Spectral and directional control of thermal emission holds substantial importance in different kinds of applications, where heat transfer is predominantly by thermal radiation. Several configurations have previously been proposed, like using gratings, photonic crystals, and resonant cavities. In the present work, we theoretically investigate the influence of periodic microstructures such as micro-scale gratings and photonic crystals on the thermal radiative properties of a structure constituted with these periodic microstructures. The enhanced thermal emission is found to be due to different excitation modes and the coupling between them. In order to offer insight into the mechanisms, we calculate and visualize the electromagnetic field profile at specified emission peaks. Furthermore, the emissivity pattern is calculated as a function of the emission angle and the angular frequency. The results reveal detailed spectral and directional dependence, and omnidirectional feature of thermal emission from the proposed structure. We show that it is possible to flexibly control the emission behavior by adjusting the structure dimensional parameters properly.

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