同轴电缆芯线电容测量方法研究

同轴电缆或高速数字通讯电缆芯线电容,是影响电缆性能的重要参数.在完成屯缆编织工艺前,准确测量芯线的电容,及时控制电缆单位长度的电容,使电缆具有均匀传输阻抗,是保证电缆质量的重要措施.文章从芯线测量原理、电容测量装置设计、测量仪器选择、测量步骤、影响测量的误差来源分析等方面对测量方法进行阐述.     

关于芯线供电若干问题探讨

芯线供电即通过同轴电缆的芯线与外屏蔽传输安全交流低电压,对网络中的有源器件进行供电。采用芯线供电,就必须考虑,电缆的外导体质量、抗腐馈性能、环路电阻及电缆连接的可靠性和接头的抗腐蚀性能,随着国产优质器材的成功生产(如QR540,MC~2500,铝管—12等),芯线供电由于其可靠性和安全性能,成为有线电视网升级改造中最     

无限冲击响应滤波器在屏蔽电缆耦合分析中的应用

运用一阶并联结构的无限冲击响应(Infinite Impulse Response,IIR)滤波器模型对转移阻抗和转移导纳进行建模,结合时域有限差分（Finite-Difference Time-Domain,FDTD）法对屏蔽电缆屏蔽层和芯线的时域响应进行同步求解.计算结果表明,该方法可以精确地反映电缆的转移阻抗和转移导纳特性,且易于FDTD算法实现.与传统方法相比,该方法能够得到更完整的芯线响应,从而为屏蔽电缆的时域分析提供更为精确的手段.     

均衡量及均衡偏差与电缆长度的关系分析

1　同轴电缆的衰减频率特性同轴电缆对所传输的信号有衰减作用 ,其衰减量不仅与同轴电缆的内外导体直径和绝缘材料的相对电容率 (介电常数 )有关 ,还与信号频率有关 ,并且电缆越长衰减量越大。把单位长度 (如 10 0ｍ)电缆对信号衰减的分贝值称作同轴电缆的衰减常数 ,常温下 (2 0℃ )其大小为 :ｌ=2 .6 3εｆ1ｄ+ 1Ｄｌｇ Ｄｄ　　 (ｄＢ/ 10 0ｍ) (1)式中　ｄ———内导体 (芯线 )外径 (ｍｍ) ;Ｄ———外导体 (屏蔽层 )内径 (ｍｍ) ;ε———绝缘层相对电容率 (介电常数 ) ;ｆ———传输信号频率 (Ｈｚ)。当电缆的型号和规格确定之后 ,(1)…     

屏蔽电缆屏蔽效能与转移阻抗关系研究

阐述了转移阻抗和屏蔽效能的定义,并从辐射角度出发,分析了屏蔽电缆屏蔽效能与芯线电流及屏蔽层电流之间的关系,同时结合传输线理论,推导了屏蔽效能与转移阻抗的数学关系,并通过仿真计算,比较了不同条件下的屏蔽效能与转移阻抗。     

大电流作用下电缆转移阻抗非线性特性研究

为了研究屏蔽电缆受外界电磁脉冲作用可能产生的非线性效应,提出了屏蔽电缆表面转移阻抗的大电流注入测试方法.建立了大电流注入测试系统,通过注入测试方法获得了不同电流等级下电缆转移阻抗曲线,对比了两类屏蔽多芯电缆的芯线电磁脉冲耦合情况.实验表明：加入一层铁磁性屏蔽层的多芯电缆在注入电流峰值超过2 kA时,芯线耦合电压会呈现非线性效应.并分析了该现象产生的原因.     

单端接地屏蔽电缆低频耦合干扰分析与仿真

为分析线路单端接地时的信号低频干扰问题,基于有限元软件Ansys分析了屏蔽层周围空间的电磁场分布,以及地表电位对芯线串扰电压的影响,通过仿真求得了多导体系统的耦合电容,建立了低频信号下传输线的电路模型。分析了屏蔽层电位、屏蔽层与两芯线耦合电容的差值、信号源输出阻抗对芯线串扰电压的影响,给出了线缆串扰电压的计算公式,并对比了一起轻型轨道衡工频干扰事故的实测数据,验证了理论的正确性。     

架空多芯电缆对高功率微波耦合特性研究

通过数值计算和试验研究地面附近有限长架空多芯电缆对高功率微波的耦合特性,为指挥工程中电缆耦合特性研究提供参考。数值计算和试验结果表明,架空多芯电缆对窄带高功率微波和超宽谱高功率微波具有耦合作用,不同芯线之间存在互耦,耦合特性受电缆接头处理方式、电缆长度、电缆类型、电缆与来波方向(极化方向)夹角、屏蔽层是否接地、微波频率等影响严重。数值计算和试验结果在规律上比较一致,证明了计算模型和试验方法的正确性和有效性。     

结构化布线系统中的高频补偿技术

在结构化布线系统中,传输介质是非屏蔽双绞线(UTP)电缆和RJ45连接硬件,这些介质具有100欧姆的阻抗。 数据传输受到传输线路限制,即阻抗、电容和电感。其中电容和电感在高频时的影响明显要高得多。     

