Place a guard trace around each and every clock trace if the board is single or double sided (no ground plane present). Make the distance spacing as close as possible. With minimal distance between the signal and guard trace, and otherwise obey the 3-W rule. This minimizes crosstalk and provides a return path for RF current.

For high-threat signals, use of a shunt trace provides additional RF suppression by providing an additional ground return path for common-mode currents that may exist on a trace in a board with dual stripline topology.

When using guard and shunt traces, make connections to the ground planes at irregular intervals throughout the route. Symmetrical grounding allows for a tuned circuit to be created that may be resonant at a particular harmonic or wavelength of a particular clock signal.

Use of both guard and shunt traces allows for a coaxial based transmission line to exist in the middle of the board.

Do not route two different signals between the same guard traces / crosstalk could develop. If the traces are paired (differential), then only these two traces may be routed with the same guard trace.

Crosstalk may be eliminated or reduced by guard traces or routing 3-W.

Another technique to prevent crosstalk is to route parallel traces separated by 2 mils/inch (0.002”/inch) of trace spacing.