John O'Sullivan (CASS)

Phased Array Feeds - Beamformers, beams and flat field of view calibration - John O'Sullivan Colloquium

ATNF Marsfield Lecture Theatre

Abstract

The Phased array feed is proposed as a viable method for increasing the field of view and survey sensitivity for the SKA. The dense phased array and phased array feed have multiple overlapping beams so that high degrees of coupling between each beam emerge as a fundamental property which must be taken into account. The ASKAP approach is to use a digital beamformer to form separate beams which can be correlated separately. Each of these beams can be formed with maximum gain or sensitivity or indeed, many other criteria. When seen as a part of a full imaging process however, it can be seen that there is one prefered solution - the maximum sensitivity solution and that the individual beams are of interest only in that they can be combined into a single large, "flat" field of view.

Following this line further, it is found that the field of view will be smooth in some sense provided an appropriate choice of an image beamforming method is used. If this is the case then there might be a real possibility of fully calibrating the fields of view for each telescope using known point-like radio sources present in large numbers in each 22-30 degree field of view of the ASKAP array.