Linearity–Nonlinearity-Separation FDTD Method for Nonlinearity Analysis of Passive Microstrip Circuits

A linearity–nonlinearity-separation (LNS) finite-difference time domain (FDTD) full-wave method is suggested for the weak nonlinearity analysis of the passive microstrip circuits, which is effective for the passive intermodulation (PIM) and harmonics evaluation induced by the material nonlinearity. The nonlinear Maxwell curl equations are linearized by dividing the fields into linear and nonlinear parts. The linear part field can be solved using the traditional FDTD method excited by the input carriers, while the nonlinear part field is calculated using the equivalent excitation sources controlled by the linear part field. The PIM effect of a microstrip line with dielectric nonlinearity was calculated to demonstrate the effectiveness of this method. This method could be useful to evaluate the PIM and harmonics of different microstrip structures at the design stage to develop the low nonlinearity microstrip circuits.