RU2246736C1 - Device for detecting moving objects provided with protection against active noise interference - Google Patents

Abstract

FIELD: radiolocation.

SUBSTANCE: device can be used at radiolocation stations with continuous probing signal. Device for detecting moving objects has aerial connected in series with receiver, autocompensator, detector, low frequency filter and solving unit. Device also has additional rejecter filter and one or several compensation channels each of which has aerial connected in series with receiver and rejection filter which has output connected with compensation input of autocompensator. Auotcompensator is brought between receiver of main channel and detector. Additional rejection filter is brought into feedback circuit of autocompensator.

EFFECT: improved autocompensation.

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Description

The invention relates to radar and can be used in radar with a continuous probing signal, in particular in bistatic radar systems according to the method of location “in the light”.

Devices that detect moving objects are considered in [1-3]. A device that implements the method for determining the parameters of the object’s motion, proposed in [3], consists of a spatially spaced transmitting system and a receiving system consisting of a serial connection of an antenna, receiver, detector and low-pass filter (LPF), the output of which is connected to a direction measuring unit the arrival of the interference signal and the Doppler frequency measuring unit connected to the position surface determining unit, which in turn is connected to the input of the trajectory parameter calculation unit to, to the second input of which is connected to the output measure signal arrival directions of the interference block and the yield calculation unit trajectory parameters is the output of the entire device. The blocks for measuring the direction of arrival of the interference signal, measuring the Doppler frequency, determining the position surface and the block for calculating the path parameters together with their connections are a decisive device.

Systems with this principle of signal separation of a moving target belong to radars with external coherence [4, p.146]. The undoubted advantage of this approach is the possibility of autonomous operation of the receiving position, in which there is no need to use the coherent voltage of the transmitter. This in turn leads to a significant simplification and cheapening of the bistatic system as a whole.

A device that implements a method for determining the motion parameters of an object described in [3] is taken as a prototype.

The main disadvantage of the prototype is the complexity of its protection from noise active interference (ShAP). Protection of a radar with a continuous probing signal from ShAP is difficult, because, for example, when using an auto-compensator [5, p. 704-708], the target harmonic signal will be subtracted due to its coherence in the main and compensation channels.

The technical result of the invention is to achieve the effect of auto-compensation of ShAP in a radar with a continuous probing signal.

To achieve this technical result, one or more compensation channels are introduced into the device adopted as a prototype and consisting of a serial connection of an antenna, receiver, detector, low-pass filter and a resolver, each of which consists of a series-connected antenna, receiver and notch filter. An additional notch filter and an auto-compensation unit are also introduced, which is connected between the output of the receiver of the main channel and the input of the detector. The outputs of the notch filters of the compensation channels are connected to the compensation inputs of the auto-compensator, in the feedback circuit of which an additional notch filter is included.

For a more complete understanding of the essence of the claimed device should refer to the following description and drawings illustrating the invention.

Figure 1 presents a functional diagram of a device that implements the claimed invention, where it is indicated:

1 - antenna of the main channel;

2 - receiver of the main channel;

3 - auto-compensation unit;

4 - detector;

5 - low-pass filter;

6 - a decisive device;

7 - antenna compensation channel;

8 - receiver compensation channel;

9 - notch filter;

10 - additional notch filter.

Figure 2 presents the functional diagram of the device adopted for the prototype, where the same designations as in figure 1, are used.

Figure 3 shows one of the options for constructing the auto-compensation unit [5, p. 705], where it is additionally indicated:

11 - multiplier;

12 - integrator;

13 - device for phase rotation by 90 °;

14 - adder;

At _about - the input of the main channel of the auto-compensator;

U _to - input compensation channel auto-compensator;

У∑ - auto-compensator output;

In _wasps - feedback compensator.

The auto-compensator (Fig. 3) has two inputs, one output and includes two quadrature subchannels with real transfer functions K and K⊥. At the output of the device 13 phase rotation by 90 °, a signal U _K форми is formed.

Selection of coefficients in calculating the weighted amount

Y∑ = Y ₀ + KU _K + K⊥ U _to ⊥

provides compensation of mutually correlated noise coming to the inputs. In the gradient search for the optimum [5, p.705], the transfer coefficients at the output of the integrators 12 are equal to:

K = -γ <Y ₀ Y _k > / (l + γ <Y $\genfrac{}{}{0ex}{}{\text{2}}{\text{to}}$ >),

K⊥ = -γ <Y ₀ Y _to ⊥> / (1 + γ <Y $\genfrac{}{}{0ex}{}{\text{2}}{\text{to}}$ ⊥>),

where γ is the coefficient of proportionality.

