[evlatests] X-band power levels

[Rick Perley]

    My 'demo science' run, taken on Sept 2, has shown some issues at 
X-band.  Six antennas have power levels well below the norm -- and one 
of them is spectacularly low. 

    They are:

    Antenna 6 R and L:   6dB low
    Antenna 10, R and L:  12 dB low  *******
    Antenna 13, R and L:  5 dB low
    Antenna 16, R only:    7 dB low
    Antenna 20, R and L:  6 dB low
    Antenna 23, R only:   6 dB low

    Antenna 10 is certainly special:  Not only is its power low, but 
it's cross-polarization is far too high -- 10 to 12 %, when nearly all 
the other (old-style) X-band antennas are 1 -- 2%.  However, this is not 
an issue with R and L being interchanged. 
    Polarization calibration does not correct for for antenna 10's 
apparent high polarization -- we have an apparent failure of closure, 
but the reasons are (to me) quite unknown.  The high polarization alone 
is not likely -- at C-band, where the antennas are normally this highly 
polarized, we get excellent calibration results. 

    Curiously, antenna 20 is also highly cross-polarized -- 6 to 10%.