CPW analytical model?

Hello. I am wondering are there any analytical formula to calculate the characteristic impedance and propagation constant of co-planar waveguide with/without ground back? Thanks.

I think the program linegauge of IE3D calculates the characteristic impedance using some formula, since it calculates the coplanar parameters pretty fast. but I don't know what is the formula

i have matlab programs for that. or else u can look into a book by Lee and Dalman.
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