[mmaimcal] Re: [Almasci] Two antennas

[Al Wootten]

Bryan

TWO ALMA designs?  Last time I counted we were likely to have seven--three
prototypes, three production 12m and one 7m!  All different designs though
all to the same spec and some more same than others.

Thanks for pointing this out.  Proper modeling would be great.  I'm not sure
but will find out what the antenna IPT has in its plans.

Clear skies,
Al
Bryan Butler writes:
 > 
 > you all may be interested in a paper in the most recent Radio Science:
 > 
 > Ng, T., T.L. Landecker, F. Cazzolato, D. Routledge, A.D. Gray,
 > R.I. Reid, & B.G. Veidt, Polarization Properties of reflector antennas
 > used as radio telescopes, Radio Science, v40, RS5014, 2005
 > (DOI 10.1029/2004RS003209)
 > 
 > ADS link: 
 > http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005RaSc...40S5014N&db_key=PHY&data_type=HTML&format=&high=412b55317309610
 > 
 > it would be nice to do some proper GRASP8 modelling of this for the two ALMA 
 > designs...
 > 
 > 	-bryan
 > 
 > 
 > On 11/7/05 12:40, Mark Holdaway wrote:
 > > Bryan Butler wrote:
 > > 
 > >>
 > >> if it really *is* only 0.3%, then the nearly obvious conclusion would 
 > >> be that the antenna-to-antenna variation will be almost that large 
 > >> anyway, so nothing need be done.  i don't think we can even measure 
 > >> the beam (polarized or not) to 0.3% in any case.
 > >>
 > >> i'd be surprised if it really *were* only 0.3%, though, theoretically 
 > >> or in practice.  how much do we trust the beam simulation?  has 
 > >> anybody put it through GRASP yet?  if it's only 0.3% difference 
 > >> between the two designs, then this means that the entire effect of the 
 > >> feed legs on the polarization beam is only 0.3% (peak), and that the 
 > >> differences between the two designs have little to no area where they 
 > >> give opposite effects.  seems a bit small to me - if you simulate the 
 > >> polarization beam with and without the feed legs, you only get 0.3% 
 > >> difference?  and is that absolute or relative difference?
 > >>
 > > That 0.3% is an RMS difference for some PB level (ie, all pixels with PB 
 > > value ranging from 0.05 to 0.10). The peak difference (given the 
 > > geometrical shadowing profiles I was given)
 > > will be.....   huh?   3.3%    OK, I was expecting a bigger number too.
 > > 
 > > Keep in mind that there will likely be other beam effects which are 
 > > different between the two
 > > antennas -- for example, the dishes will deform differently from 
 > > gravity, so at high freqs, the
 > > beams will behave differently with elevation.   While things look good 
 > > at the moment for
 > > two different ant designs, there is a whole mountain of work we will 
 > > need to do, and at each
 > > step we will need to determine if we can treat the antennas as the same 
 > > or as different.
 > > 
 > >    -Mark
 > > 
 > >>     -bryan
 > >>
 > >>
 > >> On 11/7/05 11:35, Richard Hills wrote:
 > >>
 > >>> Dear All,
 > >>>
 > >>> It would certainly be good to get a definite statement from the 
 > >>> software IPT as to what is presently planned and budgeted in this 
 > >>> area.  Meanwhile, could we go back to the original issue please, 
 > >>> which was whether anyone thinks that the 0.3% (peak) difference 
 > >>> between the patterns caused by the different blockage patterns 
 > >>> requires that we implement special data processing and/or makes a 
 > >>> case for having the legs rotated.
 > >>>
 > >>> Best Richard
 > >>
 > >>
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 > >> mmaimcal at listmgr.cv.nrao.edu
 > >> http://listmgr.cv.nrao.edu/mailman/listinfo/mmaimcal
 > > 
 > > 
 > > 
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