Re: NEC-LIST: NEC-4 and Antennas Near Ground

Yes, Merv, there is a Santa Claus, and NEC-4 does work for antennas
near the air-ground interface. Gerry Burke has published one case, for
a 6-MHz horizontal dipole. I have independently verified the case for
the 6-MHz dipole, with data taken at a site where I had measured the
ground constants at 6 MHz with the SRI Open-Wire Line (OWL) ground
constants measuring kit. I developed that kit, which SRI sells, during
the timeframe of the Vietnam War, to get sigma and epsilon r for
jungle and for the soil beneath the jungle. The OWL kit data, when
used in the 3-layer slab model (air-jungle-ground) gave predictions
that were accurate for the lateral wave (up to about 100 MHz to 500
MHz, depending on how accurate the predictions need to be). Models for
antenna patterns of antennas in jungle also were predicted and
validated with SRI's full-scale HF/VHF XELEDOP (see G. Barker, IEEE
Trans. AP, special issue on antenna measurement organized by Searcy
Hollis, July 1973) antenna pattern measurement system, when the models
were fed SRI OWL data for the media.

Jack Belrose used NEC-3, which is incorporated into NEC-4, to check
some of my Thailand data, and he has published that. He got good
agreement with my data after he figured out which of the two sets of
ground constant data for the same site applied to the antenna data
set.

Regarding NEC-4 availability, that is a question for Gerry Burke, but
Jack Belrose may be able to advise you about export to Canada.

Hope this helps.

George

P.S. I did a project for Jim Breakall, then working with Gerry at
Lawrence Livermore National Lab on NEC-3, to validate NEC-3. We set
up various antennas outside the gate at LLNL, Livermore, CA, and I
measured the input impedance vs frequency. I used my OWL kit to
measure the soil in the HF band. Dick Adler helped me take the data,
along with Jim and A. Christman (a grad student doing his PhD thesis
on the validation). NEC-3 looked excellent, when fed OWL kit data for
input on the soil electromagnetic parameters. These results are
published in Christman's thesis, and some of them are given in papers
I presented at ACES (e.g., 3rd, in 1987, and reprinted inadvertently
in the proceedings of the 4th ACES, 1988). The data in the ACES
proceedings are in error, but not irretrievably in error. I published
an errata in the ACES Newsletter, Vol. 6, No. 1, p. 35, March
1991. This error correction does not apply to the Thailand data used
by Jack Belrose, but it does apply to the data published in the ACES
documents.

P.P.S. In another validation of NEC-3 (and hence NEC-4), I got an
agreement in maximum gain of a vertical monopole (7.5-ft high, with 16
radials that were 40 ft long and buried 7 inches) of +/- 0.3 dB when
compared with measurements made with the SRI RELEDOP full-scale HF
antenna pattern measurement system (see R. H. Stehle, et al., IEEE
Trans. Broadcasting, Vol. 34, No. 2, pp. 210-220, June 1988, special
issue on shortwave broadcasting edited by D.J. LeVine, then of VOA).

P.P.S.S. The final published data on validation of NEC-3 (and hence
NEC-4) done by me is in G.H. Hagn, "Receive Antenna Directivity
Patterns and Gain for Ionospheric Propagation Model Predictions for
Shortwave Broadcasting," IEEE Trans. Broadcasting, Vol. 34, No. 2,
pp. 221-229, June 1988.
Received on Fri Mar 12 1999 - 19:01:46 EST