Re: NEC-LIST: Unusual modeling problem

Those concerned about the relative dielectric constant and
conductivity of the Earth should consult ITU-R Recommendation (P)
527-3, "Electrical Characteristics of the Surface of the Earth" last
revised in 1992.

The Recommendation states ".....that the permeability of the ground,
m(u), can normally be regarded as equal to the permeability in a
vacuum and that values of the relative permittivity and the
conductivity are needed as a function of frequency for various types
of surface;".....

The Recommendation goes on to show curves of relative permittivity and
conductivity over a wide frequency range, in many cases beyond 100
GHz. With the exception of ice, the relative permittivities are shown
as constant to a few *GHz* while conductivities are shown constant to
at least 30 *MHz*, for materials including sea, fresh and pure waters,
for wet, medium dry and very dry grounds, and (the more variable) ice.

The usual cautions about inhomogeneities, layering, very wet-fertile
or snow covered grounds, and lake and river conductivities being a
function of impurities are voiced. The skin depth is given a good
discussion; it generally reduces as the reciprocal of frequency.

Now the purpose of the Recommendation is obviously to assist
prediction of ground wave radio propagation over macro distances. Use
of these 'broad-brush' ground surface values to a few meters of
specific soil (*any* data looks great when plotted on 6x6-cycle
log-log paper) must be interpreted and carefully applied.

The von Hippel book is indeed a great source for the EM properties of
dielectric materials. As I recall there is even an entry (not so
curious, actually) for "raw beef" (at 2450 MHz).

Regards

dan bathker
Received on Tue May 30 2000 - 07:27:01 EDT