Passive intermodulation (PIM) by metal contacts limits the bandwidth and capacity of radio links used in mobile and satellite communications. In this work, we investigate the effect of nonlinearities of metal-to-metal contacts and their effects on PIM generation. An analytical expression is obtained for the tunneling current density which has an error of ~1.6% in the case of a very thin insulator and low voltages in MIM (Metal-InsulatorMetal) junctions. The presented analytical model of the contact surfaces with the fractal geometry is applied to simulate PIM products of third-order (PIM3) and fifth-order (PIM5) versus the contact resistance and applied pressure. The simulation results are validated experimentally by an open-ended rectangular coaxial structure with a slotted enclosure. The measurement results demonstrate that the presented model predicts the PIM with a mean error of about 4.8 dB when the contact pressure varies from 0.5 MPa to 1.7 MPa.

Nonlinear signal distortion, caused by passive intermodulation (PIM), presents a major challenge to modern multi-carrier communications and radar systems. Reverse PIM products generated by discrete nonlinear sources are analyzed in this paper, and the means of PIM mitigation are proposed. The developed model is validated experimentally using an open-ended coaxial waveguide with a movable iron insert, which acts as a main PIM source. The PIM generation mechanisms revealed in this study have identified alternative means for PIM mitigation. A novel circuit, proposed in the paper, enables an effective reduction ofthe reverse PIM for more than 44 dB.