Wire over ground

>Re: Semi-buried transmission line, King's book, etc.

King has a transmission line approximation for the propagation constants
on a wire over ground. It is in his book and also:

R.W.P. King and L.C. Chen, "The horizontal wire antenna over a conducting
or dielectric half space: current and admittance," Radio Science, Vol. 9
No. 7, pp. 701-709, 1974.

King's transmission line approximation needs reasonably high ground
conductivity or permittivity to be accurate. A more accurate solution
without this limitation is by Chang and Olsen (Radio Science, pp. 823-831,
August-September 1975). King's solution is in closed form with I and K
Bessel functions, while Chang and Olsen's requires an iterative solution
of an equation involving infinite "Sommerfeld" integrals.

A comparison of these solutions with NEC results is in the 1992 ACES
Conference Proceedings, pages 168 to 175. In general, NEC and
Chang/Olsen's solution are in close agreement, and King's is also when
conductivity is high enough.

A paper was presented at the 1991 IEEE APS Symposium in London, Ontario
by Rama Rao and Jones who measured the current on a Beverage antenna.
They claimed to show that King's formula was in agreement with their
measurements while NEC showed a smaller attenuation. However, they
apparently did not use enough terms in evaluating the Bessel functions
in Kings formula (there is cancellation of a leading term). When King's
formula is evaluated accurately it is in agreement with NEC and Chang
and Olsen rather than the measurements. That leaves an unexplained
excess attenuation in the measurements, which seem to have been
carefully made.

Jerry Burke
LLNL
Received on Sat Jan 06 1996 - 06:21:00 EST