Experimental verification of dipole radiation in a conducting half-space

A laboratory size model of the flat earth-air (two-layer) problem, constructed to verify certain proposed theories on electromagnetic propagation through the sea, is described. The modeling system is used in scaling and measuring electromagnetic field components of electric or magnetic antennas submerged in sea water. Specifically, the experimental results are compared with the theory of radiation from a horizontal electric dipole antenna submerged in the sea. The results presented here verify that 1) the cyclindrical coordinate
E_{r}
, and
E_{\phi}
field components measured in the sea vary with radial distance from the antenna as
\rho^{-3}
in the near-zone and
\rho^{-1}
and
\rho^{-2}
, respectively, in the far-zone; 2) all field components vary with depth,
z
, as exp (
-z/\delta
), where
\delta
is skin depth; 3) the
E_{r}
, and
E_{\phi}
components vary with
\phi
as
\cos \phi
and
\sin \phi
, respectively; 4) all field components vary linearly with length
l
and dipole current,
I
. In addition, the
H_{\phi}
,
H_{r}
, and
E_{z}
components were measured in the air as a function of
\rho
for the static-zone, near-zone, and far-zone. The modeling system representing the sea includes a cylindrical tank 11.5 feet in diameter, 2-feet deep, containing a salt solution of 4 mhos/meter conductivity. The transmitting frequency varied from 100 to 400 Mc. For submerged antennas that can be validly scaled at least
10^{-2}
in size and
10^{+4}
in frequency, this model can conveniently be used to verify experimentally the radiation characteristics of these antennas.