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Published January 2013 | public
Journal Article

A Circularly Symmetric Antenna Design With High Polarization Purity and Low Spillover


We describe the development of two circularly symmetric antennas with high polarization purity and low spill-over. Both were designed to be used in an all-sky polarization and intensity survey at 5 GHz (the C-Band All-Sky Survey, C-BASS). The survey requirements call for very low cross-polar signal levels and far-out sidelobes. Two different existing antennas, with 6.1-m and 7.6-m diameter primaries, were adapted by replacing the feed and secondary optics, resulting in identical beam performances of 0.73° FWHM, cross-polarization better than - 50 dB, and far-out sidelobes below -70 dB. The polarization purity was realized by using a symmetric low-loss dielectric foam support structure for the secondary mirror, avoiding the need for secondary support struts. Ground spill-over was largely reduced by using absorbing baffles around the primary and secondary mirrors, and by the use of a low-sidelobe profiled corrugated feedhorn. The 6.1-m antenna and receiver have been completed and tested. Results show that the co-polar beam matches the design simulations very closely in the main beam and down to levels of - 80 dB in the backlobes. With the absorbing baffles in place the far-out ( >; 100°) sidelobe response is reduced below -90 dB. Cross-polar response could only be measured down to a noise floor of - 20 dB but is also consistent with the design simulations. Temperature loading and groundspill due to the secondary support were measured at less than 1 K.

Additional Information

© 2012 IEEE. Manuscript received November 11, 2011; revised March 21, 2012; accepted July 02, 2012. Date of publication September 19, 2012; date of current version December 28, 2012. This work was supported in part by NSF grants AST-0607857 and AST-1010024, and in part by the University of Oxford Department of Physics. The work of A. C. Taylor was supported by a Royal Society Dorothy Hodgkin Fellowship. The authors would like to thank the staff of the Mechanical Engineering group in the Oxford University Department of Physics, particularly M. Tacon, P. Rossiter and M. Brock, for the construction of the C-BASS optical components. They also thank the staff of the Owens Valley Radio Astronomy Observatory, particularly R. Keeney, for support of the operations of the C-BASS North telescope.

Additional details

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October 20, 2023