FDTD modeling of common-mode radiation from cables

Radiation from cables attached to printed circuit boards and shielding enclosures is among the primary concerns in meeting FCC Class A and B limits. The finite-difference time-domain (FDTD) method can be employed to model radiation from printed circuit boards and shielding enclosures with complex geometries, but difficulties in modeling wires and cables of arbitrary radii are encountered. Modeling the wire by setting the axial component of the electric field to zero in the FDTD method results in an effective wire radius that is determined by the mesh discretization. Neglecting the wire radius in applications, such as electromagnetic interference (EMI) or printed circuit board modeling, may result in gross errors because near-field quantities are typically sensitive to wire thickness. Taflove et al. (1988) have developed a subcellular FDTD algorithm for modeling wires that has been shown to work well for plane wave scattering. The method uses a quasistatic field approximation to model wires with a well defined radius independent of the mesh dimensions. The wire model is reviewed and investigated for application to common-mode radiation from cables attached to printed circuit boards, where the source is often a noise voltage at the connector. Also investigated is energy coupling to attached cables through enclosure apertures resulting in common-mode radiation from the cable. The input impedance for a center-fed dipole antenna, as well as a monopole connected to a conducting half-sheet, is computed with FDTD methods and compared to moment method input impedance results. A simulation of a shielding enclosure with an attached cable demonstrates the utility of FDTD analysis in modeling common-mode radiation     

The Capacitances and Surface-Charge Distributions of a Shielded Balanced Pair

The capacitance matrix of a straight pair of uniform wires symmetrically placed in a shield is determined theoretically. Exact expressions for the elements of the capacitance matrix are determined as particular elements of the inverse of an infinite matrix which relates the Fourier coefficients of the surface-charge densities on the inner conductors and the shield to the applied voltage excitations on the cable conductors. If the wire diameter is small relative to the wire separation, and if the wire separation is small relative to the shield diameter, then accurate numerical approximations for the elements of the capacitance matrix are obtained to any degree of accuracy by suitably truncating the infinite matrix. Once the elements of the capacitance matrix are determined, then the distributions of the surface-charge densities on the peripheries of the inner conductors, and the shield are determined for any arbitrary excitation of the cable structure. In particular, the various capacitances associated with the cable structure, e.g., the direct, ground, and mutual capacitances, are determined from a comparison of the surface-charge densities resulting from a "balanced" excitation and a "longitudinal" excitation. The Fourier coefficients of the surface-charge densities are required to determine the propagation parameters and the associated propagation modes of the cable structure. The surface-charge distributions are evaluated numerically for a typical standard production cable using 22-gauge wires. The results of this paper will be extended by a perturbational method to include twisted wires in a shield; also, certain types of asymmetries in the cable geometry will be considered. Hence, the propagation constants and the associated propagation modes of unbalanced and/or twisted shielded pair cables can also be determined.     

大长度低损耗半硬同轴电缆的研制

设计了一种采用膨体聚四氟乙烯作为绝缘,连续激光焊接铜管作为外导体的新型低损耗半硬同轴电缆,以打破传统的半硬同轴电缆制造长度的局限性,同时对电缆工艺的可行性进行了探讨。膨体聚四氟乙烯绝缘的采用降低了电缆的介电常数,减小了半硬同轴电缆高频段的传输损耗。连续焊接铜管外导体的采用不但增加电缆的制造长度,并且保留传统半硬同轴电缆良好的阻抗均匀性和屏蔽特性,同时也提高了生产效率,降低了材料消耗。     

Geometric Analysis and Manufacturing Considerations for Optimizing the Characteristics of a Twisted Pair

The geometry of a twisted pair largely determines its electrical characteristics. To improve and refine the value of these characteristics according to preset values, the optimization of the manufacturing processes requires comprehensive knowledge of twisted pair geometry and of how electrical magnitudes are affected by the construction features of the twisted pair. This paper studies the relation between the length of a twisted pair cable and the length of each of the wires that compose the cable, by analyzing concepts such as pitch angle and radius of the helix. In addition, it examines the deformations and irregularities that can occur in the twisted pair during the manufacturing process and their effects on the geometry of the twisted pair. Results showed in this paper are a part of a larger research project carried out in association with the R&D department of a cable manufacturing company, and these results are being applied into the design department of this company.     

Transmission of 155 Mbit/s (SONET STS-3) signals over unshielded and shielded twisted pair copper wire

The feasibility is demonstrated of transmitting 155 Mbit/s SONET-ATM signals over 131 m of unshielded 24 AWG single twisted pair copper cable and 213 m of shielded 22 AWG twisted pair cable with bit error ratios of less than 10/sup -13/. The transmission performance of the single-pair unshielded cable is compared with that of four-pair unshielded twisted pair cables.<>     

ADSL技术发展及应用

ADSL技术是一种调制技术,在双绞铜线的两端分别接入ADSL调制解调器,即可利用其高频宽带特性高速传送数据.本文全面阐述了实现用户线路高速化的ADSL的技术以及应用.     

