Production of low PIM RF coaxial connectors

Jun 16, 2019
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As the number of distributed antenna systems (DAS) and small cellular devices continues to increase, low PIM RF coaxial connectors have become popular in low passive intermodulation distortion (PIM) interconnects and components. Modern complex multi-carrier communication systems, such as DAS and small cells, are now very broadband and support multiple wireless standards such as WiFi, cellular, military, government, public safety and emergency bands. Any wireless standards and technologies that are only under 6 GHz, including Internet of Things (IoT) devices, new 5G-NR sub-6 Ghz services, TV white space (TVWS) devices, and more. Many of these standards cover frequencies that would otherwise be mixed if they were mixed in a passive manner. The greater the system bandwidth, the greater the likelihood that PIM distortion will result in reduced throughput.

Therefore, low PIM coaxial cable assemblies consisting of low PIM cables and low PIM connectors are more commonly used as jumpers and interconnects between wireless system components. The value of low PIM cable assemblies is that they are tested and expected to be certified for low PIM operation. If properly installed in systems designed for low PIM performance, these interconnects should not add any significant PIM and mitigate the distortion typically provided by cables with higher PIM ratings.

The construction of a low PIM cable assembly typically involves three main sections, two end connectors and the coaxial cable itself. Each end connector (usually for DIN 7 / 16, 4.3-10, N and 4.1 / 9.5 for communication system applications) should have a low PIM rating and include hardware connected to the coaxial cable, which also helps Installed at low PIM. Since any other connection may result in an increase in the system's PIM level, the connector should be chosen to eliminate the adapter requirements at both ends. This may require a male to male or male to female connector, or a different connector type and gender at each end.

Cable assemblies having different connector types are often referred to as being between series, where cable assemblies having the same connector type are referred to as series. In addition, right angle adapters are often used for narrow and difficult installations. However, using low PIM and right angle connectors for cable assemblies may result in better PIM performance than relying on other right angle adapters.

Coaxial cables should also have low PIM ratings and also meet building code requirements. For building codes, the UL910 rating for plenum coaxial cables meets most building code requirements. Typically, low PIM coaxial cables are made of solid inner and outer conductors because solid conductors tend to be better than braided in low PIM applications. Due to the poor flexibility of solid conductors, corrugated outer conductors are often used to achieve some flexibility and ease of installation. The solid outer conductor also provides better shielding than the braided conductor, which may be useful for installations with a dense number of services and connections and nearby emitters.

Finally, the assembly of the entire cable needs to be done in a manner that ensures low PIM operation, and must also be tested to ensure that any manufacturing defects in any component or assembly process do not result in a failed unit. When evaluating PIM performance for the entire system, especially during troubleshooting, listing PIM performance on the cable can make installation easier.