Finite-difference time-domain method for antenna radiation

The finite-difference time-domain (FDTD) method is used to model and predict the radiation patterns of wire and aperture antennas of three basic configurations. A critical step in each is the modeling of the feed. Alternate suggestions are made and some are implemented. The first antenna is a quarter-wavelength monopole and the second is a waveguide aperture antenna. In both bases the antenna is mounted on ground planes, either perfectly conducting or of composite material. The results obtained using the FDTD technique are compared with results obtained using the geometrical theory of diffraction (GTD) and measurements. The third configuration of interest is a pyramidal horn antenna. To model the flared parts of the horn, a staircase approximation was applied to the antenna surface. The computed radiation patterns compared well with measurements     

The radiation pattern of a monopole antenna attached to aconducting box

A system investigation was undertaken to determine the radiation patterns of a monopole antenna mounted on a cubical conducting box over a ground plane. The effects of the location of the monopole and the electrical size of the box were noted as compared to similar patterns measured over a flat ground plane. Experimental results were also compared with numerically predicted values obtained from a method of moments patch code. It was concluded that the location at which a monopole antenna is mounted on a conducting box and the electrical size of the box clearly affect the overall radiation pattern of a monopole antenna. In general, mounting the antenna away from the center of the box will increase the depth of the nulls     

FDTD calculation of radiation patterns, impedance, and gain for amonopole antenna on a conducting box

The ability of the finite-difference-time-domain (FDTD) method to calculate radiation patterns, input impedance, and gain for a monopole antenna on a conducting box is demonstrated. Results are given for the bare box and with the box coated with a dielectric layer. Radiation patterns are compared with measurements and with the method of moments for the bare box. Radiation patterns for the dielectric-covered box and all impedance and gain results are compared with measurements only. Good agreement is obtained in all cases. The FDTD approach includes a dielectric covering quite easily, while this would be quite difficult for a method of moments approach. The FDTD method requires similar computer time as the method of moments for a single-frequency result, but produces wide-bandwidth impedance and gain results with much less computer time     

Performance analysis of antennas for hand-held transceivers usingFDTD

The design of antennas for hand-held communications devices depends on the implementation of simulation tools that can accurately model general topologies. The paper presents the analysis of small antennas mounted on hand-held transceivers using the finite-difference time-domain (FDTD) method. The key features of the FDTD implementation are discussed, with particular emphasis placed upon modeling of the source region. The technique is used to predict the gain patterns and broadband input impedance behavior of monopole, planar inverted F, and loop antenna elements mounted on the handset. Effects of the conducting handset chassis, the plastic casing around the device, and lumped elements integrated into the antenna design are illustrated. Experimental results are provided to verify the accuracy of the computational methodology. The concept of antenna diversity is discussed, and key assumptions and expressions are provided that characterize the multipath fading fields. Several computational examples demonstrate the diversity performance of two receiving antennas on a single handset     

Radiation from quarter-wavelength monopoles on finite cylindrical, conical, and rocket-shaped conducting bodies

A theoretical-numerical technique, based on Maue's integral equation, is applied for the determination of radiation patterns of airborne antennas comprising one or more quarter-wavelength monopoles, straight or bent, on finite cylindrical, conical, and rocket-shaped conducting airframes. The induced surface currents on the conducting body are first determined whence the total radiation fields are obtained. In the cases of a single monopole on a conducting body, the surface currents and radiation patterns are studied in view of varying the geometrical parameters of the body as well as the position and relative orientation of the monopole. For the case of two diametrically opposite monopoles on a finite cylinder, the effect of varying the relative phasing is studied. A physical interpretation of the variation with various parameters of the surface currents and the radiation fields is endeavored wherever feasible, and important results are concluded. Experimental investigation of radiation from one of the theoretically treated models, namely that of a bent monopole on a finite frustum of a cone, showed excellent agreement with computed results. This establishes the validity of the theoretical-numerical technique as well as the computed radiation patterns for various cases.     

