| 摘要 |
PROBLEM TO BE SOLVED: To provide a reader/writer antenna which can secure the symmetry of magnetic fields produced by respective loops of a loop antenna composed of the loops such as an 8-shaped antenna. SOLUTION: A structure which has a plurality of loops driven by a high-frequency power source and one or more parasitic loop driven with an induced current flowing by magnetic coupling with at least one loop and has a conductor at the outer circumference of the loop antenna, a structure which adjusts a shift in the current phase by connecting a capacitor, etc., a structure which puts currents almost in phase by twisting and connecting an 8-shaped antenna, etc., in series, a structure which uses a parasitic loop in such a shape that pieces of linked magnetic flux at parts overlapping with the respective loops are nearly equal, a structure which generates and feeds a current 90 deg. out of phase with the high-frequency power source of the 8-shaped antenna by installing a center loop in the center between two loops, etc., are provided and the current phases of the two loops of the 8-shaped antenna are controlled to maintain the symmetry of the magnetic fields. |
