A weighted full-spectrum signal combining technology for cislunar Space-VLBI

In the Chang'E-7 mission of the fourth stage of China's Lunar Exploration Project, the relay satellite will carry a 4.1-m aperture X-band parabolic telescope. This and the ground-based telescopes will form a lunar orbit very long baseline interferometry (VLBI) experimental system with the space-ground baseline up to 400000 km. To improve the sensitivity of this baseline, we propose a weighted full-spectrum signal combining method. First, we derive the optimal weighting coefficient ratio for combining the signals of the two telescopes. Then, we propose the VLBI weighted full-spectrum combining method whose optimal weight coefficient is determined by investigating the data, and the obtained result is consistent with the theoretical derivation. Finally, we use Chang'E-4 original VLBI observation data for method testing. The results show that the signal combining method proposed in this work can greatly improve the signal-to-noise ratio for VLBI observations.