G.I. Costache

Finite element method applied to modeling crosstalk problems on printed circuit boards

In modeling crosstalk on printed circuit boards, the distributed parameter transmission line model is applied to include the effects of electromagnetic coupling between tracks. Starting with a finite element approach, a computer model for predicting crosstalk voltages and currents in a general n+1 multiconductor configuration is outlined. After the currents on each track are calculated by using the finite element method and modal analysis, a simple radiation model is used to calculate the radiated field produced by the printed circuit boards for a frequency range of 30-1000 MHz. The algorithm presented was implemented in a series of Fortran programs, and the results obtained using this procedure compare very well with available theoretical and experimental data. >

Propagation of transients in dispersive dielectric media

The propagation of transient electromagnetic fields in dispersive dielectric media is studied. The dielectric medium is assumed to be linear, isotropic, and homogeneous, and is described by the Debye model. Incident fields are assumed to be transverse electromagnetic plane wave pulses. The dielectric body can assume the form of infinite half space or an infinite circular cylinder, either of which may be homogeneous or stratified. The electric fields induced in the dielectric are calculated from time-domain Maxwells equations using the finite-difference time-domain method. >

SPICE simulation used to characterize the cross-talk reduction effect of additional tracks grounded with vias on printed circuit boards

In analog and digital electronic systems, cross-talk between tracks on a printed circuit board can degrade the performance of equipment operations. A technique based on additional tracks grounded by vias, with which the cross-talk can be reduced by 50-90%, is presented. The circuit analysis code SPICE is used to analyze a lumped-circuit Tee structure model of three coupled lines. The via discontinuities are modeled in a novel way, which accounts for their transient skin-effect resistance. Both the cross-talk model and the cross-talk reduction technique are validated with measured results for signals of 50-1000 MHz, and risetimes of 5 ns. It is also shown how the far-field radiation from the circuit board is reduced with the introduction of additional grounded tracks. >

Transmission line matrix modeling of disperse wide-band absorbing boundaries with time-domain diakoptics for S-parameter extraction

A numerical modeling procedure based on Johns time-domain diakoptics approach with space interpolation techniques for efficient transmission-line matrix (TLM) analysis of two-dimensional microwave circuits is discussed. Frequency-dispersive boundaries are represented in the time domain by their characteristic impulse response or numerical Greens function (Johns matrix). Almost perfect wide-band absorbing boundary conditions have been obtained with this technique, permitting accurate characterization of waveguide discontinuities and compounds. The application of these techniques saves considerable computer run time and memory when compared with conventional TLM analysis. >

Skin-effect considerations on transient response of a transmission line excited by an electromagnetic pulse

The electromagnetic pulse can cause degradation of modern digital and analog devices. Many analytical models have been used extensively to study the susceptibility of equipment related to EMI/EMC (electromagnetic interference/electromagnetic compatibility) engineering, but the emphasis has been mainly on lossless transmission lines. This work takes into account the transient skin-effect of a transmission line exposed to a time-varying electromagnetic field. Beginning with the classical transmission line theory, the transient skin-effect of a transmission line and the equivalent sources due to the external fields are incorporated. As a result, an integral-differential equation is derived. By using the finite-difference-time-domain (FD-TD) approach, the induced voltages onto the line are predicted. There is also a discussion of the numerical approach and the propagation of the predicted induced voltage. >

Finite-element method applied to EMC problems (PCB environment)

In a printed circuit board environment, the solution domain is highly inhomogeneous, and analytic expressions for design parameters are very difficult to obtain, even for the simplest configuration. The finite element method (FEM) offers an attractive alternative for solving the problem in all its aspects including the determination of parasitic effects. A problem of practical interest, related to crosstalk, is formulated to be solved using the FEM. The technique is first applied to obtain the field distribution, and then the field is used to calculate transmission line parameters of conducting tracks on printed circuit boards. FEM is used to solve a radiation problem in three dimensions. The solution is used to predict far-field radiation levels of electronic equipment from near-field measurements. >

Numerical extraction of partial inductance of package reference (power/ground) planes

This paper presents a numerical approach for extracting the partial inductance of package reference (power/ground) planes using the finite element method. A simpler method is proposed to determine the partial inductance between two or three sources and sinks which are of importance in EMC/EMI considerations. An application is presented to verify the partial inductance obtained by R. Lee Hill et al (see Proc. IEEE Int. Symp. EMC, p.116-120, August 1994), where the partial inductance was modeled by a symmetrical coplanar circuit. Good agreement has been found between the numerical and theoretical results.

Far-field predictions from near-field measurements using an exact integral equation solution

This paper presents a new approach to derive far-field data needed in antenna and EMI/EMC testing from near-field measurements. An exact integral equation solution to the wave propagation problem is used to transform the near-field data to the far field. The method requires near-field measurements on two closed surfaces enclosing all sources and inhomogeneities. The approach is validated with numerical simulation of measurements of fields radiated from a known antenna. >

Finlines in rectangular and circular waveguide housings including substrate mounting and bending effects-finite element analysis

The finite-element method is used to derive the dispersion characteristics and field components of dominant and higher order modes in finlines. The method is accurate and covers the metallization thickness, substrate mounting grooves, bending of the substrate, and arbitrary cross sections. Results for structures already obtained with other methods have been found to agree well with available data. As a new contribution, the effect of substrate bending on the propagation constant is studied. The dispersion characteristics for the dominant and higher order modes for bilateral finlines in circular waveguide housing are calculated. The field plots for all the modes are given. >

Radiation from microstrip transmission lines

The radiation properties of a microstripline configuration are investigated. The electric field produced by a microstripline on a printed circuit board is calculated analytically using the magnetic vector potential and numerically using the method-of-moments technique, for comparative purposes. To simplify the calculations the microstripline is replaced by an open-wire transmission line. A frequency of 100 Hz, which is in the range known to cause problems with FCC compliance of digital products, is used. The objective is to calculate the electric field one would expect to measure at a test site used for FCC compliance measurements, as opposed to the free-space results obtained when ground reflections are not considered. It is shown that replacing the microstrip structure with a two-wire transmission line for the calculations, although not rigorous, provides suitable accuracy for EMC applications.<<ETX>>