mmaimcal

[Leonia Kogan]

Al,

Min asked me to calculate dependence of sensitivity loss on the beam width 
due to tapering.  I have carried out it using the AIPS task IMAGR for 
the four configurations including VLA.
The result is given in the attached .ps file.

Several comments:

1. Mark supposed that this dependence should be the straight line with slope 
   45 degrees. This is corect as a first approach. This is of cource correct if
   the configuration has an ideal uniform UV coverage and if the tapering 
   looks like cutting off the outer baselines.

2. In the general case of tapering this simple dependence is not correct 
   even for an ideal uniform UV coverage.

3. IMAGR provides gaussian tapering with the width UVTAPER as a parameter.
   It is possible that another type of tapering will give another dependence.
   But I think the difference should be small.

4. The ring-like array (circle) loses less sensitivity than donuts 
   configuration. This statement is in contradiction with Mark statement 
   (memo 199). The two reason can explain the contradiction:

     1) Mark considered the simple type of tapering: cuttoff the outer baseline.
     2) Plot of the ring like UF coverage (circle) looks like uniform. 
        But it can be ilusion because of big redundancy: many diferent baseline 
        represented by the same point at the UV plane.


Leonia

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X-Sun-Data-Name: SENSWIDTH.PS
X-Sun-Content-Lines: 424
X-Sun-Charset: us-ascii

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