by a metallic ribbon arranged in a planar loop which is closed in the present example this loop surrounding a space devoid of any metallic element the various components of the transponder are fastened to a support of dielectric material which has not been shown since it may be of any desired form the operation of the transponder of fig1 is identical to that of the transponder described in the european patent application ep a 0 172 445 already mentioned hereinabove and which will not be further explained it is nevertheless to be noted that with equal outer dimensions the surface of the metallic parts of the transponder according to the invention in particular the surface of the antenna elements 1 and 2 is much less than the surface of the metallic parts of the transponder described in the patent application mentioned hereinabove due to the fact that the antenna elements have the general form of a loop surrounding a space devoid of any metallic element the capacitance of the stray capacitor formed by these antenna elements 1 and 2 and the body of the person bearing the transponder is thus much less in the transponder of fig1 than in that of the prior art there results therefrom that the gain of the transponder in accordance with the invention is greater than that of the known transponder for the reasons explained hereinabove in the embodiment shown on fig2 the transponder in accordance with the invention includes as in the case of the transponder of fig1 two antenna elements designated by 11 and 12 which are coupled on the one hand by a diode.