Antenna device and radio frequency IC device
An antenna device is arranged to transmit or receive a radio frequency communication signal to or from an external device such as a reader/writer, and is arranged such that an antenna resonance circuit including an antenna coil and a capacitor is connected to an additional resonance circuit including an inductor and a capacitor. A radio frequency IC device preferably includes the antenna device and a radio frequency IC. The antenna device is constructed such that a change in characteristics thereof caused by a change in the distance between a radio frequency IC device and a reader/writer is minimized, and the radio frequency IC device performs communication with high reliability.
1. An antenna device included in a radio frequency IC device that is arranged to perform radio frequency communication with an external device, the antenna device comprising:
an antenna element arranged to transmit or receive a radio frequency communication signal to or from the external device; and
an additional resonance circuit connected to the antenna element, including at least one inductor, and having a resonance frequency different from a resonance frequency of the antenna element; wherein
the resonance frequency of the additional resonance circuit is higher than the resonance frequency of the antenna element, and the resonance frequency of the antenna element is higher than a communication frequency used by the radio frequency IC device.
2. The antenna device according to claim 1 , wherein the antenna element and the inductor included in the additional resonance circuit are arranged to be magnetically coupled.
3. The antenna device according to claim 1 , wherein the additional resonance circuit is a parallel resonance circuit.
4. The antenna device according to claim 1 , wherein the antenna element is connected in series to the additional resonance circuit.
5. The antenna device according to claim 1 , wherein the inductor included in the additional resonance circuit is magnetically shielded.
6. The antenna device according to claim 5 , wherein the additional resonance circuit is provided in a multilayer substrate including a magnetic substance.
7. The antenna device according to claim 6 , further comprising an output inductor that is connected in series to an input portion that is arranged to receive a signal transmitted from a radio frequency IC and is provided in the multilayer substrate.
8. The antenna device according to claim 6 , wherein the additional resonance circuit includes a chip capacitor disposed either on a surface of the multilayer substrate, or in the multilayer substrate.
9. A radio frequency IC device comprising:
the antenna device according to claim 6 ; and
a radio frequency IC disposed either on a surface of the multilayer substrate of the antenna device, or in the multilayer substrate of the antenna device.