Xref: utzoo rec.ham-radio:6287 sci.electronics:4022
Path: utzoo!attcan!uunet!husc6!mailrus!purdue!decwrl!ucbvax!hplabs!hplabsz!dleigh
From: dleigh@hplabsz.HPL.HP.COM (Darren Leigh)
Newsgroups: rec.ham-radio,sci.electronics
Subject: Re: Circular polarization vs omnidirectionality
Summary: try this
Keywords: antenna
Message-ID: <2419@hplabsz.HPL.HP.COM>
Date: 7 Oct 88 00:43:08 GMT
References: <17770@glacier.STANFORD.EDU>
Reply-To: dleigh@hplabsz.UUCP (Darren Leigh)
Organization: Hewlett-Packard Laboratories
Lines: 51

In article <17770@glacier.STANFORD.EDU> jbn@glacier.STANFORD.EDU (John B. Nagle) writes:
>
>     Is it possible to construct a UHF antenna which is both circularly
>polarized and omnidirectional in the horizontal plane?  Or are these
>requirements mutually exclusive?  I'm looking for an antenna for 1.2GHz
>with these properties.  Any ideas?  I'm trying to reduce the effect of
>reflection nulls on my robot TV link.

I'm not an antenna expert, but I'll dig deep into my electrodynamics
and see what I can come up with.  My guess would be to have a vertical
dipole and a circular loop like this:


                                  |
                                  | <- Vertical dipole
                                  |
                                  |
                      ____________|____________
                     (_________________________)
                                  |    ^
                                  |    |
                                  |    Circular loop
                                  |    (seen edge on)
                                  |


For circular polarization, drive these so that the magnetic field from
the vertical is 90 degrees out of phase with the magnetic field of the
loop when it reaches the loop, and so that the magnetic field from the
loop is in phase with the magnetic field of the other side of the loop
when it gets there.  In other words, make the radius of the loop an
even multiple of quarter wavelengths and drive the two parts 90
degrees out of phase.

This antenna should be omni-directional in the plane of the loop.
Directly above and below you're going to get nulls so this design will
be no good if your robot flies.  ;-)

Real RF types please correct me if I'm wrong.


>					John Nagle
>					KA2XXF (part 5 experimental, not ham)

Sounds like a neat project, John.  Good luck with it!

========
Darren Leigh -- (not part 5 experimental; not ham until I memorize
                 the code instead of the code tapes)
Internet:  dleigh@hplabs.hp.com
UUCP:      hplabs!dleigh