I believe that you will find that a 10"x10" power/ground plane
with a 4mil dielectric with a dielectric constant of 50 will
begin to resonate at about 82MHz. Above that it will be inductive
instead of capacitive.
In our experiments, we have found that we can't treat a small
area of a power/ground system as a lumped circuit element. I
don't think you would get good results analyzing the first
fraction of a wavelength of a traditional transmission line
as a lumped circuit unless the whole structure is electrically
small. The principal appears to hold for power/ground systems.
-- Bob Techentin email@example.com Mayo Foundation (507) 284-2702 Rochester MN, 55905 USA http://www.mayo.edu/sppdg/sppdg_home_page.html