Recently, daytime radiative cooling has drawn much attention because of its sustainability and energy-saving capability. For better radiative cooling performance, spontaneous thermal emission from an object should be superior to heat influx. From the standpoint of thermal emission, omnidirectionally high emissivity is desirable for greater emissive power since a thermal radiation is emitted through entire hemi-spherical direction. In this work, to achieve omnidirectional emission in both polar and azimuthal angles, a complex grating in hexagonal array is proposed and optimized by a surrogate model based on an artificial neutral network. The optimized structure demonstrates about 20 W/m(2) higher emissive power compared to other radiative cooling structures due to its omnidirectional feature. The optimal structure results in the daytime radiative cooling power of 89.2 W/m(2) and the associated cooling temperature of 10.1 C below the ambient temperature under the air-mass 1.5 condition. (C)& nbsp;2022 Elsevier Ltd. All rights reserved.