A low phase noise frequency synthesizer includes arranged in series, a first mixer receiving a reference signal at a reference frequency Fr, a loop filter and a voltage-controlled oscillator delivering a microwave signal at a second frequency FO slaved to a multiple of reference frequency Fr, the frequency synthesizer further includes: means of multiplication of the frequency FO of the microwave signal by a factor N strictly greater than 1, means of correction of the frequency N·FO of the output signal of the multiplication means to restore frequency N·FO to an interval [FOmin, FOmax] where output frequency FO would vary if multiplication factor N=1, means of division of the frequency Fj of the output signal of the correction means by a factor equal to the expected ratio between frequency Fj and reference frequency Fr, the frequency division means connected at output to the second input of the first mixer.