电小线圈近场分析

天线的近场分析在近场通信(NFC)、电磁兼容(EMC)、阵列天线设计等领域越来越受到关注。准确高效的近场分析方法对于近场的分布控制和引导机制等有着重要的作用。本文针对典型天线磁偶极子(电小线圈)的近场进行了初步的理论研究,主要分析了磁偶极子的近场平均能量密度分布、有功功率和无功功率的关系和分布。并通过磁偶极子的场分量计算平均坡印廷矢量,从而定性分析了线圈"储能"和"辐射能量"的关系,同时根据平均坡印廷矢量给出了电小线圈的近场"储能"中能量流动的物理图像。本文还计算了磁偶极子的平均电场能量密度和平均磁场能量密度,并进一步分析了二者的分布以及比较了二者的大小关系。     

GTD分析阵列天线在复杂电磁环境下的近场受扰

给出了应用几何绕射理论(GTD)分析计算机载电大尺寸阵列天线方向图的一种方法,比较好地解决了在复杂电磁环境下,大型阵列天线近场受扰分析的问题.该方法将阵列天线的每个阵元看成电偶极子,由于电偶极子尺寸很小,因而可以认为阵列的近场区仍然是单个电偶极子的远场区.根据这样的远场近似,可以利用几何绕射理论用解析方法计算每个电偶极子受到遮挡影响的场分布.通过独立地对阵列天线的每个阵元单独寻迹计算,并且将所有阵元的场进行叠加,就可以得到整个阵列天线受到处于近场的障碍物遮挡影响的场分布.应用此方法计算了一个阵列天线受到近场遮挡之后的方向图,并与应用HFSS仿真软件计算的结果进行了比较.计算结果表明,这一方法可以很好地应用于复杂电磁环境中大型阵列天线的近场受扰问题分析.     

智能终端设备低成本NFC天线设计方法

近场通信(Near Field Communication,NFC)系统通信频率为13.56 MHz,采用近场磁耦合方式进行信号传输,具有通信距离近、安全度高等特点,广泛应用在银联、公交、门禁等领域。随着NFC技术的发展,越来越多的智能终端设备中配备了NFC系统。由于NFC系统工作频率低,NFC天线面积较大,天线尺寸通常为30 mm×40 mm,而且配置磁性基板用于金属环境使用,这使NFC天线制造成本较高,不利于NFC系统应用。本文通过空间磁场分布理论计算,采用分布式磁性基板设计,大幅降低磁性基板使用面积,并通过NFC天线结构设计,提高天线磁场辐射性能。仿真与实验证明,该设计方法使NFC天线磁性基板使用面积下降约40%,且天线辐射能力增强。在提升天线性能的同时,有效降低天线成本。     

基于旋转永磁体的低频通信技术研究

旋转永磁体天线作为一种新型低频磁天线,克服了传统低频线圈体积大、功耗高、效率低的缺点,主要应用于近场低频磁通信中。该文利用FEKO分析了天线近区磁场随方向的变化规律,探究了近场范围内无限大地面对天线近区磁场分布的影响,结果表明:天线在其径向辐射强度最大,在其轴向辐射强度最小。并且在较近的通信距离范围内,地面对磁场信号的影响较小。分析了转动惯量和磁矩之间的关系,对永磁体结构参数进行了优化,研制了两款样机,并对优化前后的旋转永磁体天线功耗进行测试,实验结果表明:在质量大30 g的情况下,优化后的永磁体天线比优化前的天线平均功耗低5.5 W左右。利用直接天线调制方式磁场的2FSK调制,通过非相干解调恢复码元信息,测试结果表明:复杂电磁环境下,优化后的永磁体天线可以在20 m范围内实现码元速率为3.5 bps的超低频通信。     

