Beginning with the ideal passband, which is constant from Nf_s/2 to (N+1)f_s/2 and zero elsewhere, where N=0,1,2,... is the Nyquist interval number for sampling rate f_s, we examine the effect of deviations from that form on radio telescope performance. The implications for both continuum and spectroscopic observations are considered. Among the deviations of interest are: finite band edge slope, leading to non-zero response outside the Nyquist interval (aliasing); gain slope across the passband; gain ripple across the passband; and mismatch of the responses among antennas in an array. When analog filters are involved, the variation of response with temperature is also a consideration. Most of this report is applicable to radio telescopes in general, but numerical examples are selected for relevance to the ALMA telescope and specific recommendations for ALMA are given.
View a pdf version of ALMA Memo #452.
Last modified: 2003-04-15
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