RU2734233C1 - Device for compensating for direct and reflected from stationary object of radar signals of radio transmitter in bistatic radar system receiver - Google Patents

Abstract

FIELD: radar ranging.

SUBSTANCE: invention relates to radar ranging and can be used to create a radar system receiver using a ground-based probing radio signal as a signal for illuminating aerial targets. Device comprises a quadrature radar signal shaper, an adder, a storage device, a weight coefficient estimating unit, a multiplier, a matched filter, a switch and a control device. This device provides separation of weak radar signal scattered by air target, and allows estimating time of its delay relative to radar signal emitted by radio transmitter. In a similar manner, this device can operate in the presence of reflected radio signals from several stationary objects.

EFFECT: technical result is enabling compensation of direct and reflected from a stationary object of radio signals of a radio transmitter in a receiver of bistatic radar system, which does not require obtaining accurate estimates of parameters of interfering signals: delays, initial phases and amplitudes.

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Description

The proposed invention relates to radar and can be used to create a receiver for a radar system (radar), using the sounding radio signal of a ground transmitter as a signal to illuminate air targets.

Known bistatic radar [1], consisting of a transmitter and a receiver. The work of the bistatic radar is to emit a sounding radio signal by the transmitter, measure the distance to the target and the direction to the target. But in this bistatic radar there is no possibility of compensating for the direct sounding and reflected from the surrounding stationary objects of radio signals, which can enter the receiver in the form of additive signal-like interference.

To compensate for interfering radio signals, spatial selection of useful radio signals is used by adaptive antenna arrays with controlled "zeros" of the radiation pattern, formed in the directions to the sources of interfering signals [2, 3].

However, if the direction from the receiver to the air target is close to the direction to the sounding or reflected radio signal, then along with the interfering radio signals, the radio signal reflected from the air target will also be suppressed.

Known is a device for detecting and evaluating the radio navigation parameters of a signal of a space navigation system, scattered by an air target [4], consisting of a radio frequency unit and two channels - a direct signal channel and a scattered signal channel, a quadrature correlation receiver, a parameter tracking device, a radio frequency unit, a reference generator, a signal recovery device, a memory device, and a subtractor.

In this device, when a weak scattered navigation signal is received by an air target, a powerful direct propagation navigation signal is compensated for, which plays the role of interference. For this, the input implementation is written into the RAM in the form of a mixture of a powerful direct navigation signal, a weak navigation signal scattered by an air target, and the receiver's own noise. The tracking of the direct propagation navigation signal is carried out with an accurate assessment of all its parameters: propagation delay, Doppler frequency, initial phase, amplitude. Using these parameters, a compensation signal is generated, which is subtracted from the stored input implementation. The result of the subtraction will be an approximate estimate of the signal reflected from the air target.

The main disadvantage of this device is the need to obtain accurate estimates of the parameters of all interfering signals: delays, initial phases and amplitudes. To obtain estimates of these parameters, a two-channel receiver is used, in each of the channels of which separate tracking and estimation devices are provided. The latter is characterized by an estimation error of the parameters, and the value of the uncompensated residual will depend on the accuracy of the tracking and estimation device, as well as the number and level of beams that form signal-like interference.

A compensation device for direct and reflected from a stationary object of radar signals of a radio transmitter in the receiver of a bistatic radar system from all available sources was not found.

The aim of the invention is to create a device for compensating direct and reflected from a stationary object radar signals of a radio transmitter in a receiver of a bistatic radar system, which does not require accurate estimates of the parameters of interfering signals: delays, initial phases and amplitudes.

This goal is achieved by the fact that the compensation device for direct and reflected from a stationary object radar signals of a radio transmitter in the receiver of a bistatic radar system consists of a quadrature radar signal generator, an adder, a memory device, a weight coefficient estimation unit, a multiplier, a matched filter, a switch and a control device, which have the following connections among themselves, the output of the quadrature radar signal generator is connected to one of the switch inputs, the output of the storage device and the first output of the control device are connected to the other inputs of the switch, one of the switch outputs is connected to one of the inputs of the storage device, the other input of which is connected to the second the output of the control device, the other output of the switch is connected to one of the inputs of the adder and to one of the inputs of the weighting coefficient estimation unit, the third output is connected to the other input of the block o values of the weighting coefficient and to one of the inputs of the multiplier, in the weighting coefficient block the weighting coefficient is estimated:

w (t + 1) = (1-μ) w (t) + μy (t) × conj (u (t)),

where 0 <μ <1, conj is the operation of complex conjugation, w (0) = 1, y (t) is the signal at the output of the quadrature signal shaper connected after recording copies of the direct and reflected from the stationary object of radar signals, u (t) is the signal generated by the device for storing the quadrature copy of the direct and reflected from the stationary object of the radar signal, the output of the weight coefficient estimation unit is connected to another input of the multiplier, the output of which is connected to another input with a minus sign of the adder, the output of the adder is connected to the input of the matched filter, while the input of the quadrature radar signal generator is connected to the output of the receiver's intermediate frequency filter, and the matched filter output is connected to the input of the control device and to the receiver's radar signal secondary processing device.

