RU2504799C2 - Radar target simulator when probing with primarily long signals - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to devices designed to simulate the frequency-time structure of a radar signal reflected from an underlying surface, from one or more targets, and can be used, for example, to simulate false targets and interference for protecting present targets and to simulate echo signals of radar sets and radar altimeters. Parameters of bright points of targets come from a separate external device. The invention enables to do without a multi-input adder of signals of bright points of targets and a set of modulators that are complex for implementation with a large number of bright points, especially during digital signal processing. Instead of an adder, the disclosed simulator has a synchroniser, one or two switches and a common modulator. In the version with two switches, only one common modulator is used instead of a set of modulators.

EFFECT: simple requirements for the simulator during both analogue and digital signal processing without considerable deterioration of quality of simulated target portraits when probing with primarily long signals.

Description

The invention relates to radar, and in particular to devices designed to simulate the time-frequency structure of a radar signal reflected from the underlying surface from one or more targets located in a fixed direction, and can be used, for example, to simulate false targets and interference for protecting present targets, to simulate the combat operation of a radar system (radar), as well as to simulate the echo signals of radio altimeters (PB) - flight altitude meters.

Depending on the type of signal and radar scanning methods, various methods and algorithms for generating a simulated signal will be optimal. For pulsed radar, the shape of the probing signal is, as a rule, constant and accurately known, therefore, the reflected signal can be prepared in advance in the signal memory taking into account simulation parameters and output to the radar input by the signal of a peak detector detecting the beginning of the probing pulse. In modern radars, to protect against interference, they can use not only a variable modulation period, but also a variable type of the probing signal. Therefore, the calculation of the reflected signal and its subsequent reproduction must be performed in real time based on the received implementation of the signal.

This leads to the need for a direct simulation of the reflected signal as the sum of the signals reflected by various small enough surface areas or equivalent shiny points in comparison with the irradiated area.

A device for simulating radar portraits of real targets [1, p.134-135, Fig.5.2] - figure 1, in which the probe pulse from the radar, for which a radar portrait is created, comes through a receiving antenna, amplifier 1, coarse delay device 2, an accurate delay device 3, modulators of a set of modulators 4 and an adder 10 to the output of the simulator. The coarse delay device 2 carries out a time delay corresponding to the distance to the nearest brilliant point of the simulated target. The delay line with taps 3 provides an imitation of the brilliant points of the target. Amplitude and phase modulations are performed in the modulators of the set of modulators 4 using the reference signals U _i corresponding to the characteristics of the targets. From the outputs of the modulators 4, signals simulating the corresponding brilliant points are fed to the adder 10 and further to the transmitting antenna.

The described simulator device in terms of structure and principle of operation corresponds to a system for increasing the radio frequency response [2], the device of an electromagnetic target generator [3], the method of deceiving a sonar or radar and a false target using this method [4], the method of electronic increasing of radar targets (equipment) [5] , 6].

As a prototype, you can choose a typical device for this task and, being the first chronologically from the scanned literature, a device for simulating high-resolution radar targets [6], which fully corresponds to the above described device for simulating radar portraits of real targets [1], shown in Fig. 1. The presence of the DAC 9 for controlling the modulators of a set of modulators 4 in the form of separate blocks is a feature of a particular hardware solution and is not essential for describing the operation and device of the simulator.

In the practical application of the described methods and devices for simulating radar targets, the accuracy of signal formation is determined not only by the number of taps of the delay line, and by their discrete time, but also by the signal processing method: digital or analog.

For example, with analog processing (see Fig. 1), the signal quality is consistently reduced in devices of coarse and multi-tap delay lines, then in modulators and adders, and the number of DACs used is equal to the number of channels with delay line taps.

Delay lines, modulators and adders can be analog or digital, and the reference characteristics of the target in the simulators are always formed in digital form, so all simulation devices contain a number of DAC and ADC conversion blocks.

