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[TowerTalk] Delta (Quad) Loop Polarization

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Subject: [TowerTalk] Delta (Quad) Loop Polarization
From: (Tom Rauch)
Date: Mon, 10 Sep 2001 07:47:24 -0400

> I have modeled quad loops for dual polarization (H and V) and contrary
> to W8JI claims and others, they have dual polarization components
> nicely filling nulls in the pattern of the "other" polarization. I had
> 3 el. dual polarization quad mounted over salt water on the boat ramp,
> half wave up, 90% of the time beating 4 square over "salty beach
> sand."

Hi Yuri,

The reason you see that "dual polarization" is because Eznec only 
considers the polarization as two pure distinct polarizations.

When you have a tilted wave, it shows up as a mixture of V and H 
even though it is actually a plane wave of one pure polarization.

If you stood out in front of the antenna with a small antenna and 
checked the radiation, what you would find is a peak at some angle 
other than flat or vertical, and a perfect null 90 degrees from that tilt.

The only way to get two distinct polarizations at the same time is 
to excite two similar antennas mounted at right angles in the same 
physical location with 90 degree phase shift, to mount a small loop 
with a small complementary dipole running through the axis and 
feed them both in phase,  or to stagger two right-angle antennas 90 
degrees distance and feed them in phase.

In those cases, you will generate a circular rotating wave.

It is physically impossible to generate more than one polarization 
in any given direction at the same time without doing one of the 
above, and without a rotating wave (circular polarization). People 
wrongly think it happens because modelling programs display 
results as mixtures of pure V and pure H when the wave is actually 
just skewed. 90 degrees from that skew the field is zero, so you 
have a single polarized wave that is simply tilted.

For example, a horizontal dipole has a perfectly horizontal electric 
field broadside. As we move off towards the ends, the wave starts 
to "tilt".  Straight off the ends, the electric field is vertical. But it has 
ONLY one polarization in any point in space looking back at the 
antenna. A loop is no different, neither is a Carolina Windom, 
neither are a vertical and dipole that are centered and fed in-phase.

73, Tom W8JI 

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