Momentum help for CPW design

Hello all. I want to design at Momentum a tapered CPW as depicted in the picture I attached because I want to simulate the S parameters,but need help. First of all, how can I define the black area as conductor and the red area as nonconductive layer?

Right click on red, Properties, and chose metal layer.
For black area (substrate layer) go to Momentum, Substrate, Open, and modify or chose a different substrate layer.

If your layout is as the attached, you need to map a slot layer on the substrate layer. and draw the red polygons on this layer.

To check the layout, you could use EMDS-> 3D EM preview to see the real layout.