[evlatests] Bad Polarizers on ea03 and 13 at Ku-band

[rperley at nrao.edu]

The Ku-band polarizers on the JVLA are in general really outstanding.  For
almost all antennas, the cross-polarization is below 4% over almost the
entire 12 -- 18 GHz band.

But two antennas, ea03 and ea13, clearly have something wrong with their
polarizers.  Both show cross-polarization of over 50% (!!!) at the high
frequency end.  Both are fine below 16 GHz.

I attach a plot to show the effect.  Yellow is ea03, blue is ea13.  The
plot spans 16 -- 18 GHz.  At 16 GHz, the polarization is normal -- about 2
-- 3%.  But with increasing frequency, both show resonance-like structure
in the cross-polarization.

The top panel shows the leakage from LCP into RCP, the bottom panel the
leakage from RCP to LCP.  Each panel shows the phase (narrow plot on top)
and, below this, the voltage amplitude (in tens of percent, so 100 = 10%.

Rick
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