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62-755: The AN/APG-83 Scalable Agile Beam Radar ( SABR ) is a full-performance active electronically scanned array (AESA) fire control radar for the General Dynamics F-16 Fighting Falcon and other aircraft developed by Northrop Grumman . In a 2013 competition, Lockheed Martin selected SABR as the AESA radar for the F-16 modernization and update programs of the United States Air Force and Republic of China Air Force . The capabilities of this advanced AESA are derived from

124-787: A $ 2.43 billion deal. At August 2018, Northrop Grumman conducted an APG-83 fit test on an F-18 . A derivative of the AN/APG-83, the SABR-GS (Global Strike), will be fitted to the Rockwell B-1 Lancer beginning in 2016. In February 2019, Northrop Grumman offered SABR for retrofitting Boeing B-52H Stratofortress , which currently uses mechanically scanning AN/APQ-166 attack radar. In July 2019, Boeing selected AN/APG-82(V)1 /( AN/APG-79 ) from Raytheon for its B-52H radar modernization program. Northrop Grumman to offer SABR radar for Seoul's FA-50 Block 20 fighter. The US Air Force

186-595: A design predecessor and competitor to the Sprint missile, as it was a similar high-acceleration missile in the early 1960s, with a technological transfer from that program to the Sprint development program occurring. Both were tested at the White Sands Launch Complex 38 . Although HIBEX's initial acceleration rate was higher, at near 400 g , its role was to intercept reentry vehicles at a much lower altitude than Sprint, 20,000 feet (6,100 m), and it

248-497: A much simpler radar whose primary purpose was to track the outgoing Sprint missiles before they became visible to the potentially distant MAR. These smaller Missile Site Radars (MSR) were passively scanned, forming only a single beam instead of the MAR's multiple beams. While MAR was ultimately successful, the cost of the system was enormous. When the ABM problem became so complex that even

310-441: A much wider range of frequencies, to the point of changing operating frequency with every pulse sent out. Shrinking the entire assembly (the transmitter, receiver and antenna) into a single "transmitter-receiver module" (TRM) about the size of a carton of milk and arraying these elements produces an AESA. The primary advantage of an AESA over a PESA is the capability of the different modules to operate on different frequencies. Unlike

372-420: A narrow range of frequencies to high power levels. To scan a portion of the sky, the radar antenna must be physically moved to point in different directions. Starting in the 1960s new solid-state devices capable of delaying the transmitter signal in a controlled way were introduced. That led to the first practical large-scale passive electronically scanned array (PESA), or simply phased array radar. PESAs took

434-456: A rotating antenna, or similar passive array using phase or amplitude comparison . Typically RWRs store the detected pulses for a short period of time, and compare their broadcast frequency and pulse repetition frequency against a database of known radars. The direction to the source is normally combined with symbology indicating the likely purpose of the radar – airborne early warning and control , surface-to-air missile , etc. This technique

496-451: A signal and then listening for its echo off distant objects. Each of these paths, to and from the target, is subject to the inverse square law of propagation in both the transmitted signal and the signal reflected back. That means that a radar's received energy drops with the fourth power of the distance, which is why radar systems require high powers, often in the megawatt range, to be effective at long range. The radar signal being sent out

558-415: A signal from a single source, split it into hundreds of paths, selectively delayed some of them, and sent them to individual antennas. The radio signals from the separate antennas overlapped in space, and the interference patterns between the individual signals were controlled to reinforce the signal in certain directions, and mute it in all others. The delays could be easily controlled electronically, allowing

620-636: A system like MAR could no longer deal with realistic attack scenarios, the Nike-X concept was abandoned in favor of much simpler concepts like the Sentinel program , which did not use MAR. A second example, MAR-II, was abandoned in-place on Kwajalein Atoll . The first Soviet APAR, the 5N65 , was developed in 1963–1965 as a part of the S-225 ABM system. After some modifications in the system concept in 1967 it

