Isn't this a "Vertical dipole"? Two quarter wave radiating elements? And
tower behind it will be some kind of reflector/director depending on
height. The radials seem unimportant if thought of this way.
Antennas radiate because of the current flow.
So you would have two current maximums, one maximum near the earth for the
lower element, and another maximum higher up about 1/4 wave away from
earth.
The end result would be earth conductivity dependent, but somewhere between
a little better or a little worse than a 1/2 wave vertical. The spacing of
current maximums would be a little wider than a vertical dipole or half wave
vertical, but still too close for any real significant gain. Because a
current maximum would be at earth level, ground losses might eat up any very
small gain.
Maximum stacking gain with 1/4 wave between current maximums is about 0.5
dB. This is reduced because the bottom element is against earth, and could
even go negative. Most of any gain, if it had gain, would come from the top
element and the earth reflection.
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Topband Reflector
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