A high-efficiency Ka-band dual-offset reflectarray antenna using two element types is presented. Two elements are used to achieve 360° reflection phase coverage, low phase sensitivity, and insensitive angle of incidence. An equivalent circuit model is used to analyze the characteristics of each unit cell. Dual-offset design is proposed to reduce volume and avoid blockage loss. Aluminum honeycomb is used to realize panel flatness and low weight. The aperture efficiency of the proposed antenna is maximized by optimizing the position of the feed and the reflector based on geometrical optics. The simulated and measured efficiency of the proposed antenna is 65.16%, and 52.14% respectively, at 35.75 GHz.