Passive radiofrequency transponder intended to be integrated into a mass made of elastomer blend, comprising: - a radiating dipole antenna consisting of a single-strand helical spring having an axis of revolution, a winding diameter (D1, D2), a helix pitch (PI, P2), a median plane and a wire diameter defining inside and outside diameters of the radiating antenna, the length of which is suitable for communication in a frequency band with a radiofrequency-transmitting reader, and - an electronic portion located inside the radiating antenna, comprising: i. an electronic chip; ii. a primary antenna electrically connected to the electronic chip and electromagnetically coupled to the radiating antenna; iii. said primary antenna having an axis substantially parallel to the axis of revolution of the radiating antenna; iv. said primary antenna having a median plane which is substantially superposed with the median plane of the radiating antenna; and v. said primary antenna being circumscribed by a cylinder the axis of revolution of which is parallel to the axis of the primary antenna and the diameter of which is larger than or equal to one third of the inside diameter of the radiating antenna, located plumb with the primary antenna; characterized in that a first inside diameter of the radiating antenna corresponding to the inside diameter of the radiating antenna in a first region (101, 101a, 101b) not located plumb with the electronic portion is smaller than the second inside diameter of the radiating antenna corresponding to the inside diameter of the radiating antenna in a second region located plumb with the electronic portion and in that the electronic portion is circumscribed by a cylinder the axis of revolution of which is parallel to the axis of revolution of the radiating antenna and the diameter of which is larger than or equal to the first inside diameter of the radiating antenna. - a radiating dipole antenna consisting of a single-strand helical spring having an axis of revolution, a winding diameter (D1, D2), a helix pitch (PI, P2), a median plane and a wire diameter defining inside and outside diameters of the radiating antenna, the length of which is suitable for communication in a frequency band with a radiofrequency-transmitting reader, and - an electronic portion located inside the radiating antenna, comprising: i. an electronic chip; ii. a primary antenna electrically connected to the electronic chip and electromagnetically coupled to the radiating antenna; iii. said primary antenna having an axis substantially parallel to the axis of revolution of the radiating antenna; iv. said primary antenna having a median plane which is substantially superposed with the median plane of the radiating antenna; and v. said primary antenna being circumscribed by a cylinder the axis of revolution of which is parallel to the axis of the primary antenna and the diameter of which is larger than or equal to one third of the inside diameter of the radiating antenna, located plumb with the primary antenna; i. an electronic chip; ii. a primary antenna electrically connected to the electronic chip and electromagnetically coupled to the radiating antenna; iii. said primary antenna having an axis substantially parallel to the axis of revolution of the radiating antenna; iv. said primary antenna having a median plane which is substantially superposed with the median plane of the radiating antenna; and v. said primary antenna being circumscribed by a cylinder the axis of revolution of which is parallel to the axis of the primary antenna and the diameter of which is larger than or equal to one third of the inside diameter of the radiating antenna, located plumb with the primary antenna;