NEC-LIST: How to model finite-sized rectangular ground plane?

Puck,

With options on the GN and RP commands you can specify a circular or
linear "cliff". However this is not the same as a ground plane. It
is only used in computing radiated field. For each (theta, phi)
direction of the radiated field, the code determines where the ray
from each segment of the antenna would reflect from the ground. If
that point is within the radius of the "circular cliff" or on the
antenna side of the "linear cliff" it uses the ground parameters for
medium 1, otherwise it uses medium 2. This has no effect on the
antenna currents or input impedance. Also missing are effects due to
diffraction from the screen edge or resonances of the screen. The
only way to accurately model a ground screen with NEC is to model it
as a wire mesh. That gets difficult when the screen is large. But
for large screens the reflection approximation may be adequate, or it
may be acceptable to treat the screen as infinite. I have seldom used
the "cliff approximation". Some people have been happy with the
results for their problems, despite the small discontinuities that
will appear in the radiation pattern as the rays from different
segments fall off the cliff.

Jerry Burke
LLNL
Received on Mon Apr 17 2000 - 20:23:01 EDT