With TV and radio stations, and now cellphone networks jostling to broadcast, it is hard to find a wavelength that has not already been claimed. Bandwidth is in high demand, and therefore expensive. So cellphone companies will be delighted by a report in Nature 1 of how to boost the data-carrying capacity of radio signals by a factor of six. Michael Andrews of Lucent Technologies in Murray Hill, New Jersey, and colleagues now show that there is in fact more room within any given band than we think.
Radio waves consist of an oscillating electromagnetic field, as do light waves.
A magnetic field oscillates in the third direction, perpendicular to the electric field. The direction of the electric field determines the signal's 'polarization state'. In principle, each of these polarization states can be used to send independent signals at the same frequency. They can be picked up separately by antennas pointing in the different respective directions. In practice, this possibility is rarely exploited.