RU2327185C1 - Nonlinear radar for eavesdropping devices - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: nonlinear radar contains a reference amplifier, a frequency divider, a linear FM generator, five band-pass filters, two units of the FM linear probing signal generation, two power amplifiers, a lower frequency filter, receiving and transmitting antennas, two mixers, a receiver, an indicator, two gates, two directional couplers, a power adder and HF amplifier interconnected so that, apart from reducing the probing signal harmonics coming into the receiver from both the transmitting antenna and those reflected by the underlying surface, it ensures a frequency isolation of a useful signal from the noise, given there are no time differences between them, thus allowing the detection of radio electronic devices in the search near zone.

EFFECT: wider zone of nonlinear objects detection.

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Description

The invention relates to the field of radar and can be used in the development of portable non-linear radars for detecting listening devices.

Nonlinear radars are known [Andreev G.A., Potapov A.A. Millimeter waves in radar. Target indication systems. Foreign electronics, No. 11, 1984, and US patent No. 4053891, G01S 9/02, 1977], which contain a series-connected master oscillator, power amplifier, low-pass filter and a transmitting antenna, as well as a series-connected receiving antenna, a bandpass filter, a receiver and an indicator device, while the second input of the power amplifier is connected through a series-connected modulator and synchronizer to the second input of the receiver.

The above non-linear radars cannot be used to measure the distance to radio sources.

Known non-linear radar for the detection of executive electronic control devices for explosion [Russia. Patent for invention No. 2234715 G01S 13/26, publ. August 20, 2004], containing a reference oscillator, a frequency divider, a linear frequency-modulated oscillator, the second input of which is connected to the output of the reference oscillator, a power amplifier, a low-pass filter and a transmitting antenna, as well as a series-connected receiving antenna, the first bandpass a filter, a mixer, a second band-pass filter, a receiver and an indicator device, while the second input of the mixer through a series-connected third band-pass filter and amplifier-limiter is connected to output of a linear frequency-modulated generator.

In this radar, in the absence of differences in range between the desired object and local objects on the screen of the indicator device, the selection of a useful signal from interference is impossible.

The closest in technical essence to the proposed one is a non-linear radar for detecting executive radio-electronic explosion control devices according to the invention patent No. 2251708, GO1S 13/02, publ. May 10, 2005, taken as a prototype.

The prototype device contains a series-connected reference oscillator, a first frequency divider, a linear frequency-modulated generator, the second input of which is connected to the output of the reference generator, the first and second band-pass filters, the output of the first band-pass filter through a series-connected second frequency divider, a sixth band-pass filter, third mixer, seventh band-pass filter, block for generating a probing linear frequency-modulated (LFM) signal, power amplifier and low-pass filter access to the transmitting antenna, a receiving antenna connected in series, a third bandpass filter, a first mixer, a fourth bandpass filter, a second mixer, a fifth bandpass filter, a notch filter, a fourth mixer, an accurate selection filter unit, a receiver and an indicator device, the second input of which is connected to the output the first frequency divider, and the second input of the third mixer is connected to the output of the reference generator and the input of the heterodyne voltage generation unit, the corresponding outputs of which are connected to respectively to the second inputs of the second and fourth mixers, and the output of the second bandpass filter through a heterodyne unit for forming a linear frequency-modulated signal is coupled to a second input of the first mixer.

In practice, the search for eavesdropping devices is carried out from small distances of units — tens of centimeters. Therefore, at the input of the receiving antenna, along with the useful signal reradiated by the search object, interference comes in the form of reflections from the underlying surface, consisting of the emitted linear frequency-modulated signal and its harmonics that have passed the low-pass filter. The absence of time differences between the useful signal and the interference not only does not provide frequency selection of the useful signal from the interference in frequency, but also its passage through the notch filter of the device. An increase in the frequency deviation of the probing linear frequency-modulated signal will only lead to a shift to the right along the frequency axis of the useful signal and interference.

Thus, the disadvantage of the known non-linear radar is the presence of restrictions on the detection of listening devices located in the near search zone.

The objective of the invention is to expand the search area of nonlinear objects by providing frequency selection of a useful signal from interference, in the absence of time differences between them, by applying a double linear frequency modulation in the probing signal and phased processing of the signals received at the input of the receiving antenna.

