Рассекречены ТТХ F-22A Raptor

[wind]

полный бред

- Оригинал вышеприведённого перевода статьи - может быть, так до тебя лучше дойдёт?

Title: FIGHTER EW.

Date: 7/1/2000; Publication: Journal of Electronic Defense; Author: Sweetman, Bill

THE NEXT GENERATION

The fourth Lockheed Martin F-22 Raptor, aircraft 4004. Is due to make its first flight from Marietta. GA, in late July. As the first F-22 to carry offensive avionics. Its task is to demonstrate that a stealthy aircraft can be a fighter. Under a deal struck with Congress last year, the F-22 has to prove this key technology by the end of this year if the next ten aircraft are to be authorized.

The F-22 represents a radical departure from the traditional approach to EW. Passive systems, once considered to be defensive in nature, are now critical to detecting, tracking and even attacking the target. The active radar, while still a primary sensor, is used sparingly for specific tasks. Active jamming in the traditional sense has disappeared. The F-22 approach is echoed to some extent in most of today's advanced fighter programs, including the Dassault Rafale, Eurofighter typhoon and Saab JAS Gripen. It is also fundamental to the future of the Joint Strike Fighter (JSF).

The F-22's EW philosophy is rooted in some of the earliest work on stealth. As the US Air Force (USAF) defined requirements and operational doctrine for the F-117 stealth strike aircraft and B-2 bomber, in 1980-81, A "Red Team" headed by Dr. Paul Kaminski was charged with looking for weaknesses and vulnerabilities in stealth technology. One of the Red Team's Most important conclusions was that a stealth aircraft could not survive by low radar cross-section (RCS) alone, but by stealth and tactics.

In the case of the F-117 the Red Team's recommendation resulted in the development of one of the first automated mission-planning systems, but this left the aircraft dependent on a pre-programmed flight plan. The B-2 was designed to feature a sophisticated defensive management system (DMS) which would allow the crew to respond to threat radars not anticipated by the mission plan. The initial DMS was abandoned in the late 1980s. Its successor is the APR-50, developed by IBM Federal Systems (later acquired by Loral and now part of Lockheed Martin).
The USAF's Advanced Tactical Fighter project, which led to the F-22, presented greater challenges. In the air-to-air regime, the primary threats are airborne and move rapidly, making identification, location and tracking more complex. The F-22's sustained speed also shortens engagement timelines by as much as 40 percent.
At the same time, the fighter's classic tool for situational awareness -- a powerful search radar -- can render its stealth characteristics moot. Low-probability-of-intercept (LPI) techniques are not very compatible with continuous searches over a large volume. The fighter's stealth is also of little use if it has to close to visual range in order to identify its targets. Passive search and track and non-cooperative target recognition (NCTR) are not luxuries for a stealthy air-superiority fighter.
The solution to this problem on the F-22 is sensor fusion. The principal sensors are the Northrop Grumman APG-77 radar and the Sanders ALR-94 passive receiver system. The fighter also has two datalink systems: one using the standard VHF/UHF radio frequencies and the other, the intraflight datalink (IFDL), a low-power LPI link which connects two or more F-22s at close range. The sensors are apertures connected to the fighter's Common Integrated Processor (CIP) banks in the forward fuselage.

The data from the APG-77, ALR-94 and the datalinks are correlated according to their azimuth, elevation and range. Data is combined into a track file, and the final target picture is obtained by choosing the read-out from the most accurate sensor. For example, the passive system may provide the best azimuth data, while the radar produces the most accurate range.

CIP software controls the APG-77 according to emission-control principles. The radar's signals are managed in intensity, duration and space to maintain the pilot's situational awareness while minimizing the chance that its signals will be intercepted. More distant targets get less radar attention; as they get closer to the F-22, they will be identified and prioritized; and when they are close enough to be engaged or avoided, they are continuously tracked.