682-419: A wide band even in a single pulse, a technique known as a "chirp". In this case, the jamming will be the same frequency as the radar for only a short period, while the rest of the radar pulse is unjammed. AESAs can also be switched to a receive-only mode, and use these powerful jamming signals to track its source, something that required a separate receiver in older platforms. By integrating received signals from

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744-409: A wider angle of total coverage. This high off-nose pointing allows the AESA equipped fighter to employ a crossing the T maneuver, often referred to as "beaming" in the context of air-to-air combat, against a mechanically scanned radar that would filter out the low closing speed of the perpendicular flight as ground clutter while the AESA swivels 40 degrees towards the target in order to keep it within

806-409: A wider range of frequencies, which makes them more difficult to detect over background noise , allowing ships and aircraft to radiate powerful radar signals while still remaining stealthy, as well as being more resistant to jamming. Hybrids of AESA and PESA can also be found, consisting of subarrays that individually resemble PESAs, where each subarray has its own RF front end . Using a hybrid approach,

868-411: Is a simple radio signal, and can be received with a simple radio receiver . Military aircraft and ships have defensive receivers, called " radar warning receivers " (RWR), which detect when an enemy radar beam is on them, thus revealing the position of the enemy. Unlike the radar unit, which must send the pulse out and then receive its reflection, the target's receiver does not need the reflection and thus

930-402: Is believed to have contained alternating layers of zirconium "staples" embedded in nitrocellulose powder, followed by gelatinizing with nitroglycerine , thus forming a higher thrust double-base powder . The Sprint was controlled by ground-based radio command guidance , which tracked the incoming reentry vehicles with phased array radar and guided the missile to its target. The Sprint

992-417: Is common on ships, for instance. Unlike the radar, which knows which direction it is sending its signal, the receiver simply gets a pulse of energy and has to interpret it. Since the radio spectrum is filled with noise, the receiver's signal is integrated over a short period of time, making periodic sources like a radar add up and stand out over the random background. The rough direction can be calculated using

1054-486: Is considered to be a last-ditch anti-ballistic missile "in a similar vein to Sprint". HIBEX employed a star-grain "composite modified double-base propellant", known as FDN-80, created from the mixing of ammonium perchlorate , aluminum , and double-base smokeless powder , with zirconium staples (0.125 inches (3 mm) in length) embedded or "randomly dispersed" throughout the matrix. The British " Thunderbird " rocket of 1947 produced an acceleration of 100 g with

1116-612: Is installing the AN/APG-83 SABR on 608 of its F-16C/D Block 40/42 and F-16C/D 50/52 fighters. Active electronically scanned array The AESA is a more advanced, sophisticated, second-generation of the original PESA phased array technology. PESAs can only emit a single beam of radio waves at a single frequency at a time. The PESA must utilize a Butler matrix if multiple beams are required. The AESA can radiate multiple beams of radio waves at multiple frequencies simultaneously. AESA radars can spread their signal emissions across

1178-454: Is much less useful against a radar with a frequency-agile (solid state) transmitter. Since the AESA (or PESA) can change its frequency with every pulse (except when using doppler filtering), and generally does so using a random sequence, integrating over time does not help pull the signal out of the background noise. Moreover, a radar may be designed to extend the duration of the pulse and lower its peak power. An AESA or modern PESA will often have

1240-434: Is then disconnected and the antenna is connected to a sensitive receiver which amplifies any echos from target objects. By measuring the time it takes for the signal to return, the radar receiver can determine the distance to the object. The receiver then sends the resulting output to a display of some sort . The transmitter elements were typically klystron tubes or magnetrons , which are suitable for amplifying or generating

1302-442: Is used. Target motion analysis can estimate these quantities by incorporating many directional measurements over time, along with knowledge of the position of the receiver and constraints on the possible motion of the target. Since each element in an AESA is a powerful radio receiver, active arrays have many roles besides traditional radar. One use is to dedicate several of the elements to reception of common radar signals, eliminating

