Antenna matching circuit, antenna device, and method of designing antenna device

A method of designing an antenna device including an antenna element and an antenna matching circuit connected between the antenna element and a feed section, the method comprising:

• forming the antenna matching circuit with a reactance changing section connected to a base portion of the antenna element and a matching section connected between the feed section and the reactance changing section;
• and
• forming the matching section with a parallel inductor and a parallel capacitor each shunt-connected between the feed section and ground, wherein
• the reactance changing section is switchable to one of plural resonant frequencies compatible with respective plural frequency bands, and finely adjustable in response to a change in the switched resonant frequency caused by the influence of the human body,
• the parallel inductor is set to cause the locus of impedance as viewed from the feed section toward the antenna matching circuit to draw a small circle locus in substantially the first quadrant of a Smith chart, and
• the capacitance of the parallel capacitor is adjustable to move the small circle locus to the center on the Smith chart.