Full-wave modelling of coaxial cables by FDTD technique

Coaxial cables are commonly used in microwave systems but are difficult to model rigorously in the finite-difference time-domain (FDTD) method, particularly with coarse meshes. Various techniques are investigated and the optimum method identified. In addition, attention is paid to strategies for the computation of the characteristic impedance.     

同轴馈电耦合微带贴片天线的时域有限差分法分析

提出一种融合曲线坐标和直角坐标的区域网格划分方法。在同轴线区域采用曲线坐标网格,用以代替传统的阶梯剖分,在其它区域及边界上采用直角坐标网格,从而极大地提高了计算效率。同时,在时域有限差分法中还采用了非均匀网格划分,PML吸收边界和Prony外推法等技术,对同轴馈电的耦合微带贴片天线进行了分析。     

Transmission characteristics of a coaxial optical fiber line

A coaxial optical fiber line is proposed and studied as a long-distance transmission medium. The radial structure consists of a core surrounded by two clads. The inner clad has higher refractive index than the core and the outer clad. Guided modes are thus characterized by a concentrated field in the inner clad and evanescent fields in both the core and the outer clad. Using a rigorous modal analysis, characteristic curves for a monomode coaxial fiber line are presented. It is shown that the zero-dispersion wavelength can be placed at any desired value by proper choice of the refractive index contrast and the fiber dimensions. The proposed coaxial line compares well with the known W-profiled line with respect to ease of manufacture and dispersion characteristics     

Variational analysis of a gap in the central conductor of arectangular coaxial line

Rectangular coaxial line (RCL) discontinuity in the form of a gap in the central conductor and steps in the outer conductor in the planes of discontinuity has been analyzed by a variational method. The orthogonal-mode functions of an RCL required for numerical computation of the discontinuity parameters have been determined using the Ritz-Galerkin technique. The capacitances of the equivalent Pi-network are presented as function of gapwidth, normalized frequency, and ratio of outer conductor dimensions for complete characterization of the discontinuity. The low-frequency series and shunt capacitance values are verified against the static capacitances computed separately by the finite-difference technique     

Electromagnetic scattering from a coaxial dielectric circularcylinder loading a semicircular gap in a ground plane

An exact dual series solution of a plane wave incident on a coaxial dielectric circular cylinder imbedded in a semicircular gap of a ground plane is presented. Both TM and TE cases are considered here. The scattered field is represented in terms of an infinite series of cylindrical waves with unknown coefficients. By applying the boundary conditions and employing the partial orthogonality of the trigonometric functions the scattering coefficients are obtained. The resulting infinite series is then truncated to a finite number of terms to produce numerical results. For the sake of comparison with the published data some special cases are introduced first. The comparisons showed excellent agreement in all cases     

Cylindrical-Cartesian FDTD model of a 17-element conformal antennaarray

A novel hybrid cylindrical-Cartesian finite difference time domain (FDTD) method is presented, which permits a dramatic increase in the flexibility of the basic FDTD algorithm. It is shown to be particularly well-suited to the analysis of faceted conformal antenna arrays and its accuracy is demonstrated by comparison with experimental measurements of couplings within a 17-element array     

Propagation characteristics of a dielectric-coated coaxial helicalwaveguide in a lossy medium

In this paper, the authors discuss the propagation characteristics of a dielectric-coated coaxial helical waveguide in a lossy medium. The authors place emphases on the phase constant, propagation modes, magnetic fields distribution, and attenuation constant, when permittivity of the internal region is relatively small, two propagation modes exist and dominant components of their magnetic fields are different. Lastly, the authors discuss the relation between the attenuation constant and permittivities     

HIRF penetration and PED coupling analysis for scaled fuselage models using a hybrid subgrid FDTD(2,2)/FDTD(2,4) method

A hybrid method of subgrid FDTD(2,2) with FDTD(2,4) is presented. Both the standard FDTD(2,2) as well as the hybrid technique are applied to shielding effectiveness analysis of a scaled model of a Boeing 757. Also, analysis of EMI generated by personal electronic devices is performed on the same scaled fuselage model.     

FDTD simulations and measurements for cell phone with planar antennas

The Finite-Difference Time-Domain (fdtd) method is used to calculate the cellular phone far and near field and the specific absorption rate (sar) in the user’s head. The conventional λ/4 monopole and a simple planar antenna are simulated and measured. The simulated results are in good agreement with those measured for thevswr and for the radiation patterns on the horizontal and vertical planes. These results show that significant improvements in the antenna radiation efficiency and in the reduction of thesar in the head are obtained when planar antennas are used.     

Frequency characteristics of superconductive coaxial lines

By precise manufacturing methods, 1.6-mm 50-Ω superconductive coaxial lines having few impedance irregularities (0.2 to 0.3 Ω) have been produced. Their attenuation constant at 4.2 K shows a smooth gradual increase upto 12.4 GHz in proportion to frequency. The loss at 1 GHz is 0.7 dB/km for the line using tetra fluoroethylene-hexa fluoropropylene (FEP) and 1.6 dB/km for the line using polyethylene (PE).     

