[eagle] Re: Eagle Microwave Antenna Arrays -- mechanical concepts

Franklin Antonio antonio at qualcomm.com
Fri Mar 23 13:32:24 PST 2007


At 12:42 PM 3/23/2007, Alan Bloom wrote:
>If each antenna/amplifier had its own RF generator controlled by
>separate (I & Q) DACs, then it would be easy to control the phase of
>each element precisely with "infinite" interpolation between steps.

That's a lot of DACs.  2 per antenna element.  High speed DACs 
consume a lot of power.

A much better approach would be to use a digitally controlled phase 
shifter at the input of each PA.  I believe that 3-bit phase shifters 
will prove adequate, but hey, you could use phase shifters with more 
bits if you want.  Remember, all of these phase shifters don't jump 
at once as the spacecraft rotates.  Therefore the phase discontinuity 
in the resulting composite signal is much smaller than the phase 
discontinuity at one element.

I don't think its necessary to do I & Q.  Why not just put the phase 
shifter in the RF path right before the PA?  That avoids a zillion mixers.

There are many possible solutions.  The trick is to choose one that 
has a low power consumption and weight and complexity (hence high reliability). 



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