[alma-config] Re: Near-in sidelobes

[Min Yun]

As Holdaway suggested, Morita-san's report on the near-in sidelobe
for the zoom spiral may be wrong -- I hope Morita-san can clear up
this for us.  The old comparison John mentioned is outdated
since Morita-san is using his latest topo-friendly zoom spiral.
The new donut arrays also have rather different characteristics 
from the old ones.  Of course, all I wanted was to include all of
the latest strawperson configurations in the analysis Morita-san is
conducting at the moment.

Using a smaller Gaussian beam to get around the problem of weak 
sources on the Gaussian wing of a brighter source is not a real
answer -- we are all familiar with problems associated with
super-resolution, and this ad hoc answer goes against what makes
the Gaussian dirty beam attractive.  The VLA example I mentioned 
was just an illustration of the problem I was trying to describe.  
As Leonia will discuss further in his own e-mail, the dirty beam
from zoom spiral has a large wing around it, most of which also
has to be negative (to have zero net power under the beam, the
true dirty beam should have a negative DC offset).  I suspect the
ring of near-in sidelobes in the donut arrays will ultimately
limit its imaging capability at some point, but the Gaussian
wing, which is negative, is also of some concern.




					-- Min