Patent ID: 6924767

Claim:
A core around which electric wire is wound to form each of three antenna coils, the core that has a shape of at least one of a cylinder and a prism whose section is symmetrical to a point where e a center axis of the core passes through, the core comprising: a first groove member that is formed on a surface of the core and orbits along a perimeter of a first virtual sectional plane, which includes the center axis of the core; a second groove member that is formed on the surface of the core and orbits along a perimeter of a second virtual sectional plane, which includes the center axis of the core, wherein the second virtual sectional plane is orthogonal to the first virtual sectional plane; and a third groove member that is formed on the surface of the core and orbits along a perimeter of a third virtual sectional plan that is orthogonal to the central axis, the perimeter of the third virtual sectional plane is on a curved surface that is disposed between base surfaces of the core, the base surfaces which are symmetrical to the point where the center axis passes through.