Two-dimensional semiconductor analysis using finite-element method

Two-dimensional simulation of semiconductor devices using a finite-element formulation is described. In the present analysis, Poisson's equation is solved by a finite-element method, based on the variational principle, and current continuity equations are solved by a method of weighted residuals. The advantage of this method is mentioned. In order to demonstrate the validity of this method, a bipolar n-p-n transistor is analyzed, considering the generation-recombination term. Not only voltage-current characteristic, but also junction capacitance and cutoff frequency are calculated. Then transistor behavior under inverse mode by using the n-type buried layer as a common emitter is discussed.     

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     

Microwave imaging using the finite-element method and a sensitivity analysis approach

A method for reconstructing the constitutive parameters of two-dimensional (2-D) penetrable scatterers from scattered field measurements is presented. This method is based on the differential formulation of the forward scattering problem, which is solved by applying the finite-element method (FEM). Given a set of scattered field measurements, the objective is to minimize a cost function which consists of two terms. The first is the standard error term, which is related to the measurements and their estimates, while the second term, which is related to the Tikhonov regularization, is used to heal the ill posedness of the inverse problem. The iterative Polak-Ribière nonlinear conjugate gradient algorithm is applied to the minimization of the cost function. During each iteration of the algorithm, the direction of correction is computed by using a sensitivity analysis approach, which is carried out by an elaborate finite-element scheme. The adoption of the finite-element method results in sparse systems of equations, while the computational burden is further reduced by applying the adjoint state vector methodology. Finally, a microwave medical imaging application, which is related to the detection of proliferated bone marrow, is examined, while the robustness of the proposed technique in the presence of noise and for different regularization levels is investigated.     

Shaped reflector antenna analysis using the Jacobi-Bessel series

The physical optics approximation is employed to derive the radiation integral for a doubly curved offset reflector antenna illuminated by an arbitrary source. A novel procedure is presented for expressing the radiation integral in terms of a summation of Fourier transforms of an "effective" aperture distribution which includes the effect of the curvature of the surface. The Jacobi-Bessel series is used to evaluate the Fourier transforms. The vector nature of the far-field pattern is studied by evaluating its three Cartesian components in a unified fashion. The rapid numerical evaluations of the expressions obtained are demonstrated via extensive test cases. In particular, the scattering characteristics of symmetric and offset parabolic, spherical, and shaped reflectors are studied in detail, and comparisons are made with other available data.     

Electrooptic mapping and finite-element modeling of the near-fieldpattern of a microstrip patch antenna

A comprehensive electrooptic field-mapping technique is applied to the characterization of near-field radiation patterns above a microstrip patch antenna. The amplitude and phase maps of three orthogonal electric-field components, measured using electrooptic crystals above the patch, also have revealed the transition from the near field to the far field of the radiation pattern. In addition, experimental results have been compared with a finite-element method (FEM) simulation. The measurememts show superior results to the FEM simulation, especially in terms of spatial resolution and data acquisition times. Furthermore, the scattering parameter S₁₁ for the patch antenna has been calculated from the electrooptic measurement results of standing waves on the feeding line and compared with results from a conventional network analyzer     

Scalar finite-element analysis of optical-fiber facets

A numerically efficient scalar analysis of optical-fiber-facet problems based on the finite-element scheme is presented. By adopting the Taylor's series expansion of the characteristic matrix at the discontinuity plane, an accurate and yet numerically efficient approach is suggested for calculating the reflected and transmitted fields at discontinuities with circular symmetry. The scattering of the scalar LP/sub 01/ mode and higher order LP/sub 0m/ modes at both uncoated and coated optical-fiber facets has been analyzed, and the accuracy of the present finite-element approach is revealed through the excellent agreement of its results with those in the literature.     

Channel characterization using bispectral analysis

A method of characterizing a slowly varying linear channel in the presence of white Gaussian noise is proposed. The method uses a non-Gaussian probing signal and performs a bispectral analysis of the received signal     

Wide-angle finite-element beam propagation method using Padeapproximation

A wide-angle beam propagation method using a finite-element scheme is presented. The method is based on Pade approximations expressed with polynomial matrix functions. Tilted-waveguide propagation characteristics are calculated, and an analysis for a steeper waveguide is shown to be allowed when proposed higher-order Pade approximations are used     

FDTD分析准八木天线的算法实现

介绍时域有限差分（FDTD）法计算准八木天线驻波比的算法实现方法。文中利用模型描述文件对天线进行了建模和网格划分;将各向异性完全匹配层（UPML）吸收边界分区编写,并利用区域的对称性简化了程序;采用带内阻的电压源作为激励源;最后从总电压中分离出入射电压和反射电压,得到了准八木天线的驻波比。实际制作了一个准八木天线并进行了测试,计算结果与实测结果基本一致,表明该实现方法是正确和有效的。     

Magneto-transport characterization using quantitative mobility-spectrum analysis

A quantitative mobility spectrum analysis (QMSA) of experimental Hall and resistivity data as a function of magnetic field is presented. This technique enables the conductivity contribution of bulk majority carriers to be separated from that of other species such as thermally generated minority carriers, electrons, and holes populating n and p doped regions, respectively, and two-dimensional species at surfaces and interface layers. Starting with a suitable first trial function such as the Beck and Anderson mobility spectrum analysis (MSA), a variation on the iterative procedure of Dziuba and Gorska is used to obtain a mobility spectrum which enables the various carrier species present in the sample to be identified. The QMSA algorithm combines the fully automated execution and visually meaningful output format of MSA with the quantitative accuracy of the conventional least-squares multi-carrier fitting procedure. Examples of applications to HgCdTe infrared detector materials and InAs/GaSb quantum wells are discussed. The ultimate goal of this paper is to provide an automated, universal algorithm which may be used routinely in the analysis and interpretation of magneto-transport data for diverse semiconductor materials and bandgap engineered structures.     

