双臂圆锥对数螺旋天线的研究

本文利用曲线段三角基展开,伽略金法检验的矩量法对一种非频变天线－双臂圆锥对数螺旋天线进行了分析,通过曲线段拟合线结构以及利用阻抗矩阵的中心对称笥减少计算量。使得计数精度,速度大为提高。本文的方法和程序也适用于平面螺旋和圆柱螺旋天线的设计和计算。文中同时给出大量曲线数据,并将计算结果与文献和实验进行对比,吻合良好。     

计算曲线天线电流分布的一种新途径─参数形式下的B样条有限元法──Ⅱ：应用实例─多臂螺旋天线的电流分布

多臂螺旋天线由于其宽频和多模特征，它在空中和地面天线系统中得到了广泛的应用。本文详细描述了基于第一部分提出的参数形式下的Ｂ样条有限元法计算等角螺旋天线和阿基米德平面螺旋天线电流分布的实施过程。通过与有关文献比较，计算实践表明本文方法具有实施简便、计算量少等优点。     

Electromagnetic characteristics of superquadric wire loop antennas

The analysis of antenna configurations in the form of a generalized superquadric loop, which includes circular, elliptical and rectangular loop geometries, is presented in this paper. Use of a Galerkin form of the moment method with piecewise sinusoidal subsectional basis and testing functions provides rapid numerical convergence and accurate representation of the antenna current. A convenient parametric representation for the superquadric curve is developed to allow a subsectional formulation using curved wire segments, rather than the commonly employed piecewise linear segments, to construct the geometry. Both magnetic frill and delta gap source models are implemented to allow a detailed study of input impedance, directivity, radiation pattern and current distribution as a function of various geometrical parameters. The results are shown to compare well with previous results for the special case of a circular loop antenna. Some useful curves are presented to aid in the design of practical superquadric loop antennas     

Input impedance of thin dipoles by moment method

The input impedance of half-wave dipoles with decreasing diameters has been calculated using the moment method of analysis with a stepped approximation of the current distribution. It is shown that the solution becomes increasingly inaccurate when the wire radius decreases and only a few segments for the antenna are used, and that it also diverges from the accurate answer when the length/diameter ratio of each segment is such that the axial-line-current and charge approximations become insufficient.     

Numerical analysis of arbitrarily shaped probe-excited single-armprinted wire antennas

A general integral equation technique is described for analysis of an arbitrarily shaped single-arm printed wire antenna excited through a vertical probe. A unified current integral equation is formulated on the basis of dyadic Green's functions and the reciprocity theorem. The current distribution is obtained by using a parametric moment method in which parameter segments are adopted for the printed wire instead of the commonly employed wire length segments. The radiation field solution involving both the printed antenna and vertical probe is also presented. The validity of the formulation is verified by comparing the numerically obtained input impedance and radiation patterns for a linear antenna and a meander antenna with measured data. A circular open loop and an Archimedian spiral are investigated to illustrate the applicability of the present technique     

Input impedance of arc antennas and short helical radiators

The problem of the input impedance of curved wire antennas is generally formulated in terms of an integral equation. A stationary formula is used in evaluating the input impedances of arc antennas and short helical radiators of which the cylindrical antenna is a special case. The computational results are presented in graphical form. The impedance characteristics of these curved antennas are discussed.     

Electrically small self-resonant wire antennas optimized using agenetic algorithm

One of the major limitations of electrically small antennas is that as the size of the antenna is decreased its radiation resistance approaches zero and its reactance approaches plus or minus infinity. Most small antennas are inefficient, nonresonant and, thus, require matching networks. In this investigation, we use a genetic algorithm (GA) in conjunction with the numerical electromagnetics code to search for resonant wire shapes that best utilize the volume within which the antenna is confined. Antenna configurations, over a ground plane, having from two to ten wire segments, were optimized near 400 MHz and then built and tested. As the cube size deceased from a side length of 0.096λ to 0.026λ, the computed Qs increased from 15.8 to 590. The measured Qs increased from 16.0 to 134 for cubes of 0.093 to 0.037λ on edge. This process for designing small antennas using a GA produced new self-resonant antenna configurations     

Design of a vehicular antenna for GPS/Iridium using a geneticalgorithm

In this paper, we describe a vehicular wire antenna, designed using a genetic algorithm that may be used for both the GPS and Iridium systems. It has right-hand circular polarization, near hemispherical coverage, and operates over the frequency band from 1225 to 1625 MHz. This antenna was simulated using the numerical electromagnetics code (NEC) and then fabricated and tested. The antenna consists of five copper tubing segments connected in series, has an unusually odd shape, and is very inexpensive. It fits in a volume approximately 10 cm×10 cm×15 cm, The input voltage standing wave ratio (VSWR) and circular polarization radiation patterns were computed and measured. The VSWR was under 2.2 at the design frequencies of 1225, 1575, and 1625 MHz. The gain varied by less than 12 dB for a 170° sector; it generally fell off near the horizon so the variation was less for 150° and 160° sectors. This new design process, which uses a genetic algorithm in conjunction with an electromagnetics code, produces configurations that are unique and seem to outperform more conventional designs     

