The present invention relates to a modulation device of a microwave signal, a transponder comprising such a device and a transponder provided with such a transponder. The field of the invention is in particular that the location of targets, moving or stationary, using transponders. For this location, it is necessary to use transponders, for example for the detection of moving objects or substantially zero speed such as a helicopter hovering in particular. In this context, a problem to solve is to produce low cost transponders offering good performance. To carry transponders, the solutions of the prior art use of nonlinear systems, including microwave mixers. They implement amplitude or phase modulation. The transponder and retransmits a received signal with an amplitude modulation or a phase modulation. To this end, a first input of a mixer receiving the signal received by the transponder and a second input receives the modulation signal, the modulated signal being obtained at the output of the mixer. This type of modulation by means of mixers results of harmonic lines following the non-linear cut-outs made on the signal as shown in amplitude modulation described below. Consider a signal CW (t) received by the transponder, this signal is continuous, of amplitude A, frequency and phase shift φι, it has the following form: CW(t) = A sin(27r it +