Analysis of higher order regular polygonal loop antennas

Higher order regular polygonal loop antennas are analyzed. The input impedance of higher order antennas varies gradually when the operating frequency or the order of polygon changes. This behavior of input impedance provides a wide range of input impedance and many resonant points to antenna designers. The higher order regular polygonal loop antenna generally possesses higher directivity but poorer broadband impedance property. As the operating frequency becomes higher its directivity increases remarkably and the broadband property becomes more prominent. To achieve the desired properties one may select one of the many design data sets with a trade-off between broadband property and directivity     

FDTD法计算高频单极天线特性

用时域有限差分法（Ｆｉｎｉｔｅ Ｄｉｆｆｅｒｅｎｃｅ Ｔｉｍｅ Ｄｏｍａｉｎ Ｍｅｔｈｏｄ）计算天线阻抗特性,可以使用不同的激励方式,文章比较了采用不同激励方式时,天线的输入阻抗。文中的主要内容是将表面阻抗法用于ＦＤＴＤ中,计算架设在介质平面上单极天线的辐射特性,并用ＦＤＴＤ法计算了介质平面上铺设不同尺寸的导体平面时,单极天线的输入阻抗随导体平面尺寸变化的特性。     

Moment method analysis of infinite stripline-fed tapered slotantenna arrays with a ground plane

A full-wave method of moments solution for infinite arrays of stripline-fed tapered slot antennas is described. The formulation of the problem is sufficiently general to permit performance evaluation of most of the geometries that have been proposed for stripline-fed antennas as well as of several other types of array antennas. Computed results for some well-known antenna arrays are presented to demonstrate the validity and accuracy of the method. Excellent agreement with published results has been obtained for scattering from corrugated surfaces and grounded dielectric slabs and for the input impedance of dipole and monopole arrays. Catastrophic effects such as scan blindness are accurately predicted. A sample result showing the measured and computed input impedance of a stripline-fed tapered slot antenna array is also presented     

利用FDTD方法比较手提电话天线的方向图,输入阻抗及人头部的比吸收率(SAR)(英文)

本文给出了利用FDTD电磁模拟方法对常用的五种个人通信手提电话的天线和人头部组织相互作用的比较研究。在研究中考虑的蜂窝通信手提电话常用的天线种类为单极子、偶极子和倒F型（IFA）天线。不均匀的实际人头模型被用于预测天线特性（包括输入阻抗，方向图和辐射效率等）和对操作作者耦合的电磁效应。天线在人头部的潜在危险影响是用1W辐射功率在人组织产生的比吸收率（SAR）来评估。     

A closed-form expression for the driving-point impedance of thesmall inverted L antenna

The conventional, small, monopole antenna is sometimes modified and bent into the shape of an inverted L. The inverted L antenna displays less capacitive reactance and higher radiation resistance than the monopole. Using a novel method, we derive a formula for the input impedance of the inverted L antenna. The technique involves extending the conventional Pocklington integral equation and the use of the antenna's effective length. The method can be adapted to other electrically small antennas     

基于IRA天线的辐射波模拟器天线辐射性能研究

将通常用于超宽带领域的IRA天线应用到辐射波电磁脉冲模拟器中,提出一种基于反射器脉冲辐射天线的核电磁脉冲辐射波模拟器,分析其天线结构,给出四种馈臂形式,通过仿真比较了四种馈臂形式天线的辐射效率、远场和近场波形以及频率增益特性。结果表明:该天线的低频辐射效率有待进一步提高;具有锥形渐缩形式馈臂的天线能产生较好的远场和近场波形。IRA天线相较笼形天线具有体积小、方向性好等优点,如果能进一步提高其低频辐射性能,IRA天线将成为理想的辐射波模拟器天线。     

A new class of electrically small antennas

This paper describes a new class of electrically small antennas, of which the principal advantages are the resistive input impedance, the radiation resistance transformation which may be obtained within the structure, and the variety of shapes which the antennas may take. The antennas incorporate resonant half-wave windings, and a simple transmission line theory is presented by which antenna efficiency and bandwidth may be calculated. Experimental methods and results are described for antennas in the order of 0.01 wavelength in height and 0.05 wavelength in diameter.     

