RU79186U1 - RADAR DEVICE FOR RECOGNIZING AIR TARGETS INVARIANT TO THE INFLUENCE OF TURBO-SCREW EFFECT - Google Patents

Abstract

Radar device for recognition of air targets, invariant to the influence of the turboprop effect. The utility model relates to radar technology and can be used in target tracking radar. The purpose of the utility model is to ensure the operability of the device for recognition of air targets in the face of the negative influence of the turboprop effect. To solve this problem, it is proposed to additionally introduce a low-pass filter into the circuit of the known device by connecting its input to the output of the receiver. This filter should pass the useful low-frequency signal reflected by the target glider and eliminate high-frequency modulation caused by the turboprop effect. The passband of the filter is chosen smaller in relation to the frequency of the first turboprop components of the spectrum of the reflected signal. When passing through such a filter, the reflective characteristic of an air target gets rid of turboprop modulation and becomes informative for extracting information about the size of air targets. As a result, through the use of an informative feature that analyzes the magnitude of the change in signal levels reflected by targets on each pair of adjacent bearing angles during random yaw, pitch and roll, high recognition accuracy is ensured.

Description

The utility model relates to radar technology and can be used to recognize airborne targets of various classes.

A known radar target recognition device [1], consisting of an indicator and a transceiver containing a generator, a pulse modulator, a power amplifier, an antenna switch, an antenna, first and second mixers, a local oscillator, an intermediate frequency amplifier and a phase detector. In this case, the local oscillator, mixers, an intermediate frequency amplifier and a phase detector are included in the receiver, the generator is connected by its output to the first input of the first mixer and the first input of the power amplifier, the output of which is connected to the antenna through an antenna switch, the output of which is connected to the first input of the second mixer, the second input of which is connected to the output of the first mixer, and the output is connected to the input of the intermediate frequency amplifier, the output of which is connected to the second input of the phase detector, the output of which is connected to the indicator Hur, a first input connected with a local oscillator which is also connected to a second input of the first mixer, and moreover, the pulse modulator output is connected to a second input of the power amplifier.

This device does not provide high recognition efficiency for air targets, since it cannot recognize stationary or inactive targets against local objects and meteorological conditions, as well as targets that have the same radial components of the velocity vector.

A radar recognition device for air targets [2] is also known, containing a recognition unit and a transceiver, and the transceiver includes a pulse modulator, a generator, an antenna connected to its input-output with the input-output of the antenna switch, the output of which is connected to the input of the receiver, the output of which connected to the second input of the first switch, the first input of which is connected to the output of the frequency divider, the input of which is connected to the output of the pulse modulator and the input of the generator, the output of which is is accessed to the input of the antenna switch, and the recognition unit contains a quadrator connected by its output to the input of the first delay line, the first input of the first amplitude storage

with a reset and the first input of the adder, the second input of which is connected to the output of the first delay line, and the output to the input of a half-wave rectifier connected with its output to the first input of the second amplitude storage device with a reset, the second input of which is connected to the output of the second delay line and to the second input the first amplitude drive with a reset, the output of which is connected to the second input of the divider, the first input of which is connected to the output of the second amplitude drive with a reset, and the output to the first input of the second switch, the second input of which is connected with the output of the reset pulse generator and the input of the second delay line, and the output is connected to the input of the identification unit, and the output of the first switch is connected to the input of the quad.

This device is capable of recognizing air targets of various classes in tracking mode with a sufficient probability of correct recognition. The recognition sign Q used in the proposed device and expressing the intensity of the change in the amplitude of the reflected signal in accordance with the view of the location and the size of the targets is a dimensionless quantity that does not depend on the distance to the target, which allows for good quality recognition of targets in a wide range of ranges. However, the used recognition feature Q provides high-quality operability of the device only in relation to targets that do not have open structures of propulsion systems. In the presence of reflections of radio waves from the rotating elements of the propulsion systems, the reflective characteristic of the air target will be modulated (cut) by the turboprop components [3], as a result of which the recognition sign will lose effectiveness. The reflective characteristic of the target is the dependence of the amplitude of the signal reflected by the target on time in real conditions of tracking an air target. This is its difference from the backscatter diagram. For the reflective characteristic, the change in the angular position of the target occurs with a variable angular velocity, which can even change its direction at the attacking angles.

The objective of the utility model is to ensure the operability of the device for recognition of air targets in the face of the negative influence of the turboprop effect (TVE).

To achieve this goal, a low-pass filter is additionally introduced into the known recognition device, the output of which is connected to the second input of the first switch, and the input to the output of the receiver, breaking the connection between the receiver and the input of the first switch.

