Help with 50 ohm microstrip with copper fill

[swen_s]

I have calculated the correct width of a trace to give it a 50 ohm impedance. But how near the 50 ohm trace can I do a copper fill so I don't effect the 50 ohm impedance?

 

[FvM]

Exact impedance of "surface coplanar waveguide" (microstrip with embedding ground plane) will be calculated by advanced tools. As a rule of thumb, you will see less than 5% impedance reduction with ground separation >= substrate height.

 

[sivamani]

maintain more gap than the gnd reference.