Coplanar waveguide width and gap

I am currently doing a research on flexible high frequency circuits using coplanar waveguide (CPW). I was wondering whether you can give me formulae for an accurate calculations to determine the width of the centre strip as well as the width of the separating gap.

See "Coplanar Waveguide Circuits, Components, and Systems" by Rainee N. Simons

Not a formulae but if you have AWR Microwave Office in your university lab or in your workplace there is a txline tool built in. You can use that tool calculate width, height, gap etc.