单脉冲寻向天线和目标的一体化仿真及测角误差分析

本文通过矩量法及其高效数值方法（MLFMA）对近距离目标--单脉冲收发天线的电磁互作用进行一体化数值仿真,定量研究了单脉冲天线的近场角度测量特性.在该近场模型中,目标散射近场的幅、相分布和同轴探针激励的喇叭单脉冲天线的辐射场（对应远场和波束）、接收端响应（对应远场差波束）均采用全波数值模拟获得.首先,计算单脉冲天线的辐射场并将其作为对目标照射的激励条件;接着,计算目标散射近场的空间分布;并计算出单脉冲天线所接收到的目标散射场;最后,使用幅值法和相位法计算出单脉冲天线近场测角角度,并在此基础上对近距离测角误差进行研究.在导弹目标算例中,将天线--目标一体化建模和天线口径面上散射近场的幅、相分布计算结果用于近距离条件下单脉冲天线测角误差的研究,并通过频率、距离的变化对测角精度做了对比分析;发现目标近场散射幅、相分布的非均匀性,是导致单脉冲天线近距离角度测量产生较显著的测角误差的主要原因;而频率较低时,测角误差较小.文中给出了物理解释,并提出近距离测向时借助于较低频信号的校正以降低测角误差的建议.     

一种确定磁环天线最佳接收效益线圈参数的方法

研究了用于雷电测向的正交磁环天线(OMLA)的低频电磁脉冲接收特性,提出了一种确定磁环天线接收效益达到最佳时线圈参数的方法.实验通过测量不同参数磁环天线对低频电磁脉冲信号激励下接收到的感应电动势,分析了影响正交磁环天线接收特性的参数,包括线圈尺寸、匝数等.引入频率比例系数η、集肤效应损耗系数Kj和邻近效应系数Kx,理论...     

超低频机械天线通信模型及信号接收线圈研究

机械天线作为超低频通信技术,是当今国际瞩目的一个新兴研究领域,在远距离通信、水下通信等方面具有广泛的应用前景.为实现小型化和低功耗的超低频机械天线,提出旋转偶极子式机械天线结构和通信模型.针对提出的通信拓扑结构及通信信号辐射强度,研制三轴正交线圈作为信号接收单元.提出基于线圈热噪声电压与感应电压比值的灵敏度归一化表征方法.并对研制线圈的灵敏度及工况进行实验.实验结果表明:灵敏度理论模型可用于高灵敏度线圈设计,研制的空芯线圈可用于机械天线信号接收;铁制品的存在对线圈接收性能有影响.该实验研究为超低频机械天线接收线圈的优化设计提供理论参考.     

口径/谱域积分-表面积分法的研究

 通过分析口径积分、平面波谱理论关于天线近场计算的特点,获得一种混合的天线近场计算方法.结合表面积分技术,提出了口径/谱域积分-表面积分法,用于三维天线-罩系统电性能数值仿真.该方法吸取了口径积分和平面波谱理论的优点,对于天线近场的分析更为精确、实用.以弹载天线罩为仿真实例,结果表明,与口径积分-表面积分法和平面波谱-表面积分法相比,口径/谱域积分-表面积分法的计算结果与实验结果更为吻合,证明了该算法具有更高的精确度.     

终端近场通信天线研究北大核心CSCD

近场通信(NFC)已成为无线终端的标配功能,工作范围小、抗干扰性和安全性较高的特性使其被广泛应用于终端的移动支付和虚拟卡片等领域。由于近场天线产生的感应磁场会在临近的金属上耦合出反向涡流,并且金属屏蔽物覆盖会降低收发天线间的磁场耦合,紧凑终端中的电池、主板、外壳等金属元件将大幅影响NFC天线性能。本文从近场通信的历史、标准、系统结构出发,以终端NFC天线工作环境中的金属覆盖情况作为分类依据,对终端近场通信天线的研究进展进行了简要介绍。     

天线近场计算的卷积积分法

本文提出了一种天线近场计算的新方法，文中详细叙述了用于近场快速计算的卷积积分法，并用该方法得到了偏馈反射面天线的近场分布。文中还将该方法的计算结果与物理光学法的计算结果进行了对比，从而验证了该方法的准确性和有效性。     