The proposed construction of the circuit allows the inventive device to recognize air targets of different sizes or configurations in the presence of TVE. Recognition is supposed to be provided, as in [2], by analyzing the magnitude of changes in signal levels reflected by targets on each pair of adjacent bearing angles during random yaw, pitch and roll.

Figure 1 shows the structural diagram of the proposed radar device for the recognition of air targets, invariant to the influence of the turboprop effect.

The device consists of a transceiver 1 and a recognition unit 2.

The transceiver 1 contains: pulse modulator 3, generator 4, antenna switch 5, antenna 6, receiver 7, frequency divider 8, first switch 9, low-pass filter 21. Pulse modulator 3 is connected by its output to the input of the frequency divider 8 and the input of the generator 4, output which is connected to the input-output of the antenna 6 through the antenna switch 5, the output of which is connected to the input of the receiver 7, which contains frequency converters, filters, amplifiers and a detector (not shown in Fig. 1). The video signal from the output of the receiver 7 is fed to the input of a low-pass filter 21, which selects the low-frequency glider component of the reflected signal [3]. The filtered signal from the output of block 21 is fed to the second input of the first switch 9, which, according to the signals supplied to its control (first) input from the output of the frequency divider 8, switches the output signal of the low-pass filter 21 with the output of the first switch 9 (input of the recognition unit 2) according to the law determined by the frequency divider 8.

Recognition unit 2 contains: a quadrator 10, a 1st amplitude storage with a reset 11, an adder 12, a 1st delay line 13, a half-wave rectifier 14, a 2nd amplitude storage with a reset 15, a divider 16, a second switch 17, a reset pulse generator 18, the 2nd delay line 19 and the identification unit 20. In this case, the output of the first switch 9 of the transceiver 1 is connected to the input of the quad 10 connected to its output simultaneously with the first input of the 1st amplitude drive with reset 11, the input of the 1st delay line 13 and the first (inverse) input of the adder 12, the second (direct) input of which is the output of the 1st delay line 13. The output of the adder 12 is connected to the input of a half-wave rectifier 14, the output of which is connected to the first input of the 2nd amplitude storage 15, the output of which is connected to the 1st input of the divider 16 whose second input

is the output of the 1st amplitude drive with a reset 11. The output of the divider 16 is connected to the 1st input of the switch 17, the output of which is connected to the input of the identification unit 20. The output of the reset pulse generator 18 is connected simultaneously with the second (control) input of the switch 17 and input 2 -th delay line 19, the output of which is connected simultaneously with the second input of the 1st amplitude drive with reset 11 and the second input of the second amplitude drive with reset 15.

At the first input of the adder 12, it is assumed that there is an inverter, which ensures the formation at the output of the adder of a voltage proportional to the difference of the signals at its second and first inputs, which is necessary for the correct operation of the proposed device. Unlike the adder, at the output of which the signal amplitude is defined as the sum of the amplitudes of the signals supplied simultaneously to all its inputs, the amplitude storage devices 11 and 15 form a signal at the output equal to the sum of the amplitudes of the signals arriving at its input in series.

A radar device for the recognition of air targets, invariant to the influence of the turboprop effect, works as follows.

In the transceiver 1, using a pulse modulator 3, a high-frequency generator 4 is excited, generating radio signals at the carrier frequency f _o , which, having passed the antenna switch 5, are emitted in the direction of the air target through the antenna 6. The reflected signal is received by the antenna 6 and fed through the antenna switch 5 to the input the receiving device 7, from the output of which the video signal is input to the low-pass filter 21. The low-pass filter 21 extracts its low-frequency component from the received signal [3, 4], due to Reflections of waves only from the glider of an air target. For this, the passband of the low-pass filter should be no more than 500 Hz, because frequencies of turboprop components modulating the reflective characteristic of an air target range from units to tens of kHz [5]. The output signal of the low-pass filter 21 is fed to the input of the first switch 9, which, at the moments when the signal from the output of the frequency divider 8 arrives at its control input, directly transmits the output signal of the low-pass filter 21 to the input of recognition unit 2, namely, to the input of quad 10.

