On Sun, Jul 07, 2013 at 06:01:17AM +0000, 間 幸久/JA5FP wrote:
> So,it has no polarity and will be sensitive for E-field at its point.
It is physically impossible that an antenna has no polarization.
Let me explain why, by describing a thought-experiment.
Suppose you would have such an antenna which really has no polarization
at all.
Then put a transmitter some distance away from it. First let this
transmitter be vertically polarized, and next horizontally.
A non-polarized antenna should respond equally strongly in both cases,
so the only difference can be a difference of phase; measure this phase
difference.
Next, transmit both vertically and horizontally at the same time, with
a phase difference which is 180 degrees minus the difference that was
measured in the previous step.
The antenna's response to this must be the sum of the responses to the
separate signals, and due to how we chose the phase difference, these
responses will be equally large but opposite, so their sum is zero.
In other words, this _combination_ of horizontal and vertical polarization,
which can be a linear (diagonal) or circular polarization, is not
received by the antenna, contradicting the claim that it receives all
polarizations equally well.
B.t.w., this is also an argument why a miniwhip consisting of say a
metal sphere with an optical cable coming out of it, cannot work: the
antenna is completely synnetric and has nothing which could determine
its polarization, even though it must have one.
73, Pieter-Tjerk, PA3FWM
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