[asac][almanews] ALMA Memo 479 Released

[Stacy Oliver]

ALMA MEMO #479 

Requirements for Subreflector and Feed Positioning for ALMA Antennas 

Bryan J. Butler 
National Radio Astronomy Observatory

2003-12-08

This memo presents some calculations related to requirements on subreflector and feed positioning for the ALMA antennas. In order to
keep gain loss at less than 1%, the axial (vertical) positioning error in the subreflector should be less than about 0.09 λ, and in the feed 
should be less than about 0.9 λ. The lateral positioning error for the subreflector should be less than about 0.45 λ, and for the feed should 
be less than about 10 λ. The rotational (tilt) error of the subreflector should be less than about 5.5 λmm arcminutes if the rotation is about 
the vertex of the subreflector. If the rotation is about the prime focus, then this error can be much larger: about √λmm degrees. 

View a pdf version of ALMA Memo #479. 
http://www.alma.nrao.edu/memos/html-memos/alma479/memo479.pdf
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