Figure:
Fit of the receiver temperature added by the presence of the
dual band dichroic on the optical path. The blue/red curves show the
data for a LSB and USB LO tuning, respectively. The two curves per
frequency and color show the measured results for the two
polarizations.
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The receiver temperature has two main contributions.
- The first one comes from the receiver when used in single band
mode. The quality of current receivers and associated optics ensures that
this one is to first order independent of the radio-frequency for each
receiver, except at the edges of the receiver band. We thus model it as a
constant receiver temperature per band. This contribution is shown on the
bottom panels of Fig.
to
.
- The second ones comes from the dichroic that splits the beam as a
function of the wavelength when in dual band
mode. Figure
shows the variations of the dichroic
receiver temperature as a function of the radio frequency. This
contribution has a non-negligible contribution to the overall receiver
temperature budget. We thus only add it when in dual band mode. Moreover
it varies much as a function of the radio frequency. We thus model it as
the sum of a linear contribution, plus a Gaussian centered around
240 GHz. This last bump corresponds to a physical phenomenon, named Wood
anomaly, which occurs in the dichroic when it operates in reflection
under oblique incidence.