Antonije R. Djordjevic

Time-domain response of multiconductor transmission lines

Evaluation of the time-domain response of multiconductor transmission lines is of great importance in the analysis of the crosstalk in fast digital circuit interconnections, as well as in the analysis of power lines. Several techniques for the computation of the line response, starting from the known circuit-theory parameters, are presented and evaluated. These methods are: time-stepping solution of the telegrapher equations, modal analysis in the time domain, model analysis in the frequency domain, and a convolution technique which uses line Greens functions. The last method can treat the most general case of lossy transmission lines with nonlinear terminal networks. Numerical and experimental results are presented to illustrate these techniques and to give insight into the crosstalk problems in fast digital circuits.

Wideband frequency-domain characterization of FR-4 and time-domain causality

FR-4 is one of the most widely used dielectric substrates in the fabrication of printed circuits for fast digital devices. This material exhibits substantial losses and the loss tangent is practically constant over a wide band of frequencies. This paper presents measured data for the complex permittivity of this material from power frequencies up to the microwave region. In addition it gives simple closed-form expressions that approximate the measured data and provide a causal response in the time domain.

Analysis of Lossy Transmission Lines with Arbitrary Nonlinear Terminal Networks

A novel method for transient analysis of Iossy transmission lines with arbitrary nonlinear terminal networks is presented. The uniqueness of this approach is that we develop time-domain Greens functions for the multiport transmission-line systems by terminating the ports in quasi-matched loads. This ensures Greens functions of a short duration. Hence, the amount of frequency-domain data necessary to obtain time-domain Greens functions is modest. These Greens functions are then convolved with the line port voltages. With this technique one can analyze responses of multiconductor transmission lines with arbitrary nonlinear loads (even with memory) as we have at any instant of time Thevenins equivalent of the linear portion of the system. An example is presented to illustrate the application of this technique to multiconductor nonlinearly loaded transmission lines.

Analysis of Time Response of Lossy Multiconductor Transmission Line Networks

Systems are considered consisting of an arbitrary number of multiconductor transmission lines joined and terminated by arbitrary linear networks. The fines are assumed to be Iossy, with frequency-dependent parameters. The system is analyzed in the frequency domain, and the inverse Fourier transform is used to obtain the time-domain response.

Microstrip antennas with suppressed radiation in horizontal directions and reduced coupling

Microstrip (patch) antennas usually strongly radiate in directions along the ground plane. This effect causes unwanted radiation patterns and increased coupling among array elements. Dielectric polarization currents are identified as physical sources of this radiation. A general technique is proposed to compensate these currents and suppress radiation in horizontal directions.

Closed-form formulas for frequency-dependent resistance and inductance per unit length of microstrip and strip transmission lines

Based on numerical results obtained from solutions to integral equations, other numerical results and theoretical considerations, a set of closed-form formulas is presented for approximate calculation of frequency-dependent resistance and inductance per unit length of microstrip and strip transmission lines. Extensive verifications reveal that the accuracy obtained by these closed-form formulas is better than 10% for a wide range of parameters. >

An investigation of delta-I noise on integrated circuits

Delta-I noise is the voltage induced between the power conductors (e.g. the ground and the V/sub cc/ planes) when a circuit connected between them switches from one state to another. The authors show that the physics of the noise is more complex, and that it is related to wave propagation effects. Delta-I noise should be present not only in integrated circuits (chips), but also in multilayered boards, where it should be pronounced when the transients are of the order of 1 ns or less. Investigation of the delta-I noise is carried out for a simplified model of power planes, using a wire-antenna numerical simulation program. The model includes the wave propagation effects, as well as radiation, but it does not include the effects of the dielectric filling the space between the planes. The results of the analysis clearly show that the inductive effects are important only for slower transients. For fast digital circuits the power planes actually form a resonator,which can have a high quality factor, and the delta-I noise can build up to very high voltage levels. >

Analysis of Arbitrarily Oriented Microstrip Transmission Lines in Arbitrarily Shaped Dielectric Media Over a Finite Ground Plane

A numerical analysis is presented for a multiconductor transmission line in multilayered Iossy, dielectric regions where the ground plane is of finite extent. The transmission fines are infinitely long and vary in cross section from finite to infinitesimally thin. The Greens function for such a two-dimensional transmission line involves an arbitrary constant. If the ground plane is infinite, the method of images could be used where this constant cancels out. However, in the case of a finite ground plane, the constant has to be evaluated. Here a numerical method is presented where the constant could be eliminated rather than evaluated by imposing the condition for the total charge to be zero. The transmission lines, dielectric regions, and the ground plane can have arbitrary cross sections.

Analysis of Finite Conductivity Cylindrical Conductors Excited by Axially-Independent TM Electromagnetic Field

A method is presented for the analysis of a system of cylindrical conductors, of large but finite conductivity, situated in a uniform dielectric and excited by an axially-independent TM electromagnetic field. The analysis is based on separating the space into the region exterior to the conductors and regions interior to the conductors, placing equivalent electric and magnetic currents on the boundary surfaces, applying the boundary conditions for the tangential fields and, hence, obtaining a system of coupled integral equations. Due to the special geometry and the chosen excitation, the problem treated is a two-dimensional one. The distribution of the unknowm surface currents is approximated by pulses, and the amplitudes of these pulses are determined by a point-matching technique. This method is applied to the problem of determining the inductance and resistance of two-wire transmission lines.

Enhancing the gain of helical antennas by shaping the ground conductor

We have observed that the size and shape of the ground conductor of axial mode helical antennas have significant impact on the antenna gain. By shaping the ground conductor, we have increased the gain of a helical antenna for as much as 4 dB. Theoretical results are verified by measurements.