[mmaimcal] [Fwd: Antenna Differences]

[Richard Hills]

This was my second e-mail, being circulated now in the interests of 
openess rather than any claim to be saying anything profound.

Also just to say that I talked to a number of people at URSI about 
this.  As usual James Lamb put it most precisely and economically:  he 
said,  "If you are going to ignore the effects of the sidelobes it is 
better to have antennas with diffierent configurations;  if you are 
going to correct for it than it is easier if they are all the same."  
Time Cornwell's comment however was to the that even if you do correct 
for it is no big deal to allow for the case of anteanns with different  
patterns.

I also sent this to Tom from URSI.  Thinking a little harder about the 
diffraction due to the legs: The most important effect in probably in 
the outer part of the main beam and the first side lobe. A bright source 
in this region will stay in the pattern for a long time. Here the 
pattern caused by the blocking will interfere with the Airy pattern of 
the dish giving it a 4-fold symmetry which modulates the signal from the 
source as the pattern rotates relative to the sky. I think this the case 
where it is most likely that one would have to make the correction and 
one would need to do it separately for the different antennas.

Best Richard
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Subject: Antenna Differences
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