3D Receptive ultrathin LF band antenna

The 3D receptive LF band antenna used in vehicle smart key system is realized with ultrathin thickness of 0.32 mm. The antenna consists of three planar coils having a magnetic core of sheet type. For 3D reception, the magnetic axis representing the direction of maximum sensitivity of each coil should be orthogonal with one another. In this paper, a novel technique is introduced to realize that. The coil is made by inserting the thin magnetic core into the center hole of the flat winding wire, and contacting them closely. With this unique structure, the magnetic axis of each coil inclines to the horizontal plane and the inclined angle is adjusted to 35.3°. The antenna structured by placing the coils in rotational symmetry with angles of 120° in the same plane has three orthogonal magnetic axes.