Abstract-This paper proposes an efficient and automatic means of achieving a reduced model of a transfer function for UWB antenna design. According to the formulation of a transfer function, we have derived two factors, which are critical in determining the radiation pattern and input impedance respectively. Their special formula allow us to establish a reduced model automatically using the Model Order Reduction (MOR) techniques of a second order system. The process is free of any human factors and suitable to any antenna systems, thus enabling a direct and efficient interface with the optimization process in the design of a UWB antenna system. In addition, the proposed way of establishing a transfer function of the whole antenna system has successfully cascaded the entire system into separate subsystems, thus offering deeper insights in analyzing a UWB antenna system.