EMC测试中的电流注入技术

文章综述了在系统电磁兼容性(EMC)测试中替代直接辐照的电流注入技术的最新研究成果。电流注入技术主要有两种：大电流注入(BCI)和直接电流注入(DCI)。BCI技术主要用于辐射敏感度测试，尤其是测试电缆束对射频耦合的敏感度。DCI技术是一种用在高场强辐射场(HIRF)下系统级EMC安全裕度测试的新技术，研究的热点是其相对自由场辐照的有效性及等效关系。     

直接电流注入技术对高场强辐射场的模拟与实践

本文介绍了高场强电磁兼容安全裕度测试工具的一个替代技术:直接电流注入技术。文中通过理论计算和试验测试,分析和验证了直接电流注入技术中注入功率与产生场强的关系及直接电流注入技术模拟高场强辐射场的可行性,为进一步研究和应用直接电流注入技术提供了依据和基础。     

On the interpretation for radiation from simple currentdistributions

It is indisputable that Maxwell's equations provide a unique electromagnetic field for any reasonable distribution of charge/current. However, the interpretation of the results from such calculations may not be unique; different physical models may be used to explain the same results. We examine the radiation from similar filamentary current distributions (traveling-wave and uniform) for pulse excitation. For pulse excitation, it is easier to establish the causal relationship between the elements of current and the radiated field. We also show, for these simple distributions, that the total energy radiated for pulse excitation depends on the length of the filament in the same way as for the time-harmonic case     

On the excitation of a circular loop antenna by travelling-and standing-wave current distributions

Presented here is an exact formulation of the electric and magnetic (EM) fields radiated by a circular loop antenna, assuming both travelling- and standing-wave current distributions. By using a differential current element positioned in an azimuthal direction as the starting point, the paper systematically develops the EM fields radiated by the circular loop via a vector potential theory. This approach leads to a general integral representation for the radiation characteristics of the loop antenna where we completely evaluate the resulting expressions, when the excitations of the loop assume travelling- and standing-wave distribution forms. In addition, this paper briefly examines a method to generate approximately such current distributions by coupling the loop to a two- or four-wire transmission line. Furthermore, the paper discusses a graphical representation of the current distribution plotted as a function of frequency or loop size. From the field expressions determined, we derive generalized closed-form results for some important design parameters for the loop antenna. These parameters include the radial component of the Poynting vector, the total power radiated by the loop, the directivity, the radiation resistance, and the effective area and height of the antenna. When we specialize to the important case of uniform current excitation, the exact values of the parameters deduced from the general expressions, are summarized and exhibited in a comprehensive table. This table facilitates the computations of these important physical parameters. Further analysis involving small argument and asymptotic approximations in the residts for the travelling-wave current excitation leads to closed-form expressions in terms of tabulated functions. Numerical results presented, include the fields radiated by the loop when the standing-wave current excitation admits a Fourier series representation. The present approach via potential theory reveals that the fields can be calculated in any arbitrary direction : this is consistent with a previous observation of Knudsen (1951, 1953) who employed a different approach.     

On the transient radiation of energy from simple currentdistributions and linear antennas

Smith (1998) examined the radiation from two simple filamentary current distributions: traveling-wave and uniform. The radiated or far-zone electric field was computed for an excitation that was a Gaussian pulse in time. Two interpretations for the origin of the radiation were presented, based on the far-field results. The present article continues this investigation; however, the emphasis is on an examination of the near field and the related transport of energy away from the current filament. We examine traveling-wave and standing-wave current distributions, because these distributions are frequently used to model practical antennas. Exact analytical expressions are presented for the electric and magnetic fields of the assumed, filamentary current distributions when the excitation is a general function of time. For the filamentary distributions, the current and charge are confined to a line (a line source). There is no radius associated with the filament. The expressions for the fields apply in both the near and far zones, and are used to determine the Poynting vector. For an excitation that is a Gaussian pulse in time, exact analytical expressions are obtained for the energy leaving the filament per unit time per unit length, the total energy leaving the filament per unit length, and the total energy radiated. Graphical results based on these expressions are used to study the energy transport from the filamentary current distributions. The results for the standing-wave current distribution are compared with those from an accurate analysis of a pulse-excited, cylindrical monopole antenna, performed using the FDTD method     

Reciprocity in reverberation chamber measurements

Even though reverberation chambers have been used primarily for radiated immunity testing, they are reciprocal devices that are equally applicable for radiated emissions testing. This short paper presents the theory for radiated emissions testing and uses electromagnetic reciprocity theory to demonstrate the link between radiated emissions and immunity testing.     

