S/X/Ka coaxial feed for the tri-band receiver for RAEGE antennas

Félix Tercero, Instituto Geografico Nacional (IGN) JA.López-Fdez, Instituto Geografico Nacional (IGN) JA.López-Pérez, Instituto Geografico Nacional (IGN)

The tri-band cryogenic receiver for the first light observations of the first RAEGE project antenna in Yebes observatory is being developed, in the framework of the VLBI2010 project. The 13m new ring focus antennas are suitable to be feed by a broad-band feed like the Eleven Feed. However other feed configurations are possible to cover narrower bands, like the S, X and Ka bands. With this frequency arrangement, the feed makes possible the backward compatibility with classical VLBI and it will be especially useful for the Ka commission in of the antenna. X/Ka simultaneous observation will be also possible to link this antenna with another VLBI networks. The feed, designed to illuminate the ring focus antenna, is made of a coaxial waveguide, for the S and X bands, and a circular waveguide for the Ka band. Four outputs from their corresponding field probes at S and X bands must be combined with 180º and 90º hybrid circuits to get dual-circular polarization. In the Ka band case, the dual-circular polarization is obtained with a septum polarizer. The feed, hybrids and polarizer will operate at cryogenic temperature.