Ed,
while I do not have any carbon fiber statistics or specs for you I can tell you that carbon fiber in general does not make even a poor ground plane for RF antenna applications. I have been fortunuate to try many materials for different frequencies and applications and depending on the exact composition of the carbon fiber product, it usually makes for a lousy ground plane. That is why Indy race cars have a small metallic plate underneath the body where their antenna attaches. If carbon fiber is your only available ground plane material, I suggest that you try to make the composite fibers embedded with as much metal as possible. From the highlands, MacCloed