To improve the quality of the simulation, the signal formation itself can also be performed digitally on a multi-tap digital delay line 3 and modulators 4 (Fig. 2a, b). In this case, to digitize the input signal, it is sufficient to use one high-speed ADC 8, and to generate the output signal of the simulator, it is necessary to use many DACs 9 and one analog adder 10 (Fig.2a) or a multi-input digital adder 11 and one DAC 9 (Fig.2b).

The notation in FIG. 2: A (f) is the signal from the receiving antenna, X (t) is the signal output to the emitting antenna, U ₁ ... U _n are the amplitude-phase modulation parameters for controlling n modulators.

Additional amplifiers, attenuators for level matching and possible mixers, for example, with a local oscillator signal for matching the working frequency band of signal processing units are not shown, but can be used and calculated in accordance with [7]. To exclude the output signal from the transmitting antenna to the input of the receiving antenna, you can use the circulator, the operation gating and / or spatial diversity of the antennas [1, p. 184]. In stationary tests, it is possible to directly connect cables to the studied radar system without the use of antennas.

When digitally processing a signal using buffers in the memory line of sufficient size as delay lines, it is possible to vary the values of all delays of the shiny points of targets without a separate coarse delay device. At the same time, it is possible to form radar portraits of an arbitrary number of targets of almost arbitrary length with a limit to the total number of brilliant scene points by the capabilities of a hardware solution — the number of individual modulators of a set of modulators 4.

High-speed multi-input digital adder or a set of DACs for each channel with an analog adder are difficult to implement.

The aim of the invention is to simplify the design of signal conditioning devices for a radar target without compromising the quality of simulated radar portraits of targets.

When simulating typical radar targets - aircraft, it is enough to modulate only the individual amplitudes of individual signals, and the Doppler shift simulation can be performed in a separate additional modulator.

This option for generating a signal of a typical radar target is shown in FIG. 3: n multipliers 12 are left by coefficients E ₁ -E _n and an additional modulator 7 for shifting the frequency by an average value f ₀ = mean (f ₁ ... f _n ) corresponding to Doppler shifts n shiny dots of simulated target.

Instead of a multi-input adder 10, in some cases (for signals whose spectral density is currently concentrated in a narrow frequency band, for example, LFM signals of radio altimeters with "slow" modulation), with the correct choice of operation parameters, a switch can be used that cyclically connects one output to one output of n signals.

With a pulsed radar method, the simulated target will flicker. With continuous emission or emission of the probe signal by pulses with a duration longer than n · Δt, where Δt is the duration of the switching interval of each signal, the output signal X (t) (for Fig. 3) will contain equal Δt segments of the emitted signal with a variable delay and phase jumps in switching moments, which in the frequency domain will lead to the fact that harmonics corresponding to the sum and difference of the frequencies of the “useful” signal and the switching frequency multiplied by an integer are added to the original harmonics of the signal. When choosing a switching frequency several times lower than the carrier frequency and outside the band of “useful” signal modulation frequencies, taking into account the actual presence in all radar receivers of limiting signal frequency filters, the resulting signal in the working (usually low-frequency) region will be equivalent in spectral composition to the signal formed by the usual summation of signals. Obviously, with an average value of E _i = Re {U _i } = 1, the output signal from the switch is weaker than n times in amplitude, therefore, we assume that according to the previously introduced notation E _i = n Re {U _i } or multiplication by n is performed in an additional amplifier while matching and ensuring the optimal signal level [7].

Violation of the instantaneous spectra and the appearance of extra phase jumps will not affect the operation of a typical radar, because search / capture / tracking of targets is performed without regard to signal phases with averaging over several resolution elements and, as a rule, over several periods of modulation and scanning. In high-resolution radars with the construction of an image of the background-target environment and recognition of target types, mathematical averaging is also performed over several periods of modulation and scanning.