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1364-406: Is why AESAs are also known as low probability of intercept radars . Modern RWRs must be made highly sensitive (small angles and bandwidths for individual antennas, low transmission loss and noise) and add successive pulses through time-frequency processing to achieve useful detection rates. Jamming is likewise much more difficult against an AESA. Traditionally, jammers have operated by determining

1426-492: The 'building blocks' of an AESA radar. The requisite electronics technology was developed in-house via Department of Defense research programs such as MMIC Program. In 2016 the Congress funded a military industry competition to produce new radars for two dozen National Guard fighter aircraft. Radar systems generally work by connecting an antenna to a powerful radio transmitter to emit a short pulse of signal. The transmitter

1488-444: The 1960s, followed by airborne sensors as the electronics shrank. AESAs are the result of further developments in solid-state electronics. In earlier systems the transmitted signal was originally created in a klystron or traveling wave tube or similar device, which are relatively large. Receiver electronics were also large due to the high frequencies that they worked with. The introduction of gallium arsenide microelectronics through

1550-448: The 1980s served to greatly reduce the size of the receiver elements until effective ones could be built at sizes similar to those of handheld radios, only a few cubic centimeters in volume. The introduction of JFETs and MESFETs did the same to the transmitter side of the systems as well. It gave rise to amplifier-transmitters with a low-power solid-state waveform generator feeding an amplifier, allowing any radar so equipped to transmit on

1612-465: The AESA system of a Raptor to act like a WiFi access point, able to transmit data at 548 megabits per second and receive at gigabit speed; this is far faster than the Link 16 system used by US and allied aircraft, which transfers data at just over 1 Mbit/s. To achieve these high data rates requires a highly directional antenna which AESA provides but which precludes reception by other units not within

1674-517: The AESA's 60 degree off-angle limit. With a half wavelength distance between the elements, the maximum beam angle is approximately ± 45 {\displaystyle \pm 45} °. With a shorter element distance, the highest field of view (FOV) for a flat phased array antenna is currently 120° ( ± 60 {\displaystyle \pm 60} °), although this can be combined with mechanical steering as noted above. The first AESA radar employed on an operational warship

1736-505: The ARPA study came at the height of the debate over the Zeus system in the early 1960s. The new Secretary of Defense, Robert McNamara , convinced President Kennedy that Zeus was simply not worth deploying. He suggested using the funds allocated to its deployment to develop the ARPA system, which became known as Nike-X , a name given by engineering professor Jack Ruina when he was reporting on

1798-619: The Army gave Bell Labs , who had developed the earlier Nike missiles, a contract to study the ABM issue. They returned a report saying the concept was within the state of the art and could be built using modest upgrades to the latest Army surface-to-air missile , the Nike Hercules . The main technological issues would be the need for extremely powerful radars that could detect the incoming ICBM warheads long enough in advance to fire on them, and computers with enough speed to develop tracks for

1860-710: The F-22's AN/APG-77 and the F-35's AN/APG-81 . It is designed to fit F-16 aircraft with no structural, power or cooling modifications. The SABR is scalable to fit other aircraft platforms and mission areas. In 2010, a SABR was installed on a USAF F-16 at Edwards AFB and flew 17 consecutive demonstration sorties without cooling or stability issues. In addition to equipping F-16V for Taiwan and other US allies, US Air Force also selected APG-83 SABR to upgrade 72 of its Air National Guard F-16s. In January 2014, Singapore ordered 70 AN/APG-83 SABR for its 60 F-16C/D/G+ Block 52 upgrade, in

1922-498: The PESA, where the signal is generated at single frequencies by a small number of transmitters, in the AESA each module generates and radiates its own independent signal. This allows the AESA to produce numerous simultaneous "sub-beams" that it can recognize due to different frequencies, and actively track a much larger number of targets. AESAs can also produce beams that consist of many different frequencies at once, using post-processing of