Moment-method analysis of printed wire spirals using curvedpiecewise sinusoidal subdomain basis and testing functions

Archimedian and logarithmic printed wire spirals are analyzed using a moment-method incorporating curved piecewise sinusoidal subdomain basis and testing functions. Results for spiral parameters including input impedance and current distribution are presented and are shown to have good agreement with published results for the same antennas obtained using linear segmentation. Since the curved basis functions exactly follow the spiral contour, significantly fewer curved segments are, therefore, required for accurate analysis compared with linear segmentation     

Design of electrically small wire antennas using a pareto genetic algorithm

We report on the use of a genetic algorithm (GA) in the design optimization of electrically small wire antennas, taking into account of bandwidth, efficiency and antenna size. For the antenna configuration, we employ a multisegment wire structure. The Numerical Electromagnetics Code (NEC) is used to predict the performance of each wire structure. To efficiently map out this multiobjective problem, we implement a Pareto GA with the concept of divided range optimization. In our GA implementation, each wire shape is encoded into a binary chromosome. A two-point crossover scheme involving three chromosomes and a geometrical filter are implemented to achieve efficient optimization. An optimal set of designs, trading off bandwidth, efficiency, and antenna size, is generated. Several GA designs are built, measured and compared to the simulation. Physical interpretations of the GA-optimized structures are provided and the results are compared against the well-known fundamental limit for small antennas. Further improvements using other geometrical design freedoms are discussed.     

Design of a loaded monopole having hemispherical coverage using agenetic algorithm

A genetic algorithm is used to design a monopole loaded with a modified folded dipole so that it radiates uniform power over the hemisphere. Each of the wires that make up the antenna are given a range of possible lengths. The genetic algorithm randomly selects a sample population of possible antenna configurations from the total population of all configurations. The radiation pattern of each sample configuration is computed using the numerical electromagnetics code (NEC). The solutions are compared with the desired pattern and ranked in terms of performance. The best solutions are retained and mated with one another and the process is repeated until an optimal solution is obtained. The genetic algorithm quickly produced an antenna that has a nearly uniform power over the hemisphere. Although the antenna was designed to operate at a frequency of 1.6 GHz, it performed satisfactorily over the frequency range from 1.4 to 1.8 GHz. The antenna was fabricated and the computational results were verified experimentally. We have shown that the genetic algorithm is a very powerful tool for designing wire antennas; it is expected that this process can be used to design any antenna that can be analyzed using an electromagnetic code     

Wire-antenna designs using genetic algorithms

There is a large class of electromagnetic radiators designated as wire antennas. As a rule, an inductive process is used to design these antennas. Either an integral equation is formulated or a simulator is used that gives the current distributions on the wires of the antenna, from which the electromagnetic properties of the antenna can then be determined. Once the antenna properties are known, the parameters are optimized, using guides such as intuition, experience, simplified equations, or empirical studies. However, using an electromagnetics simulator in conjunction with a genetic algorithm (GA), it is possible to design an antenna using a completely deductive approach: the desired electromagnetic properties of the antenna are specified, and the wire configuration that most closely produces these results is then synthesized by the algorithm. In this paper, we describe four antennas designed using GAs. The first is a monopole, loaded with a modified folded dipole that was designed to radiate uniform power over the hemisphere at a frequency of 1.6 GHz. The second antenna consists of seven wires, the locations and lengths of which are determined by the GA alone, that radiates waves with right-hand-circular polarization at elevation angles above 10°, also at 1.6 GHz. The last two antennas are modified Yagis. One is designed for a broad frequency band and very low sidelobes at a center frequency of 235 MHz. The other is designed for high gain at a single frequency of 432 MHz. We have built and tested these antennas     

Formulation for wire radiators on bodies of translation with and without end caps

A formulation, based on the method of moments (MM), is presented for active and passive wire radiators attached to, or near, a broad class of bodies and surfaces, including open or closed cylinders of arbitrary cross section as well as finite flat or curved panels. The development expands the utility of the MM theory for various antenna problems. The analysis incorporates a special junction basis set for the antenna attachment points. Total domain and piecewise continuous expansion functions are used on the surfaces. The formulation is primarily intended for prediction of radiation patterns of wire antennas (such as monopoles and loops) on asymmetric bodies of translation, open or closed (capped). The present method has shown satisfactory agreement with published data in the prediction of antenna input impedances as well.     

