In late August 2017 the U.S. delivered a mobile naval radar system to the Philippines. Called TARS (Tethered Aerostat Radar System) it is one of many similar systems that saw heavy use by American and NATO forces after 2001. Israel and the U.S. are major developers of and suppliers of such systems. Systems like TARS have been around for decades but have become more useful since the 1990s as radar and other sensors became smaller, lighter and more reliable. The TARS given to the Philippines has a radar with a range of about 400 kilometers and the aerostat carrying the radar aloft can carry about a ton of sensors. The U.S. agreed to deliver the TARS over a year ago.
Aerostats are helium filled balloons shaped to remain stationary in bad weather. Aerostats are blimp like vehicles designed to always turn into the wind and stay in the same place. The U.S. developed larger aerostat systems (JLENS) to detect cruise missiles but the U.S. Army, since 2004 used dozens of smaller and cheaper aerostat systems for local security in Iraq and Afghanistan. These aerostats operated at about 330 meters (a thousand feet) up, tethered by a cable that provides power and communications to the day and night cameras up there. Larger aerostats can hover at 3,000 meters altitude and carry up to two tons of sensors. These blimps can stay up for about 30 days at a time before it has to be brought down for maintenance on its radars.
Often two radars are carried on larger systems like JLENS and TARS. One is a surveillance radar, the other is a precision track and illumination radar (PTIR). The surveillance radar provides long-range coverage (up to 500 kilometers) while the PTIR, which is a steerable system capable of tracking multiple targets, can focus in on items of interest. TARS will give the Philippines persistent surveillance of offshore areas, where poachers, smuggler and Chinese military vessels are increasingly a problem. It the Philippines finds TARS useful the Americans can supply more such systems for free or at very low cost.