|Frequency (GHz)||No. det.||FWHMb (arcmin)||Band-averaged FWHMc||Ellipticityd||Band-averaged Ellipticitye||SR Spilloverf (%)||PR Spilloverg (%)|
Notes. (a) The characteristics
listed in this table correspond to those of monochromatic beams at band
centre; the typical effect of including band-averaging is indicated for
FWHM and ellipticity. Mean, minimum, and maximum are drawn from
the set of all detectors at a given frequency; polarised and
unpolarised detectors are separately indicated.
(b) The mean of the minor and major axis at half-power found by fitting a bivariate Gaussian to the beam.
(c) Mean FWHM (in arcmins) for beams averaged across the detector bandwidth, based on straight averaging of 5 frequencies equally spaced within the bandpass. This is indicative only, as it does not account for the bandpass shape of the detector, nor for the spectrum of the source. A more optimal way to account for broadband optical effects in the near sidelobes is described in Yurchenko et al. (2005); their analysis indicates that the effect of increasing the number of frequencies averaged from 3 to 9 is well below 1% in total power.
(d) The ratio of major and minor axis.
(e) Mean ellipticity of beams averaged across the detector bandwidth. This is indicative only, as for the FWHM.
(f) The percentage of power reaching the detector without having reflected on either SR or PR.
(g) The percentage of power reaching the detector having reflected only on the SR.
(h) Since the shape of the multi-moded beam patterns is not Gaussian, the FWHM only partially represents it. A different parameter to use is the half-power angle in the azimuthally integrated power, whose mean is 4.08 and 3.3 arcmins for 545 and 857 GHz, respectively.
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