Backscattering of a microwave signal is considered in the Kirchoff approach and in two-scale model of the scattering sea surface. The effective reflection coefficients in Ku (0.021 m), C (0.055 m), and S (0.09 m) bands are calculated. Dependences of the radar cross section on wind speed, wind fetch, and swell height are studies and closeness of numerical estimations and experimental data is shown. The dependence of difference radar cross section on wind speed or one of the backscattering radar cross sections in two-frequency measurements is analyzed. It is shown that the developed model allows describing the nonmonotonic behaviour of the difference radar cross section observed in the experiments. The proposed model enabled us to predict the behaviour of the difference radar cross section for the new pair of frequencies (C - S bands).