Accurate characterization of planar printed antennas usingfinite-difference time-domain method

The finite-difference-time-domain method (FD-TD) is used to characterize complex planar printed antennas with various feed structures, which include coaxial probe feed, microstrip line feed, and aperture coupled feed structures. A coaxial probe model is developed by using a three-dimensional FD-TD technique. This model is shown to be an efficient and accurate tool for modeling coaxial line fed structures. A novel use of a dispersive absorbing boundary condition is presented for a printed antenna with a high dielectric constant. All the numerical results obtained by the FD-TD method are compared with experimental results, and the comparison shows excellent agreement over a wide frequency band     

Microwave Measurement of Dielectric Constant of Liquids and Solids Using Partially Loaded Slotted Waveguide (Short Papers)

An accurate method is described for the measurement of the dielectric constant of liquids and solids. The dielectric material partially loads a slotted rectangular waveguide and the guide wavelength is measured for two different thicknesses of the dielectric. The guide wavelengths are related to the dielectric constant of the material through a characteristic equation which can be solved graphically or numerically. Some experimental results are obtained and found to be in close agreement with the values of the dielectric constant available in the literature.     

A Microwave Technique for the Measurement of the Dielectric Properties of Soils (Correspondence)

During a recent investigation of antennas mounted flush with the earth, it was necessary to measure the dielectric properties of soil. Many different techniques for the measurement of dielectric constants and loss tangent have been developed. These techniques generally fall into two categories: those which utilize transmission through a sample and those which use the reflection from the sample. The particular technique employed is modified to suit the range of parameters being measured and the physical characteristics of the sample. In general, a measurement that provides an accurate determination of dielectric constant is relatively insensitive to variations in loss tangent and vice versa. The technique described here utilizes both types of measurements to find in a practical manner the dielectric constant and loss tangent of relatively moist loamy soil at microwave frequencies.     

Patch antennas on externally perforated high dielectric constantsubstrates

Smaller physical size and wider bandwidth are two antenna engineering goals of great interest in the wireless world. To this end, the concept of external substrate perforation is applied to patch antennas in this paper. The goal was to overcome the undesirable features of thick and high dielectric constant substrates for patch antennas without sacrificing any of the desired features, namely, small element size and bandwidth. The idea is to use substrate perforation exterior to the patch to lower the effective dielectric constant of the substrate surrounding the patch. This change in the effective dielectric constant has been observed to help mitigate the unwanted interference pattern of edge diffraction/scattering and leaky waves. The numerical data presented in this paper were generated using the finite-difference time-domain (FDTD) technique. Using this numerical method, a patch antenna was simulated on finite-sized ground planes of two different substrate thicknesses, with and without external substrate perforation. The computations showed the directivity drop in the radiation pattern caused by substrate propagation was noticeably improved by introducing the substrate perforation external to the patch for the case of a patch antenna on a relatively thick substrate without any loss of bandwidth. Measurements of a few patch antennas fabricated on high dielectric constant substrates with and without substrate perforation are included for completeness. Good correlation between the computed results and measurements is observed     

椭圆柱二维光子晶体带隙特性的数值模拟

本文应用平面波展开法数值模拟了椭圆柱二维光子晶体TM模带隙特性,数值模拟椭圆长短半轴对带隙特性的影响,结果得到:当椭圆长短半轴趋于相等时形成带隙宽度逐渐增加。数值模拟四种材料即SiC、GaAs、Ge和ZnO构成椭圆柱正方晶格二维光子晶体时,TM模带隙特性和第一带隙变化情况,结果得到介电常数高的材料形成较宽带隙,随着介电常数的增加,第一带隙上下边界的归一化频率逐渐降低,但是,第一带隙带隙宽度逐渐增加。     

Radiation and scattering analysis of infinite arrays of endfireslot antennas with a ground plane

A Green's function moment-method analysis of infinite arrays of endfire slot antennas is described that includes the constant width slot antenna (CWSA) and the linearly tapered slot antenna (LTSA), with a ground plane. The method utilizes an application of equivalence at a plane in front of the array which facilitates the extension of this analysis to antennas printed on protruding dielectric sheets and/or the addition of a radome. Numerical calculations are compared with waveguide simulator experiments for CWSA and LTSA arrays as well as several less complex problem. Relevant numerical considerations and convergence issues are also discussed     

A New Class of Miniature Embedded Inverted-F Antennas (IFAs) for 2.4 GHz WLAN Application

A new class of miniature printed embedded inverted-F antennas are proposed for operation in the 2.4–2.485 GHz wireless local-area network band. One of the proposed antennas on FR4 substrate (dielectric constant = 4.4) measures 9.2 mm by 4.1 mm and has a bandwidth of 3.5%. The peak gain of this antenna is 1.4 dBi. An overall size reduction of 70% is achieved compared to a conventional inverted-F antenna. Effects of dielectric loss tangent and material conductivity on the bandwidth and efficiency of these antennas are also investigated. Finally, two embedded antenna elements are analyzed to demonstrate the feasibility for a decoupled antenna pair consisting of switched and combining diversity schemes.     

