The Growing Demand for Active Antenna Systems in LTE MIMO Networks

As of today, over 200 LTE networks are in operation globally, and this number is expected to double within the next five years, according to 4G Americas. A common thread running through all these networks is the requirement for active antenna systems, essential to meet LTE’s Multiple Input, Multiple Output (MIMO) demands.

MIMO technology is crucial for both base stations and user devices. However, implementing MIMO at the device level presents unique challenges:

1. Multiple Antennas: MIMO requires at least two antennas, compared to the single antenna used for 3G. As MIMO evolves to more advanced configurations like 4×4 and 8×8, the need for more antennas grows. This creates a space issue in modern devices, especially as 3G/2G fallback, GPS, Wi-Fi, Bluetooth, and NFC antennas are also needed. As devices get thinner, fitting all these antennas becomes increasingly difficult.
2. Band Fragmentation: LTE is designed to work across more than 40 frequency bands between 450 MHz and 2.7 GHz. With about half of these bands currently in use, building devices capable of supporting LTE globally (without relying on 3G fallback) is a challenge. Even supporting a few bands in MIMO configurations can be difficult, especially when other technologies like Wi-Fi also require antenna space.
3. Preference for Lower Bands: Operators prefer using lower-frequency bands like 700 MHz for LTE because it requires fewer base stations, reducing operational and capital expenditures. Lower bands also offer better in-building coverage, important for customer satisfaction and the growing Internet of Things (IoT) market. However, these lower frequencies require physically larger antennas, making it harder for device manufacturers to include them in sleek designs. IoT devices, with their limited space, face an even bigger challenge.
4. Thinner Devices: The trend toward thinner smartphones and tablets means there is 25% less internal space each year. Batteries and displays get priority, leaving limited room for the processor, memory, and antenna systems. With MIMO and the need for larger antennas at lower frequencies, design teams face mounting pressure to make everything fit.
5. Lack of Experience: As LTE networks expand, device manufacturers are under pressure to integrate LTE into their products. This can be challenging even for established vendors, as LTE requires a steep learning curve. For Machine-to-Machine (M2M) vendors, many of whom have little to no experience with cellular technology, the challenge is even greater.

Despite these hurdles, device manufacturers and RF suppliers have two options: work harder or work smarter. Active antenna systems represent the smarter approach.

The Advantages of Active Antenna Systems

Active antenna systems offer greater flexibility, performance, and reliability than traditional passive antennas, making them ideal for overcoming the challenges posed by LTE’s MIMO and band fragmentation requirements. These systems are particularly well-suited for accommodating operator preferences for lower bands and the trend toward thinner devices.

Here are some key advantages of active antenna systems:

• Flexible Tuning: Active antennas can cover multiple LTE bands, even those that are widely spaced, like Band 17 (704 MHz to 746 MHz) and Band 41 (2,496 MHz to 2,690 MHz). Some active antennas can tune across the entire 698 MHz to 2.7 GHz range, which is essential as LTE-Advanced carrier aggregation makes band fragmentation even more complex. Active antenna systems allow designers to meet these demands efficiently.
• Improved Performance and Reliability: Active systems, like those using null steering (a form of beam steering that changes the radiation pattern), help mitigate the effects of multipath fading, where signals scatter and reflect off obstacles. This dynamic response improves download speeds and connection reliability, which users immediately notice.
• Cost-Effective and Efficient: Active antennas reduce the cost and lead time for new devices. Unlike passive systems, active antennas can be dynamically re-tuned to accommodate different environmental conditions or design changes, reducing the number of product SKUs and simplifying global deployment.
• User Experience Benefits: Smartphones and tablets with active antennas provide more consistent uplink and downlink speeds, reducing the likelihood of dropped calls. This translates to better user satisfaction, which benefits both the device manufacturer and the mobile operator by reducing troubleshooting calls and enhancing brand reputation.

The Ideal Active Antenna Solution

With the increasing demand for active antenna systems, RF vendors are introducing a variety of active tuning solutions. However, selecting the most effective solution depends on a few key factors: performance, reliability, flexibility, and ease of integration.

• System-Level Optimization: The best active antenna systems are co-designed, where the antenna, active components, and algorithms are developed and optimized together. This integrated approach allows device manufacturers to bring products to market faster while minimizing costs and simplifying integration. A system optimized at the antenna level ensures better performance than sourcing antenna and chip components separately.
• Dynamic Impedance Matching: Tuning should be done at the antenna feed point to maximize performance. When tuning occurs further back in the system, such as at the transceiver chipset, it can introduce delays and losses that degrade performance.
• Bandswitching and Impedance Matching: Bandswitching, also called active aperture, allows antennas to dynamically change their frequency response, providing coarse tuning of the antenna element. Active impedance matching provides finer tuning at the feed-point. Modern RFIC designs combine band switching and tunable capacitors to enable tuning across wide frequency ranges, particularly below 1 GHz, where antenna size poses the greatest challenge.

The ideal solution combines both band switching and dynamic impedance matching in a single module. This reduces the need for custom integration, lowering development costs and shortening time-to-market. For M2M devices, which often have limited RF expertise, this plug-and-play approach is particularly valuable.

Conclusion

Active antenna systems are essential for device manufacturers looking to meet the challenges of LTE MIMO and band fragmentation. By incorporating these systems, OEMs can gain a competitive edge, offering better reliability, performance, and cost efficiency in their products. As LTE adoption continues to rise, active antennas will be critical in maintaining and enhancing connectivity in an increasingly competitive market.