Simulator of false radar target during linear frequency-modulated signal probing

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to devices for simulating the frequency-time structure of a radar signal reflected from an underlying surface, from one or more targets lying in a fixed direction, and can be used to simulate false targets, including targets near a carrier, for simulating combat performance of a radar system and for simulating echo signals of radar altimeters when probing with signals with different types of linear frequency-modulation. The invention enables to simulate two identical targets independent of the direction and combination of signs of the rate of linear variation of frequency, wherein the first target, which is the primary target, can be simulated in a range shorter than the range of the radar carrier, and the second target will be treated according to range and with appropriate selection of parameters, will not hinder correct monitoring of the primary target.

EFFECT: simulating a target with a range greater than or shorter than the range of the carrier with both analogue and digital processing of the signal without deterioration of quality of the simulated images of the targets.

2 cl, 6 dwg

The invention relates to radar systems, and in particular to devices designed to simulate the time-frequency patterns of the radar signal reflected from the underlying surface, from one or more targets in a fixed direction, and can be used, for example, to simulate a false goals, including those located closer to the medium to simulate combat operation of a radar system (radar), as well as to simulate the echoes radio altimeters (PB) - measures altitude, operating with signals with linear frequency modulation (chirp).

Depending on the type of signal and methods of scanning radar optimum will be a variety of methods and algorithms simulating signal. For radar pulse shape of the probing signal, usually constant and accurately known, so the reflected signal can be prepared in advance in the signal memory within the parameters of the simulation and issued to the input radar signal peak detector detecting the beginning of the probe pulse. In modern radars for more information about the purpose may use frequency modulation with variable parameters. Therefore, the calculation of the reflected signal and its subsequent reproduction must be performed in real time on the basis of taking the emnd realization of the signal, keeping the possibility of further coherent processing in radar systems.

Similarly, in most RV with the chirp currently witness the reception of the reflected signal with the stabilization of the ranging frequency due to the change of the modulation parameters. The parameters of the probing signal when data movement parameters over the surface with the given statistical characteristics have random variations due to the random nature of even small irregularities of the underlying surface. This fact excludes the possibility of pre-calculation of the reflected signal even in the case of deterministic trajectories and simulated topography of the underlying surface.

This leads to a direct simulation of the reflected signal as a sum of the signals reflected different rather small compared to the irradiated area of the surface shiny or equivalent points.

A device for simulating radar portraits of real purpose [1. str-135, RES], in which the probe pulse from the radar to generate radar portrait, passes through the receiving antenna, the amplifier, the unit coarse delay device for the precise delay, set of modulators and the adder to the output of the simulator. The unit coarse delay provides for the Erico time, corresponding to the distance to the nearest shiny point of the simulated target. The delay line with taps provides a brilliant imitation of target points. Amplitude and phase modulation are performed using reference signals corresponding to characteristics of targets. With modulator output signals simulating the corresponding brilliant point, proceed to the adder and further to the transmitting antenna.

The described device simulator according to the structure and functioning principle corresponds to the system increasing the frequency response [2], device generator of electromagnetic targets [3], the method of deception sonar or radar and false goals using this method [4], the method of electronic zoom radar is solid (technique) [5, 6].

As a prototype, you can choose the model for this task and which is viewed from the literature chronologically the first device to simulate radar targets with high resolution [6] - 1. The presence of a DAC to control the modulators and devices coarse delay in the form of individual blocks is a feature specific hardware solution and not principally for job description and device simulator.

In the practical application of the described methods and devices simulate radar portraits with variable modulation parameters arises the problem is and simulation purposes with a range less than the range of the carrier, protected from the running of the station. Similar difficulties arise in the use of simulators signal to study the characteristics of the radio altimeters with scaled-down modeling work in the laboratory: it is impossible to provide a simulated signal with a delay less than the length of the signal paths in processing and forming simulating signal.

