Fengchao Xiao

Analysis of crosstalk between finite-length microstrip lines: FDTD approach and circuit-concept modeling

Two approaches, one based on the circuit concept and the other based on field theory, are used to model the crosstalk between two microstrip lines of finite length and arbitrary orientation. In the circuit-concept modeling, a set of equations for the line voltages and currents has been derived from a modified telegraphers equation. A four-port network expression is resultantly obtained by solving the equations, thus the crosstalk can be predicted by applying terminal conditions to the network expression. On the other hand, the extended finite-difference time-domain (FDTD) method has been used to model the terminal resistors and the feeding resistive voltage source in the crosstalk analysis. Several physical models have been fabricated and experiments performed. The calculated results are compared to measurements. In our experiment, for microstrip lines of finite length and arbitrary orientation, there are short line-sections or vias at each of the four ports, which should be incorporated into the crosstalk analysis. This effect has been investigated numerically and experimentally.

Modeling and Analysis of Crosstalk between Differential Lines in High-speed Interconnects

The crosstalk between a single-ended line and a differential pair, and between differential pairs are investigated in this paper. First, the telegrapher’s equations for multiconductor line are applied. Then the telegrapher’s equations are solved by using the mode decomposition technique. Finally the mixed-mode S-parameters are derived to investigate the crosstalk and mode conversion.

Susceptibility characterization of a cavity with an aperture by using slowly rotating EM fields: FDTD analysis and measurements

This paper describes the evaluation of the susceptibility of a cavity with an aperture using the finite-difference time-domain (FDTD) method and experimentally. To reduce the computing time, the FDTD method is used for the radiation from the cavity and the susceptibility is obtained by using the reciprocity theorem. The cavity used here is modeled after a full-tower desktop enclosure with a 3.5-in bay. The susceptibility characteristics are evaluated by measuring outputs of a monopole antenna and transmission lines installed in the cavity. The susceptibility characteristics, using a three-dimensional (3-D) map, are studied from the computed and the measured results by applying slowly rotating electromagnetic fields to the cavity on a turntable. Measured and modeled results are in good agreement, indicating the merits of the proposed approach for susceptibility/immunity evaluation. Moreover, some discussions are made to check the susceptibility mechanism.

Application of a six-port wave-correlator for a very low velocity measurement using the Doppler effect

A new technique is proposed for measuring the Doppler frequency of a moving object by using the six-port correlator. The examination of this new proposal has been done with an object moving at a very low speed. The experiment and simulation results show the target velocity around 0.2 mm/s has been successfully inferred, which proved the validity of the proposed scheme.

Crosstalk Analysis for Two Bent Lines Using Circuit Model

The crosstalk phenomenon, wich occurs between transmission lines, is caused by electromagnetic fields of currents flowing through the lines. Crosstalk between two bent lines is studied by using a set of solutions of modified telegraphers equations. By expressing electromagnetic fields in terms of voltages and currents in the line ends, the resultant network function in the form of an ABCD matrix is obtained. Electromagnetic fields caused by currents flowing in risers at transmission line ends are taken into account in addition to those fields in line sections. The validity of the proposed approach was confirmed by comparing experimental results with computed results and those simulated by a commercial electromagnetic solver for some bent-line models.

The use of via holes for controlling the crosstalk of nonparallel microstrip lines on PCBs

In this work, the metal filled via holes are constructed into fences between the nonparallel microstrip lines to control the crosstalk. In practice, coupling between nonparallel traces is common. On the other hand, via holes are easy and inexpensive to build using the current fabrication process for the commonly used PCBs. The effects of the via holes for alleviating the coupling are investigated experimentally and numerically. The crosstalk is controlled by adjusting the position of the via holes, the structure of via fence, and the length of the via fence. Some design guidelines for the proper placement of the via holes are concluded. Experiments are conducted and the calculated results are compared with the measured data.

Mode-Port-Network Approach to Analyze Power-Line EMC Problems for PLC

In Japan, a power-line communication (PLC) is in use as an indoor system in the frequency band of 2 MHz to 30 MHz. However, the radiated emission in this frequency band, which is caused by the common-mode current generated in the power-line systems, is a serious matter. To analyze the high-frequency behavior of the line system, a two-port-network model using differential- and common-mode ports is proposed here. As an example, the network-function expression is effectively used to analyze characteristics such as longitudinal conversion loss (LCL), induced common-mode currents in a power line having a load circuit, and an impedance stabilization network 1 (ISN1) attached to a PLC modem.

Crosstalk Analysis Method for Two Bent Lines on a PCB Using a Circuit Model

We propose a method of crosstalk analysis for two bent transmission lines with vias at both ends on a PCB using a circuit-concept approach in the quasi-static condition. In this condition, the electromagnetic fields can be approximately estimated by the quasi-static terms of the accurate Greens function in an inhomogeneous medium. Thus we obtain a circuit model in an ABCD matrix by taking account of the fields generated by a longitudinal line and a vertical via on a PCB. To verify the proposed approach, we conducted some experiments and compared our approachs results with measured results and a commercial electromagnetic solvers results.

Common-mode inductance and radiation of edge placed differential traces on printed circuited board

With respect to the single-ended trace (track), differential signaling is most advantageous to signal integrity and common-mode radiation level reduction. However, to guarantee the required signal transmission, the two tracks in the differential pair should be perfectly balanced. Edged placement of a differential pair on the PCB causes balance disruption and creates common-mode (CM) currents resulting in an increased electromagnetic interference level. We quantify the CM inductance and radiation from differential tracks with edge placement. The common-mode inductance of an edged-placed differential pair on a PCB is derived. Then the characteristics of the common-mode inductance of a differential pair are studied for different geometries. Finally, the total radiation powers for several geometries due to the edge placement of the differential pair are measured.

Numerical dispersion relation for FDTD method in general curvilinear coordinates

The numerical dispersion relation (NDR) of the finite-difference time-domain method in general curvilinear coordinates (FDTD-GCC) is discussed for a two-dimensional (2-D) uniformly skewed mesh. The analysis shows that the average scheme, which is being used in the FDTD-GCC method, causes an additional numerical dispersion error. When this dispersion error is considered, the FDTD-GCC method holds the same NDR as that of the FDTD discrete surface integral (FDTD-DSI) method. It also indicates that the stable range of the FDTD-GCC method, with respect to the skewing angle in the 2-D case, is narrowed due to the average scheme.