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