RU2645910C1 - Method of reducing aircraft radar visibility, equipped with gas turbine engines - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: method of reducing the aircraft radar visibility, equipped with gas turbine engines is that a plasma formation absorbing the probing radiation of the radar station is created in front of the engine elements contributing a great deal to the power of the reflected radiation. Plasma formation is created by means of a high-voltage corona avalanche streamer discharge, and the probing radiation of the radar station is intercepted and directed to the plasma formation zone by means of an adjustable waveguide in the engine with a variable cross-section decreasing from the amount providing a cover from the radiation of the engine element contributing greatly to the reflected radiation power of the radar station to the value equal to the cross section of the plasma formation zone, the waveguide walls are made of a conductive mesh, providing a gas flow passage.

EFFECT: ensuring the possibility of reducing the region of plasma formation, while maintaining the effectiveness of radar protection, reducing the region of plasma formation will reduce the dimensions and weight of the device creating the plasma and reduce the energy consumed by it.

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Description

The invention relates to techniques for radio communications, radar and electronic warfare and can be used in aviation and space technology.

Known methods for reducing the radar visibility of aircraft, based on the creation near the apparatus of a plasma formation that absorbs electromagnetic waves. In the patent for US invention No. 3127608 (IPC G01S 7/38, 03/31/1964) to create a plasma formation, it is proposed to use a beam of high-energy particles (electrons). The disadvantage of this method is its applicability only at high altitudes (20 km and above), since with decreasing altitude, the necessary energy consumption for beam formation increases significantly.

There is a method of reducing the radar visibility of an object, which consists in creating a plasma formation in front of the element of the object, which makes a large contribution to the reflected radiation (RF patent No. 2469447, IPC H01Q 17/00, 10.12.2012). The method allows to reduce the power of radiation reflected from antennas installed on the object. For this purpose, a sealed radiolucent cavity is installed in the antenna location zone, the cavity is filled with a gas mixture, an electron beam is introduced into the gas mixture, the composition of the gas mixture, the electron energy and the beam current are controlled so that an absorbing plasma volume and / or reflecting plasma volume is formed, profile which provides less radar visibility than the radar visibility of the antenna. A sealed radiolucent cavity is installed in front of the antenna or the antenna is placed inside the cavity.

The known method has several limitations on the application:

a) The method cannot be used to reduce the visibility of objects that create an intense gas stream, for example, turbojet engines. At the same time, it is known that these engines make a great contribution to the radar visibility of aircraft during sounding from the air intake and nozzle.

b) It is problematic to use the method in environments with a high temperature, which the transparent material of the sealed cavity may not withstand.

c) Installation of a cavity on a number of objects is impossible due to the negative impact on the functioning of the objects as intended.

A known method of reducing the radar visibility of an aircraft, for example, a missile equipped with a radar homing head (RF patent No. 2565158, IPC B64C 1/36, B64D 45/00, F42B 10/46, 10.20.2015). The method allows to reduce the power of radiation reflected from the antenna of the head. The method consists in placing the antenna in a sealed cavity of a radiolucent fairing, filling the cavity with a plasma-forming gas mixture with a pressure of 1-100 kPa, and introducing an electron beam into the mixture. The beam creates a plasma volume that absorbs the radar probe sound.

The method also has a number of application restrictions:

a) The flight of the aircraft should be performed at an altitude with atmospheric pressure less than the pressure of the gas mixture in the cavity of the fairing. During the flight, it is necessary to additionally supply the gas mixture into the cavity, taking into account its tightness.

b) The electron beam injector must have a relatively high power.

c) The method cannot be used to reduce the radar power reflected from turbojet engines.

There is a method of reducing the radiation power reflected from an aperture antenna mounted on an aircraft (Mikhailov G.D., Sergeev V.I., Solomin E.A., Voronov M.A. Methods and means of reducing the radar visibility of antenna systems // 3arubezhnaya Radio Electronics, 1994, No. 4-5, p. 54-59). The method consists in creating a plasma screen under the fairing of the antenna, matching the shape of the fairing. To create a screen, an electron stream ionizing the gas medium is used. When the electron concentration in the plasma is above a certain critical level, the screen scatters the probe radar radiation to the sides other than the direction to the radar, which leads to a decrease in the visibility of the aircraft.

