PURPOSE: To transmit and receive signals in the same direction by arranging a primary radiator, where helical lines for left-handed and right-handed circularly polarized waves are attached on one reflection plate in specific positional relations, in a specific state.

CONSTITUTION: A reflection plate 4 and helical lines 3R and 3L form the primary radiator for circularly polarized wave. Helical lines 3R and 3L are arranged and fixed in the right and the left of a focus F on the same plane of the Z axis and the Y axis such angle θ apart from an axis of revolution symmetry that deviations of beams due to circularly polarized wave are cancelled. Right-handed and left-handed circular polarized waves coming in the same direction from the front are reflected by a reflector 2, and directions of main beams are changed, and they are received by helical lines 3R and 3L simultaneously or individually. In case of the use as a transmission antenna, right-handed and left-handed circular polarized waves are radiated to the front in the same direction.