The paper aims to develop a geophysical model function that allows retrieval of the wind speed vector from a radar signal scattered from the sea surface. During in situ experiments on the stationary oceanographic platform in 2022-2024, a database was created which contained radar information, frequency spectra of sea surface elevations, wind speed and direction, and geometric properties of breaking wave crests in the active phase. An MRS-1011 360-degree marine radar (X-band, 3 cm wavelength) transmitting and receiving horizontally polarized signal at large incidence angles was used in the experiments. For these observation conditions, the main informative parameter that governs the radar cross section is the fraction of the sea surface covered by wind wave breaking crests (whitecap coverage). The role of this parameter is qualitatively confirmed by the fact that the radar power and whitecap coverage have similar wind speed dependencies. It was shown that the radar cross section was proportional to the whitecap coverage with 1.47 as the proportionality coefficient. The intensity of wave breaking also depends on the wave age, which leads to the dependency of the radar cross section on the wave development stage. The influence of the wave age on the radar signal level was confirmed experimentally. It was shown that the level of the wind dependency of the radar signal in the "up-wind" direction increased by a factor of 5 when the wave age increased from 0.1 to 1.2. Based on the in situ data and physical grounds of the sea surface radar backscatter formation, we suggest a geophysical model function allowing retrieval of wind speed fields in areas within a radius of about a kilometer. The error in wind speed vector magnitude and direction retrieved from radar data was 1.2 m/s and 30°, respectively, compared to the data obtained by the anemometer.