关于RL与C并联电路阻抗的最大值

在谐振电路中,教材[1]讨论了线圈RL与电容器C并联电路的谐振问题,给出了谐振时电路的阻抗模值最大等结论,但容易使学生产生误解。实际上,如果通过调节电源频率使电路达到谐振,谐振时电路的阻抗模并不是最大值,一般教材对此没有给出阻抗模的最大值。本文通过推导,给出了RL与C并联电路阻抗模最大值的精确表达式及阻抗模达到最大时电路的频率。     

三频阻抗变换器的设计

通过对传输线阻抗特性的分析,提出一种基于λ/8(λ为波长)传输线的新型线性阻抗变换器,这种阻抗变换器能同时在频点f0、频点f0的第一个谐振频点2f0及第二个谐振频点3f0实现阻抗变换,且给出此传输线参数.在阻抗变换K值不超过5时,得到的传输误差|Г|不超过0.024,可满足大多数工程应用的需要.该文推断结果可推广到n个频点阻抗变换器,即在某一个基本频点f0和其所有不能被n+1整除的谐振频点上同时实现阻抗变换.     

具有三陷波特性的超宽带带通滤波器

采用阶跃阻抗谐振理论,改进了一种三角环阶跃阻抗谐振器,并利用奇偶模分析法详细分析了三角环阶跃阻抗谐振器的谐振特性,将三角环阶跃阻抗谐振器与平行交叉耦合线相耦合,实现了紧凑型超宽带带通滤波器。随后引入产生三陷波特性的E型和C型谐振单元,将三个陷波频率调整到3.5,5.2,8 GHz频点上,实现三陷波特性的超宽带带通滤波器,有效地抑制超宽带内WiMAX、无线局域网和X卫星等频段的干扰。最后将三陷波滤波器结构进行HFSS仿真和实物加工测试,带内外特性良好,且实物测试与仿真结果一致,在特定的通信领域具有一定的应用价值。     

印刷电路板供电系磁性材料涂层的应用

印刷电路板（PCB）的电磁兼容问题,随着数字电路的工作频率越来越高而变得尤为重要。本文以印刷电路板中的电源接地层供电系构造为切入点,讨论与其相关的电磁兼容问题。在高频段,印刷电路板的电源和接地层构造相当于一个平行平板谐振器,对周围的电路产生电磁干扰（EMI）。基于全腔模模型,已经发展了用于高效准确计算供电系阻抗的快速算法。利用此算法,通过计算机仿真,结果表明PCB电源接地层导体内侧增加磁性材料涂层能够提高表面阻抗,进而减小端口输入阻抗的谐振峰并改善信号完整性。     

一种应用于n77/n78/n79频段的双频滤波天线

提出了一种基于双层结构的双频滤波天线,工作在n77/n78/n79频段。该天线由上层基板的2个矩形辐射贴片和下层基板的阶跃阻抗谐振器、2个“L”型枝节组成。2块介质基板材料均为FR4,且通过探针相连。上层介质基板上的2个矩形辐射贴片激发2个谐振模式,其中高频谐振用于形成n79频段,低频谐振用于形成n77/n78频段。为了获得双通带滤波效果,在下层介质基板中引入阶跃阻抗谐振器,在2个频段间形成带外辐射零点。此外,下层基板上的“L”型枝节可以引入额外的谐振点来扩大天线的带宽。该结构经过高频仿真软件(HFSS)优化,其仿真结果和测试结果均在3.37~3.53 GHz(n77/n78),4.55~4.64 GHz(n79)2个频段范围内,可用于6 GHz以下5G的无线通信应用。     

高速嵌入式系统中电源噪声抑制方法

根据平面腔体谐振模型理论推导出高速嵌入式电路电源平面对阻抗函数关系式,分 析了电源平面对的谐振特性与PCB板材、介质层厚度以及导体平面的电导率之间的关系,得 出可通过减小介质层厚度、使用高介电常数的介质材料以及增加介质损耗等3种方法来抑制 电源平面对的谐振效应,并使用全波仿真方法验证了可行性。从时域仿真了高速电路中的噪 声传播与电源平面谐振的相互关系,结果表明,通过抑制电源平面对谐振阻抗可将电源噪声 减 小至原有结构的15%,从而有效提高系统的电源完整性。     

