At 10:38 AM 12/28/2005, Clay Curtiss W7CE wrote:
>Jim,
>I'm tilting the entire array in my simulation. I forgot to mention in my
>earlier email I'm simulating the array on 20M. At 0 degrees elevation or
>tilt (E) the vertical beamwidth (VB) is 5.4 degrees, the horizontal
>beamwidth (HB) is 31 degrees and the gain in dbi (G) is 21.5 (according to
>EZNEC). At E=16, VB=24, HB=32 and G=17.2.
>
>For comparison, I simulated a single antenna at 65' and stacked antennas at
>65 and 110'. For the single antenna, VB=15, HB=57 and G=14.3. For the
>stacked antennas, VB=11, HB=56 and G=16.8.
That's interesting.. The beamwidth doesn't change much, but you get a 2.5
dB gain in forward gain. In free space, you'd normally see gain*beamwidth
be a constant, so a doubling of gain (3dB) results in half the beamwidth
(if the beamwidth in the other axis remains constant).
There must be some huge high angle lobe in the single antenna case that's
getting suppressed. Or, there's some funky ground interaction thing going on.
>Comparing the stacked antennas against the 6 antenna array tilted at 16
>degrees elevation, the array's vertical beamwidth is much wider and
>horizontal beamwidth is much narrower for about the same amount of gain.
Interesting, also. The 6 array is wider, so one might expect the
horizontal beamwidth to be narrower, but, the elements in the array are
superdirective already, so it doesn't always work that way.
>For my money, I'd probably go with the stacked antennas. But then my money
>is limited. If it wasn't, I'd probably have 25 acres on a hilltop and would
>build something similar just for fun.
>
>Like others, I've wondered if the 5 degree take-off angle of this array (at
>0 degrees tilt) is too low to be practical. Then I remembered the signal
>that Lou, EA3JE has with his 6/6/6 stack at 250'. He is always the loudest
>European on 20M when he's on the air.
>
>Clay
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