[mmaimcal] Quadripod Calculations

[Alwyn Wootten]

Hi Mark

Thanks a lot Mark, this is real progress.  I think the biggest risk 
remains the cost and the possibility that as a result of two antenna 
designs we'll end up with 40 or none.

Clear skies,
Al

Mark Holdaway wrote:

> Primary beam differences for a Heterogeneous Array
> 
> OK, I ran the beams for the actual feedleg shadowing profiles given to me
> by Robrt Lucas, 12 dB taper in the PB at the edge of the dish, and a 
> perfect surface.
> I formed the three primary beams and looked at the RMS difference 
> between the
> beams divided among primary beam regions of similar PBlevel.  The fact the
> the Vertex - EIE  rms  is essentially twice the Vertex-Cross RMS means 
> that these
> errors are systematic, but they are still very small.   Still the 
> largest error is at the
> 0.3% level -- a factor of 20 below the 6% specification.
> 
> These rms differences are larger than my previous uninformed calculation 
> -- the
> actual feed leg shadows are larger than what I had started out assuming.
> 
> The beams have been normalized to have a peak of 1.0, yet the
> integral of the Vertex and EIE beams differ by 0.4% -- if left uncorrected,
> this would translate into something like a 0.4% flux scale error -- 
> hardly something
> to get too excited about.
> 
> PBLev    Vert-EIE  Vert-Cross   EIE-Cross
> 0.025   0.000306  0.000158  0.000158
> 0.05    0.001798  0.000893  0.000905
> 0.1     0.003080  0.001519  0.001560
> 0.2     0.001435  0.000715  0.000719
> 0.3     0.002300  0.001146  0.001154
> 0.4     0.001272  0.000636  0.000636
> 0.6     0.001974  0.000986  0.000988
> 0.8     0.000710  0.000355  0.000355
> 1       0.000501  0.000250  0.000250
> 
> 
> While it is a pitty that we have two different array designs, mostly
> for those scientists who will have to figure this stuff out and the 
> technicians
> and engineers who will have to turn the bolts, I cannot say anything too 
> bad
> about the two antenna designs from the point of view of the primary beam 
> differences.
> 
> 
>     -Mark
> 
> 
> 
> 
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