PURPOSE: To prevent the direction of a beam from being changed due to the change of a driving frequency, by arranging a strip conductor curved periodically on the surface of a dielectric substrate, and meanwhile, performing phase control by arranging a single or plural resonance devices at every cycle of the strip conductor at a strip line antenna on the surface of which a ground conductor is provided.

CONSTITUTION: The strip conductor 12 is formed in a curved shape periodically with an arranging cycle L at every unit 22 of antenna, and a feeding line 16 which feeds to a first resonance device 14 is provided at a position with length L1 along the strip conductor 12 from the start end 12a of each cycle. Also, a feeding line 17 which feeds to a second resonance device 15 is provided at the position with length L2 in a direction from the terminating end 12b of a cycle period to the start end 12a. In the antenna having such structure, a beam of circularly polarized wave is radiated by the strip conductor 12, and also, the beams generated from the resonance devices 14 and 15 are changed to the circularly polarized waves, then, they are synthesized. In such a way, it is possible to improve the radiation efficiency of the beam radiated from the antenna 1, and also, to suppress the change of the direction of a generated beam even when the driving frequency changes.