Coplanar Waveguide With Ground plane

[DDavid]

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

 

[flyhigh]

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

 

[DDavid]

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

 

[henryhd]

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.