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Re: Can anyone clarify dBic?



Howard,

I think you are right. The two 10 dBi antennas will produce 10dBic when
orthogonal and phased orthogonal. Now that you have made circular
polarization using two antennas orthogonal to each other, it is clear to see
how the average power goes down by 3dB when you only use a single antenna.
So if you receive a circular signal with a linear antenna you get 3dB less
on average because you only get the vertical or horizontal component of the
circular signal. Since the vertical component is Sin(a)  and the horizontal
is Sin(90-a) they both carry equal average energy. Getting rid of one drops
3dB. Now, if the signal is elliptical and it no longer follows the
parametric equation v=sin(a) and h=cos(a) then you can have a lot more than
3dB drop from elliptical to linear. Remember than "really" elliptical means
linear. I think this all makes sense. It's been a long day.

Pieter


----- Original Message -----
From: "Howard Long" <howard@howardlong.com>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, June 12, 2001 2:47 PM
Subject: [amsat-bb] Can anyone clarify dBic?


> 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
>
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