An efficient approach to the synthesis of large-aperture slotted-waveguide antennas (SWA) is proposed. The approach is based on a combined usage of a full wave simulation and physical properties of SWA. The proposed approach was applied to the development of a large-aperture Ka-band antenna with a 1 meter aperture. The obtained antenna gain is close to the theoretical maximum for such aperture. The antenna is also characterized by a relatively wide frequency operational range that is achieved by application of the subarraying technique. The influence of the systematic and random manufacturing errors on the antenna performance is investigated. A comparison of the simulation results with the antenna measurement results is presented as well.