[eagle] Re: Eagle Microwave Antenna Arrays -- RF concepts -- quad element RF modules
antonio at qualcomm.com
Mon Apr 2 14:22:37 PDT 2007
At 01:35 PM 4/2/2007, Bill Ress wrote:
>you throw in the differential change of phase between all of them
>due to differences in heat (temperature changes will translate to
>phase changes in the components of PLL) and you can be chasing phase
>adjustments all day.
Uh... That's a pretty nonquantitative statement. How much phase
change do you think will occur due to temperature? Why do you narrow
in on a PLL as something that might have phase change due to
temperature? All components do! The PA for example does. Cables
do. Any architecture for this antenna has phase shifts vs
temperature. I believe that the temperature differential between
elements will be small (after all, the PAs are all dissipating the
same amount of power, and the satlelite is spinning), and also the
phase change as a function of temperature will be very small. In the
end it will be irrelevant.
Tom can do some simulation to demonstrate how much phase error we can
tolerate. I was only gonna put phase shifters with something like 4
bits of control anyway. (Probably overkill.) Those are 22.5 degree
steps. That means the phase error due to quantization is between 0
and 11.25 degrees, and will average 6.125 degrees. There is another
error term caused by the phase shifter's internal error. Maybe
that's a few degrees. If you want to throw in a few degrees for
temperature variations, everything will still work fine.
Remember that the resulting signal is the sum of 35 or so elements,
so a phase error in one element has a very small affect on the
composite signal. This summing is a huge effect.
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