Sharpen up

日期:2019-03-07 09:01:18 作者:胥邴篪 阅读:

By Ian Sample ASTRONOMERS trying to catch a glimpse of the birth of galaxies billions of years ago are being thwarted by one of our most up-to-date technologies—mobile phones. Now an international team planning a radio telescope that will cover a square kilometre of ground has worked out a way round the problem. Most galaxies formed when the Universe was young, and they are so far away that the radiation they emitted then is only reaching us now. Having travelled such long distances, the radiation is very faint. What’s more, the red shift caused by the expansion of the Universe has shifted the radiation out of the band reserved for astronomers and into bands used by mobile phones and broadcasters. “Many of these signals are millions to billions of times brighter than the sources we want to study,” says Harvey Butcher of the Netherlands Foundation for Research in Astronomy in Dwingeloo, one of the scientists working on the new telescope, which is called the Square Kilometre Array (SKA). To tackle the problem, Butcher’s group has developed a phased array, a flat grid of antenna elements. Similar arrangements have long been used in radar systems. Altering the phase of the signal from each individual antenna leads to costructive interference in some directions and destructive interference in others, so the direction of a beam can be controlled without physically moving the antennas. The phased array can be used to detect and boost signals coming from some directions, while creating “blind spots” in others, such as that of a mobile phone base station. In lab tests on a 64-element array, Butcher reduced unwanted signals by a factor of up to 10 000. Butcher concedes that the degree of suppression is relatively small. For this reason, scientists are now looking for the best site to build the SKA. “The question is,” says Butcher, “can we find somewhere on Earth where the interference that’s killing us is not present?