What's the meaning of the Zo in HFSS? Is it characteristic impedance?

What's the meaning of the Zo in HFSS? Is it characteristic impedance? If so, what is wrong with this HFSS model? The Zo of the grounded CPWG (Co-Planar Waveguide) is varying a bit obvious with the frequency while the Zo of the microstrip is not. According to the Lincalc tool in ADS, both the impedance should be the same under diffierent frequencies. So would like some one to check my model or tell me where I am wrong? Thanks. The attachment is the HFSS model and the result of the simulation. In the result the word "CPWG" means grounded CPWG and the "microstrip" means the result of the "microstrip" model.

I've simulated your CPWG design. I haven't changed anything and I get the results attached in the text file below.

I use HFSS v13 however.

Maybe you should try to refine your mesh, especially for the high frequencies. I don't know the possibilities of HFSS 10.

In my case I've the following total number of mesh elements:

In Setup 1 (1 to 10 GHz): 18000
In Setup 2 (10 to 20 GHz): 28000

Thanks Kodar. I will make more meshes in the simulation.