Gridded Vivaldi Antenna Feed System for the Northern Cross Radio Telescope

The design of a broadband antenna feed system for the cylindrical offset parabolic reflector of the Italian Northern Cross radio telescope is described. Its operative frequency band spans from the Low Frequency Array (LOFAR) upper band, i.e. 120-240 MHz, to the present telescope operative band centered at 408 MHz. The proposed configuration consists of a linear array of gridded Vivaldi (tapered slot) radiators inside a wired subreflector. Numerical simulations have been carried out using both commercial software and a specialized Method-of-Moments approach. They show that the designed feed system provides both a good impedance matching and an efficient illumination of the main reflector in the overall frequency band.