Twisted Radio Waves Could Expand Mobile-Phone Bandwidth by a Factor of 9

radio waves
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Spiralling radio waves could revolutionize telecommunications.

The bandwidth available to mobile phones, digital television and other communication technologies could be expanded enormously by exploiting the twistedness as well as wavelength of radio waves. That is the claim being made by a group of scientists in Italy and Sweden, who have shown how a radio beam can be twisted, and the resulting vortex detected with distant antennas.

The simplest kind of electromagnetic beam has a plane wavefront, which means that the peaks or troughs of the beam can be connected by an imaginary plane at right angles to the beam’s direction of travel. But if a beam is twisted, then the wavefront rotates around the beam’s direction of propagation in a spiral, creating a vortex and leaving the beam with zero intensity at its centre.

Physicists have been able to create twisted beams of visible light for about 20 years, having initially noticed that such beams were being produced inside some laser cavities. These twisted beams of light are useful in nanotechnology, as optical ‘tweezers’ or ‘spanners’ to manipulate tiny particles. To date, however, no-one has attempted to do the same thing at the radio wavelengths used in telecommunication.

Spiral waves

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Now, a group led by Bo Thidé of the Swedish Institute of Space Physics in Uppsala and Fabrizio Tamburini of the University of Padua, Italy, has succeeded in twisting the waves emitted by the type of antenna used by standard wireless routers to transmit data over long distances. The team did this by reflecting the waves off an eight-stepped, spiral-staircase-like structure positioned a couple of metres from the antenna, the axis of which lined up with the beam. The idea was that different sections of the wavefront would bounce off different steps, introducing a delay between the reflection of neighbouring sections and so causing the wavefront to become twisted and take on the shape of the reflector.

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