CARMA Holography

Stuartt Corder 
Division of Physics, Mathematics & Institute of Technology, Pasadena

and 

Melvyn C. H.  Wright
Radio Astronomy Laboratory, University of California, Berkeley


We obtained low resolution holography of the 15 antennas of the Combined
Array for Research in Millimeter Astronomy (CARMA) to determine the
primary beam voltage patterns, antenna illumination patterns and large
scale surface errors.  The strong, unresolved source 3c273 was used to
measure the voltage patterns of the six 10.4 m antennas using the nine 6.1
m antennas as reference antennas and vice versa.  We obtain a resolution
of 27" and 46" on the sky for 10 m and 6 m antennas, respectively.  These
give amplitude and phase in the aperture plane with a resolution of 0.71 m
for 10 m antennas and 0.42 m for 6 m antennas.  The holography
measurements showed that the dominant error for the 10 m antennas was an
offset in the antenna illumination pattern. These errors were corrected
using optical alignment. For the 6 m antennas, the dominant error was
large surface deviations which were directly measured from the holography,
and were corrected by mechanical adjustments of the panels.