10% error
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#12 10% error
I used Wcalc for CPW grounded, 50 ohms, RO4350, and calculations give a number that is about 10% lower than the ones given by www.polarinstruments.com Si8000m ~$6k program.
These guys also close the loop, by making the hardware tools that does physical measurements, using TDR.
Wcalc gives the same results as many other programs, like AWR Txline, Rogers calc, and PCB Toolkit, so I assume the underlying assumptions are the same.
45 Ohms instead of 50 may be a big deal.
I agree that 10% is pretty large. I've moved development over to github, https://github.com/dmcmahill/wcalc
If you are able to share the dimensions you used for this case and maybe add to an issue here:
https://github.com/dmcmahill/wcalc/issues
I'd appreciate it. I'm guessing that the metal is relatively thicker compared to the width and spacing than what was typical during the development of the equations used by wcalc and others.
As I'm looking at the source code for wcalc, I see this note I left for myself:
https://github.com/dmcmahill/wcalc/blob/30bd6d8e43ef2a14f8ede3477b0e3e7615e81183/libwcalc/coplanar.c#L237-L245
So in the grounded case I'm not including metal thickness correction. Thicker metal will give lower Z0 and so I'm not surprised that a high end tool is predicting something less. I would love to get a better result in here. I have created this issue:
https://github.com/dmcmahill/wcalc/issues/16
Marking as closed, will continue at https://github.com/dmcmahill/wcalc/issues/16