[time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nut can answer

[Dr. David Kirkby]

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