屏蔽电缆单端接地与双端接地电容效应仿真研究

屏蔽电缆的屏蔽层主要是作为电磁辐射、电磁干扰和接地保护的作用。屏蔽层悬浮电位的接地主要有单点接地、多点接地、交叉互联和连续交叉互联等方式。对于接地的屏蔽电缆是由电容效应和电感效应组成的。本文通过仿真模拟137/220 kV屏蔽电缆单端接地与双端接地的电容效应，研究不同高压输电线路下屏蔽电缆的电压电流分布特性，进而分析220、330、500 kV屏蔽电缆屏蔽层的电压电流特性和损耗特性。     

Evaluation of measured complex transfer impedances and transferadmittances for the characterization of shield inhomogeneities ofmulticonductor cables

Besides the knowledge of the primary line parameters per unit length, the determination of the complex transfer impedances and transfer admittances of shielded multiconductor cables is the prerequisite for the calculation of the propagation of disturbing currents on the inner wires of the cable. With a measurement procedure based on triaxial measurement setups using multiconductor transmission line theory for evaluation, it is possible to determine individual transfer impedances and admittances for each inner conductor of a shielded multiconductor cable over a broad frequency range. This paper shows the measurement procedure, the method of evaluation: and from measurement results, the determination of the location and the calculation of the area of single-shield inhomogeneities by the evaluation of measured transfer impedances and transfer admittances     

Perturbations impulsionnelles créées par des câbles ďénergie sur des câbles de transmission de données

This paper presents the study of coupling between multiconductor cables from the multiconductor lines theory and the assumption of perfectly conducting ground. The cables can be excited by generators of arbitrary waveforms and terminated by arbitrary impedances. The medium surrounding the conductors can be homogeneous or inhomogeneous and the conductors can have finite conductivity. Once the used assumptions indicated, we formulate the complete solutions of induced currents and voltages at the ends of the multiconductor line, by using the state variable theory. We give numerous comparisons of numerical results, obtained by our numerical code, with literature (microstrip lines) and experimental results (shielded cables, unshielded RNIS bus).     

An analytical solution for the coupled stripline-like microstripline problem

An analytical method is presented for determining the Maxwell's capacitance matrix of multiconductor shielded microstrips with coupled conductors of arbitrary widths, spacings, and inhomogeneous media, in terms of elliptic integrals. The method is based on conformal mapping and the theory of singular integral equations. Two kinds of problems are presented as examples: the first consists of simple structures with one or two coupled striplines; the other type concerns the general case of multiconductor coupled structures for which simple analytical expressions are not available     

Calculation of transverse waves in a shielded transmission line containing circular cylindrical conductors

A method is proposed for calculating a shielded homogeneous multiconductor transmission line containing conductors of circular cross section. Formulas are obtained for the matrix of the conductor capacitance per unit length and the electric parameters of transverse electromagnetic waves.     

多芯屏蔽视频电缆转移阻抗的测试研究

本文讨论了基于"三同轴法"的多芯屏蔽视频电缆转移阻抗的测试原理和方法,据此方法我们设计给出了使用矢量网络分析仪作为信号源及接收器实现多芯屏蔽视频电缆转移阻抗测试的测量装置和测试结果,最后基于测试结果我们对多芯屏蔽视频电缆的屏蔽效能进行了验证,从而证明了多芯屏蔽视频电缆转移阻抗对信息安全的重要意义.     

Analysis of a shielded transmission line containing circular cylindrical conductors and coplanar lines on a grounded shield

For the first time, a method is proposed for numerical calculation of a monolithic multiconductor shielded transmission line integrated with planar coupling circuits. Formulas for the matrix of the per-unit-length capacitance of coupled conductors are derived. The electric parameters of fundamental modes are calculated in the quasi-static approximation. The computation results can be used for designing monoblock microwave filters.     

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.     

Analytically determined quasi-static parameters of shielded or openmulticonductor microstrip lines

An exact analytical expression for the capacitance matrix of a shielded or open multiconductor microstrip structure is derived by solving the system's dual integral equations by constructing a Volterra boundary-value problem (BVP). The solution is expressed in terms of infinite matrices with very good convergence properties. This new approach uses a series of Bessel functions rather than trigonometric series to approximate the solution which results in an efficient algorithm. Simplified formulas are given for the even and odd capacitance of symmetric coupled microstrip lines and compared to the results given by the finite analytical solution available in this particular case. Numerical examples demonstrate that the method yields accurate results and is computationally effective for structures having a large number of conductors     

外部电磁场对屏蔽多导体电缆系统耦合影响的分析

本文给出了一个有效的、用以分析外部电磁场对屏蔽多导体电缆系统电耦合影响的方法，适用于电缆的频域或时域电磁兼容分析。     

SPICE-like models for the analysis of the conducted and radiated immunity of shielded cables

The aim of this work is the development and validation of compact SPICE models suitable to analyze the conducted and radiated immunity of shielded cables. The reference structures are coaxial cables, and shielded cables with two parallel wires (i.e., twinax cable). The conducted and radiated immunity of the shielded cables are evaluated considering as source a known injected current on the cable shield, and the coupling with an external plane wave electromagnetic field, respectively. The circuit models are validated by comparing the results with those obtained by other approaches. The developed models are then used to quantify the main grounding practices of shielded cables.