Differential Coplanar Waveguide Impedance ?

[chris_leyson]

Hi

I'm using a short length of 0.5mm pitch flat flex as differential coplanar waveguide for routing 1000Base-T ethernet, and I'm using a single ground trace between the differential pairs, sketch attached. I haven't found any online calculators that cover this particular arrangement. The flat flex material is PET so the relative permittivity is around 3.0, does anybody have a calculator or field solver that will give me a ballpark estimate for differential impedance ?

Many thanks Chris.

[bktemp]

0.5mm FFC should have an impedance of around 100ohms for differential pairs. Here is an appnote about using FFC for USB:
http://ww1.microchip.com/downloads/en/AppNotes/00001579A.pdf

[chris_leyson]

Thanks bktemp  I guessed it wouldn't be to far from 100 Ohms.

[chris_leyson]

I just found this paper if anyone is interested, http://meritec.com/wp-content/uploads/2014/03/FFC-Impedance-Tests.pdf