John Boyer wrote:
><
> Can anyone tell me if using -ve values for cliff heights using a GD
> card in NEC-2 to produce a rise in the ground is valid?
>
> Also is it possible to use multiple GN cards to provide an
> approximation to a slope?
I have used the GD card to simulate the radiation pattern of a
vertical 20 metres high half wave dipole over the sea, while it is
placed over a flat beach a few wavelengths inland. The sea was
simulated as a second medium with the conductivity s = 5 S/m and the
relative permittivity e = 80. The elevation pattern had a sharp peak
at elevation angles below 15 degrees. This sort of pattern could be
obtained by employing the optical approximation, which is probably
used in NEC-2 and is apparantly not applicable in the situation
described above.
My analytic approach to the problem of radiation from a sloping
beach, which includes flat coastal land as a possibility, gives a
different sort of results. Since the analysis does not rely on any
assumption about the sea having high conductivity the derived formulas
remain valid for when ground replaces sea. The reference is
S.P. Tarnavskii, "Propagation of radio waves over coastal sloping
land", The Sixth Australian Symposium on Antennas, Sydney, February,
1999, web page: http://www.tip.CSIRO.AU/events/asa99/papers.html .
Kind Regards,
Dr. Stan Tarnavskii
Centre for Sensor Signal and Information Processing
SPRI Building, Mawson Lakes Boulevard
Mawson Lakes, SA 5095
AUSTRALIA
Tel: (+61 8) 8302 5841
Fax: (+61 8) 8302 3124
E-mail: stan_at_cssip.edu.au
Received on Thu Nov 04 1999 - 20:41:16 EST
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