Off-axis beam performance of Focal Plane Arrays for the Westerbork Synthesis Radio Telescope - Initial results of a prototype system

This paper reports on the off-axis beam performance of reflector antennas fed by Focal Plane Arrays (FPAs). The FPAs are comprised of many electrically small (< 0.5lambda) elements that can be used to generate multiple closely overlapping beams on the sky. As a result, both the size and continuity of the telescope´s Field Of View (FOV) can be substantially improved with respect to conventional reflector systems fed by single-horn or cluster feeds in a one-horn-per-beam configuration. The size of the FOV, in combination with the system sensitivity and instantaneous bandwidth, constitutes an important figure of merit, that is, FOV x BandWidth x Sensitivity, and is proportional to the survey speed of a telescope which should be maximized. One example of such a design, based on this new technology, is APERTIF (van Cappellen and Bakker, 2009), which aims at increasing the survey speed of the Westerbork Synthesis Radio Telescope (WSRT) with a factor of ~20.