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 that is arranged to perform radio frequency communication with an external device, the antenna device comprising:
an antenna element including a resonance circuit and configured to transmit or receive a radio frequency communication signal to or from an antenna element of the external device; and
an additional resonance circuit that is connected to a radio frequency IC and magnetically coupled to the antenna element, that includes at least one inductor, and has a resonance frequency lower than a frequency in the radio frequency communication; wherein
a resonance frequency of the resonance circuit and the resonance frequency of the additional resonance circuit are both near the frequency in the radio frequency communication;
the resonance frequency of the resonance circuit and the resonance frequency of additional resonance circuit are in a same frequency band as the frequency in the radio frequency communication;
the resonance circuit is not directly physically connected to the additional resonance circuit; and
the additional resonance circuit is a feeding circuit disposed between the radio frequency IC and the antenna element of the antenna device and is configured to prevent a change in the frequency of the radio frequency communication signal transmitted from the antenna element of the antenna device due to a positional relationship between the antenna device and the external device.
2. The antenna device according to claim 1 , wherein the antenna element is coupled to the antenna element of the external device via a magnetic field coupling.
3. The antenna device according to claim 2 , wherein the frequency in the radio frequency communication is 13.56 MHz.
4. The antenna device according to claim 1 , wherein a physical dimensional size of the inductor of the additional resonance circuit is smaller than a physical dimensional size of the antenna element.
5. The antenna device according to claim 1 , wherein the inductor of the additional resonance circuit is magnetically shielded.
6. A mobile telephone comprising the antenna device according to claim 1 .
7. The antenna device according to claim 1 , wherein the resonance frequency of the resonance circuit is higher than the frequency in the radio frequency communication and the resonance frequency of the additional resonance circuit is lower than the frequency in the radio frequency communication.