Wide-band network characterization by Fourier transformation of time-domain measurements

A novel method of measuring driving-point and transfer impedance over a wide spectrum rapidly and with good accuracy uses a digital computer to transform the pulse response of a network into the frequency domain. A sampling oscilloscope provides the time transformation needed for data acquisition. The method and laboratory technique are discussed. Experimental data show agreement within 12 percent between the data from a single pulse measurement and bridge measurements over a band of 40 harmonic frequencies, i.e., 25-1000 MHz. Fundamental accuracy and bandwidth are believed to be substantially greater than these figures.     

A two-dimensional time-domain near-zone to far-zone transformation

A 2D version of a time-domain transformation useful for extrapolating 3D near-zone finite-difference time-domain (FDTD) results to the far zone is outlined. While the 3D transformation produced a physically observable far-zone time-domain field, this is not convenient for the 2D case. However, a representative, 2D far-zone time-domain result can be obtained directly. This result can then be transformed to the frequency domain using a fast Fourier transform, corrected with a simple multiplicative factor, and used, for example, to calculate the complex wideband scattering width of a target. If an actual time-domain far zone result is required, it can be obtained by inverse Fourier transform of the final frequency-domain result     

Transient analysis of a cable with low-conducting layers by a finite-difference time-domain method

The impedance and admittance formulas of a cable with low-conducting layers have not yet been derived, and thus a transient analysis considering the layers cannot be carried out sufficiently by an existing transient analysis program such as the Electro-Magnetic Transients Program. The present brief has analyzed a transient response of a power cable including low-conducting layers using a finite-difference time-domain method. Transient current waveforms at both ends of the cable are distorted depending on the conductivity of the low-conducting layers. Also, the propagation velocity of a surge current is dependent on it. When the conductivity of low-conducting layers is around 10/sup -3/ S/m, the shunt admittance of the cable dominates the above phenomena. On the other hand, they are ascribable to the series impedance when the conductivity is about 10 S/m.     

Finite-volume time-domain analysis of a cavity-backed Archimedean spiral antenna

This paper presents a comprehensive analysis of a broadband (2-18 GHz) cavity-backed Archimedean spiral antenna. The simulation of the device is performed using the finite-volume time-domain method. The high geometrical flexibility of this method permits a detailed modeling of the antenna including the thin substrate, the feeding balun, and the cavity loaded with a honeycomb absorber. The simulated far-field radiation patterns and the return loss are compared to measurements, showing an excellent agreement over the whole frequency band. The radiation mechanism of the spiral is visualized by observing the current distribution on the spiral arms for both pulsed and harmonic excitation modes.     

An improved near- to far-zone transformation for thefinite-difference time-domain method

Near- to far-zone transformation for the finite-difference time-domain (FDTD) method can be performed by integration of the equivalent electric and magnetic currents originating from scattered electric and magnetic fields on a surface enclosing the object. Normally, when calculating the surface integrals, either the electric or magnetic fields are averaged since the electric and magnetic fields are spatially shifted in the FDTD grid. It is shown that this interpolation is unnecessary and also less accurate than if an integration is performed on two different surfaces. It is also shown that the accuracy of the far-zone transformation can be further improved if the phase is compensated with respect to a second-order dispersion corrected wavenumber. For validation, scattering results for an empty volume, a circular disk, and a sphere are compared with analytical solutions     

Optical adaptive equalization of high-speed signals using time-domain optical Fourier transformation

This paper describes a new distortion-free optical transmission method that can eliminate any kind of linear perturbation including jitter, polarization-mode dispersion, and higher order dispersion as well as time-varying dispersion. This method uses transform-limited pulses and time-domain optical Fourier transformation (OFT). With this technique, particular attention is given to the spectral envelope profile of the transmitted signal, which is unchanged regardless of the type and magnitude of the linear perturbation in the transmission fiber. OFT converts the unchanged spectral profile into the time domain and allows to obtain undistorted original waveforms at the output. Experimental and analytical results to show the effectiveness of this method are presented, especially when the method is applied to high-speed signals up to 160 Gb/s, which are sensitive to both higher order and time-varying dispersions. This paper also describes a new all-optical time-domain Fourier transformation technique that uses an optical parabolic pulse. This technique is promising, with a view to improving the elimination of distortion at 160 Gb/s and above.     

