Benefon Twig Discovery

TWIG Discovery GSM smart phone by Benefon

Sarantel's antenna allowed us the luxury of not having to compromise navigation performance while at the same time keeping the TWIG Discovery mobile small enough to meet consumers' expectations

Jonathan Bate, CEO
Benefon

The Company

Benefon was founded in late 1987, when the first managing director of Nokia decided with two colleagues to found a company of their own. Beginning with the Benefon Forte NMT 450, the world's first mobile phone to include an in-built answering machine, Benefon has introduced dozens of wireless communication instruments to NMT- and GSM-systems in Russia, Scandinavia, Europe and Asia. Then in 1999, EU's Mobile Rescue Phone project resulted in a new, revolutionary product concept: a mobile phone and a GPS-navigator integrated in one portable product. This concept took shape in Benefon's GSM+GPS products, of which Benefon Esc! was launched in late 1999 and Benefon Track in 2000.

The Challenge

As advances in electronics and changes in consumer tastes have led to the shrinking of mobile phones, it has become much more difficult to produce an efficient GPS receiver in such a device. While receiver microelectronics have improved and shrunk, physics dictates limits on the size of the antenna receiving system - smaller antennas are less efficient than larger ones. Conventional antennas use a ground plane to increase the apparent size of the antenna to the size of the phone itself. In larger devices, this strategy provides sufficient signal to the receiver for navigation applications. In smaller devices, the apparent antenna size is reduced to a point where impairments from loading, such as when the user's hand grasps the phone, decrease the efficiency such that navigation becomes unreliable.

Common strategies to circumvent this problem have significant drawbacks. 'GPS-enabled' mobile phones commonly use a method called 'A-GPS' in which the mobile network either provides assistance data to the phone or computes part of the phone's location in ancillary network equipment. This strategy leaves the phone tethered to a particular carrier's network, unable to compute a navigation solution without assistance from the network. Further, the sensitivity gained by network assistance is often lost by poor antenna implementations and user loading effects.

A Complication

Benefon wanted to design a fully autonomous navigation phone with a form factor that would be attractive to consumers. This meant that the GPS antenna had to be completely embedded within the phone. Embedding an antenna for a service like GPS introduces a number of problems for the phone designer, but none more critical to performance than self-jamming of the GPS receiver. GSM transceivers, oscillators, microprocessors, and other components squeezed into a small space generate common-mode noise that couples with the GPS antenna ground plane, which in turn channels that noise into the receiver. Other antennas in close proximity can couple with the near-field of the GPS antenna, providing an additional source of interference that reduces the usable signal available to the receiver.

The Solution

Benefon turned to Sarantel to embed the GeoHelix GPS antenna. GeoHelix antennas are physically small for embedding, yet large enough to provide reception efficiency required for autonomous navigation. Importantly, GeoHelix antennas are balanced, and therefore are isolated from the common mode noise resident on the ground plane in the mobile phone. Because they do not couple with the ground plane, GeoHelix antennas are incapable of conducting this noise to the GPS receiver. Their tightly constrained near-field makes them much less capable of coupling to interfering transmissions from the GSM or other subsystems in the mobile phone. Therefore, the problem of self-jamming is very much reduced by the GeoHelix antenna.

The GeoHelix antenna's constrained near-field has another important impact on the user's navigation experience. When the user grasps the phone, the antenna does not de-tune or lose efficiency. This ensures maximum signal to the receiver in all modes of use, resulting in a reliable, accurate navigation solution from the mobile phone.

These characteristics of the GeoHelix antenna allowed Benefon to design the TWIG Discovery with an eye toward aesthetics and consumer appeal without sacrificing GPS performance.

Their Comment

"We did not set out to design a mobile phone, then tack on a GPS receiver," said Jonathan Bate, Benefon's CEO. "It was very important to Benefon that the user get the full benefit of the GSM and GPS technology we built into the TWIG Discovery mobile. Autonomous navigation is much harder to accomplish from a GPS receiver if it's not a core technology of the phone. Benefon has designed its best navigation technology into the TWIG Discovery for a reliable and accurate navigation experience for the consumer. Sarantel's antenna allowed us the luxury of not having to compromise navigation performance while at the same time keeping the TWIG Discovery small enough to meet consumers' expectations."

Markets

Europe, Asia

Where To Buy

http://www.benefon.com and leading on-line mobile phone retailers.