Patent ID: 7304615

Claim:
An antenna device comprising: a substrate formed of a dielectric body or a magnetic body; a first radiation conductor that is wound in a spiral around a portion of the substrate, one end of the first radiation conductor serving as a feed end for a radio-frequency signal; a second radiation conductor that is wound around another portion of the substrate in a spiral whose length is equal to the spiral of the first radiation conductor, one end of the second radiation conductor serving as a feed end for the radio-frequency signal; a third radiation conductor that is wound in a spiral around another portion of the substrate and that is connected in series with the second radiation conductor; a plurality of variable capacitance elements spread over the first and second radiation conductors by being connected in series with split conductor portions acquired by splitting each of the first and second radiation conductors into a plurality of sections; and a high-frequency switch that is interposed between the feed ends of the first and second radiation conductors and that is connected to an external high-frequency circuit, wherein the first radiation conductor and the second and third radiation conductors are selectively connected to the high-frequency circuit by supplying a switch control signal to the high-frequency switch so that the first radiation conductor and the second and third radiation conductors resonate in frequency bands different from each other, and a resonant frequency changes within a selected frequency band by supplying a bias control signal to each of the variable capacitance elements to change a capacitance.