RU2622908C1 - Radar location method for detecting aircrafts - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: in the proposed radar location method for detecting aircrafts, probing radio signals are emitted alternately with linear polarization and with quadrature polarization, and each radiated probing radio signal with quadrature polarization is phase-synchronous with the previous linear-polarizing probing signal. After the spectra comparison of the demodulated reflected radio signals with linear polarization and reflected radio signals with quadrature polarization, it is judged that the aircraft is detected by the presence of the value multiplicity of their amplitude modulation periods.

EFFECT: possibility of detecting unobtrusive aircrafts.

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Description

The invention relates to radar detection of aircraft (LA), in particular aircraft, helicopters, both single and in the group, as well as small unmanned aerial vehicles (MBPLA), when the effective dispersion area (EPR) is σ _c = 0.01 ... 0.001 m ² .

A known method for detecting aircraft, including MBPLA, which consists in emitting into space using a radar station (radar) pulsed sounding signals, reflecting them from the aircraft, receiving the reflected signals by the radar antenna system, filtering the reflected signals by frequency to extract reflections from moving aircraft against the background of local objects, comparing filtered reflections with a threshold and, in case of exceeding the established threshold, deciding that a moving aircraft was detected [1].

This method is used in most survey radars of the old and new parks, however, it has the disadvantage that reliable detection is possible only in the case of reflections of electromagnetic waves (EMW) from typical objects with EPRs of the order of tens of square meters. In the case of reflection of electromagnetic waves from MBPLA, the EPR of which can be 0.01 ... 0.001 m ² , the power of the reflected signals to exceed the threshold is clearly insufficient, and the detection of such objects is extremely difficult.

There is also a method of detecting subtle aircraft (including MBPLA), which involves the accumulation of reflections from aircraft obtained in different periods of the pulse repetition of the radar [4]. Coherent accumulation (addition) of reflected signals allows you to exceed the detection threshold even in the case of low reflectance of the aircraft. To ensure coherent addition of the reflected pulse signals, the pulse repetition rate F _{p is} increased or, which is the same, the pulse repetition period T _{p is} reduced. This method requires that at a given speed of viewing the space the minimum number of pulses M _min received after reflection from the aircraft was sufficient to detect the aircraft with a given probability [4, p. 71-72, 89-90]. This detection method also does not allow to effectively detect subtle MBPLA, since there are no methods to determine the required number of accumulated pulses M _min , and with increasing F _p there is an ambiguity in determining the range to the detected object.

In modern surveillance radars, the number of accumulated pulses does not exceed 10-100, which is clearly not enough to detect low-reflecting MBPLA.

Detection methods are also known that use, along with the Rayleigh and quasi-optical scattering regions, a resonance region in which the EPR increases substantially [5, p. 15-30].

Another well-known method for detecting aircraft with low reflectivity is based on this effect. In accordance with the principles of operation of the devices described in [6, p. 74-82], as well as using traditional methods of correlation-filter processing [1-3], a known method for detecting aircraft, including low-reflecting MBPLA, is as follows. By tuning the frequency of the probe signal in a fairly wide range from 150 MHz (λ = 2 m) to 6 GHz (λ = 5 cm) with a resolution of 10 MHz, high-frequency electromagnetic oscillations are generated at all frequencies and, after coordinated processing of the received reflected signals, the resonant frequency ƒ _p corresponding to a wavelength λ _p commensurate with the size of a typical subtle LA. The spectral responses of the reflected signals are compared with a threshold value, and if the spectral response exceeds a threshold, the frequency ƒ _p is set equal to the carrier frequency of the packet, from the reflections of which a one-time excess of the threshold value is obtained. After exceeding three consecutively received packs of radio pulses reflected at the resonant frequency, a decision is made to detect an inconspicuous aircraft at the appropriate range.

The described method for detecting MBPLA is more effective than previously indicated, since it provides an analysis of the entire frequency range at which modern MBPLA reflect EMW in the resonance region, and also eliminates the adoption of random, unconfirmed decisions about the detection of MBPLA. However, this method also has certain disadvantages. Firstly, the tuning of the carrier frequency of the probe signal in such a wide range (from 150 MHz to 6 GHz), i.e. four decades when using directional reception, will require the creation of a very complex and expensive antenna-feeder system. Secondly, the formation of the probing signal, the process of coordinated reception and processing of the received reflected signals will require a sufficiently long time to review the space.

