Meaning
Propagation speed of an electromagnetic wave along a conductive trace separated from a ground plane by a dielectric. Because the field exists partly in the substrate and partly in the air, microstrip phase velocity is slower than the speed of light in a vacuum. This parameter determines the electrical length of delay lines and resonators.
Effective Permittivity
Mixing of the two different dielectric environments results in a composite value that governs the signal speed. Calculation of microstrip phase velocity requires an accurate model of the trace geometry and the thickness of the board. Narrow traces see more air and thus travel faster than wide traces on the same material.
Timing Accuracy
High speed digital designs rely on matched trace lengths to ensure signals arrive at a chip simultaneously. If the microstrip phase velocity varies across the board, the resulting timing jitter can cause data errors in a memory interface. This is especially true for parallel buses where the strobe signal must align with the data window.
Designers use simulation tools to predict these effects.
Frequency Dependency
Dispersion causes different spectral components of a pulse to travel at slightly different speeds. Understanding this shift is necessary for wideband communication systems.