Modeling of normal-mode helical antennas at 900 MHz and 1.8 GHz formobile communications handsets using the FDTD technique

A simple technique is proposed for modeling short normal-mode helical antennas using a commercial finite-difference time-domain (FDTD) code with a rectangular grid and a nominal extension of the wire. The approach allows affects on the input impedance and radiation performance of the helix to be examined and importantly does not require modification of the excitation subroutines. Normal-mode helical antennas for mobile communications use at 900 and 1800 MHz were designed using the proposed method and good agreement with measurements of impedance and near-magnetic field strength was found. The radiating performance of the helix was compared to that of a λ/4 monopole and generally found to be inferior at 900 MHz due to only 19.2 % efficiency in the presence of the head. At 1.8 GHz the two antenna types showed similar characteristics except in regard to bandwidth, 36.1 % for the monopole and 7.8 % for the helix, in the presence of the head. The modeled helix antennas produce spatial peak specific absorption rate (SAR) figures that are up to 27 % greater at 900 MHz and up to 49 % greater at 1.8 GHz than the corresponding monopole values due to the shorter antenna     

Three orthogonal polarisation DRA-monopole ensemble

A dual feed HE/sub 11/spl delta// mode dielectric resonator antenna (DRA) loaded monopole antenna ensemble is described. The two antennas were unaffected by co-location, having coupling less than -25 dB at 2.33 GHz, making the ensemble capable of radiating all three orthogonal linear polarisations. The dielectric resonator antenna had an input impedance bandwidth of 1.9%, while the monopole gave 56%. This small volume ensemble antenna is suitable for mobile communications terminals.     

Two-stage Parany monopole antenna with triangular complements

A new multiband and broadband antenna based on the traditional fractal equilateral Parany monopole is presented. In general, Parany and Sierpinski monopoles are resonant, log-periodic and multi-band antennas. For example, a traditional two-stage Parany monopole antenna provides three bandwidths. In this Letter, the input impedance behaviour of this antenna is improved by adding two conductor triangles to a traditional two-stage Parany monopole and eliminating two connections between the conductor triangles that shape such an antenna. For VSWR<3, the resultant fractal two-stage Parany monopole antenna with triangular complements shows bandwidth improvements compared to the traditional two-stage Parany monopole antenna. Good agreement between simulated and measured results was observed.     

Analysis and size reduction of various printed monopoles withdifferent shapes

A simple analysis based on the transmission line model applied to printed dipole antennas, and the Babinet principle allows different shapes of printed monopole antennas to be easily optimised. A shortening ratio (ρ) of 48% (respectively 30%, 40%) is achieved for the monopole antenna by using a step change in line width (respectively a triangular monopole, and a line with a triangular cap). Theoretical input impedance of these various monopoles compare closely with experimental results     

Impedance characteristics of planar bow-tie-like monopole antennas

The impedance characteristics of planar bow-tie-like monopole antennas have been studied experimentally. The planar bow-tie-like monopole antenna achieves a broad bandwidth, typically of >75%. A modified formula is suggested to accurately evaluate the frequency corresponding to the lower edge of the impedance bandwidth     

模式匹配法分析有限圆盘地面单极天线

本文给出了一种严格分析有限尺寸圆盘地面单极天线的新方法———模式匹配法 .该方法通过在天线上、下两边平行放置两个无限大良导电平面 ,以及合理划分区域 ,使得每个分区中的场分量能够采用柱谐展开式解析表示 ,且展开系数由导体表面边界条件及分区交界处场分量连续条件加以确定 .在此基础上 ,进一步分析天线的输入阻抗等电性能 .计算结果表明 :对不同尺寸圆盘地面单极子天线 ,理论分析与文献中的实验结果均十分吻合 .同时 ,由于场量的解析表示 ,使得计算速度较快     

Wide-band sleeve-cage and sleeve-helical antennas

A sleeve-cage monopole has parasitic wire elements that form a sleeve around the driven cage antenna. Appropriate placement and dimensions of the wire parasites lead to bandwidth enhancement. Genetic algorithms and an integral equation solver are employed to determine the position and lengths of the parasitic wires in order to minimize voltage standing wave ratio (VSWR) over a band. The cage is replaced by a normal-mode quadrifilar helix for height reduction and the resulting structure is referred to as a sleeve helix. Measured VSWR and input impedance data are in good agreement with computed data. A fabricated sleeve-cage monopole has a bandwidth ratio of 4.4:1 and a sleeve helix has a bandwidth ratio of 3.5:1 for measured VSWR less than 3.5.     