Frequency characterization of a thin linear antenna using diakopticantenna theory

A frequency-dependent analytical expression for the input impedance of a thin wire antenna is obtained using diakoptic theory. The linear antenna is diakopted into electrically short segments, where each is treated as a component with two terminals (except for end pieces, which have only one terminal). An impedance matrix is found which characterizes coupling between all segments. By expanding the free-space Green's function in a power series in wavenumber k, each entry in the resultant impedance matrix is obtained as an explicit function of frequency. The input admittance is found as a ratio of two polynomials in wavenumber k. A more systematic approach for the solution of the input admittance is achieved by expanding both the unknown current vector and the Green's function in power series in k. Equating coefficients of like powers in k leads to a numerically efficient algorithm which is used to determine the input admittance as a function of frequency. Numerical results compare well with the input impedance obtained from a conventional integral equation solution     

New designs of ultra wide-band communication antennas using agenetic algorithm

The paper investigates new designs of loaded wire antennas with broad-band characteristics. A two-step design procedure is proposed for the design. First, different unloaded antennas configurations are examined with a view to identifying candidates that exhibit the lowest voltage standing wave ratio (VSWR) and highest gain characteristics. Multi-armed antennas with straight wire segments that branch off symmetrically from a central stem are found to be excellent potential candidates. Next, the antenna with the best performance is loaded with resonant tank circuits and a matching network is designed. The loads can enhance the antenna characteristics to yield high gain and low VSWR by modifying the current distribution and can force it to radiate nearer to the horizon in the elevation plane with an almost omnidirectional pattern in the azimuth plane. An efficient optimization procedure based on the genetic algorithm is employed to simultaneously determine the load components, their locations, and the parameters of the matching network. Several examples of four- and eight-arm antennas with bandwidth of 7.5:1 and 15:1 illustrate the effectiveness of the design procedure     

Imaginary part of antenna's admittance from its real part usingBode's integrals

The imaginary part of an antenna input admittance is calculated from its real part using Bode's integrals. Since the real part is typically a smoother function of the frequency than the imaginary part, the procedure presented here requires computation at a smaller number of frequency points, thus saves time, and is ideal for systems whose input conductance exhibits sharp peaks. A numerical procedure to evaluate the singular Bode's integral is also presented. Numerical examples using a wire antenna are used to illustrate the advantages of this approach compared to calculations involving a densely scanned frequency range. The noise stability and robustness of the algorithm are demonstrated through the successful prediction of the susceptance and the resonant frequencies of the antenna in the presence of random noise in the conductance     

采用FDTD/FVTD混合算法分析蝶形微带天线

用FDTD和FVTD混合算法分析了蝶形微带天线的反射损失.在适于矩形网格的区域采用常规的非均匀FDTD算法,在微带贴片天线的斜边或PEC弯曲表面处采用FVTD算法,重叠区域的场通过邻近场的线性插值得到.程序仿真和实际测量结果的比较表明在较宽的频带内,该算法在不损失精度,不显著增加CPU时间和内存的情况下,极大地降低了常规FDTD所要求的网格密度.     

The moment method solution for printed wire antennas of arbitraryconfiguration

A printed wire antenna of arbitrary configuration is analyzed. The electric field tangential to the wire is derived using the current expanded by piecewise sinusoidal functions. These functions are also used to form the impedance matrix elements. Use of the stationary phase method leads to a simple expression for the radiation field. Numerical analyses based on the present formulation yield radiation characteristics of a zigzag dipole antenna, a loop antenna, and a round spiral antenna     

SuperNEC: antenna and indoor-propagation simulation program

SuperNEC is a hybrid MoM-UTD antenna and electromagnetic simulation program, developed by Poynting Software (Pty) Ltd. The UTD primitives available in the code are dielectrically coated, multi-faceted plates and elliptical cylinders. The MoM primitives supported are wire segments. The program is capable of running in parallel on a heterogeneous network of processors. A Matlab-based, interactive graphical user interface is used to define the geometry to be simulated, as well as to view the simulation results. The program has been extensively verified using a multitude of test cases, which include comparison to published results and measurements     

扇区波束赋形基站天线分析与综合

本文分析了几种复杂结构基站天线 ,并使用遗传算法进行了方向图综合设计。对天线结构采用线栅网格近似 ,用矩量法分析。并针对方向图参数要求 ,采用遗传算法对天线方向图进行了综合。在优化过程中对方向图参数构造了综合目标函数 ,保证了增益、满足了扇区波束宽度 ,并控制了后瓣。此方法可用于同种类不同振子排列形式的天线。本文的结果对工程和理论研究都有重要意义