Today, even in the best known schemes DSP memory minimum delay is 40 NS, which corresponds to a distance of 6 meters With regard to use in real simulators amplifiers, attenuators, cables corresponding simulated minimum distance (from the beginning of the input signal) is 10-20 m or more, which limits how the possibility to hide the true position of the carrier, protected from radar high resolution and the possibility of imitation low altitudes when checking radio altimeters.

In radar and radio with continuous radiation is used probing signals with linear frequency modulation (chirp). In this case, to retrieve information about the distance is measured fundamental frequency or harmonics are investigated frequency spectrum of the so-called converted signal obtained at the output of the mixer of the transmitted and received signals.

The operation of the radio altimeter with C is unbalanced, the chirp (SLCM) signal at a constant distance to the surface explains the timing diagram of figure 2. Upper graph describes the change in frequency of the emitted (solid line f_And) and accept (dotted line f_Withvibrations with an average frequency f₀the modulation period T_Mand frequency deviation of W. the Lower graph reproduces the change in the differential distance measuring frequency F_D. The frequency of the radiated oscillations f_Andvaries continuously linearly with speed Y_M=df_And/dt=2W/T_M:

$$f_{\mathrm{And}}=f_0+Y_{M}t=f+\frac{2W}{T_M}t$$.

The frequency of the received oscillations f_Withsimilarly varies continuously in a linear fashion, but delayed by the propagation time of the signal τ_D=2H/C, where C is the speed of light:

$$f_C=f_0+Y_M(t-t_D)=f+\frac{2W}{T_M}\left(t-\frac{2H}{c}\right)$$.

From area the frequency difference between the emitted and the received oscillations, determine the distance measuring frequency F_D, also called the frequency of the beating:

$$F_D=f_{\mathrm{And}}-f_C=\frac{4W}{c{T}_M}H.\text{(1)}$$

The resulting expression does not take into account the failures of the curve F_D(t) in the areas of treatment when f_and≈f_with., when considering which frequency will record the average frequency of the beating over the modulation period:

$$F_{D_{\mathrm{with\; a}p}}=\frac{4W}{c{T}_M}H\left(\frac{T_M-t_D}{T_M}\right)$$.

If the condition τ_D<<T_Mthe treatment zones can be neglected, the average frequency of the beating F_Dcp≈F_D. Therefore, when SLCM height H is proportional to the frequency of the beating:

$$H=\frac{c{F}_{D\mathrm{with\; a}p}}{4W}{T}_M\approx \frac{c{F}_D}{4W}{T}_M$$

It is known that the Doppler shift and time delay of the reflected chirp signal can be simulated by the corresponding offset of the carrier frequency [9, 10]. Therefore, to reduce the minimum simulated height and compensate its own delay in any hardware implementation may use a specific frequency shift: a radio altimeter with an asymmetric chirp (NLCM) will register the equivalent of a small height, if the signal processing to perform additional frequency shift Δf in the direction of "social glue" on the measuring plot graphs of f_suc(t) and f_forms(t) - figure 3. The frequency of the beating: f(t)=f_suc(t)-f_forms(t). In non-growing pile chirp in the main part of the measuring area (excluding the area of treatment) f(t)=const=Fb. It is seen that a positive frequency shift Δf signal, delayed by τ_minwill lead to a decrease in the values of the average frequency of beating Fb and, consequently, to reduce the height to be measured.

The application of this method at SLCM in the main part of the measuring area (excluding the area of treatment) will give 2 frequency beating: a positive frequency shift Δf signal, delayed by τ_minthat will decrease the value of Fb in one half-cycle and the same increased the Yu Fb in the second half. If the transmitter of such a radar worked on the leading edge of the spectrum, the task of reducing the measured distance would be solved. But, for example, used SLCM RV uses an estimate of the distance according to frequency of beats corresponding to the center of gravity of the spectrum, averaged over the entire modulation period, so this splitting of the main harmonics of the spectrum will not affect the measured height value in the RV.

