Patent ID: 8915448

Claim:
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.