基于介电非线性机制的微带电路无源互调效应研究

微带电路无源互调产生机制尚无定论并且缺乏可靠的理论预测方法,本文基于等效受控源模型,建立了基于介电非线性机制的微带线无源互调的解析计算模型,同时,通过对比测试聚四氟乙烯玻纤布介质微带线和空气介质微带线的三阶互调规律验证了介质非线性是微带电路无源互调的一种主要非线性来源,并提取了非线性参数.实验结果显示聚四氟乙烯玻纤布介质微带线比空气介质微带线的传输互调高了约20dB,反射互调高了约15dB,表明介质非线性是聚四氟乙烯玻纤布介质微带线互调的主要来源.同时,根据本文建立的微带线互调计算解析模型,提取聚四氟乙烯玻纤布介质基板的三阶非线性相对介电常数.本文研究方法可以进一步用于其它微带电路无源互调规律计算研究.     

微带电路无源互调干扰问题综述

无源互调（PIM）干扰是微波射频电路面临的主要可靠性问题之一,随着微波射频电路小型集成化发展,微带电路无源互调效应研究开始受到工业界和学术界广泛关注。研究微带电路无源互调机理、评估和抑制方法,对于制备小型化、高可靠性微波射频电路具有重要价值。与腔体部件相比,微带电路的非线性往往是分布的,且与基材选择、制造工艺和器件结构等方面都有重要关系,因此研究难度更大。近年来虽然关注微带电路互调的研究越来越多,但依然难以直接指导微带电路的实际设计。基于此,本文系统论述了近年来微带电路无源互调领域的研究情况,包括非线性机理、仿真建模以及测试诊断等方面,为未来更深入地研究微带电路无源互调效应提供参考。     

波导法兰连接的无源互调分析与测量

在卫星通信系统中,非铁磁性微波无源器件的无源互调(PIM)问题非常严重,产生PIM的根源在于天线、波导法兰等无源器件的非线性效应,例如场发射、量子隧穿、热电子发射、电致伸缩、微放电等[1]。文中通过对波导法兰无源互调模型的分析和测量,得出波导间接触压力越大,各阶PIM越小;PIM阶数越高,载波功率之比对其影响越大。     

基于正态分布宽带信号的无源互调特征行为分析

在现代无线通信中,无源互调是影响通信信号传输质量的重要因素。双音互调测试能够有效衡量无源器件的非线性特性,却无法准确预测出器件在宽带信号激励下的非线性失真。因此本文提出了一种基于正态分布的宽带信号激励下的射频连接器无源互调特性分析方法。通过双音互调测试,建立射频连接器无源非线性传输数学模型,并将基于正态分布的等效宽带信号作为非线性传输模型的激励源进行模拟仿真。结果表明,宽带无源互调功率分布与宽带信号功率分布相同,n阶宽带无源互调带宽为原宽带信号带宽的n倍,宽带信号的无源互调产物相较于双音测试信号有所增强,且信号的信噪比下降,说明宽带信号在传输过程中受到的干扰更加严重。电路仿真和数值计算呈现出良好的一致性,证明了本分析方法的有效性。     

无源互调产生的物理机制

随着无线通信和卫星通信技术的迅速发展,无源互调（PIM）对通信系统的干扰越来越显著。该文主要介绍了PIM产生的非线性物理机制（包括接触非线性和材料非线性）。接触非线性主要来源于接触中的隧穿效应、热电子发射等,并受到接触表面粗糙度、接触间机械应力与对称性等因素的影响。材料非线性主要来源于材料中的热电耦合和非线性源散射效应,其几何结构与点状污染等因素也会对PIM产生影响。未来,PIM底层物理机理的研究需求更加迫切,需要深入到微观领域,并且与多物理场建模与分析技术相融合,才能深入全面地揭示无源互调机理,进而指导无源互调抑制的相关设计。     

5G和卫星通信中无源互调电磁干扰研究

现代通信技术向着高密度、高集成、广域覆盖方向快速发展,无线接入终端数量大幅提升,微波器件固有寄生的无源非线性导致的互调干扰严重制约了现代频谱资源的高效利用.文章从无源互调机理研究出发,梳理了国内外无源互调机理研究中的经典问题以及最新进展,总结了近几十年来关于无源互调建模、检测、抑制与对消的研究成果,并结合现代通信技术特点,指出多物理场、多调制模式、多信道重合条件下的PIM问题将成为研究热点.     

