A novel method considering nonlinear conduction mechanism is proposed to calculate the passive intermodulation (PIM) at waveguide connection and to deal with the prediction difficulty of PIM under high power condition. By taking the fact into account that the surface of the waveguide is always rough and that there is usually a dielectric thin film on it, the waveguide connection is regarded as a metal-insulator-metal structure, and the rough surface contact model and the equivalent circuit model are given. Then, the quantum tunneling current and the thermionic emission current are assumed to be the main nonlinear sources of PIM across the real waveguide connection, and the PIM power levels are obtained with the aid of the Fourier Transformation.Compared with the conventional power series method, the proposed method can compute any order of PIM rapidly without parameter fitting. Simulations on rectangular aluminum waveguide operating at TE10 mode are performed. The results show that the PIM power have a lower level under heavier contact pressure; higher order PIM power have more dependence on the power ratio of the input power; and the growth rates for 5-, 7-, 9- order PIMs power are all about 2, which is more realistic than the theoretical results from the classic power series method.%针对大功率条件下金属波导连接的无源互调(PIM)难以预测的问题,提出了一种金属波导结的PIM非线性物理机制和计算方法.考虑到波导表面的粗糙度和薄介质层,将波导连接视为MIM(Metal-Insulator-Metal)结构并确立其粗糙表面接触模型和等效电路模型,然后依据MIM结构的导电机理将量子隧穿电流和热发射电流视作引起PIM的非线性根源,最后运用傅里叶变换计算各阶PIM功率.相比传统的幂级数方法,该方法能快速计算各阶PIM且无需进行参数拟合.以双载波条件下工作于TE10模式的铝质矩形波导为例进行仿真实验.结果表明:波导间接触压力越大,各阶PIM越小;PIM阶数越高,载波功率之比对其影响越大;新方法预测的5、7、9阶PIM功率相对于载波功率的增长率约为2,比传统幂级数展开法估计的结果更符合实际.
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