PURPOSE: To obtain an antenna system apparatus which conducts sectoral scanning within a plane at a high speed.

CONSTITUTION: Two wedges A and B each having a vertical surface and a slanting surface are disposed so that the vertical surface is perpendicular to a reference line of scanning and the axis X. These two wedges A and B are rotated at the same angular velocity and in the reverse direction to each other and parallel beams of an electromagnetic wave are made to pass through the two wedges, whereby a beam scanning in a sectoral shape within a plane is obtained. By selecting the relative initial positions of the two wedges A and B, the tilt of a scanning plane can be selected. Since only a mechanism rotating continuously in the same direction is provided and no mechanism element conducting a reciprocating motion is provided, scanning of high speed can be executed and an apparatus thus obtained is excellent in stability and durability.