  A low-divergence beam is an essential prerequisite for a high-efficiency
longdistance optical link, particularly for satellite-based quantum
communication. A point-ahead angle, caused by satellite motion, is always
several times larger than the divergence angle of the signal beam. We design a
novel transmitting antenna with a point-ahead function, and provide an
easy-to-perform calibration method with an accuracy better than 0.2 urad.
Subsequently, our antenna establishes an uplink to the quantum satellite,
Micius, with a link loss of 41-52 dB over a distance of 500-1,400 km. The
results clearly confirm the validity of our model, and provide the ability to
conduct quantum communications. Our approach can be adopted in various free
space optical communication systems between moving platforms.