Transient response of the duoconical monopole

Large area radiators such as the duoconical monopole are less frequency sensitive than thin antennas. The dispersive nature of antennas is important especially when they are used to transmit video pulses. This paper presents the numerical results obtained for the duoconical monopole under pulsed excitation. Results include the current distribution on the monopole at different instants of time, the radiated waveforms in different directions, and the waveforms of transmitted and reflected signals on the feeding coaxial line. Numerical results were obtained by applying the inverse Fourier transform to the steady-state time harmonic current distributions and radiation patterns. The above results are then used to find a simple incident voltage waveform that will radiate a "pulse" of "good" shape. The radiated field in different directions are then presented for different parameters of the incident double exponential voltage waveform.     

On determining the maximum emissions from electrically largesources

This paper examines the use of measurements of the total radiated power from an arbitrary source, combined with theory-based estimates of directivity or quality factor, to accurately predict the maximum electric field radiated by the source either at a line-of-sight distance or in a resonant volume. The approach using total radiated power avoids source rotations during testing and is an efficient alternative to current emission test methods. Examples of simulated (random source set) and measured (box with holes) planar-cut radiation-patterns for electrically large sources are presented. Both simulated and measured data agree well with theoretical estimates     

Excitation loss of open resonators

Reported here are the results on level and structure of the radiated field of an open resonator at and off resonance. On the basis of the modelling problem rigorous solution and the measurements at 4-millimeter wavelength we find there are no ways to compensate the radiated field from an open electromagnetic structure at resonance. Analysis of open resonator excitation efficiency shows that the mismatch loss of a slot-fed open resonator runs to 34% while at the aperture-feed excitation this is not more than 6% for the same-geometry resonator.     

Matrix pseudo-inversion technique for diagnostics of planar arrays

It is shown, by means of numerical simulation, that the Moore-Penrose pseudoinverse of a matrix taken from an overdetermined system can be applied to retrieve the excitation distribution of a planar array of parallel dipoles with faulty elements, by measuring the complex radiated field in its near zone. Failures on voltage (considering mutual coupling) and current of several elements, and systematic or random measurement errors, are considered in the simulation.     

脉冲激励的长方形发射天线的分析与波形优化

在脉冲激励天线中，脉冲波形对于辐射功率有着重要的影响。对长方形行波天线的激励电流脉冲波形与其辐射功率的关系进行了分析。提出了激励电流的优化问题，使得天线在给定方向上的辐射能量最大化。并且给出了优化问题的解法和几种参数下的优化波形。通过具体的数值计算，与其他参考文献中使用的波形相比，优化波形在主辐射方向上可以辐射出更大的能量。     

无线移动终端辐射杂散测试

辐射杂散测试是评估无线移动终端辐射性能的有效方法。文章阐述了进行无线移动终端辐射杂散测试的技术要求、限值和测试方法;着重总结和归纳了在测试过程中需要注意的技术细节;同时对LTE移动终端辐射测试的带来的新问题进行了预分析。     

基于阻抗分析法的电桥式涡流检测系统研究

涡流检测技术采用频谱丰富的正弦信号作为激励源,响应中包含多个频率成分,增强了涡流检测的抗干扰能力.将涡流检测技术、数据采集技术与虚拟仪器技术有机结合起来,开发了适用于在线检测的涡流检测系统.系统由脉冲涡流检测硬件电路、PXI总线系统以及相关软件组成.硬件电路可产生性能良好,频率、幅值稳定的激励信号,频率范围为0～5 M...     

