[evlatests] P-band Dipole Rotations

[Barry Clark]

A very nice result.  So the XY correlations can almost be used as taken, 
with corrections only amounting to about 0.3% rms.  These give something 
like (Q + U), depending on your choice of coordinates.  The other 
direction of polarization, (Q - U) is derived from XX - YY.  What is 
calibrating that like?

On 10/20/23 13:38, Rick Perley via evlatests wrote:
> 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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