Most of us have been using incorrect values for the propagation speed of our microstrip traces! The correction factor for Er we have been using all this time is based on an incorrect premise. In particular, it results in a value for propagation speed that is independent of variations in trace width and height above the reference plane. But the propagation speed for microstrip traces depends significantly on such variations. This article explains why and develops a superior model for estimating propagation speeds and propagation delays for microstrip configurations.

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