Characterization and comparison of noise generation forquasi-resonant and pulsewidth-modulated converters

A buck converter with a given output filter is operated with pulse-width modulated and quasi-resonant switching schemes at the same nominal load and switching frequency. Electromagnetic interference generated by the natural switching action of the converter is examined by spectral analysis. Interference caused by excitation of parasitic elements is examined experimentally. Quasi-resonant converters are found to have a lower switching frequency harmonic bandwidth than the equivalent pulse-width modulated converter, even with switching frequency control. The most significant parasitic responses are the turn-on current and turn-off voltage of the catch diode and the gate current of the MOSFET. A significant decrease in radiated and conducted noise occurs when the gate drive voltage rise and fall times are increased, which is possible without loss of efficiency using quasi-resonant switching     

Analysis of Radiated Fields for the Design of a RJ45 Connector Using FDTD Method

The finite-difference time-domain (FDTD) method is successfully used to calculate the electric fields radiated from a prototype of a RJ45 connector for Ethernet transmission. Simulation results of the electric fields radiated from the prototype of this RJ45 connector are validated by measurement data for vertical and horizontal polarizations in 300 ~ 1000 MHz frequency range. It is also found that simulation and measurement results for both vertical and horizontal polarizations are over the regulation limit at 600 MHz. In order to meet regulation limits, further studies are also conducted by taking numerous possible affecting factors on radiated electric fields into consideration for FDTD simulations; these include the aperture area, the location of the excitation, the material used for the aperture, enclosures with and without grounding. From simulation results presented in this paper, it is found that the magnitude of the higher emission levels can be reduced by reducing the aperture area, putting the location of excitation deeper into the connector, using materials with smaller dielectric constants and conductivities for the aperture, and adding a grounding enclosure on the RJ45 connector.     

Power pattern synthesis of reconfigurable conformal arrays with near-field constraints

A conformal array power pattern synthesis technique is presented which makes it possible to take into account near-field constraints and to reconfigure the radiated pattern by controlling only the phases of the excitation coefficients. Far-field pattern specifications are given by masks while near-field constraints are given by prescribing the maximum allowable field intensity at points arbitrarily located in a given near-field region. The amplitude of the excitations, common to all radiated beams, and the phases corresponding to each one are obtained as a result of the synthesis algorithm.     

Electrical fast-transient test: conducted and radiated disturbancedetermination by a complete source modeling

Tests against electrical fast transient/burst (EFT) represent a serious threat for modern high-speed electronics: besides the conducted injection of high amplitude pulse, a strong radiated field is produced during this test. The prediction of the effects of this test during the equipment early design stage requires the equivalent circuit of the generator: the output waveform into a resistive 50-Ω load is not sufficient to recover the complete circuit, including inductive component and parasitic elements. These are essential to predict the disturbance produced in arbitrary loads, as the equipment under test can be viewed. This paper describes how to characterize the EFT generator by means of the measurement of the output voltage and current produced in presence of known loads; moreover, a procedure to calculate the current on the equipment power cord is shown, based on the use of a circuit simulator (PSPICE). Finally, the disturbance produced on different loads and the radiated field during the test are calculated and experimentally validated     

Theoretical Analysis of the Rhombic Simulator Under Pulse Excitation

An analysis is given of the electromagnetic pulse generated in the space between the wires of a rhombic simulator by pulses of current traveling along the wires. After the mechanism of pulse excitation is clarified with the help of measured results, the electromangnetic pulse is investigated in terms of a current pulse with known shape that travels along the rhombic wires. The calculated pulse sequences agree very well with the measured ones. The "subpulse" radiated by each small segment of the wires as the current pulse traverses it is also studied. The time delays of the sequence of subpulses play an important role in the formation of the complete electromagnetic pulse. The amplitudes of the subpulses are relatively less important.     

PCB辐射电磁干扰快速建模方法及实验研究

该文提出了基于射频电压参数测量的辐射场快速建模方法和基于射频电流参数测量的辐射场快速建模方法,并通过近场探头测量方法和电波暗室标准测试实验验证了快速建模理论的有效性,达到操作简便、节约成本的目的。