Radiation characteristics of coaxial waveguides as a small primary feed

The radiation patterns of coaxial waveguides with a TE11 exciting mode are computed numerically. It is shown that by a proper selection of the coaxial aperture dimensions the symmetry of the copolar patterns can be improved considerably. Coaxial radiators can therefore be designed as a useful small primary feed for paraboloid reflector antennas.     

Radiation and matching characteristics of a novel dual-band dielectric loaded coaxial horn

Copolar and crosspolar radiation as well as matching characteristics of a novel dual-band coaxial hybrid-mode feed horn with partial dielectric loading [1] for reflector antennas have been numerically and experimentally investigated. In comparison with dual-band corrugated horns this horn has higher crosspolar level, but provides larger band separation and rather good electrical performances over a wide frequency range (20% and more) within each operational frequency band. Furthermore, the main concept of the coaxial feed system can be easily extended for multi-band cost-effective applications in reflector antennas with polarization diversity.     

Conformal finite-different time-domain (FDTD) with overlappinggrids

It is shown how to use many overlapping conformal grids in the neighborhood of the scatterer while using a rectangular grid away from the scatterer for solving Maxwell's equations. The locally conformal grids allow better approximation of the boundary condition on the scattering object while the rectangular grid preserves the simplicity and accuracy of the regular finite-difference time-domain (FDTD) algorithm. These grids overlap typically about three zones. It is shown how to connect together the calculations done in different overlapping grids     

Finite-difference time-domain (FDTD) analysis of magnetic diffusion

Problems with very slow waveforms or very long diffusion times may be difficult to treat using finite-difference time-domain techniques because of the Courant stability condition. Problems of this class, however, often prove to have a response which does not depend on the speed of light. The examples presented here show cases where internal fields do not change if c is reduced by as much as five orders of magnitude. This permits Δt to be proportionally increased. For simplicity much of this paper is restricted to one dimension, although generalization to three dimensions is also presented. The author considers an aluminum enclosure. Initially, the transient field will induce eddy currents on the enclosure which exactly cancel the external field and exclude it from the enclosure interior. This scheme has been, in fact, proposed to shield large systems which contain magnetic memories     

Radiation characteristics of a cavity-backed cylindrical gap antenna

The input impedance and the equatorial radiation patterns of a VHF cavity-backed cylindrical gap antenna are derived and compared with experiments. The experiments generally support the computations, provided that the gap dimension is neither larger than about 1/100 of a wavelength, nor so thin that mechanical tolerances in the feed design become important. The results show that the tuning, impedance bandwidth, and the radiation patterns of this antenna can be controlled very accurately by adjusting the internal radius and height of the cavity. Salient points of this antenna are its wide-band characteristics (10-percent bandwidth), its pattern circularity, and particularly the fact that it can be made an integral part of a space vehicle.     

Propagation characteristics of inhomogeneous dielectric-filled coaxial cables

A general program has been written for calculating the attenuation and phase characteristics of the first TM surface-wave mode in an inhomogeneous dielectric-filled coaxial cable. As an example, the program has been used to study the special case of a coaxial cable with a very thin dielectric layer on the inner conductor.     

耦合型漏泄同轴电缆传输和耦合特性研究

针对泄漏同轴电缆作为分布式传感器应用于物联网和智能家居的室内安防入侵检测时，运用全波仿真软件HFSS不能有效仿真长距离的耦合漏缆的问题，提出了一种等效电路模型.利用参数提取软件，先提取单个开槽的缝隙单元的等效电路模型，然后借助于传输线理论，利用四个传输矩阵级联得到整段漏泄同轴电缆的传输矩阵.并考虑两根漏缆缝隙间相互耦合，提出了表征耦合特性的等效电路模型.将等效电路模型利用商用软件高级设计系统（advanced design system，ADS）进行电路搭建与仿真.仿真结果表明，本文提出的两根漏缆的等效电路模型与全波仿真结果非常符合，可以快速地仿真长距离的耦合漏缆结构，并大大节约了仿真时间.     

FDTD treatment of partially magnetized ferrites with a newpermeability tensor model

This paper outlines the finite-difference time-domain (FDTD) treatment of partially magnetized ferrites characterized by a permeability tensor model, which was recently published. Its causal aspect makes this tensor well adapted to time-domain simulations. Validation is demonstrated for a resonant ferrite structure, Numerical and analytical results are compared, showing good agreement     

波导电路中运用FDTD法时的激励问题

本文总结了在波导管电路中运用ＦＤＴＤ法时的激励方法,包括建立连接边界和选择合适的激励波形,数值计算结果证实,建立连接边界和选择合适的激励波形可以在尽量小的计算空间中,利用尽量少计算时间得到波导电路的响应。