Calculation of passive intermodulation between rough waveguide flanges induced by quantum tunneling

A theoretical model is presented for calculation of passive intermodulation (PIM) in waveguide junctions. First, the Weibull distribution, instead of Gaussian distribution, is used to simulate the roughness of interconnecting waveguide surfaces because of its capability of characterizing the rough surfaces with asymmetric distribution of asperity heights. And then, based on (1) the assumption that the only passive intermodulation source is the tunnel current flowing through the insulator film on the metal surfaces of the flanges, (2) the equivalent circuit model derived from the contact rough surfaces model, (3) the Fourier Transformation method, the passive intermodulation products of some orders have been calculated. The calculation results are in qualitative agreement with previous research and this justified its application in engineering.