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Re: On phased arrays with azimuth and elevation beam



> From:          Dquagliana@aol.com
> Date:          Tue, 29 Aug 2000 06:55:12 EDT
> Subject:       [amsat-bb] On phased arrays with azimuth and elevation beam forming
> To:            amsat-bb@AMSAT.Org

> Recently I've read several (old) articles about the use of phased arrays
> to create a steerable "beam" (in azimuth).    I'd like to build a phased
> array system which I can switch in azimuth and elevation.   
> 
> Can someone point me to a reference, article, or web page which 
> describes the theory behind changing the elevation of the beam ?  

> Douglas KA2UPW
> dquagliana@aol.com
> "1200 baud BPSK uplinks with just a soundcard!"

Dear Doug

Most of the early WWII radars operated in the 1 to 2 meter bands.  At
first the developers tried Yagi antennas.  These were soon abandoned
as the theory behind Yagi's was not well understood at that period.
The antenna of choice turned out to be a flat array of colinear dipoles.

To increase gain and range, the arrays were simply made larger.
Some of the German colinear arrays were huge.  Naturally it soon
became desirable to find a way to electrically steer the beams from
these huge dipole arrays, both in the horizontal and vertical plane.
Thus the phased array was born (in a limited fashion) right at the start
of radar development.

>From what I have been able to read, the phase shift scanning was mechanical.
One brief discription spoke of a pipe like rotary switch that cut phase shifting
lenghts of coax in and out of the feed line to each antenna.  In the microwave
10cm region one U.S. Navy fire control radar used mechanical phase
shifting to give a 30 degree scan in the horizontal plane.  The meter 
range radars used phase shifting in the vertical plane as a aid to 
height finding.   That is, the horizontal plane was scanned by rotating the 
antenna.  The beam's vertical angle of radiation was phase scanned to 
determine target height.

Natually the size of any phased array antenna goes down as the frequency
goes up.  For 2M, I would guess the array would be the size of your 
house's roof!  Today you would switch the delay lines in and out with PIN diodes.
Just how complex the phase shifting network would have to be I'll leave
to the experts on the reflector.  Just consider that you would have to scan 
in both axis.  Now things are getting complicated!

It is possible that a small array could be built for the microwave bands
using printed circuit technology for the dipoles and delay lines.  As I 
recall, this has been discussed in the past on the reflector.  Perhaps
a dual band (up and down link) phased array antenna could be built.

"What's that flat thing on my roof?  Oh, its my... ah.... solar collector!"

Is anyone out there still experimenting with such a thing?
> 
--73-- Dave Metz WA0AUQ

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