Folded loop antenna for mobile hand-held units

The vertical folded loop antenna, modeled as wire and printed radiating element mounted on a conducting box, simulating a cellular telephone with and without dielectric coating, is analyzed. The finite-difference time-domain (FDTD) method is used to calculate radiation patterns and input impedance. The results are compared with measurements and with NEC data. Very good agreement is obtained in all cases. Parasitic loading is used to enhance the bandwidth of the printed element. The antenna meets the design requirements for existing and future mobile communication systems     

FDTD technique for modelling eight-element circular antenna array

An eight-element circular antenna array consisting of an eight wire monopole mounted on a circular ground plane is modelled using the finite-difference time-domain (FDTD) method. Examples of frequency response as well as the far-field radiation pattern are presented. Comparisons against measured responses of the actual array show that the FDTD method provides an accurate model of the antenna array.     

The input impedance of a monopole antenna mounted on a cubical conducting box

An experimental investigation has been performed to determine the input admittance characteristics of a monopole antenna mounted on a conducting cubical box over a ground plane. Input admittances of monopoles from 2 to 6 cm long mounted on a 10 cm box were considered in the investigation so that effects of changes in the electrical size of the box could be evaluated. The monopoles were placed at various points to determine the functional dependence of input admittance on the position of the monopole antenna. A numerical analysis of the radiating structure was performed using the method of moments to compare the experimental data with the computed input admittance. This comparison and the observed empirical behavior of the input admittance were then utilized to predict the effects of the conducting box on the overall admittance of the radiator.     

Radiation from a short dipole or monopole near a thick conducting cylinder of resonant length

Using a theoretical-numerical technique involving the magnetic field integral equation, the radiation fields are determined for configurations comprised of a centrally located dipole and a thin quarter-wave monopole near conducting cylinders of finite lengths. Such configurations are important since they give measures of the radiation effects of fuselages of aircraft or other structures which the cylinders may model. The radiation fields are determined in the three principal planes for wavelengths passing through the resonant length of the cylinder, i.e.,L approx lambda. The radiation patterns for both the dipole and monopole sources when normalized with respect to one another are similar to within approximately 1 dB. The vertically polarized patterns in the horizontal plane (the plane orthogonal to the dipole axis and containing the cylinder axis) show small deviations from their near omnidirectional characteristics for cylinder electrical lengths of 0.5, 1.0, and1.5lambda. On the other hand, the cross polarized component (the horizontal component) in the same plane shows a substantial enhancement of the intensity of the lobe structure at resonance. The patterns are compared to those acquired experimentally in an anechoic chamber and close agreement is demonstrated.     

介质平面上高频单极天线特性分析

该文用时域有限差分法(Finite Difference Time Domain,FDTD)计算介质平面上单极天线的阻抗特性。用FDTD法计算天线的辐射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。文章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,天线的阻抗特性。     

Study of the coupling between human head and cellular phone helical antennas

The interaction between normal-mode helical antennas and human head models is analyzed, using both a novel accurate semi-analytical method and finite-difference time-domain (FDTD) simulations. The semi-analytical method is based on the combination of Green's functions theory with the method of moments (Green/MoM) and is able to model arbitrarily shaped wire antennas radiating in the close proximity of layered lossy dielectric spheres representing simplified models of the human head. The purpose of the development of the Green/MoM technique is to provide a reliable tool for preliminary (worst case) estimation of human head exposure to the field generated by different antenna configurations with emphasis on the helical antenna, representing the most diffused antenna type used in modern cellular handsets. Furthermore, the accurate semi-analytical character of the Green/MoM technique permits the accuracy assessment of purely numerical techniques, such as the FDTD, which is currently the most widely used computational method in mobile communication dosimetric problems, since it allows modeling of anatomically based head models. After appropriate benchmarking, FDTD simulations are used to study the interaction between a heterogeneous anatomically correct model of the human head exposed to a normal-mode helix monopole operating at 1710 MHz mounted on the top of a metal box representing a realistic mobile communication terminal. The study of both canonical and realistic exposure problems includes computations of specific absorption rates (SARs) inside the human head, total power absorbed by the head and assessment of antenna performance. Emphasis is placed on the comparative dosimetric assessment between adults and children head models.     

