Measured Aperture-Array Noise Temperature of the Mark II Phased Array Feed for ASKAP

TL;DR

This paper reports the measurement of the noise temperature of the Mk. II phased array feed for ASKAP, achieving record low noise levels across a broad frequency range, demonstrating its suitability for fast, wide-field astronomical surveys.

Contribution

It provides the first measured aperture-array noise temperature data for the Mk. II phased array feed, showing record low noise temperatures for ambient-temperature phased arrays.

Findings

Achieved noise temperature less than 40 K from 0.78 to 1.7 GHz.

Achieved noise temperature less than 50 K from 0.7 to 1.8 GHz.

Demonstrated suitability for wide-field, fast astronomical surveys.

Abstract

We have measured the aperture-array noise temperature of the first Mk. II phased array feed that CSIRO has built for the Australian Square Kilometre Array Pathfinder telescope. As an aperture array, the Mk. II phased array feed achieves a beam equivalent noise temperature less than 40 K from 0.78 GHz to 1.7 GHz and less than 50 K from 0.7 GHz to 1.8 GHz for a boresight beam directed at the zenith. We believe these are the lowest reported noise temperatures over these frequency ranges for ambient-temperature phased arrays. The measured noise temperature includes receiver electronics noise, ohmic losses in the array, and stray radiation from sidelobes illuminating the sky and ground away from the desired field of view. This phased array feed was designed for the Australian Square Kilometre Array Pathfinder to demonstrate fast astronomical surveys with a wide field of view for the Square Kilometre Array.