There is also known a method for radar detection and classification of aircraft (in particular, helicopters), based on the analysis of the reflections of the probe signal from the rotor blades, the use of propeller modulation characteristics contained in the spectrum of the received reflected signal, and described in RF patent No. 2293350 dated 02.10.2007 . [8]. The known method involves processing the reflected signals by means of a fast Fourier transform (FFT), determining the amplitude modulation period of the signal, which corresponds to the signals reflected from the rotor blades of the rotor of the helicopter (hereinafter referred to as LA), further comparing the obtained value of the amplitude modulation period of the signal with the base data and determining the basis of this speed and model of the aircraft.

A disadvantage of the known method is the impossibility of unambiguous recognition of MBPLA, since when a rotating rotor is irradiated with a probing radio signal with circular polarization, the amplitude modulation of the reflected signal does not occur at all, and with linear (vertical or horizontal) polarization of the probing radio signal there is no unambiguous answer for aircraft recognition due to multiple reflection from main and tail rotors.

The objective of the invention is the ability to detect MBPLA with a small ESR in the range of 0.0 ... 0.001 m ² against the background of intense reflections from the underlying surface. The essence of the proposed technical solution is based on the analysis of the structure of the reflected sounding signal from the blades of the rotating rotor of an unmanned aerial vehicle.

The problem is solved in that in the radar detection method of aircraft, including the radiation of sounding radio signals, receiving and performing fast Fourier transform of the reflected radio signals, determining the peaks and the amplitude modulation period in the Doppler spectrum of the reflected signal and storing it, according to the invention, the sounding radio signals emit alternating with linear polarized and quadrature polarized, with each probing radio signal with quadrature polarization it is phase in phase with the previous probing radio signal with linear polarization, the spectra of demodulated reflected radio signals with linear polarization and reflected radio signals with quadrature polarization are compared and the detection of an aircraft is judged by the presence of the multiplicity of the values of their amplitude modulation periods.

In FIG. 1 schematically shows a device for implementing the inventive radar method for detecting aircraft. In FIG. Figure 2 shows the experimental spectral diagrams of the reflected signals on the indicator after the Fourier analysis performed by the microcontroller for various angular positions of the screw plane of the irradiated MBPLA model.

A device for implementing the proposed method (Fig. 1) includes a radar transmitter (PER) 1 connected to a transmitting antenna 2 and a receiver 3. The receiver 3 contains a series-connected amplitude detector 4 (AD), an analog-to-digital converter 5 (ADC), and a microcontroller 6 (MK) and indicator 7 (IND). The input HELL 4 is the input of the receiver 3 and is connected to the receiving antenna 8. The transmitting antenna 2 generates a radiation pattern 9 in the direction of the flight path 10 of the aircraft with a rotary screw 11.

The method is as follows. Formed by the radar transmitter 1, the high-frequency sounding signals are emitted by the transmitting antenna 2 in the direction of the flight path 10 of the aircraft moving at a certain speed V _c . At the same time, the high-frequency probing signal is fed to the receiving antenna 8 (direct signal 12), where it is subsequently mixed with the reflected signal at the amplitude detector 4. Radio signals reflected from the aircraft and modulated in amplitude due to the rotation of its screw 11 are received by the receiving antenna 8 within its radiation patterns 13 and are fed to the input of the amplitude detector 4 of the receiver 3. Then, through an analog-to-digital converter 5, they are transferred to a digital processing device - a microcontroller 6, the output of which dklyuchen to the indicator 7.

The principle of highlighting the beat frequency of the reflected signal from the rotation of the screw 11 of the aircraft is as follows.

The sequence of radio signals reflected from the rotating rotor of the aircraft can be written as follows:

- нормированная по дальности амплитуда огибающей последовательности отраженного сигнала;

- range-normalized amplitude of the envelope of the sequence of the reflected signal;

F _j - screw speed, Hz;

S is the envelope of the sequence of reflected signals;

t _i is the delay time, s;

T - the period of the probing radio signals, s;

N is the number of reflected radio signals received at the input of the receiver 3 during the time the aircraft was within the width of the radiation pattern 13 of the receiving antenna 8.

