Coplanar Waveguide With Ground plane

Hi guys,

I have a question about CPWG.
Some details: I use FR4 [ε=4.5, H[pcb height] = 32mil, T[copper] = 1.41mil=1oz.

I am using Linecalc or AppCad and the results: w=21mil, g[gap]=6mil

But I readied that when working with CPWG must keep for two conditions:
1) g/T>1
2) H/(w+2g)>1

In another place I see that they want H/(w+2g)<=10

With second condition I can live but the first condition make me a little problem.
What I suppose to do?

TNX a lot
David

Hi,

I am not sure what the second condition is exactly for, but I have a guess. CPWG supports the propagation of surface wave modes with virtually 0 cut-off frequency, this might be the condition to keep the propagaton constant of this mode far below the propagation constant of the dominant mode.

flyhigh

Hi,

Flyhigh thank you for the replaying.
What disturb me it's I can't find rule of thumb about how to make correct CPWG just like microstrip.

David

I think the conditon should be:
1) g/T>=4
2) H/(w+2g)>=3
I get them from ansoft's help and try it.