On 3/20/13 6:32 AM, Joe Subich, W4TV wrote:
> But given current distribution on a dipole, isn't it generally
> understood that drooping ends have relatively little effect?
"Drooping" ends result in a small amount of vertically polarized
radiation. Horizontally folded (or bent) elements result in some
degree of radiation at 90 degrees (think crossed dipoles) to the main
lobe. Since the side lobe structure in a yagi (or phased arrays -
consider what broadcast stations sometimes need to do to "detune"
nearby structures) is very sensitive, even a small amount of "off
axis" radiation can make a significant difference.
Yes indeed.. think of this.. a -20dBc sidelobe is 1% of the forward
radiated power.. It doesn't take much current in the wrong place to turn
-20 into -15
This is why folks who design very low sidelobe antennas (where very low
is <-50dBc) tear their hair out...
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