An optical phased array (OPA), the most promising non-mechanical beam steering technique, has great potential for solid-state light detection and ranging systems, holographic imaging, and free-space optical communications. A high quality beam with low sidelobes is crucial for long-distance free-space transmission and detection. However, most previously reported OPAs suffer from high sidelobe levels, and few efforts are devoted to reducing sidelobe levels in both azimuthal (φ) and polar (θ) directions. To solve this issue, we propose a Y-splitter-assisted cascaded coupling scheme to realize Gaussian power distribution in the azimuthal direction, which overcomes the bottleneck in the conventional cascaded coupling scheme and significantly increases the sidelobe suppression ratio (SLSR) in the φ direction from 20 to 66 dB in theory for a 120-channel OPA. Moreover, we designed an apodized grating emitter to realize Gaussian power distribution in the polar direction to increase the SLSR. Based on both designs, we experimentally demonstrated a 120-channel OPA with dual-Gaussian power distribution in both φ and θ directions. The SLSRs in φ and θ directions are measured to be 15.1 dB and 25 dB, respectively. Furthermore, we steer the beam to the maximum field of view of 25° × 13.2° with a periodic 2λ pitch (3.1 μm). The maximum total power consumption is only 0.332 W with a thermo-optic efficiency of 2.7 mW∕π.