I took a scan through Kraus "Antennas" since he did much of the
definitive work on Helical antennas. In his chapter on Wave Polarization
he gives a mathematical definition of Left- and Right-circular
polarization, then quickly mentions that the IEEE definition is the
opposite. He has a footnote: "This IEEE definition is opposite to the
classical optics definition."
So it seems our current antenna engineering uses the IEEE definition for
RHCP and LHCP, but earlier work on EM wave theory had defined
right-circular and left-circular exactly reversed from IEEE. So, combine
that with the reflection flipping and it is not hard to think why there
might be confusion.
I looked all around for a simple definition of the RH, LH quality of the
wave from a helix antenna. I assume I might have extracted it from pages
of formulas and theoretical explanations, but why not just clearly state
it in a book that is largely about helical antennas. Somewhere else (in
Kraus) I read that the IEEE definition of a RHCP or LHCP wave from or to
a helical antenna had the same handedness as the helix of the antenna.
Unfortunately in that writing he did not bother to explicitly mention
what he meant by the handedness of a helix. I assume he meant it to be
the same as the handedness of a screw, but he didn't say that, so once
again, a missed opportunity.
I'm not arguing with you, Chuck, just pointing out why there might be
room for confusion in some circles. (Pun intended.)
On 6/5/2012 6:23 AM, Chuck Harris wrote:
I guarantee you it doesn't cause any controversy among those that
use circularly polarized antennas.
That the polarization changes from RHCP to LHCP when reflected is
certainly the cause of some confusion about the antennas. A RHCP
antenna that directly emits a wave towards the source will become a LHCP
antenna if it is illuminating a parabolic dish.
The easiest way to think about it is to mentally think of the path from
the transmitter to the receiver as a very long piece of threaded rod, and
the wave being emitted as being a nut traveling on the rod. No matter
which side of the rod you are observing from, you will observe a nut
traveling away from that end turning in the same direction (clockwise
for RHCP).
Another point of confusion could be that if you are standing at the
transmitter watching the nut travel away from you, it will be rotating
clockwise.... but if you are standing at the receiver watching the
nut traveling towards you, it will be rotating counter-clockwise.
Both cases are RHCP.
If I hired an engineer to work on circularly polarized antennas and he
didn't know this, I too would be thinking of firing him!
-Chuck Harris
David Kirkby wrote:
On 5 June 2012 01:12, Dave Martindale<[email protected]> wrote:
I don't think that's correct.
This is a funny topic. No matter where see it discussed, there are
people with different views on it. I looked on the edaforum
http://www.edaboard.com/forum26.html
and found a thread (can't find it now unfortunatey), where someone was
adament they needed to be one way (I forget whether both RHCP or
RHCP+LHCP), and someone else was adament a colleague nearly lost his
job after making that mistake. I think there was about a 50:50 mix of
views on the topic
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