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Supporting Advanced Services in Slim Devices
An antenna that optimizes the RF system is critical to ensure a positive user experience with today’s small, stylish devices.
By Paul Tornatta, SkyCross
Figure 1. The Samsung Blackjack is an example of a stylish smartphone packed with features. The single, small SkyCross antenna in this device supports 3G UMTS/HSDPA, Quad-Band EDGE/GPRS, and Bluetooth. |
Worldwide sales of wireless devices continue to grow dramatically. As markets mature, customers everywhere increasingly integrate wireless functionality into their daily lives. They also demand more advanced services requiring multifunction, multiband devices with reliable performance.
With the growing popularity of advanced voice services, mobile TV, music, data/internet, navigation and cameras, the "real estate" inside the wireless device
is at an all time premium. At the same time, device size, form factor and cost have become dominant considerations. Form factors are shrinking just at the time when they must simultaneously support a growing list of data protocols.
Manufacturers of these devices must combat tough design constraints associated with radio-frequency (RF) interference and rapidly develop slim, differentiated designs at compelling price points. In addition, they must accomplish these tasks under intense market and cost pressures, but maintain profitability in a highly competitive industry.
Through advanced technology and flexible designs, manufacturers of embedded antennas help empower device designers to create a full range of consumer electronics with wireless connectivity. Embedded antennas are found in a wide range of mobile platforms including slim mobile handsets, smartphones, notebook computers, PC cards including Express34, personal media players, ultra-mobile PCs, and wireless earphones.
Consumers worldwide demand a satisfying user experience:
•Small, thin, stylish devices
•Prolonged battery life
•Preferred combinations of advanced voice, data, music, video, and location services
•Choice of networks
•Attractive price points.
Historically, small antennas offered performance values equivalent to their size. Today RF design freedom provides the ability to expand wireless device capabilities. Antenna-centric RF technology is empowering device designers to create a full range of consumer electronics products that meet consumer expectations for small and stylish devices and manufacturers’ needs for differentiation.
Flexible Antenna Technology
Antenna technology can be manipulated to form wideband designs (performance across a wide range of frequencies with no breaks) or multiband designs (several discrete resonances in specific
Antenna Technology
How do designers of embedded antennas support multiple advanced services i.e., voice, mobile TV, music, data/Internet etc., and fit the required RF components into very slim phones? How can all RF components in a device work better together to help optimize overall device performance? Antenna-centric RF technology is enabling device designers to create consumer electronics products that meet consumer demands for small and stylish devices. This technology is no longer tied to a specific shape or size. Instead it can be manipulated to fill the available volume, which is crucial for optimizing efficiency and maintaining a sleek industrial design. |
frequency bands). This is important in selecting the starting point for the design.
Wideband designs are more immune to detuning effects, e.g., the detrimental effect a user’s hand, head, or body may have on the performance of an antenna. Also, they are more tolerant to coupling to nearby structures within the device, such as a camera or speaker. However, wideband designs tend to be larger and pick up out-of-band interference.
PC cards are an excellent example of a device that benefits from wideband antenna designs. The higher tolerance to detuning effects from nearby structures becomes very important when the PC card must operate in the laptop, which is packed with structures that can cause detuning. In general, the wideband antenna is an ideal solution for applications that have the space available for the larger design. The tolerance to its environment can make a single antenna design applicable to a variety of applications, reducing design time.
Multiband designs occupy less space and have more favorable out-of-band rejection characteristics, but tend to be more sensitive to detuning effects.
Handsets typically employ a multiband antenna because of the limited space in the device. Handsets often have many closely spaced radios for GSM or CDMA, Bluetooth, GPS, UMTS, HSPDA, etc. The out-of-band isolation becomes very important to mitigate interference in such a tight space.
Antenna technology is no longer tied to a particular shape or size. It can be manipulated to fill the available volume. This is crucial for optimizing efficiency and maintaining a sleek industrial design.
Offering the best design at the lowest cost requires freeing the antenna technology from expensive, exotic materials or processes. In other words, the antenna must be made from low-cost, off-the-shelf materials and easily assembled with low-cost labor.
With experience it is possible to tell in advance if a proposed device implementation will be problematic. Engineers must evaluate the customer’s industrial design by looking at the structure in terms of
wavelength. Normalization techniques allow performance comparisons between seemingly unrelated applications and implementations. This knowledge is used to steer the customer’s design team towards optimum implementations.
Figure 2. Historically, small antennas offered performance values equivalent to their size. Today, antenna technology is no longer tied to a particular shape or size. It can be manipulated to fill the available volume. (From left to right, here are: Conventional Antenna; Embedded Wideband Antenna: This SkyCross antenna covers 800-2500 MHz; Embedded Multiband Antenna: This SkyCross antenna covers 900/1800/1900/2400 MHz.)
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There are several design guidelines related to the antenna positioning, clearance from ground, and proximity to noise structures that can avoid implementation issues.
