[mmaimcal] Band 6 Optics Question

[Mark Holdaway]

On Wed, 11 Jul 2001, Al Wootten wrote:

> Hi Mark
> 
> No, I haven't done any analysis.  My comment was only based on the
> fact that the optics was designed to -12 dB and in fact missed entirely
> only achieving -8 to -11.  As you mentioned, errors in this direction
> affect various spillovers; I would imagine they can only make ground pickup
> etc a more severe problem.  

There is an optimization that can be done:

We want to minimize ground pickup, we want to maximize aperture
efficiency.  These two effects push us in opposite directions, so
optimizing for the global sensitivity should pin us to some optimal taper
(though we also need to specify some observing strategy -- do we always
observe near the zenith, or are we dipping down to low elevations....)

The optimization will be very different for interferometric or total
power.  For single dish, we are also worried about cancelling out the
details of the ground pickup when the dish is pointed in slightly
different directions. For interferometric, we only worry about the
increase in noise due to the spillover as the spillover emission will be
uncorrelated from antenna to antenna.

I am guessing that the 12 dB design spec came back when we were going to
observe total power with every dish.  If the design now precludes total
power with every dish (I don't know if it does or not), might we be better
off with a smaller taper interferometrically and a larger taper for
total power?

Is such an optimization worth while at this moment?

	-Mark