1. A method for measuring the radar cross-section of a given object from a diffraction model of said object, said model being able to be represented by a matrix (A b ) of ratios of diffracted wave and incident wave complex amplitude, for a first plurality (4N 2 ) of pairs of respective incident wave and diffracted wave observation directions and polarizations, characterized in that: a modal decomposition of said matrix is carried out and the most significant modal vectors of said thereby diagonalized matrix are then selected; complex amplitudes of an incident wave and an object diffracted wave are measured for a plurality of pairs of directions and at least one pair of respective incident wave and diffracted wave observation polarizations; a second plurality (N μ ) of ratios of said measured diffracted wave and incident wave complex amplitudes are calculated; the vector (a μ ) formed by the thereby measured ratios is projected on said most significant modal vectors; from the thereby projected vector and from the most significant modal vectors, a reconstructed vector (ã) is generated, the components of which are representative of the ratios of incident and diffracted wave complex amplitudes for said first plurality of pairs of directions and of polarizations; and a measurement of said radar cross-section is obtained from at least one component of the reconstructed vector.