NEC-LIST: Ground Constants

>From: hagn_at_sri.com (George Hagn)
>To: NEC-LIST_at_ee.ubc.ca, PROPAGATION-LIST_at_gweep.ubc.ca
>Date: Mon, 05 Jun 2000 10:22:19 PST
>Subject: NEC-LIST: Ground Constants
>
>I have followed with interest the discussions on ground constants. Let
>me add to the discussion:

I have followed, but not in the detail commented on by George Hagn,
the discussions concerning the parameters for finite ground used for
numerical modelling.

I have carried out many studies (analysis not published) concerning
ground induced loss associated with GP type antennas, and I have
sometimes noted anomalies (that is a ground loss simulated is not
consistent with the trend, as conductivity (sigma) is changed).

I have discussed this matter with Gerry Burke several years ago
[Burke, private communications, 1995]. The complex permittivity that
Burke, Miller and others (developers of the NEC code) use is:real part
= dielectric constant; imaginary part = 60 x wavelength in metres x
conductivity in S/m. Thus the complex permattivity for average ground
(at least a value I have used sigma = 3 mS/m, epsilon = 13) at a
frequency of 3.75 MHz is 13 - j 14.4. Some studies have shown that
ground induced loss associated with GP antennas with radial ground
systems tend toward a maximum when the loss tangent is one; that is
the real and imaginary parts of the complex permittivty are equal.
This is the close to the case for 3.75 MHz, and so "average ground"
for this frequency may not result in "average ground-induced loss".

John S(Jack) Belrose, VE2CV

_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
Communications Research Centre
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2779
FAX 613-998-4077
e-mail <john.belrose_at_crc.ca>
_____________________________________________
Received on Sun Jun 11 2000 - 06:34:16 EDT