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

• Published in: IEEE transactions on antennas and propagation Vol. 61; no. 1; pp. 117 - 124
• Main Authors: Holler, C. M., Taylor, A. C., Jones, M. E., King, O. G., Muchovej, S. J. C., Stevenson, M. A., Wylde, R. J., Copley, C. J., Davis, R. J., Pearson, T. J., Readhead, A. C. S.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.01.2013; Institute of Electrical and Electronics Engineers
• Subjects: Antenna measurements; antenna radiation patterns; Antennas; Applied sciences; Astronomical and space-research instrumentation; Astronomy; Earth, ocean, space; Exact sciences and technology; Extraterrestrial measurements; Feeds; Fundamental astronomy and astrophysics. Instrumentation, techniques, and astronomical observations; Joints; Mirrors; radio astronomy; Radio telescopes and instrumentation ; heterodyne receivers; Radiocommunications; reflector antennas; Telecommunications; Telecommunications and information theory; Performance evaluation; Lateral lobe; Antenna measurements; reflector antennas; Cross polarization; Centimetric wave; Reflector antenna; Radio astronomy; Foam; Simulation; antenna radiation patterns; C band; Radiation pattern; Receiving antenna
• ISSN: 0018-926X; 1558-2221
• DOI: 10.1109/TAP.2012.2219843

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.