Figure 4 presents an embodiment of a resolving device 6, discussed in detail in [3]. In figure 4 are indicated:

15 is a block measuring the direction of arrival of the interference signal;

16 - unit for measuring Doppler frequency;

17 - block determining the position surface;

18 is a block for calculating trajectory parameters.

Let us explain the operation of the solving device 6, implemented according to the scheme of figure 4.

It is known [2, p.30] that the Doppler frequency shift (ie, the frequency of the interference signal) for a two-position radar along the path is the transmitting position - target - receiving position is described by the equation

where R ₁ (t) is the distance from the transmitting position to the target,

R ₁₀ (t) is the distance from the target to the receiving position.

It is quite obvious that when the target approaches the baseline (line L, the straight line connecting the transmitting and receiving positions), the frequency Fd decreases and vanishes at the time t = t ₀ where the target is on line L. At this moment, the function R∑ (t) has a minimum value equal to L. From equation (1) it follows that

where R∑ - total distance transmitter - target - receiver;

λ is the radiation wavelength;

t ₀ is the instant of transition of the frequency of the interference signal through zero;

Fd is the frequency of the interference signal;

L is the distance between the transmitting and receiving positions.

It is shown above that at the moment t ₀ , when Fд (t ₀ ) = О, R∑ (t ₀ ) = L. Thus

If, from the moment of detecting the target (t = 0), Fd is measured, then for any moment, both preceding t ₀ and the next, the value R∑ (t) can be determined. This value, as is known [1, p.560], determines the position surface in space (ellipsoid) or the position line (ellipse) on the plane with the foci at the location of the transmitting and receiving positions. This operation is performed in the block determining the position surface (block 17).

In parallel with the Fd measurement, the bearing is measured to the target. The bearing is determined in the unit for measuring the direction of arrival of the interference signal (block 15) by the maximum of the envelope of the signal at the low-pass filter output generated by scanning the beam of the radiation pattern of the radar antenna, or by a single-pulse method with a multipath beam of the radar antenna. The spatial coordinates of the target are determined in the block for calculating the trajectory parameters (block 18) at the intersection of the bearing line and the surface (or line) R∑ (t).

If the detection and, accordingly, the measurement of the Doppler frequency and the bearing are carried out discretely in time, then known approximate methods can be used to determine the coordinates. So, for example, in case of equidistant in time detection, recurrence relations can be used:

...

where Δ _t is the detection period,

Figure 5 shows the dependences of the signal amplitude in the unit for measuring the Doppler frequency (curve 1), the measured Doppler frequency (curve 2) and the measured azimuth of the target (curve 3) in the unit for measuring the direction of arrival of the interference signal for a target of the Mi-8 type.

Figure 6 shows the trajectory of the target built in the unit for calculating the trajectory parameters, such as the Mi-8 helicopter (curve 1) and its true trajectory (curve 2).

The proposed device for the detection of moving objects with protection from active noise interference consists of a series-connected antenna 1, receiver 2, auto-compensator 3, detector 4, low-pass filter 5, resolver 6 and one or more compensation channels, each of which consists of a compensation antenna 7 channel, receiver 8 of the compensation channel and notch filter 9, the output of which is connected to the compensation input of the auto-compensator 3. An additional notch filter 10 is included in the feedback circuit and auto-compensator 3.

The inventive device operates as follows. The transmitting system irradiates the sector, in the direction of the receiving system, with a continuous quasi-monochromatic signal. The input signal of the main channel antenna 1 receives the total signal generated by interference of the direct signal of the transmitter and the signal reflected from the target, and through the receiver 2 of the main channel is fed to the input of the auto-compensator 3, to the compensation input of which from the receiver 8 of the compensation channel through the notch filter 9 the signal received by the compensation antenna 7. Autocompensator 3 provides compensation for mutually correlated interference received at its inputs. Noise active interference (ShAP) is subtracted in accordance with their correlation coefficient in the main 2 and 8 compensation receivers. In the feedback circuit of the auto-compensator 3 and at its compensation input there are notch filters 10 and 9, the band of which is chosen equal to the band in which the spectrum of the target signals is located taking into account the temporary departures of the transmitter frequency.

Notch filters are introduced to adjust the auto-compensator outside the band of possible arrival of target signals. At the target signal, the auto-compensator 3 will not be tuned and the narrow-band target signal from the output of the auto-compensator 3 is fed to the input of the serial connection of the detector 4 and the low-pass filter 5, where low-frequency oscillation is detected and highlighted.

