Hi Jim,
The next question then is; Do two horizontal, crossed dipoles, feed 90° out of
phase have an even power distribution across the hemisphere, horizontal across
the horizon and circular above and below or is there a direction with a higher
power density?
-----Original Message-----
From: Jim Lux <jimlux@earthlink.net>
To: Hans Hammarquist <hanslg@aol.com>
Sent: Mon, Dec 8, 2014 9:58 pm
Subject: Re: [TowerTalk] Dipole gain?
On 12/8/14, 6:45 PM, Hans Hammarquist via TowerTalk wrote:
That way you should
> subtract 3 dB to get a comparison between an antenna gain give over
> the isotropic. I was also told that two crossed dipoles were as close
> to an isotropic radiator you could get.
Not really. two crossed dipoles fed in phase is the same as a dipole at
45 degrees. two crossed dipoles fed 90 degrees out of phase is
circularly polarized in the direction normal to the plane containing the
dipoles. Other arrangements of dipoles (e.g. a Lindenblad or a
turnstile) may have better circularity in some directions.
An antenna that is isotropic and has the same polarization in all
directions cannot exist (there's the interestingly named "hairy ball
theorem" about this).
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