The aim of the invention is to simulate targets with range less than the range of media without compromising the quality of the simulated radar images of targets when the sensing signals with different types of linear frequency modulation.

Figure 4 shows the principle of the formation of harmonics spectrum envelope of the signal beating with SLCM: to reduce the simulated height of each harmonic with τ<τ_minis replaced by two harmonics with τ=τ_formsand for the first (f_And-f_C1) was made positive, and the second (f_And-f_C2) negative offset frequency Δf.

As a result of this option produces a splitting of the spectra at each point in time (and in the first and second half-periods): harmonics with τ<τ_minform two pairs of envelope spectrum, spaced along the frequency axis at 2 Δf. By varying only the value of τ_forms≥τ_minyou can choose a constant value Δf, the pain is half the bandwidth of the filter signal beating; to calculate the delay τ_formscorresponding to H_forms.

Optional, but improves the perception of harmonic (f_And-f_C0) corresponds to the signal with a delay τ_minno shift in frequency, its position in both half cycles of the modulation period in figure 4, it forms the caudal part of the low-frequency envelope of the signal spectrum of the beating.

As a result, when the processing in the receiver radio and radar high-frequency harmonics will be suppressed or discarded, because the simulated range are far from the goal, and the measured value range goal will be to match the center of gravity of the low-frequency envelope of the spectrum with a smaller value of the simulated height.

The proposed technical solution is the simulation of a target with a range of more or less than the range of the carrier sensing signals with different types of linear frequency modulation without compromising the quality of simulated images of targets. In this case, to simplify the design can be shifted over the entire range radar portrait objectives without consideration of the ability simulate some part of it (for example, harmonics of f_C04) using only the delay lines.

To achieve this, the technical result of the prototype (patent GB 2134740 [6]), containing connected in series amplifier signal receiving antenna and lots of the gate delay line, the outputs of which are connected with the first inputs of the set of modulators, the second inputs of which are the coefficients of the amplitude-phase modulation, and outputs which are connected with the inputs of the adder is supplied to a variable delay line, the two devices of the frequency shift and the second adder, and to the first input of the variable delay line receives the signal from the output of the adder, the second input signal, the delay "τ", which determines the offset of the simulated target range down (when τ<Δf/V_fwhere V_fmodule speed ramp frequency radar, Δf is a parameter chosen approximately equal to or greater than the width of the electoral filter capture/tracking radar) or higher (when τ>Δf/V_f), and the output of the variable delay line connected to the inputs of the two devices of the frequency shift, the frequency shifts are performed on the same value "Δf", but with opposite signs: "+Δf and-Δf", the output signals of the devices of the frequency shift is coming to the inputs of the second adder, the output signal of which is issued to the transmitting antenna.

The device comprises (figure 5):

1 - power;

2 - multi-tap delay line;

3 is a set of modulators;

4 - the first adder;

5 - the variable delay line;

6 - the unit of frequency shift "+Δf";

7 - the shifter is astate "-F";

8 - the second adder.

The device of figure 5 operates as follows: the probe pulse from the radar to generate radar portrait comes from the receiving antenna through the amplifier, multi-tap delay line, a set of modulators, the first adder, delay, frequency shift and the second adder to the output of the simulator. Multi-tap delay line provides a simulation brilliant points objective (s) with individual delays. Individual amplitude and phase modulation are performed using the respective coefficients generated by an external device. Depending on the values of the delay τ in the delay line is the simulated displacement of the simulated target range relative to the range of media:

in the smaller side when τ<τ₀=Δf/V_f,

in a big way when τ > τ₀,

where τ₀- delay in the simulator, in which the offset of the target is missing;

V_fmodule speed ramp frequency radar,

Δf is the option chosen approximately equal to or greater than the width of the electoral capture filter and target tracking in radar.

