The generalized system function, associated with the radiated or scattered fields is presented in this paper, which is constructed by applying a windowed interpolation model-based parameter estimation technique. By analyzing the characteristics of poles of this system function in the operational frequency band, the resonant frequency and Q-value of the antenna and scattering systems are determined. Compared with the generalized MBPE procedure, this windowed scheme can reduce Pade function to only four orders, which effectively alleviates the problem such as ill-condition, low calculation efficiency etc. caused by high-order matrix.