辐射场中金属接触无源互调干扰研究

为了评估辐射场中金属接触结构引起的无源互调（passive intermodulation，PIM）对接收天线的干扰程度，提出并验证了一种可以预测被天线接收的PIM幅值的计算方法.应用PIM点源模型，并基于接触结处载波激励电流幅值和PIM信号耦合效率的仿真建立辐射场中金属接触PIM的计算方法；采用缝隙波导工装基于近场耦合测试原理对两根铜丝搭接而成的接触结构在缝隙波导近场辐射场中的三阶无源互调（third-order passive intermodulation，PIM₃）及其按位置分布规律进行测试分析.理论计算和实验测试结果比较吻合，证明本文提出的计算方法能够预估辐射场中金属接触PIM幅值.本研究工作为评估辐射场中PIM产物提供了分析方法，同时有助于深入理解辐射场中金属接触PIM的产生机理.     

用控制量转移求解含受控源的戴维宁等效电路

在电路分析中,常需要求解含受控源的戴维宁等效电路,其核心是求等效电路端口的开路电压U_∞及等效电阻R_0 。通常要列方程,运算量较大,特别是对多网孔和多节点电路。另一种方法是用电路等效求解,要求在等效过程中控制量支路不能变动,这种要求对电路等效带来很多限制。本文提出先采用控制量转移,然后进行电路等效的方法。 如何进行控制量转移,控制量转移到何处合适呢?通过对电路的考察分析,含受控源的电路按控制量所在位置大致可分为下述三类。 第一类:受控电流源的控制量为该受控源两端电压,或受控电压源的控制量为该受控源所在支路的电流,这两种受控源可以用置换定理将受控源置换为电阻。含有这两种受控源的电路在置换定理使用后,电路中不再含受控源,用电路等效的方法可以得出戴维宁等效电路。     

含受控源网络的传输矩阵分析法

本文论述了通过计算机混合传输矩阵求取含受控源网络响应电压和响应电流的方法。此法适用于计算机编程计算。     

蝶形电阻网络圆周边界任意端口间等效电阻的计算

本文将电路理论中的网孔分析法与递归变换法相结合,给出了一种求解蝶形电阻网络圆周边界任意端口间等效电阻的简捷方法.计算过程中,首先基于网孔分析法建立了非线性的差分方程组,随后利用矩阵变换方法,将非线性差分方程组转化为线性的差分方程组.此外,本文将一般外加单一电流源求等效电阻的策略推广为外加多个电流源,由此获得的等效电阻解析表达式可适用于计算任意端口的等效电阻.     

Near-field scanner for the detection of passive intermodulation sources in base station antennas

Passive intermodulation (PIM) distortion is a challenging problem in the design and manufacturing of base station antennas. Small nonlinearities, typically in junctions, may cause a distortion signal that interferes with the receiver even with a level of -155 dBc in a GSM900 system. The PIM level specification of an outdoor base station antenna is difficult to achieve and the sources of PIM generation are laborious to track down. In this paper, a near-field measurement method is presented to localize and investigate passive intermodulation sources in antennas and open transmission lines. The principle of the PIM near-field measurement is otherwise the same as in a common reactive near-field measurement, but instead of measuring the signal at the input frequency, the signal amplitude and phase at the PIM frequency of interest are acquired. The constructed measurement system is capable of measuring PIM signal levels down to -110 dBm with 2/spl times/43 dBm transmit power in the GSM900 frequency band. As demonstration measurements, PIM sources in a two-element base station antenna and in a microstrip line are localized.     