When τ=0 and a constant value of the velocity modulus linear change of frequency of the radar position of the simulated target range decreases by the amount of

$$\Delta R_{mi>\; max}=\frac{c{t}_0}{2}=\frac{c\Delta f}{2V_f},\text{(3)}$$

where C is the speed of light.

A feature of the described solutions to build a simulator is that regardless of the direction and character combination of speed ramping frequency radar simulated two identical goals, and the first - main - aim can be simulated at a range less than the range of media radar, and the second goal will be assigned range by 2·ΔR_maxand with proper selection of values of Δf will not interfere with the correct tracking radar for the main purpose. The value Δf is chosen approximately equal to or greater than the width of the electoral capture filter and target tracking in radar, however, in compliance with the conditions of correct processing of the received signal in the radar: τ₀<<T_Mand, therefore, Δf<<T_M·V_fwhere T_Mthe modulation period.

During the ground tests SLCM radio and radar described solution allows you to compensate for your own hardware delay circuit simulator and to provide simulation ranges from 0 m while maintaining all of the hardware and functionality of the simulation of the complex.

In modern radio and radar is the chirp to improve the accuracy of the work can vary not only the sign, but the value of the linear speed of frequency change. In this case, the dependence of ΔR_maxfrom V_fis not directly proportional, but can be found in the well-known principle of operation of radar in the case of dependence of the parameters of the linear frequency modulation of the value of the measured range goals.

Assume that the radar performs tracking range goals so that the signal frequency of the beating was a constant: F_D=const. Then from (1), given that when SLCM V_f=2W/T_Mwill get:

$$V_f=\frac{c{F}_D}{2H}.\text{(4)}$$

In some cases, the exact values of F_D, H, V_funknown, it is therefore desirable to provide a simulator of radar targets with an independent assessment of the current values of parameters of a linear frequency modulation. Direct measurement of current values of W and T_Mdifficult, as it requires the use of signal processors, when tested in laboratory conditions it is possible to get the parameters from radar on additional interface [11].

But, in General, it is possible to estimate the values of V_fdirectly on the input signal using the sample further machining work : the first line delay τ _refand mixer detainee and nesuderinama signals [12]. For NLCM and SLCM modulation signal frequency f_refgenerated at the output of the mixer is proportional to the desired value V_f:

$$V_f=\frac{f_{ref}}{t_{ref}}.\text{(5)}$$

As a signal with an exemplary delay line τ_refcan be taken signal from any convenient for subsequent processing of the output tap of the delay line 2.

For independent determination of the parameters of a linear frequency modulation radar device 5 is further provided with series-connected mixer and forming device delay, and to the inputs of the mixer receives signals from the output of the amplifier and a single output multi-tap delay line, the second input device formation delay comes the size of the desired offset of the signal in the delay Δτ, and the output connected with the control input of the delay line.

The device includes (6):

1 - power;

2 - multi-tap delay line;

3 is a set of modulators;

4 - the first adder;

5 - the variable delay line;

6 - arrange the creation of the frequency shift "+Δf";

7 - the unit of frequency shift to the "-F";

8 - the second adder;

9 - mixer;

10 - forming device delay.

The device of figure 6 operates in a similar manner as previously described for figure 5, but at the inputs of the mixer 9 receives signals from the output of the amplifier 1 and a single output multi-tap delay line 2, thus at the output of the mixer, a signal is generated f_refwith which the device formation delay of 10 according to expression (5) is the value of the rate of change of frequency V_fand later on coming from external devices to the value of the desired offset of the signal in the delay Δτ, and the expression (6) is the delay value τ of the variable delay line 5:

$$t=\Delta t+\Delta f/V_f-t_{\mathrm{int}}=\Delta t+\Delta f\frac{t_{ref}}{f_{ref}}-t_{\mathrm{int}},\text{(6)}$$

where τ_int- private (internal) delay in the circuit simulator;

Δτ is the desired offset signal delay: when reducing the simulated range or compensate for its own delay - knowledge which begins with a minus sign.

