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From: wjc@XN.LL.MIT.EDU (Bill Chiarchiaro)
Newsgroups: rec.ham-radio,sci.electronics
Subject: Re: Circular polarization vs omnidirectionality
Summary: Lindenblad & quadrifilar helix
Keywords: antenna
Message-ID: <1122@xn.LL.MIT.EDU>
Date: 7 Oct 88 17:31:23 GMT
References: <17770@glacier.STANFORD.EDU>
Organization: MIT Lincoln Laboratory, Lexington, MA
Lines: 38



The ARRL Satellite Experimenter's Handbook shows some
omni-az/circular-pol antenna designs.  The most interesting is the
quadrifliar helix, which is fashioned from wire in the form of four
intermingled helices.  It has been used on amateur satellites and with
GPS receivers.  Its radiation pattern does, however, favor the long
axis of the antenna.  Also, it is supposedly quite sensitive to its
environment.

Perhaps a more workable design is the Lindenblad antenna, which
comprises a number of dipoles (at least four) spaced around the
periphery of an imaginary, horizontal circle.  The dipoles are tilted
about 30 degrees out of the horizontal plane.  I believe the
"swastika" antenna mentioned earlier is of this design.  Also, I
remember once seeing such an array spaced around an observation deck
on the Empire State Building -- I think it was for FM radio
broadcasting.  The Lindenblad concentrates its radiation at low
angles; it's truly omniazimuthal.

There is also the turnstile (crossed dipoles over a ground plane), but
its circularity is not good at low angles.

Some references from the Satellite Experimenter's Handbook are:

	Lindenblad:
		Brown & Woodward: "Circularly-Polarized
		Omnidirectional Antenna," RCA Review, Vol. 8, June
		1947, pp. 259-269

	Quadrifilar heilx:
		Kilgus, "Resonant Quadrifilar Heilx Design," Microwave
		Journal, Dec. 1970, pp. 49-54


Have fun,
Bill
N1CPK