The solution to this problem is provided due to the fact that in a non-linear radar containing a reference oscillator, a frequency divider, a linear frequency-modulated generator, the second input of which is connected to the output of the reference generator and two band-pass filters, the inputs of which are connected to the output of the linear frequency-modulated generator, connected in series with the first block of the probing linear frequency-modulated signal and the first power amplifier, as well as a low-pass filter, the output of which connected to the transmitting antenna, in addition, the receiving antenna is connected to the input of the third bandpass filter, a first mixer, a fourth bandpass filter, a second mixer and a fifth bandpass filter, as well as a receiver whose output is connected to the first input of the indicator device, the second input of which is connected according to the invention, a first valve, a first directional coupler and a power addition unit, the output of which is connected to the input low-frequency filter, serially connected to a second block for generating a probing linear frequency-modulated signal, a second power amplifier, a second gate and a second directional coupler, the output of which is connected to the second input of the power addition unit, while the outputs of the first and second bandpass filters are connected to the inputs of the first and the second blocks of the formation of the probing linear frequency-modulated signal, respectively, the output of the first power amplifier is connected to the input of the first valve, the second the passages of the first and second directional couplers are connected to the second inputs of the first and second mixers, respectively, as well as a high-frequency amplifier, the output of which is connected to the input of the first mixer, and the input to the output of the third band-pass filter, and the output of the fifth band-pass filter is connected to the input of the receiver.

To implement the frequency selection of the useful signal from the interference in the absence of time differences between them in the known nonlinear radar, a second probing linear frequency-modulated (LFM) signal generating unit, a second power amplifier, two valves, two directional couplers, a power addition unit and a high-frequency amplifier are introduced .

The second power amplifier is designed to prevent the appearance of harmonics of the probing signal at the output of the transmitting antenna at a frequency

where f _{REL. 01} (t), f _{RL. 02} (t) are the center frequencies of the probing chirp signals arriving at the first and second inputs of the power addition block, respectively.

As a result of the simultaneous sounding of two LFM signals on a nonlinear element of the search object due to its nonlinear dependence of the current-voltage characteristic, the irradiated signal undergoes nonlinear transformation into a set of combinational components of their harmonics:

where k, m, n are positive integers and zero.

Physical processes with simultaneous sounding by two LFM signals of the search object are described as follows.

The nonlinear element of the search object is affected by two chirp signals of the form

where I ₀ - the amplitude of the chirp signals;

ω ₀₁ = 2πF ₀₁ ; ω ₀₂ = (ω ₀₁ + Δω ₀ ) = 2π (F ₀₁ + ΔF ₀ ) are the angular frequencies of the first and second chirp signals, respectively;

ΔF ₀ is the increment of the center frequency of the second chirp signal;

- скорость перестройки угловой частоты ЛЧМ-сигналов;

- speed adjustment of the angular frequency of the chirp signals;

Δω = ω ₀₂ -ω ₀₁ = 2πΔF is the frequency deviation.

It is known that the current-voltage characteristic of a nonlinear element is approximated by the expansion in a Taylor series. Then the signal I _S (t) reradiated by the nonlinear element can be found as

where α, β, δ are the transformation coefficients for the corresponding power terms of the series.

Substituting acting signals (3) in (4), we find that the first term in the series is linear and the signals do not undergo non-linear transformations. By revealing the quadratic term of series (4), transformed by a nonlinear element of the search object, the signal of higher harmonics will have the form

where Δω ₀ = ω ₂ -ω ₁ .

Thus, the signal transformed by the nonlinear element of the search object at the frequency (1) is an LFM signal with doubled frequency deviation and absolute amplitude modulation.

The entire spectrum of the signals of the combination components of the secondary radiation (5) is re-emitted into the ether. These signals arrive at the input of the receiving antenna of the device almost simultaneously and differ from the signals (3) by the delay time τ and the doubled value of the frequency deviation. Suppose that the resonant frequency of the third band-pass filter is only consistent with the central frequency of the second term in expression (5), i.e., ω _FP3 = ω ₀₁ + ω ₀₂ , and the passband Δω _FP3 = _2Δω . After frequency conversion and a two-stage correlation convolution of signals (5) at the output of the second mixer, omitting the intermediate calculations, we obtain

where Δω _τ = μ · τ is the increment of the angular frequency due to the delay time τ.

значение девиации частоты первого и второго зондирующих сигналов (3) ΔF=25,0 МГц, длительности ЛЧМ-импульса τ_И=500·10^-6с и задержки полезного ЛЧМ-сигнала и помехи τ=10·10^-9с приращение частоты для второго слагаемого

составит 500 Гц, а частоты первого и второго слагаемых из (6) составят 99,5 кГц и 100,5 кГц соответственно. Поэтому для обнаружения подслушивающих устройств, находящихся в ближней зоне поиска, полоса пропускания пятого полосового фильтра должна находиться в пределах от 300 Гц до 3400 Гц.So, for example, to increment the center frequency of the second chirp signal

the frequency deviation of the first and second sounding signals (3) ΔF = 25.0 MHz, the duration of the LFM pulse τ _И = 500 · 10 ^-6 s and the delay of the useful LFM signal and interference τ = 10 · 10 ^-9 s the frequency increment for second term

will be 500 Hz, and the frequencies of the first and second terms from (6) will be 99.5 kHz and 100.5 kHz, respectively. Therefore, to detect listening devices in the near search zone, the passband of the fifth bandpass filter should be in the range from 300 Hz to 3400 Hz.

