Abstract: The invention relates in one aspect to antenna useful with for example a flat a radio device. In one embodiment, the antenna comprises and internal monopole antenna that has an arrangement for improving its characteristics, including a planar monopole radiator and an auxiliary element. The auxiliary element can be a mere conductor strip, or a ceramic plate partly coated with a conductor for example. The conductor of the auxiliary element is connected to the ground at a point (SP), which is relatively close to the feed point (FP) of the planar element. The planar element can be shaped to form two operating bands for the antenna. The auxiliary element can be used to increase the bandwidth of the internal monopole antenna and/or to improve the omnidirectional radiation of the antenna.