基于自适应遗传算法的寄生电流抑制结构设计与研究

为了抑制同轴线外导体表面存在的寄生电流，设计并研究了基于自适应遗传算法的寄生电流抑制结构.该结构是一个与同轴线外导体相连且两侧有五对对称I型开槽的金属板，在开槽处加载集总电容以实现小型化要求.该结构工作原理可等效为一组串联LC谐振电路，当有外部因素导致同轴线外导体表面有寄生电流存在时，该等效电路呈现的高阻抗特性会抑制寄生电流的流经.为了选取合适的电容，提出了一种自适应遗传算法来优化计算加载电容的大小，该遗传算法实现了交叉率和变异率的非线性自适应调整，与标准算法相比，该算法有更优的收敛速度以及鲁棒性.利用此算法完成了相应的计算和分析，结果表明该结构能够在5 250~5 925 MHz范围内对寄生电流实现-10 dB以上的抑制效果.本文方法能够指导寄生电流抑制结构设计，并进行寄生电流抑制效果的定量分析.     

T型槽加载扼流器设计

针对扼流巴伦带宽窄、尺寸大等问题,设计了一种工作于VHF/UHF波段的宽带小型化扼流器,扼流器两侧开轴向对称的不等长T型槽,并在槽边缘加载高功率电容。根据电流分析,T型槽在结构可等效为2个串联短路传输线,呈现出较大的感性,加载电容可拓展其工作带宽,具有较好的电流抑制效果。为了验证扼流器对寄生电流的抑制效果,在仿真软件中建立对称振子天线模型,并将扼流器与振子一臂贴合放置,通过电流仿真结果验证了扼流器对寄生电流具有抑制效果。     

椭圆开缝同轴线的特性

本文采用保角变换方法，确定了外导体开缝的椭圆同轴线的特性，给出了单位长度电容和特性阻抗。     

电容加载对频率选择表面传输特性的影响

有源频率选择表面,是指在频率选择表面中加入变容二极管或PIN二极管等有源器件构成的FSS结构,通过有源器件的可调性来实现对FSS性能的控制。文中根据有源器件的电容等效原理,设计了一种方形缝隙FSS结构,研究了电容加载对FSS传输特性的影响。仿真结果表明,加载电容后其谐振频点向低频偏移,带宽减小,且加载电容对FSS传输特性有较好的可控性。     

同轴线型低通滤波器的设计

该文介绍了同轴线型低通滤波器的设计原理与方法,并以结构二,即同轴线内导体外直径统一,外导体内直径呈阶梯变换实现了截止频率为4GHz的同轴线型低通滤波器。结构二相比于结构一,即外导体内直径统一,内导体外直径呈阶梯变化的优势是其设计简单,体积较小且性能更好。测试结果表明,所制作的同轴低通滤波器有良好的性能指标,在整个通带内插入损耗小于0.4dB,回波损耗大于15dB,在通带外6GHz处的抑制约为36dB,整体满足了设计要求。     

一种小型多频微带天线的分析与设计

针对普通微带天线在低频端辐射板尺寸较大的缺点,设计了一种新型的小型微带天线结构.通过在普通微带天线辐射板周围加载寄生贴片,并在寄生贴片上进行馈电的方法,有效延长了辐射板上的电流路径,从而减小了天线的谐振频率,达到了天线小型化设计的目的,同时,加载的寄生贴片也产生了新的电流路径,获得了天线的多频工作特性.仿真结果表明,当...     

基于电容加载的圆环缝隙频率选择表面研究

 介绍了一种新型小型化频率选择表面（FSS）,在圆环缝隙周期单元表面加载电容以缩小FSS尺寸,并引入法拉第笼结构以消除单元间的干扰. 对这种加载FSS进行了数值仿真和分析,提出了一种适用于1~4GHz频段的电容加载FSS谐振频率经验计算式,并在此基础上设计研制了谐振频率为2.45GHz的加载FSS,其物理尺寸仅为传统FSS的百分之三十四,仿真和实测结果表明该FSS具有谐振频率稳定、对入射波入射角不敏感、对TE、TM极化一致性好等优点.     

