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

John B. Stephensen kd6ozh at comcast.net
Fri Mar 23 13:48:21 PST 2007


And the same scheme would work with the receiver with the addition of an 
attenuator and switch. The LNA feeds the phase shifter and attenuator. The 
attenuator compensates for LNA gain variation and phase shifter loss 
variation. The switch would be used to remove antenna elements from the 
receive path so each element could be calibrated individually. All outputs 
would feed a passive combiner.

73,

John
KD6OZH

----- Original Message ----- 
From: "Franklin Antonio" <antonio at qualcomm.com>
To: <n1al at cds1.net>
Cc: "AMSAT Eagle" <Eagle at amsat.org>; <K3IO at verizon.net>
Sent: Friday, March 23, 2007 21:32 UTC
Subject: [eagle] Re: Eagle Microwave Antenna Arrays -- mechanical concepts


> 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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