Thus, the replacement of the adder by the switch as a whole ensures the equivalence of the signal on the time axis and in its working frequency band with respect to the spectral composition with violation of the instantaneous spectra and the appearance of extra phase jumps. Additional research and simulation results will be given after the description of the proposed simulator scheme. The constancy of the amplitude of the output signal of the switch (in the presence of a signal at the input of the simulator) can be compensated in the additional modulator by multiplying by a noise factor with an average value of 1.

When using a switch 6 controlled by a synchronizer 5, it is possible to replace individual amplitude signal transformations by clocking the switch so that the duration of the signal switching intervals is proportional to the corresponding signal amplitudes E ₁ -E _n - Fig. 4. The necessary overall amplification of the amplitude is performed in the additional modulator 7: E ₀ = ΣRe {U _i }. The total frequency shift f ₀ = mean (f ₁ ... f _n ).

To simulate several targets, reflections from the underlying surface with simulated radar movement, it is necessary to use various individual Doppler shifts f ₁ ... f _{n of} all the brilliant points of all targets, which is performed in frequency modulators: (phase) 4, but using a switch 6 controlled by a synchronizer 5 by the values of the amplitude coefficients E ₁ -E _n it is possible to simplify the overall design of the device for generating a signal of a radar target both with analog and digital signal processing without deterioration improve the quality of simulated radar portraits of targets - Fig.5.

Depending on the capabilities of the hardware implementation, it is possible to combine the summation and switching of the signals of individual shiny points of the targets; to change the amplitude and frequency shift, use digital or analog modulators.

The proposed technical solution simplifies the requirements for the equipment of the device for generating a signal of a radar target both with analog and digital signal processing without significant deterioration in the quality of simulated portraits of targets when probing mainly with long signals.

To achieve this technical result, the prototype (patent GB 2134740 [6]), containing a series-connected signal amplifier of the receiving antenna 1, a coarse delay device 2, an accurate delay device 3, the outputs of which are connected to the first inputs of the modulators of a set of modulators 4, is equipped with a synchronizer 5, a switch signal 6 and an additional modulator 7, and from the output of the synchronizer 5 to the additional control input of the signal switch 6, a signal is selected to select the number of the input signal supplied to the switch 6 with the output one of the modulators of the frequency (phase) of the set of modulators 4, the phase or frequency modulation coefficients are supplied to the second inputs of the modulators of the set of modulators 4, the amplitude modulation coefficients are applied to the inputs of the synchronizer 5 to proportionally control the duration of the intervals of the signal 6 switch, the output of the signal 6 switch is connected to the first input of additional modulator 7, phase and amplitude modulation coefficients are supplied to the second and third inputs of additional modulator 7, add the output signal nogo modulator 7 is issued to the transmitting antenna.

The device contains (Fig.6):

1 - amplifier;

2 - coarse delay device;

3 - device accurate delay;

4 - a set of modulators of frequency (phase);

5 - synchronizer;

6 - signal switch;

7 - additional modulator.

The device operates as follows: a probe pulse from a radar, for which a radar portrait is created, comes through a receiving antenna, an amplifier 1, a coarse delay device 2, an accurate delay device 3, a set of frequency (phase) modulators 4, a signal switch 6 and an additional modulator 7 on simulator output. The coarse delay device 2 carries out a time delay corresponding to the distance to the nearest brilliant point of the simulated target. An accurate delay device based on a multi-tap delay line 3 imitates shiny points of a target (s) with individual delays. Individual amplitude and phase modulations are performed using the corresponding coefficients generated by an external device, and the amplitude modulation coefficients are supplied to the synchronizer 5, and the phase modulation coefficients are supplied to the set of frequency modulators (phases) 4. From the outputs of the set of modulators 4 signals simulating the corresponding brilliant points, arrive at the signal switch 6 and then to the additional modulator 7. In the additional modulator 7, additionally specified amplitude and phase modulations are performed ( coefficients f ₀ and E ₀ is formed in an external device). Next, the signal is issued to the simulator output - to the transmitting antenna.

