Recent developments in measuring signal and noise in phased array feeds at CSIRO

Abstract

Abstract-We describe recent developments in measuring both signal and noise in phased array feeds for radio astronomy at CSIRO. We introduce new techniques including aperture array noise measurements with beamforming weights matched to a reflector's focal field. Weights are calculated via antenna-range and in-reflector measurements. We also describe the separation of system temperature and aperture efficiency via drift scans.

Australian square kilometre array pathfinder: I. system description

“…We expect to reduce the calibration signal level as we gain experience in its use. The calibration noise is currently on continuously during all observations, but it is largely cancelled by beamforming with maximum signal-to-noise ratio beamformer weights resulting in less than 1% increase to beamformed system temperature (Chippendale, Button, & Lourenço 2018).…”

“…We use the technique of Chippendale et al (2016a) to decouple the PAF element gains from the beamformer weights and estimate the focal plane field matched by beamformer weights …”

“…Since the ODC system is constantly injecting a low-level broadband reference signal into the feed (Chippendale et al 2018), the array covariance measurements used for beamforming also capture a measure of the complex response of each element to the ODC signal. When we wish to update the beamformer weights, we record a smaller data product from part of the beamformer known as the calibration correlator (see Sections 5.6 and 7.2).…”

Testing a modified ASKAP Mark II phased array feed on the 64 m Parkes radio telescope

“…This is a log-periodic dipole array antenna (Aaronia HyperLOG 7025) with linear polarisation that can be manually rotated, but is nominally left at 45 • to the polarisation planes of the PAF elements. PAF port gains may be estimated via correlation of the the PAF RF signals with a direct copy of the radiated calibration noise [6]. Additional fibre was placed in the link carrying the reference copy of the calibration noise so it reaches the digital receiver with the same delay as the noise that is radiated into the PAF.…”

“…Initial measurements suggest that calibration via the vertex source will be more complicated on the Parkes 64 m than the promising first attempts on an ASKAP 12 m antenna in [6]. This is due to multipath interference caused by the reflection of the calibration noise from the large floor of the focus cabin at Parkes and then the concentration of this reflection back into the PAF by the paraboloidal reflector.…”