Electronic Design

Dielectric Antenna Solves Tough Integration Problems

A novel helical design, consisting of a helical loop on a ceramic dielectric, reduces the near field and eliminates the need for a ground plane.

One nagging problem with microwave antennas in cell phones and other products is that the user's presence seriously affects them. Bringing the antenna near the user detunes it. Also, a huge portion of the radiated or received energy is lost in the user's hand, head, or body. The near-field energy produced by the antenna is literally sucked into any nearby object with a dielectric constant greater than one, which means just about everything else. Most of this energy is wasted, making transmission and reception considerably worse than desired.

Sarantel Ltd. has come up with a solution in its GeoHelix antenna. The antenna conductor is a helical loop made on a ceramic dielectric. This design confines the near field to a volume not much larger than the antenna itself. The twisted loop structure also reduces induced noise and serves as a superior filter. A built-in balun performs unbalanced to balanced conversion.

Because the antenna is a balanced loop, no ground plane is required in the cell phone or other device, which is usually the case. The resulting antenna is about the size of a pencil eraser, providing a 15% to 50% greater transmission range over antennas several times its size. The radiation pattern is omnidirectional and right-hand circular polarization (RHCP), which is compatible with GPS systems. It also receives either vertical or horizontal polarized signals equally well. A key benefit of the antenna is that it greatly reduces specific absorption rate (SAR), a measure of the amount of power radiated and absorbed into a unit mass of body tissue. The dielectric loading of the antenna core and the twisted conductors reduce the rear field to minimize the local absorption effects.

The multipatented GeoHelix antennas are now available for GPS service in GPS receivers and in cell phones that use GPS as the basis for implementing the E911 mandate. Versions for WCDMA 3G cell phones and Wi-Fi wireless local-area-network (WLAN) service are in development and will be available shortly.

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Sarantel Limited
www.sarantel.com

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