Fig. 1. Schematic diagram of the light trajectory of Luneburg lens

Fig. 2. Working principle diagram of Luneburg lens retroreflector

Fig. 3. Schematic diagram of numerical simulation of Luneburg lens retroreflector

Fig. 4. Total electric field patterns under different angles between beam and optical axis of retroreflector. (a) 0°; (b) 30°; (c) 60°

Fig. 5. Normalized reflection amplitude distributions when angle between beam and optical axis of retroreflector is 0°, 30°, and 60°

Fig. 6. Total electric field patterns under different vertical distances between central optical axis and center of sphere. (a) 5λ; (b) 10λ; (c) 15λ

Fig. 7. Normalized reflection amplitude curves under different vertical distances between central optical axis and center of sphere. (a) 5λ; (b) 10λ; (c) 15λ