平板宽带单极与偶极天线的全波分析

采用时域有限差分法（FDTD）计算圆盘天线及宽带变形vivaldi天线的输入阻抗及方向图。利用镜像原理得到三角形单极、圆盘单极天线的输入阻抗。采取激励源区的准静态模型在保证精度的同时又无须将复杂的具体馈电结构建模，三角形单极天线和圆盘单极天线的计算结果与有关文献的比较验证了该方法具有准确、实用性强等优点，对宽带变形vivaldi天线FDTD分析得到电流分布及输入阻抗，经傅立叶变换由近场值得到天线远场方向图，结果表明变形vivaldi天线具有输入阻抗和方向图的宽带特性。     

Antenna Evaluation by Normalized Analogical Technique

The impedance of a vertical antenna (monopole) normalized to 189 ?, or its reciprocal, is equal to that of three different antennas in half space. This equality derived by the formulation of a common effective height, and therefrom a common Q, offers a technique for antenna evaluation in electromagnetic compatability (EMC).     

标签天线弯曲对射频识别系统性能影响的研究

探讨了工作在微波段的无源射频识别(Radio frequencyIdentification, RFID)系统中标签天线的弧形弯曲对RFID系统性能的影响。分析比较了几种典型的半波振子标签线天线弧形弯曲的情况。通过理论分析确立标签天线的方向系数与输入阻抗为RFID系统性能的主要影响因子。弯曲振子天线特性参数由线天线分析软件NEC WinBasic数值模拟得到。分析结果表明,标签天线的弧形弯曲使得无源RFID系统的工作距离明显变短。因此,为避免此类问题有必要在RFID系统中考虑对于弯曲具有低敏感性的天线结构。     

Superconducting microstrip antennas: an experimental comparison oftwo feeding methods

The recent discovery of high-temperature superconductors (HTSs) has generated a substantial amount of interest in microstrip antenna applications. However, the high permittivity of substrates compatible with HTS causes difficulty in feeding such antennas because of the high patch edge impedance. Two methods for feeding HTS microstrip antennas at K- and Ka-band are examined. Superconducting microstrip antennas that are directly coupled and gas-coupled to a microstrip transmission line have been designed and fabricated on lanthanum aluminate substrates using Y-Ba-Cu-O superconducting thin films. Measurements from these antennas, including input impedance, bandwidth, efficiency, and patterns, are presented and compared with published models. The measured results demonstrate that usable antennas can be constructed using either of these architectures, although the antennas suffer from narrow bandwidths. In each case, the HTS antenna shows a substantial improvement over an identical antenna made with normal metals     

Calculated and experimental response of thin cylindrical antennas to pulse excitation

We have computed the response of a thin, cylindrical monopole antenna to dc pulse excitation, both in transmission and reception, by use of Fourier transforms and the complex impedance and complex effective height, for pulses of space length ranging from two tenths to twice the monopole length. We have also experimentally determined the reponse and have obtained similar results. We conclude from this comparison that present steady-state antenna theory together with Fourier methods will yield reliable results in calculating the response of cylindrical antennas to dc pulses. We have also made certain other measurements of response to pulses and step functions which are reported herein.     

Impedance of a monopole antenna over a ground plane and immersed in a magnetoplasma

A treatment of the input impedance of a monopole antenna over a ground plane covered with a magnetoplasma with any arbitrary direction of the static magnetic field is presented. The analysis is restricted to a cold plasma with uniaxial and quasi-static approximations. It has been found that for parallel and perpendicular directions of the static magnetic field with respect to the ground plane perfect mirror reflections can be obtained. For other directions of the static magnetic field, the reflection is birefringent so that the monopole impedance becomes modified over a dipole impedance. These modifications can be significant under hyperbolic plasma conditions. A short and a long monopole were considered. From laboratory measurements of a long monopole impedance, the resonance cone and the resonances corresponding to the antenna length have been observed.