Compact dual-polarized 1.2 - 10 GHz Eleven feed by folding outer elements for large decade-bandwidth radio telescopes

The Eleven antenna is a log-periodic folded-dipole-pair array which has two unique radiation characteristics: constant beamwidth and fixed phase center location over decade bandwidth. Therefore, the Eleven antenna is very suitable as a feed for reflector antennas. This paper presents a new compact design of 1.2 - 10 GHz Eleven antenna by folding down the outermost elements of the array. By doing so, it is possible to put the Eleven feed inside a compact cryostat, which is critical for applications in radio telescopes. The new compacted Eleven antenna has only 40% volume of the original standard Eleven antenna with similar performance. Simulations and measurements have verified the design and are presented in the paper.