电源与地平面间谐振电压噪声和阻抗特性仿真

多层PCB板中的电源与地平面间的谐振效应会引发电压噪声及电磁辐射问题。利用Cadence Sigrity软件,从电源和地平面间谐振电压噪声和阻抗特性两个维度对谐振效应进行了评估。通过控制变量,对比不同PCB设计下的仿真结果,发现增加去耦电容、减小平面间距和合理的平面分割方式可以降低谐振效应。     

新型多频蝶形微带天线

微带天线工作频带较窄,若能同时激励多个谐振点,可以变相拓展带宽,因此设计一种多频蝶形微带天线。3块介质基板构成"U"型半封闭腔体,天线的辐射臂采用1 4周期正弦轮廓结构,在辐射臂上开取3对"工"字型缝隙,同时在馈电端口处加载枝节。实验结果表明,蝶形微带天线在5个雷达波段(S,C,X,Ku,K)各有1个谐振频点,分别为2.6 GHz,6.8 GHz,11.7 GHz,16.5 GHz,18.45 GHz。通过对比分析可知:在不改变天线整体尺寸的情况下,正弦边结构可调节谐振频点位置;加载的矩形枝节有利于改善天线的阻抗匹配度,降低回波损耗;"U"型半封闭腔体可有效提高增益,其中C波段的增益由0.71 dB可提升到4.30 dB。     

W波段交错双栅色散测量与比较

采用谐振法,基于小孔耦合设计了W波段矩形槽交错双栅色散测试方案。考虑了倒圆角带来的影响,采用精密计算机数控技术(CNC)工艺加工慢波结构进行测试,获得了辨识较高的谐振峰,得到了0-p 相移范围内所有对应的本征谐振点。基于小孔耦合谐振法的仿真值与严格谐振法、准周期法的仿真值相比最大偏差0.1%,证明了色散测试方案的合理性。基于小孔耦合谐振法的实测值与仿真值相比最大偏差0.3491%,充分说明慢波结构的加工精度满足工程应用需求,这些结果为深入开展下一步试验打下良好基础。     

RL-C谐振电路阻抗与Q关系的探讨

本文以归一化频率 为变量,推导了RL-C谐振电路阻抗的模|Z|与Q及 的关系表达式,并推导给出了阻抗的最大值发生时的归一化频率 与Q的关系式。通过举例进一步分析了谐振点处阻抗与阻抗的最大值发生的频率及相对误差随Q的变化而变化的规律。     

Impedance and polarization characteristics of H and IHI slot antennas

Slot antennas can be end loaded to tune input impedance for use with active devices and to decrease overall slot length at a given resonant frequency. Cross polarization and impedance of end-loaded slots in an H configuration are analyzed. For an H antenna of approximately equal height and width, D-plane cross polarization was found to be -20 dB, and the resonant frequency decreased by 34% over a slot with a length equal to the width of the H. The cross polarization can be reduced with our new IHI configuration, which is introduced. The impedance at the second resonance can be tuned over a range of 26-82 /spl Omega/.     

Microwave surface impedances of BCS superconducting thin films

The microwave propagation-dominated problem in the multilayer structure made of a BCS superconducting film and a dielectric substrate is investigated theoretically by using the modified two-fluid model and transmission line theory. The effective microwave surface impedances are studied as functions of temperature, frequency, and film thickness, as well as substrate thickness. Special attention is paid to the substrate resonance phenomenon in the resonant structure. The influence of BCS coherence effects on surface impedance and resonant behavior is clearly demonstrated. The resonant effect in the stack structure is well interpreted with the help of the transverse resonance technique in the microwave theory     

