矩形反射柱体近旁天线辐射特性的计算应用几何绕射理论

本文用几何绕射理论分析计算了矩形反射柱体近旁偶极子和双环天线的水平辐射特性。研究了到达场点的直达波、反射波和柱体稜边各次绕射波之间的量值关系。分析了柱体边长、天线与柱体之间的相对位置和天线的馈电方式对合成场强方向图的影响。计算结果表明,需要对天线系统的有关参数进行优化设计,以得到最佳的全向辐射特性,本文的分析方法和结果为这类天线系统的优化设计提供了手段和依据。     

圆柱导体上天线的辐射特性及互耦分析

基于几何绕射理论,计算了位于导体圆柱上的单极子天线和惠更斯元面天线的辐射方向图;利用该方向图,分析比较了不同天线之间的隔离随天线指向的变化情况。结果表明:选择适合的天线类型及适合的安装角度能够改善天线间隔离度;几何绕射理论是解决导电圆柱体上天线的辐射问题的一种有效方法;应用远区辐射场的方向函数估算耦合系数是一种简单可行的方法。     

一种宽频带共形天线的特性研究

设计了一种具有宽频带特性的柱面共形天线,通过改变柱体曲率半径、长度和介电常数等参数,详细分析了其变化对共形天线性能的影响。结果表明:柱体各个参数的变化会导致天线的谐振频率、阻抗带宽以及辐射特性发生显著的改变。对设计宽频带共形天线时共形载体的选取提供了可靠依据。实际加工制作了天线,测量结果表明:该天线具有宽频带特性,可用频段覆盖2～16GHz,在工作频段内具有较好的辐射特性,增益稳定。     

Analysis of microstrip antennas on circular-cylindrical substrateswith a dielectric overlay

The use of dyadic Green's functions and the moment method is explored for the solution of microstrip antenna problems on circular cylindrical substrates. The dyadic Green's functions of the electric type are obtained for a medium consisting of three cylindrical dielectric layers concentric with a perfectly conducting cylinder, and integral equations are developed for the evaluation of the electromagnetic fields. The effect of a dielectric overlay on the resonant frequency of a cylindrical-rectangular microstrip antenna is analyzed. The patch is directly fed by means of a microstripline printed along the cylinder axial direction. The results show that the effect of the dielectric overlay is substantial when its relative permittivity and thickness are increased, such that this effect has to be very carefully considered in the design of microstrip antennas     

Design method of Yagi-Uda two-stacked circular loop array antennas

A design method which works as a single balanced feed antenna is presented for the Yagi-Uda two-stacked circular-loop array antenna. The antenna is analyzed with a theoretical model consisting of loop elements and feeder sections. The results are compared with experiments. By using the computed and measured antenna currents, the gain enhancement of the antenna is confirmed to be due to both the stacked-loop-array and endfire-array effects. A method of compensation for the reflection loss and a design procedure are discussed in detail. A graphical method is given to estimate the optimum size of the antenna without detailed numerical calculations, and the performance of the designed antenna is demonstrated by experiments. Experimental results are presented for several antennas arranged with different numbers of loops in the endfire and broadside directions     

一种圆柱共形的全向微带天线

提出了一种全向的圆柱共形矩形微带天线。阐述了这种在薄圆柱形介质基片上的矩形微带天线的分析方法和设计方法，并给出了理论和实验结果，证实了这种天线在垂直于柱体轴的平面内辐射出全向性的方向图。     

用于瞬态电磁场测量的宽带脉冲天线

脉冲天线是脉冲雷达、瞬态电磁场测量等应用的关键设备之一。本文描述了用于瞬态电磁场测量的一种宽带脉冲天线的设计，给出了测量结果，测量结果表明，该天线具有高保真和宽频带特性，有有效地发射或接收毫微秒脉冲信号。实际制作的天线已成功地应用于外场瞬态电磁测试系统。     

Parallel particle swarm optimization and finite- difference time-domain (PSO/FDTD) algorithm for multiband and wide-band patch antenna designs

This paper presents a novel evolutionary optimization methodology for multiband and wide-band patch antenna designs. The particle swarm optimization (PSO) and the finite-difference time-domain (FDTD) are combined to achieve the optimum antenna satisfying a certain design criterion. The antenna geometric parameters are extracted to be optimized by PSO, and a fitness function is evaluated by FDTD simulations to represent the performance of each candidate design. The optimization process is implemented on parallel clusters to reduce the computational time introduced by full-wave analysis. Two examples are investigated in the paper: first, the design of rectangular patch antennas is presented as a test of the parallel PSO/FDTD algorithm. The optimizer is then applied to design E-shaped patch antennas. It is observed that by using different fitness functions, both dual-frequency and wide-band antennas with desired performance are obtained by the optimization. The optimized E-shaped patch antennas are analyzed, fabricated, and measured to validate the robustness of the algorithm. The measured less than - 18 dB return loss (for dual-frequency antenna) and 30.5% bandwidth (for wide-band antenna) exhibit the prospect of the parallel PSO/FDTD algorithm in practical patch antenna designs.     