The essence of the invention is illustrated by drawings. FIG. 1 shows a block diagram of a bistatic radar system, FIG. 2 shows a block diagram of a device for compensating radar signals of direct and multipath propagation, in which the switch is set to the mode of storing direct and reflected signals; FIG. 3 shows a block diagram of a device for compensating direct and multipath radar signals, in which the switch is set to the compensation mode for direct and reflected signals; FIG. 4 shows the response of the matched filter to the direct and reflected from the stationary object radar signal in the absence of the radar signal reflected from the air target. FIG. 5 shows the response of a matched filter to a radar signal reflected from an air target in the presence of direct and reflected from a stationary object radar signals without compensation, FIG. 6 shows the result of compensation of direct and reflected from a stationary object of radar signals at the output of the adder of the compensation device, FIG. 7 shows the response of the radar signals of the remainder of the direct, reflected from the stationary object and reflected from the air target at the output of the matched filter after compensation.

The compensation device for direct and reflected from a stationary object of radar signals of the radio transmitter in the receiver of the bistatic radar system consists of a ground radio transmitter 1, a ground receiver 2.

In the receiver 2, a compensation device 2.1 of direct and reflected from a stationary object 4 radar signals (Fig. 2) is introduced, consisting of a quadrature radar signal generator 2.1.1, an adder 2.1.2, a storage device 2.1.3, a weight coefficient estimation unit 2.1.4 , multiplier 2.1.5, matched filter 2.1.6, switch 2.1.7 and control device 2.1.8, which have the following connections.

The output of the shaper of the quadrature radar signal 2.1.1 is connected to the input of the switch 2.1.7, the output of the storage device 2.1.3 and the output of the control device 2.1.8 are connected to the other inputs of the switch 2.1.7. One of the outputs of the switch 2.1.7 is connected to the input of the storage device 2.1.3, the other output of which is connected to one of the inputs of the storage device 2.1.3, the other input of which is connected to the second output of the control device 2.1.8, the other output of the switch 2.1.7 is connected to one of the inputs of the adder 2.1.2 and to one of the inputs of the unit for estimating the weight coefficient 2.1.4, the third output is connected to the other input of the unit for estimating the weight coefficient 2.1.4 and to one of the inputs of the multiplier 2.1.5. The output of the unit for evaluating the weighting coefficient 2.1.4 is connected to another input of the multiplier 2.1.5, the output of which is connected to another input with a minus sign of the adder 2.1.2. The output of the adder 2.1.2 is connected to the input of the matched filter 2.1.6. In this case, the input of the quadrature radar signal generator 2.1.1 is connected to the output of the intermediate frequency filter of the receiver 2 (not shown in Fig. 2), and the output of the matched filter 2.1.6 is connected to the input of the control device 2.1.8 and to the device for secondary processing of the receiver radar signal 2 (not shown in Fig. 2).

The quadrature radar signal generator 2.1.1 separates the input radio signal into two quadrature components, the adder 2.1.2 calculates (compensates) the direct and reflected radio signals from the received radio signal, the storage device 2.1.3 stores the quadrature copies of the direct and reflected from the stationary object of the radar signals , the unit for estimating the weighting coefficient 2.1.4 determines the weighting coefficient that compensates for the direct and reflected from the stationary object 4 radar signals, the multiplier 2.1.5 multiplies the mixture of estimating the direct and reflected from the stationary object 4 radar signals by the weighting coefficient, the matched filter 2.1. 6 selects the cross-correlation function of the input radar signal, the switch 2.1.7 switches to write a quadrature copy in the memory 2.1.3 and its compensation, the control device 2.1.8 os it controls the recording of the quadrature copy in the memory 2.1.3 and its compensation in the adder 2.1.2.

The switched on radio transmitter 1 emits a radar signal, which propagates multibeam to the receiver 2: in a straight line, reflected from the local stationary object 4 and reflected from the air target 3, which at this moment may be in the range of the bistatic radar system. At the input of receiver 2, the levels of the direct propagation signal and the signal reflected from the stationary object 4 will be higher than the level of the intrinsic noise of the receiver 2 and significantly exceed the level of the signal reflected from the air target 3. In this case, the level of the signal reflected from the air target 3 will not be exceed the intrinsic noise level of receiver 2. The resulting mixture of signals enters the input of receiver 2, where it is processed, transferred to an intermediate frequency (not shown in the diagram) and then enters the input of the quadrature radar signal generator 2.1.1 of the compensator 2.1.

