Hi Gary,
> A lot of people are under the impression that the higher
the current in
> a particular part of the antenna the greater the radiation
from that
> part.
I'm under that impression, as are all the textbooks and
modelling programs I have.
>That is not the case. In the instance of a quarter wave
length
> antenna the current is highest at the feed end and lowest
at the open
> end. That theory should then say that only the lower part
of that
> antenna radiates and the top, high impedance part, does
little
> radiating. But all of that antenna shares nearly equally
in the
> radiation of the signal.
Sorry, but I strongly disagree.
It is a well established and accepted fact the open ended
region of any linear conductor...be it a vertical or
dipole....contributes very little to radiation. That's why
we can replace the open end areas with hats or other forms
of "current sink" and have very little change in pattern or
radiation resistance.
Basic physics tells us EM radiation is directly tied to
charge acceleration, not voltage. There are significantly
more charges moving in high current areas of the antenna
than at open ends.
This is why inverted L antennas are so effective as vertical
radiators, and why there is very little pattern or radiation
resistance change when the end of an antenna is bent.
It all comes down to ampere-feet.
73 Tom
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