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Path: utzoo!attcan!uunet!pyrdc!pyrnj!rutgers!mcnc!unccvax!dya
From: dya@unccvax.UUCP (York David Anthony @ WKTD, Wilmington, NC)
Newsgroups: rec.ham-radio,sci.electronics
Subject: Re: Circular polarization vs omnidirectionality
Keywords: antenna
Message-ID: <1157@unccvax.UUCP>
Date: 7 Oct 88 13:38:23 GMT
References: <17770@glacier.STANFORD.EDU>
Organization: Univ. of NC at Charlotte, Charlotte, NC
Lines: 25

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

	The requirements are not mutually exclusive, as many TV stations,
even UHF, utilise circular polarisation.  Scala Electronics (Medford,
Oregon), Bogner (Long Island) and Dielectric Systems (?) manufacture
these antennas, but they are quite large and very expensive.

	If you don't care about efficiency (much) try a normal mode 
helical antenna. This is one where would orient the helix normal 
to the floor, and obtain the dreaded sin(theta) radiation characteristic
for both electrical modes.   They are very easy to construct and you
should be able to get an axial ratio in the .8 to 1.2 range very
easily (in which you'll have elliptical polarisation).

	Computing the helix dimensions will be easy, but determining
the operating impedance will be more difficult.  Any good antenna
text should have this information; you'll be able to get up and
running with this probably in one day or so.

York David Anthony
DataSpan, Inc