In mathematics, a nonlinear system is one that does not satisfy the superposition principle, or one whose output is not directly proportional to its input; a linear system fulfills these conditions. One of the greatest difficulties of nonlinear problems is that it is not generally possible to combine known solutions into new solutions.

Regard to non-linear circuit system analysis, the most widely applied techniques used is the linearization, which separate the non-linear system into a linear part plus a non-linear part. Give small amount of vibration at a large operating point. This forms the foundation of analyzing semiconductor based non-linear circuits analysis, such as transistors and diodes. Large and small signal models, DC and AC analysis are all derived from this principle.

Another popular techniques applied in analyzing non-linear circuit systems is transient iterative method, which sets a external control parameter such as gate and cut-off voltage to perform a switch control. Such method is relatively simpler because the control parameters can be easily modeled and implemented locally within the non-linear devices. And the non-linear behaviors will be coupled into the system through iterative interactions between the non-linear devices and other systems.

In this page, we simulated several examples using the software Wavenology EM, showing some abilities of the software in performing full-wave analysis of non-linear microwave devices.

To add a non-linear device to the microwave structure, we first investigate how to make a real SPICE model in Wavenology EM to represent the real devices. As an example, a varactor diode is chosen. We first use a microstrip line benchmark with a 50 Ohm lumped port terminating one end and the varactor terminating the other, as shown in Fig. 1.

The semiconductor parameters of the varactor diode is shown in Fig. 2, where the SPICE model and related control parameters are also listed. Such model can be easily built in Wavenology EM. Simply click the