Weather radar system which uses antennas constituted by the elongated aperture of waveguides, and form at least an array (510, 520) mounted on a rotating horizontal (502), and the said apertures are as wide as one wavelength (λ) and length higher than 20λ, wherein the small aperture in azimuth ranges from 0.5° to 2° and is synthesized by high rotational speeds together with signal processing techniques such as ROSAR.