An integral equation and its application to spiral antennas onsemi-infinite dielectric materials

This paper presents an integral equation that can handle wire antennas on a semi-infinite dielectric material. The integral equation is reduced to a set of linear equations by the method of moments. For efficiency, the impedance matrix element Z_m,n is divided into two parts on the basis of weighted Green's function extractions. The far-zone radiation field, which is formulated using the stationary phase method, is also described. After the validity of the presented numerical techniques is checked using a bow-tie antenna, a spiral antenna is analyzed. The current distribution, radiation pattern, axial ratio, power gain, and input impedance are discussed. It is found that the radiation field inside a dielectric material is circularly polarized. As the relative permittivity of the dielectric material increases, the angle coverage over which the axial ratio is less than 3 dB becomes narrower     

Two port analysis of dielectric resonator antennas excited in TE01 mode

Results of a numerical and experimental study of the transmission and input reflection coefficients of a two element array of half-split cylindrical dielectric resonator (CDR) antennas are presented. The antenna elements are situated on a ground plane and fed by a coaxial probe. A procedure based on the method of moments (MoM) for the coupling of a body of revolution (BOR) to a non-BOR geometry together with classical microwave network theory is implemented. Some of the numerical results are verified experimentally     

改进型超宽带Vivaldi天线设计与仿真

在传统Vivaldi天线结构的基础上,设计了两种适用于宽带信号收发系统的改进型渐变槽Vivaldi天线以及同轴馈电型对踵Vivaldi天线,并利用电磁仿真软件HFSS对这两种Vivaldi天线的性能进行优化分析.通过对不同结构Vivaldi天线的对比分析结果可以看出改进型渐变槽Vivaldi天线和同轴馈电型对踵Vivaldi天线在频段、带宽、驻波比等方面均达到宽带传输系统的设计要求.     

Analysis of Printed Antennas Mounted on a Coated Circular Cylinder of Arbitrary Size

An efficient numerical algorithm for the analysis of printed antennas on a dielectric coated circular cylinder is presented. The formulation employs the spectral domain approach. Green's function is evaluated via Olver's uniform asymptotic expansions. The Fourier summation is transformed into integration and the asymptotic part of the integral is evaluated in closed form. The whole procedure results in a numerical algorithm that is at least as accurate and efficient as the respective one for the planar structure. The present approach can be applied for any source-receiver position and any cylinder radius.     

Comparative study on the mutual coupling between different sized cylindrical dielectric resonators antennas and circular microstrip patch antennas

A systematic comparative study on the mutual coupling (S/sub 21/) between dielectric resonator antennas (DRAs) and microstrip patch antennas is presented. The mutual coupling between two cylindrical probe-fed DRAs is studied for different radius to height (a/L) ratios. It is found that the mutual coupling decreases with the radius to height ratio. Comparison between mutual coupling of probe-fed cylindrical DRAs and circular microstrip patch antennas with different dielectric substrates are also studied. The mutual coupling between DRAs is 2 dB stronger than between microstrip patch antennas when the patch is etched on a dielectric substrate of a dielectric constant close to the permittivity of the DRA. The mutual coupling of the circular patch antennas reduces with the dielectric constant of the substrate.     

用于超宽带介电常数测量的Vivaldi天线设计与仿真

在传统Vivaldi天线结构的基础上,设计了两种适用于混合材料介电常数测量的改进型渐变槽Vivaldi天线以及同轴馈电型对踵Vivaldi天线,并利用三维电磁仿真软件HFSS对这几种Vivaldi天线的性能进行优化分析。通过对不同结构Vivaldi天线的对比,分析结果可以看出这两种改进型渐变槽Vivaldi天线和同轴馈电型对踵Vivaldi天线在频段、带宽、驻波比等方面均达到超宽带介电常数测量系统的设计要求,可应用于测量混合材料的介电常数。     

An automated SAR measurement system for compliance testing ofpersonal wireless devices