Sensor fusion and emission control are closely linked. The more the datalinks and ALR-94 can be used to build and update the tactical picture, the less the system needs to use the radar. The IFDL provides another layer of protection against tracking, because any one F-22 in a flight can provide radar data to the others.
The APG-77 and ALR-94 are unique, high-performance sensors. The APG-77 has an active, electronically scanned array (AESA) comprising some 1,200 transmitter and receiver modules. One vital difference between an AESA and any other radar that has a single transmitter (including a passive electronically steered array) is that the AESA is capable of operating as several separate radars simultaneously. An AESA can change its beamform very readily, and its receiver segments can operate in a passive or receive-only mode. Unlike a mechanical antenna, too, its revisit rates are not constrained by the antenna drive, and it can concurrently revisit different points within its field of regard at different rates. The F-22 has space, weight and cooling provision for auxiliary side arrays on either side of the nose. If installed, these would provide radar coverage over almost 270[degrees]. The ALR-94, meanwhile, is the most effective passive system ever installed on a fighter. Tom Burbage, former head of the F-22 program at Lockheed Martin, has described it as "the most technically complex piece of equipment on the aircraft."

The F-22 has been described as an antenna farm. Indeed, it would resemble a signals-intelligence (SIGINT) platform were it not for the fact that the 30-plus antennas are all smoothly blended into the wings and fuselage. The ALR-94 provides 360[degrees] coverage in all bands, with both azimuth and elevation coverage in the forward sector.

A target which is using radar to search for the F-22 or other friendly aircraft can be detected, tracked and identified by the ALR-94 long before its radar can see anything, at ranges of 250 nm or more. As the range closes, but still above 100 nm, the APG-77 can be cued by the ALR-94 to search for other aircraft in the hostile flight. The system uses techniques such as cued tracking: since the track file, updated by the ALR-94, can tell the radar where to look, it can detect and track the target with a very narrow beam, measuring as little as 2[degrees] by 2[degrees] in azimuth and elevation. One engineer calls it "a laser beam, not a searchlight. We want to use our resources on the high-value targets. We don't track targets that are too far away to be a threat."

The system also automatically increases revisit rates according to the threat posed by the targets. Another technique is "closed-loop tracking," in which the radar constantly adjusts the power and number of pulses to retain a lock on its target while using the smallest possible amount of energy.

High-priority emitters -- such as fighter aircraft at close range -- can be tracked in real time by the ALR-94. In this mode, called narrowband interleaved search and track (NBILST), the radar is used only to provide precise range and velocity data to set up a missile attack. If a hostile aircraft is injudicious in its use of radar, the ALR-94 may provide nearly all the information necessary to launch an AIM-120 AMRAAM air-to-air missile (AAM) and guide it to impact, making it virtually an anti-radiation AAM.

Of course, there are some targets that do not emit signals. "We prefer it that way, because he's dumb," remarked one Boeing engineer. In this case, the F-22 can use its LPI features to track the target -- which is not a threat unless another radar is tracking the F-22 and datalinking information to the "quiet" aircraft -- and can, if necessary, identify it.

NCTR is a highly classified area. One of the few known techniques is jet-engine modulation, which involves analyzing the raw radar return for the characteristic beat produced by a combination of the radar-pulse frequency and the rotating blades of the engine. This technique is already used on operational radars (including the APG-70 in the F-15) but is vulnerable to countermeasures and dependent on target aspect.

Other NCTR techniques involve very precise range measurements. If the target's orientation is known, the distribution of the signature over very small range bins can yield a range profile which is characteristic of a certain aircraft type. It is possible that the F-22, which has a great deal of onboard processing power -- as well as a flexible, frequency-agile radar -- is designed to use an NCTR technique of this kind.

Unlike the Eurofighter Typhoon , the F-22 does not have an electro-optical (EO) system for target identification. F-22 program managers have said consistently that they believe that the F-22 pilot will be able to identify any target -- emitting or not -- beyond visual range (BVR). "We are confident that we can demonstrate to our leadership that we know what's out there, and that we will operate with rules of engagement that reflect that fact," USAF program manager Gen Mike Mushala remarked at a conference in 1997.

The ALR-94 drives the F-22's defensive displays. The system determines the bearing, range and type of the threat, and then computes the distance at which the enemy radar can detect the F-22. The pilot is the decision-maker and is provided with timely, graphic information to guide defensive maneuvers. On the main defense display, usually shown on the left-hand screen in the cockpit, threat surface-to-air missile (SAM) and airborne early warning (AEW) radars are surrounded by circles that show their computed effective range. On the right-hand attack display, fighter radars are shown as blue beams extending towards the F-22's position.