Incorporación de dispositivos activos en simuladores FDTD a partir de parámetros S medidos y de técnicas de ajuste racional

The equivalent circuit approach is the most common choice to account for lumped components in the finite-difference time-domain (FDTD) method. However, when dealing with active devices, equivalent circuit models are not easy to obtain and, even, some components are not described reliably by such an approach. In this work, we combine the two-port lumped-network FDTD method with rational fitting techniques to incorporate active devices characterized by S-parameters into FDTD simulators. To this end, the Y -parameters are approximated by rational functions of the complex frequency s. Finally, the polynomial coefficients of the rational functions are used directly as input parameters of the TP-LN-FDTD method. This technique is applied to the calculation of the S-parameters of a hybrid structure including a field effect transitor as active device. The results obtained are compared with those provided by a commercial simulator and with measurements