At 6:40 AM -0500 2001/3/20, John Blackburn wrote:
>I'm trying to model the behaviour of an antenna over a ground plane
>which is finite in size and not perfectly flat (corresponding to the
>actual groundplane that we have). My idea for doing this is to build
>up the ground plane out of wires and possibly also have one of NEC's
>perfect ground planes underneath to simulate the actual ground
>underneath the wire groundplane. Could anyone give me advice on this,
>for instance how far should the wires of the wire grid be from the
>infinite ground plane underneath; and is it ok to attach the edges of
>the wire grid to the ground plane (to avoid reflections from these
>edges)?
A mesh of wires, length about 0.05 wl, should work well (at least with
NEC-4). Set the wire radius equal to the wire spacing divided by 2
pi. However, _don't_ connect the edges of the finite GP to anything
unless that's how the real antenna's finite GP is connected. The
edges of the finite GP are important determinants of an antenna's gain
pattern etc. Waves on the finite GP are reflected from the edges to
create a standing-wave pattern, and current flows on the underside of
the finite GP as well as the top. An object in the near field of the
underside of the finite GP will couple to the antenna and affect its
pattern etc.
-Chuck W1HIS
Received on Sun Mar 25 2001 - 20:26:10 EST
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