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From: dleigh@hplabsz.HPL.HP.COM (Darren Leigh)
Newsgroups: rec.ham-radio,sci.electronics
Subject: Re: Circular polarization vs omnidirectionality
Summary: I screwed up!
Keywords: antenna
Message-ID: <2427@hplabsz.HPL.HP.COM>
Date: 7 Oct 88 19:15:09 GMT
References: <17770@glacier.STANFORD.EDU> <2419@hplabsz.HPL.HP.COM>
Reply-To: dleigh@hplabsz.UUCP (Darren Leigh)
Organization: Hewlett-Packard Laboratories
Lines: 39

In article <2419@hplabsz.HPL.HP.COM> dleigh@hplabsz.UUCP (Darren Leigh) writes:
>In article <17770@glacier.STANFORD.EDU> jbn@glacier.STANFORD.EDU (John B. Nagle) writes:

[John wanted an omni-directional, circularly polarized antenna.
 I offered the following design but got it wrong: see below]

|
|
|                                  |
|                                  | <- 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.

I forgot that the current on the far side of the loop is going the
opposite direction as that on the near side; therefore the diameter
should be an odd multiple of half wavelengths.  To do this antenna
right then, the radius of the loop should be an odd multiple of
quarter wavelengths and the two elements should be driven in phase.

========
Darren Leigh
Internet:  dleigh@hplabs.hp.com
UUCP:      hplabs!dleigh