[evlatests] L-Band Polarization

[Rick Perley]

    Bob Hayward noted that EVLA antenna 23 has by far the best 
ellipticity, as measured in the lab, so should make a good reference 
antenna for polarization. 

    Rerunning the 'PCAL' program with 23 as reference gives the 
following 'D-terms' (in percent).  Roughly speaking the numbers give the 
false degree of linear polarization on a baseline to antenna 23, for an 
unpolarized source. 

Freq         13            14            16            17            
18           23            24            26
---------------------------------------------------------------------------------------------------

1250 R   2.4            4.5           3.0          3.5            
6.8           0.0           5.9            7.1
1250 L   2.5            9.1           7.3          8.9            
6.9           1.3           5.4            5.3

1360 R   DNT       10.7         4.3          5.6            
3.8           0.0            7.2            9.3
1360 L   DNT        9.4          2.8         10.9            3.1         
2.0             7.2            9.0

1485 R    6.2          6.9           2.1           7.6           
2.3           0.0            5.7           8.2
1485 L    4.0         10.2         4.0           12.1          
5.0           4.3            7.0           8.3

1612 R   1.8          7.4           1.8            4.1           
1.7           0.0            6.0           6.9
1612 L   2.5          8.3           2.0            8.5           
2.1           1.8            6.7           9.0

1725 R   4.1          6.3           3.5            3.6           
1.2           0.0            6.1           5.6
1725 L   3.8          7.6           2.8            5.0           
1.7           1.7            6.7           4.8

1825 R    3.0         7.7           2.0            1.6           
2.9           0.0            5.8           3.3
1825 L    6.2          8.2          2.9             8.0          
0.1           2.9            8.3            8.2

1950 R   14.0        7.4          11.0           1.4           
3.8           0.0            5.1           4.3
1950 L     6.4        10.0          1.6           4.1            
2.4          6.0            5.4            4.0
----------------------------------------------------------------------------------------------------------------

DNT = 'Did Not Tune'

Some EVLA antennas -- nnotably 16 and 18 (for a reasonable part of the 
frequency range) have quite low spurious polarizations when matched 
against antenna 23.  Some (notably antenna 14) are rather worse.  All 
are quite poor at 1950 MHz -- but at this far end of the range, good 
results were not expected.