Solution Of The Nonlinear Circuit And Electro-thermal Analysis

Passive intermodulation(PIM) has gradually become a serious electromagnetic interference due to the higher power,broader frequency band and higher sensitivity RF/microwave communication system. On the one hand, this thesis proposes a time-domain finite-difference(FDTD) method for passive intermodulation analysis of MM contact. And a power series model and an equivalent circuit model are used to describe the nonlinear metal-to-metal(MM) contact. On the other hand, electro-thermal coupling is found to be a PIM source and the electro-thermal distortion is studied. The prime tasks and outcomes are as follows:1. A FDTD method for passive intermodulation analysis of MM contact is proposed. There are two kinds of model to describe the nonlinear MM contact named a power series model and an equivalent circuit model. Then the FDTD method is applied to analyze the nonlinear circuit constructed by above MM contact models so that the nonlinear current through the MM contact point can be calculated. Taking the electric current as a new electromagnetic wave source, the far-field scattering can be obtained by the FDTD method. The PIM power level can be calculated by Friis transmission equation. Finally, a comparison between simulation and experimental results is illustrated to verify the validity of the proposed method.2. Microwave load, as a common microwave device, is used to improve the matching performance of circuit and absorb the microwave energy. The electrical resistivity of load is affected by the joule heat leading to the nonlinear I-V characteristics. This process results in the generation of the passive intermodulation products. The difference of electro-thermal time scale is the primary problem for the analysis of electro-thermal passive intermodulation. In order to analyze the electro-thermal passive intermodulation problem, a fractional heat conduction model of microwave load is constructed by fractional calculus firstly. According to the fractional heat conduction model, a fractional electro-thermal circuit model is established secondly. Eventually, combining thermo-resistance effect, the PIM power level expression is derived from the fractional electro-thermal circuit model. The magnitude of the temperature coefficients of resistance, thermal resistance and thermal capacity is analyzed to diminish the electro-thermal distortion PIM power level.3. MATLAB GUI module is adapted in programing the above established models with the parametric graphic interface. The program can be used to calculate the PIM power level caused by nonlinear contact and electro-thermal distortion.