What’s All This PIM Stuff Anyways?
Wireless network operators upgrading to next generation systems such as LTE must ensure low passive intermodulation (PIM) in order to achieve bandwidth optimization and maximum Quality of Service (QoS). PIM represents third-order mixing products (in-band) generated by two distinct frequencies co-located within a system. These “ghost” signals act as interference for the cellular receiver and consume system capacity as well as causing false phone calls.
PIM can be caused by a number of characteristics, including the effects of corona generation, current saturation and the nonlinear characteristics of certain materials, all of which can be introduced by the cable assemblies used to interconnect the network’s modules and components for effective signal flow.
Specific connector design features are meant to lower PIM. For instance, connectors designed for high RF power levels typically employ chamfered transitions to avoid localized ionization. To further minimize PIM, mating conductive surfaces should have smooth surface finishes at all component and connector/cable transitions, with optimum mating force maintained between conductive surfaces. Hard versus soft materials within press fits and the use of strong wiping action between mating center contacts can mechanically break down oxide layers and generate a clean conductive path, also helping to minimize the generation of PIM.
A new white paper from San-tron discusses the causes of PIM and its impact on next generation wireless networks as well as the design features in the company’s eSeries connector products designed to mitigate PIM and is available on the Microwave Journal website at www.mwjournal.com/SantronPIM.