Abstract <p>The paper describes an original setup for studying the contribution of capillary waves in the range of wave numbers <i>k</i> = 100–1200 rad/m to the microwave radiation of the surface. A feature of the technical solution is the generation of an almost monochromatic capillary grid of waves on the surface of a flat vessel, which allows for a “pure” study of critical phenomena occurring in the microwave radiation of the surface at certain observation angles. The generation of capillary waves of a given frequency and amplitude was carried out by a thin bar on the surface and its oscillations were set by the author’s device located under the water surface. The shape of the resulting wave was recorded with the accuracy of 0.03 mm by an original method based on reflections from the surface. The vertical observation angle varied from 8° to 70° and the azimuthal rotation angles of the capillary grating changed by 360°. The microwave radiometer made it possible to measure variations in brightness temperature in four polarizations with the sensitivity of 0.1 K and with the accumulation time of 1 s. It was found that capillary waves with the amplitude of only 0.15–0.20 mm cause a resonant increase in the radiation intensity, reaching 5–6.5 K. Both the amplitude and the position of the resonant peak, which shifted to smaller elevation angles as the capillary wave length tended to the radiation wavelength, are consistent with the theory.</p>