#13 Comparing Microstrip and Coplanar Waveguide calculations

[John Sherman]

I was comparing and evaluating the option of running a microstrip vs. coplanar waveguide for a signal trace. During this evaluation, I discovered an oddity with the coplanar waveguide calculations. Based on the illustrations, I would expect the trace impedance for a coplanar waveguide to be identical to microstrip when the waveguides are very far away (say 12"). I did not find this to be true.

For an identical structure with trace width 10 mil, height of dielectric of 6 mil, and Er of 3.97, the microstrip calculation indicates 53 ohm while the coplanar calculation indicates 68 ohm. All other parameters are the same. I've attached screenshots of each setup for review.

Do you think this is caused by an error in the calculation or is it due to the equations used for the coplanar waveguide? It seems the two solutions should approach to the same value.

[Dan McMahill]

My apologies for the very very slow response. I've moved development over to github, https://github.com/dmcmahill/wcalc and am going through all the bugs over here on sf to address them before turning off the sf trackers. I've copied this to issue https://github.com/dmcmahill/wcalc/issues/19 and will have some more to add to the issue shortly.

[Dan McMahill]

closing here and moving to https://github.com/dmcmahill/wcalc/issues/19