An efficient finite-element analysis of magnetooptic channelwaveguides

A finite-element method based on the scalar-wave approximation is developed for the analysis of magnetooptic waveguides. A simple and efficient iterative method is proposed for solving a nonlinear eigenvalue equation derived from the scalar finite-element approach. To show the validity and usefulness of this method, examples are computed for magnetooptic rib-type and ridge-type waveguides. The waveguide structures which have larger nonreciprocal phase shift are discussed     

Transient characterization of a novel ultrawide-band antenna: the scissors antenna

A new ultrawide-band (UWB) antenna named the "scissors antenna" has been designed specially for transient ultrawide-band applications. The scissors antenna, which is composed of conducting wires, radiates ultrashort pulses with very low dispersion. The radiation of this antenna has been characterized by a transient measurement method suitable for characterizing UWB antennas with very low dispersion. After a presentation of the scissors antenna, this measurement method is described. The last part of the paper presents a comparison between the radiation characteristics of the scissors antenna obtained by the transient measurements and those obtained by the classical harmonic measurements.     

Quasi-static finite-element analysis of a skewed microstripcrossover

In this work, we present a quasistatic analysis of a microstrip crossover on a dielectric substrate. The microstrips are located at different planes and may cross at an arbitrary angle. Capacitances and inductances are calculated from scalar potentials. For magnetostatic formulation, the boundary conditions for scalar potential are introduced by means of partitioning surfaces. The use of the adaptive finite element method provides the required flexibility with respect to the analyzed geometry, optimal discretization and good efficiency     

Holey fiber analysis through the finite-element method

A holey fiber (HF), having very complex hole geometry, is studied by means of a numerical simulator for modal analysis based on the finite-element method (FEM). Polarization and dispersion properties as well as the full vector field distribution of the fundamental mode are investigated. The obtained numerical results show a good agreement with experimental ones reported in literature     

A two-dimensional finite-element analysis of reverberation chambers

A two-dimensional (2-D) analysis of reverberation chambers is performed at cutoff. The structure considered is lossless and corresponds to an infinite quality factor (Q) chamber. The concept of frequency stirring is used to generate field data for a discrete set of modes and the resulting statistics are analyzed. The field statistics are examined for TE and TM modes. This analysis yields statistics similar to the expected reverberation chamber statistics for the fields. Mechanical stirring is also examined and a connection to the peak-frequency deviation is presented     

Accurate finite-element analysis of dual-mode highlyelliptical-core fibers

A scalar finite-element method is used for investigating propagation characteristics of dual-mode highly elliptical-core fibers. The dispersion property, polarization modal birefringence, and spatial modal birefringence are calculated. To improve the accuracy of solutions, isoparametric curvilinear elements are introduced. The applicability of the scalar finite-element method for highly elliptical-core fibers is assessed by comparing the results obtained with the vector finite-element method. An approximate simple approach, in which an elliptical-core is replaced by an appropriate rectangular-core, is also examined     

利用体面结合积分方程分析表面波天线辐射问题

提出了一类新型表面波天线,并分析其辐射特性。研究结合预修正快速傅里叶变换方法和矩量法的算法求解体面结合积分方程,快速准确分析金属介质混合问题。通过对比表面波天线的辐射方向图和驻波测试曲线,验证了算法的准确性。分析了该表面波天线的金属电流分布,说明该天线具有单振子天线的辐射特性,为天线高增益、小型化设计提供了思路。     

Evaluation of Sommerfeld integrals using Chebyshev decomposition[antenna analysis]

Sommerfeld integrals ensue when one uses a spectral-domain transformation to calculate fields of a dipole source in a homogeneous space or in a layered medium with planar boundaries. A new and efficient method of evaluating these integrals is presented. This method still converge in the case of unbounded homogeneous media or when source and observer are both on the boundary itself, as in microstrip lines. The integration is based on decomposition of the integrand into Chebyshev polynomials. Numerical results are given and compared with published literature     

Cross-shaped dielectric resonator antenna analysis using conformalfinite difference time domain method

A cross-shaped dielectric resonator antenna, designed for circular polarisation, is analysed via the conformal finite difference time domain technique. The conformal technique, which can handle canted surfaces that do not conform to the Cartesian system of co-ordinates, is used to generate accurate results with a relatively coarse mesh, e.g. it is shown that the conformal FDTD offers a 2:1 advantage over staircasing, without compromising accuracy