多芯屏蔽电缆屏蔽效能的脉冲电流注入法测量

为了测量脉冲电流注入电缆的时域屏效,采用皮电流I0与短路芯电流Id峰峰值之比的分贝数求解电缆的屏蔽效能方法,给出了某百芯屏蔽电缆的等效电压源内阻和屏蔽效能值,并对外场辐射试验法中的某百芯初样电缆总的屏蔽效果进行了计算和讨论。     

Equalization for DMT based broadband modems

Faced with fierce competition from cable operators, telephone companies are now aggressively investing in digital subscriber line technology with the objective of providing an economic broadband access alternative. However, high-bit-rate transmissions over the metallic access network is far from trivial. The subscriber loop predominantly consists of interconnection of twisted pair copper sections. This causes severe attenuation of the high-frequency components of the transmitted signal. Equalization refers to the signal processing in the transceiver to combat the effects of the dispersive channel on the transmitted signal. This article overviews equalization methods for discrete multitone modulation (DMT). The interference structure created by a non-ideally equalized channel is analyzed. Time modulation as well as frequency domain equalization methods are addressed     

Electromagnetic coupling of twisted pair cables

Increasing deployment of digital subscriber line (DSL) technology operating in the long wave, medium wave and sometimes short wave frequency ranges, has raised the question of how such systems interact with rival radio frequency sources and equipment. Two of the major standards bodies in the field, ITU and ETSI, imposed by the standardization of such promising technologies like ADSL, SHDSL and VDSL, have begun to elaborate performance tests for radio frequency interference (RFI) scenarios for inclusion into their standards documents. Existing out-door loops of the copper telephone network can have large dimensions, are often unshielded and sometimes not even twisted, thus, they can act like antennas for both RFI egress and ingress. The RFI egress issue requires basic knowledge of the relationship between a given current distribution I(l) on a twisted pair communication cable and the electromagnetic fleld E, H generated by that current distribution at a given distance d. This problem is reciprocal to the RFI ingress issue, which requires knowledge of the relationship between a disturbing high-frequency electric field E in the surroundings of a twisted pair cable, and the terminal voltage of that cable across a load impedance. This contribution provides the theoretical background to the field theoretical problem and supplies simple yet accurate approximation formulae for the prediction of RFI egress and RFI ingress     

Measuring Connector Shielding Effectiveness During Vibration

This paper describes the equipment and technique used to measure shielding effectiveness* of threaded electrical connectors during vibration. The vibration fixture is a modified coaxial trough of which the connector is a part. The connector is mechanically loaded with a short section of cable. A known current is applied on the shield of this short cable section and across the receptacle/plug interfaces. RF leakage into the interior of the cable is determined by forming the interior wiring of the cable into a closed loop and measuring the current in this loop. The logarithmic ratio of the current in the shield to the current in the interior loop is the shielding effectiveness of the cable-connector combination. The cable shield is composed of brass convolute with a braid covering and provides, by itself, 100 dB isolation. This isolation was demonstrated by testing the shielding effectiveness (S.E.) of a base-line specimen which substituted a brass fitting for the connector. It is demonstrated that this method of testing connectors can be used to determine S.E. under vibration. The method is proposed as a standard method of qualification testing of connectors.     

全面的接入网技术和解决方案

交换的功能和业务正趋于集中在少量的大中型交换局结点上，同时尽量缩短双绞线铜缆的长度，在几公里范围内，用光纤接近终端用户也成为一种趋势，目前，针对各种特定环境所用的技术多种多样。本文就有关铜缆，光缆及无线方面的技术以及阿尔卡特部分产品作一个简单的介绍。     

Radiation properties of a pigtail-terminated coaxial transmissionline

The method of moments is used to study the shielding effectiveness of a pigtail-terminated shielded wire (coaxial line) above a perfectly conducting ground plane. Numerical computations are performed in the RF frequency range, i.e. 25-1000 MHz. Pigtail wires on either or both ends of the shield are considered. Results are compared to those from the ungrounded case (floating shield). Results show that the presence of pigtail wires as ground connections at RF frequencies is undesirable and may further enhance radiation. The impedance terminations have a small effect on the shielding effectiveness of the antenna structure     

综合布线系统（二）：第二讲 综合布线系统的网络结构,布线部件和指标参数

概述了综合布线系统的网络结构和主要布线部件等基本内容;较全面地介绍了综合布线系统的信道和链路;说明了各段缆线的最大长度;系统列出了对绞线和对绞电缆布线链路和光缆布线链路的性能指标和主要参数。     

On Reducing the Lightning Transients in Buried Shielded Cables Using Follow-On Earth Wire

This paper investigates the importance of a follow-on buried bare earth wire for the lightning protection of buried shielded cables. The use of follow-on bare wires for lightning protection of communication towers was suggested as a recommendation in certain standards, without being complemented either by theory or experiments. When lightning transients couple to the cable shields, it induces large currents (depending on the type of coupling) causing transient overvoltages between the inner conductors and the shield. It is shown by simulations based on multiconductor transmission line theory that if the follow-on bare earth conductor is placed in parallel with the shielded cable with the bare earth wire connected to the shield at the current injection end, then the shield current, and thereby, the internal transient voltages of the cable are reduced considerably.     

