Designing 5G Installations With Innovative RF Interconnects
5G small cell deployments are booming — and redefining the requirements for coaxial cables and connectors.
Global connection and data sharing depends on a high performance communication infrastructure that supports 5G and sets the stage for future 6G network connectivity. Next generation technologies, including increased streaming, automation, and AI depend on accelerating data speeds, ultra-low latency, enhanced reliability, enormous network capacity, and increased availability.
This revolutionary technology is undergoing a substantial expansion/upgrade to existing network infrastructure and prepare for future 6G installations. To achieve this goal, the network must be densified, which means more cell sites in more locations to get the signal closer to users. Small cells are one of the most practical means of attaining this densification.
5G small cell applications use MIMO antennas to enable the delivery of high speed and latency in the millisecond range. This type of antenna has multiple-in/multiple-out feeds, which has led to substantial growth in the number of RF ports, making installation increasingly complex. Furthermore, 5G antennas continue to shrink in size as higher frequency bands are used to accommodate larger bandwidth requirements, which translates into more antennas — as well as the corresponding RF cables and connectors needed to attach them — in a much smaller space.
The cables, connectors, and RF solutions deployed in 5G applications are integral components in enabling a signal to successfully be transmitted with minimal loss or interference. There are emerging bundled coaxial cable and cluster connector solutions that support optimal speed, coverage, and latency requirements of 5G, along with the high-density infrastructure needed to make it accessible. Key considerations for optimizing RF interconnect systems to accommodate the unique requirements of 5G deployments include component density and low PIM performance.
Component Density
In urban and suburban areas, direct line-of-sight MIMO antennas are capable of meeting the speed, coverage, and latency requirements of 5G — but operating at millimeter wave frequencies, their range is short, requiring a dense network of antennas. These small cells are also packed much closer than traditional telecom towers were years ago; at times, they are only about 100 yards apart.
This densification creates numerous challenges related to installation, torquing, ensuring proper weather sealing, and more to design a crucial interconnect system that will perform well, withstand the extraordinary environmental and technical conditions over long periods of time, and facilitate future maintenance. In addition, 5G small cells have limited space for equipment so minimizing size and weight are also key goals for connectors and cable assemblies.
The majority of 5G small cell applications are installed around lamp poles, rooftops, and telephone poles and may be 30-40 feet or more above the ground. As a result, 5G antennas require a lot of RF cable feeds, RF jumpers, jumper cables, and feeder cables, which can visually create a rat’s nest if not installed properly. All these cables must withstand the elements.
Moreover, installation can be a time-consuming, labor-intensive, and logistical nightmare, creating the potential for cables to be the weakest link in the system. There are numerous variables to consider: is it the right cable or the right port? Is that connector properly terminated to that cable? Is the coupling properly torqued down? Is the whole assembly properly weather sealed? Are those cables properly captivated? Are the cables properly secured to the structure? Do they have the proper UV resistance?
Passive Intermodulation
Passive Intermodulation, or PIM, is a type of distortion that may occur in passive, non-linear components such as RF cables and connectors. In these dense 5G systems, more customer usage can generate competing signals. When two or more signals mix, they can produce an additional undesired frequency. Cables and connectors play a large role in PIM, which may occur because of something resistive in the interconnect, the junctions between different types of passive components such as the connector and cable, ferrous materials, inadequate tolerance, poor torquing, etc.
While PIM is an issue for almost every wireless system, it is more noticeable in cellular applications because the frequency bands used are very close to each other. PIM can create interference that limits receiving sensitivity, lowering the reliability, data rate, and capacity of the cellular system. This has the potential to result in decreased system capacity and data rates, as well as dropped calls. To prevent this, carriers often require low-PIM coaxial cables to ensure the cable and connectors are performing properly and are free of interference.
The solution: Bundled coaxial cable and cluster connectors
A bundled cable design can help create the perfect flexible antenna jumper for applications requiring multiple runs, such as on 5G small cells located on towers or building-top sites. A spiral configuration of multiple flexible and ultra-flexible, low-PIM, plenum rated jumper cables can be created under a common polyurethane outer jacket to promote ease of installation and improved operation. The individual coaxial cable runs are spun together in such a way that the combination easily flexes, essentially creating a bundle, which is then run through a large jacket extruder where a rip cord is placed. This enables four or five individual cables to be fed into the back of a cluster connector. By using this method and creating a round cable bundle, a seal is also formed to provide extra protection, as the inner cables are protected by the outer jacket.
High coverage antennas like those used in 5G applications have led to substantial growth in the number of ports on antennas and RF devices. Hooking up the right cables, the right ports, and proper torquing are all concerns. Proper weather sealing is also a necessity; it is imperative to make sure that seal is good, but not over-torqued.
The use of MQ4/MQ5 connectors is an optimal solution as this type of “RF cluster connector” incorporates multiple RF ports. There are bundle cable designs manufactured with standardized MQ4/MQ5 connectors that encompass a four-contact connector and a five-contact connector. These can greatly reduce the number of cables that have to be hooked up, saving a lot of labor, and creating a more rugged solution. They also make the assembly more weatherproof and UV resistant.
Therefore, the bundled cables simply have to go into this cluster connector. Using the five-conductor solution eliminates the need to create five individual weather seals, resulting in tremendous labor savings. Furthermore, this reduces the need to worry about coupling torque. This is critical because all it takes is any kind of error on just one weather seal to create a point of ingress for water that could create a multitude of problems and even potentially shut the system down. With this cluster connector solution, any potential system troubleshooting becomes much easier.
Finally, the possibility of hooking up the wrong cable to the wrong port is eliminated. The solution is keyed, so the cables can only be hooked up a certain way — no torque wrenches, know-how, or special technique required.
Additionally, the standardized four-contact and five-contact connector designs use a spring outer contact so that PIM performance is not tied to how well the tip of the outer contact is engaging with its mate. The connection between the male and female cluster connectors is sealed to IP67 as are the connector bodies and the transition from the cluster connector to the bundled cable. In addition to the male-to-male bundled harness, the female bulkhead connector can also be built as a finished assembly that is ready to be installed into the box and engaged with the printed circuit board.
The bundled coaxial cable and cluster connector technology solution detailed in this article not only looks better in terms of appearance, but it also trims labor costs and offers a more rugged solution for 5G small-cell deployments with better UV resistance and weatherproofing.
Visit Times Microwave Systems to see innovative RF interconnect products.
Article Contributed by Times Microwave Systems
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