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Better mobe antennas a stretch goal for radiocomm boffins

Signal isolation using modulation, not magnets, improves silicon-scale antennas

By Richard Chirgwin, 15 Mar 2016

Antennas can be tuned by changing their shape, and a group of University of Texas Austin researchers wants to use that simple phenomenon to help get rid of noise in silicon-scale antennas.

The idea is to get rid of the magnetic isolation between transmit and receive antennas, which among other things would help shrink the RF part of products like mobile phones.

Conventional antennas are reciprocal – that is, an antenna that's designed to transmit efficiently in (for example) the 2.4 GHz WiFi band is also a good receiver in that band.

The problem for product designers is that they don't want the transmit and receive signals interfering with each other, so a lot of effort goes into isolation – for example, to stop nearby reflections interfering with the signal at a transmitter.

The University of Texas researchers, electrical and computer engineering associated professor Andrea Alù and postdoctoral fellows Yakir Hadad and Jason Soric, added a low-frequency modulation to the transmitted signal.

As the university blurb (at Eureka Alert) explains, the modulation “slowly changes the properties of the antenna as the radio-frequency signal travels along it. This modulation breaks the inherent symmetry of the antenna in transmission and reception, overcoming the reciprocity constraints.”

In other words, the low-frequency signal causes small changes in the shape of the antenna, and that changes its directional tuning without damaging its frequency response.

Their paper is due for publication in PNAS, but hadn't landed at the time of writing. However, in a 2014 publication in Nature Physics, Alù outlined a similar scheme and claimed six orders of magnitude non-reciprocity.

In that paper, Alù noted that since there's no need to modify the antennas, his techniques can be applied to antennas fabricated onto integrated circuits.

Beyond radio communications, the researchers want to investigate whether they can see similar behaviours all the way up to light, which would offer a path to make photovoltaics more efficient. ®

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