4G Devices Demand Active Antenna Solutions
As the deployment of 4G networks continues to ramp up, the competition becomes ever fiercer for the fastest networks and best coverage areas. Consequently, consumers now experience faster download speeds and access to information in a seamless way.
However, what consumers don’t see—as they shouldn’t—is the mounting challenge to provide fast data rates in cool, thin devices. Luckily, the first wave of solutions has arrived (with more on the horizon), simplifying 4G delivery for both operators and OEMs.
LTE’s Spectrum And Form-Factor Challenges
In terms of Long-Term Evolution (LTE) networks, OEMs and operators face two main issues: efficient spectrum management, which means more frequency bands to cover, and shrinking device sizes. These factors have a direct ripple effect on component count, since more must be squeezed within the same amount of space.
One long-overlooked yet important component has been the antenna. Designed in at the last minute during the conception phase, its size can no longer be ignored in the mechanical stackup. The reason is simplistic: passive antennas have reached their performance limits. Fortunately, the right antenna and RF system design can offer a new perspective on designing the entire phone, delivering the desired connectivity experience to consumers.
Given the growing demand for wireless, radio spectrum is now a top concern for operators worldwide. As a result, band harvesting has become a necessity, with operators using whatever spectrum they can get their hands on. Thus, 4G now operates across a wide range of different frequency bands. For operators in the U.S. and some other markets, much of this spectrum resides at low, 700-MHz frequencies.
Operating at lower frequencies poses a significant challenge for LTE devices. Most consumers expect LTE to provide a better experience than with 3G—global roaming, battery life supporting a full day of work and/or activities, and backward-compatibility to 2G and 3G legacy bands—all wrapped up in a thin, sexy device with a big screen.
Global roaming with LTE requires more than 13 bands for ubiquitous coverage, resulting in devices crowded with antennas. It isn’t uncommon for a device to need five antennas, given the current requirement for multiple-input multiple-output (MIMO) and the additional antennas necessary for 3G, GPS, Wi-Fi, and other functions. In addition, larger antennas are needed to cover the lower frequency bands.
If devices were growing in size, this wouldn’t be an issue. But consumers want thinner, sleeker devices, which equates to less real estate for antennas and other components, and more headaches for engineers trying to deliver on the promises of LTE.
One problem, for example, surrounds LTE’s MIMO requirement. The need for two antennas makes it difficult to achieve isolation, because both antennas operate at the same frequencies and are near each other. Integrating a poorly performing antenna would lead to significant interference, depriving the user of the 4G experience.
The antenna is the air interface and acts as a sensor. The more antennas incorporated into the device, the greater the risk of performance becoming compromised by body effects and phone placement. This causes further de-tuning to all the antennas, leading to dropped calls and/or slower data rates.
4G Demands An Antenna (R)Evolution
Much of 4G’s success hinges on the device itself. In fact, the type of antenna and RF design within a particular device can directly affect the user experience.
For antenna and RF engineers, 4G requires some serious innovation to deliver on the promises of high performance and connectivity. “Passive” antennas used for 2G and 3G devices have reached their limits. Consequently, the passive approach will likely fall short of the more demanding 4G MIMO and global roaming requirements.
Therefore, 4G devices require “active” antenna and RF systems. Unlike legacy passive antennas, active antenna systems infuse more “smarts” into the RF system. This enables the antenna system and modem to interact with one other, reaping a number of benefits for OEMs, operators and consumers. Thanks to innovative technologies such as band switching and active impedance matching, Ethertronics is now delivering active antenna systems to market.
Active band switching covers more than 13 bands, meeting LTE’s multiple bands challenge to provide ubiquitous coverage. Band switching lets the active antenna system switch between different sub-frequency bands, since it has a reduced instantaneous bandwidth requirement (i.e., the antenna only needs to service one or two bands at any one time). This makes it possible to implement and actively enable a smaller, more resonant antenna, providing dynamic tuning across a wide frequency range.
The active antenna system’s design could include two or three narrow to moderate bandwidth resonances. These can be tuned in unison to allow for instantaneous coverage of two or three frequency bands at any given time. By handling significant spreads in frequency range, from the low 700-MHz U.S. bands to 2.7 GHz, simultaneous voice and data usage can occur without compromising performance. Band switching also enables the smallest physical volume antenna systems to fit in the thinnest devices.
Active impedance-matching techniques will be key drivers toward ensuring that OEMs meet carrier specs and consumers are pleased with their wireless experiences. These techniques are derived from tunable matching circuits, which address form-factor and frequency coverage issues.
Such circuits offer many benefits, including the ability to reduce the antenna’s physical volume by 50% without compromising performance. Reduced size becomes a critical factor, particularly due to ever-larger batteries and the integration of more antennas into the device. Alternatively, these techniques can be used to cover a wider bandwidth in the same antenna volume.
Innovations leveraging active impedance matching seem certain to continue. The number of input parameters will substantially increase to dynamically keep the antenna matched over a wide variety of use cases by using a feedback loop, including body effects and phone placement (e.g., on a table or in the hand). Forward and reflected power can be sampled at the antenna port, and an algorithm can be implemented to quickly adjust the matching circuit to re-match the antenna.
Ethertronics employs active band switching techniques for its EtherBook 1.0. OEMs can integrate the antenna inside LTE notebook computers to cover the more than 13 bands needed for global operation. It features a small antenna volume to fit into very thin notebook displays and faster approval cycles from regulatory bodies and carriers as well.
Also, Ethertronics uses active impedance matching techniques for its EtherSmart LTE 1.0. It resolves a number of issues in mobile devices, including more bandwidth coverage in the same volume, enabling smaller size with no performance degradation, and offsetting head and hand effects. The use of active techniques creates faster time-to-market and improves spec compliance across bands. The solution is currently integrated into Samsung’s Galaxy S II LTE SC-O3D for NTT DOCOMO subscribers in Japan.
Expect rollouts of LTE and 4G networks to expand throughout 2012. Delivering on the promises of LTE will no doubt require an antenna (r)evolution, buttressed by advanced active antenna and RF systems. The introduction of these antenna systems coupled with ongoing innovation will make many of 4G’s major issues a thing of the past and ultimately deliver on the promises of the LTE experience desired by consumers.
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