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Re: On phased arrays with azimuth and elevation beam forming



"laura halliday" <marsgal42@hotmail.com> writes:

> I had some notions of making a phased array antenna with
> a main lobe about 45 degrees up, matching the gain require-
> ments of the low-orbit digital satellites (and possibly
> others as well). This was based on a thesis I had read
> that had, apparently for the first time, actually studied
> just what antenna gain was needed...

Laura,
I believe a LEO antenna with a fixed elevation would be more effective with the main lobe at about 30 degrees.  A 6 dB antenna with a 60 degree beamwidth would be down only 3 dB at 0 and 60 degrees.  The amount of time a LEO spends above 60 degrees is practically insignificant and the proximity (square law) more than compensates for the drop off in gain overhead.

You could build a "simple" phased array system with variable elevation (azimuth is easy and well documented in the low band HF texts) by switching GP vertical elements from 1/4 wl to 3/4 wl (using relays?).  The former has a main lobe at less than 20 degrees (great for low elevation passes)and the latter has a main lobe at about 45 degrees (great for high elevation passes).  When it is all said and done, IMHO, a mechanically rotated array would be easier.
73,
Jerry, K5OE
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