Longbow, a joint venture between Lockheed Martin and Northrop Grumman, sealed the deal as a foreign military sales contract, a statement from both companies said.
Under the contract, the Republic of Korea will get six FCR systems, spares and in-country support.
The systems will be installed in Boeing's AH-64E Apache attack helicopters.
Production is scheduled through 2016, with assembly of the systems at Lockheed Martin's Ocala and Orlando, Fla., facilities, and Northrop Grumman's Baltimore, Md., facility, the statement said.
The radar is used by the U.S. Army in its Apache AH-64D attack helicopters.
"The Republic of Korea is the 10th international customer for Longbow systems," Tom Eldredge, Longbow president at Lockheed Martin Missiles and Fire Control, said.
"The Longbow FCR is a battle-proven radar system that will provide Republic of Korea Apache pilots with increased situational awareness, survivability and lethality."
Mike Galletti, director of the Tactical Sensor Solutions-Aviation business unit for Northrop Grumman's Land and Self Protection Systems Division, said the FCR system provides the Apache helicopters with the highest level of protection and "promotes greater regional security."
Longbow's range is nearly 5 miles in all weather and battlefield conditions. It automatically searches, detects, locates, classifies and prioritizes multiple moving and stationary targets on land, air and water.
Target coordinates are automatically available to all sensors and weapons-enabling target confirmation systems to reduce fratricide.
Target data also is digitally available through the improved data modem for real-time transfer to other platforms and command posts.
The self-contained radio frequency interferometer ensures rapid identification and accurate azimuth to enemy air-defense units, a Longbow statement said.
South Korea announced in April that it had chosen Boeing's AH-64E Apache Guardian helicopters under a $1.6 billion deal.
The contract for 36 Apaches was signed amid tensions with North Korea, the South Korean Defense Acquisition Program Administration said at the time.
Boeing's four-blade twin-engine Apache beat Bell's AH-1Z and the Turkish Aerospace Industries T-129, a joint development with AgustaWestland as the primary partner and based on its A129 Mangusta.
"We can beef up our military strength that might be weakening due to (our) aging helicopters," the DAPA said in a statement.
"This new helicopter fleet will help handle the threat posed by North Korea's mechanized forces and possible provocations such as maritime infiltrations."
The fleet will play a crucial role in countering North Korean amphibious infiltrations into western border islands should they occur, a report by The Korea Herald newspaper said at the time of the contract announcement.
The Herald report said the Apache's speed of upward of 160 mph will counter communist North Korea's use of attack hovercraft.