Magnetic Field Pickup by Flexible Braid Coaxial Cables

Cabling systems have long been known to be a source of unwanted pickup of radio-frequency interference. A typical source of pickup occurs when the outer sheath of a coaxial cable system forms part of a ground return for potentially interfering electromagnetic energy. Another source of penetration arises from a magnetic field which is perpendicular to the axis of the coaxial cable. A previous study demonstrated that the field emanating from a coaxial cable could be characterized as an equivalent open-wire pair. This particular effect is caused by the eccentricity between the centers of the outer and the inner conductors or because of other asymmetrical characteristics. The susceptibility of a coaxial cabling system to perpendicular magnetic fields can also be characterized in terms of an equivalent open-wire pair for short runs. The purpose of this investigation was to measure the shielding effectiveness of a typical flexible braid coaxial cable to magnetic fields perpendicular to its axis and to demonstrate that a coaxial cable may be considered as an equivalent open-wire pair in a cylindrical shield. A test setup employed a parallel plane transmission line to generate a uniform magnetic field perpendicular to the axis of the coaxial cable. The shielding effectiveness of the braid was measured for several classes of braid conditions. Then, using the same braid, a coaxial cable with an experimentally induced known eccentricity was employed and the overall pickup measured. The results confirmed the objectives of the investigation.     

基于xDSL技术群与远程监控传输方式的研究

对现行、主要的二种远程通讯方式进行了比较,指出了光纤传输方式的缺点和采用视频电缆传输方式的不足。重点介绍了基于普通双绞线的xDSL技术群的特点,并结合视频监控系统和移动通讯系统的实际情况,给出了笔者初步研发成功的系统级模型。实践表明:在现行条件下,基于普通铜质双绞线的xDSL技术群是远程监控更为现实、可行的传输方式。     

xDSL技术及其应用

ｘＤＳＬ技术是一种调制技术，在双绞铜线的两端分别接入ｘＤＳＬ调制解调器，即可利用其高频带特性传送高速数据，本文全面阐述了实现用户线高速比的ｘＤＳＬ技术及其应用。     

Nutzung der Schirmwirkung der Kabelträger

Cable racks and cable trays do not only support the cables laid on them, continuous conducting metallic cable trays connected to the equipotential bonding system or the shielding of the structure reduce the induced voltage due to electromagnetic influence. Different constructions of cable racks and cable trays and their effects are described.     

Application of phase detection frequency domain reflectometry for locating faults in an F-18 flight control harness

The performance of a phase-detection frequency-domain reflectometer (PD-FDR) for locating open and short circuits (hard faults) in a Navy F-18 flight control harness has been tested, and the analytical expressions for accuracy verified. Nine different types of aircraft wires appear in this harness: twisted pair, shielded wires with 1-4 inner conductors, "filter wire," and bundles of individual wires. PD-FDRs in a variety of frequency ranges (12-25, 100-220, 150-300, and 180-400 MHz) are compared. Signal processing techniques are utilized to remove the reflections where the PD-FDR is connected to the wire harness, which is critical to obtaining accurate measurements, particularly for short lengths of wire. For this specific application, open and short circuits are located to within 2.5 cm (1 in) for PD-FDR200 and 11 cm (5.5 in) for PD-FDR25 for wires ranging from 9 cm to 9.15 m (6-360 in).     

Shielding properties of an ensemble of thin, infinitely long,parallel wires over a lossy half space

A determination of the total electric field produced by an ensemble of thin, infinitely long, parallel wire scatterers over a flat lossy half space illuminated by a plane wave whose polarization is parallel to both the wires and the interface is presented. By invoking the thin wire idealization, a matrix equation is obtained for determining the currents on each wire, from which the total electric field is obtained. Several plots are given to show how the wires' radii, the earth's conductivity, the incident angle, and the total number of wires affect the shielding for a semicircular shell. In many cases, it is demonstrated that the shielding effectiveness can be as much as 70 dB; for other cases, when the structure is of resonant dimensions, the shielding can be degraded to 20 dB. It is also shown that a wire grid model can give shielding results similar to those of a continuous perfectly conducting structure of similar dimensions