When the receiver is turned on, the switch 2.1.7 of the compensator 2.1 is set to the position (Fig. 2), at which the quadrature signal y (t) from the output of the quadrature radar signal generator 2.1.1 is fed to the summing input of the adder 2.1.2. To the other (subtractive) input of the adder 2.1.2. no signals are received from the output of the multiplier 2.1.5, since in the storage device 2.1.3 there is no record of the mixture of radar signals and, accordingly, nothing comes from its output to the inputs of the unit for estimating the weight coefficient 2.1.4 and the multiplier 2.1.5. The signal y (t) through the adder 2.1.2 is fed unchanged to the matched filter 2.1.6, tuned to receive the pseudo-random sequence of transmitter 1 and forming at its output the cross-correlation function of the received signal and the pseudo-random sequence of transmitter 1. At the moment of receiving the direct signal from transmitter 1 at the output of the matched filter 2.1.6. a cross-correlation function response will be formed, which is fed to the input of the control device 2.1.8, synchronizing its internal clock generator.

On the leading edge of the response of the cross-correlation function to the forward propagation signal, the control device 2.1.8 switches the switch 2.1.7 to the "setting" position, connecting the output of the shaper 2.1.1 to the input of the memory device for the quadrature copy 2.1.3 (Fig. 3), and the output the storage device 2.1.3 disconnects from the input of the unit for evaluating the weight coefficient 2.1.4 and the multiplier 2.1.5. In this case, the mixture of radar signals is recorded in the storage device 2.1.3. The storage time is counted by the clock pulses coming from the control device 2.1.8, and is equal to t _zap = T _pseud + τ _co , where T _psp is the duration of the pseudo-random sequence, τ _co is the delay of the signal reflected from the most distant local stationary object relative to the signal direct distribution.

After memorizing the mixture of radar signals, i.e. after t _zap , the control device 2.1.8 switches the switch 2.1.7 to the "work" mode (Fig. 2). In this mode, the switch 2.1.7 connects the output of the shaper 2.1.1 to the summing input of the adder 2.1.2 and to the input of the unit for estimating the weight coefficient 2.1.4, and the output of the storage device 2.1.3 switches to the other input of the unit for estimating the weight coefficient 2.1.4 and to the input of the multiplier 2.1.5.

In this case, a mixture of radar signals at an intermediate frequency is still supplied from the receiver 2 to the input of the quadrature signal generator 2.1.1 of the compensator 2.1. In the shaper of the quadrature signal 2.1.1, a signal y (t) is generated, which is transmitted through the switch 2.1.7 to the unit for estimating the weight coefficient 2.1.4 and to the summing input of the adder 2.1.2.

The storage device 2.1.3 generates a quadrature signal u (t), which is a copy of the mixture of direct and reflected from a stationary object 4 radar signals against the background of the receiver's own noise (when recording a copy, the signal reflected from the air target 3 was below the noise level of the receiver). According to the clock pulses of the control device 2.1.8, synchronized with the forward propagation radar signal, the signal u (t) through the switch 2.1.7 enters the unit for estimating the weight coefficient 2.1.4 and the multiplier 2.1.5.

In block 2.1.4, the weighting factor is estimated as follows:

w (t) = (1-μ) w (t-1) + μy (t) × conj (u (t)),

where 0 <μ <1 is a coefficient that affects the speed and accuracy of the weighting coefficient estimate, conj is the complex conjugation operation, w (0) = 1, y (t) is the signal at the output of the quadrature signal generator 2.1.1 (mixture of radar signals) , u (t) - a copy of the direct and reflected from a stationary object of radar signals, generated at the output of the storage device 2.1.3.

The weight coefficient w (t) obtained in the weight coefficient estimation unit 2.1.4 enters the multiplier 2.1.5, into which a quadrature copy u (t) of the sum of the direct propagation signal and the signal reflected from the stationary object is received from the storage device 2.1.3. The multiplier 2.1.5 generates the signal w (t) u (t), which is fed to the subtractive input of the adder 2.1.2. At the same time, the signal y (t) from the quadrature signal shaper 2.1.1 is fed to the summing input of the adder 2.1.2. In the adder 2.1.2, a difference signal y (t) -w (t) u (t) is formed, in which a powerful direct propagation signal and a signal reflected from a stationary object are compensated. The difference signal is fed to the matched filter 2.1.6. In the matched filter 2.1.6, a response is formed to the sum of the direct radar signal, the radar signal reflected from the stationary object 4, as well as the radar signal reflected from the air target 3, which is transmitted to the device for secondary processing of the radar signal of the receiver 2 (in Fig. 1 not shown).