一种新型小型化窄带腔体滤波器的设计

该文设计实现了一种高抑制、小型化结构的窄带腔体滤波器,利用加载电容的原理,在盖板一侧添加矩形金属柱,增大了耦合电容,缩小了相邻谐振腔之间的距离,从而实现了滤波器的小型化。通过CST仿真,设计了中心频率为7.325 GHz、带宽为0.25 GHz的窄带腔体滤波器。最终经过实物测试表明,频带内驻波比良好,带外抑制高,实物体积减小。     

一种新型加载Sierpinski垫片天线的设计

提出一种新型分形结构加载的Sierpinski垫片天线。该天线采用新型加载技术并充分利用了此新型结构的空间自填充能力。结果表明,此新型分形结构加载的Sierpinski垫片天线比Koch分形加载更能缩减天线的尺寸,并且能降低谐振频率,具有宽频带特性,可以实现Sierpinski分形天线的小型化、多频段特性。     

一种宽阻带窄带腔体滤波器的设计

该文介绍了一种窄带带通腔体滤波器的原理和设计方法,通过加载电容原理,使滤波器的寄生通带远离通频带,并设计了带哑铃型横杆的谐振器结构,在谐振器连接点形成电压驻波零点,从而进一步抑制滤波器的寄生通带,实现了具有宽阻带的带通腔体滤波器。最后,利用微波仿真软件CST设计了一款中心频率为2.45 GHz,相对带宽为4.08%的窄带带通腔体滤波器。仿真结果表明,滤波器带外抑制高,阻带范围宽,通带内驻波良好,满足设计指标要求。     

A novel UWB feeding mechanism for the TEM horn antenna, reflector IRA, and the Vivaldi antenna

This work proposes a method for feeding a balanced IRA with an unbalanced transmission line. This method is based on the current distribution on the surface of the antenna. The method of moments (MoM) simulations show that for the IRAs, there are some areas with low current density in comparison to the current density of the feeding points, almost over the entire frequency range. The coaxial cable is attached to the antenna's body all the way from the feeding point to an area of low current density, and extends out of the antenna structure at that point. This tremendously reduces the current density on the body of the coaxial cable. As a result, the current balance between two parts of the antenna is not disturbed. This method is applied to the TEM horn antenna, the reflector IRA, and the Vivaldi antenna. The TEM horn antenna was simulated using the HEMI software, and was fed by an unbalanced coaxial cable, both directly at the feeding point and using this method. This method was also applied to the reflector impulse-radiating antenna. Also, the Vivaldi antenna was fed both by considering the low-current density area and direct feeding. The E-plane far-field pattern of the new feeding method had good agreement with the result generated by the HEMI software for the balanced-fed antenna.     

Bridge-arm current reduction in DC-AC inverter

When building single-phase inverter with power Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), switching action may cause poor reverse recovery characteristic due to body parasitic diode of MOSFET, which can produce peak current in the circuit loop and the high transient voltage and current (dv/dt, di/dt) during the turning-on period. In this article, a novel method to reduce the bridge arm current spike in DC-AC inverter is proposed. The presented method uses the improved and simplified coupled inductor which is connected between the upper and lower power devices. The parasitic capacitors of MOSFET are charged and discharged by the coupled inductor and the energy is released in the new loop; therefore, the bridge peak current is diminished. The time-domain model of transient-state analyses is given in detail. The current spike of the main switch is clamped efficiently. By increasing switching frequency, the volume of the magnetic core can be further reduced which is resulted from reduction in the reverse recovery current in parasitic diode. Because of the suppression of the spike current via the device, the switch-on loss of the power loss is reduced, and low on-state resistor of the power device can be adopted to suppress the conduction loss. The proposed approaches are validated with experimental results.     

OTA-C Filters with Finite Zeros

In this paper we present a novel technique for OTA-C filter realizations with finite zeros based on doubly loaded passive ladder networks. Only grounded capacitors are needed; all floating capacitors are replaced with active simulations eliminating bottom-plate parasitic capacitors and non-observable poles. Bandpass, highpass and bandstop filters are easily obtained from a lowpass OTA-C prototype applying standard frequency transformations that preserve the active simulation of floating capacitors, i.e. the finite zeros realization. Also, we address the high frequency stability problem of highpass and bandstop OTA-C filters simulating doubly loaded passive ladder networks. These filters usually have floating nodes where the OTA excess-phase acting over the nodal parasitic capacitance can introduce unstable poles at high frequencies. The stability problem is fairly the same for highpass and bandstop OTA-C filters based on approximations with and without finite zeros; only the most complex case (filters with finite zeros) will be addressed here.     

