Example differential impedance results

[kevinhikaruevans]

I'm trying out the differential impedance example located here: https://github.com/antmicro/gerber2ems/tree/main/examples/differential

When I run this example, the differential impedance value seems OK and the smith chart seems reasonable. It's roughly matching the results from the coupled microstrip line impedance calculator in kicad.

I noticed that when I change fab/stackup.json to use a thinner substrate (like in the case of a flex pcb) with a dielectric height of 35 um, I would expect to see a substantially smaller differential impedance. But instead, I'm seeing the impedances increase which doesn't seem right. Do I need to adjust the mesh in simulation.json for this case?

Here's what the impedance looks like with the thinner substrate:

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Another question, I'm seeing these warnings when I run the example as-is. Is this expected?

[14:43:27][WARN] Port #-1 is defined twice on the board. Ignoring the second instance
[14:43:27][WARN] Port #0 is defined twice on the board. Ignoring the second instance
[14:43:27][WARN] Port #1 is defined twice on the board. Ignoring the second instance
[14:43:27][WARN] Port #2 is defined twice on the board. Ignoring the second instance