Topband: Multiple Ground Systems

[Brian Machesney]

Forgive my ignorance, as I am not an antenna engineer. I apologize for a
long post, but I would like to hear the opinions of the professionals on the
line.

Between jobs last year, I spent nine months, full-time, simulating antennas
with a NEC2 engine in an attempt to figure out how they actually work. Like
so many others down the years, I focused my energies on electrically small
antennas for low frequencies. Even though I live on several acres in the
country, I don't particularly want to visibly dot the property with big
antennas, spend all my money on wire or mow over a field of radials.

To summarize one of the conclusions I drew from my odyssey, it appears to me
that a quarter-wave monopole with radials is nothing more than a bent
vertical dipole with the horizontal leg split into two or more wires so that
radiation from the horizontal wires cancels.

Thus there is no point in regarding *elevated* "radials," at least, as a
"ground screen" or "counterpoise" or anything else - notwithstanding the
fact that the driving point impedance characteristic is similar to a
quarter-wave monopole over infinite ground. I would think that a defining
characteristic of a "ground screen" would be that the voltage is everywhere
the same, which is certainly not the case for radials - their voltage and
current vary in the same way as one half of an ordinary doublet. I also
think that the difference between "ground" and "radials" is driven home by
the fact that the finite lengths of "radials" affect the resonant frequency
of the antenna (the point at which the reactance is zero), whereas "ground"
is always *modeled* as being infinite in extent.

I would therefore expect that connecting together the "radial fields" of
vertical radiators driven with currents of different amplitudes and/or
phases would have numerous and relatively serious consequences because the
boundary conditions at the ends of the "radials" are changed.

Brian K1LI