Abstract: The G/T value of active phased array antenna is a key figure that determines the sensitivity and operating range of radar and communication systems. In engineering practice, there is an urgent need to establish an accurate noise figure budgeting method applicable to non-ideal conditions such as channel failure and amplitude weighting. In this paper, by combining the scattering matrix characteristics of the Wilkinson power-combining network and the signal correlation mechanism, an equivalent noise figure model for the receiver of an active array is established. The degradation of the array noise figure caused by the inherent loss of unequal-ratio power-combining networks, active channel failure, and amplitude weighting are systematically analyzed, providing theoretical support for the optimal design of phased array receiver and the accurate budgeting of the G/T value. Based on this model, a Ka-band phased array antenna RF frontend was developed, comprising 1,840 waveguide radiating slot elements and integrating 96 independent active T/R channels. Anechoic chamber measurements of the antenna system radiation pattern and G/T value were completed, validating the effectiveness and engineering accuracy of the noise model, and providing a basis for G/T budgeting and performance optimization of phased arrays.