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1984-466: The Soviets claimed to be turning them out "like sausages", this became a serious problem. However, other issues also became obvious in the late 1950s. One issue was that nuclear explosions in space had been tested in 1958 and found that they blanketed a huge area with radiation that blocked radar signals above about 60 kilometers (37 mi) altitude. By exploding a single warhead above the Zeus sites,

2046-517: The Soviets could block observation of following warheads until they were too close to attack. Another simple measure would be to pack radar reflectors in with the warhead, presenting many false targets on the radar screens that cluttered the displays. As the problems piled up, the Secretary of Defense Neil H. McElroy asked ARPA to study the anti-missile concept. ARPA noted that both the radar decoys and high-altitude explosions stopped working in

2108-472: The Zeus program ended in favor of the Nike-X system in 1963. The MAR (Multi-function Array Radar) was made of a large number of small antennas, each one connected to a separate computer-controlled transmitter or receiver. Using a variety of beamforming and signal processing steps, a single MAR was able to perform long-distance detection, track generation, discrimination of warheads from decoys, and tracking of

2170-454: The antennas beamwidth, whereas like most Wi-Fi designs, Link-16 transmits its signal omni-directionally to ensure all units within range can receive the data. AESAs are also much more reliable than either PESAs or older designs. Since each module operates independently of the others, single failures have little effect on the operation of the system as a whole. Additionally, the modules individually operate at low powers, perhaps 40 to 60 watts, so

2232-496: The beam to be steered very quickly without moving the antenna. A PESA can scan a volume of space much quicker than a traditional mechanical system. Additionally, thanks to progress in electronics, PESAs added the ability to produce several active beams, allowing them to continue scanning the sky while at the same time focusing smaller beams on certain targets for tracking or guiding semi-active radar homing missiles. PESAs quickly became widespread on ships and large fixed emplacements in

2294-607: The benefits of AESA (e.g., multiple independent beams) can be realized at a lower cost compared to pure AESA. Bell Labs proposed replacing the Nike Zeus radars with a phased array system in 1960, and was given the go-ahead for development in June 1961. The result was the Zeus Multi-function Array Radar (ZMAR), an early example of an active electronically steered array radar system. ZMAR became MAR when

2356-429: The capability to alter these parameters during operation. This makes no difference to the total energy reflected by the target but makes the detection of the pulse by an RWR system less likely. Nor does the AESA have any sort of fixed pulse repetition frequency, which can also be varied and thus hide any periodic brightening across the entire spectrum. Older generation RWRs are essentially useless against AESA radars, which

2418-657: The combined signal from a number of TRMs to re-create a display as if there was a single powerful beam being sent. However, this means that the noise present in each frequency is also received and added. AESAs add many capabilities of their own to those of the PESAs. Among these are: the ability to form multiple beams simultaneously, to use groups of TRMs for different roles concurrently, like radar detection, and, more importantly, their multiple simultaneous beams and scanning frequencies create difficulties for traditional, correlation-type radar detectors. Radar systems work by sending out

2480-474: The concept. Nike-X required great improvements in radars, computers, and especially the missile. Zeus had an attack profile lasting about a minute; Nike-X's interceptions would last about five seconds. Work on initial investigations into "Follow-On Sprint" was underway in the second quarter of 1968. Los Alamos were examining two warheads for the Upstage II design variation. By third-quarter 1971, Sprint II

2542-576: The few seconds before the RV reached its target. Sprint accelerated at 100   g , reaching a speed of Mach 10 (12,000 km/h; 7,600 mph) in 5 seconds. Such a high velocity at relatively low altitudes created skin temperatures up to 6,200 °F (3,400 °C), requiring an ablative shield to dissipate the heat. The high temperature caused a plasma to form around the missile, requiring extremely powerful radio signals to reach it for guidance. The missile glowed bright white as it flew. Sprint

