[alma-config]Re: comparison of the boone's and kogan's compact configurations

[Leonia Kogan]

Hi David,

I carried out my calculations at the normalized coordinate:

Radius = number of the lambda/D = number of resolutions;  D = arrray diameter

The two side primary beam for the flat illumination is 
2.4*lambda/d; d is diameter of the dish

Introduce alpha is a portion of the two side primary beam.

Then Radius = Alpha*2.4*D/d;

Subtitude D= 200; d=12 and get 

Radius = alpha*40; 

My calaculations  indicate sidelobes of 9.3% at Radius=20 (alpha=0.5).

Of cource the multiplication of the PSF by the primary beam will reduce 
the sidelobes. And this explain our difference. But:

1. The actual 12 meter dish will have wider primary beam because 
   the illumination will not be flat.

2. But I do not think that the multiplication of the PSF by the primary beam
   is the right operation.
   You wrote:

>You are correct that for
>mosaicing you need to consider a wider area and Mark said that
>twice the primary beam should be enough.

I think even for not mosaic observation twice the primary beam should be 
required. Effect of the primary peam on the sidelobes of PSF is not simple 
multiplication ( I think so). The primary beam multiply the sky.

Consider the PSF pointed at the edge of PM. Then the sky at this point 
will be reduced by the PB. But the sidelobes at the oposite edge of the PB
(remoted by twice distance) will be reduced by the same factor.
So the ratio of the sinal and the sidelobe at the oposite edge of the PB 
will be determined by the PSF exclusively.

Thanks

Leonia


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>From dwoody at ovro.caltech.edu Mon Jan 28 20:21 MST 2002
Reply-To: "David Woody" <dwoody at ovro.caltech.edu>
From: "David Woody" <dwoody at ovro.caltech.edu>
To: "Leonia Kogan" <lkogan at zia.aoc.NRAO.EDU>
Cc: "douglas bock" <dbock at astron.berkeley.edu>,
        "Al Wootten" <awootten at cv3.cv.nrao.edu>
References: <200201271622.JAA00901 at bonito.aoc.nrao.edu>
Subject: Re: comparison of the boone's and kogan's compact configurations
Date: Mon, 28 Jan 2002 19:21:58 -0800
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Hi Leonia
My calculations always include the primary beam, i.e. the FT of the
UV samples multiplied by the primary beam, and hence I do not
see the far out sidelobes beyond ~15.  You are correct that for
mosaicing you need to consider a wider area and Mark said that
twice the primary beam should be enough.  ALMA memo 389
argues that for a Gaussian primary beam, the correct beam to
multiple the FT of the UV samples by is only a sqrt(2) larger
Gaussian beam.  I will run this case soon and send you the
results for both configurations.  I will also scale Boone's configuration
down to give the same magnification as your configuration (including
margin for close packing) so that we are comparing the same capability.
My guess at this point is that the differences will not be important,
i.e. very small.
Cheers
David
----- Original Message ----- 
From: "Leonia Kogan" <lkogan at aoc.nrao.edu>
To: <dwoody at ovro.caltech.edu>; <frederick.boone at obspm.fa>
Cc: <alma-config at cv3.cv.nrao.edu>
Sent: Sunday, January 27, 2002 8:22 AM
Subject: comparison of the boone's and kogan's compact configurations





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