CPW vs. GCPW? Ground stitching?
When I try to calculate the optimal gap width I get values that vary between 0.09 mm and 0.13 mm, depending on which tool I use for calculation.
Is this going to be a CPW or a GCPW? I get different results for the gap width using CPW and GCPW calculators. What is the proper calculation method for geometry/impedance that takes everything into account? And does the placement of ground stitching vias have an effect on the optimal gap width?
I did quite a bit of reading on this subject but now I'm confused.
Thanks a lot.
---------- Post added at 22:37 ---------- Previous post was at 22:13 ----------
When I follow the guidelines given in Coplanar waveguides (CPW) (taking into account the bottom ground plane, finite copper thickness, and the frequency dependent dispersion) I'm getting an optimal gap width of 0.13 mm. When I use AWR microwave office, the gap width should be 0.10 mm. But I'm not sure if ground stitching vias are taken into account in either case.
I think AWR result is true.
The calculation is based on very good ground, so you should make more vias to ground very well.
Thanks for the reply.
About these vias to ground / ground stitching: are there any guidelines how to do that properly? I found something like: "The best placement of these [vias] is near the trace at a distance of 1/4 wavelength of the highest frequency." Does that refer to the distance between 2 vias or the distance between a via and the CPW gap?
On both sides ground, The distance between vias should be at least 1/4 lamda, but I often make the distance be 2mm in horizon distance, and the next line vias should be 1mm from the the middle point of the previous vias line. This can work until 20GHz.
Good luck.
Thanks a lot.
2mm and 1mm, shouldn't that be frequency dependent? I'm working in the 10GHz regime.
Where can I find a sketch of this layout?
I have said 2mm and 1mm can work up to 20GHz.