grounded co-planar waveguide design advice/thoughts please
 

Hi,

I'm designing an RF multilayer board that is to work over 10-200MHz.

For the transmission line I'm using grounded co-planar waveguide.

Material is 10 thou Rogers 4350B, with a 50ohm track width of 0.46mm
and a track to top ground gap of 0.146mm.
This is working OK.

I now want to shield the board to prevent crosstalk, but I am
restricted to very little height.

My plan is to get a flat plate of say 1mm material half mm deep etched
with pockets that follow the RF lines and is grounded all elsewhere.

My worry is, will the fairly close proximity (but nearly 4 times the
track to gnd distance) of the metal plate above the transmission lines
cause problems, and/or will I have resonating cavities too?
I can make the cavities be 3 or 4 times wider that the gnd to gnd gap
around the lines if need be.

What do you think?

73