5G: As Wavelengths Get Smaller, so Must the Devices
The first substantial deployments of 5G infrastructure began in 2019, along with the release of handsets advertising 5G capabilities. Although rollouts to true mmWave 5G at scale have been slow to materialize, some of the biggest wireless component manufacturers have supported both sub-6 GHz and mmWave access with their products. In anticipation of greater access to the mmWave spectrum, component releases have focused on dual-band operation to support low, mid and high frequency 5G networks.
The current trend in 5G continues pushing towards higher operating frequencies to access greater data rates and lower latency. For systems designers and product designers, higher frequencies bring design challenges that are only solved with more specialized components.
What Happens in 5G Systems at Higher Frequencies?
Devices operating at higher frequencies are subject to greater signal loss, which requires anything interacting with a 5G signal to potentially be re-engineered. Connectors, antennas, cables and enclosures are all components that can interact with an incoming or broadcast 5G signal; the components and materials normally used in 4G systems and deployments are not always compatible with the higher frequencies used in 5G infrastructure and devices.
Some of the major themes driving designs to smaller form factors include:
- Greater antenna density for high-frequency antenna arrays
- 5G connectivity requires more battery power and the need for a physically larger battery, which consumes more real estate in a device
- Alternative packaging strategies and materials for RF components
- Demand for greater feature density in 5G-enabled devices
Within these broader themes, where is miniaturization occurring at the system level?
With 5G devices being wireless, the antenna is obviously an essential component. Antenna arrays are driven smaller at high frequencies because their operating frequency is inversely proportional to their size. This has required size reduction in antenna arrays, and it creates etching difficulties for PCB fabricators, as well as packaging manufacturing for antenna-in-package modules and modems, and component manufacturers. As smaller sizes bring manufacturing difficulties, this creates a challenge in designing a land pattern for a connector that can support the required signal bandwidth.
For component manufacturers, support for mmWave-capable antenna arrays enables smaller devices. This is then beneficial for system/product designers as they will free up real estate on their board for other components.
Antenna arrays used in 5G-capable handsets are typically 2×2 patch antenna arrays. As these arrays are driven smaller, manufacturers need to take an additive approach when fabricating components for use in the mmWave regime. Fabrication limits can be pushed off with lower Dk/lower loss materials, but eventually antenna arrays for 5G/6G will reach the limit of what can be reliably fabricated with standard and additive processing.
Board-to-Board and Flex-to-Board Connectors
Interconnects between boards and components are built using off-the-shelf connectors or custom connectors. In the past, connectors that would typically be used for mmWave systems would interface with coaxial cables as this was often the only way to transfer signals in 5G frequency ranges. Handsets require physically smaller connectors as there is no space for bulky coaxial connectors and cable assemblies, which has led to the introduction of surface-mount flex/board mating connector systems.
In handsets, flex-to-board and board-to-board connectors have very small form factors that allow stacking of components or connection to a flex ribbon cable. These connectors often need to transfer power and digital signals, and possibly an RF signal, in a low-profile form factor.
The size of the supporting PCB and the relevant operating frequencies (both for data and RF) are the main drivers forcing the use of smaller board-to-board/flex-to-board connectors. Smaller connectors then require smaller land patterns to ensure signal integrity, which also enables more space in an assembly for components and batteries. These systems may use landing pad pitches below 0.5 mm, which is required to operate in the mmWave range without signal loss into a PCB substrate.
Coax Cables and Connectors
Coaxial cables and connectors are used in RF devices where form factor is not a major challenge, yet high power handling is needed with minimal dispersion and losses. While standard larger form factors (e.g., SMA connectors) can operate at mmWave frequencies with wideband connector lands, greater feature density and size constraints in small deployments require a physically smaller connectors that can still operate in mmWave bands. These connectors may be customized when off-the-shelf components do not hit form factor targets.
Another challenge that appears in 5G systems is passive intermodulation (PIM), which interferes with data transmission in wireless systems that use carrier aggregation. In fact, passive intermodulation is sometimes called the “rusty bolt effect.” Connectors can also be a source of PIM, and a very small amount of PIM near the carrier frequencies is sufficient to create errors that reduce data transmission rates.
Some smaller or custom connectors can provide lower PIM values that are essential in systems operating at higher frequencies. With mmWave signals experiencing higher loss, the link budget for a system will be smaller, and thus the allowed PIM specifications in a system are brought lower. This may require smaller connectors and cable assemblies to reduce the opportunity for PIM to occur.
Other Specifications on Small Components
Small components used in handsets, micro/pico cells, and 5G-enabled modules have another set of specifications that are complicated by reduced component size. As there is a drive to accommodate higher frequencies with smaller components, this complicates the mechanical design and durability of these components. Handsets and cell equipment must operate in harsh environments at a range of temperatures with perpetual uptime, requiring components that meet environmental specifications:
- Weatherproofing and waterproofing – Components exposed to the environment (particularly connectors) may require an IP6x rating to ensure reliability.
- Retention in mated connectors – Retention mechanisms help to prevent unintentional disconnects in a system due to vibration or mechanical shock.
- Consolidated connectors – Smaller devices have less room for multiple connectors, so pinouts may need to support both power and signal on the same cable.
Why 5G Designers Choose Molex
Molex provides a range of engineering solutions and components for 5G-enabled systems, including interconnect and connector solutions. Molex takes a collaborative approach to system design, offering test expertise and custom component design to help customers scale their 5G products to high volume. Molex’s goal is to produce high-yield, cost-effective products in form factors useful to the communications industry, IOT and automotive markets, enabling a smoother transition to 5G, despite the complexities.