Reimagining Antenna Design Solutions for Next-Generation Mobile Devices

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Reimagining Antenna Design Solutions for Next-Generation Mobile Devices [Copy link]

Rapid innovation in next-generation mobile devices presents significant engineering challenges in antenna implementation. The key issue is that 5G phones typically have more than twice the RF path of LTE phones due to new frequency bands and requirements defined by cellular, Wi-Fi, ultra-wideband (UWB), millimeter wave (mmW) and GPS standards. However, lack of space limits the ability to add new antennas and/or share antennas between multiple bands, which further complicates the issue. Industrial design innovations such as foldable or rollable screens and the use of virtual controls instead of physical buttons place significant constraints on antenna design and layout. Additional challenges arise from the conflict between increased carrier power requirements and OME system efficiency goals and improvements such as battery life. Qorvo has extensive experience helping companies solve tough RF problems, and its reimagined Qorvo Antenna Solutions (QASR) helps engineers address space, design and performance challenges to harness antenna power in RF architectures.

The fast-growing mobile industry

The pace of innovation in the mobile industry continues to accelerate as smartphone and wearable device manufacturers and mobile operators compete to deliver greater coverage, higher data rates, new wireless communication capabilities and transformative industrial designs.

Smartphone manufacturers are beginning to expand 5G support across their product lineups to meet the growing demand for data-intensive services such as video streaming, video conferencing, music, and gaming. As a result, 5G’s high-bandwidth sub-6 GHz bands (n77/n78 and n79) and wider mmWave bands (n257-n261) used in premium phones are now also being used in mid-range and mass-market phones. While increasing RF complexity, 5G requires not only the addition of new cellular bands, but also support for 4x4 MIMO on higher frequency bands for faster data speeds.

Manufacturers are also adding more non-cellular bands to phones to provide faster networks and support new location services. For example: Wi-Fi 6E/7 extends Wi-Fi to the 6 GHz band and provides ultra-wide 160-320 MHz channels to provide higher performance for applications such as HD streaming, virtual reality, and peer-to-peer gaming, while alleviating congestion caused by widespread use of the Wi-Fi spectrum.

Initially used in high-end mobile phones, UWB technology is now also being used in mid-range and mass-market mobile phones. UWB can calculate distance and position with unprecedented accuracy (within a few centimeters) indoors or outdoors, and is beginning to support new positioning applications and devices. As the name implies, UWB uses a channel width of at least 500 MHz and a frequency range of 3.1-10.6 GHz, while mobile applications currently mainly use the frequency range of 6-9 GHz. Manufacturers are also beginning to add new GPS L5 and L2 bands, which provide various advantages such as higher positioning accuracy for mission-critical applications.

At the same time, smartphones are beginning to add more and more complex combinations of multiple cellular bands as mobile operators seek to optimize the use of existing spectrum to increase data rates. Many operators are starting to use EN-DC (E-UTRAN New Radio — Dual Connectivity), which allows for faster deployment of 5G data rates in certain areas by using a 4G anchor band combined with a 5G data band. Carrier aggregation (CA) combines multiple component carriers (CCs) to achieve greater bandwidth and higher data rates. CA is now becoming more complex as more and more bands are added to the combination options. 5G defines hundreds of new combinations of up to 16 CCs, each with up to 100 MHz of contiguous bandwidth and a total aggregate bandwidth of around 1 GHz. These include challenging new aggregations of two or more low-bands, such as B20 + B28 in Europe or Asia and B5 + B12, B13 or B14 in North America, which offer advantages such as greater range and throughput.

Manufacturers are also beginning to use higher transmit powers to extend the range of high-frequency signals, which do not travel as far as low-frequency signals. Power Class 2, which doubles the transmit power of an antenna (to 26 dB), is already widely used, and the industry is now beginning to explore Power Class 1.5, which further triples the power (to 29 dB).

Industrial design innovation

Smartphone industrial design is evolving rapidly as manufacturers seek new ways to differentiate their products and deliver exciting new consumer experiences. Transformative designs include phones with rollable screens and clamshell phones with foldable screens. Screens that wrap around the phone’s bezels offer a cutting-edge, sleek look while maximizing the screen real estate available to consumers. Physical buttons are beginning to be replaced by virtual controls, often located on the bottom or side bezels of the phone. In addition, manufacturers are adding other new features that users value, such as better displays, more cameras, multiple biometric authentication methods, higher-quality speakers, and larger batteries. While they are attractive to consumers, these features take up space, reducing the space available for the RF front end (RFFE), and they also place new constraints on the location of RFFE components and antennas.

These trends have led to an explosion of small Internet of Things (IoT) devices, including watches, other wearables, and small tracking devices, that use cellular and/or non-cellular connectivity. In these devices, space is critical and squeezing RF content into a tiny space is important.

Antenna Challenge

These innovations in connectivity and industrial design present a variety of interrelated antenna challenges for engineers working on the next generation of smartphones and other mobile devices.

