Fig. 1. Working principle of QD

Fig. 2. Structural schematic of Cassegrain optical antenna system

Fig. 3. Models of facula with Gaussian distribution energy. (a) Complete circular facula; (b) annular facula

Fig. 4. Structural schematic of APT system. (a) Beam alignment detection system for fine tracking; (b) beam transverse drift; (c) angle error of beam and receiving antenna boresight

Fig. 5. (a) Schematic of annular facula detection; (b) distribution of calculated values of x at (0.14, 0)

Fig. 6. Annular facula energy distributions of QD. (a) Beam has been aligned; (b) 0

Fig. 7. Error analysis of annular facula and complete facula algorithms. (a) X-axis output results and position of actual facula; (b) detection sensitivity

Fig. 8. Variation in target facula offset x with facula center coordinate X' when Rd=1 mm

Fig. 9. Variation in target facula offset x with facula center coordinate X' when Rx=0.3 mm

Fig. 10. Schematic of compensation algorithm. (a) Compensation value; (b) compensation of angle error

Fig. 11. Diagram of experimental system

Fig. 12. Schematic of facula search process. (a) Path of helical scanning; (b) output data of scanning process

Fig. 13. Measured data of variation in target facula offset x with facula center coordinate X' when shading ratio is determined

Fig. 14. Detection value of position offset of annular facula

Fig. 15. Miss distance of facula in fine tracking