Without knowing the details of your problem it is hard to give specific recommendations.
On-line help under "impedance calculations" has useful suggestions. CPW lines are mode rich to that can add confusion. About the port size, why not just make the port bigger?
I prefer to use modal solutions and examine the port fields (display port fields) to see if the excitation is as I anticipated.
When the ground width of a CPW is very narrow, the wave port should be modified for the ground plane to touch the edge of the wave port. So, first you draw small 2D rectangles that touch both the ground plane and wave port, and then you need to substrate these rectangles from the original wave ports. Please see the attached file. The figure shows what I want to tell you.
Hello All!
Help me please! How to set port for air coplanar lines without groud? Whether it is necessary to set a layer of air as a dielectric substrate?