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Passive intermodulation (PIM) distortion is a wireless communication system degrading phenomenon that has been a concern for cellular telecommunications, satellite communications, and wireless network development. PIM is such a concern in cellular/wireless communications that there are entire distinct Low PIM Components and Cable Assemblies product lines designed to aid in preventing or mitigating PIM distortion.
PIM occurs only in parts of a signal chain and wireless communication channels that are passive and where two or more signals are present. When the conditions are right and two or more signals pass through a PIM generation condition, the result is nonlinear distortion products. If the input signal power levels are high enough, these distortion products could result in relatively high-power distortion signals within one or more receive bands of a sensitivity receiver. If this happens, the receiver could be desensitized, the noise floor may increase, and in extreme conditions, the receiver may be damaged by the combination of PIM distortion products combining with the power level of other signals.
Where nonlinear distortion is common and expected with active devices and can therefore be predicted and readily mitigated, it is very difficult to predict and troubleshoot for PIM. PIM issues may also appear over time and may be difficult to identify and determine the PIM generator(s). There are a variety of potential PIM generators, including close proximity of dissimilar metals in the signal path, oxides/metallic contact points, loose connectors, damaged cable conductors, dirty/debris laden connections, poor quality duplexers, corroded antennas etc. The common anecdote on PIM generators is that a PIM source could be virtually any conductor, even a rusty bolt on the antenna tower or mast.