Effects of Geometrical Discontinuities on Distributed Passive Intermodulation in Printed Lines

This paper presents the results of experimental study of passive intermodulation (PIM) generation in microstrip lines with U-shaped and meandered strips, impedance tapers, and strips with the profiled edges. It is shown that the geometrical discontinuities in printed circuits may have a noticeable impact on distributed PIM generation even when their effect is indiscernible in the linear regime measurements. A consistent interpretation of the observed phenomena has been proposed on the basis of the phase synchronism in the four-wave mixing process. The results of this study reveal new features of PIM production important for the design and characterization of low-PIM microstrip circuits.      

A Coupled-Line Model for Dispersion in Parallel-Coupled Microstrips (Short Papers)

A new circuit model is derived for parallel-coupled microstrip consisting of two separate pairs of coupled lines. Each pair consists of a homogenoeus TEM line coupled to a homogeneous TE line. One pair represents the hybrid even mode, the other represents the odd mode. Data calculated from the model are compared with experimental dispersion data for various parallel-coupled microstrip geometries. Agreement is excellent. The procedure for deriving the equivalent circuit is an example of a general technique for using coupled lines to model longitudinally uniform but transversely inhomogeneous lossless waveguide.     

Modeling and Characterization of Microstrip-to-Coaxial Transitions

A simple circuit model for the transition from a Iossy microstrip to coaxial line has been developed on an experimental basis. The proposed model can be used to predict accurately the insertion loss and insertion phase over a wide frequency range. Since explicit formulas for the model element values are given, these elements, representing the parasitic of the transitions, can be taken into account very easify when the microstrip is used as a test fixture for measuring the parameters of solid-state devices. The practical use of the model has been examined for several Z/sub 0/=50-omega lines on both Epsilam-10 and 99-percent alumina substrates with standard SMA coaxial connectors.     

Passive-Intermodulation Analysis Between Rough Rectangular Waveguide Flanges

A new model is presented for the calculation of passive intermodulation (PIM) in waveguide connections. The model considers the roughness of interconnecting waveguide surfaces and the presence of an insulator layer (oxide and contaminants) on these metal surfaces. This results in the generation of a contact resistance, which can excite the PIM level. In particular, the case in which metal–insulator–metal regions are the PIM source is especially investigated. The intermodulation level response is calculated for different waveguide junction parameters like applied mechanical load, surface finish, or metal properties showing qualitative agreement with the measured data published by previous authors.     

Generalized Partial-Element Equivalent-Circuit Analysis for Planar Circuits With Slotted Ground

A generalized partial-element equivalent-circuit (PEEC) method is proposed for modeling a planar circuit with a thin narrow slot on the ground. The approach is based on the coupled mixed potential integral equations for a problem with mixed electric and magnetic currents. The coupled integral equations are converted into a lumped-element circuit network using Kirchhoff's voltage law and Kirchhoff's current law of the circuit theory. The full-wave Green's functions for a grounded dielectric substrate problem are used. The interactions between electric current on a microstrip line and magnetic current on a slot are taken into account by introducing two kinds of controlled sources. This generalized PEEC model will be very useful in signal-integrity analysis for multilayered circuits. To validate the generalized model, three numerical examples consisting of microstrip lines and slots on the ground are presented. The results obtained by the proposed generalized PEEC model are compared with those obtained by commercial electromagnetic simulation software and published experimental results. Good agreement is obtained.      

超薄微带线信号完整性的矩量法分析

超薄（或说零厚度）微带线是微波电路设计的重要组成部分。基于矩量法,推导了零厚度微带线电磁参量的公式,计算了微带线的特性阻抗和相应的等效介电常数,探讨了微带线的准静电边缘效应和两条微带线间的近端串扰问题。计算结果与已有结果相比较,一致性良好。