и частот F_j записывается в модуль оперативного запоминающего устройства (ОЗУ) микроконтроллера 6 и подается в нейрокомпьютерную программу обнаружения и распознавания класса ЛА. Параметры ЭПР являются дополнением к признакам распознавания класса ЛА. При этом обучающая программа нейрокомпьютера формируется на этапе летных испытаний моделей ЛА для конкретного типа РЛС.In microcontroller 6, a spectral analysis of the detected reflected radio signals in the frequency band of the screw 11 (of the order of 20 ... 1000 Hz depending on the speed of rotation of the screw) takes place, the result of which is displayed on indicator 7. At the same time, the result of spectral analysis in the form of a set of normalized amplitudes

and frequencies F _{j is} recorded in the module random access memory (RAM) of the microcontroller 6 and is fed to a neurocomputer program for detecting and recognizing an aircraft class. The EPR parameters are in addition to the recognition features of the aircraft class. At the same time, the neurocomputer training program is formed at the stage of flight tests of aircraft models for a specific type of radar.

The aircraft class is determined by the set of measured parameters of the reflected signal, in particular for a linear recognition model

α ₁ , α ₂ , ..., α _i - weighting factors selected in the process of training a neuro-PC,

,

, …,

- параметры отраженного сигнала,

,

, ...,

- parameters of the reflected signal,

j is the class number of the aircraft.

As parameters (signs) of the aircraft will be used:

- rotational speed of the screw along the four coordinate axes, 0 °, 45 °, 90 °, Z (zenith);

- the amplitude of the spectral components;

- effective dispersion area of the aircraft;

- the speed of the aircraft,

only about 12 signs, which allows you to form the image (class) of the aircraft.

In order to verify the fundamental possibility of implementing the inventive method for detecting aircraft, laboratory tests were conducted to detect small unmanned aerial vehicles (MBPLA) by modulating the reflected signal by the rotational speed of the screw in the Iridium radio laboratory of the Military Engineering Institute of the Federal State Autonomous Educational Institution of Higher Education of the Siberian Federal University.

The purpose of the tests: determination of the fundamental possibility of radar detection MBPLA weighing 1 ÷ 10 kg by extracting from the reflected signal the rotational speed of the screw.

Used equipment.

1. Aircraft model - analog-MBPLA: WINDS 50Е (Sebastiano Silvestri) with the following characteristics:

The length of the fuselage - 1600 mm;

Wingspan - 1580 mm;

Engine power - 1500 W;

Battery power - LiPo, 22.2 V, (6S), C = 4500 mA / h;

Screw rotation speed n - 50 ÷ 100 r / s.

2. An autodyne-type experimental radar with a transmitter power of 5 mW, an operating frequency of 2.4 GHz, a linear horizontal signal polarization, a mirror antenna (solid) with a diameter of 0.8 m (antenna gain in power G _a = 25 dB).

3. Means of measurement: external ADC / DAC module E-154 for USB bus: resolution - 12 bits; sampling rate - 10 kHz; input signal measuring range -1.6 ÷ 1.6 V.

4. Software: a digital spectrum analyzer based on a personal computer (laptop).

The MBPLA model was installed indoors 40 m long with a cross section of 3 × 3 m. The radar mirror was placed on a tripod, at a height of 1 m from the floor. The distance between the MBPLA model and the radar was 30 m.

From the output of the radar detector, the reflected video signals with a realization length of 3 seconds were fed to a personal computer with a spectral analysis program.

The plane of rotation of the screw 11 of the aircraft was set relative to the axis of the radiation diagram at an angle θ: 0 °, 45 °, 90 °.

We studied two types of screws: dielectric (length 406 mm) and carbon fiber (length 559 mm).

The measurement results are presented in the form of corresponding spectrograms and are shown in FIG. 2. An analysis of the results shows that the radar registers the speed signals of both types of screws with a signal-to-noise ratio of 30–35 dB.

For the angular position of the MBPLA at 0 °, the 1st and 2nd harmonics of the frequency corresponding to twice the rotational speed of the propeller are noted, which is logical given the linear polarization of the emitted E-wave, because for one rotation of the screw rotation, its position twice coincides with the line of polarization of the E-wave.