Figure 7 shows an example of modeling and comparing the low-frequency envelope of the signal received at the output after the mixer with a probing signal of a radar with continuous radiation with linear frequency modulation - a beating signal.

The simulated beat signal consists of segments of sinusoids - harmonics corresponding to the simulated range of the brilliant points - figa. Alternation of segments represents the result of switching signals with different parameters. On figb shows the corresponding spectrum of the signal obtained from segments of sinusoids.

It is known that for classical spectral estimates, the height of the spectral peaks serves as a reliable indicator of the relative power of the signal harmonics. In the spectrum of harmonics of the “useful” signal obtained by comparison, the frequencies have from 28 to 45 kHz: in Fig. 7c (enlarged fragment of Fig. 7b), all 6 preset harmonics of the “useful” beat signal are viewed separately, because High signal duration selected. The corresponding initial beat signal during normal summation of sinusoids is shown in Fig. 7d, and its spectrum contains only 6 harmonics and coincides with the spectrum in Fig. 7c.

In the low-frequency region (in the working band of the radar receiver), the harmonic amplitude ratios for the presence and absence of switching are the same, therefore, the received signals will be equally perceived by the radar equipment, which, if there is sufficient resolution, will determine the given simulated values of the range estimates of the corresponding brilliant points of the target's radar portrait.

All the main elements of the signal conversion circuit in the simulator of a radar target when probing with predominantly long signals of FIG. 6 are implemented in analog and / or digital form. To improve the quality of the simulation, it is advisable to perform signal generation in digital form on digital delay lines and modulators, for example, using VLSI 1879BM3 (DSM), you can implement a variable delay line, a frequency shifter of the converted signal, program-controlled switching of several processed signals and other digital processing functions signals [8].

Literature

1. Perunov Yu.M., Fomichev K.I., Yudin L.M. Radio-electronic suppression of information channels of weapon control systems / Under. Ed. Yu.M. Perunova. Ed. 2nd, rev. and add. - M .: "Radio Engineering", 2008. - 416 p. (p. 134-135, fig. 5.2)

2. Patent US 2008/018525. Radio frequency signature augmentation system. Date of publication: 09/23/1986 (Fig. 22)

3. Patent US 5892479. Electromagnetic target generator. Date of publication: 04/06/1999.

4. Patent FR 2596164. Method for deceiving a sonar or radar detector, and a decoy for implementing the method. Date of publication: 09.25.1987.

5. Patent US 4613863. Electronic augmentation of radar targets. Date of publication: 09/23/1986 (Fig. 2)

6. Patent GB 2134740. Electronic augmentation of radar techniques. Date of publication: 08/15/1984.

7. Patent RU 2412449. A simulator of a radar target. Priority Date: 12/26/2008.

8. Integrated circuit 1879BM3 (DSM), Technical description. Version 1.1, UFKV 431268 001 TO1 K, Scientific and Technical Center "Module". M. 2002.

Claims (1)

A simulator of a radar target when probing mainly with long signals, comprising a series-connected signal amplifier of the receiving antenna, a coarse delay device, an accurate delay device, the outputs of which are connected to the first inputs of the modulators of a set of modulators, characterized in that the simulator is equipped with a synchronizer, a signal switch and an additional modulator, from the output of the synchronizer to the control input of the signal switch, a signal for selecting the number of the input signal arriving phase or frequency modulation coefficients are applied to the switch from the output of one of the modulators set of modulators, phase or frequency modulation coefficients are supplied to the second inputs of the modulator set of modulators, amplitude modulation coefficients are supplied to the synchronizer inputs to proportionally control the duration of the signal switch operation, the output of the signal switch is connected to the first input of the additional modulator, to the second and the third inputs of the additional modulator are fed the common phase and amplitude modulation coefficients, the output signal of the additional modulator is issued to the transmitting antenna.

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