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2604-527: The fiberglass silo cover. As the missile cleared the silo at 0.6 seconds, the first stage fired and the missile was tilted toward its target. The first stage was exhausted after only 1.2 seconds, but produced 650,000 pounds-force (2,900 kilonewtons) of thrust. On separation, the spent first stage disintegrated due to aerodynamic forces. The second stage fired within 1 to 2 seconds of launch. Interception at an altitude of 1 to 19 miles (1.5 to 30 km) took at most 15 seconds. The first stage's Hercules X-265 engine

2666-533: The first quarter of 1972, the system was renamed Site Defense and its purpose was to defend Minuteman silos. Over the original Sprint missile, the Sprint II interceptor had slightly reduced launch dispersion, increased hardness to the effect of nuclear weapons, and decreased miss distance. Los Alamos staff expected a request for warhead development sometime in FY-1972-1974. A Phase 2 feasibility study report

2728-562: The need for a large high-voltage power supply is eliminated. Replacing a mechanically scanned array with a fixed AESA mount (such as on the Boeing F/A-18E/F Super Hornet ) can help reduce an aircraft's overall radar cross-section (RCS), but some designs (such as the Eurofighter Typhoon and Gripen NG ) forgo this advantage in order to combine mechanical scanning with electronic scanning and provide

2790-464: The need for a separate radar warning receiver. The same basic concept can be used to provide traditional radio support, and with some elements also broadcasting, form a very high bandwidth data link . The F-35 uses this mechanism to send sensor data between aircraft in order to provide a synthetic picture of higher resolution and range than any one radar could generate. In 2007, tests by Northrop Grumman , Lockheed Martin, and L-3 Communications enabled

2852-433: The one to be used to jam. Most radars using modern electronics are capable of changing their operating frequency with every pulse. This can make jamming less effective; although it is possible to send out broadband white noise to conduct barrage jamming against all the possible frequencies, this reduces the amount of jammer energy in any one frequency. An AESA has the additional capability of spreading its frequencies across

2914-472: The operating frequency of the radar and then broadcasting a signal on it to confuse the receiver as to which is the "real" pulse and which is the jammer's. This technique works as long as the radar system cannot easily change its operating frequency. When the transmitters were based on klystron tubes this was generally true, and radars, especially airborne ones, had only a few frequencies to choose among. A jammer could listen to those possible frequencies and select

2976-472: The outbound interceptor missiles. MAR allowed the entire battle over a wide space to be controlled from a single site. Each MAR, and its associated battle center, would process tracks for hundreds of targets. The system would then select the most appropriate battery for each one, and hand off particular targets for them to attack. One battery would normally be associated with the MAR, while others would be distributed around it. Remote batteries were equipped with

3038-558: The period Zeus was being developed, several problems arose that appeared to make it trivially easy to defeat. The simplest was that its 1950s-era mechanical radars could track a limited number of targets, and it could be easily overwhelmed by numbers; a report by the Gaither Committee suggested a salvo of four warheads would have a 90% chance of destroying a Zeus base. This was of little concern during early development when ICBMs were enormously expensive, but as their cost fell and

3100-477: The signal drops off only as the square of distance. This means that the receiver is always at an advantage [neglecting disparity in antenna size] over the radar in terms of range - it will always be able to detect the signal long before the radar can see the target's echo. Since the position of the radar is extremely useful information in an attack on that platform, this means that radars generally must be turned off for lengthy periods if they are subject to attack; this

3162-572: The targets in engagements that lasted seconds. Bell began development of what became Nike Zeus in 1956, working out of the Nike development center at Redstone Arsenal . The program went fairly smoothly, and the first tests were carried out in the summer of 1959. By 1962, a complete Zeus base had been built on Kwajalein Island and proved very successful over the following year, successfully intercepting test warheads and even low-flying satellites. During

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3224-530: The targets' own radar along with a lower rate of data from its own broadcasts, a detection system with a precise RWR like an AESA can generate more data with less energy. Some receive beamforming-capable systems, usually ground-based, may even discard a transmitter entirely. However, using a single receiving antenna only gives a direction. Obtaining a range and a target vector requires at least two physically separate passive devices for triangulation to provide instantaneous determinations, unless phase interferometry