Further, from the output of the low-pass filter 5, the low-frequency oscillation is fed to the input of the deciding device, namely, to the input of the block 15 for measuring the direction of arrival of the interference signal, where the bearing is measured at the target by the maximum envelope of the signal at the output of the low-pass filter 5, and to the input of the block 16 for measuring the Doppler frequency, where the Doppler beats of the signal of moving targets are distinguished by the method of spectral analysis. Since the signal from a moving object has a continuous harmonic character, it is effectively accumulated. If the Doppler frequency exceeds the detection threshold, the level of which is determined by the specified probability of false alarms, a sign of target detection is formed.

Doppler beats of the target signal are input to the block 17 of the position surface, where the position surface is determined.

Further, based on the data obtained from the block 15 for measuring the direction of arrival of the interference signal and the block 17 for determining the position surface, in the block 18 for calculating the path parameters, the path parameters of the target are determined.

The spatial coordinates of the target are uniquely determined as the coordinates of the point of intersection of the position surface and the direction line to the target from the receiving position (bearing line). The output of the decider 6 is the output of the entire device.

Depending on the method used to determine the direction of arrival of the interference signal, the block 15 for measuring the direction of arrival of the interference signal can be performed on the basis of various blocks. For example, in the case of a monopulse phase determination method, block 15 may be a phase meter; in case of a single-pulse amplitude method, block 15 may be performed on the basis of amplitude comparison schemes or subtraction schemes.

The Doppler frequency measuring unit 16 may be a low-frequency frequency meter, for example, a spectrum analyzer or a Doppler filter unit.

The position surface determining unit 17 integrates the input voltage with subsequent scaling.

The trajectory parameter calculating unit 18 performs functional transformations of the input oscillation, which can be described as simple dependences of the output voltage on the input signal. The main elements of this block can be multipliers and adders.

The blocks used in the inventive device can be implemented both on typical radio engineering elements, and programmatically on a special computer.

The achievement of the technical result in the proposed device for protection against active noise interference is determined by the fact of the difference of the spectra - ShAP and the target signal. The ShAP spectrum is broadband and occupies the entire receiver band (at least 0.3-0.5 MHz). The Doppler spectrum of target signals in a bistatic radar is narrow-band (no more than 1 kHz) near the transmitter radiation frequency. Taking into account temporary departures of the transmitter frequency, the spectrum of target signals is in a band not exceeding 50 kHz. The magnitude of the notch filter band is selected of this magnitude.

Thus, in the proposed device, the auto-compensator (AK) is configured outside the band of possible arrival of target signals, outside the band of 50 kHz. For this, notch filters are introduced at the input of the compensation channel AK and in its feedback circuit. AK will not tune in to a signal from targets. As a result, the ShAP in the AK is subtracted in accordance with its correlation coefficient in the main and compensation receivers [5, p. 704–708], and the narrow-band target signal passes through the AK and after the detector and low-pass filter is fed to the input of the decider, where it is effectively accumulated , and when the threshold of the solving device is exceeded, a detection signal is generated.

The mathematical modeling showed that the proposed device for detecting moving objects has effective protection against active noise noise and practically does not weaken the signal amplitude of a narrow-band target.

The inventive detection device with protection against ShAP is supposed to be implemented in the 52E6M radar, currently being developed by the Nizhny Novgorod Research Institute of Radio Engineering.

Literature

1. Theoretical foundations of radar. / I.D. Shirman, V.N. Golikov, I.N. Busygin and others. Ed. Y.D. Shirman - M .: Sov. Radio, 1970, p.560.

2. B.C. Chernyak, L.P. Zaslavsky, L.V. Osipov. Foreign Radio Electronics, 1987, No. 1, pp. 29-30.

3. Blyakhman A.B., Samarin A.V. Radar method for determining the movement of an object. Patent No. 2133480 with priority from 02/02/98 (prototype).

4. I.S. Gonorovsky. Radio engineering circuits and signals, part 2 - M .: Sov. Radio, 1967, p.146.

5. Radio-electronic systems: fundamentals of construction and theory. Directory. Ed. Professor Y.D.Shirman. Moscow, ZAO MAKVIS, 1998, p. 704-708.

Claims (1)

A device for detecting moving objects with protection against noise active interference, comprising a series-connected antenna, receiver, detector, low-pass filter and a resolving device, characterized in that an auto-compensator, an additional notch filter and one or more compensation channels are introduced, each of which consists of a serial connecting the antenna, receiver and notch filter, the output of which is connected to the compensation input of the auto-compensator connected between the receiver of the main channel and detector, and an additional notch filter is included in the feedback loop of the auto-compensator.

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