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Printed Circuit Board Design and Layout Questions

2. How does the accuracy of the PCB expert system software compare to full-wave numerical modeling tools?

Expert system tools should not be compared to full-wave numerical modeling tools because they are used for very different purposes. Expert system tools are useful for finding EMC problems with a particular design. Numerical modeling software is useful for analyzing a specific, well-defined source configuration. Numerical modeling software does not do a very good job of identifying EMC problems and expert system tools do not do a very good job of calculating the exact radiated field strength from a specific source configuration.

There is a tendency to want to compare expert system software to numerical modeling software because expert system software calculates the maximum radiation from certain (perhaps not well defined) pcb source configurations. Also, numerical modeling software is sometimes marketed as a tool for identifying EMC problems, even though it is a very poor choice of tool for this purpose.Plot of radiation from a PCB-Cable configuration

It is possible to use numerical modeling software to validate expert system algorithms. For example, in the figure to the right numerical modeling software was used to calculate the exact radiated field (maximum 3-meter electric field strength) from a printed circuit board with an attached cable one meter above a ground plane [1-volt, swept-frequency source]. The various curves indicate the field strength calculated as the cable length and position were varied. The dashed blue line indicates the results of the expert system calculation [1]. The expert system calculation does not yield the exact result. It indicates the maximum possible radiation as a function of frequency given that the cable length and position are not known in advance.