In this article, low-sidelobe cavity-backed slot antenna array with simplified feeding structure for vehicular communication is proposed. Conventional low-sidelobe antennas were realized using power dividing network to obtain the in-phase and nonuniform-amplitude excitation, which causes complicated antenna's structure and design. To tackle these challenges, a simplified feeding method without using power dividing network is introduced to design the low-sidelobe slot antenna array. The slots at the top walls serve as the radiation elements, and the slots are directly fed by the electric field of the cavity mode. Nonuniform amplitude is obtained by simply modifying the slots' sizes and positions, while the in-phase excitation of the elements is remained. The nonuse of power dividers brings out a simpler antenna structure than conventional full-metal waveguide-based antennas. Besides, the full-metal structure introduces a high power-handling capacity. Then, two linear arrays with 1 × 4, 1 × 7 elements and a planar array with 5×4 elements are presented to show the design feasibility. Finally, the 5 × 4 antenna array is fabricated and measured, which can achieve 18.2 dBi gain, -20 dB sidelobe level, 94% radiation efficiency, and -42 dB cross-polarization. Good agreement between measurement and simulation verifies the feasibility of the proposed design concept.