The Allen Telescope Array is a joint effort between the SETI Institute and the Radio Astronomy Laboratory of the University of California, Berkeley, and is being constructed at Berkeley's Hat Creek Observatory in the Cascade Range of northern California. This rural site has a low population density, ensuring a radio quiet environment.

The Allen Telescope Array will be an astronomical instrument unlike any other. First and foremost, it is the only major radio telescope purposely built for the "Search for Extraterrestrial Intelligence" (SETI). It is a telescope of unusual design, constructed from a very large number of relatively small antennas. Forming a large radio "mirror" in this way has long been recognized as a technically sound idea, but - until now - an impractical one for an array of such capability. The cost of electronically connecting hundreds of antennas together was prohibitively high. However, thanks to the rapid pace of the digital revolution, what was once impossible is now both feasible and attractive. The Allen Telescope Array will cost only about one-fifth as much as conventional radio telescopes of similar collecting area. And because it is an array, rather than a single dish, it can rapidly make detailed radio "photographs" of the cosmos.
 

For more information visit the SETI site.