PURPOSE: To remove bad influence of mutual coupling between elemental antennas by arranging metallic chips close to the elemental antennas constituting an array antenna so that the mutual coupling between the elemental antennas is cancelled.

CONSTITUTION: Electric power directly coupled from circular horn antennas 1a, 1c to a circular horn antenna 1b through a courses A1, A2 is so-called mutual coupling. A part of the electric power radiated from the circular horns 1a, 1c are reflected by the metallic chips 6a∼6c and enters into the circular horn antenna 1b through courses B1∼B4. A part of the radiated electric power of the circular horn antenna 1b itself is also reflected by the metallic chip 6b and returned to the circular horn antenna 1b. Adjustment of a position of the metallic chips 6a∼6c makes it possible to form the relation of reversed phases between a signal directly coupled through the courses A1, A2 and a signal cupled through the courses B1∼B5 and cancel the mutual coupling.