A wide-beam planar backfire and bidirectional circularly-polarized antenna. An entire planar sectorial magnetic dipole is of a semi-closed structure, the planar sectorial magnetic dipole comprises two identical sectorial patches and a vertical short-circuit wall, and the vertical short-circuit wall is connected with straight sides of the two sectorial patches along a radial direction of the planar sectorial magnetic dipole; two sets of concentric annular electric dipoles are respectively used as a top concentric annular radiating element and a bottom concentric annular radiating element, as well as a top concentric annular reflector and a bottom anti-concentric annular reflector; and the top concentric annular radiating element is connected with an upper surface of the planar sectorial magnetic dipole through a top connecting branch, and the bottom concentric annular radiating element is connected with a lower surface of the planar sectorial magnetic dipole through a bottom connecting branch.