PURPOSE: To obtain satisfactory unidirectional directivity group and input/output matching characteristic and to simplify the system by arranging a radio wave absorbing body on the rear face of an antenna to form a unidirectional beam and turning the radio wave absorbing body to rotate this beam.

CONSTITUTION: A radio wave absorbing body 2 is attached to rotation fulcrums provided upper and lower positions in the expansion direction of a dipole antenna 1D, for example, rotating pieces 12A and 12B rotated around a shaft 11, which is pierced in the center by the output cable of the antenna and consists of an insulating material, in a plastic dome 10 of less radio loss and is turned around the antenna 1D, and the lower rotating piece 12B is rotated by a rotating mechanism consisting of a motor 13, a belt pulley mechanism 14, etc., to rotate the unidirectional beam. Thus, a satisfactory input/output matching characteristic is obtained because the radiation characteristic on the rear side is erased by the absorbing body 2, and the whole of the system is made small-sized and lightweight because the directional beam is rotated by only turning the absorbing body.