... As I understand, the primary loss mechanism for ground mounted vertical
systems is EM field penetrating the lossy material below. To lower this
loss, one needs to prevent this ground penetration. ...
A monopole will not radiate without a return path for the r-f current
flowing into/on it. In the case of a ground-mounted vertical monopole, the
first part of that return path is provided by the capacitive coupling of the
monopole to the earth around its base. Currents are generated in that
region of the earth by radiation from the monopole. For greatest radiation
efficiency those currents need to be collected and returned to the
antenna/transmit system. *That* is the function of the buried radials.
Consider that even if a vertical monopole is installed over a perfect,
infinite ground plane providing NO penetration of EM fields below it, that
monopole will not radiate if there is no path for the current in the ground
plane to return to the transmit system.
The link below shows a simple block diagram and pictorial of these systems.
To clarify my earlier statements in this thread -
My posts on this topic are based on the classic 1937 BL&E paper on ground
systems. That paper includes a considerable amount of measured data along
with a detailed discussion about the performance of monopole antennas using
buried radials. It is well worth serious study, and comprehension.
The BL&E paper shows that the currents flowing along buried radials used
with a monopole are *not* distributed along their lengths in the same manner
as if the only current source for those radials was placed at its common
point with other radials, at the base of the monopole.
The source for the current flowing on buried radials is the current in the
earth produced by radiation from the monopole. That earth current varies in
amplitude and phase at different physical locations along the length of the
radial, which causes variations in the net amplitude and phase of the
current flowing on that radial at various physical locations along its
length.
For these reasons the current variation on a buried radial wire used with a
vertical monopole is not the same as the variation along an end-fed wire in
free space, for a given physical/electrical length of conductor (and other
things equal).
http://s20.postimg.org/lgq8fdkz1/Part_15_AM_Block_Diagram.jpg
R. Fry
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