NEC-LIST: Help with modeling buried wire grid

I am trying to model a wire grid buried between 5 and 20 meters
underground. I am exciting the grid with a plane wave. Has anyone
done anything like this? Some of the results I'm getting don't seem
to make sense and I'm not sure if it's a problem with the grid model
itself or if NEC is not able to do calculations for underground
antennas. HELP!

-- 
Katie Kodan
SRI International
Kodan_at_washpost.wdc.sri.com