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Re: Can anyone clarify dBic?

OK, here goes...
You're mostly correct.  The "polarization mismatch loss" of a perfectly CP
antenna to a perfectly linear antenna is 3dB.  There is a complicated
formula that can be used to calculate the maximum and minimum loss seen for
imperfect CP antennas (axial ratios not equal to 1.0), and if anyone is
truly interested in that minor detail I will gladly pass it along.

In making a CP antenna using two linear antennas, the two linears need to be 
1. Orthogonal (perpendicular) in linear polarization
2. Quadrature (90 degrees out of phase) in electrical excitation.

If 1 and 2 are achieved (and there are various ways of doing so; the ARRL
Handbook, Antenna Book, and Satellite Handbook go thru them all fairly
well), the resultant gain of the CP antenna will be (linear gain+3dB).

So "CP-ing" a pair of 10dBi yagis will give you a 13dBic antenna (system).

(Or look at it another way...if you "CP" a pair of 10dB yagis, and receive
them on a linear antenna, the CP pair will look like 13dBic-3dB
(polarization mismatch)=10dBi, which is the gain of one of the linear yagis).

At 07:47 PM 6/12/01 +0100, Howard Long wrote:
>A fly in the ointment for my understanding when calculating EIRP is whether
>your antenna gain is dBi (for a linear antenna) or dBic (for a circularly
>polarized antenna).
>Here's my understanding...
>There's potentially up to a 3dB _loss_ directly pointing a linear antenna at
>a circular antenna compared to directly pointing circular to circular (of
>the same sense of course). My understanding is that if you correctly phase
>two, say, 10dBi linear antennas mounded perpendicularly to each other with
>the boom at the axis, you get a 10dBic gain circular antenna.
>Perhaps someone will confirm or correct me on this simplistic view.
>73 Howard G6LVB
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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Scott Townley		
Gilbert, AZ  DM43
HF/VHF/UHF/Satellite MOBILE station

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