Implementation of a Correlator onto a Hardware Beam-Former to Calculate Beam-Weights

Abstract

One of the main technologies to open up a wider field of view for today’s radio telescopes are phased arrays. This is especially the case for radio astronomy instruments operating below 2[Formula: see text]GHz. Nowadays, the existing dish-type instruments are being upgraded with phased array feeds (PAF) in the focal plane. This increases the field of view at the expense of needing more analog electronics and digital signal processing. One of the digital signal processing functionalities used to combine the digitized signals from the PAF is a beam-former which creates multiple high sensitivity beams within the field of view of the dish. Before beams can be formed, the signals from the PAF need to be calibrated using a correlator. In this paper, we present a solution where these two operations are combined by using the beam-former also as a correlator. The statistics unit used as part of the beam-former implementation, can be used as well for calculating correlation products. With the proper settings of the beam-former weight of each beamlet, a frequency sub-band with a direction, can be used as a single cross correlation product. By implementing the correlator on the beam-former, the digital resources and development time can be reduced. To validate the idea, two versions of the algorithm are implemented in the Apertif PAF system on the Westerbork Synthesis Radio Telescope (WSRT). Results show that two full-bandwidth correlation matrices per beam, needed to determine the static beam weights for the calibration, and a single column of the correlation matrix, used to compensate for any drift between the receiver chains, can be performed.