Fast and Rigorous Analysis of EMC/EMI Phenomena on Electrically Large and Complex Cable-Loaded Structures

A fast and comprehensive time-domain method for analyzing electromagnetic compatibility (EMC) and electromagnetic interference (EMI) phenomena on complex structures that involve electrically large platforms (e.g., vehicle shells) along with cable-interconnected antennas, shielding enclosures, and printed circuit boards is proposed. To efficiently simulate field interactions with such structures, three different solvers are hybridized: (1) a time-domain integral-equation (TDIE)-based field solver that computes fields on the exterior structure comprising platforms, antennas, enclosures, boards, and cable shields (external fields); (2) a modified nodal-analysis (MNA)-based circuit solver that computes currents and voltages on lumped circuits approximating cable connectors/loads; and (3) a TDIE-based transmission line solver that computes transmission line voltages and currents at cable terminations (guided fields). These three solvers are rigorously interfaced at the cable connectors/loads and along the cable shields; the resulting coupled system of equations is solved simultaneously at each time step. Computation of the external and guided fields, which constitutes the computational bottleneck of this approach, is accelerated using fast Fourier transform-based algorithms. Further acceleration is achieved by parallelizing the computation of external fields. The resulting hybrid solver permits the analysis of electrically large and geometrically intricate structures loaded with coaxial cables. The accuracy, efficiency, and versatility of the proposed solver are demonstrated by analyzing several EMC/EMI problems including interference between a log-periodic monopole array trailing an aircraft's wing and a monopole antenna mounted on its fuselage, coupling into coaxial cables connecting shielded printed circuit boards located inside a cockpit, and coupling into coaxial cables from a cell phone antenna located inside a fuselage.     

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.     

一种复用传输射频和基带信号的新方法

介绍了一种在同轴电缆上,射频和基带信号复用传输的新方法。设计了射频信号和基带信号隔离电路,采用C-MBUS标准传输基带信号,在长为1 km、传输射频信号功率为40 d Bm的同轴电缆上,达到了4 800 b/s的数据传送速率,且同时可以为通信从机节点提供10 m A的电流。该方法具有硬件电路简单、成本低廉,容易组网的优点,适用于在射频线路上同时传输低数据速率的附加信息。     

Efficient Methods for Determining the Coupling to Wires in Circular Cavities

The electromagnetic field coupling to a loaded thin wire in a cylindrical/coaxial cavity is investigated. Computationally efficient methods are presented for determining the coupling to a thin wire located near a cavity wall in a system of cascaded and/or overlapping coaxial and circular cylindrical cavity sections, and the accuracy and limitations of these methods are established. The sections are coupled through apertures and conducting elements common to more than one section, which may have different axial and radial dimensions and which may be filled with material having different magnetic and electric properties. The loaded thin wire is close to the outer wall of a cavity section and may represent a cable or, perhaps, a conducting tube. The coupling of the cavity field to the wire is determined from an analysis of a distributed voltage and current source model based on transmission line theory as well as via coupled integral equations techniques. The accuracy of the results obtained from these analyses is supported by experimental data measured on a laboratory model of the cavity-wire structure.     

Radio frequency coupling between an antenna and two unshieldedparallel wires above a metal sheet-measurement precautions

An unshielded 1 m transmission line, made of two parallel wires suspended 0.1 m above a plane metal sheet, is illuminated in the VHF and UHF bands by a log-periodic dipole array (LPDA). A network analyzer is used to measure the voltage induced at one end of the line. The measured signal is compared to the predictions of a moment method numerical analysis, using the NEC code. The measured and predicted coupling are in reasonable agreement only once two measurement precautions are taken. First, the illuminating antenna has to be well-balanced to suppress common mode radiation from the coaxial cable connecting the transmitter to the antenna. Second, an output balun must be inserted between the unshielded transmission line and the coaxial cable to the network analyzer. This is needed to prevent common mode signals on the coaxial cable from contaminating the measurements. Besides these practical steps, it is also necessary to use physical insight and high frequency circuit theory to develop a good equivalent circuit of the output balun for use in the computational model     

Absorptive Lines as RFI Filters

A new class of ?distributed constant? filters has been recently developed using the normal propagation path of the electrical current in a wire, a cable, or a line to suppress interference. The three basic characteristics are the following: 1) Instead of using lumped reactive components (inductors, capacitors) connected to the wire, one superposes the suppressive effect to the normal straight and flexible conductor without any additional components. 2) The problem of mismatch at the interfaces with the generator and with the load (for example, a classical ? filter connected to a reactive load) is nonexistent, because the suppression is due to an absorption of the critical frequency components. The Q factor of such a line is substantially equal or less than unity in the frequency range considered. 3) In the case of nonsheathed cables (general case), if the suppression of the conducted interference is sufficiently high along the line (for example, a 20-dB attenuation is obtained for a linelength equal to a tenth of the wavelength at the considered frequency), radiation and induction of parasitic frequencies is automatically suppressed. The necessary absorption can be introduced on the cable or the line by using separately or together three different physical effects: 1) Absorption due to magnetic and dielectric losses. These losses are achieved by the use of special products, like magnetic ferrites with high Fe and Zn content, semiconductive and ferroelectric dielectrics, and with bulk or synthesized dispersive effects.