1]).     

Electromagnetic field analysis of a four-wire anechoic chamber

The electromagnetic field characteristics and plane-wave generating ability of a parallel four-wire anechoic chamber which is to be operated in the VHF range is analyzed. The analysis considers three cases: the first is a four-wire chamber when only a thin layer of absorber material covers the chamber walls, the second is a four-wire chamber when only free space surrounds the four wires of the system, and the third is a four-wire chamber when a thick layer of absorber material covers the anechoic chamber walls. The three cases are analyzed by a variety of mathematical methods including the method of moments, waveguide theory, and a finite-difference time-domain method. Numerical results for the propagation constants and electromagnetic fields that are generated in the chamber in the three cases are presented     

Design and construction of a multipurpose wideband anechoic chamber

An electromagnetic anechoic chamber has been constructed at the Multimedia University. It is designed to operate over a very wide frequency range from 30 MHz through 18 GHz. It can be used for electromagnetic compatibility (EMC) tests, antenna measurements, radar cross section (RCS) measurements, testing RF transceivers, calibration of scatterometers, and other electromagnetic research experiments. The geometry of the chamber is asymmetrical, consisting of a combination of rectangular and tapered volumes. The size of the chamber is about 64 ft /spl times/ 32 ft /spl times/ 24 ft high. Ease of construction and ease of lining of the absorbers were preserved so that the actual quietness is comparable to the theoretical simulation result. The transmitting source is placed at one end of the chamber, and the receiving antenna or object under test is placed in a designated quiet zone at the other end. The walls and ceilings are configured such that no first-order and or second-order reflections (except those reflected from the floor) propagate into the quiet zone. Hence, less-expensive absorbers can be used to achieve the required wideband performance. Reflection from the floor is required by the international EMC standards for radiated electromagnetic interference (EMI) emission tests; therefore, the chamber is designed for this capability. However, absorbing material can be placed on the floor to convert a semi-anechoic chamber into a fully anechoic chamber for radar and antenna measurements.     

A photonic technique for microwave frequency measurement

A novel photonic technique for microwave frequency measurement utilizing dispersion in a multichannel chirped fiber Bragg grating is presented. The technique is based on the amplitude comparison of power fading functions generated by double sideband modulated optical carriers propagating through a dispersive medium.     

Oblique scattering from lossy periodic surfaces with applicationsto anechoic chamber absorbers

Plane wave scattering from lossy, periodic surfaces with periodicity in one direction is considered for arbitrary polarization and incidence angles. The material is assumed to be homogeneous and characterized by complex values of permittivity and permeability. Muller-type coupled integral equations are derived for the surface electric and magnetic currents. The power reflection coefficient is defined in terms of the scattered far fields. The integral equations are solved by the boundary element method (BEM) with constant elements. Arbitrary surfaces are accommodated by approximating the actual profile by means of linear segments. Other speed-up techniques are utilized to generate a numerically efficient solution. Substantial comparison is made for special cases to verify the formulation. The reflection coefficient is calculated for a variety of surface shapes. A new profile shape is presented that results in a lower reflection coefficient than the commonly used triangular shape     

A microwave oscillation loop for dielectric constant measurement

We designed and analyzed a microwave oscillation loop formed by a dielectric loaded cavity, amplifiers and transmission lines for the dielectric constant measurement of samples at both room and very high temperature. An oscillation condition for an arbitrary loop is derived in S-parameter notation, by which the commonly used oscillation condition in loop phase and gain notation is proved to be valid only in the special case when either S₁₁=S₂₁=0 or S₂₂ =S₁₂=0. Based on the S-parameter oscillation condition, a theoretical model is established and verified with a discrepancy of less than 0.041% between the calculated and the measured oscillation frequencies. With this model, the loop characteristics are investigated. From the measured loop oscillation frequency, the cavity resonant frequency, and thereby the dielectric constant of the sample in the cavity, can be predicted. Based on this analysis, an active dielectrometer is constructed with resultant errors of less than 4% for ϵ'<20 and less than 11% for ϵ'<80. This dielectrometer requires no tuning and no external microwave power source. Moreover, a high power (>100 W) oscillation loop for the dielectric constant measurement of a microwave heated sample (1000°C) is developed     