The disadvantages of the method:

a) The relatively high energy consumption of the electron injector.

b) The method cannot be applied in the working frequency band of the aircraft’s own radar.

c) The method cannot be used to reduce the radar power reflected from turbojet engines.

A known method of reducing the radar visibility of an aircraft, which consists in reducing the radar radiation power reflected from a jet engine in the rear hemisphere, i.e. from the nozzle side (RF patent No. 2311707, IPC H01Q 17/00, 11/27/2007). The decrease in power is provided by the plasma formation created by the electron beam in the gas stream passing through the engine output channel. Plasma formation is created due to the ionization of fuel combustion products. The effectiveness of the method can be improved by taking measures to reduce the content of oxygen molecules in the plasma volume, by maintaining the gas temperature above 500 K and by adding substances forming positive atomic ions to the plasma volume or fuel.

The method described above is closest to the proposed one and is therefore selected as a prototype.

The prototype method also has a number of application restrictions.

a) The method is applicable only to reduce the radar radiation power reflected from the output channel of the engine.

b) In the volume where the plasma is created, it is necessary to ensure the content of oxygen molecules is not more than 10%, as well as a gas temperature in excess of 500 K.

c) The injector creating the electron beam must have a relatively large power.

The technical result of the invention is the ability to reduce the area of plasma formation while maintaining the effectiveness of protection against radar radiation. Reducing the plasma formation region will reduce the size and weight of the device that creates the plasma, and reduce its energy consumption.

The objective of the invention is the expansion of the application of the method of reducing the radar visibility of aircraft, based on the use of plasma formation (expanding the range of pressures and temperatures of the environment, including the Earth’s atmosphere, in which it is necessary to create plasma) and reducing the energy consumption for plasma formation. In this case, the problem is solved in relation to aircraft equipped with gas turbine engines, which, as you know, make a big contribution to the power of radar reflected from the apparatus.

The problem is solved in that in the method of reducing the radar visibility of aircraft equipped with gas turbine engines, which consists in the fact that in front of the engine elements that make a large contribution to the reflected radiation power of the radar station, a plasma formation is created that absorbs the probing radiation of the radar station. A plasma formation is created using a high-voltage corona avalanche-streamer pulsed discharge, and the probe radiation of a radar station is intercepted and sent to the plasma formation zone using a waveguide with a variable cross section installed in the engine, decreasing from the value that provides cover from the radiation of the engine element, which makes a large contribution to power of the reflected radiation of the radar station, up to a value equal to the size of the cross section of the plasma formation zone. Moreover, the walls of the waveguide are made of a conductive mesh that allows the passage of the gas stream.

For gas turbine engines, elements contributing greatly to the reflected power of a radar station are, for example:

- from the air intake side - a guide apparatus and the first compressor stages;

- from the nozzle side - turbine and flame stabilizers.

Further in the description, elements that make the main contribution to reflected radiation are called objects for brevity.

In the proposed technical solution, in contrast to the prototype, a plasma formation is created using a high-voltage corona avalanche-streamer pulse discharge. A distinctive feature of this discharge is that in the system of electrodes between which a discharge is created, the ionization zone, i.e. the plasma zone covers the entire gap between the electrodes. Due to this, not only a large volume region of the ionization zone and plasma is obtained, but also a large corona discharge current. Accordingly, a low-temperature plasma with a high electron concentration is obtained, which provides the necessary degree of absorption of the probe radio emission. In addition, the plasma lifetime increases with decreasing pressure in the gas medium (for example, with increasing altitude) and with increasing temperature (for example, when creating a discharge in a jet engine nozzle). In this case, a discharge and plasma can be created in the atmosphere at a pressure corresponding to any altitude, including on the surface of the Earth.

