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AN/APG-77 Radar System

Northrop Grumman's and Raytheon's AN/APG-77 for the Raptor (Northrop Grumman has the larger workshare) was originally designed as a pure air-to-air system. Its AESA antenna and high power provide by far the longest detection range of any fighter radar, greater than 120 n.mi. Combined with the extended range AIM-120 AMRAAM missile, this allows the F-22 to obtain multiple kills well beyond the reach of any current or foreseen enemy.

The AN/APG-77 radar is the F-22's primary sensor and is a long-range, rapid-scan, and multi-functional system. A Northrop Grumman-led joint venture with Raytheon is developing the active-element electronically scanned array radar. Northrop Grumman is also responsible for the radar sensor design, software, and systems integration.

The AN/APG-77 radar is an active-element, electronically scanned (that is, it does not move) array that features a separate transmitter and receiver for each of the antenna's several thousand, finger-sized radiating elements. Most of the mechanical parts common to other radars have been eliminated, thus making the radar more reliable. This type of antenna, which is integrated both physically and electromagnetically with the airframe, provides the frequency agility, low radar cross-section, and wide bandwidth necessary to support the F-22's air dominance mission. The radar is key to the F-22's integrated avionics and sensor capabilities. It will provide pilots with detailed information about multiple threats before the adversary's radar ever detects the F-22.

Northrop Grumman's AN/APG-77 radar employs a different type of electronically scanned phased array. In what is the most advanced airborne radar in the world, individual transmit and receive modules will be located behind each element of the radar array. The transmit function of the solid-state microwave modules will supplant the travelling wave tubes used in prior radars like the APQ-164.

The AESA configuration will have a wider transmit bandwidth while requiring significantly less volume and prime power. The system represents about half the weight of an equivalent passive ESA design. Each of the hundreds of individual solid-state devices generates only small amounts of power, but the aggregate for the entire array will be substantial.

The APG-77's active aperture antenna offers attractive benefits. The system exhibits a very low radar cross section, supporting the F-22's stealthy design. Reliability of the all-solid-state system is expected to be substantially better than the already highly reliable F-16 radar, with MTBF predicted at more than 450 hours. AESA life-cycle costs are expected to be significantly lower than those of MSAs. The active arrays on the F-22 should have almost twice the expected life of the airframe.

Northrop Grumman has successfully demonstrated the capability to generate high-resolution, in-flight synthetic aperture radar (SAR) maps. Flight tests, on board a company BAC 1-11 test bed aircraft, have proved that the F-22 fighter's mission capabilities have expanded to include directly identifying and targeting enemy ground defenses and mobile forces.

Northrop Grumman ES is responsible for the overall design of the AN/APG-77 radar system, including the control and signal processing software. Northrop Grumman also has responsibility for radar systems integration and test activities. The main component of the radar sensor is a highly reliable Active Electronically Scanned Array (AESA), which provides the rapid beam agility, low radar cross section and target detection capability that enables the air dominance fighter to achieve "first look, first kill" capability. The system exhibits a very low radar cross section, supporting the F-22's stealthy design.

In February 2008 Northrop Grumman Corporation successfully demonstrated the capability to generate high-resolution, in-flight synthetic aperture radar (SAR) maps using the AESA (active electronically scanned array) radar being produced for the U.S. Air Force's F-22 Raptor fighter aircraft. "The flight tests, on board a company BAC 1-11 test bed aircraft, have proved that the F-22 fighter's mission capabilities have expanded to include directly identifying and targeting enemy ground defenses and mobile forces," said Teri Marconi, vice president of Combat Avionics Systems at Northrop Grumman. "This is a hugely significant event for the F-22 program because it ensures that Raptor pilots will have access to critical detailed information about both air and ground threats before the enemy's radar ever detects the F-22." The test flights were the first phase of a planned multi-year contract with The Boeing Company (NYSE:BA) to incorporate SAR capability into the existing fleet of F-22s and new production aircraft in support of future air-to-ground requirements.

