[evlatests] P-band Dipole Rotations

[Rick Perley]

A 'copious' amount of P-band data was obtained last weekend.  The 
purpose for this was further refinement of our P-band polarization 
calibration regimen.  For this purpose, only the D-configuration station 
data were retained -- 19 antennas.

The data permit a careful examination of the 'd-term' leakages as well.  
Previous work has shown these are dominated by misorientation of the 
P-band dipoles.  The signatures of this coupling are:

     1) The leakage amplitude is constant over frequency (since the 
dipole rotation is frequency-independent)

     2) The leakage phases are either 0 or 180 degrees (or, put another 
way, the complex leakages are entirely real).

Signal leakage between polarization channels can be caused by other 
effects (like electronic coupling), but will in general be complex, and 
will vary with frequency.

The new data clearly show the leakages are completely dominated by 
antenna/dipole rotation.  The characteristics meet the signatures listed 
above.  I attach a plot showing these leakages for a few antennas.  
Phases near zero indicate the amplitude is positive, phases near 180 
indicate the amplitude is negative. Negative amplitudes (phases ~ 180) 
means the mis-rotation is negative, positive amplitudes (phases ~ 0) 
means positive mis-rotation.  The misorientation angle is given by the 
arcsin of the amplitude -- so 0.1 corresponds to about 6 degrees.

Here is a table of the misorientations of the 19 antennas in the D 
configuration, with respect to ea28, which was the reference. The 
amplitude plots are in 'milliarcsin' values.  Phases are in degrees.  
The upper frame shows the 'Vertical' dipole leakage, the lower frame the 
'horizontal' dipole.  Each frame shows two plots -- the thinner upper 
one is the phase, the lower wider one is the amplitude.

Antenna    Orientation

1                    +3

5                    -1

6                    +1

7                    -5

8                    -1

9                    -1

10                  +1

11                   -7

12                    +5

14                    -7

15                    -1

16                    -2

17                    -4

18                    |<1|

20                    +2

22                    +2

23                    -2

24                    -3

26                    |<1|

28                    Reference

-------------------------------------------------------

The accuracy is about 1 degree.

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