The concept of unmanned aircraft early warning radar
Source: Aeronautica Militare
1. The main stages of AWACS development
The main problem arising in the design of AWACS is that (in order to obtain large target detection ranges) the radar must necessarily have a large antenna area, and, as a rule, there is nowhere to place it on board. The first successful AWACS was developed more than 60 years ago and has not left the scene to this day. It was created on the basis of the deck transporter and was named E2 Hawkeye.
Mushroom
The main idea of all AWACS at that time was to place a rotating antenna in a "mushroom" located above the fuselage.
The radar determines the coordinates of the target by measuring the target's range and two angles: horizontally and vertically (azimuth and elevation). It is quite easy to obtain high accuracy of range measurement - it is enough to accurately determine the return time of the echo signal reflected from the target. The contribution from the angle measurement error is usually much larger than the range error. The amount of angular error is determined by the radar beam width and is typically about 0,1 beam width. For flat antennas, the width can be determined by the formula α = λ / D (1), where:
α is the beam width, expressed in radians;
λ is the radar wavelength;
D is the antenna length along the corresponding coordinate (horizontally or vertically).
At the selected wavelength, in order to narrow the beam as much as possible, the antenna size has to be maximized based on the capabilities of the aircraft. But an increase in the size of the antenna leads to an increase in the midsection of the "mushroom" and worsens aerodynamics.
Disadvantages of pancake
The Hokai developers decided to abandon the use of flat antennas and switched to a “wave channel” type television antenna. Such an antenna consists of a longitudinal bar, across which a number of vibrator tubes are installed. As a result, the antenna is located only in the horizontal plane. And the “mushroom” cap turns rather into a horizontal “pancake”, which almost does not spoil the aerodynamics. The direction of radiation of radio waves remains horizontal and coincides with the direction of the boom. The diameter of the "pancake" is 5 m.
Of course, such an antenna also has serious disadvantages. With a selected wavelength of 70 cm, the azimuth beam width is still acceptable - 7 °. And the elevation angle is 21 °, which does not allow measuring the height of targets. If, when aiming fighter-bombers (IS), ignorance of altitude is insignificant, thanks to the ability of the on-board radar (radar) to measure the height of the target itself, then such data is not enough for launching missiles. It is not possible to narrow the beam by decreasing the wavelength, since the “wave channel” works worse at short waves.
The advantage of the 70 cm range is that it significantly increases the visibility of stealth aircraft. The detection range of a conventional IS is estimated at 250-300 km. The small mass of Hokai and its cheapness have led to the fact that its production has not been discontinued.
AWACS
The requirement to increase the detection range and improve the tracking accuracy led to the development of a new AWACS AWACS based on the passenger Boeing-707. A flat vertical antenna measuring 7,5x1,5 m was placed in the "mushroom" and the wavelength was reduced to 10 cm. As a result, the beam width decreased to 1 ° * 5 °. Radar accuracy and noise immunity have increased dramatically. The IS detection range has increased to 350 km.
Analogue of AWACS in the USSR
In the USSR, the first AWACS was developed on the basis of the Tu-126. But the characteristics of its radar were mediocre. Then they began to develop an analogue of AWACS. No heavy passenger carrier was found. And they decided to use the Il-76 transport aircraft, which was not very suitable for AWACS.
Excessive fuselage width, large mass (190 t) and uneconomical engines caused excessive fuel consumption. Twice as much as AWACS. The stabilizer, raised to the top of the keel and located behind the "mushroom", when the antenna turned to the tail sector, caused the radar beam to be reflected to the ground. And the interference caused by back reflections from the ground greatly interfered with the detection of targets in the tail sector.
No radar upgrades can eliminate the disadvantages of this carrier. Even replacing engines with more economical ones did not bring fuel consumption to the level of AWACS. Detection range and accuracy were almost as good as AWACS. But AWACS will also be removed from service in the coming years. The difference in media also affects the operators. The Il-76 is not a passenger aircraft, the level of comfort in it is low. And the fatigue of the crew by the end of the shift is significantly higher than in the Boeing-707.
