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@qualcomm.com To: n1al@cds1.net Cc: "AMSAT Eagle" Eagle@amsat.org; K3IO@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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