NEC-LIST: Question about accuracy of Sommerfeld ground with surface patches

I am using NEC 4-1 to model a scenario where two separate objects, one
a solid object with volume comprised of surface patches, and the other
an antenna made of wire segments. These objects respond to a
far-field source of relatively low frequency (~ 1 Mhz). The two
objects are within a very small fraction of a wavelength of each
other, as well as the ground, which I would like to model with the
Sommerfeld/Asymptotic approach.

Here are some questions, request for comments, regarding this scenario:

1. The theory manual indicates that "the Sommerfeld/Asymptotic
approach is implemented only for wires, but the same technique could
be extended to the MFIE patch model". So my question is, what model
is used for computing the induced surface current on patches in
proximity to an imperfect ground?!?! If nothing, it would appear
then, that a piece of physics is missing in such situations...

I ask because my results over an imperfect ground do not appear to
make physical sense, nor are they bounded by the physically limiting
cases of no-ground and perfect ground. Some further investigation
indicates that numerical errors may be dominating in this scenario, I
suspect, due to a combination of the missing physics (?) and
Sommerfeld table look-up inaccuracies at low frequency. Any thoughts
from those with experience with similar problems would be greatly
appreciated.

2. I have avoided using a wire mesh model for the solid object since
the manual advises against this when interested in near-field
measurements. My own studies indicate results that are definitely
nonsensical, physically, so I have avoided them. Would appreciate
hearing from anyone who has satisfactorily used a wire-mesh model for
a solid object in close proximity of imperfect ground.

Thanks,
Chris Teixeira

Chris Teixeira, Ph.D.
Principal Scientist
Information Systems Laboratories, Inc.
8130 Boone Blvd. Suite 500
Vienna, VA 22182
(703)448-1116 FAX: (703)356-3103
Received on Mon Sep 25 2000 - 20:09:49 EDT