Michel M. Ney

A new finite-difference time-domain formulation and its equivalence with the TLM symmetrical condensed node

A finite-difference time-domain (FD-TD) formulation is described. It is shown that the finite-difference time-domain formulation is equivalent to the symmetrical condensed node model used in the transmission line matrix (TLM) method. The TLM method can be formulated exactly in a finite-difference form in terms of total field quantities. It is shown that, due to a better field resolution and fulfilment of continuity conditions, the FD-TD formulation or its TLM equivalent model give better convergence and accuracy than the traditional FD-TD method. This is illustrated by numerical results pertaining to a finned waveguide. >

Absorbing and connecting boundary conditions for the TLM method

Absorbing and connecting boundary conditions are implemented for the transmission-line matrix (TLM) method. The approach is based on an equivalence previously established between the finite-difference-time-domain (FD-TD) method and the TLM method. Boundary conditions presently used for the FD-TD algorithm can be transformed into conditions that can be interfaced with two-and three-dimensional (2D and 3D) TLM schemes. Additional conditions are introduced for 3D-TLM symmetrical condensed node simulations to suppress instabilities caused by spurious modes, inherent to the model, and which are amplified by absorbing boundaries. Numerical results and the comparison with other methods show the good performance of the proposed algorithms. >

Striction and skin effects on the internal impedance value of flat conductors

A frequency domain analysis is used to derive closed formulas giving the internal impedance of a rectangular, flat, nonperfectly conducting solid conductor modeling a ground plane. The approach takes into account the skin effect due to the finite conductivity of the ground plane and the increase of the impedance due to the confinement of the current lines at the contact points, called the striction effect. The computed results show that, in certain situations and within the frequency range of interest for the electromagnetic interference and compatibility community, the internal impedance calculated can no longer be neglected with respect to the external impedance when return conductors are located very near the ground plane. >

A new boundary description in two-dimensional TLM models of microwave circuits

A boundary representation for the two-dimensional transmission line matrix (TLM) method of numerical analysis is described. In conventional TLM simulations, boundary conditions are realized by introducing the appropriate impulse reflection coefficients halfway between two nodes. Since the total field quantities are only defined on the nodes, their values at the boundary are not directly available from TLM solutions. The TLM procedure is modified so that boundaries can be placed across the nodes. The boundary conditions in TLM can then be formulated in terms of the field boundary conditions derived from Maxwells equations rather than in terms of impulse reflection coefficients. The essential differences between the conventional TLM and the proposed procedure are presented. Examples are given for several typical problems, and the results obtained with the two methods are compared. These are found to be in excellent agreement. >

A Study of Electric-Field Breakdown in E-Plane Lines at Centimeter and Millimeter Wavelengths

The microwave field breakdown in various E-plane transmission lines is investigated theoretically in the frequency range from 1 to 140 GHz. The influence of frequency, pressure, temperature, and inhomogeneity of the applied field on the breakdowm field value is discussed. The peak power-handling capability of unilateral and bilateral finlines is determined theoretically using a quasi-static evaluation of the field distribution. It is found that finlines, even with small gap widths, can handle pulse power levels well above the capability of present solid-state devices. Preliminary breakdown measurements in X-band have confirmed the validity of the theoretical predictions.

A new procedure for interfacing the transmission line matrix (TLM) method with frequency-domain solutions

The authors present a new procedure that interfaces the transmission-line matrix (TLM) method with frequency-domain solutions of electromagnetic fields. Frequency-domain solutions are transformed into appropriate time-domain sequences using the discrete Fourier transform (DFT). Hence, the corresponding boundary Johns matrix can be determined with minimum computational effort. The subsequent treatment consists in convolving the streams of TLM impulses incident on the boundary with a Johns matrix generated with the new approach. The method is used to obtain the time-domain reflection sequence of wideband absorbing terminations in a rectangular waveguide in the dominant mode operation. In addition, the time-domain analysis of pulse penetration through a sheet with high, but finite, conductivity is presented. Good results demonstrate the efficiency of the proposed procedure. >

Study of absorbing boundary conditions in the 3D-TLM symmetrical condensed node model

The TLM (transmission line matrix) method is a numerical technique based on temporal and spatial sampling of electromagnetic fields. As with the FD-TD (finite-difference time-domain) method, the absorbing boundary conditions are needed to truncate computational regions when open structures are simulated. The FD-TD absorbing boundary conditions have been adapted to and implemented in the 3D-TLM symmetrical condensed node model. It is demonstrated that instability may occur due to spurious modes of the 3D-TLM condensed node mesh.<<ETX>>

Transient striction and skin effects on voltage drop across flat conductors

Closed formulas for computing the time-domain voltage between the contact points of a ground plane produced by conducted currents are presented. The approach takes into account realistic effects such as the transient skin effect and the confinement of current lines at the contacts, known as the transient striction or constriction effect. The contribution of external inductance depends on the geometry and relative position of the return conductor and is not addressed in the present paper. Calculated results are presented for various parameters, such as the dimensions of the ground plane and contacts and the type of current time-function. Using a simple geometrical model, computed results show that the ground voltage may become non-negligible when short rise-time signals are considered.

A new finite-difference time-domain formulation equivalent to the TLM symmetrical condensed node

A finite-difference-time-domain (FD-TD) formulation is shown to be exactly equivalent to the symmetrical condensed node model used in the transmission line matrix (TLM) method. The proposed FD-TD formulation results in a kind of condensed model where both electric and magnetic field components are defined at the center of a unit cell and at mid-points between adjacent nodes. Due to a better field resolution and fulfillment of continuity conditions, the FD-TD formulation or its TLM equivalent model is shown to have less dispersion and better accuracy than the traditional FD-TD method based on K.S. Yees (1966) scheme.<<ETX>>

Two-dimensional transmission line matrix (TLM) simulation of the electromagnetic fields in a rectangular section of a discretized GaAs MESFET channel with arbitrary doping profile

A two-dimensional lossy shunt TLM network is adapted to simulate the Maxwell field equations of a GaAs MESFET. By discretizing the channel into rectangular sections of single thickness, the proposed TLM technique is shown to be able to simulate the calculated electromagnetic fields of an arbitrarily doped channel section. Theoretical and experimental results are compared for uniform and nonuniform channel conductivity.<<ETX>>