Era AFAR
The advent of radar with active phased array antennas (AFAR) has significantly improved radar performance. AWACS appeared without the "mushroom". For example, FALKON based on Boeing-767. But here, too, the use of the finished media did not lead to good results. The presence of a wing in the middle of the fuselage led to the fact that the lateral AFAR had to be split in half. AFAR, installed in front of the wing, radiated forward and sideways. And AFAR behind the wing - back-sideways. But it was not possible to get one AFAR of a large area.
Our A-100 was left with a "mushroom". Instead of a rotating antenna, an AFAR was installed inside the "mushroom". The media had to be replaced, but that didn't happen. The detection range has been increased (reportedly) to 600 km. But the flaws of the carrier did not disappear. The A-50 park is in a deplorable state. Of the remaining planes, 9 fly (and even then rarely). Apparently, there is not enough money for regular flights. The lack of regular AWACS flights leads to the fact that the enemy is confident that his low-altitude Tomahawk-type missile launchers will easily pass our border unnoticed.
Unlike the United States, there are no balloon radars in the Russian Federation to guard maritime borders. And the hills on the coast, where it would be possible to install a surveillance radar, are also not everywhere. On land, the situation is even worse. Tomahawks, using the folds of the terrain, can pass the radar station at a distance of only a few kilometers. It is believed that cruise missiles (CR) fly over land at an altitude of 50 m. However, modern digital maps of the area have become so detailed that they can even display individual tall objects. Then the altitude flight profile can be plotted at noticeably lower altitudes. Above the sea, KRs fly at heights of about 5 m. Consequently, the statement of the Ministry of Defense on the creation of a continuous radar field in the RF does not apply to KR.
An innovative idea
The conclusion suggests itself - it is necessary to develop a specialized carrier that allows you to place a large area AFAR, the concept of which the author proposes.
In his opinion, the mass of such an AWACS will be significantly less than the AWACS mass. And the detection range ꟷ is much greater. The cost per hour of operation will be moderate. This makes it possible to conduct regular flights (but, of course, not on schedule). It is important that the enemy does not know when, where and along what trajectory the flight will take place.
2. Substantiation of the concept of a promising UAV AWACS
The previous dominant concept in the world “AWACS aircraft - air command post” is hopelessly outdated. AWACS is capable of dumping all information on a high-speed line to a ground command post at a distance of 400-500 km. If necessary, you can use a UAV repeater, which will increase the communication range up to 1300 km. The presence of a large crew on board the former AWACS makes it necessary to allocate IS on duty for their protection. Therefore, the cost of an hour of their operation becomes prohibitive.
Further, only UAV AWACS is considered. We will also give up the requirement to ensure the same detection range in all directions. In most cases, AWACS patrols in a safe zone and monitors what is happening in the enemy's zone or in a given area of its own territory. Therefore, we will require that the AWACS must have at least one sector with a width of 120 °, where an increased detection range is provided. And in the remaining sectors, only self-defense is provided.
The only place on the plane where a large APAR can be placed is the side of the fuselage. But in the middle of the fuselage there is usually a wing. Even with the use of the upper plane (as on the IL-76), the wing will not allow viewing the upper hemisphere. The way out of the situation will be to raise the AWACS track to such a height that for it almost all targets will be below. And nothing prevents their detection.
The detection of high-altitude targets will be somewhat easier if you use a V-shaped wing. Without loss of wing quality, the climb angle can be up to 4 °. Then the maximum target detection angle at which the radar beam is not yet reflected from the wing is 2ꟷ3 °. Suppose the AWACS is located at an altitude of 16 km. Then, if the target flies at the maximum altitude for IS of 20 km, then it will be in the AWACS detection zone until it reaches a distance of less than 80 km. If it is required to accompany this target at closer distances, then the AWACS can tilt the roll by another 5 ° and continue tracking to a range of 30 km.
