The design is intended to increase power efficiency, the company said. But by directing most of a radio-frequency signal away from a user's head, manufacturers could adopt the antenna for their cell phones in response to a controversy over the effects of electromagnetic radiation from cellular telephones.

Industry organizations and official agencies, called on to guarantee the safety of mobile telephones, have repeatedly said there is no evidence of health risks from electromagnetic radiation at the energy levels used in mobile phones.

"We've developed a directional aerial [antenna] for use with mobile phones," said Ian Murphy, engineering director at Plextek. "It's in the form of a flat-plate antenna fitted to the back of a conventional hand set."

Murphy said that in light of a high-profile debate in the United Kingdom — including court cases in which users claimed that cell phones had affected their health — the company has decided to offer the design. He declined to say whether he considered cellular telephones with conventional omnidirectional aerials a health hazard.

Patch of copper

The flat-plate antenna is a simple 20-mm x 20-mm patch of copper on a printed-circuit board with a contact through the back-side. On the reverse of the board is a ground plane. The square patch resonates at the frequencies of the carrier signal, 900-MHz. Murphy said that the design had now been tested and was shown to work well at 0.5-W output with a 20-dB difference in signal strength between the primary and reverse directions. "The radiation levels in the direction of the user's head can be as low as 1 percent of those produced by some conventional designs," Murphy said.

Patch-antenna technology is well-known in the industry and is probably not easily protected in the form of intellectual property. "I don't know why this hasn't been done before," Murphy said. "It's unlikely that we can protect this, but what we have got is a design that's ready for use."

It may also pose a marketing challenge for any cell-phone makers who choose to adopt the technology. "A lot of phone manufacturers are now in a difficult position," Murphy said. "If they adopt the technology they are almost implying there is a problem with conventional aerials. But if the user population demands the technology, it could become a marketing advantage for those companies which use it."