Radar is an essential electronic system for any military force, whether at land, sea, or in the air. In 1922 the U.S. Naval Research Laboratories (NRL) discovered that pulsed radio waves could be used to detect other ships at a distance. Eight years later, the NRL would find that radio waves in radar systems could also be used to detect aircraft from a distance. The NRL’s Leo Young and Robert Page are credited with the early pioneering work on radar systems, leading to the first U.S. radar system, the XAF, installed on the battleship USS New York in 1939.
Naval Research Laboratory
The NRL would develop submarine radar the following year, as well as the ASB radar—the first airborne radar for naval aircraft. The latter was highly effective in the Pacific Theater for searching and destroying Japanese aircraft. The Navy’s ASB series radars operated at around 500 MHz with about 5 to 10 kW transmit power generated by four triodes in a push-pull oscillator configuration. Two antennas in the nose of the plane would switch back and forth between receive and transmit functions at a rate of about 30 Hz.
One of the NRL’s many contributions to early radar technology included a polar coordinate display to show the target information detected by the radar receiver (Fig. 1). The agency also developed a low-power HF radar called the Multiple Storage, Integration, and Correlation (MUSIC) system. This system measured signals from the ionosphere as well as from the target to warn against missile launches. It would later be replaced by an enhanced version of the system known as the Magnetic-Drum Radar Equipment (MADRE) system.
Early radar systems were bistatic, with separate antennas for transmit and receive functions. In fact, the first radar system for the U.S. Army Signal Corps (SCR), the SCR-268, operated at 205 MHz with one transmit antenna and two receive antennas. It achieved 75 kW peak power by means of 16 triodes from Eimac. Operators employed three oscilloscopes to translate reflected signals into target range, azimuth, and elevation. The next-generation system, the SCR-270 radar (which detected the planes attacking Pearl Harbor in 1941), used a single antenna for transmit and receive. It generated as much as 200 kW peak power at 110 MHz with a pair of triodes from Westinghouse.
Since those early years, military radar technology has gradually moved to higher frequencies, smaller antennas, and solid-state amplification in place of the triodes and magnetron vacuum tubes (Fig. 2) of the early radar systems. Over the past 30 years, radar systems have improved performance due to advances in technology, such as phased-array radars, active electronically scanned array (AESA) technology (Fig. 3), and synthetic aperture radars (SARs).
Radar systems are typically integrated within more comprehensive electronic warfare (EW) suites such as the AN/APY-7 surveillance radar system within the Joint Surveillance Target Attack Radar System (JSTARS) platform. It was first deployed in 1991 during Operation Desert Storm for long-endurance (approximate 9-hr unfueled running time) all-weather surveillance and targeting of moving and stationary targets, both on the ground and at low altitudes.
The JSTARS suite of systems incorporates secure communications technologies to share information with other intelligence, surveillance, and reconnaissance (ISR) platforms (Fig. 4). It employs a variety of communications systems, including satellite communications (satcom), wireless data links, and Single Channel Ground and Airborne Radio System (SINCGARS) radios for communications with other systems and with troops in the air and on the ground. The JSTARS program provides persistent wide-area surveillance for troops in the air and on the ground. Supplied by Northrop Grumman, the extremely reliable radar system is a collaborative U.S. Air Force and Army program managed by the Air Force at Robins AFB, Ga.
Northrop would also team with Lockheed Martin on another well-known radar system, the AN/APG-78 “Longbow” fire-control radar system. Using Ka-band frequencies, the compact radar system has an effective detection range of 8 km. Fielded on the U.S. Army’s Apache AH-64D attack helicopter (Fig. 5), the Longbow radar features low probability of intercept and can detect and locate multiple moving and stationary targets. It works in conjunction with the millimeter-wave-guided HELLFIRE Fire and Forget missile to lock onto a target before or after launch.
Aegis S-Band Radar
Lockheed might be best known for the Aegis Combat System (Fig. 6) which, like the JSTARS platform, is a fully integrated system built around an advanced radar. In this case, the radar is the AN/SPY-1 S-band radar with automatic detect-and-track functionality. The radar system features four complementary three-dimensional passive electronically scanned array antennas for wide coverage. The naval radar system is aboard vessels for the U.S. Navy, as well as numerous allied naval forces, including the Republic of Korea, Japan, and Norway.
SBX Radar System
Known as the world’s largest X-band radar system, the Sea-Based X-Band (SBX) radar system is nine stories high, built on an oil production platform. The radar system stands more than 250 ft. high (Fig. 7), patrolling the world’s oceans for ballistic missile launches. The electro-mechanically steered phased-array radar provides full fire-control sensor functions for the Ground-Based Midcourse Defense system, including search, acquisition, tracking, discrimination, and kill assessment. Raytheon Co. builds the SBX radar for Boeing, which is under contract to deliver the system to the U.S. Missile Defense Agency (MDA). The radar system platform is 240 ft. wide and 390 ft. long and includes control rooms, living quarters, storage areas, and infrastructure for the X-band radar.
For the Future
A growing trend in the use of unmanned aerial vehicles (UAVs) for military surveillance has led to the development of the Osprey multi-AESA airborne surveillance radar system by Italy’s Leonardo group. The compact X-band radar system was selected by Northrop Grumman for use on the MQ-8C Fire Scout UAV.
Radar technology must continue to evolve to detect and overcome new threats. Present-day fears of long-range ballistic missile attacks on homeland U.S. have driven the construction of the Long-Range Discrimination Radar (LRDR) in Alaska by Lockheed Martin (Fig. 8). In a geographic location to provide early detection of missile launches by North Korea, the system is based on a 2014 request for proposal (RFP) from the MDA. The S-band radar system is leveraging Lockheed’s experience in developing the Aegis system while employing the latest solid-state device technologies, such as GaN amplifiers, for high reliability.