See my comments attached to your questions. The patterns you see are general
conventions of momentary snapshots of an antenna system. These conventions, or
standards, keep us all on the same sheet of music.
> From: alwilliams@olywa.net> To: towertalk@contesting.com> Date: Thu, 12 Jun
> 2008 08:59:20 -0700> Subject: [TowerTalk] dipole in space question> > Why
> does a dipole in space have a radiation pattern shaped like a doughnut i.e.
> no or less radiation off the ends of the dipole?
A theoretical half-wave dipole in free space does indeed have a donut pattern
with the nulls over the ends of the antenna. This is because the standing wave
is generated along the length of the wire with the current strongest at center
and zero at the ends. The ends of the wire have insufficient surface area to
create a radiation pattern when compared to the length of the wire. Think of
the lines of force coming off a magnet. What we are really playing with is an
electromagnetic wave form that follows the same pattern. These patterns have
been confirmed by observation and experimentation in the real world.
> Related to this question: Why is the radiation from a dipole over ground have
> its strongest radiation from the center of the dipole.> Yes the current is
> strongest at the center, but why?
Think of your typical nice, curvey sine wave that looks like an S laying on its
side. Now take just the top or bottom half of the S. That's your half wave
that's standing on the half-wave dipole and shows the instantaneous current
distribution at the moment of maximum radiation.
> I have tried to find the explanation in a dozen or more antenna books but to
> no avail. I can speculate but perhaps some Towertalkians can explain it or
> offer their speculation?> > k7puc>
> _______________________________________________> > > >
> _______________________________________________> TowerTalk mailing list>
> TowerTalk@contesting.com>
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|