PURPOSE: To obtain the multi-beam antenna having a higher efficiency and a radiation characteristic with a lower broad angle side lobe level in comparison with the use of a horn having a circular aperture as a primary radiator.

CONSTITUTION: In the multi-beam antenna consisting of a primary radiator and a reflecting mirror, a primary radiator 3 formed by arranging minor axes of horn antennas 5 each having an elliptic aperture are arranged in a line is placed near a focus of the reflecting mirror 1. Horizontal and vertical patterns of the horn are independently changed by varying the eccentricity of the ellipse and the size of the aperture to obtain a desired beam width. The edge level of the reflecting mirror depending on the shape of the reflecting mirror and the size is set to a desired level and the multi-beam with high efficiency and a low broad angle side lobe level is obtained by reducing the spillover loss.