Northrop Grumman's Electronic Systems sector leads a joint venture with the Raytheon Company to design, develop and produce the F-22 radar system. Northrop Grumman is responsible for the overall design of the AN/APG-77 and AN/APG-77(V)1 AESA radars -- the latter of which features the new air-to-ground capabilities, including SAR. The company is also responsible for the control and signal processing software and radar system integration and test activities.

The AN/APG-77 radar a novel type of electronically scanned phased array. In what is likely to be the most advanced airborne radar in the world, individual transmit and receive modules are located behind each element of the radar array. The transmit function of the solid-state microwave modules supplants the traveling wave tubes used in prior radars like the APQ-164. The active, electronically scanned array (ESA) configuration has a wider transmit bandwidth while requiring significantly less volume and prime power. The system represents about half the weight of an equivalent passive ESA design. Each of the hundreds of individual solid-state devices generates only small amounts of power, but the aggregate for the entire array is substantial.

The F-22 s APG-77 electronically scanned array antenna is composed of several thousand transmit/receive modules, circulators, radiators and manifolds assembled into subarrays and then integrated into a complete array. The baseline design used thousands of hand-soldered flex circuit interconnects to make the numerous radio frequency, digital, and direct current connections between the components and manifolds that make up the subarray. Northrop Grumman Corporation, of Baltimore, MD, has developed an improved manufacturing process for F-22 aircraft radar components. The new process could result in a cost avoidance of nearly $87 million on the planned production run for the aircraft. By replacing the hand-soldered flex circuit interconnects with automated ribbon bond interconnects, the first pass yield of the subarray assembly has been vastly improved.

The AN/APG-77 radar antenna is a elliptical, active electronically scanned antenna array of 2000 transmitter/receive modules which provides agility, low radar cross section and wide bandwidth. The radar is able to sweep 120 degrees of airspace instantaneously. In comparison to the F-15 Strike Eagle's APG-70 radar takes 14 seconds to scan that amount of airspace. The APG-77 is capable of performing this feat by electronically forming multiple radar beams to rapidly search the airspace.

The system exhibits a very low radar cross section, supporting the F-22's stealthy design. Reliability of the all-solid-state system is expected to be substantially better than the already highly reliable F-16 radar, with MTBF predicted at more than 450 hours.

The APG-77 radar offers significant advantages over previous combat radars. Among its most attractive benefits is the integration of agile beam steering. This feature allows a single APG-77 radar to carry out multiple functions, such as searching, tracking, and engaging targets simultaneously. Agile beam steering also enables the radar to concurrently search multiple portions of airspace, while allowing continued tracking of priority targets.

The Low Probability of Intercept (LPI) capability of the radar defeats conventional RWR/ESM systems. The AN/APG-77 radar is capable of performing an active radar search on RWR/ESM equipped fighter aircraft without the target knowing he is being illuminated. Unlike conventional radars which emit high energy pulses in a narrow frequency band, the AN/APG-77 emits low energy pulses over a wide frequency band using a technique called spread spectrum transmission. When multiple echoes are returned, the radar's signal processor combines the signals. The amount of energy reflected back to the target is about the same as a conventional radar, but because each LPI pulse has considerably less amount of energy and may not fit normal modulation patterns, the target will have a difficult time detecting the F-22.

The F-22 and its APG-77 radar will also be able to employ better Non-Cooperative Target Recognition (NCTR). This is accomplished by forming fine beams and by generating a high resolution image of the target by using Inverse Synthetic Aperture radar (ISAR) processing. ISAR uses Doppler shifts caused by rotational changes in the targets position to create a 3D map of the target. The target provides the Doppler shift and not the aircraft illuminating the target. SAR is when the aircraft provides the Doppler shift. The pilot can compare the target with an actual picture radar image stored in the F-22's data base.



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