Two efficient algorithms for the analyses of a nonlinearly loadedantenna and antenna array in the frequency domain

In this paper, two efficient algorithms for the steady-state scattering responses of a nonlinearly loaded antenna and antenna array in the frequency domain are studied. One is the reflection algorithm (RA), and the other is the inexact Newton approach (INA). The analysis is equivalent to a nonlinear circuit problem with the circuit parameters of antenna element obtained by the moment method. This equivalent nonlinear circuit is then solved using the RA or the INA. In general, the RA is suitable to strongly nonlinearly circuit element. While the INA is suitable for multifrequency excitation. In dealing with the nonlinearly loaded antenna array, the infinite periodic structure Green's function, including the array mutual coupling effects, is applied to simplify the analysis. Both of the two algorithms are easy to be combined with the periodic Green's function to deal with the large nonlinearly loaded antenna array problem     

A study on stray capacitance modeling of inductors by using thefinite element method

Stray capacitance modeling of an inductor is essential for its RF equivalent circuit modeling and inductor design. Stray capacitance determines an inductor's performance and upper frequency limit. A method has been proposed for modeling the distributed stray capacitance of inductors by the finite element method and a node-to-node lumped capacitance network. The effects of wire insulation layer, ferrite core, number of segments used to model the circumference of a wire cross section, pitch and coil-to-core distances, and the capacitance between nonadjacent turns, etc., an an inductors' self-capacitance and calculation accuracy, have all been considered. The calculated equivalent lumped stray capacitance for a rod inductor with a ferrite core is compared to that estimated from measurement. Good agreement between them has been observed     

光纤传输式瞬态脉冲电场传感器分析与设计

为实现瞬态脉冲电磁场的时域测试,研制了一种基于场效应管加载的光纤传输式电场传感器。根据电场传感器的等效电路模型及其实尺仿真模型,分析了接收天线的负载阻抗及其长度等参数变化对传感器测试性能的影响,为传感器设计中的参数选择提供了参考。在此基础上,利用自行研制的电场传感器分别对核电磁脉冲场和雷电电磁脉冲场进行了实测,结果表明:传感器的高、低频响应能力均较好,基本可以满足测试瞬态电磁脉冲场的需要,验证了传感器设计的可行性。     

基于左手材料的矩形环分形微带天线研究

通过将矩形环分形天线嵌入到左手材料中,形成一种基于左手材料的矩形环分形微带天线。采用有限元法对该复合天线进行分析和仿真,发现基于左手材料的矩形环分形微带天线在各频段增益明显增大,同时具有较低的回波损耗和电压驻波比,实现了较好的匹配性,且有效地改善了天线的性能。由此可以看出基于左手材料的矩形环分形微带天线在移动通信、卫星通信以及航空航天等领域具有潜在的应用价值。     

频率选择表面的等效电路设计方法综述

本文回顾了频率选择表面(FSS)等效电路的理论发展,分析了将其应用于提高FSS设计效率的必要条件,重点介绍了利用具有准集总电感和准集总电容效应的元件,依据等效电路设计实现一系列高性能带通、带阻、单频和多频FSS 的方法。理论和实测结果表明:这类FSS普遍具有极小的尺寸,良好的入射角和极化稳定性,而且谐振频率、带宽和极化特性独立可控;同时,单元结构参数和等效电路参数之间的解析关系式为FSS的快速优化提供了条件,从而为FSS 设计提供了从构建到优化的高效解决途径。     

Distributed semiconductor R-C network analysis for various electrode configurations

The impedance of a semiconducting sheet of arbitrary boundary overlaid by a gate capacitance is analyzed as a function of frequency; the contacts are the gate contact and an ohmic contact at the sheet boundary. General asymptotic expressions for low and high frequency capacitance and for high frequency resistance are given. The low frequency equivalent series resistance is characterized by a form factor which depends on the configuration of the contact and can be determined experimentally from the frequencies at which equivalent circuit parameters extrapolated from the low and high frequency regimes intersect. The theoretical solution for the impedance pertaining to a rectangular boundary is given. The dependence of the impedance on the external a.c. circuit termination to a second gate contact is discussed for the case that the semiconducting sheet is bounded by distributed gate capacitances at both sides.     