The division coefficient K _{d of} the frequency divider 8 is selected so that the obtained (as a result of dividing the pulse repetition rate F _and pulse modulator 3) the repetition period of the selected pulses T _and ensures the rotation of an air target randomly scouring in the atmosphere with an angular

speed ω _Ψ, the angular value Δψ = ω _ψ T _di = ω _ψ T _and K _d = ω _ψ K _d / F _and. The discretization value according to the location angle Δψ should satisfy the condition for fixing the narrowest lobe of the reflection characteristic at 3-4 points. So for an aircraft with a length of L = 50 m at a wavelength of λ = 2 cm, the width of the lobe of the backscatter diagram according to [6, p.148] will be Δθ≈λ / (2L) ≈ 0.01 °. The value of angular discretization in this case will be Δψ = Δθ / 4≈0.0025 °. Then, even at the maximum angular yaw rate of the glider ω _ψ equal to 2.5 ° / s, the sampling period will be T _di ≈Δψ / ω _ψ ≈10 ^-3 s. Therefore, K _d should be selected based on the ratio of K _d ≈T _di F _and ≈10 ^-3 F _and , i.e. for radars with a repetition rate of F _and = 10 kHz we get K _d = 10.

The low-frequency signal reflected from the target at the video frequency from the output of the first switch 9 is fed to the input of a quad 10, after which it is fed to the inputs of three elements: the 1st amplitude drive with reset 11 (at its 1st input), and the 1st delay line 13 and adder 12 (at its inverse input, called the first). At the output of the 1st amplitude storage device with a reset 11, a signal is generated equal to the sum of the squares of the signals received during a certain time interval from the output of the receiver 7 through the low-pass filter 21 and the first switch 9. The delay line 13 provides a delay of the video signal for a time T _di and, thus , sends from its output a delayed signal to the direct input of the adder 12. In this case, each signal of the i-th time instant on the direct input of the adder 12 corresponds to a signal (i + 1) -th moment of time at its inverse input. In terms of time, the difference in the moments of reception of signals arriving simultaneously at the inputs of the adder 12 is T _di . The output of the adder 12 produces signals equal to the difference of the squares of the signals reflected from the target on each pair of adjacent viewing angles with an angular offset Δψ. The difference signals from the output of the adder 12 are rectified by a half-wave rectifier 14 and fed to the first input of the second amplitude drive 15, which operates similarly to the first shown by block 11. From the output of the second amplitude drive 15, the signal is fed to the first input of the divider 16, the second input of which gives the output signal of the first amplitude drive with reset 11.

At the output of the divider 16, a signal is formed proportional to the ratio of the levels of the signals received at its 1st and 2nd inputs. This signal is fed to the 1st input of the second switch 17, which passes it to the input of the identification unit 20 only when the reset signal arrives at the control input of the switch 17 from the output of the reset pulse generator 18. At the same time

with this unit 18 with a periodicity of the reset interval T _s provides reset signals to the input of the second delay line 19.

The choice of the interval T _{s is} made taking into account the analysis of a sufficient interval of change in the angle (angle of sight) of the target ψ. The width of the narrowest lobes of the backscattering diagram Δθ, as already indicated, in the quasi-optical reflection region is determined by the dependence Δθ≈λ / (2L), where L is the distance between the most distant azimuthal local scatterers on the surface of an air target, i.e. in the centimeter range, Δθ is about 0.01 °. This value corresponds to the angular discretization Δψ≈0.0025 °. The full interval of the change in the angle of the target should correspond to the angular value of the petal of the backscatter diagram of the small-sized target, i.e. be about 0.25 °. Then, for a target with a minimum angular yaw rate equal to, for example, 0.5 ⁰ / s, the reset pulse should be supplied to the second (control) inputs of the 1st and 2nd amplitude drives 11, 15 with a frequency of about 0.5 s. This time determines the duration of one recognition cycle, which corresponds to the time standards for the performance of target recognition devices in modern radars.

Upon the arrival of the reset signal, the second switch 17 passes the signal from the output of the divider 16 to the input of the identification unit 20, where it is compared with a set of threshold signals to determine the class of the target selected for recognition.

The identification unit 20 is a device structurally consisting of a threshold storage unit, a storage device, a comparison circuit, and a result display board (not shown in FIG. 1). The signal from the output of the divider 16 through the 2nd switch 17 is fed to the input of the storage device, which supplies an input signal to the 1st input of the comparison circuit for the period of time necessary to compare the input signal with a set of threshold signals that are supplied alternately to the 2nd input comparison schemes. If the memory signal exceeds the next threshold (thresholds are given in descending order), a signal proportional to the threshold level passes to the output of the comparison circuit. This signal disconnects the threshold storage unit from the comparison circuit and resets the output of the memory device until the start of the next recognition cycle. In addition, this signal enters the scoreboard, in which, in accordance with the level of the input signal, the indicator (LED, lamp) of the recognized target class lights up and locks itself.

