Patent ID: 8508420

Claim:
An antenna device comprising: a first antenna unit including a feed electrode, a first radiation electrode, and a first frequency-variable circuit connected between the first radiation electrode and the feed electrode; and a second antenna unit including the feed electrode, a second radiation electrode, and a second frequency-variable circuit connected between the second radiation electrode and the feed electrode; wherein the first frequency-variable circuit includes a first reactance circuit connected to the feed electrode, the first reactance circuit consisting of a first coil connected in series with a first variable-capacitance diode whose capacitance is variable using a control voltage; and a second reactance circuit connected between the first reactance circuit and the first radiation electrode, the second reactance circuit consisting of a second coil connected in series with a second variable-capacitance diode whose capacitance is variable using the control voltage; the second frequency-variable circuit includes the first reactance circuit; and a third reactance circuit connected between the first reactance circuit and the second radiation electrode, the third reactance circuit consisting of a third coil connected in series with a third variable-capacitance diode whose capacitance is variable using the control voltage; and the first radiation electrode has a loop shape and includes an open end that faces the feed electrode with a gap therebetween, a reactance of the first antenna unit is provided by the gap between the open end of the first radiation electrode and the feed electrode; wherein cathodes of the first, second, and third variable-capacitance diodes are connected to each other, and the control voltage is configured to be applied where the cathodes are connected to each other.