非谐振多层级联频率选择表面研究

为了减少工作在L波段的机载天线对高于其工作频率范围来波的散射,设计了一种非谐振单元组成的多层级联结构阵列.它是在十字网栅电感层基础上,通过螺旋曲折线的形式有效延长电流路径,加大电感层的感性效应,这种折线螺旋能够控制单元尺寸,还能抑制高阶模和栅瓣的出现.采用修改电容层金属图案的方法,将贴片单元变为谐振型的方环单元,并将这种带阻型方环单元的传输极点置于阵列干涉点处,可以有效抑制由阵列干涉造成的窄传输峰,从而减少高频电磁波散射的影响,达到减小电磁散射对飞机雷达散射截面的影响,从而实现表面频率选择.采用高频电磁场仿真软件对上述设计的物理模型和等效电路模型进行了仿真,并对结构尺寸进行了优化设计.通过实验对设计样品进行了测试和分析,结果表明上述设计能够达到频率选择的目的.     

Performance analysis of an open-loop resonator loaded terahertz microstrip antenna

In this paper, an enhanced electrical performance of the open-loop loaded microstrip patch antenna at terahertz frequency has been investigated. The proposed antenna is designed to radiate at frequencies in the range of 0.5-0.7 THz with high gain and radiation efficiency. The effect of various substrate parameters on the electrical performance of the proposed antenna has been analyzed and simulated. The simulation has been performed using the CST Microwave studio, a commercial simulator based on finite integral technique. The directivity and radiation efficiency of the proposed antenna is 22.58 dBi and 94.50%, respectively, at 600 GHz. Further, the simulated results have been compared with Ansoft HFSS, a commercially available simulator based on the finite element method. We have also compared this proposed analytical result with reported literature with scale down approach.     

An efficient PEEC algorithm for modeling of LTCC RF circuits with finite metal strip thickness

In this letter, a simple but effective method is introduced to facilitate the partial element equivalent circuit (PEEC) algorithm to model multilayered low-temperature co-fired ceramics (LTCC) embedded RF circuits with finite metal thickness. The method makes use of the quasistatic assumption that charges only reside on the surfaces of a conductor. In the calculation of the coefficient of potential matrix, one thick conductor plate is treated as two inter-connected zero-thickness plates. Recombining the two plates analytically can correctly account for the increase of plate-to-plate capacitance without adding extra elements to the resultant equivalent circuit model. Experimental results have verified the validation of the proposed method.     

A fully compensated active pull-down ECL circuit withself-adjusting driving capability

A new active pull-down emitter-coupled logic (ECL) circuit having full compensation against fluctuations in supply voltage and temperature is proposed. This circuit needs no capacitors but a feed-back circuit to adjust its pull-down capability to its load capacitance. The speed performance is compared between the active pull-down ECL circuit and the conventional ECL circuit using 0.8 μm SPICE parameters. The active pull-down ECL circuit is twice as fast as the conventional ECL circuit under the load capacitance of 0.8 pF with the same power dissipation. The relation between the power dissipation and the operating frequency is compared among the CMOS, the conventional ECL, and the active pull-down ECL circuits. The comparison adapts a new method in which the circuit parameters are optimized at each operating frequency. The SPICE simulation using this new method shows the conventional ECL circuit has a lower power dissipation than the CMOS circuit, even in the low operating frequency region of 100 MHz. The new active pull-down ECL circuit has the lowest power dissipation among the three circuits. The power dissipation of this circuit shows 47% lower than the CMOS circuit and 29% lower than the conventional ECL circuit at the operating frequency of 600 MHz and the load capacitance of 0.8 pF