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Re: Formula for antenna polarization loss



Chris,

What you are looking for is:

Loss (in DB) = 10*(log base 10)(cos(theta))^2 

Where theta is the angle between the polarization vectors.  Therefore, if
a vertically polarized antenna is used to copy a vertically polarized
signal, the loss due to polarization is zero DB.  If they are at 90
degrees, cross polarized, the loss is infinite.  I have been able to show,
in the classroom, using 10 GHz equipment, an isolation of greater than 40
DB between vertical and horizontal polarizations.  My equipment would only
measure to -40 DB so I don't really know how far I could have gone with
this.  In real life with reflections and Faraday rotation, etc., the loss
would be less than whatever I could show in the classroom.

A great ref for this is "Antennas" 1st or 2nd edition by J.D. Kraus.  This
can be extended to CP waves and antennas as well. Look at the discussion
on polarization by Kraus for a better understanding.

Just for grins, check the loss at 45 degrees:-)

73...Jim...W5VZF.

Dr. Jim Akers
Dept. of Electrical 
and Computer Engineering
Miss. State Univ. 


On Sat, 20 Jan 2001, Christopher Cox wrote:

> Can anybody point me to the whereabouts for the formula used to determine
> the amount of loss expected between antenna systems with different
> polarities?
> 
> I cannot find it in the 52, 63, 74, 85, or 2000 ARRL Handbooks. The only
> thing mentioned is up to 40dB of loss can occur. I also could not find it
> in "The Quad Antenna" or the Satellite Handbook.
> 
> 
> Thanks
> 
> Christopher Cox
> 
> 
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