An internal dual band antenna meant for small radio devices. In one embodiment, the antenna contains two radiators and a parasite element, which is shared between them. The parasite element is implemented on three sides of the antenna module, which are perpendicular to the side where the two radiators are implemented. The short-circuit conductor of the parasite element extends close to the supply point/points of the antenna on the circuit board of the radio device and is connected to the ground plane of the radio device. The antenna structure is dimensioned such that the two resonance frequencies on both functional bands are at a lower frequency than the resonance frequencies of the actual radiators. Accordingly, both the lower and upper frequency band is widened. The shape of the parasite element does not weaken the adaptation of the antenna in either functional band.