A radiofrequency transponder comprises a radiating antenna consisting of a single-strand helical spring having an axis, a median plane, a pitch and a diameter for a given wire diameter, and an electronic portion located inside the radiating antenna. The electronic portion comprises an electronic chip electrically connected to a primary antenna that is electromagnetically coupled to the radiating antenna. The primary antenna has an axis parallel to the axis of the radiating antenna and a median plane superposed with the median plane of the radiating antenna. The primary antenna is circumscribed by a cylinder the diameter of which is larger than one third of the inside diameter of the radiating antenna. The radiofrequency transponder is characterized in that, in a first region of the radiating antenna, in which the latter is not located plumb with the electronic portion, the inside diameter of the radiating antenna is smaller than the inside diameter of the radiating antenna that does not form part of this first region.