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Airwire antenna extends power transmission range

Posted: 19 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:antenna? battery? amplifier?

Wireless applications in the 2.4GHz band from remote controls to Zigbee industrial controllers to Wi-Fi nodes usually have to use a more powerful amplifier to expand their range. But now Texas Instruments Inc. (TI) has a better idea of changing the traditional metal antenna with a resonant slot on the PCB.

Next week, TI is expected to launch a new product after adopting Pinyon Technology Inc.'s Airwire slot-antenna for its RF reference designs disclosing fully characterized and FCC-approved schematics to its OEMs. TI said the designs will nearly double the range of its RF front-end chips.

"What's good about the Pinyon Airwire antenna is that you can almost double the range using the same output power," said Richard Williams, RF applications engineer responsible in updating TI's free online reference designs for its RF front-end chipsets. "If you don't need an extended range, in case your application is a remote control, switching to Pinyon's antenna will allow you to use only about half the power you need with a traditional antenna which will give longer battery life," he noted.

Unexpected creation
Pinyon's slot-antenna design was an "accidental" invention of Forrest Brown, chief technology officer, Pinyon, who discovered through experimentation that a resonant slot in a copper-clad PCB can boost the antenna's range. The technique is implemented by matching the length of the slot to the RF wavelength, then cutting it out across the middle with a small microstrip, an electrical transmission line consisting of a conducting strip separated from the ground plane by a dielectric.

The resistance of the embedded microstrip converts the voltages detected on the antenna into a current that drives the RF front-end chip. TI said this nearly doubles the range of the antenna or allows it to hold the range constantly with about half the power. The icing on the cake is cost, about 25 cents for the PCB material plus a few resistors, diodes and capacitors.

Testing targets
TI's first reference design will be for its CC2430 RF front-end chip, which in laboratory testing has a range of about 460ft with a traditional antenna. However, by merely etching the antenna into a circuit board, following TI's schematics, the CC2430's range can be extended to over 880ft, according to TI. "We have created a reference design for the CC2430, which includes the Pinyon antenna as a part of its circuit board," said Williams. "We have fully characterized this design and had FCC certification so that anyone using our RF chips can produce their own slot-antenna," he added.

TI plans to continue to release reference designs for its other RF front-end chipsets, including the CC2591 power amplifier, its newest range-boosting chip, whose range can be almost doubled from about 2.5mi to 5mi, by simply switching to the Pinyon antenna.

In the future, the company plans to go back and do new reference designs using the Pinyon Airwire antenna for its portfolio of RF front-end chips, including its older 900MHz RF chipsets.

- R. Colin Johnson
EE Times

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