Topband: Modeling "Ground" and losses

[Richard Fry]

>... 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