3286-409: The thickening lower atmosphere. If one simply waited until the warheads descended below about 60  km, they could be easily picked out on radar again. However, as the warheads would be moving at about 5 miles per second (8 km/s; Mach 24) at this point, they were only seconds from their targets. An extremely high-speed missile would be needed to attack them during this period. The result of

3348-424: Was armed with an enhanced radiation nuclear warhead with a yield reportedly of a few kilotons, though the exact number has not been declassified. The warhead was intended to destroy the incoming reentry vehicle primarily by neutron flux . The first test of the Sprint missile took place at White Sands Missile Range on 17 November 1965. The "HIBEX" (high boost experiment) missile is considered to be somewhat of

3410-532: Was built at Sary Shagan Test Range in 1970–1971 and nicknamed Flat Twin in the West. Four years later another radar of this design was built on Kura Test Range , while the S-225 system was never commissioned. US based manufacturers of the AESA radars used in the F-22 and Super Hornet include Northrop Grumman and Raytheon. These companies also design, develop and manufacture the transmit/receive modules which comprise

3472-494: Was completed by Los Alamos in third-quarter 1972 and investigations into warhead design continued into first-quarter 1973. It is unclear when Sprint II was canceled; however, a report on Sprint II electrical connectors was published in April 1977. The conical Sprint was stored in and launched from a silo . To make the launch as quick as possible, the missile, which was ejected by an explosive-driven piston, simply blasted through

3534-436: Was designed to intercept incoming reentry vehicles (RV) after they had descended below an altitude of about 60 kilometres (37 mi), where the thickening air stripped away any decoys or radar reflectors and exposed the RV to observation by radar. As the RV would be traveling at about 5 miles per second (8,047 m/s; 26,400 ft/s; Mach 24), Sprint needed to have phenomenal performance to achieve an interception in

3596-547: Was incorporated into a new module for Safeguard called Hardsite Defense (HSD) and a joint Atomic Energy Commission/DoD working group was examining new warheads that would require less tritium. HSD was described as: ... [consisting] of an autonomous module for close-in, low-altitude intercept (≈10,000 to 30,000 ft) and is based upon three radar/data-processor units located about 10 nautical miles apart. The module will have six or seven firing sites containing about 100 modified Sprint interceptors to defend approximately 21 silos. By

3658-542: Was itself changed to become the Safeguard Program , which was operational only for a few months from October 1975 to early 1976. Congressional opposition and high costs linked to its questionable economics and efficacy against the then emerging MIRV warheads of the Soviet Union, resulted in a very short operational period. During the early 1970s, some work was carried out on an improved Sprint II, which

3720-722: Was mostly concerned with the guidance systems. These were to be dedicated to the task of protecting the Minuteman missile fields. Further work was canceled as US ABM policy changed. The US Army had considered the issue of shooting down theater ballistic missiles of the V-2 missile type as early as the mid-1940s. Early studies suggested their short flight times, on the order of 5 minutes, would make it difficult to detect, track, and shoot at these weapons. In theory, it would be easier to attack intercontinental ballistic missiles , with their longer flight times and higher trajectories. In 1955,

3782-669: Was the Japanese OPS-24 manufactured by Mitsubishi Electric introduced on the JDS Hamagiri (DD-155), the first ship of the latter batch of the Asagiri-class destroyer , launched in 1988. Sprint missile The Sprint was a two-stage, solid-fuel anti-ballistic missile (ABM), armed with a W66 enhanced-radiation thermonuclear warhead used by the United States Army during 1975–76. It

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3844-414: Was the centerpiece of the Nike-X system, which concentrated on placing bases around large cities to intercept Soviet warheads. The cost of such a system quickly became untenable as the Soviets added more ICBMs to their fleet, and Nike-X was abandoned. In its place came the Sentinel program , which used Sprint as a last-ditch defense against RVs that evaded the much longer-ranged LIM-49 Spartan . Sentinel

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