Experimental study of the characteristics of top-loaded microstrip monopoles

The characteristics of microstrip monopoles fed at the center with antiphase currents are investigated experimentally. First the impedance is measured as a function of frequency. It is found that the radiation resistance at the resonance nearL simeq 05 lambda, is very low while the radiation resistance at the resonance nearL simeq lambdais very high. For a given physical length of the monopole, the resonant frequency is dependent on the strip width and the substrate thickness. The effect of substrate thickness and strip width on the input impedance and bandwidth has also been studied. Finally theE-plane radiation pattern is found to contain two maxima, occurring at approximatelypm 40degfrom broadside.     

Broad-Band Coupling to High-Q Resonant Loads

Broad-band coupling between a resistive source and a resonant load is considered for coupling networks consisting of a uniform transmission line of impedance Z/sub I/ and length equal to a quarter wavelength at the load resonant frequency. An approximate analysis is used to show that either maximally flat or ripple insertion loss frequency response can be obtained by proper choice of Z/sub I/, and the 3-dB bandwidth obtained in either case is always greater than 1/Q. Depending on the ratio of load and source resistances, the bandwidth may be greater than 1 octave. Network design curves for maximally flat operation with a variety of load parameters are computed without approximation. The design of lumped element approximations for the transmission line network is also described.     

Analysis of gap-coupled microstrip antenna

In the present paper the analysis of a gap-coupled microstrip antenna (GCMSA) is carried out using the circuit concept and consequently various parameters such as input impedance, VSWR and return-loss are investigated for different air gap lengths. It is observed that the resonant frequency of the antenna with different substrates depends on the gap length. The gap-coupled antenna behaves as an RL network below the resonant frequency for all substrate materials and gap lengths, whereas the antenna behaviour above resonance is like an RC network. It is further observed that the resonant frequency of the GCMSA decreases with increasing gap length.     

Perturbation of a resonant cavity by a small bianisotropic sphere

Perturbation of a resonant cavity by the introduction of a small bianisotropic sphere in its interior is analyzed. It is shown that the resonance frequency can be altered merely by rotating the bianisotropic sphere at a fixed location.     

开关电容V/Q变换器及其在接地阻抗模拟中的应用

文中提出一个V/Q变换的广义跨导概念,并应用在开关电容阻抗模拟中。使用V/Q变换器,可以用电压传递函数实现所希望的阻抗函数。由此概念出发,分别导出了前差FD,后差BD和双线性S/Z变换的三种接地开关电容频变负阻SC-FDNR电路。如果所选用的电压传递函数电路对杂散电容不灵敏,那么实现的模拟阻抗电路对杂散电容也是不灵敏的。作为文中的一个例子,用FD-FDNR电路组成一个谐振回路,实验表明其频响特性与理论分析相一致。     

Design of an efficient miniaturized UHF planar antenna

The design aspects and the measured results of a novel miniaturized planar antenna are described. Such architectural antenna design is of great importance in mobile military communications where low visibility and high mobility are required. Slot radiating elements, having a planar geometry and capable of transmitting vertical polarization when placed nearly horizontal, are appropriate for the applications at hand. Slot antennas also have another useful property, so far as impedance matching is concerned. Basically, slot dipoles can easily be excited by a microstrip line and can be matched to arbitrary line impedances simply by moving the feed point along the slot. Antenna miniaturization can be achieved by using a high permittivity or permeability substrate and superstrate materials and/or using an appropriate antenna topology. We demonstrate miniaturization by designing an appropriate geometry for a resonant narrow slot antenna. A very efficient radiating element that occupies an area as small as 0.12/spl lambda//sub 0//spl times/0.12/spl lambda//sub 0/ is designed and tested. Simulation results, as well as the measured input impedance and radiation patterns of this antenna, are presented. This structure shows a measured gain of 0.5 dBi on FR4 substrate, which has a loss-tangent of the order of 0.01. Also, the effect of finite ground plane size on gain and resonant frequency is investigated experimentally.