New RF Interconnect Solutions Power Mission-Critical 5G Networks

By Kevin Moyher

Originally Published in RadioResource Media Group

5G technologies are being rapidly deployed to deliver increased peak data speeds, ultra-low latency, enhanced reliability, enormous network capacity and increased availability. However, this requires a substantial expansion/upgrade to existing network infrastructure. For example, 5G networks must be densified to get the signal closer to users, which means more cell sites in more locations.

Small cells have emerged as the most practical means of attaining the densification needed to support the speed, coverage and latency requirements of 5G. These 5G small cell applications use multiple input multiple output (MIMO) antennas with multiple in/multiple out feeds, which substantially increases the number of RF ports. Additionally, unlike previous cellular technology generations, which focused on a specific frequency band, 5G deals with a much larger potential frequency range. For example, 4G frequency bands are typically below 3 GHz. 5G, on the other hand, can range from 450 MHz to 3.9 GHz and up to 20 – 56.2 GHz millimeter-wave (mmWave) bands for high-speed operations. 5G also encompasses unlicensed frequency bands, such as the 6 GHz band.

As a result, 5G antennas are shrinking in size as higher frequency bands are used to accommodate more extensive bandwidth requirements, which translates into more antennas and the corresponding RF cables and connectors needed to power them in a much smaller space. This equipment is also packed much closer than traditional telecom towers were years ago; at times, they are only about 100 yards apart. This requires new coaxial cables and connector solutions to deliver high signal integrity and reliability in increasingly dense environments.

The combination of smaller antennas with large numbers of cable connections also creates unique challenges related to installation, torquing, proper weather sealing and more. 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 thing properly weather sealed? Are those cables properly captivated? Are they hooked up to the right connector and port? Are they flapping around in the wind? Are they protected from the sun, or if not, do they have the proper UV resistance?

We will discuss these concerns in more depth and provide a strategy for mitigating the challenges through the use of a bundled coaxial cable assembly solution designed for the ultra-demanding 5G small cell environment.

Bundled Cable Assemblies
A bundled cable solution can help create a flexible antenna jumper for applications requiring multiple runs, such as 5G. A spiral configuration of multiple flexible and ultra-flexible jumper cables can be created under a common polyurethane outer jacket to promote easy installation and improved operation. The individual coaxial cable runs are spun together in a way that easily flexes, essentially creating a bundle, which is then run through a large jacket extruder where a ripcord is placed.

This design enables four or five individual cables to be fed into the back of a single connector such as those based on the industry-standard MQ4/MQ5 design that encompasses a four-contact connector and a five-contact connector. The most common bundled cable constructions are built with inner cables that are one quarter of an inch and smaller and can be used on both non-low passive intermodulation (PIM) and low PIM interconnects. Constructions to address low PIM bundled harnesses include corrugated copper outer sheaths as well as ultra-flexible flat braid constructions.

Ensuring connectors are properly and securely tightened and eliminating any nonlinear or poor electrical contacts within the RF interconnect can also help reduce PIM issues. The MQ4 and MQ5 cluster connectors use an outer spring contact so that PIM performance is not tied to how well the tip of the outer contact is making to 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. The solution is also keyed, eliminating the possibility of hooking up the wrong cable to the wrong port as the cables can only be hooked up a certain way; no torque wrenches, know-how or special technique required.

Using the four- or five-conductor solution eliminates the need to create individual weather seals, resulting in tremendous labor savings. Furthermore, it reduces the need to worry about coupling torque. This is critical because all it takes is an 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.

As a result, bundled solutions are optimal for high-density challenges as they permit installation in tight spaces; instead of connecting multiple threaded connectors, just one will do the job. They are faster and easier to install and maintain and provide one firm, reliable connection to support consistent high performance. An example of this type of solution is the TMQ4 and TMQ5 bundled cable assemblies from Times Microwave Systems^®.

The bundled coaxial cable assembly solution detailed above looks better in terms of appearance and cuts a lot of labor cost, and offers a more rugged solution with better UV resistance and weatherproofing. This helps support the densification needed for the speed, coverage, high frequency and latency requirements of 5G.

When it comes to selecting the right high-density RF cables and connectors, it is best to work with a partner whose engineers can identify the application’s unique needs and design an optimized solution that is ultimately easier to use, creating better electrical, mechanical and environmental performance. Look for a supplier with a long history of building quality cable and connectors, along with the skill, processes, techniques and materials to bring custom solutions for specific application needs to life.