在时域分析Zobel网络

为使电抗性的负载对于易发生稳定性问题的驱动源来说变成纯电阻负载,采用Zebel网络是十分适宜的(参考文献1).典型的情况就是驱动扬声器的音频功率放大器,其中,扬声器的初步近似模型是一个电感器和一个电阻器串联(图1a).增加一个与R1L串联网络并联的R2C串联网络,便可组成一个Zobel网络(图1b)电路.如果R2阻值和C电容值选择得当,则驱动源就会是一个纯电阻性负载.     

Finite-element time-domain analysis of axisymmetrical radiators

A method of analysis which permits the computation of electromagnetic fields directly in the time domain using the finite element method (FEM) is presented. The method considers coaxially-driven axisymmetrical structures. A new way of implementing absorbing boundary conditions for the coaxial feed is discussed. The method has been successfully used to model coaxially-driven axisymmetrical monopole antennas for a Gaussian pulse excitation. Generally, the results obtained show good agreement with previously published numerical and experimental data     

Numerical analysis of the whispering gallery modes by thefinite-difference time-domain method

The finite-difference time-domain (FDTD) method is used to analyze the whispering-gallery modes of microdisk lasers. The method takes no a priori assumption. It solves the Maxwell's equations directly while taking into account the actual structure of the microdisk. The numerical results are in agreement with experimentally measured spectrum. Our Q values, however, are higher than previously published theoretical results. By calculating the resonant wavelengths and Q factors for different disk sizes, we demonstrate that the FDTD can be used to optimize the design of microdisk lasers     

Scattering analysis by the multiresolution time-domain method usingcompactly supported wavelet systems

We present a formulation of the multiresolution time-domain (MRTD) algorithm using scaling and one-level wavelet basis functions, for orthonormal Daubechies and biorthogonal Cohen-Daubechies-Feauveau (CDF) wavelet families. We address the issue of the analytic calculation of the MRTD coefficients. This allows us to point out the similarities and the differences between the MRTD schemes based on the aforementioned wavelet systems and to compare their performances in terms of dispersion error and computational efficiency. The remainder of the paper is dedicated to the implementation of the CDF-MRTD method for scattering problems. We discuss the approximations made in implementing material inhomogeneities and validate the method by numerical examples     

A time-domain analysis of CCD video integrators

An analysis of the growth of spurious signals in recirculating CCD delay lines or video integrators is presented. Calculated values of the relative magnitudes of the primary and first two secondary signals are given as functions of the loop gain, the transfer efficiency and the number of transfers.Three techniques are discussed for reducing the limiting effects of secondary growth on the loop gain, and thereby increasing the possible signal to noise ratio improvement of CCD integrators.     

Nonlinear time-domain analysis of injection-locked microwave MESFEToscillators

In this paper, injection-locked MESFET oscillators are analyzed using several numerical models. The injection-locking behavior of the van der Pol equation and of a more complex representation using the Curtice-Cubic MESFET model are investigated. Analysis and experimental results are compared for an NE71083 transistor oscillator operating at 0.5 GHz. The deficiencies of using a van der Pol oscillator model are pointed out. Time-domain results from the complex model exhibiting multicycle and apparently chaotic behaviors are also examined, and point to problems with common nonlinear simulation techniques for these circuits     

金属透镜的色散时域有限差分法研究

为克服传统时域有限差分法(FDTD)不能计算色散材料的困难,给出了一种基于Drude模型的色散FDTD算法,并推导出具体的差分公式。将该方法用于模拟金属透镜的聚焦功能,结果与已有理论吻合。本文方法完全适用于分析电导率与频率有关的各种色散材料所构建的光波导。     

Discussion of de-embedding techniques using time-domain analysis

De-embedding is a mathematical inverse operation used in network analysis to separate and obtain differences. The time-domain analysis process saparates reflections, identifies them, and allows selected reflections to be analyzed. This paper uses both techniques to explain and illustrate the results.     

