Twisting radio waves could boost capacity

Radio congestion could be dramatically eased by twisting the waves into spirals.

A group of Italian and Swedish researchers says the technique could allow a potentially infinite number of channels to be broadcast and received – eliminating the increasing pressure on capacity caused by smartphones, wireless internet and the like.

“You just have to try sending a text message at midnight on New Year’s Eve to realise how congested the bands are,” says lead author Dr Fabrizio Tamburini.

The answer, they say, is to manipulate waves so that they can hold more than one channel of information. A wave can twist about its axis a certain number of times in either a clockwise or anti-clockwise direction, giving it several possible configurations.

“In a three-dimensional perspective, this phase twist looks like a fusilli-pasta-shaped beam,” says Tamburini.

“Each of these twisted beams can be independently generated, propagated and detected even in the very same frequency band, behaving as independent communication channels.”

And the team’s demonstrated this, by beaming their pasta-shaped waves across the waters of Venice.

They transmitted two twisted radio waves, in the 2.4GHz band, over a distance of 442 metres from a lighthouse on San Georgio Island to a satellite dish on a balcony at the Palazzo Ducale on the mainland of Venice, where it was able to pick up the two separate channels.

Tamburini says that by using multiplexing, it should be possible to give 55 channels on the same frequency band.

And there are other applications to the research, too. Black holes, for example, are constantly rotating and as waves pass them, they are forced to twist in line with the black hole.

According to Tamburini, analysing the incoming waves from the supermassive black hole at the centre of the Milky Way, Sagittarius A, could help astronomers obtain crucial information about its rotation.