The Hidden Challenges of 5G RF Design

The arrival of 5G has introduced a wide range of RF design challenges—some obvious, some less so. The difficulties associated with millimeter wave (mmWave) have been widely discussed, for example, but signal integrity and hardware costs are also major issues.

Before we reveal the full scope of these challenges, let’s take a moment to consider who is impacted. 5G is unusual in that it is a major step change for the entire ecosystem. To achieve its full benefits, both the mobile carriers and their end users must adopt new mindsets. Antenna designers, microwave circuit designers, and even those working on seemingly unrelated areas like PCB design are all facing new problems.

Now let’s take a closer look at the issues to see why 5G offers such wide-ranging and subtle design challenges (and a few solutions, too!)

Poor propagation vs. array antennas

Let’s begin with the headline-grabber: signal propagation. Unlike prior cellular technologies, mmWave doesn’t travel far. Buildings, terrain, people, and even weather can attenuate mmWave signals. One obvious consequence is that mobile carriers need more base stations, closer to their end users.

But even with plenty of base stations, signal propagation can be a problem. After all, human bodies are excellent absorbers of mmWave frequencies. This means just a hand holding a phone can make a signal unusable. As a result, mmWave systems typically require multiple antennas—and more significantly, antenna arrays.

Since many antenna engineers lack experience with antenna arrays, this requirement is a significant challenge. In many cases, engineering teams will need to bring in additional talent familiar with beamforming and beam-steering techniques to ensure that mmWave signals can find a low-attenuation path. (See Figure 1.)

Figure 1. Beam steering manipulates the direction of the main lobe of an antenna array.

Signal integrity and interference

But there is another angle to consider: when dealing with weak signals, every fraction of a dB counts. That means the challenges related to mmWave reach far beyond the antenna.

The feeds, traces, and connections that go into that antenna must all be designed with excellent end-to-end signal integrity (SI) in mind. Given that these components are handling frequencies above 40 GHz, this is no small challenge.

Compounding the challenge is the fact that mmWave signals are only one of many RF signals found within a typical 5G device. For starters, the 5G spectrum includes sub-6 GHz frequencies in addition to mmWave. Sub-6 GHz signals are more familiar to cellular equipment designers, and they readily coexist with LTE technologies. However, their mere presence means that designers must deal with a broader spectrum than before.

What’s more, 5G devices are typically packed with a host of other RF technologies including Wi-Fi, Bluetooth, UWB, and NFC. Any leakage from the mmWave system has the potential to affect the other frequency bands. Given that higher-frequency signals are inherently more prone to leakage, this risk should not be underestimated.

To deal with these challenges, engineering teams must become more collaborative.  

In our “Design Engineer Tell-All” survey, 90% of engineering teams have changed in recent years, with design engineering teams increasing in scope, expertise, and specialization proving collaboration is vital.

While SI engineers need to assess interconnect and transmission line performance, electromagnetics experts must simultaneously examine RF leakage. Keep in mind that design choices are usually compromises. For example, a change that improves SI might well introduce new leakage problems, and the teams must work together to evaluate the tradeoffs.

Circuit board design and cost considerations

Of course, 5G device design involves plenty of materials and construction choices as well. The entire manufacturing process for RF systems and antennas has changed dramatically over the past few years, opening up a new landscape of design options.

Consider the humble printed circuit board (PCB). Already, many PCBs have given way to flexible printed circuits (FPCs) as they are easier to package. This change has many implications that go beyond the scope of this article, but the materials used within FPCs continue to evolve, creating complex tradeoffs in cost and performance.

Now there is a move toward plated plastics, molded and laminated materials made from low-loss liquid crystal polymers (LCPs). These materials can significantly cut costs, but they also create new concerns related to permittivity. Returning to our point about the propagation problems and weak signal strengths associated with mmWave, it’s easy to see how a poor choice of laminated materials could cause unacceptable signal degradation.

The bottom line? When it come to the success of 5G devices, materials engineers and manufacturing experts are just as important as antenna experts and microwave circuit designers.

Collaboration starts early

Indeed, all teams must work in harmony to achieve the right balance of design variables. To achieve the best outcomes, this collaboration must begin early in the design process. Old patterns of waiting to start RF design until a device was nearly complete are no longer viable. Similarly, manufacturability must be considered from the beginning.

Getting started with this holistic mindset is important not just to avoid conflicting design goals. It also informs how well prepared suppliers should support difficult design decisions. This is where Molex can help.

Molex engineers bring decades of expertise in RF, signal integrity, antennas, and manufacturing that is needed to solve multi-faceted 5G design challenges. Our investments in 5G enable us to craft components with highest precision thanks to state-of-the-art 5G manufacturing equipment and techniques—and our high frequency RF test chambers help us ensure the performance of products right into the mmWave spectrum.

While Molex may be best known for our expertise in connectors, these other areas of excellence are critical to supporting our customers. Our goal is to act as an advisor on your journey to 5G design. We understand the complexities of this new era of cellular communications, and we are excited to help you produce leading-edge devices.