A time-domain feedback analysis of filtered-error adaptive gradientalgorithms

This paper provides a time-domain feedback analysis of gradient-based adaptive schemes. A key emphasis is on the robustness performance of the adaptive filters in the presence of disturbances and modeling uncertainties (along the lines of H^∞-theory and robust filtering). The analysis is carried out in a purely deterministic framework and assumes no prior statistical information or independence conditions. It is shown that an intrinsic feedback structure can be associated with the varied adaptive schemes. The feedback structure is motivated via energy arguments and is shown to consist of two major blocks: a time-variant lossless (i.e., energy preserving) feedforward path and a time-variant feedback path. The configuration is further shown to lend itself to analysis via a so-called small gain theorem, thus leading to stability and robustness conditions that require the contractivity of certain operators. Choices for the step-size parameter in order to guarantee faster rates of convergence are also derived, and simulation results are included to demonstrate the theoretical findings. In addition, the time-domain analysis provided in this paper is shown to extend the so-called transfer function approach to a general time-variant scenario without any approximations     

Performance analysis of FET microwave devices by use of extended spectral-element time-domain method

The extended spectral-element time-domain (SETD) method is employed to analyse field effect transistor (FET) microwave devices. In order to impose the contribution of the FET microwave devices into the electromagnetic simulation, the SETD method is extended by introducing a lumped current term into the vector Helmholtz equation. The change of currents on each lumped component can be expressed by the change of voltage via corresponding models of equivalent circuit. The electric fields around the lumped component must be influenced by the change of voltage on each lumped component, and vice versa. So a global coupling about the EM–circuit can be built directly. The fully explicit solving scheme is maintained in this extended SETD method and the CPU time can be saved spontaneously. Three practical FET microwave devices are analysed in this article. The numerical results demonstrate the ability and accuracy of this method.     

Finite-difference time-domain analysis of HF antennas on helicopterairframes

In this paper, the finite-difference time-domain (FDTD) method with the Berenger perfectly matched layer (PML) absorbing boundary condition (ABC) is used to model the radiation characteristics of high frequency (HF) antennas operating in the 2-30 MHz range on a full-scale helicopter. The computed input impedance of both antennas is compared with actual measurements from an operational full-scale helicopter and also with measurements on a scale model NASA generic advanced attack helicopter (GAAH). To study the coupling effects of the helicopter fuselage on the antenna systems, the S-parameters are computed and compared with measurements on the NASA GAAH scale model. Finally, computed gain patterns are compared with actual in-flight measurements of the antenna systems on an operational full-scale helicopter     

Finite-difference time-domain analysis of flip-chip interconnectswith staggered bumps

This paper presents finite-difference time-domain (FDTD) analysis of flip-chip interconnects. Transitions between coplanar waveguides on the chip and the mother board are investigated over a broad band of frequency by means of Fourier transform of the time-domain results. Objectives of the analysis include the evaluation of bump reflection and insertion loss as well as the reconfiguration of the transition to improve package performance. Novel designs have been developed and presented to reduce the effects of package discontinuities and asymmetry. Staggering the bumps has been found to reduce reflection and insertion loss over a broad band of frequency. A reduction In bump reflection of up to 8 dB per transition can be achieved by staggering the ground and signal connects. The degradation in package performance due to structure asymmetry is also studied. The present designs have also been found to reduce the effects of flip-chip asymmetry on insertion and reflection losses     

Finite-difference, time-domain analysis of lossy transmission lines

An active and efficient method of including frequency-dependent conductor losses into the time-domain solution of the multiconductor transmission line equations is presented. It is shown that the usual A+B√s representation of these frequency-dependent losses is not valid for some practical geometries. The reason for this the representation of the internal inductance the at lower frequencies. A computationally efficient method for improving this representation in the finite-difference time-domain (FDTD) solution method is given and is verified using the conventional time-domain to frequency-domain (TDFD) solution technique     

Finite-difference time-domain analysis of the Celestron-8 telescope

Electromagnetic interference analyses of large complex systems demand large computational resources and give limited information on general types of systems. A finite-difference time-domain (FDTD) code was used to determine the response of a “generic” optical system to microwave radiation. A plane wave with a Gaussian pulse excitation was used along with “point sensors” within the system model to determine time and frequency response. In the low-frequency region, ramped sinusoidal excitation from a point within the sensor was used to determine angles of high sensitivity and field distributions within the sensor. From these field distributions, resonance modes were identified that are similar to those found in a simple cylindrical cavity