Re: Could DirecTV satellite dishes be used for the Square Kilometer Array - and a more radical proposal[Re: Can DirectTV-type satellite dishes be used for SETI?]

From: Rob Dekker (rob_at_verific.com)
Date: 02/15/05 

Date: Tue, 15 Feb 2005 00:34:55 GMT

Thanks for a good overview of trade-offs for phased arrays Steve !

"Steve Willner" <willner@cfa.harvard.edu> wrote in message news:421115a4$1@cfanews.cfa.harvard.edu...
[....]
> Joe is an expert and can correct me if I have something wrong here,
> but I think it might be useful to point out some of the qualitative
> issues.
>
[....]
> A third issue is the one RD and Joe mention: correlator cost. Cost
> ought to go roughly linearly with number of baselines, which for N
> antennas is N*(N-1)/2. This pushes towards fewer but larger
> antennas.

I'm not a total expert in this field, but know enough to be dangerous..:)

If I'm not mistaken, to phase correlate N elements, you do not need
to phase-correlate all N^2 baselines, but (after time/phase-adjusting each of the
individual N signals to intended beam direction), you can simply create a correlator tree
of 2->1 phase correlators. The tree would then consist of N correlators,
which counts for linear complexity of computation power.

I could be off with this, but I seem to remember this from college (long ago).

Question for Joe : Which part of the SKA system would be the bottleneck in
computational effort, and create a problem even in 2020 ?

Rob

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