[mmaimcal] Text of AI on antenna quardupod design from Beasley

[Mark Holdaway]

On Beam issues:

I'm not sure that the different quadripod positions will be a big deal for
polarization.  Or more exactly stated, I don't know how to do that 
calculation
to get the polarized beams.

The total intensity beams are simple to calculate, and the feed legs 
will make
sidelobes of order 1-3%.   However, we never fixed the incorrect 
specification
that we know the primary beam to 6% accuracy, so it won't be too
convincing a problem.  Doing the calculations will at least tell us what 
level this
is, and using real feed leg data (the two times I did this in the past, 
I just made
stuff up and passed  it by people like Tim Cornwell or Darrel Emerson
or JingQuan, who said "Yup, a bit more like *this* and it should be sort of
realistic").

And a final security blanket statement: in principle, we will be able to 
deal with
either the differing total intensity or the polarization beams in 
software;  this is an
effort we knew we would have to address at some point -- these 
algorithms may have
been priority 3 in the SSR's list, having two antenna contracts probably 
brings
that priority up to 2.

I have no insight into the subreflector hole, except that at least I 
have the right hole
in my head.

   -Mark

Alwyn Wootten wrote:

> Folks,
>
> Here is the text of our action item and my preliminary response.  
> Comments?
>
> Action Item to the Science IPT (Al and Tom) from Tony Beasley could 
> you write me a few-paragraph response to each of these and return 
> asap? Regarding the Quadrupod position - the text you sent yesterday 
> [from the May 2003 Report to the Board] should cover it. ASAC opinions 
> the only one we respond to.
>
> (second point - question to Jeff Z- what did we do for Vertex?)
>
> Thanks... Tony
>
> Text from SS:
> > Science related:
> >
> > 1.     Quadripod position.
> > Members of ESAC/ASAC have different views on the impact of the feed leg
> > design on polarization. Instead of throwing numbers and statement on 
> how this
> > is going to affect the science of the antenna, it would be better to 
> use a program
> > (Grasp?) to quantify the effects.  It must be remembered  that the 
> beams of the antennas
> > will be different anyway. The japanese also have different feed 
> legs.   This may justify
> > or not  a request for a change the feed leg of AEM. Please pass an 
> action to Science IPT ( I will discuss it with AEM anyway)
> >
>
> > 2.      Subreflector hole diameter
> > We have specified 48 mm. In the past  I do believe I was told that 
> this should be 60 mm
> > (probably by Richard Hills?) This is something that I would like to 
> be checked by science.
> > If implemented now (on both antennas it is likely to be a minor 
> issue). If not needed
> > better so. Please pass an action to Science/SE
> >
>