Size of GND planes in CPW structure

Hello:

I come to you guys with a question.
I am designing and simulating a CPW structure in Momentum ADS 2009. On the layer I am working on I have defined slot structure, so basically I place 2 slots that have between the conductor line and on the other side of each slot there are the "semi infinite GND planes " of the CPW structure. The ports are defined as coplanar and placed on the slots.
No problems so far and the simulation runs well.

The problem comes now. When passing to the manufacturing step, how large (in width) should the two GND planes be since as I have defined slots on my layer and the rest(that is not a slot) it is directly considered strip. And in this case in simulations the GND planes of my structure are considered infinite.
I chose to simulate like this (with CPW ports and defining slots) due to the better results that can be obtained, but this causes me problems now when I need to pass to the fabrication process since I do not know exactly how big should the 2 GND planes be.

I wait for your answer and thanks in advance.

hi
i am desgning CPW band pass filter in ADS 2009. in slot mode. i have simulated and obtained reuslts but not with desired centre frequency. please send me the cpw designs in slot mode with layer mapping. i am struggling a lot with the design of cpw in slot mode. i have designed hair pin filter with air bridge and vias . what will be the layer mapping for the design without bridge and vias. and how how should i represent the gap between the two resonators in cpw design.
please do reply. waiting for ur reply
thanks in advance

To have a ground "electrically" equivalent to infinite in ungrounded CPW, you should take the width of the ground 10 times the width of the signal trace.