San-tron Inc. has written a white paper on passive intermodulation (PIM), its effects on modern communications systems, and how it can be minimized in high-frequency cables, connectors, and cable assemblies. PIM is the result of the nonlinear behavior of a communications system and certain of its components. It is evidenced when multiple signals mix to create unwanted harmonic signals. At sufficiently high levels, PIM can disrupt the operation of a cellular base transceiver station (BTS), resulting in dropped calls for cellular customers and lost capacity for cellular network operators.
Written by San-tron’s Director of Engineering, Fred Hull, the informative white paper explains how different mechanical structures, such as connector interfaces, can contribute to the generation of high PIM levels. It also describes how current flow through certain materials, notably paramagnetic materials such as stainless steel and nickel-plated metals, can also produce unwanted PIM signal energy.
In addition to exploring the different causes of PIM in high-frequency connectors, cables, and cable assemblies, the white paper also reviews San-tron’s efforts to create connector interfaces with low-PIM mechanical structures and to minimize the use of paramagnetic materials in its connectors. The literature highlights some of the “safe” materials that are selected to minimize PIM in connectors, including beryllium-copper (BeCu), aluminum, silver, gold, and Albaloy. The firm’s low-PIM cable assemblies are constructed with commercial low-loss, low-PIM cables and advanced connector designs, such as San-tron’s low-PIM versions of its 50 Ohm eSeries connectors, which are usable at frequencies to 20 GHz. The white paper provides a table of different connector and cable combinations, detailing PIM levels as low as -174 dBc.
The 7-page white paper, “Minimizing PIM Generation From RF Cables And Connectors,” is available for free download in PDF file by visiting http://www.santron.com/SRXLowPIMCableAssembliesWhitePaper.cfm.