Szczepan Białek wrote:
In my antenna radiate the end where the voltage is doubled. In your
something alse. What?
Unfortunately, the voltage doubling is accompanied by
transmission line currents at the ends of the antenna
which are known not to radiate. The reason is obvious.
When two currents are equal in magnitude and opposite
in phase, they do not radiate (much) because their fields
engage in destructive interference. These currents
are commonly known as transmission line currents but
also exist at the ends of a dipole as forward and
reflected currents.
When the phases of two currents are equal they engage
in constructive interference and radiate. These currents
are commonly known as antenna currents and exist at
the middle of a dipole that is equal to or less than
0.5WL long.
Unfortunately for your theory, since the standing wave
voltage is ~90 degrees out of phase with the standing
wave current (in standing wave antennas), the higher
the standing wave voltage the greater the destructive
interference between the forward and reverse currents,
i.e. the higher the voltage, the lower the radiation.
Sorry, but that is a simple fact of physics. If you
want the ends of a dipole to radiate, you need to
terminate those ends in the characteristic impedance
of the antenna in order to prevent transmission line
currents on the antenna.
If one models a 1/2WL dipole with the center 1/4WL part
horizontal and the 1/8WL ends vertical, one will get
a magnitude more horizontal radiation from the center
half of the antenna than vertical radiation from the
vertical half of the antenna. That's easy proof that the
center of a 1/2WL dipole radiates more than the ends.
The vertical radiation is 10 dB down from the horizontal
radiation even though equal lengths of horizontal and
vertical wire exists. Is EZNEC wrong?
Running the above dipole at double the frequency
results in equal currents in each 1/8WL of antenna and
indeed, the vertical radiation equals the horizontal
radiation.
--
73, Cecil, IEEE, OOTC,
http://www.w5dxp.com