Near-Field Loop Antenna for the UHF RFID Reader

A loop antenna for near field readers is proposed. Through periodic interdigital capacitors, the phase of the current on the loop is compensated and kept in phase. Hence, a loop with a perimeter of one wavelength at 900 MHz achieves a uniform near magnetic field distribution inside the loop. A novel method is proposed to evaluate the performance of the coplanar waveguide （CPW） to coplanar stripline （CPS） transition, which is used as a balun for the feeding network in this paper. This loop antenna has a 70 MHz operating bandwidth and 12 cm maximum reading range when the output power is 24 dBm, which is suitable for most near field radio frequency identification （RFID） applications.

IMPEDANCE THEORY AND BANDWIDTH OPTIMIZATION OF THE TWIN-LOOP ANTENNA

The Twin-Loop Antenna(TLA)has been widely used because of itsbroadband property and simply feeding,and some modified structures have been devel-oped from its prototype by Chinese engineers.But the exact design theory for TLA accord-ing to the impedance calculation has not yet been published.In this paper,the impedanceof loop in a TLA is analysed and computed by using the method of moments,and the de-sign formulae and a two-step optimization program for extending the bandwidth of inputimpedance of TLA are detailed.An example of optimized design shows that the bandwidthcan be increased up to 36.4% for VSWR≤1.10,which is wider than the bandwidth of ra-diation pattern.

Electromagnetic Field Due to a Loop Antenna Buried in a Medium with Complex Boundaries

The radiation of a loop antenna embedded in a dissipative medium with complex boundaries isanalyzed by a perturbation method and an efficient fast multiple-integration technique. But theperturbation method can not be used directly because there is a finite-length metal cylinder in the vicinityof the loop antenna. The prolate ellipsoid equivalence of the metal cylinder is made, then the cylinder maybe removed and the perturbation method is valid. Numerical results indicate that the approach is accurateat low frequencies and stable.

Closed-loop transmit diversity systems with hybrid antenna selection

The paper investigates closed-loop transmit diversity （CLTD） systems with antenna selection technique. The expected received signal-noise-ratio （RxSNR） of the proposed systems is analyzed and compared with CLTD systems. An algorithm is proposed for determining the number of increased transmit antennas in terms of a reduced RF chains without performance degradation. Since a feedback channel is bandwidth-limited, we present a method of quantizing transmit-weight vectors. Simulation results demonstrate advantage of the proposed systems with full and quantized feedback information. Quantized feedback has less effect on the proposed systems than CLTD systems.

Bi-BASED HIGH T_c SUPERCONDUCTING LOOP ANTENNA

INTRODUCTIONIn order to improve the efficiency of the electrically small antenna, which has the physical extension smaller than the maximum free space wavelength transmitted or received, superconducting materials began to be utilized in fabricating antennas since 1960s. In 1988, the Birmingham group of UK made for the first time the small dipole antennas

Triple Notched Band Characteristics UWB Antenna Using C-Shaped Slots and Slot-Type Capacitively-Loaded Loop (CLL)

Ultra wide bands antennas with notched bands characteristics have recently been considered for efficient communication between devices. In this paper, a compact ultra-wideband antenna (UWB) for UWB applications with triple bandnotched characteristics is presented. The proposed antenna consists of a square patch with four truncated corners and a partial ground plane with a rectangular slit. The operation bandwidth of the designed antenna is from 2.66 GHz to more than 13.5 GHz. Band-notched characteristics of antenna to reject the frequency band of 3.18 - 3.59 GHz and 4.70 - 5.88 GHz, is realized by inserting two C-shaped slots in the patch, the third band of 9.54 - 12.22 GHz is achieved by slottype capacitively-loaded loop (CLL) inserted in the patch near the feed line. Details of the proposed antenna design and simulated results are presented and discussed.

井下NFC天线的研究及仿真分析

为实现井下复杂环境中的近场通信,首先用三维有限元电磁仿真软件对铁氧体天线结构进行建模仿真,结果表明:线圈半径、导线半径、天线间距对天线正向传输系数的影响较大,铁氧体相对磁导率的影响较小。其次,为探究井下环境对天线传输性能的影响,用阻抗匹配工具对天线进行阻抗匹配,并建立带钻井液介质的金属钻具模型,结果表明:井下金属环境导致正向传输系数衰减3.3dB;钻井液电导率从0S/m增加到2S/m后,正向传输系数衰减8.2dB。将天线仿真模型与相同参数的实物模型进行对比,结果表明基本模型正向传输系数误差小于0.3dB,扩展模型正向传输系数误差小于5.5dB,仿真结果与实物测试结果具有一致性,可指导井下NFC天线设计。

