Effect of Impedance Discontinuity Induced by Line Bending on Passive Intermodulation in Connector-Microstrip Assemblies

Scattering parameters (S-parameters) and passive intermodulation (PIM) characterize the signal integrity for small signal excitation and nonlinearity for high-power excitation. In this letter, a model that relates the S-parameters and PIM is theoretically proposed and experimentally verified. A simplified PIM model is presented to investigate the effect of impedance mismatch between two nonlinear points on the reflected intermodulation (IM) powers. Considering the impedance discontinuity induced by line bending, the impact of different bending angles on transmission phase and signal reflection is simulated. Through the combination of S-parameter modeling and passive nonlinear transfer functions, an equivalent circuit is developed to simulate the IM3 powers resulting from connector–microstrip assemblies with different line bending angles. In addition, a series of PIM tests are conducted with customized samples. Experimental results are consistent with the predictions, showing the effect of the scattering characteristics on the PIM.