Abstract: A high performance radome for satellite communication phased array antenna on high speed rail platform is designed in this paper. The proposed antenna radome has an ultralow profile and a symmetric aerodynamic structure, which satisfies the demand of low air resistance for bidirectional high-speed carrier. Based on the beam-scanning requirement of the adopted phased array antenna, a sandwich radome structure with variable thickness of the core layer is designed for the realization of high transmission rate at large incident angles. An engineering prototype at Ku satellite communication band is co-designed, manufactured and measured. Over the 2.5 GHz operating bandwidth from 10.5 GHz to 13.0 GHz, for arbitrary polarization direction, the measured transmission rate is maintained above 80% through an incident angle range of 0-70°. Meanwhile, the pointing error of the radome to the phased array scanning beam is maintained within the range of ±0.5 degrees.