一种基于微波暗室的大角域卫星导航接收机测试场景构建方法

提出了一种基于微波暗室的大角域测试场景构建方法,该方法利用已有42射频面阵,采用多状态联合校准方法对面阵天线单元到接收机的信号幅度和相位进行校准,以及采用灰色关联分析方法将外界环境下的卫星星座、动态干扰在微波暗室内实现逼真映射,构造最大视场角为160的半实物抗干扰测试场景。仿真测试结果表明:暗室天线单元与实际场景下的卫星星座在角域关系下最大误差在高增益3 dB 波束宽度内,暗室模拟的动态干扰与实际环境下到达接收机的功率基本一致;最后实现了对多波束抗干扰接收机的测试,并通过干信比与有效载噪比的关系曲线说明了该方法能够在室内实现导航接收机测试环境的逼近模拟,并准确地测试出多波束接收机的抗干扰性能。     

Compact antenna test range without reflector edge treatment and RF anechoic chamber

There are several types of CATRs (compact antenna test ranges) used in antenna-pattern measurements. An offset reflector is generally used to generate the quiet zone of a CATR. Serrated edges, rolled edges, or R-cards are generally chosen along the reflector's edge to reduce the edge-diffraction field inside the quiet zone of the CATR. In order to reduce stray signals from the environment, a high-quality RF anechoic chamber is required for a CATR. In this paper, a new type of CATR, without either a reflector edge treatment or an RF anechoic chamber, is developed. A commercially available DBS (direct-broadcast satellite) reflector antenna, without edge treatment, is used as the reflector antenna of the CATR to generate the quiet zone of the antenna test range. In order to improve the quiet zone's performance, the fields due to feed spillover, edge diffractions, and other stray signals are gated out by the ITDAMS (impulse time-domain antenna measurement system). The RF interference in the environment can also be reduced by time synchronization and pulse integration of the impulse time-domain antenna measurement system. In order to verify the capabilities of the proposed CATR, three kinds of antennas (a low-directivity horn antenna, a high-directivity 60 cm direct-broadcast satellite reflector antenna, and a 25 cm Ka-band Cassegrain LMDS - local microwave distribution system - antenna) were measured by the proposed CATR. The antenna-pattern results agreed quite well with those of a near-field range and a far-field range.     

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.     

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.     

多馈源微波加热腔体的研究

提出了一种在空腔情况下多馈源长方体加热腔的设计方法。通过调整馈孔间的位置与距离,研究其S参数及腔体内的电磁场分布。仿真结果表明,当多个馈源两两正交,且互相距离为1/4个波长的奇数倍时,腔内电磁场分布最为均匀。此项研究为工业上微波多源加热腔的优化设计提供了参考。     

Three-port scattering parameters for microwave transistor measurement

A 1- 12-GHz swept-frequency nondestructive three-port s- parameter measurement system for small-signal characterization of microwave transistor chips is described and its merits are discussed. The parameter f/SUB s/ is defined as the frequency at which the transducer power gain becomes unity and is introduced as a useful and directly observable parameter for the s-parameter measurement system. Some measurement results for TI L-187 transistors are given and a physical interpretation of the s-parameter data is discussed.     

A new method for fiber chromatic dispersion measurement with microwave interference effect

The chromatic dispersion (CD) is a key parameter for optical fibers. Based on the microwave interference effect, a new method for CD measurement of optical fibers is proposed. The radio frequency (RF) signals carried by two light-waves with different wavelengths transmit through the dispersive optical fiber under test. After photo-detector they interfere with each other due to the different phase shifts induced by the CD of fiber. The CD can be obtained by monitoring the changing interference RF power with scanning the wavelength of tunable laser source. The CD values of single mode fiber and dispersion compensating fiber are measured within the wavelength range from 1525 to 1605 nm. The common phase shift method is used to measure the CDs of the two types of fiber, which demonstrates the feasibility and veracity of the proposed method.     

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