Crosstalk between two microstrip traces

What is the main reason of crosstalk in PCB and packaging interconnects? If you ask Bing AI, it will give you correct answer about the electric and magnetic coupling. But what is the reason for that coupling? - It is the use of open waveguiding structures - microstrip lines and striplines. As Ralph Morrison put it “energy travels in spaces, not the traces“. The signal energy propagates in space around the traces and is coupled to anything that gets into that space. That is the reason of crosstalk. The most sever coupling may occur in the surface traces or microstrip lines. This short video demonstrates how signal propagating in aggressor link from port 3 to port 4 injects some energy to the victim link between ports 1 and 2. This is 1-inch tight coupling case illustrated with the power flow density at 16, 28 and 42 GHz, computed with Simbeor 3DTF solver. The coupling increases with the frequency and at 42 GHz almost all signal energy is transferred into the victim link as the far-end crosstalk! That is how bad it can be. Unintentionally, one can create a directional coupler, if crosstalk is not restricted by design during pre-layout analysis and not evaluated at the post-layout stage. It can be effectively done with new Simbeor SI Compliance Analyzer tool - it allows 5 different ways to model and analyze the crosstalk. Note that the observed effect is not high-frequency only - if the coupling length is increased by 4, the same total signal loss due to the coupling happens at 4 times lower frequency. See more on the crosstalk in microstrip lines and how to reduce it at #simbeor #electromagnetic #signal_integrity