AbstractA methodology will be presented for incorporating arbitrary, multiport, nonlinear devices into a three‐dimensional (3D) condensed node TLM mesh. Gear's second‐order predictor‐corrector algorithm with a variable step size is used to solve the differential equations of the device. Two examples are given to demonstrate the concepts and the versatility of the method. These include a waveguide cavity varactor‐tuned oscillator and a diode switch. © 1993 John Wiley&S