An automated specific absorption rate (SAR) measurement system has been developed for compliance testing of personal wireless devices. Unlike other systems, this system uses a model with a lossy ear-shaped protrusion and the accuracy of this experimental setup has been checked by comparing the peak 1-g SARs for ten cellular telephones, five each at 835 and 1900 MHz, with the results obtained using a 15-tissue anatomically based model with the finite-difference time-domain (FDTD) numerical electromagnetic technique. The SAR measurement system uses a three-dimensional (3-D) stepper motor to move a Narda Model 8021 E-field probe to measure the SAR distribution inside a head-shaped tissue-simulant phantom near the radiating device. The head and neck part of the model with an ear-shaped protrusion of 3 mm thickness is made of a lossy outer shell of 5-7 mm thickness of epoxy laced with KCl solution. The phantom is filled with appropriate frequency-specific fluids with measured electrical properties (dielectric constant and conductivity) that are close to the average for gray and white matters of the brain at the center frequencies of interest (835 and 1900 MHz). The implantable E-field probe is calibrated using the FDTD-calculated SAR variations for a slab model at two commonly used frequencies, 835 and 1900 MHz and is checked to have good isotropic characteristics (±0.23 dB) and a wide dynamic range (0.01-10 W/kg). The system is validated using a 223-mm-diameter sphere model. Peak 1-g SAR's for ten telephones using different antennas are within ±1 dB of those obtained using the FDTD numerical method for the anatomical model of the head and neck region     

Properties of Near and Far Fields for the Electric Line Source Illumination of a Lossy Metamaterial Covered Dielectric Cylinder

The electric field properties of the electric line source radiation in the presence of a lossy metamaterial covered dielectric cylinder are investigated. Firstly, the electromagnetic model configuration is given. The exact solution of the electromagnetic is presented. Secondly, the near field and the far field properties are investigated according to the electromagnetic and geometrical parameters. The different “focus” phenomenon, the directivities and the normalized radiation resistance are discussed and important conclusions are obtained. During all the numerical computation, the lossy conventional material covered dielectric cylinder is utilized as the reference.     

Impedance transformation through material of linearly varying dielectric permittivity: comparison of two common techniques

Sub-surface measurement of the properties of dielectric material often requires a model for referring impedance through the material and where the material has a dielectric permittivity that varies linearly with respect to depth. There are two common techniques for doing this. The derivation of the less common of the two techniques is described, followed by comparison of the performance of the techniques.     

Different formulations for numerical solution of single or multibodies of revolution with mixed boundary conditions

A numerical method for determining the electromagnetic field in the presence of one or several bodies of revolution is presented. The objects can be made of conductors, dielectrics or their combinations. The excitation is assumed to be due to a plane wave or infinitesimal electric dipoles located within or outside the dielectric. Several formulation types are considered and used to investigate the scattering by different objects. It is found that for moderate values of the dielectric constant, all formulation types give satisfactory results. However, for small or large relative permittivities the solution accuracies depend on the formulation type. As an application of the method to practical problems, two special cases of dielectric rod and microstrip antennas are considered. These antennas have widespread applications and the proposed method can be used to investigate their performance accurately.     

Temperature dependence of composite microwave cavities

Composite microwave resonant cavities contain several regions of different dielectric materials. The variation of the resonant frequency with temperature is described in terms of a linear model. One part of the frequency variation is caused by the physical expansion of material parts, and the other by the change in the relative dielectric constant. The frequency sensitivity coefficients for both types of variation are obtained with the use of a computer code for numerical analysis of the electromagnetic field inside bodies of revolution     

Dielectric constant measurements of finite-size sheet at microwavefrequencies by pseudo-Brewster's angle method

Dielectric constant (ϵ_r) measurements for finite-size dielectric sheets (DS's) at centimeter wavelengths are presented using the method-of-measuring pseudo-Brewster's angle. This method is applied to measure ϵ_r of sheets of Plexiglas and window glass. In the experiment, two horn antennas are used to transmit and receive p-polarized waves. A dielectric sheet is located between the two antennas and rotated 180°, which produces two peaks in the transmittance curves. For a more accurate measurement of Brewster's angle, an optical spectrometer with 1-min accuracy is also used. By this method, ϵ_r of Plexiglas and window glass are obtained to be 2.55±0.13 and 5.35±0.1, respectively. This method measures |ϵ_r|, but the measurement is easy and nondestructive for DS's. Finally, an accurate method of error calculation is used to calculate the error in the measured values of ϵ_r     

介电常数的概念研究

在设计电路、天线、电容器等过程中经常会涉及所用材料的介电常数,所以深入了解介电常数的相关概念对实际工作有重要意义。首先介绍了介质和导体、半导体的区别,然后解释了介电常数的基本概念,并给出相对介电常数的另一种导出定义。介质极化的微观模型这一部分讲清楚了4种不同的极化。最后介绍介电常数的一些宏观特性,得出电介质介电常数将会影响电介质中电场强度的结论。