When pressed, Taiwan will admit that their new early warning radar atop Leshan Mountain in central Taiwan is probably the most powerful such phased array radar in the world. American experts hint that while the Leshan radar may not be the most powerful, it is among the most powerful.
Taiwan put the Leshan radar into service in January 2013, and have been quite pleased with its performance. Not only can the radar spot missile launches up to 5,000 kilometers away, it can give Taiwan about six minutes warning of a Chinese missile attack. That’s enough to alert the missile defenses and Taiwanese defense installations. China has over 1,400 ballistic missiles within range of Taiwan, and any invasion attempt is expected to start with the launching of many, if not most, of these missiles.
Early warning of a Chinese missile attack is not what the Leshan radar is used for most of the time. No, much to the distress of China the Leshan radar can also keep track of most aerial activity over China. That 5,000 kilometers range of the Leshan radar pretty much covers most of China, not to mention North Korea and, well, you get the picture. The radar covers areas closer (than 2,000 kilometers) in even more detail, and this provides excellent coverage of most key Chinese military bases and weapons production facilities.
The Leshan radar has been under construction for a decade and costs $1.4 billion. The radar operates on a mountain over 3,000 meters (10,000 feet) high. Much of the equipment and building materials had to be flown in, and the climate up there is a lot colder than most Taiwanese are accustomed to. Putting the radar at such a high altitude gave it a clear view of eastern China. Despite Chinese objections, the United States provided much of the needed radar design data and some of the equipment.
The Leshan radar is based on the U.S. Air Force Pave Paws early warning radar. The U.S. has five of these radars in service as part of the American BMEWS (ballistic missile early warning system), a half century old system using radars and satellites to monitor the planet for ballistic missile launches (specifically ICBMs, but any large missile launch is detected). Early on, BMEWS consisted of long range radars (like Pave Paws) that could spot warheads coming over the North Pole (from Russia). When SSBNs (ballistic missile carrying nuclear subs) entered the Russian arsenal in the 1970s, BMEWS was augmented by DSP (Defense Support Program) satellites equipped with heat sensors that could detect the enormous amount of heat generated by a ballistic missile launch (or any large explosion, like an above-ground nuclear weapons test). The BMEWS satellites covered the entire planet, while the radars only covered most of the northern hemisphere.
Taiwan was allowed to get the Pave Paws technology as an alternative to the four Aegis destroyers the Taiwanese wanted to buy. The U.S. agreed to sell Pave Paws in part because the U.S. Air Force found that the existing Taiwan air defense network can be modified to integrate the new Pave Paws technology.
Pave Paws is an ultra-high-frequency system with a phased array radar capable of covering a vertical arc from 3 degrees to 85 degrees out to over 5,000 kilometers. It was designed to track ballistic missiles and has a limited capability to track satellites. Apparently having a Pave Paws type radar so close to China gives the user the ability to constantly monitor Chinese air space. In return for access to all this data, the U.S. will keep the Leshan radar up to date and provide Taiwan with additional intel on China the U.S. has collected using other means. Thus, most of the time the Leshan radar is an intelligence asset with a secondary job of providing early warning.