一种用于局部放电检测的超宽带环形-单极子天线

为提高电气设备局部放电检测准确度和灵敏度,提出一种超宽带环形-单极子天线。该天线主要由环形天线、类三角形单极子、金属枝节和金属地板构成。其中,类三角形单极子嵌入在环形天线内部,并通过金属枝节与环形天线连接,从而引入电磁耦合和产生新的谐振模式,改善天线阻抗匹配,扩展天线工作带宽,实现超宽带阻抗匹配和辐射特性。研究结果表明,天线在0.29~3.10 GHz频段的仿真反射系数低于-10 dB,最大仿真增益为8.8 dBi,在超宽频段内实现了良好的阻抗匹配和辐射特性。测试结果和仿真结果吻合良好,天线在0.29~3.16 GHz频段的测试反射系数低于-10 dB,最大测试增益达到9.3 dBi,适用于电气设备局部放电检测。

索驱动环形网状天线展开过程动力学分析及轨迹规划

【目的】为准确减小环形网状天线展开过程中所受冲击并降低能耗,提出一种基于动力学分析的天线展开过程规划策略。【方法】首先,采用Bezier函数拟合驱动索的收纳过程,获得驱动索的输入轨迹;其次,采用Lagrange法、Bushing力法、等效作用力法建立具有绳索—滑轮的天线系统动力学模型,并通过仿真分析驱动索柔性、索网力对天线展开过程的影响;最后,采用神经网络模型构建天线系统的动力学代理模型,并基于多岛遗传算法优化获得驱动索的最优输入轨迹。【结果】优化结果表明,基于动力学分析的天线展开过程规划策略,能够在保证代理模型精度的条件下有效地降低天线展开角加速度峰值和功率峰值。【结论】提出的基于动力学分析的天线展开过程规划策略,进一步提高了天线的展开可靠性,具有一定的工程借鉴意义。

基于电流探头法的环天线校准系统研究

为解决电磁兼容检测领域环天线溯源的问题,根据电流探头法的校准原理,利用数字电磁学代码(NEC)建模分析了环天线校准系统的关键影响因素,推导了校准系统的天线系数计算公式。在3米法半电波暗室建立了基于电流探头法的环天线校准系统,并校准了辐射骚扰试验常用的两款环天线,校准结果与标称值最大误差为0.56 dB,且在天线系数的最大允差范围内,验证了环天线校准系统的可信性和精确性。为表征校准结果的区间半宽度,根据推导的天线系数计算公式,阐述了标准不确定度分量的评定过程,校准系统的扩展不确定度为1.3 dB(k=2)。

Two Types of Compact UHF Antennas for Partial Discharge Measurement

To investigate the partial discharge (PD) online monitoring of transformers by ultra-high-frequency (UHF) approaches,high-qualified UHF antennas are focused on as one key technique. The size of UHF sensor used for PD UHF online monitoring in transformer is excessively large,therefore,it is not convenient for internal installation of transformer. Two types of compact UHF antennas with small sizes,a Hilbert fractal antenna and a small loop antenna are presented. PD experiments of three typically artificial insulation defects are executed and both antennas are used for PD measurement. The spectra of power via frequency of detected PD signals are analyzed and compared. The experimental results show that the Hilbert fractal antenna and small loop antenna are qualified for PD online UHF monitoring.

A Low Profile Four-Way Directional Antenna with Dual Polarization

This paper presents a low profile dual polarized directional antenna composed of loop and dipole arrays mounted on a ground plane with each loops and dipoles being fed independently. Each loop antenna is paired with a reflector while each dipole antenna is paired with a director and a reflector. The proposed antenna is intended for an indoor base station (BS) with resonance frequency of 2.4 GHz and capable of producing four orthogonal directional pattern with downward elevation angle equals to 30°;and half power bandwidth (HPBW) less than 80°;in both vertical and horizontal polarization. The reflection characteristics of the loop and dipole arrays are less than -10 dB and the mutual coupling between the vertical and horizontal polarization elements is nearly less than -20 dB. In later progress, the dipole antenna was substituted with printed dipole antenna to achieve a better performance. Both the calculated and measured results demonstrated that the desired radiation patterns were achieved, and the measured results agreed well with the calculated ones. Consequently, a low profile antenna with a thickness of 0.16 λ (20 mm) having the expected radiation pattern is successfully designed.

Interference Management for DS-CDMA Systems through Closed-Loop Power Control, Base Station Assignment, and Beamforming

In this paper, we propose a smart step closed-loop power control (SSPC) algorithm and a base station assignment method based on minimizing the transmitter power (BSA-MTP) technique in a direct sequence-code division multiple access (DS-CDMA) receiver with frequency-selective Rayleigh fading. This receiver consists of three stages. In the first stage, with constrained least mean squared (CLMS) algorithm, the desired users’ signal in an arbitrary path is passed and the inter-path interference (IPI) is reduced in other paths in each RAKE finger. Also in this stage, the multiple access interference (MAI) from other users is reduced. Thus, the matched filter (MF) can use for more reduction of the IPI and MAI in each RAKE finger in the second stage. Also in the third stage, the output signals from the matched filters are combined according to the conventional maximal ratio combining (MRC) principle and then are fed into the decision circuit of the desired user. The simulation results indicate that the SSPC algorithm and the BSA-MTP technique can significantly reduce the network bit error rate (BER) compared to the other methods. Also, we observe that significant savings in total transmit power (TTP) are possible with our methods.

