The extension of 5G frequency bands into the millimeter-wave spectrum makes the electrical, mechanical, and environmental characteristics of RF connectors even more critical to overall performance. To address evolving market demands, Johnson & Johnson has been actively launching a range of new products to support higher frequencies and smaller sizes, driven by the rollout of 5G.
5G is coming
5G has arrived, with operators announcing plans to trial and launch services by the end of 2018 and a full rollout of 2020G networks starting in five years. The industry is preparing for this launch; equipment manufacturers like Qualcomm have released 5G modems (Snapdragon), test equipment manufacturers have updated their product portfolios, and companies such as Huawei, Nokia, and Ericsson are working on antenna and beamforming technologies to enable MIMO functionality in 5G. RF connectors are ubiquitous across all areas of 5G technology, and the demands of millimeter-wave frequencies place critical requirements on their manufacturing precision. The prevalence of cellular networks is also putting downward pressure on the cost of these connectors, whose use has historically been limited to military and aerospace applications. For over 50 years, Johnson connectors have been at the forefront of RF applications, supporting previous generations of wireless networks. In this article, we will discuss 5G, its requirements for connector technology, and how Johnson is addressing these challenges with new products.
The deployment of 5G is driven by the increasing number of devices requiring high-bandwidth internet access, putting pressure on existing networks. 5G will address this issue by using frequencies ranging from below 1 GHz to eventually 26 GHz and higher. The total bandwidth used by 5G will significantly exceed the amount of spectrum used by 4G and previous wireless network technologies.
5G spectrum allocation
The spectrum allocation is decided by the World Radiocommunication Conference, which is held every three to four years. WRC-19 will be held in Sharm el-Sheikh, Egypt, from 22 May 2019 to 24 May 2019, but at the same time, an agreement is being reached on the 28 GHz spectrum, with carrier frequencies of 38, 1 and 2083 GHz expected. At these frequencies, the latency will also be extremely low, with the target of ITU-R specification M.16 [1] being less than 1000 m seconds.
As can be seen from the specifications, 5G broadband connections are expected to provide downlink speeds of up to 20 Gbps and latency as low as 1 millisecond. 5G will also enable a gradual increase in the amount of data transmitted over wireless systems by providing more bandwidth at higher frequencies designated for 5G.
Figure 1: 5G Technical Requirements (Source: GSMA)
Use Cases and Large-Scale IoT
The telecommunications industry has begun referring to this as the Massive Internet of Things (MIoT), while ITU-R IMT-2020 (5G) includes three main use case categories: enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable and low-latency communications (URLLC). The spectrum allocated to 5G networks will be divided into three frequency bands, consistent with the use case categories, as shown in Figure 2.
Applications within each use case category will have different requirements, and 5G's enhanced network management capabilities (including network slicing) will enable operators to provide applications-tailored services. For example, autonomous vehicles will require extremely fast, low-latency connections to support real-time navigation. On the other hand, many IoT sensors transmit data in periodic bursts and do not require high speeds, so lower service levels will be appropriate.
The higher frequencies allocated to 5G and their corresponding shorter wavelengths will allow for the use of smaller antennas, enabling the use of massive MIMO technology to increase wireless connectivity capacity without requiring more spectrum. While this means more 5G base stations will be needed to provide the expected coverage, they will utilize multiple antennas within each base station, allowing 5G to support over 1,000 more devices per meter than 1G. Consequently, 4G networks will be able to send ultra-fast data to more users with high accuracy and low latency, meeting the growing demand for high-speed data from emerging wireless applications such as MIoT.
millimeter wave region
Designing RF devices for the millimeter-wave region of the spectrum presents numerous opportunities and challenges. As mentioned above, higher frequencies enable smaller antennas, allowing each base station to accomplish more. Advances in technologies such as nano-CMOS are significantly reducing the size of many devices connected to 5G networks (e.g., IoT sensors) and increasing antenna density. This leads to a corresponding reduction in the size of base station components. These trends of higher speeds, greater bandwidth, greater density, and smaller size place specific demands on connector technology, which is crucial for any electronic device or system at millimeter-wave frequencies.
Radio frequency connectors must transmit electromagnetic energy from one transmission line to another while ensuring minimal loss and reflection, so the precision of their design is crucial.
5G RF Connector Design Considerations
Driven by the pursuit of higher frequencies, smaller sizes, unique interfaces, and better performance, RF connector designs must meet constraints based on geometry, size, and transmission characteristics while ensuring that the connector impedance matches the impedance of the rest of the transmission line. Maintaining impedance becomes increasingly complex as frequencies rise; the electrical, mechanical, and environmental characteristics of RF connectors all play a crucial role in ensuring their performance.
Key electrical characteristics include impedance (typically 50 ohms), VSWR, PIM (passive intermodulation distortion), and maximum frequency. VSWR is particularly important, as it determines how much electromagnetic radiation the connector will reflect, resulting in signal loss. VSWR varies with frequency but can remain relatively flat within a given frequency range, such as 1.3:1 to 40 GHz.
Mechanical characteristics, such as engagement/disengagement forces, coupling nut torque, contact retention, and durability (number of insertions and removals), are equally important for ensuring connection stability. Unexpected gaps in the connection due to misalignment can cause drastic changes in the electrical characteristics of the connection (Figure 3).
Figure 3: RF connector alignment
Finally, environmental characteristics such as operating temperature range, moisture resistance, and corrosion resistance must be matched with the deployment conditions of the connector.
5G connector solutions
Given the trend towards higher 5G network density, connector size is a general parameter. 4.2 mm SMA connectors are already mature in RF implementations, and now, with increasing frequencies and shrinking module sizes, ultra-miniature variants are becoming increasingly common. Table 1 shows some of the main connector types currently in use. The design of 5G applications will require a variety of high-frequency connector and adapter types, extending to adapters, multi-port linkage solutions, and cable assemblies.
With over 50 years of industry experience, Johnson offers one of the most comprehensive RF connector portfolios on the global market and has consistently leveraged its experience and resources to develop and expand its product range to meet the evolving needs of the 5G market. Johnson's extensive range of 50-ohm SMA connectors is rated for frequencies up to 26.5 GHz, available in brass or stainless steel, and supports a variety of configurations, including PCB mounting (through-hole and surface mount), end-emitter, bulkhead flange mounts, and cables.
To address evolving market demands and driven by the rollout of 5G, Johnson & Johnson has been actively launching a range of new products to support higher frequencies and smaller sizes, including:
92.40mm series with up to 2 GHz
4.50mm series with speeds up to 2 GHz
85.67mm series with speeds up to 1 GHz
SMP series extended up to 40 GHz
SMPM series extended up to 65 GHz
Connects to 4 SMP ports, with frequencies up to 40 GHz.
With sales, design, and manufacturing centers in the U.S. and China, Johnson & Johnson is well-positioned to support the needs of emerging 5G markets and will continue to invest in its product portfolio to support the emerging demands of 5G networks.
