An electric transformer device (balun) is formed on a support plate having a first base face and an opposite second base face. The balun includes a first port (40) connectable to an electrical line for a differential signal and a second port connectable to an electrical line for a single-ended signal. A first printed conductive track is associated to the first base face of the support plate for connecting the first port to the second port. A printed conductive path is associated to the second base face of the support plate for connecting the first port to the second port. The printed conductive path is formed of a symmetric second and third printed conductive tracks.