[TowerTalk] Effect of element shape was: Re: InnovAntennas contact info

[Jim Lux]

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...