Passive intermodulation (PIM) effect in base stations

Active devices are known to have nonlinear effects on the system. A variety of techniques have been developed to improve the performance of such devices during the design and operation phases. It is easy to overlook that passive device can also introduce nonlinear effects that, while sometimes relatively small, can severely impact system performance if not corrected.

PIM stands for "passive intermodulation". It represents the intermodulation product produced when two or more signals are transmitted through a passive device with nonlinear characteristics. The interaction of mechanically connected parts generally causes nonlinear effects, which are particularly pronounced at the junction of two different metals. Examples include loose cable connections, unclean connectors, poor performing duplexers, or aging antennas.

Passive intermodulation is a major problem in the cellular communication industry and is very difficult to solve. In cellular communication systems, PIM can cause interference, reduce receiver sensitivity, or even block communication entirely. This interference can affect the cell that produces it, as well as other receivers nearby. For example, in LTE band 2, the downlink range is 1930 MHz to 1990 MHz and the uplink range is 1850 MHz to 1910 MHz. If two transmit carriers at 1940 MHz and 1980 MHz, respectively, transmit signals from a base station system with PIM, their intermodulation produces a component at 1900 MHz that falls into the receiving band, which affects the receiver. In addition, intermodulation at 2020 MHz may affect other systems.


As the spectrum becomes more crowded and antenna-sharing schemes become more common, the likelihood of intermodulation of different carriers producing PIM increases. Traditional approaches to avoiding PIM with frequency planning are becoming increasingly unfeasible. In addition to the above challenges, the adoption of new digital modulation schemes such as CDMA/OFDM means that the peak power of communication systems is also increasing, making the PIM problem "worse".

PIM is a prominent and serious problem for service providers and equipment vendors. Detecting and resolving this problem as much as possible increases system reliability and reduces operating costs.

As the designer of RF duplexers, Jingxin can help you out on the issue of RF duplexers, and customize the passive components according to your solution. More detail can be consulted with us.

Post time: Jan-06-2022