Silicon photonic optical phased array is a promising solution for solid-state LIDAR. But the nonlinear absorption significantly saturates the optical power in the waveguides at 1.5-um wavelengths. Besides, the high refractive index contrast of silicon grating exhibits a strong diffraction strength of the antenna, which results in a limited aperture of the device. These ultimately place a limit on the detection accuracy and reach. Here, shallow etched two-dimensional subwavelength grating structure are proposed to improve the efficiency and aperture of the waveguide antenna. A reduction of diffraction strength is achieved via nanohole structure instead of conventional grating lines. Thus, a millimeter-long optical antenna is demonstrated with peak efficiency of 71%. The far-field diffracted beam width of 0.035 and vertical field-of-view of 17.5 are achieved within 100 nm wavelength range from 1.95 um to 2.05 um. The operation at 2-um waveband also guarantees better eye-safety and significantly reduces the nonlinear absorption in silicon waveguide compared with conventional 1.5-um band.