The positioning signals broadcast by the GNSS constellations on civilian frequencies are likely to be counterfeited, while the use of authentic signals is becoming increasingly critical for certain applications. According to the invention, the authentication of GNSS signals is performed by analysis of consistency between the measurements of parameters characteristic of the signals (direction of arrival, amplitude, phase) and their state model, said state model taking account of an emulation by software and electronic means of displacements of the phase centre of the antenna and/or of the main lobe of the radiation pattern. Advantageously, these displacements are generated by a pseudo-random code. Advantageously, the analysis of consistency between measurements and models is a multiple-criterion analysis, the combination of criteria being chosen as a function of a reception quality indicator and/or of a presumed location.