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20th of August 2019
The GMIMS survey at Parkes
by Wolleben et al.
The Global Magneto-Ionic Medium Survey (GMIMS) was designed to study polarized radio emission from our Galaxy and characterise the strength and configuration of the Galactic magnetic field. The survey team designed and built a feed and receiver covering the 300 to 900 MHz band for the Parkes 64m radiotelescope in order to survey the sky between declinations of -90 degrees and +20 degrees. The specifications for the feed called for constant illumination of the 64-m reflector over the band 300 to 900 MHz, and detection of left-hand and right-hand circular polarization. The Parkes Telescope has a diameter of 64 m and a focal length of 26 m, with a focal ratio f/D of 0.41, and an opening angle of the reflector as seen from the focus of 126 degrees. The feed design was based on the Eleven Feed of of Per-Simon Kildal, which consists of a pair of parallel half-wave dipoles above a ground plane. Each dipole is expanded to become an approximately log-periodic array of folded dipoles fed by a twin-wire transmission line. The feed is shown above, supported above a ground plane of dimensions 1.2×1.2 m. The survey is described in more detail in the paper by Wolleben et al. (2019) in the Astronomical Journal.

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