In the practical implementation of the delay line modulators and combiners can be analog or digital. To improve the quality of the simulation, the signal processing can be performed in digital form on a digital delay lines and modulators, for example, using VLSI 1879BM3(DSM) [8], it is possible to implement a variable delay line in the form of a ring buffer in the internal RAM with software-controlled frequency shift is converted signal. Additional amplifiers, attenuators to negotiate levels and possible faucets, for example, with the lo signal for the coordination of the working bandwidth of the signal processing units figure 5, 6 are not shown, but can be used and calculated in accordance with [7].

To prevent the output signal from the transmitting antenna to the input of the receiving antenna, you can use the circulator, the Gating operation and/or space diversity antennas [1, str]. When stationary tests possible direct connection of cables to the analyzed radar system without the use of antennas.

Literature

1. Perunov, Y.M., Fomichev SURDS, Yudin L.M. Electronic suppression of information channels control systems weapons / Under. Ed. Umirov. Ed. 2nd, Rev. and more. - M.: "radio", 2008. - 416 S.

2. Patent US 2008/018525. Radio frequency signature augmentation system. Date of the public, the tion: 23.09.1986 (Fig)

3. Patent US 5892479. Electromagnetic target generator. Publication date: 06.04.1999.

4. Patent FR 2596164. Method for deceiving a sonar or radar detector, and a decoy for implementing the method. Publication date: 25.09.1987.

5. Patent US 4613863. Electronic augmentation of radar targets. Publication date: 23.09.1986 (2)

6. Patent GB 2134740. Electronic augmentation of radar techniques. Publication date: 15.08.1984.

7. Patent RU 2412449. Simulator of radar targets. Publication date: 10.07.2010,

8. Chip integrated 1879BM3(DSM), Technical description, Version 1.1, UFCW 431268 001 TO1, Scientific-technical centre "Module". M. 2002.

9. Vinitsky A.S. Essay fundamentals of radar with continuous exposure. M: Owls. radio, 1961. - 496 S.

10. The summary : modified compositions obtained V.V. features of the simulated reflected signal for radar chirp / Cam, A.A. Shcherbakov // Izvestiya vuzov. The electronics. M. 1987, C. P. 84-86.

11. Patent US 7327308. Programmable method and test device for generating target for FMCW radar. Publication date: 05.02.2008.

12. Patent US 4661818. Electronically adjustable delay-simulator for distance-measuring apparatus operating on the frequency-modulated continuous wave principle. Publication date: 28.04.1987.

1. The radar simulator aims at probing mainly long signals containing connected in series amplifier signal receiving antenna and multi-tap delay line, the outputs of which are connected with the first inputs of the set of modulators, the second inputs of which are the coefficients of the amplitude-phase modulation, the outputs of which are connected with the inputs of the adder, characterized in that it is equipped with a variable delay line, the two devices of the frequency shift and the second adder, and to the first input of the variable delay line receives the signal from the output of the adder, the second input signal, the delay "τ", which determines the offset of the simulated target range down (when τ<Δf/V_fwhere V_fmodule speed ramp frequency radar, Δf is a parameter chosen approximately equal to or greater than the width of the electoral filter capture/tracking radar) or higher (when τ>Δf/V_f), and the output of the variable delay line connected to the inputs of the two devices of the frequency shift, the frequency shifts are performed on the same value "Δf", but with opposite signs: <<+Δf>> and <<-Δf>>the output signals of the devices of the frequency shift is coming to the inputs of the second adder, the output signal of which is issued to the transmitting antenna.

2. The radar simulator aims at probing mainly long signals according to claim 1, characterized in that it is equipped with series-connected mixer and forming device delay, and to the inputs of the mixer receives signals from the output of the amplifier and a single output multi-tap delay line, the second input device formation delay posturetoken the desired offset of the signal in the delay Δτ", and the output is connected to the second input of the delay line.