An antenna device for a signal having a frequency within an operation band comprises a ground element, a radiating element short-circuited to the ground element, a positive feed connected to the radiating element, and a ground feed coupled to the ground element by a capacitive element. The capacitive element is a substantially open circuit for signals having a frequency lower than the operation band. The capacitive element is a substantially short circuit for signals having a frequency within or higher than the operation band.