For example, consider the results of attenuation of the proposed compensator of a direct radar signal and a radar signal reflected from a stationary object 4. As a sounding radar signal, we use a phase- _{shift keyed} signal of the M-sequence, with a repetition period T _psp equal to 100 ms. The amplitude of the forward propagation radar signal at the input of the compensation device 2.1 is equal to 100. The amplitude of the radar signal reflected from the stationary object 4 is 50. The amplitude of the radar signal reflected from the air target 3 is 2, which is 50 times less than the amplitude of the forward propagation signal. The radar signal reflected from the air target 3 is delayed relative to the direct propagation radar signal by 225 counts, the re-reflected radar signal from the stationary object 4 is delayed by 48 counts. Direct signal-to-noise ratio in the channel is 16 dB. The amplitudes of the quadrature copies of the direct radar signal and the radar signal reflected from the stationary object 4 at the output of the storage device 2.1.3 are 100 and 50, respectively. FIG. 3 on a logarithmic scale shows the responses of the matched filter to the signals of direct propagation and reflected from the object in the absence of their compensation.

FIG. 4, on a logarithmic scale, the responses of the matched filter 2.1.6 to a radar signal reflected from an air target 3, direct and reflected from a stationary object 4 are shown radar signals without compensation.

From a comparison of the drawings FIG. 3 and FIG. 4 it can be seen that the peak values of the radar signal reflected from the air target 3 lag behind the peak values of the direct propagation radar signal by 225 counts, and the radar signal re-reflected from the stationary object 4 by 48 counts.

FIG. 5 shows the results of compensation of the direct radar signal and the radar signal reflected from the stationary object 4 at the output of the adder 2.1.2 of the compensation device 2.1 at μ = 0.0002. It can be seen from this figure that the levels of the reflected and direct radar signals during the compensation process significantly decrease after about 4 * 10 counts.

FIG. 6 shows the responses of the matched filter 2.1.6 to the received radar signals on a logarithmic scale after compensation of the direct radar signal and the radar signal reflected from the stationary object 4. This figure shows weakened responses to the direct radar signal and the radar signal reflected from the stationary object 4, and also the response to the radar signal reflected from the air target 3 is clearly visible. In this case, the delay of the peak of the radar signal reflected from the air target 3 relative to the direct propagation radar signal is 225 counts, and the radar signal reflected from the stationary object 4 is 48 counts ...

Thus, the proposed device for compensating the direct radio signal of the radio transmitter and the radio signal reflected from the stationary object in the receiver 2 of the bistatic radar system provides the selection of a weak radar signal scattered by the air target 3 and allows us to estimate the time of its delay relative to the radar signal emitted by the radio transmitter 1. Similarly, the proposed device can function in the presence of reflected radio signals from several stationary objects.

Sources of information:

1. Kovalev F.N. V.V. Kondratyev Features of the goniometric-rangefinder method for determining the location of the target in translucent bistatic radars. Journal of Radioelectronics: electronic journal. No. 4, 2014.

2. Widrow B., Stearns S. Adaptive signal processing: Per. from English. M .: Radio and communication. 1989.440 s.

3. Griffiths L. Simple adaptive algorithm for processing antenna array signals in real time // TIIER. 1969. T. 57. No. 10. S. 6-14.

4. Patent 2591052 RF, IPC G01S 5/06, G01S 13/95. A method for detecting and evaluating the radio navigation parameters of the signal of a space navigation system, scattered by an air target, and a device for its implementation. Kiryushkin, D.A. Cherepanov, A.A. Disenov and others 9 p.

Claims (1)

A device for compensating direct and reflected from a stationary object radar signals of a radio transmitter in a receiver of a bistatic radar system, consisting of a quadrature radar signal generator, an adder, a memory device, a weight coefficient estimation unit, a multiplier, a matched filter, a switch and a control device, which have the following connections , the output of the shaper of the quadrature radar signal is connected to the input of the switch, the output of the storage device and the output of the control device are connected to the other inputs of the switch, one of the outputs of the switch is connected to the input of the storage device, the other output of which is connected to one of the inputs of the storage device, the other input of which is connected to the second output of the control device, the other output of the switch is connected to one of the inputs of the adder and to one of the inputs of the weighting coefficient estimation unit, the third output is connected to the other input the unit for estimating the weighting coefficient and to one of the inputs of the multiplier, the output of the unit for estimating the weighting coefficient is connected to another input of the multiplier, the output of which is connected to another input with a minus sign of the adder, the output of which is connected to the input of the matched filter, while the input of the quadrature radar shaper signal is connected to the output of the intermediate frequency filter of the receiver, and the output of the matched filter is connected to the input of the control device and to the device for secondary processing of the receiver's radar signal.

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