Feed horn – Wikipedia

Feed horn (right) on a military radar antenna. The feed horn must be shaped to produce a radiation pattern tailored to adequately illuminate the reflector. A feed horn (or feedhorn) is a small horn antenna used to couple a waveguide to e.g. a parabolic dish antenna or offset dish antenna for reception or transmission of microwaves. [1]

 https://en.wikipedia.org/wiki/Feed_horn