[evlatests] ea05 P-band beam cuts

[Rick Perley]

     I took two beam cuts of the the VLA antennas at P-band yesterday.  
Attached are the results for ea05, in both power and phase.  Note the 
power plot is in dB.

     The previous noted 'shoulder' is easily seen.  Now that (think) we 
know which labeled output (R,L) is which polarization (H,V), it can now 
be stated that the elliptical 'shoulder' is oriented orthogonally to the 
polarization.  Thus, for the 'H' polarization, the shoulder is vertical, 
for the 'V' polarization, it is horizontal.   A physical explanation is 
still wanting ...

     The phase plots show an interesting feature, previous unknown to 
me:  There is a radial phase gradient in the primary beam, slightly 
steeper in the directions of the shoulder.   The phase becomes opposite 
at about where the first null would be (if there were one ...), and 
stays near -180 degrees as far as the raster cuts went (about 15 degrees).

     These plots are of one antenna (hopefully typical), and at one 
frequency.  I know from 'SPFLG' plots that the beam and sidelobes obey 
the law of diffraction (more or less).  But some more work to check for 
details would be useful.  (Any volunteer?)

     It would also be really interesting to do a full holography (say, 
41 x 41) to determine the full electrical weighting.

     Rick
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