A new topology for 2-D scanning multibeam array antenna (MAA) design is proposed. Different from the traditional 2-D scanning scheme, this new design approach is composed of a 1-D beam-forming network (BFN) and a set of 1-D pattern-reconfigurable antennas, which can together realize 2-D multibeam scanning. Compared with traditional schemes, the proposed topology has advantages of uniplanar configuration and better flexibility in scaling up the array. To demonstrate the validity of the proposed topology, a high-gain 2-D scanning leaky-wave MAA operating at 10 GHz is designed. A horn BFN and a fixed-frequency leaky-wave antenna (LWA) are designed as the feeding part and radiation part, respectively. A number of new techniques are also developed for the design. For the horn BFN, a new phase-compensation method to reduce the gain drop is presented and phase inverters are introduced to provide an extra 180° of phase shift. Meanwhile, some modification of the LWA is conducted for better compatibility between the horn BFN and the LWA. A substrate integrated waveguide (SIW) to half-mode SIW (HMSIW) transition is introduced between the horn BFN and the LWA. The LWAs are terminally shorted to avoid the usage of matched loads. The width of the LWA is investigated to achieve suitable beam coverage and S-parameters. Finally, the antenna is fabricated and experiments are conducted to verify the agreement between simulation and measurement.