> If you double the received energy, you gain 3 dB.
> It is hard to imagine how doubling the number
> of antennas could receive more than double
> the energy. Typically stacks produce LESS
> than 3 dB peak gain over a single antenna.
Physical size has little to do with gain, and nothing directly to do
with received energy. Gain comes from pattern interference, where
the radiation from each antenna cancels more in some directions
than others. System loss caused by increased currents from
mutual coupling in elements and phasing lines (of course) reduces
available gain.
As I recall maximum theoretical "stacking gain" of two broadside
antennas is actually around 5dB at almost 0.7WL spacing, but
many real-world factors reduce the real gain. The more directional
each individual antenna, the less likely you are to see the
maximum theoretical gain.
You'd have to be careful in reaching any conclusions where the
gain came from Pete, because the effects of earth complicate
matters. You could have an antenna at a bad height for the wave
angle you want, and obtain " gain" from stacking just because you
changed the mean height of the array!
73, Tom W8JI
W8JI@contesting.com
|