A reset pulse delayed in the 2nd delay line 19 by the amount of T _{di is} supplied from its output to the second (control) input of the 1st and 2nd amplitude drives with a reset of 11 and 15 to put them in the zero position, i.e. to prepare for the next cycle of accumulation of reflected signals in the interest of recognizing targets based on the assessment of the Q attribute. This feature in the proposed device, with the exception of the initial recognition cycle, into which the first of the impulses reflected by the target falls, is expressed

Where - the amplitude of the reflected target signal at the output of the receiving device in the next, selected by the first switch 9, the n-th time; N is the number of signals selected by the switch 9 per time interval T _c .

As can be seen from the formula, the recognition sign Q used in the proposed device is a dimensionless quantity independent of the range to the target. This allows you to ensure good quality recognition of air targets, accompanied by radars in a wide range of ranges.

However, with turboprop modulation of the reflected signal, the reflection characteristic of the target becomes very rugged. The presence of unpredictable amplitude emissions in the reflection characteristic leads to a violation of the laws between the size of the air target and the width of the narrowest lobes of the reflection characteristic. In TVE, the narrow lobes of the reflection characteristic belong to the turboprop components [5]. Their width does not depend on the size and configuration of the target. As a result, the recognition sign Q ceases to respond to the indentation of the glider component in the reflection characteristic. To ensure the operability of the recognition sign Q, the reflection characteristic cut by the turboprop modulation (Fig. 2a) must be smoothed, i.e. pass through a low-pass filter. This filter should pass a useful low-frequency signal and eliminate high-frequency modulation. For this, the filter band is selected smaller in relation to the frequency of the first turboprop components of the spectrum of the reflected signal. Since the frequencies of the components of the fuel assemblies lie in the range from units to tens of kHz [5], it is advisable to select the passband of the filter 21 equal to 500 Hz. When passing through such a filter, the reflection characteristic gets rid of turboprop modulation

(figb) and becomes informative for extracting information about the size of air targets.

Thus, the addition of the device circuit with a low-pass filter ensures the achievement of the formulated task of the utility model and the feasibility of using the inventive object in modern and promising radars.

Information sources

1. Aviation radar devices / Ed. P.I. Dudnika. M .: VVIA them. N.E. Zhukovsky, 1986, C.201, Fig. 7.13 (analogue).

2. RF patent No. 2079857. IPC ⁶ G01S 13/02. Radar recognition device for air targets. Mitrofanov D.G., Ermolenko V.P., Maksakov I.M., Anikina E.A. Application No. 95104681. Priority May 31, 1995 Publ. 05/20/97, (prototype).

3. Mitrofanov D.G. The formation of radar images with the negative impact of turboprop modulation. M .: Measuring equipment. Number 7. 2005.S.60-64.

4. Mitrofanov D.G., Prokhorkin A.G., Nefedov S.I. Measurement of the transverse dimensions of aircraft by the frequency extent of the Doppler portrait. M .: Radio engineering. No. 1. 2008.S. 84-90.

5. Radio-electronic systems. Directory. Fundamentals of construction and theory / Ed. J.D. Shirman. - M .: Radio engineering. 2007.510 s.

6. Finkelstein M.I. Basics of radar. - M: Radio and communications, 1983 .-- 536 p.

Claims (1)

A radar recognition device for air targets, invariant to the influence of the turboprop effect, containing a recognition unit and a transceiver, the transceiver comprising a pulse modulator, a generator, an antenna connected by its input-output to the input-output of the antenna switch, the output of which is connected to the input of the receiver, and also the first switch, the first input of which is connected to the output of the frequency divider, the input of which is connected to the output of the pulse modulator and the input of the generator, the output of which is connected It is connected to the input of the antenna switch, and the recognition unit includes a quadrator connected by its output to the input of the first delay line, the first input of the first amplitude storage with a reset and the first input of the adder, the second input of which is connected to the output of the first delay line, and the output to the input a half-wave rectifier connected by its output to the first input of the second amplitude storage device with a reset, the second input of which is connected to the output of the second delay line and to the second input of the first amplitude storage with a reset, the output of which is connected to the second input of the divider, the first input of which is connected to the output of the second amplitude storage with a reset, and the output to the first input of the second switch, the second input of which is connected simultaneously with the output of the reset pulse generator and the input of the second delay line, and the output - with the input of the identification unit, and the output of the first switch, being the output of the transceiver, is connected to the input of the quad, which is the input of the recognition unit, characterized in that the transceiver includes They include a low-pass filter, the output of which is connected to the second input of the first switch, and the input to the output of the receiver.