To reduce the weight of the AFAR, it must be performed using the technology of radiant sheathing, in which the radiating slits are cut into the sheathing and sealed with fiberglass. The transceiver modules (TPM) of the AFAR are attached to the skin, and the excess heat from the TPM is dumped directly onto the skin. As a result, the mass of APAR significantly decreases.
3. The design and tasks of the UAV
It should be recalled that the author is not a specialist in aircraft construction. Shown in Fig. 1, the layout (as well as dimensions) reflects rather the requirements for the placement of radar antennas. This is not a drawing of a real UAV.
Figure 1.
It is assumed that the take-off weight of the UAV will be 40 tons. The wingspan is 35ꟷ40 m. The flight altitude is 16ꟷ18 km. At a speed of about 600 km / h. The engine must be economical. Modeled on the Global Hawk design, the engine of a passenger plane should be taken. For example, PD-14. And modify it for high-altitude flight. Fuel mass 22 tons. Flight time not less than 20 hours. Takeoff / run length 1000 m.
The high wing position will not allow the use of a conventional three-pillar landing gear. We'll have to use a bike chassis like the U-2. Of course, striking the runway with the wing at the end of the run, as on the U-2, will not work here. And it is difficult to use the support wheels extended to the side. Due to the fact that the side surface was occupied by the AFAR.
It is proposed to make the last 7 m of the wing folding, like on ship aircraft. But they should not rise, but descend downward at an angle of 40ꟷ45 °. So as not to touch the runway. Support wheels are installed on the wingtips. Which, with sudden gusts of wind, run into the runway. The long wing length will provide a low load on the wheel. At the end of the run, the UAV rests on one of them.
Next, we will consider the possibilities of placing a side AFAR. The best radar performance is obtained when the antenna has the largest possible area and the antenna shape is close to a circle or square. Unfortunately, on a real UAV, the shape will always differ significantly from the optimal one - the height is much less than the length.
The choice of the shape and size of the fuselage can only be performed by experienced aircraft engineers. Well, for now, let's consider two theoretically possible versions of the APAR shape, having the same area. The first option (16x2,4 m) will be considered the most realistic. And the second (10,5x3,7 m) - requiring additional study.
Consider the first option, in which the fuselage length is 22 m. The design feature is the presence of an elongated air intake passing under the wing. This made it possible to increase the height of the side surface of the fuselage. AFAR is shown by dash-dot line.
AFAR operate in the wavelength range 20 - 22 cm, which will allow using one AFAR to solve the problems of radar, state identification and anti-jamming communication with the command post. Another advantage of this range (in comparison with the range of 10 cm for the A-50) is that the image intensifier of stealth targets, starting from wavelengths of 15ꟷ20 cm, increases with increasing wavelength.
In the nose (under the fairing) there is an elliptical AFAR measuring 1,65 × 2 m.Due to the fact that the nose antenna does not provide the required azimuth measurement accuracy, two additional purely receiving AFARs are located in the leading edges of the wing. The distance from the fuselage to the wing antenna is 1,2 m. The wing AFAR is a line of 96 receiving modules with a total length of 10,6 m.
Working range of angles nasal AFAR ± 30 ° * ± 45 °. The use of wing-mounted APARs will slightly increase the detection range (by 15%). But the measurement error of the azimuth will decrease radically (by 5–6 times).
The tail section contains only the communication line antenna. Therefore, in the field of view of the rear hemisphere there is a “dead” zone with a width of ± 30 °.
To save the weight of the aircraft, the communications complex uses the same AFAR as the main channel. With their help, high-speed (up to 300 Mbit / s) and noise-immune transmission of information to a ground or ship communication point is provided. To receive information at communication points, transceivers of the 20ꟷ22 cm range are installed. There are no special requirements for the antennas of these transceivers. The enemy cannot create interference of such power, which could suppress the signal of the AWACS radar. And it is possible to transfer information from a communication point to AWACS at low speeds.
