Antenna device, RFID tag, and communication terminal apparatus

摘要

An RFIC element includes a capacitance therein. By this capacitance and an inductance of a loop-shaped conductor, an LC resonant circuit is provided. When UHF-band high-frequency power is supplied to the loop-shaped conductor from the RFIC element, the loop-shaped conductor is coupled to a flat conductor in an electromagnetic field by a current flowing through the loop-shaped conductor, and induced currents flow through the flat conductor. By propagation of the induced currents through the flat conductor, the flat conductor acts as a radiation element. It is preferred that the dimension in the longitudinal direction of the flat conductor be a half wavelength of the used frequency band. Accordingly, the flat conductor acts as a half-wave radiation element.

主权项

1. An antenna device comprising:
an antenna module including a loop-shaped conductor to which a feed circuit is connected or coupled, and a magnetic sheet provided in parallel or substantially in parallel to the loop-shaped conductor; and a flat conductor disposed so as to face the antenna module, and having an area larger than the loop-shaped conductor; wherein the loop-shaped conductor includes a first portion facing the flat conductor with the magnetic sheet therebetween, and a second portion directly electrically connected or coupled in an electromagnetic field to the flat conductor without the magnetic sheet therebetween; the loop-shaped conductor includes a feed point connected or coupled to the feed circuit, and a current maximum point spaced away from the feed point, and the second portion is a region including the current maximum point; the loop-shaped conductor is disposed close to the flat conductor such that a surface defined by the loop-shaped conductor extends along a surface of the flat conductor; and the loop-shaped conductor is disposed at a location where the second portion is closer to an end edge portion side of the flat conductor than a center or approximate center of the flat conductor.