Abstract: Traditional weather radar calibration frameworks primarily focus on discrete components and are unable to calibrate the radar system as a whole, particularly the antenna subsystem. In recent years, passive far-field calibration methods have been proposed; however, they are highly susceptible to environmental influences, exhibit weak interference resistance, and introduce large calibration errors for rapidly varying parameters such as velocity and range. In this study, an active far-field calibration system for weather radar is developed. By receiving and retransmitting the transmitted signal of the radar under test, the system generates simulated targets with known amplitude, delay, and velocity, thereby enabling full-chain calibration under realistic radar sensing conditions. Laboratory experiments and field tests demonstrate that the proposed system can electronically configure simulated targets with high accuracy and repeatability, effectively reducing uncertainties associated with scattering effects and rapidly varying parameters (e.g., velocity) in field calibration. Moreover, by flexibly modulating the characteristics of the retransmitted signal, the system enables full-chain calibration testing and experimentation for arbitrary parameters of interest.