System design and calibration of SITARA -- a global 21 cm short spacing\n interferometer prototype

Abstract

Global 21-cm experiments require exquisitely precise calibration of the\nmeasurement systems in order to separate the weak 21-cm signal from Galactic\nand extragalactic foregrounds as well as instrumental systematics. Hitherto,\nexperiments aiming to make this measurement have concentrated on measuring this\nsignal using the single element approach. However, an alternative approach\nbased on interferometers with short baselines is expected to alleviate some of\nthe difficulties associated with a single element approach such as precision\nmodelling of the receiver noise spectrum. Short spacing Interferometer\nTelescope probing cosmic dAwn and epoch of ReionisAtion (SITARA) is a short\nspacing interferometer deployed at the Murchison Radio-astronomy Observatory\n(MRO). It is intended to be a prototype or a test-bed to gain a better\nunderstanding of interferometry at short baselines, and develop tools to\nperform observations and data calibration. In this paper, we provide a\ndescription of the SITARA system and its deployment at the MRO, and discuss\nstrategies developed to calibrate SITARA. We touch upon certain systematics\nseen in SITARA data and their modelling. We find that SITARA has sensitivity to\nall sky signals as well as non-negligible noise coupling between the antennas.\nIt is seen that the coupled receiver noise has a spectral shape that broadly\nmatches the theoretical calculations reported in prior works. We also find that\nwhen appropriately modified antenna radiation patterns taking into account the\neffects of mutual coupling are used, the measured data are well modelled by the\nstandard visibility equation.\n