What is LOW PIM antenna

What is PIM?

PIM, also known as "passive intermodulation" (Passive Intermodulation), is a kind of signal distortion. Since 4G LTE networks are extremely sensitive to PIM, how to detect and reduce PIM is more and more important.

PIM results from nonlinear mixing between two or more carrier frequencies, and the resulting signal contains additional unwanted frequencies or intermodulation products. Just like the meaning of the word "passive" in the name "passive intermodulation", the above-mentioned nonlinear frequency mixing that causes PIM does not involve active devices, but is usually made of metal materials, interconnection devices process, or other passive components in the system. Causes of nonlinear mixing can include the following:

Imperfections in Electrical Connections: 

Since there are no flawless, smooth surfaces, there may be areas of contact between different surfaces that have high current densities. These parts heat up due to the restricted conduction path, which causes a change in resistance. For this reason, connectors should always be tightened exactly to the target torque.

Most metal surfaces have at least one thin layer of oxide that causes tunneling, or simply, a reduced area to conduct electricity. Some people think that this phenomenon can produce Schottky (Schottky) effect. This is why rusted bolts or rusted metal roofs near cell towers can cause strong PIM distorted signals.

Ferromagnetic materials: 

Materials such as iron can produce large PIM distortions and should not be used in cellular systems.

Wireless networks become more complex as multiple different technologies and generations of systems begin to be used within the same site. When various signals are combined, PIM, a distortion that interferes with 4G LTE signals, is produced. 

Antennas, duplexers, cables, dirty or loose connectors, damaged RF equipment, and metallic objects located near or within a certain distance of a cellular base station can all be sources of PIM. Since PIM interference can have a significant impact on LTE network performance, wireless operators and contractors attach great importance to the measurement, source location and mitigation of PIM. The acceptable PIM level varies from system to system. For example, when the PIM level increases from -125dBm to -105dBm, the download speed drops by 18%, while the former and the latter Both values are considered acceptable PIM levels.

Which links need to be tested by PIM?

Typically, each component is tested for PIM during design and production to ensure that it will not become a significant source of PIM after installation. In addition, since the correct connection is crucial for PIM control, the installation process is also an important part of PIM control. In a distributed antenna system, sometimes it is necessary not only to perform PIM test on the system as a whole, but also to perform PIM test on each component separately. Today, people are increasingly adopting PIM-certified devices. For example, LOW PIM antenna (below -150dBc) can be considered PIM-compliant, and the requirements for such indicators are becoming increasingly stringent.

In addition, the site selection process for cell sites, especially prior to cell site and antenna setup, and subsequent installation phases, also involves PIM assessment.

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