AN/SPS-48

The AN/SPS-48 is a US naval electronically scanned array, air search three-dimensional radar system manufactured by ITT Exelis and deployed in the 1960s as the primary air search sensor for anti-aircraft warships. The deployment of the AN/SPY-1 and the end of the Cold War led to the decommissioning of many such ships, and many of these vessel's AN/SPS-48 sets were reused on aircraft carriers and amphibious ships where it is used to direct targets for air defense systems such as the Sea Sparrow and RIM-116 SAM missiles. Existing sets are being modernized under the ROAR program to AN/SPS-48G standard for better reliability and usability.

In accordance with the Joint Electronics Type Designation System (JETDS), the "AN/SPS-48" designation represents the 48th design of an Army-Navy electronic device for surface ship search radar system. The JETDS system also now is used to name all Department of Defense electronic systems.

A three-dimensional radar is mounted on a base that allows for 360 degrees of rotation. The target can be located at a given azimuth. The range of the target is also identified due to the time it takes the beam to go out and back to the receiver. What makes this radar system different is its ability to detect the height of the target above the surface of the water. With these three pieces of data the radar's central processor has the ability to place the target in an X,Y,Z, 3 dimensional space.

For the SPS-48 in particular, the antenna is mechanically rotated to scan azimuth, while beams are electronically steered to cover elevation by varying the transmitter frequency. The 4,500 lb (2,000 kg) antenna is capable of rotating at 7.5 or 15 rpm.

According to ITT Exelis, the system has a range exceeding 200 nmi (370 km) and can track targets up to 69 degrees in elevation. The AN/SPS-48E is capable of providing target range, bearing and altitude information using a frequency-scanning antenna using a range of different frequencies in E band and F band with three power modes: high, medium and low. SPS-48 radars stack multiple beams in a train of pulses at different frequencies. The beams scan different elevation areas, allowing the stack to cover up to 69 degrees of elevation.

The NTDS Technical and Operational Requirements, written in 1956, called for two radar systems: a three-dimensional search radar with a range of more than 200 miles that can turn over targets to missile and gun radars, and a two-dimensional long-range search radar able to detect relatively small targets at ranges over 250 miles, which can hand targets to the three-dimensional radar once they enter its range. The former eventually became the AN/SPS-48; the latter became the AN/SPS-49.

Development of the SPS-48 in particular started in 1960 in response to shortcomings of the AN/SPS-39. A development contract for two service models (XN-1 and XN-2) was awarded in June 1960. XN-1 completed system testing in April 1962 and was operated until December 1962 to collect reliability data ashore. XN-2 was delivered July 1962 and installed aboard USS Preble (DLG-15) for shipboard evaluation.

A production contract of 13 radars was awarded in June 1963. Unit #6 was installed on USS Worden (DLG-18) between March and June 1965 for reliability testing by the Operational Test and Evaluation Force. Testing results were positive, and the AN/SPS-48 was formally approved for service use by the Chief of Naval Operations on 21 February 1966. The AN/SPS-48 replaced AN/SPS-39 on the Belknap, Coontz and Leahy classes between 1967 and 1975 under the Guided Missile Frigate Anti-Air Warfare Modernization Program.