Abstract: Noise figure is one of the core metrics of active phased array radar and is closely related to radar detection range. With the development of broadband, sub-arrayed, and distributive active phased array antennas, the active link design becomes increasingly complex, requiring urgent to development of precise analysis methods for calculating the cascaded noise figure in multi-level, multi-port link system. Firstly, a generalized noise figure formula for sub-arrayed active phased array antennas is derived based on the definition of noise figure, which can be simplified to the conventional cascaded noise figure formula in handbook under specific boundary conditions. Then two engineering practical application scenarios are implemented, including different power division ratio designs in antenna array feeding networks and low-sidelobe amplitude-weighted hierarchical design, providing guidance and theoretical basis for the design of sub-arrayed broadband active phased array antenna.