旋转对称体天线宽带特性研究

应用扩展矩量法，分析了旋转对称单极子天线的宽带特性，得出了最佳锥角。文中给出了下降频率随天线高度、宽度和体积的变化曲线，讨论了宽度、高度对增益的影响，为实际设计提供了理论依据，理论计算与实验结果进行了比较，两者较好地吻合。     

Mobile radio signal correlation versus antenna height and spacing

In mobile radio communications, a given correlation value between two signals received at a base station can be achieved by adjusting the antenna spacing and height; this has been experimentally verified [1], [2]. From this fact, a parameter η, defined as η=antenna height/antenna spacing is proposed as a measure of correlation for design purposes. Data from field experiments using horizontally spaced, vertically polarized base-station antennas have been analyzed in terms of η and are presented here. These data provide an upper bound correlation coefficient for any antenna separation and height. The upper bound value can be directly applied in system design.     

超小型高屏效金属盒体的屏效测试技术

为解决工程中超小型、高屏效金属盒体的屏蔽效能测量问题,测试天线必须具备尺寸小、频带宽以及辐射强度高的特点。使用HFSS对天线尺寸参数进行优选,采用双锥和套筒结构分别覆盖100 MHz~2 GHz和2~5 GHz两个频段,由该天线所构成的测试系统的动态范围比早期的球形偶极子天线提高了50 dB左右。最后对3种不同的机箱状态在半电波暗室中进行了屏蔽效能测试,试验获得的数据为今后的机箱屏蔽设计提供了依据。     

Microwave radiation of cylindrical plasma column

The travelling wave antennas representing a column of isotropic plasma and a plasma column placed into external infinitely large magnetic field have been theoretically and numerically investigated and compared. The relationships of radiation patterns as a function of the plasma density, geometrical parameters of the plasma cylinder and the radiation wavelength were also investigated. We considered both the linear antennas and the radiating antennas with wavelengths close to the antenna radius. An axially symmetric E-wave was studied. The need of taking into account the radial distribution of antenna current was shown. The dependence of normalized radiation patterns on the wave-slowing was analyzed. The characteristic value of plasma density was found; if this value is exceeded, the normalized radiation patterns are sharp directional and have the main lobe located at small angle towards the antenna axis. For the magnetized plasma this characteristic value of density is much smaller than for the isotropic one. With the rise of the plasma density the level of side lobes gets smaller.     

Experimental evaluation of the spherical near field test range

In aircraft manufacturer firms there is the need for measuring antenna patterns of large beamwidth communication/navigation antennas with the scale modeling technique. A series of tests has been carried out to verify the use of the spherical near field (SNF) test range for this purpose. The comparison is made between measured and calculated data of stub and waveguide antennas installed on a cylinder. From the results it appears that the agreement is reasonable. The advantages and disadvantages of the SNF test range for this particular application are discussed.     

Nonuniform Luneburg and two-shell lens antennas: radiationcharacteristics and design optimization

Design optimization of radially nonuniform spherical lens antennas is the focus of this paper. In particular, special attention is given to the optimal design of nonuniform Luneburg (1964) lens antennas. One of the important engineering objectives of designing an optimal Luneburg lens antenna is to use as small number of shells as possible while maintaining an acceptable gain and sidelobe performance. In a typical radially uniform design, by reducing the number of shells, the gain is decreased and the grating lobes are increased. This deficiency in the radiation performance of the uniform lens antenna can be overcome by designing the nonuniform lens antenna. This necessitates the optimum selection of each layer thickness and permittivity. A genetic algorithm (GA) optimizer with adaptive cost function is implemented to obtain the optimal design. In this manner, the GA optimizer simultaneously determines the optimal material and its thickness for each shell by controlling the gain and sidelobes envelope of the radiation pattern. Various lens geometries, including air gaps and feed offset from the lens surface, are analyzed by using the dyadic Green's functions of the multilayered dielectric sphere. Many useful engineering design guidelines have been suggested for the optimum construction of the lens. The results have been satisfactory and demonstrate the utility of the GA/adaptive cost-function algorithm. Additionally, the radiation characteristics of a novel two-shell lens antenna have been studied, and its performance is compared to the Luneburg lens     

