EMC Question of the Week: May 29, 2023

A guard trace between two microstrip signal traces on a circuit board

To reduce the crosstalk between signals on microstrip lines, guard traces should be

  1. shorted at both ends
  2. matched at both ends
  3. floated at one end
  4. avoided


The best answer is “d.” Guard traces routed between two parallel microstrip lines have almost no impact on the crosstalk compared to simply providing an equivalent amount of space between the two signal lines. In fact, guard traces that resonate at a particular frequency can actually increase the crosstalk. Since guard traces provide virtually no benefit and can make things worse, they are rarely appropriate.

The best way to reduce crosstalk between microstrip traces is to increase the distance between them or reduce their height above the return plane. Another way is to route them in a stripline configuration between two return planes. If there are only two signal lines that need to be isolated, they can be routed on opposite sides of same plane.

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