Another difference from the prototype is that to reduce the distance between the electrodes in the device for creating a discharge, and thereby reduce the energy consumption for creating a plasma, a waveguide is installed in front of the plasma formation zone, which receives radar radiation and directs it to the plasma. The waveguide has a variable cross section. The larger side of the section is facing the radar. Its dimensions overlap the size of the object from which it is necessary to reduce reflection. The small side of the cross section is directed toward the plasma zone. Its dimensions are equal to the size of the zone. Such a device makes it possible to intercept radar radiation directed at an object and direct it into the plasma formation zone. In order for the waveguide to pass the gas stream, its conductive walls must be made in the form of grids of strong conductive threads.

The proposed method of reducing the radar visibility of the object is illustrated by drawings. In FIG. 1 shows a diagram of the application of the proposed method to reduce the radar power reflected from the air intake or nozzle of a gas turbine engine of an aircraft. Here 1 is the radar, 2 is the air intake or nozzle of the engine, 3 is the waveguide that receives radar radiation and directs it to the plasma formation zone, 4 is the plasma formation zone. In FIG. 2 is a schematic representation of a waveguide in which reflective surfaces are made of conductive networks. In FIG. 3 shows a block diagram of the installation with which the experiment was performed. In FIG. 4-7 presents the results of experimental verification of the invention.

The method is as follows.

To reduce the power of the reflected signal inside the object 2, a plasma formation 4 is created using a high-voltage corona avalanche-streamer pulse discharge generated by the discharge generator. To create a region with a plasma of the required size, the discharge generator described in the article (Lepekhin N.M., Priseko Yu.S., Filippov V.G., Bulatov M.U., Sukharevsky D.I., Sysoev BC Modulated corona nanosecond discharge in atmospheric pressure air.Letters in ZhTF, 2015, Volume 41, Issue 7, pp. 96-102), in which a voltage with the form is applied to a system of electrodes installed in front of an object that makes a large contribution to the power of reflected radiation pulses, providing the occurrence of an avalanche-streamer (flare) discharge. For this, a discharge current is modulated in a high-voltage source using a special method of performing a power supply circuit. The essence of the method is that the cathode is separated from the negative pole of the high-voltage power source by a spark initiating spark gap, and a choke with a large inductance is introduced into the discharge circuit from the anode side. The throttle does not allow an avalanche-streamer discharge to pass into a spark discharge. This allows you to accumulate a large positive charge in the gap between the electrodes. Then, when the cathode is forcedly switched to ground, a high electric field strength arises between the cathode and the positive charge, leading to the appearance of a plasma. In this case, the discharge current strength increases significantly, increasing the concentration of electrons in the plasma.

The waveguide 3, receiving the radar 1 radiation and directing it into the plasma zone 4, allows to reduce the distance between the electrodes. This, in turn, allows to reduce the voltage required for the occurrence of a discharge, and to reduce the energy consumed. The waveguide 3 is made of two metal frames (Fig. 2), interconnected by metal rods, providing structural rigidity. Depending on the shape of the protected object, the frames are rectangular, oval or round. One frame of the pair has dimensions that overlap an object that is closed from radiation, and the second has dimensions equal to the dimensions of the plasma formation zone. A grid of conductive threads is stretched over the frames. To exclude leakage of radiation outside the waveguide, the maximum mesh cell size should not be larger than 0.1 × λ, where λ is the minimum radiation wavelength of the radar group from which it is supposed to protect the object (Kontorovich M.I. et al. Electrodynamics of mesh structures. Moscow, Radio and Communications, 1987).

The proposed method of reducing visibility is tested in the experiment. A block diagram of the apparatus with which the experiment was performed is shown in FIG. 3. Here 2 - a hollow closed parallelepiped simulating an air intake or a nozzle of a turbojet engine, 3 - a mesh waveguide intercepting the probe radiation, 4 - a plasma formation zone, 5 - a transmitter consisting of a microwave oscillator and a pulse modulator, 6 - a directional coupler of electromagnetic waves 7 - receiver of radiation reflected from the simulator 2, 8 - device for recording and processing received signals, 9 - high-voltage plasma generator, 10 - pulse synchronizer of the transmitter, receiver and gene plasma radiator. A crescent-shaped figure depicts an antenna emitting and receiving electromagnetic waves.

