New BOR1 and decoupling efficiencies for characterizing ultra-wideband reflectors and feeds for future radio telescopes
Paper i proceeding, 2011
This paper presents some new topics that will be lectured in the December 2011 course within European School of Antennas course on Reflector and Lens Antennas. The new material is mainly related to characterization of wideband feeds for reflector antennas for future radio telescopes, such as for SKA and VLBI 2010. The lectures will contain details of how to design decade bandwidth log-periodic antenna feeds and in particular the so-called eleven feed, as well as focal plane arrays (FPA) for producing multiple beams shaped for optimum system performance. The designs has taken advantages of two newly defined efficiencies that are essential for optimum system performance: i) The socalled BOR1 efficiency characterizing the power loss due to higher order azimuthal variations in the far field function being very important in characterizing decade bandwidth feeds. And, ii) the decoupling efficiency being of importance for characterizing non-uniformly excited arrays such as FPAs, and being related to the classical embedded element efficiencies of normal phased arrays as well as their active (scanned) impedance.