Date of Award

8-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Electrical and Computer Engineering

Advisor

Hubing, Todd

Committee Member

Pearson , L. Wilson

Committee Member

Xu , Xiao-Bang

Committee Member

Pisu , Pierluigi

Abstract

The current and field distributions of various structures can be calculated using full-wave numerical modeling codes. However, this approach is limited by the complex models and extensive computational resources required to analyze the details of each structure. In addition, brute-force modeling of the entire geometry provides relatively little physical insight into the electromagnetic interference (EMI) source mechanisms. Alternatively an effective equivalent model can be obtained by eliminating sources and structures that do not contribute significantly to the radiated emissions and focusing on the features that could possibly be significant sources of EMI. Equivalent models are generally much simpler than model-everything full-wave models and provide physical insight into the features that have the greatest impact on radiated emissions.
This dissertation includes four chapters on development of reduced complexity models for the modeling of antennas and printed circuit board (PCB) structures. In the first chapter, a simplified model for normal mode helical antennas is proposed. In this model, the highly curved structure of the helix is replaced with straight wires and lumped elements. The simplified model can be used to reduce the complexity of full-wave models that include a helical antenna. It also can be used to estimate the performance of a helical antenna without full-wave modeling of the helical structure.
The second chapter describes a model for determining the common-mode currents on cables attached to a PCB that is based on the concept of imbalance difference. The imbalance difference model is derived from research that shows that changes in geometrical imbalance cause differential- to common-mode conversion. The imbalance difference model can be used to estimate the radiated emissions from trace-board structures due to common-mode currents induced on attached cables.
The third chapter introduces a new closed-form expression for estimating the maximum radiated emissions from the board-source-cable structure. This expression is based on two improvements to a closed-form expression in a 2008 paper published in the IEEE Transactions on EMC. The accuracy of the estimate for larger frequency ranges is improved by using an expression for the envelope of F(è, k, lant) that equals the maximum value at every resonant frequency. A modified expression for calculating the effective length of the board improves the accuracy of the estimate when applied to nearly square boards.
In the forth chapter, a modeling technique is proposed to speed up the analysis of PCBs with coupled microstrip lines that induce common-mode currents on attached cables. Based on the concept of imbalance difference, differential-mode sources are converted to equivalent common-mode sources that drive the attached cable and the PCB reference plane. A closed-form expression is also developed based on the imbalance difference model to estimate the maximum radiated emissions from the PCB.

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