Broadside radiation from periodic leaky-wave antennas

A double-strip grating leaky-wave antenna consisting of two strips per unit cell is analyzed. The stopband behavior exhibited at broadside scan in the single-strip grating antenna is characteristic of all periodic leaky-wave antennas having a single strip per unit cell, and results in a drastic increase in the attenuation rate of the leaky wave as the beam is scanned to broadside. By nearly eliminating this stopband behavior, the double-strip leaky-wave antenna can scan from backward end fire to forward end fire without any large frequency regions of high attenuation. An approximate design rule for the double-strip antenna is discussed, and results are presented to show how the antenna may be further optimized to achieve the minimum possible variation in attenuation as the beam is scanned through broadside. Although the stopband behavior is never completely eliminated with the addition of the extra strip, the optimum design shows an almost negligible region of rapidly varying attenuation near broadside     

应用于MIMO系统终端的腰带式可穿戴天线

提出一种应用于MIMO无线通信系统移动终端的腰带式可穿戴外置多天线.这一MIMO多天线系统利用合理的布局,可获取各种分集增益.天线单元采用开槽的电磁耦合微带贴片天线,减小了天线尺寸,也降低了人体吸收率.通过MIMO系统试验平台的外场测试,得到了多天线系统的相关性系数矩阵以及误码率等重要的实验数据.测试结果表明:在保持总发射功率不变的情况下,相较于传统的单发单收天线,这一多天线系统可显著降低传输误码率,进而有效提高通信系统容量与质量.     

Planar Log-Periodic Antennas on Extended Hemishperical Silicon Lenses for Millimeter/Submillimeter Wave Detection Applications

In this paper, the radiation properties of log-periodic (LP) antennas on extended hemispherical dielectric lenses are investigated. The starting point is the far field pattern for the log-periodic antenna on a semi-infinite silicon substrate obtained from numerical simulation. Then the effects of extended hemispherical silicon dielectric lenses on this far field pattern are evaluated using ray tracing and field integration techniques. The far fields patterns out of the lenses are derived as a function of the extension length (L), from which the optimum L can be determined. The coupling efficiencies of the pattern to Gaussian beams are also calculated. The computation results show that the log-periodic antennas have good performance in terms of impedance and pattern and can be used in many submillimeter/THz systems. The simulation methods are verified by comparing the simulation results with experimental data from literature. The utilized approach represents an effective method for log periodic antenna-lens system design at millimeter/submillimeter wavelengths.     

一种双圆极化半球面相控阵天线的优化设计

针对全空域多目标通信的应用需求,设计了一种具有32阵元的双圆极化半球面相控阵天线。为满足低仰角目标通信需求,采用半球加圆柱的布阵方式,通过详细对比分析三种不同阵元排布方式下的天线性能,确定最优的布阵方式。仿真结果表明,该天线从0°~102.5°扫描过程中,天线增益大于13.3 dBi,增益波动小于2.5 dB。该相控阵天线能够适用于全空域多目标通信的场合。     

Main-beam polarization properties of modified helical antennas

The polarization properties of modified helical antennas are investigated for a wide range of directions using a two-dimensional polarization diagram. The current distribution on the antenna and the radiated field are calculated for several variations of the antenna shape to show the influences of the helix design on the main-beam polarization characteristics. This extended knowledge about typical polarization diagrams yields conditions for the antenna design. Special emphasis is placed on the choice of the geometrical parameters for the open end and the feed region of the antenna to meet different system requirements. The calculated results are confirmed with measured polarization characteristics and radiation patterns for experimental helices     

Ultimate signal-to-noise-ratio of surface and body antennas formagnetic resonance imaging

Approximating the human body by a homogeneous half-space or cylinder the electromagnetic fields of surface antennas or wholebody antennas for magnetic resonance imaging (MRI) can analytically be calculated. Using these expressions the signal-to-noise ratio (SNR) of a general magnetic resonance detecting antenna can be predicted. We show how the optimum magnetic resonance antenna must look like to achieve the maximum SNR, which is also presented. Finally, we apply the derived formulas to special antenna geometries like the single- and the double-loop coil, the magnetic dipole, and the “birdcage” resonator