For example, it is best not to wrap antennas around structures that generate noise such as cameras and displays or structures with magnetic materials causing loss, such as speakers. The obvious solution is to allot a different area for the antenna, but this is not always possible in tight spaces. The alternative is to use a grounded shield around the problematic structures. It is better to have the antenna closer to ground than unshielded noise.
Another classic implementation issue occurs in flip phones. Flip phones have flex film running through the hinge that connects one side to the other. This flex film moves every time the handset is opened and closed. It is best not to have the antenna near this region of the phone because the environment, and therefore the antenna, cannot be stabilized.
RF Factor — Creating Harmony
Increasing the efficiency of the entire “RF chain”, including antennas, power amplifiers, multiplexers, and switches, enhances overall device performance and enables a smaller form factor.
Engineers with expertise in embedded antennas help designers of compact mobile phones resolve the difficult internal interference issues that often influence device performance.
The antenna design philosophy should be to:
Look at the whole device implementation and performance requirements
Work in collaboration with customer design teams
Provide early feedback on industrial design features that can be identified as potential concerns.
The best approach is to tailor the antenna to the customer’s industrial design and application—not to attempt to force the customer into using a particular antenna design.
The antenna should not be treated as a stand-alone component. A small, highly efficient, embedded antenna is an integral part of the device. It cannot be designed, implemented, or evaluated as an independent part or as independent from the overall device performance.
Active measurements should be performed on the device as soon as possible in the development cycle and input offered on shield and ground configurations to optimize antenna performance and minimize interference.
Frequency Band
The frequency band is one of the most important factors in antenna design. While lower frequencies historically have physically demanded a larger antenna, fully embedded solutions are now available that operate as low as 180 MHz on some mobile video networks. Voice and data standards start at the 800 MHz band and can be covered with a single multiband antenna to simplify device design.
There is no upper boundary to the frequencies that embedded antennas can support. Ultra-wideband (UWB) applications operate at 3 to 10 GHz, which is currently the maximum of what is relevant to commercial applications.
Optimizing Components through Antenna Design
Antennas can be designed to conserve battery life and per-application performance as features are added for optimal systems performance. As applications and features are added to mobile devices, the demands on the antenna to cover more frequencies of operation increase.
The power added efficiency (PAE) of the system can be significantly improved by better matching and a higher level of integration among elements. Analysis has shown that improvements in PAE translate nearly one for one into improved battery life. So a 10% improvement in PAE translates to nearly 10% improvement in battery life.
click to enlarge
Figure 3. Optimizing Antenna Components: The red and green curves show that by focusing the instantaneous bandwidth for the high and low bands, the impedance match gets closer to 50Ω. This results in better VSWR and therefore 10% more efficiency than the wideband antenna without impedance matching demonstrated by the blue curve. |
In order to optimize the RF performance of the chain, it is crucial to eliminate losses wherever possible. Losses come in many forms including I2R (heat) and reflection losses. I2R losses can be mitigated by integrating the RF components closer together since shorter transmission lines have lower loss.
Reflection losses are mitigated by improving the impedance match between elements. In a typical RF chain, all the elements are designed to be 50Ω. If all elements are 50Ω for all operating conditions, including frequencies, temperatures, power levels, then everything is well matched and the RF chain will operate optimally. In truth, many of the elements in the RF chain are not so well behaved over all operating conditions.
For example, consider an antenna designed to cover both North American and European frequency bands. To simplify the problem, consider only the lowest frequencies of operation, 824 to 894 MHz for North America and 890 to 960 MHz for Europe. The low frequencies tend to drive the physical size of the antenna.
An antenna designed to operate from 824 to 960 MHz will never present a 50Ω impedance to the system. The impedance of the antenna circles around the 50Ω point as the frequency of operations is changed.
One way to mitigate the problem is to reduce the required instantaneous bandwidth of operation to a single frequency band of interest, say 824 to 894 MHz. By doing this, the antenna impedance will be better matched to the rest of the RF chain and the overall power-added efficiency will increase. By using a simple, single-digital control line, the antenna structure can be changed to "re-match" to operate from 890 to 960 MHz.
This simple change in architecture can increase the system’s power-added efficiency by more than 10%. This is the simplest case. Taken to its ultimate implementation, a high level of integration could improve the device performance far more than 10%.
Conclusion
Wireless device design is complicated, iterative, and time consuming. Manufacturers must design devices that perform well on multiple frequency bands and networks — even as power-consuming features such as cameras, music players, and navigation are added.
These multifaceted engineering challenges can be met with flexible, RF solutions that provide radio connectivity for nearly any device — regardless of configuration.
Ultimately, the antenna is the only component that connects the radio to wireless networks. A superior antenna that optimizes the RF system is critical to ensure a positive user experience with a small stylish device.
About the Author
Paul Tornatta is managing director for SkyCross USA and vice president of operations, 7341 Office Place, Suite 102, Viera, FL; (321) 308-6600; www.skycross.com
SkyCross Inc.
http://www.skycross.com
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2012
Advantage Business Media
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