A monopole antenna applicable especially to small mobile stations. In one embodiment, the radiator of the antenna is trough-like in shape so that it covers the head surface, front and rear surfaces and both side surfaces of the dielectric cover of the radio device at an end of the device. On the side of the side surfaces slots are formed in the radiator, starting from its edge, for increasing the electric size. The radiator is fed electromagnetically by a separate element which is shaped so that the antenna has at least two operating bands. The ground plane of the antenna is in one embodiment disposed apart from the radiator, thus not extending inside the ‘trough’.