When the MBPLA angular position is 45 ° relative to the incident wave front, several additional spectral lines appear on the spectrogram.

When changing the screw material from dielectric to carbon fiber, the amplitude of the recorded signal increases by about 10 dB.

Thus, in the course of the experimental studies, it was proved that MBPLA can be detected by the rotational speeds of its propeller, regardless of the resulting effective scattering area (ESR) of the MBPLA hull. A similar approach is possible for other rotorcraft.

An important advantage of the proposed method is the possibility of a significant improvement in the quality of detection of MBPLA due to the sequential use of first linear, then quadrature polarization of the probing radio signals with the same phase along the orthogonal radiation components.

The use of synchronously quadrature polarization of the probing radio signals can significantly improve the recognition of MBPLA objects by introducing a second verification feature - increasing the modulation frequency of the reflected radio signal by rotating the screw a multiple of times. In other words, the appearance in the spectrum of the reflected radio signal of a multiple component of the frequency with respect to the first type of polarization (linear) directly indicates a sign of rotation of the main rotor of the MBPLA.

Another undoubted advantage of the proposed method is the possibility of a significant improvement in angular resolution due to the use of the modern method of reverse synthesis of aperture along a moving aircraft in the final flight section L (see Fig. 1).

The formation of the synthesized aperture occurs in this case due to an overflown aircraft with a turning radius R _n at a constant linear speed of its movement in section L. This ensures the observation of the aircraft sequentially in time (see Fig. 1) from different angles within the angular size β ₀ . When the radar is stationary, the angular size of the synthesized aperture β ₀ is determined by the target moving speed V _c and the synthesis time T _s , i.e. β ₀ = V _c T _s / R _n In this case, the angular resolution on the target during the accumulation of the signal T _with will be [7]

So, if we assume that at a distance of 1000 m from the radar MBPLA moves at a speed of V _c = 100 km / h (≈28 m / s), then in the area L of 100 m in length the synthesis time T _s ≈ 3.5 s. During this time, the screw rotation speed n [rpm] can be considered constant (n = const). In this case, the angular resolution according to expression (3) at a wavelength of λ = 12.5 cm (ƒ = 2.4 GHz) is

Thus, when coherently summing the signals of the modulation of the rotational speed of the screw (even with a fairly wide radiation pattern of the radar antenna of the order of 3 ... 6 °), the method will allow to obtain a high angular resolution.

Information sources

1. Handbook of radar. / Ed. M.I. Skolnik. - Per. from English M .: Sov. Radio, 1967. Vol. 1. Basics of radar. - 456 p.

2. Theoretical foundations of radar. / Ed. POISON. Shirman. M .: Sov. Radio, 1970 .-- 560 p.

3. Okhrimenko A.E. Basics of radar and electronic warfare. Part 1. Basics of radar. M .: Military Publishing, 1983.- 456 p.

4. Reference on the basics of radar technology. / Ed. V.V. Druzhinina. M .: Military Publishing House, 1967 .-- 768 p.

5. Radar characteristics of aircraft. / Ed. L.T. Tuchkova. M .: Radio and communications, 1985 .-- 236 p.

6. RF patent No. 2534217 of 11/27/2014. Radar method for detecting stealth unmanned aerial vehicles.

7. Kondratenkov G.S., Frolov A.Yu. Radio vision. Radar systems for remote sensing of the Earth./ Ed. G.S. Kondratenkova. - M.: "Radio Engineering", 2005. - 368 p.

8. RF patent No. 2293350, publ. 02/10/2007. A device for the detection and classification of flying and hovering helicopters (prototype).

Claims (1)

The radar method for detecting aircraft, which consists in emitting sounding radio signals, receiving and performing fast Fourier transform of the reflected radio signals, determining the peaks and amplitude modulation period in the Doppler spectrum of the reflected signal and storing it, characterized in that the probing radio signals emit alternately with linear polarization and quadrature polarization, with each probing radio signal with quadrature polarization synchronized in phase with the previous probe conductive RF signal with a linear polarization spectra comparing the demodulated reflected signals with linear polarization and reflected signals with quadrature polarization and by the presence of period values multiplicity of amplitude modulation judging the detected aircraft.

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