Topband: Modeling "Ground" and losses

[Tom W8JI]

> 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.

I don't think a description like that paints an accurate picture of what 
actually goes on.

There are two things happening at the antenna base:

1.) Any system with a conventional two conductor transmission line, either 
balanced or unbalanced, needs at least TWO terminals to apply power to the 
antenna. A monopole antenna requires something for the feedline to "push 
against".  This is an unbendable rule.

2.) If the antenna is near earth, or near any other conductive media, it 
induces currents in that media. This always happens, this is another 
unbendable rule. If the media is lossy, we have to either "shield" the media 
from the antenna to reduce current density in the lossy media, or make the 
media more conductive (less lossy).

If we follow those two rules, we see how all antennas work.

1.) We see an end-fed antenna of any type, even a half wave or Zepp, without 
counterpoise, cannot possibly work without some feeder radiation. We either 
provide it a controlled counterpoise, or it just makes its own counterpoise 
out of the feedline or things around the feedpoint.

2.) We see any radial or counterpoise system, close to the radial or 
counterpoise, has to have external fields. Those fields must extend out of 
the counterpoise, and always cause loss when a counterpoise is near a lossy 
media.

3.) We see we only mitigate the loss by making current density in the lossy 
media as low as possible, which generally means spreading the current out as 
evenly as possible in the lossy media or moving the antenna and a 
counterpoise away from the lossy media to reduce current.

The picture of something pouring off the antenna that has to be collected 
and returned certainly has merit when we consider the electric field and 
displacement currents, but it also paints an incomplete and somewhat 
misleading picture. It is like using an etch-a-sketch drawing to describe a 
complex landscape.

73 Tom