[evlatests] EVLA antenna polarization at L, S, C, and X bands

[Bob Hayward]

You might want to inform the FE Group the Antenna numbers of the best 
and the worst D-terms for the various receiver bands you looked at. We 
can then check the Axial Ratios that we measure in the lab to see if 
they agree with your Array based measurements.

-Bob

Rick Perley wrote:
>     The data from the 'receiver rotation' experiment are now calibrated 
> and reduced.   The essential results are given below.
> 
>     L-Band. 
> 
>     Five antennas are equipped with the fully EVLA compliant receivers 
> and polarizers (6, 10, 12, 20 and 26).  For these, the antenna 
> polarizations easily meet the EVLA goal of 5% cross-polarization (D-term 
> amplitude), across the entire 1 -- 2 GHz passband. 
> 
>     S-Band.
> 
>     Four antennas are equipped with the new-design quadrature hybrids, 
> the rest are outfitted with the old design.  The new design systems 
> easily meet the cross-polarization goal over all frequencies.  Antennas 
> with the old design hybrids exceed the EVLA goals at the low end, from 
> 2000 to 2500 MHz. 
> 
>     C-Band.
> 
>     The new-design hybrids are not yet ordered, so all antennas are 
> equipped with the old design.  The antenna polarizations are highest at 
> the low frequency end, and exceed the EVLA goal of 5% below 5 GHz.   
> Most antennas meet the 5% goal between 5 and 8 GHz. 
> 
>     X-Band. 
> 
>     Five antennas are now equipped with the new wide-band X-band systems 
> (6, 7, 14, 16, and 24).  For three of these antennas, the 
> cross-polarization meet the 5% goal between 8.25 and 12 GHz.  The 
> remaining two exceed the level at the extreme ends (below 8.75 and above 
> 11.5 GHz).  The origin of this is in the wideband phase shifter. 
>     The overall performance is fine, but it is interesting to note that 
> the old (narrowband) receivers had far better (lower) cross-polarization 
> -- typically 1 to 2% between 8 and 8.5 GHz).  The higher 
> cross-polarization of these wideband receivers is the price we pay for 
> full-band coverage.  As always, it is more important that the 
> cross-polarization be stable than it be low, since the former permits a 
> post-correlation correction.
> 
>     A full report will be issued later via the Memo series -- but must 
> await Eric's return from vacation in order to sort out a few problems 
> with the 'TRUEP' program. 
> 
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