Abstract : Stimulated Raman amplification of optically carried microwave signals in optical fibers is experimentally investigated. In the backward configuration which is shown to be less noisy than the forward one, net amplification factors larger than 25 dB are demonstrated with better relative intensity noise (RIN) values than using a commercially available EDFA. A theoretical analysis of the Raman amplification in optical fibres and pump to signal RIN transfer has been performed in the spectral domain for two limiting cases of modulated monochromatic and smooth profile large bandwidth pump beams. In all cases, at large frequency detunings the RIN transfer decreases. At low frequencies an excess of noise was evidenced in the case of a modulated monochromatic pump beam which did not exist in the case of large bandwidth pseudo-incoherent sources which makes them interesting candidates for the purpose of low noise Raman amplifiers. We also studied the possibility of reducing amplified spontaneous emission noise. The use of two pump lasers (same power) whose frequency detuning is small compared to the Raman bandwidth should prove efficient. Holographic, "non linear optics" and quantum descriptions all lead to the conclusion that the pumps have to be opposed in amplitude.