Impedance conversion device, antenna device and communication terminal device

An impedance conversion device arranged to be inserted between an antenna element and a feeder circuit, the impedance conversion device comprising:

• a first circuit including a first inductance element connected to the feeder circuit;
• and
• a second circuit including a second inductance element coupled with the first inductance element;
• wherein
• frequency characteristics of a real portion of an impedance of the second circuit are different from frequency characteristics of the first circuit in a direction in which frequency characteristics of a real portion of an impedance of the impedance conversion circuit observed from the antenna element side approach frequency characteristics of a radiation resistance of the antenna element;
• the second circuit includes a capacitor that is connected to the second inductance element;
• the capacitor is connected in parallel with the second inductance element;
• and
• a first end of the first circuit is connected to the feeder circuit, a second end of the first circuit is connected to the antenna element, a first end of the second circuit is connected to the antenna element and a second end of the second circuit is connected to ground.

An antenna device comprising:

• an antenna element;
• and
• an impedance conversion circuit inserted between the antenna element and a feeder circuit;
• wherein
• the impedance conversion circuit includes:
• a first circuit including a first inductance element connected to the feeder circuit;
• and
• a second circuit connected between the antenna element and ground and including a second inductance element that is coupled with the first inductance element;
• the second circuit includes a capacitor that is connected to the second inductance element;
• the capacitor is connected in parallel with the second inductance element;
• and
• a first end of the first circuit is connected to the feeder circuit, a second end of the first circuit is connected to the antenna element, a first end of the second circuit is connected to the antenna element and a second end of the second circuit is connected to ground.

A communication terminal device comprising:

• an antenna device that includes an antenna element, a feeder circuit, and an impedance conversion circuit connected between the antenna element and the feeder circuit;
• wherein
• the impedance conversion circuit includes:
• a first circuit including a first inductance element connected to the feeder circuit;
• and
• a second circuit that is connected between the antenna element and ground and including a second inductance element that is coupled with the first inductance element;
• the second circuit includes a capacitor that is connected to the second inductance element;
• the capacitor is connected in parallel with the second inductance element;
• and
• a first end of the first circuit is connected to the feeder circuit, a second end of the first circuit is connected to the antenna element, a first end of the second circuit is connected to the antenna element and a second end of the second circuit is connected to ground.