Fung-Yuel Chang

Transient Analysis of Lossless Coupled Transmission Lines in a Non-Homogeneous Dielectric Medium

This paper presents an effective method for computing the transient response of an n-conductor, coupled transmission-line system, which is characterized by multiple propagation modes of unequal phase velocities. To derive the computational algorithm, an equivalent circuit consisting of n decoupled transmission lines in conjunction with two congruence transformers was constructed and converted into two disjointed resistive n-ports. It is shown that the electrical behavior of the coupled transmission lines can be completely described by the static capacitance matrices of the conductor system. The experimental result obtained on a three-conductor, microstrip printed circuit was found to be in excellent agreement with the computed result.

Waveform relaxation analysis of RLCG transmission lines

F.H. Branins method of characteristics (1967) has been extended for the transient analysis of transmission lines with constant RLCG parameters. It has been further generalized for iterative waveform relaxation analysis. The sequence of waveforms relaxation generated by the iteration process has been identified as the series expansion of the transmission-line response functions. By incorporating the fast Fourier transform in the waveform analysis, a phenomenal two-order reduction of CPU time and one-order savings in computer memory have been achieved. Examples of RLCG lines driven by bipolar logic gates are given to illustrate the advantage of waveform relaxation over the discrete time simulation. >

Waveform relaxation analysis of nonuniform lossy transmission lines characterized with frequency-dependent parameters

An efficient method for the transient simulation of nonuniform frequency-dependent transmission lines is presented. The method consists of iterative waveform relaxation analyses of asymmetric disjoint two-port networks constructed with FFT waveform generators and characteristic impedances synthesized by applying the Gauss-Marquardt optimization technique. The method can also be adapted for discrete-time analysis by replacing the FFT waveform generators with ideal transmission lines connected with waveshaping networks. Transient responses of uniform and nonuniform transmission lines with and without skin-effect parameters and terminated with linear and nonlinear loads are simulated for illustrations. The accuracy and efficiency of the relaxation technique are substantiated with exact analytical solutions and experimental data. >

Transient simulation of nonuniform coupled lossy transmission lines characterized with frequency-dependent parameters. I. Waveform relaxation analysis

Presents a waveform relaxation technique for simulating the transient response of nonuniform coupled transmission lines which are characterized with frequency-dependent parameters. The method consists of iterative waveform relaxation analysis of asymmetric disjoint resistive networks constructed with voltage-dependent voltage sources generated by applying the fast Fourier transform (FFT). The method requires neither convolution integration nor synthesis of lumped equivalent circuits for the simulation of the frequency-dependence of transmission-line parameters. Transient responses of uniform and nonuniform coupled transmission lines with and without skin-effect parameters and terminated with linear and nonlinear loads are simulated for illustration. The accuracy and efficiency of the relaxation technique are substantiated with exact analytical solutions and experimental data. >

Transient analysis of lossy transmission lines with arbitrary initial potential and current distributions

The method of characteristics has been generalized for the transient analysis of lossy transmission lines with arbitrary initial conditions. It is shown that traveling waves generated by the initial potential and current distributions can be simulated by voltage and current generators connecting to the terminals of the lossy transmission-line model consisting of ideal delay-lines and waveshaping networks synthesized by the modified Pade approximation. The discrete-time transient simulation requires neither the FFT nor convolution integral and is as efficient as the iterative waveform relaxation technique. Transient responses of lossy transmission lines with steady-state and transient initial potential and current distributions are simulated for illustration. >

The generalized method of characteristics for waveform relaxation analysis of lossy coupled transmission lines

The transient response of lossy coupled transmission lines is simulated by iterative waveform relaxation analyses of equivalent disjoint networks constructed with congruence transformers, fast-Fourier-transform waveform generators, and characteristic impedances synthesized by the Pade approximation. A two-order reduction of central-processing-unit time and a one-order savings in computer memory have been achieved. A lossy directional coupler is simulated for illustration.<<ETX>>

Relaxation simulation of transverse electromagnetic wave propagation in coupled transmission lines

An efficient method for computing the transient response of an n-conductor coupled transmission line system that supports transverse electromagnetic waves propagating at different velocities is presented. The method consists of iterative generations of travelling voltage waveforms by the method of characteristics and the waveform relaxation technique. It is shown that the spatial and temporal variations of conductor voltages and currents can be derived from the linear combinations of traveling waves and initial potential and current distributions. Closed-form analytical solutions and experimental data are given to substantiate the accuracy and efficiency of the relaxation technique. >

Transient analysis of microwave active circuits based on time-domain characteristic models

A modular method is presented to speed up transient simulation of microwave active circuits which consist of linear components and active devices that are often nonlinear. Firstly, the linear components and active devices are individually characterized by time-domain characteristic models (TDCMs) and lumped equivalent circuits, respectively, to reduce the computer memory. Then, based on deconvolution, the TDCMs of linear components are synthesized from the terminal voltages and currents of step voltage excitation, which are simulated by the finite-difference time-domain (FDTD) method. Finally, transient analysis of a one-dimensional (1-D) discrete-time system is applied to obtain the terminal responses of the microwave active circuits, in which a larger sampled step is chosen to reduce the simulation time. This method is employed to two realistic circuits to validate its efficiency and accuracy. The results are in good agreement with the time-consuming direct FDTD simulation of entire circuits.

Computer-aided characterization of TEM transmission lines

A method of characterizing a multiconductor transmissionline system, which supports transverse-electromagnetic (TEM) waves traveling at different velocities, has been developed. The method combines equivalent circuit concept and optimization search technique. It is shown that the coupled transmission-line parameters can be computed from a set of wave velocities and transformer ratios that characterize the decoupled equivalent network of the multiconductor system. A combination of the steepest descent and Fibonacci-search algorithms for determining the wave-propagation velocities from frequency-domain measurements has been formulated, along with an alternative method of computing the inductance parameters from the measured characteristic admittances and static capacitances. For illustration, numerical examples and experimental results are given.

TRANSIENT SIMULATION OF LOSSY COUPLED TRANSMISSION LINES CHARACTERIZED WITH FREQUENCY-DEPENDENT PARAMETERS

The method of characteristics is generalized to simulate the transient response of coupled transmission lines, which are characterized with frequency-dependent parameters. The discrete-time transient simulation is carried out from the equivalent decoupled transmission lines with an arbitrary set of characteristic impedances. The method eliminates the time-consuming convolution integration and has been adapted for iterative waveform relaxation simulation using the Fast Fourier Transform (FFT) for reduction of simulation cost. Examples are given to substantiate the accuracy and the efficiency of both discrete-time and waveform relaxation simulations.