Baryon acoustic oscillations from Integrated Neutral Gas Observations:
  Broadband corrugated horn construction and testing
  The Baryon acoustic oscillations from Integrated Neutral Gas Observations
(BINGO) telescope is a 40-m~class radio telescope under construction that has
been designed to measure the large-angular-scale intensity of HI emission at
980--1260 MHz and hence to constrain dark energy parameters. A large focal
plane array comprising of 1.7-metre diameter, 4.3-metre length corrugated feed
horns is required in order to optimally illuminate the telescope. Additionally,
very clean beams with low sidelobes across a broad frequency range are
required, in order to facilitate the separation of the faint HI emission from
bright Galactic foreground emission. Using novel construction methods, a
full-sized prototype horn has been assembled. It has an average insertion loss
of around 0.15 dB across the band, with a return loss around -25 dB. The main
beam is Gaussian with the first sidelobe at around $-25 dB. A septum polariser
to separate the signal into the two hands of circular polarization has also
been designed, built and tested.
