That's just to be able to better track and eavesdrop on visitors and to illuminate the sky with radio waves that form the basis for a passive radar system allowing the detection of stealth aircraft (see
Cassidian?s Passive Radar Detects Stealth Aircraft | Defense Technology News at DefenceTalk) - so all driven by intelligence interests.
P.S: The UK seem to be looking into a passive radar system, too:
http://www.engadget.com/2013/02/14/u...passive-radar/