Analysis of a monopole mounted near an edge or a vertex

The problem of a monopole mounted near the edge of a wedge or a vertex is considered. Three types of solutions-surface patch modeling, moment method/geometrical theory of diffraction (MM/GTD), and MM/eigenfunction-are presented, discussed, and compared with measurements. Results are in the form of input impedance and radiation patterns.     

FDTD modeling of common-mode radiation from cables

Radiation from cables attached to printed circuit boards and shielding enclosures is among the primary concerns in meeting FCC Class A and B limits. The finite-difference time-domain (FDTD) method can be employed to model radiation from printed circuit boards and shielding enclosures with complex geometries, but difficulties in modeling wires and cables of arbitrary radii are encountered. Modeling the wire by setting the axial component of the electric field to zero in the FDTD method results in an effective wire radius that is determined by the mesh discretization. Neglecting the wire radius in applications, such as electromagnetic interference (EMI) or printed circuit board modeling, may result in gross errors because near-field quantities are typically sensitive to wire thickness. Taflove et al. (1988) have developed a subcellular FDTD algorithm for modeling wires that has been shown to work well for plane wave scattering. The method uses a quasistatic field approximation to model wires with a well defined radius independent of the mesh dimensions. The wire model is reviewed and investigated for application to common-mode radiation from cables attached to printed circuit boards, where the source is often a noise voltage at the connector. Also investigated is energy coupling to attached cables through enclosure apertures resulting in common-mode radiation from the cable. The input impedance for a center-fed dipole antenna, as well as a monopole connected to a conducting half-sheet, is computed with FDTD methods and compared to moment method input impedance results. A simulation of a shielding enclosure with an attached cable demonstrates the utility of FDTD analysis in modeling common-mode radiation     

Analysis of electromagnetic radiation from shaped-end radiatorsusing the finite difference time domain method

The finite difference time domain (FDTD) technique is a popular method for analyzing electromagnetic scattering, radiation, and penetration problems. Several authors have recently applied the FDTD method to antenna radiation problems. To date, the antenna structures considered have been wire and conical monopole antennas, rectangular waveguides, pyramidal horn antennas, and microstrip antennas. Results from these analysis have been in the form of normalized field patterns and no results showing absolute gain have been presented. The article demonstrates the first staircased application of the FDTD method to the analysis of radiation from circular waveguides and other shaped-end radiators. Results of absolute gain versus angle are shown for a straight-cut circular waveguide and for two different shaped-end radiators. All FDTD analyses are full three-dimensional computations and are compared in each case with measured data     

Monopole impedance and gain measurements on finite ground planes

The possibility of making acceptably accurate monopole input impedance and gain measurements on a reduced-size ground plane is discussed. Existing measured and calculated data show that the diameter of a highly conducting ground plane should be at least 4λ (where λ is the wavelength) for measuring the input impedance of quarter-wavelength monopoles. At 25 MHz, the lowest frequency considered here, such a ground plane would require a space at least 48 m in diameter. The model impedance measurements and calculations presented imply that a reduced space of only 10 m by 11 m is required if 16 resistively loaded wire radials are connected to a 3.66 by 4.88-m rectangular aluminum ground plane, thus effectively `extending' the ground plane by the resistive loading. Measured insertion-loss data acquired using a 1:5 scale-model ground plane with resistively loaded radials indicate that the plane is sufficiently large for gain measurements as well. Measured and calculated monopole standing-wave ratio and insertion loss on a full-scale ground plane verify the results of the model measurements     

