PURPOSE: To reduce adjustment of mass balance and an increase in weight, and to rotate two split hyperboloidal subordinate reflectors by moving forth and back those reflectors in antenna axial directions, and thus rotating them.

CONSTITUTION: A hyperboloidal subordinate reflector 2 is divided into two by a plane including an antenna axis 7, and those two split subordinate reflectors 2 are arranged in such a way that their focuses deviate from an optimum position coincident with the focus of a parabolic main reflector 3 and the phase center of a primary radiator 1 forward and backward in directions of the antenna axis 7; and the subordinate reflector axis coincides with the antenna axis 7. A spherical wave from the primary radiator 1 is radiated by an antenna opening surface 12 in the form of a plane wave, but its phase distribution shows phase leading in the upper half and phase lagging in the lower half. The antenna pattern of the wave surface corresponds equivalently to that a beam axis 13 deviates from the antenna axis 7 in a phase lagging direction, and the subordinate reflectors 2 are turned by a motor 8 to obtain a conical scanning beam.