A subwavelength structure based on Ag/Al/Ag multilayer, consisting of a narrow slit and periodically patterned metallic grooves, with property of high directional radiation, is proposed and an experimental platform used for direct optical far-field measurement is designed and built. In the simulation, we analyzed the influence of beaming effect on structure parameters, and optimized the values by finite element method. The results show that the structure can radiate light with narrow divergence angle in far field by 632.8 nm TM light. Moreover, we performed experiments to test the far-field radiation performances of the slit-grooves sample. The results illustrate that the far-field divergence angle of the structure is about 4.1°, which is in good accordance with simulation results.