相控阵测控技术(二):相控阵连续闭环角跟踪的系统误差

在对机扫天线相位和差单脉冲角跟踪精度分析的基础上,针对相控阵具有相位敏感度高、电扫伴随着增益和相移变化以及多通道合成、多方向标校等特点,分析了相控阵相位和差单脉冲角跟踪系统的跟踪精度,讨论了它的误差源及其产生的物理机理,推导出了相应的系统误差表达式,并提出了减小误差的相应措施。

相控阵测控技术(三):相控阵连续闭环角跟踪的随机误差

针对相控阵角跟踪的特点,分析了相控阵中不同于机扫天线跟踪的特殊误差,包括测角子阵合成信噪比、相控阵扫描特性、电轴与指向轴不重合、基线长度、量化误差、多径干扰、阵风等误差源对相控阵相位和差单脉冲角跟踪随机误差的影响,给出了它们的数学表达式,并对相控阵相位和差单脉冲与幅度和差单脉冲角跟踪的热噪声误差进行了比较。

仿真设备对引进空空导弹仿真系统设计的影响

半实物仿真系统仿真设备的指标优劣决定着引进空空导弹半实物仿真系统设计的成败。根据飞行转台和天线阵列设备的建设指标,建立了相应设备的角度误差模型和频率响应模型,结合引进空空导弹的导引头测角能力和制导控制系统数学模型,详细分析了设备的角度误差和频域特性对引进空空导弹半实物仿真系统设计的影响。仿真结果表明,飞行转台和天线阵列设备所提建设技术指标合理,能够适应和满足引进空空导弹半实物仿真系统建设需要。

一种自动调谐高频车载电小环天线设计

针对短波通信天线难以在一套设备上实现宽频段工作且不便运输的问题,文中提出了一种适用于近垂直入射天波技术高频通信的自动调谐电小环天线。该天线安装在车辆顶部,主体由耦合环、辐射环及自动调谐控制单元等部分构成,引入两种不同调谐方法,并对两种匹配网络进行集成与自动控制,具有物理结构简单、携带方便且辐射效率较高等优点。仿真和测试结果表明,该环天线在3~30 MHz整个高频频段驻波比小于2,中心频率在25 MHz处的最大增益可达2.7 dBi,最大辐射方向为垂直方向,满足高频近垂直入射天波通信需求,是短波通信系统的重要组成部分。

一种测试用环形天线研究

探讨EN 303417 Wireless power transmission systems,using technologies other than radio frequency beam in the(19~21)kHz,(59~61)kHz,(79~90)kHz,(100~300)kHz,(6765~6795)kHz ranges[1]中无线充电设备阻塞测试的环线天线要求,并根据实验室检测实践经验,设计一款满足标准需求且可以提升检测准确性、重复性、效率的环线天线。经实际应用和数据分析,该环形天线性能与理论预期相近,满足设计目的。

低频强磁场屏蔽效能的测试方法与测试设备研制

为了合理评估屏蔽体对低频强磁场的屏蔽效果,为工程中屏蔽室质量验收提供必要的检测手段,根据小环天线法测量电磁屏蔽室屏蔽效能的原理,提出了低频强磁场屏蔽效能测试系统的整体结构和设计方案,研制了以PIC16F73单片机为核心的低频大电流源,设计和制作了磁场发射、接收环天线,构建了低频强磁场屏蔽效能测试设备;采用研制的测试设备对屏蔽室进行了屏蔽效能实测。测试结果与理论值符合较好,表明测试设备能够满足实际测量的需要,同时验证了计算结果的可信性。

TEM室法环天线校准系统建立及测量结果不确定度评定

横电磁波室法是9 kHz~30 MHz频段环天线校准中广泛采用的一种方法。环天线分为有源环天线和无源环天线两类,这两种天线的磁场天线系数在量值范围上差别大,对系统动态范围要求不同。根据这一特点,对两类环天线分别建立横电磁波室作为标准场的环天线校准系统,基于网络分析仪开展扫频测量。针对电磁兼容领域中常用的直径60 cm以下有源和无源环天线分别开展校准方法研究,给出磁场天线系数测量结果和测量结果的不确定度评定。该环天线校准系统可以扫频完成常用环天线在9 kHz~30 MHz频段内的校准,解决大动态范围问题,环天线校准效率也得到提高。