FDTD computation of temperature rise in the human head for portabletelephones

Temperature rises in the human head for portable telephones were computed with an anatomically based head model at 900 MHz and 1.5 GHz. The specific absorption rate (SAR) in the human head was determined using the finite-difference time-domain (FDTD) method, while a bioheat equation was numerically solved also using the FDTD method. The portable telephone was modeled by a quarter-wavelength monopole antenna on a dielectric covered metal box. The source geometries considered were the telephone barely touching the ear and the telephone pressing the ear, both having a vertical alignment at the side of the head. The antenna output power was set to be consistent with the portable telephones of today: 0.6 W at 900 MHz and 0.27 W at 1.5 GHz. Computed results show that a phone time of 6-7 min yields a temperature rise of approximately 90% of the steady-state value. Application of the ANSZ/IEEE safety guidelines restricting the 1-g-averaged spatial peak SAR to 1.6 W/kg results in the maximum temperature rise in the brain of 0.06°C, and application of the ICNIRP/Japan safety guidelines restricting the 10-g-averaged spatial peak SAR to 2 W/kg results in the maximum temperature rise in the brain of 0.11°C, both at 900 MHz and 1.5 GHz     

一种新型宽频带折合平面单极子手机天线的设计与分析

本文设计了一种新型微带馈电的折合平面单极子手机天线，采用时域有限差分法（FDTD）计算并分析了新型折合平面单极子天线几何参数对其性能的影响．实际测试发现，FDTD方法分析所得结果与实验结果基本一致,该天线具有结构简单、宽频带、馈电方便、便于集成等特点，为第三代移动通信手机天线增加了一种新选择.     

Vertical radiation patterns of mobile antenna in UHF band

Theoretical and experimental studies are made on radiation patterns of mobile antennas within the frequency range from 300 to 900 MHz. In order to calculate vertical plane patterns of quarter wavelength monopole and a half-wavelength dipole located on an automobile's roof, a theoretical model of an automobile body is developed, in conjunction with the geometrical theory of diffraction (GTD). The theoretical model consists of three-perfectly conducting plates. It is ascertained from a comparison between calculated and measured results for the feed point impedance and the radiation pattern that the effect of the body and the earth can be well examined with the theoretical model. The results of pattern calculation for the above two antennas show that the radiation patterns depend largely on the configuration of the automobile body and the earth condition. The technique described in this paper can be used as a design tool to estimate radiation performance of mobile antennas.     

A study of transient radiation from the Wu-King resistivemonopole-FDTD analysis and experimental measurements

The cylindrical monopole antenna with a continuous resistive loading is considered as a radiator for temporally short, broad-bandwidth pulses. Specifically, the variation of the resistance used along the monopole is one proposed by Wu and King (1965). This antenna is analyzed by the finite-difference-time-domain (FDTD) method utilizing a new, efficient technique for handling the thin-walled, conducting tube that forms the resistance. The electromagnetic field in the space surrounding the antenna is determined as a function of time, and quantities useful for describing the performance of the antenna are then calculated from these results. Graphical displays of the results are used to give new insight into the physical processes for transient radiation form this antenna. An experimental model is constructed using a discretized version of the Wu-King profile formed from a set of precision, high-frequency resistors. Measurements of both the reflected voltage in the feed line and the time-varying radiated field are in excellent agreement with the theoretical calculations     

Characterization of antennas for personal wireless communications applications

The advancement of antenna technology in personal wireless communication systems has been encouraged by the increasingly stringent demands placed upon these systems to provide low-power and highly reliable information transfer. The antenna designer must not only consider the cost, manufacturability, compactness, and system integrability of the radiator but also generate a product which satisfies rigid specifications concerning return loss, bandwidth, and gain while operating in a complex radiating environment. Successful, cost-effective approaches to the design of antennas for communication devices rely upon the implementation of sophisticated analysis tools, such as the finite-difference time-domain (FDTD) method, capable of predicting the electromagnetic behavior of complicated topologies. In this work, the behavior of planar inverted F, monopole, and loop antennas is investigated using tools based upon the FDTD approach. Such factors as the effects of the conducting chassis, plastic casing, and biological tissue on the antenna performance are investigated. Experimental measurements are used to validate the results obtained from computations and to provide further insight into the behavior of the different geometries. The use of antenna diversity to reduce the effects of multipath fading is discussed, and several examples of antenna diversity configurations are provided.