[eagle] Re: Eagle Microwave Antenna Arrays -- RF concepts -- quad element RF modules

Franklin Antonio 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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