3.1. Radar design
The lateral AFAR should be located 25 cm below the lower edge of the wing. Then it can scan the lower hemisphere in the entire azimuth range of ± 60 ° available to it. In the upper hemisphere, at elevation angles of more than 2 - 3 °, the wing begins to interfere. Therefore, AFAR is divided into two halves. The front is located under the wing and cannot scan upward. The trailing half can scan upward in an azimuth range of ± 20 °, where its beam does not touch the wing or stabilizer. The elevation scan of this half will be from + 30 ° to -50 °.
Lateral AFAR contains 2880 PPM (144 * 20). Pulse power PPM 40W. The power consumption of this AFAR is 80 kW. The beam width is 0,8 ° * 5,2 °, which is even slightly narrower than that of AWACS. Therefore, the accuracy of target tracking will be higher than AWACS. Especially big gains are expected in target detection and tracking range. First, the AWACS antenna area is 10 square meters. m. And the AFAR area is 38 sq. m. Secondly, the AWACS antenna evenly scans the entire 360 °. And the lateral AFAR only its 120 ° and even then unevenly: in those directions where there is a suspicion of the presence of a target, more energy is sent, and the uncertainty is eliminated (that is, the detection range in these directions increases).
The nasal antenna contains 184 PPMs of 80 W pulsed power and liquid-cooled. Beam width 7,5 * 6 °, scanning angles ± 60 ° in azimuth and ± 45 ° in elevation.
Maximum power consumption of the radar is 180 kW. The total weight of the radar is 2–2,5 tons. The prime cost of a serial model of the radar will apparently amount to 12–15 million dollars.
4. Tasks and functioning of AWACS
When used in a maritime theater, a UAV must provide information support for the KUG at a distance of up to 2ꟷ2,5 thousand km from the home airfield. Even at such distances, it is able to be on duty for at least 12 hours. In the area of duty, the UAV must be protected by the KUG air defense system, that is, it must be removed to a distance of no more than 150-200 km. If there is a danger of an attack, the UAV must return under the protection of the KUG at a distance of no more than 50 km. In this situation, the UAV radar and the KUG radar must distribute between themselves the detection zones of attacking air targets. In the lower hemisphere, it detects a UAV, and higher targets - an air defense system radar.
Let's take into account that with a flight altitude of 16 km, the radius of detection of enemy ships will be 520 km. That is, the achieved range of the control center will ensure the launch of the Onyx anti-ship missile system at the full flight range.
When escorting aircraft carriers and UDC that do not have deck AWACS, the UAV can participate in the actions of the air wing. In addition to the traditional detection of air and sea targets, the UAV is capable, using the extremely high energy potential of the lateral AFAR, to detect enemy radio contrast targets, as well as the trajectories of large-caliber cannon shells. In addition, the UAV can detect moving armored vehicles.
5. Tactical and technical characteristics of the radar
Lateral AFAR characteristics
Detection range in the direction of the axis of the side antenna:
- fighter type F-16 with image intensifier 2 sq. m at an altitude of 10 km - 900 km;
- RCC with an image intensifier of 0,1 sq. m - 360 km;
- guided missile type AMRAAM with an effective reflective surface (EOC) 0,03 sq. m - 250 km;
- artillery shell of 76 mm caliber with an image intensifier of 0,001 sq. m - EOP 90 km;
- a missile boat with an image intensifier of 50 sq. m - 400 km;
- destroyer with image intensifier 1000 sq. m - 500 km;
- a tank moving at a speed of 3 m / s and an image intensifier of 5 sq. m - 250 km.
At the boundaries of the azimuth scan zone equal to ± 60 °, the detection range decreases by 20%.
The error of a single measurement of angles is given for a range equal to 80% of the detection range of the corresponding target:
- in azimuth - 0,1 °,
- in elevation - 0,7 °.
During target tracking, the angular error decreases by 2–3 times (depending on the target's maneuvers). When the target range is reduced to 50% of the detection range, the error of a single measurement is halved.