The RF path has more than doubled

The addition of new cellular and non-cellular frequency bands has significantly increased the total number of RF paths in a mobile device. A typical 5G phone that supports mmW bands and UWB has more than twice the number of RF paths as a typical 4G phone. Each RF path needs to connect to an antenna, but doubling the number of antennas is simply not possible. This is because the space available inside a phone is limited: adding more antennas means they must be closer together, which reduces the isolation between the antennas. This leads to coupling-related issues, which increases the likelihood of nonlinear elements in the RFFE, which desensitizes the receiver.

Given the limits on the total number of antennas that can be implemented in a fixed form factor, the logical way to handle the growth in the number of RF paths is to increase the bandwidth of each antenna to support more frequency bands. However, this approach also presents challenges. Antennas with wider bandwidths tend to have higher losses. They may require more space, as the size of the antenna is determined by the lowest frequency it supports. In addition, using a single antenna to transmit and receive multiple bands simultaneously increases the risk of nonlinear spurious emissions from the mixed signals. Addressing these issues is not easy: careful analysis and specialized antenna design techniques are required, combined with appropriate filtering and routing solutions in the RFFE.

Ultra Wideband

Supporting UWB requires three or four relatively large patch antennas, which take up a lot of space in an already crowded phone. As a result, manufacturers are looking for ways to group some of these antennas together to reduce the overall space required. Another consideration is whether to place an antenna in the bezel of the phone to achieve excellent omnidirectional ranging performance.

Carrier aggregation and EN-DC

The rapid increase in CA and EN-DC band combinations exacerbates the antenna challenge. Today, achievable aggregations include hundreds of different combinations of high, mid, and low bands. These include multiple band combinations within each frequency range (such as low-low or mid-mid aggregation) as well as band combinations within different spectrum ranges (such as low-mid and low-mid-high aggregation). In addition, the maximum bandwidth per CC is also increasing. While 4G limited carrier bandwidth to 20 MHz, 5G increases the maximum contiguous bandwidth to 45 MHz for bands below 2300 MHz and up to 100 MHz for bands above 2300 MHz.

Because the total number of antennas is limited, each antenna may be required to provide high-performance broadband transmit and receive signals over a very wide frequency range (600 MHz-5000 MHz).

Low-low aggregation presents some of the most challenging antenna design issues. Mobile handsets typically support low-band frequencies using two main antennas located at the top and bottom of the handset. These antenna locations minimize the chance that user interaction with the phone will degrade performance, as consumers typically rest their hands on the sides of the phone, rather than on the top and bottom. The key issue is that low-low aggregation may require the use of a third antenna that supports low-band transmissions. This means that manufacturers need to find more space within the phone to place this antenna and ensure that the selected antenna location will provide adequate performance under all usage conditions.

Higher Tx power

The higher power outputs defined in the PC 2 and PC 1.5 specifications impact the battery life of smartphones. It also means that all post-PA components within the RFFE, including the antenna tuner, need to handle more power. This typically means larger components, which becomes an issue given space constraints. The increase in output power also means that the RFFE components will generate higher levels of spurious signals, requiring additional attention to mitigate desense and RSE issues.

New design reduces antenna space

New phone designs with foldable and rollable screens present a host of antenna challenges. The phone must be able to operate in different physical states (rolled or unfolded, folded or open), which severely limits the potential locations of the antenna and may also require the use of different antenna materials. Adding to the challenge, design constraints may mean that antennas must be placed in suboptimal locations, making their performance more susceptible to human interaction. Antenna grounding may be affected, affecting radiation efficiency. Careful design and positioning of antennas is required to ensure efficient operation under all conditions of use.

Using software-defined virtual buttons instead of mechanical buttons introduces additional antenna challenges. Placing these buttons on the bottom of the phone maximizes convenience and screen real estate available to the user, but it also means they may interfere with the main antenna that has been placed in this location in the past.

Who will be the first to solve the challenge?

As this article has demonstrated, the next generation of mobile devices presents a considerable number of antenna design and engineering problems. So who will be the first to solve the challenges? In addition to the well-deserved pride that comes with overcoming an extremely difficult challenge, the team that wins the innovation race will have a significant competitive advantage in the battle for consumer support.

How QASR can help

Qorvo Antenna Solutions Reimagined (QASR) is uniquely positioned to help smartphone engineers solve the antenna challenges facing next-generation smartphones and other devices.

Qorvo is committed to investing in technologies that foster innovation and support the continued evolution of mobile phones. However, innovative technologies alone are not enough to solve tough RF problems. That’s why Qorvo works closely with the mobile industry to help engineers solve the unique design challenges facing each mobile device. Qorvo has extensive experience helping manufacturers incorporate innovative solutions into smartphones and other devices, including:

The industry's first antenna tuner helps improve antenna efficiency across a wider frequency band.

Learn about the combination of antenna duplexers, new pathways, and standards to address and simplify emerging complex scenarios.

Driving the development of new customized technologies to meet 5G requirements for antenna tuning, transmit functions, and RF routing.

QASR helps you address the space, design, and performance challenges of leveraging antenna power in your RF architecture.