Installation works as follows. The synchronizer 10 starts at a certain time interval the plasma generator 9, transmitter 5 and receiver 7. Electromagnetic vibrations from the output of the transmitter 5 pass through a directional amplifier 6 to the antenna and are radiated towards the object under study 2. The directional coupler 6 separates the radiation from the transmitter and the radiation reflected from the studied object 2. The reflected radiation is sent to the input of the receiver 7. From the output of the receiver 7, the signal carrying information about the object 2, is fed to the input of the registration and processing device 8.

The probe object 2 electromagnetic radiation is intercepted by the waveguide 3 and is subjected to the following transformations.

1) The main part of the radiation is directed to the plasma formation zone 4.

2) Some, relatively small part, is reflected from the waveguide towards the antenna.

3) Part of the radiation, also relatively small, passes through the walls of the waveguide and is scattered in the cavity of object 2.

4) In the absence of plasma in zone 4, the radiation passes into the cavity of object 2, is scattered in it, and returns back through the rear opening and the walls of the waveguide. This radiation enters through the antenna and a directional coupler 6 to the input of the receiver 7.

5) In the presence of plasma in zone 4, radiation with a significantly reduced power passes through the cavity of object 2. Therefore, the radiation scattered inside the object and the radiation that passed back through the waveguide towards the antenna will have low power.

Thus, the input of the receiver 7 will receive the sum of the emissions:

- reflected from the walls of the waveguide 3;

- scattered in the cavity of the object 2 and passed in the opposite direction through the holes and walls of the waveguide 3.

The power of this sum of oscillations in the presence of plasma will be significantly less than in its absence.

The plasma action is shown in figures 4, 5, 6 and 7. Here are the oscillograms observed on the screen of the receiver 7.

In FIG. Figure 4 shows the pulse of the reflected signal with an amplitude dip in the middle caused by the action of the plasma. The pulse duration (4 μs) was specially chosen more than the plasma lifetime (0.6 μs) to ensure the visibility of the plasma action process. In FIG. 5, 6 and 7 show the process when the pulse duration of the reflected signal is equal to the lifetime of the plasma. In FIG. 5 shows a pulse in the absence of plasma. In FIG. Figure 6 shows the pulse at the initial moment of plasma formation. The waveform in FIG. 7 corresponds to the moment when the plasma is fully formed, while the amplitude of the pulse decreases to the noise level of the receiver and therefore the pulse is not visible.

The table below shows the results of measuring the decrease in the radiation power reflected from object 2. The radiation frequency is 6 GHz, the pulse duration is 4 μs, and the pulse repetition rate is 6 kHz. In parallel with the radiation pulses, a plasma is created. The decrease in power is expressed in decibels relative to the maximum amplitude of the pulse. The results were obtained with two modes of operation of the plasma generator 9: discharge voltage U _p = 35 kV, discharge current I _p = 3 mA and discharge voltage U _p = 42 kV, discharge current I _p = 5 mA. The average value of the power reduction according to the results of twenty measurements shown in the table is: in the first mode - 14.3 dB, in the second mode - 18 dB.

Technical implementation of the proposed method can be performed using existing devices and elements of technology.

1. As an active element of a discharge generator that modulates the discharge current, a thyratron or an electron beam valve can be used (Translators V.I., Matveev N.V., Stuchenkov V.M., Shapenko V.M. Features of high-voltage switching devices on based on electron beam valves. Applied Physics, 2001, No. 5, pp. 97-102).

2. For the manufacture of a waveguide intercepting radar radiation and located in a gas stream with a high temperature, conductors made of heat-resistant metals, such as tungsten or nichrome, can be used.

Claims (1)

A method of reducing the radar visibility of aircraft equipped with gas turbine engines, which consists in the fact that in front of engine elements that make a large contribution to the reflected power of the radar station, a plasma formation is created that absorbs the probing radiation of the radar station, characterized in that the plasma formation is created using a high voltage a corona avalanche-streamer pulse discharge, the probe radiation of a radar station is intercepted and sent to the plasma formation zone using a waveguide installed in the engine with a variable cross section, decreasing from a value that provides cover from the radiation of the engine element, which makes a large contribution to the reflected radiation power of the radar station, to a value equal to the cross section of the plasma formation zone, and the waveguide walls are made from a conductive grid that allows the passage of a gas stream.

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