The disadvantage of AFAR measuring 16x2,4 m is precisely the low accuracy of measuring the elevation angle. For example, the error in measuring the altitude of the F-16 IS, followed at a distance of 600 km, will be 2 km.
If it were possible to implement the second version of the lateral AFAR measuring 10,5x3,7 m, then the IS detection range would increase to 1000 km, and the altitude measurement error at a distance of 600 km would decrease to 1,3 km. The fuselage length would be reduced to 17 m.
Characteristics of nasal AFAR
Detection range in the direction of the nasal antenna axis:
- fighter with image intensifier 2 sq. m - 370 km;
- RCC with an image intensifier of 0,1 sq. m - 160 km;
- a guided missile of the AMRAAM type with an image intensifier of 0,03 sq. m - 110 km;
- missile boat with an image intensifier tube 50 sq.m - 300 km;
- destroyer with image intensifier 1000 sq. m - 430 km;
- a tank moving at a speed of 3 m / s and an image intensifier of 5 sq. m - 250 km.
Single angle measurement error:
- azimuth: 0,1 °;
- elevation angle: 0,8 °.
In the process of target tracking, the measurement error decreases by 2–3 times.
The cost of lateral AFAR depends on the batch size. We will focus on the price of $ 5 million. Then the total cost of the radar station will be $ 14 million. That is much cheaper than analogues available on the world market.
6. The tactics of using AWACS on a land theater
The tasks of the combined-arms AWACS on land are to illuminate the air situation to a great depth over the territory of neighboring states and to record the movements of large formations of troops in the border zone up to 300 km deep. In special circumstances, purely local problems can also be posed. For example, escorting a dangerous terrorist's car. In order for the watch to continue continuously during the entire threatened period, it is important to be able to minimize the cost of an hour of watch.
The UAV must patrol along the borders at distances that ensure its safety. If the enemy has a long-range air defense system or IS airfields in the border zone, this distance should be at least 150 km.
To prevent the possibility of defeat in wartime, it is necessary to ensure the protection of the UAV with its own air defense means. The cheapest way is to use a pair of air defense missile systems, which are capable of covering a loitering zone 150-200 km long. In the absence of its own air defense systems, the distance from the border can be increased to 200 km. This, while ensuring a long detection range of attacking missiles (and enemy fighters), will make it possible to carry out a retreat maneuver deep into its own territory with the rise of IS officers on duty from the nearest airfield.
In peacetime, you will not need to use such protection. And the UAV can cruise directly along the border. At the same time, it can detect moving vehicles on its own, but without recognizing their type. In this regard, the best efficiency is achieved by combining the recognition of specified targets by means of optical reconnaissance operating on the enemy's territory (or from a satellite), and tracking the detected targets using a UAV.
For example, if a scout detects a terrorist vehicle, the AWACS operator will be able to put it on automatic tracking and track the movement of this vehicle even on roads in the vicinity of other vehicles, as well as call an attack UAV to destroy them.
7. findings
The Il-76 aircraft, which is the carrier of the new A-100 AWACS complex, has not fundamentally changed. And it will not be possible to radically reduce the cost of an hour of its operation. Therefore, you cannot count on its regular use. Despite the improved characteristics of the radar.
The proposed AWACS UAV provides a detection range 1,5 times greater than the A-100. Weighs four times less. And it consumes five times less fuel.
The long detection range allows you to control the enemy's airspace from safe distances (200 km) and not use security information security.
The increased flight altitude makes it possible to detect ground and surface targets at distances up to 500 km.
The long duration of the flight makes it possible to use UAVs to escort KUGs, support amphibious operations and AUG actions at a distance of up to 2500 km from the airfield.
Integration of radar, state identification and communication functions in one AFAR made it possible to further reduce the weight and cost of the equipment.
Moderate cost of the devices will ensure the high competitiveness of the UAV.
Unfortunately, such proposals in the Ministry of Defense have not yet aroused interest and are still perceived as fantasy.
In the next article, we will consider the shipborne AWACS UAV.
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