On 06/ 5/12 04:06 PM, Rex wrote:
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."
That's basically what Wikipedia says about the optics. They don't reference it,
so if it is referenced in Krauss, that would be a worthwhile reference.
Most antenna people seem to accept the standard definitions as being "IEEE
Standard Definitions for Terms of Antennas IEEE Std 145-1983"
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'm not saying Chuck is wrong about one needing the same sense at each end, but
I would disagree with him when he says "I guarantee you it doesn't cause any
controversy among those that use circularly polarized antennas." There certainly
is a lot of confusion over this topic, even among people who design them. I
don't think the confusion is related to reflections (everyone seems to know
that) and I don't think it's related to different conventions either.
I was going to try to simulate this by putting two helix antennas and coupling
them. But setting that up is a lot more difficult for me than just building
three antennas.
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.
Quality of polarization is a very complex topic. See the paper:
"The definition of cross polarization"
Antennas and Propagation, IEEE Transactions on
Date of Publication: Jan 1973
Author(s): Ludwig, A.
California Institute of Technology, Pasadena, CA, USA
Volume: 21 , Issue: 1
Page(s): 116 - 119
I've reprinted the abstract below for completeness, though you can read it on
the IEEE site without paying.
---------------
Abstract
There are at least three different definitions of cross polarization used in the
literature. The alternative definitions are discussed with respect to several
applications, and the definition which corresponds to one standard measurement
practice is proposed as the best choice.
---------------
I printed off a copy of that paper with the intension of trying to understand
it. I think the maths gets a bit heavy for me, but the more difficult problem is
I was unable to read the small symbols on A4 paper. So it looks as though I'll
have to read it on a computer and hope the quality is good enough.
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.)
One method of logically arguing for both antennas to be the same is reciprocity
theorem. So I think Chuck is right on the engineering facts, but is wrong about
the level of confusion it causes. I wish I could find the post on the EDA forum,
as there were many people making arguments for both cases.
Dave
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