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RE: No Stupid Questions, right? (focal point)



Phase center refers to the "point" at which maximum signal is
radiated in the near-field of a feed/antenna (highest current density).  
Some of the more mathematical friends of Maxwell around
here will say this is "oversimplified" but this is the point when
dealing with dish feeds/dishes.

Focal point, of course, is the optical focal point of an object, usually a 
parabola (but a sphere has a focal "line" so other geometric objects can be 
used).

The idea is:  Put the phase center at the focal point for max gain.

This can be done by calculation, or even easier still, slide the
feed back and forth for maximum signal while listening to the bird.

Fred W0FMS



>From: "Howard Long" <howard@howardlong.com>
>To: "Rich Dailey, KA8OKH" <okh.npi@gte.net>, <amsat-bb@AMSAT.Org>
>Subject: RE: [amsat-bb] No Stupid Questions, right? (focal point)
>Date: Wed, 9 May 2001 08:03:02 +0100
>
>Rich
>
> > Ok then... what's the difference between "phase center"
> > and "focal point"?
>
>For us Microwave Newbies all this info is of interest.
>
>I have no idea, even when you know the phase center, which bit of the 
>coffee
>can / helix / yagi / log periodic / trapezoid should be putting there
>anyway.
>
>Any info greatly apprciated here too!
>
>73 Howard G6LVB
>
>----
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