Overview of developments of the eleven Feeds

An overview of different versions of the Eleven feed and recent development is presented in the paper. Eleven feeds have a nearly constant beamwidth and a fix phase center, with a performance of an aperture efficiency higher than 60%, −10 dB reflection coefficient, −0.2dB radiation efficiency, and −15dB cross-polar level, over a decade bandwidth. The Eleven feed can be very compact after applying newly developed optimization algorithms, and some new results of the feed in dual-reflector antennas are reported here