Thus, the introduction of new blocks and communication lines into the nonlinear radar ensures the frequency selection of the useful signal from the interference in the absence of time differences between them and expands its capabilities for detecting electronic devices in the near search zone.

Figure 1 presents the structural diagram of the proposed nonlinear radar.

Figure 2 - amplitude-frequency spectrum of the signal at the output of the linear frequency-modulated generator.

Figure 3 presents the amplitude-frequency characteristics of the first and second bandpass filters, respectively.

Figure 4 shows the amplitude-frequency spectra of the chirp signals at the output of the first and second bandpass filters.

Figure 5 shows the amplitude-frequency spectra of the converted frequency and spectrum of signals at the output of the second mixer.

Figure 6 shows the amplitude-frequency spectrum of the useful signal at the output of the fifth band-pass filter.

Figure 1 of the structural diagram of a nonlinear radar adopted the following notation:

1 - reference generator;

2 - frequency divider;

3 - chirp generator;

4.1, 4.2, 4.3, 4.4, 4.5 - the first, second, third, fourth and fifth band-pass filters;

5.1, 5.2 - the first and second blocks for the formation of the probing chirp signal;

6.1, 6.2 - the first and second power amplifiers;

7 - low pass filter,

8, 9 - transmitting and receiving antennas;

10.1, 10.2 - the first and second mixers;

11 - receiver;

12 - indicator device;

13.1, 13.2 - the first and second valves;

14.1, 14.2 - the first and second directional couplers;

15 - power addition unit;

16 - high frequency amplifier.

The proposed device contains a series-connected reference oscillator 1 and a frequency divider 2, the output of which is connected to the first input of the chirp generator 3, the second input of which is connected to the output of the chase generator 1, and the output of the chirp generator 3 is connected to the inputs of the first 4.1 and second 4.2 bandpass filters . The output of the first band-pass filter 4.1 through a series-connected first block for the formation of the probing LFM signal 5.1, the first power amplifier 6.1, the first gate 13.1 and the first directional coupler 14.1 is connected to the first input of the power addition unit 15, the output of which is connected to the transmitting channel through the low-pass filter antenna 8. The output of the second band-pass filter 4.2 through the second block of the formation of the probing chirp signal 5.2, the second power amplifier 6.2, the second gate 13.2 and the second directional the splitter 14.2 is connected to the second input of the power addition unit 15. In addition, the receiving antenna 9, the third bandpass filter 4.3, the high-frequency amplifier 16, the first mixer 10.1, the fourth bandpass filter 4.4, the second mixer 10.2, the fifth bandpass filter 4.5 and receiver 11 are connected in series the output of which is connected to the first input of the indicator device 12, the second input of which is connected to the output of the frequency divider 2. In this case, the second output of the first directional coupler 14.1 is connected to the second input of the first mixer 10.1, and the second output torogo directional coupler 14.2 is coupled to a second input of the second mixer 10.2.

The inventive nonlinear radar operates as follows.

на выходе генератора 3 показан на фиг.2. ЛЧМ-сигнал с выхода генератора 3 поступает на входы первого и второго полосовых фильтров 4.1 и 4.2.Highly stable oscillations from the output of the reference generator 1 with a clock frequency ω _T are fed to the input of the frequency divider 2 and to the second input of the chirp generator 3. The frequency divider 2 is designed to generate pulses of the chirp generator 3 and to synchronize the indicator device 12. The pulse repetition period is Duration of the chirp signal. Frequency response of the chirp signal

at the output of the generator 3 is shown in figure 2. The LFM signal from the output of the generator 3 is fed to the inputs of the first and second band-pass filters 4.1 and 4.2.

A view of the amplitude-frequency characteristics of the band-pass filters 4.1 and 4.2 is shown in Fig.3.

Bandpass filters 4.1 and 4.2 are tuned to the second and fourth sub-spectra of the chirp signal, respectively (see figure 2 and figure 3). From the output of bandpass filters 4.1 and 4.2, the selected LFM signals are fed to the inputs of blocks 5.1 and 5.2 of the formation of the probing LFM signals. In these blocks, the angular frequency of the reference LFM signals is multiplied by a factor of N.

The frequencies of the probing chirp signals f _PROBE.i (t) are selected from the condition

where N is the multiplication factor;

Ω _0i . _LFM = iω _T - Ω _0i is the center frequency of the i-th even sub-spectrum of the LFM signal, where i = 1, 2 ...;

Ω ₀ is the initial angular frequency of the first subspectrum of the chirp signal;

Δ Ω = μτ _И is the deviation of the angular frequency of the sub-spectrum of the chirp signal;

t is the current time.

From the output of blocks 5.1 and 5.2, the LFM signals through series-connected power amplifier 6.1 (6.2), gate 13.1 (13.2) and a directional coupler 14.1 (14.2) are received respectively at the first and second inputs of power addition block 15. At the output of power addition unit 15, a probing signal is formed from the sum of two LFM signals, the central frequencies of which are tuned from each other by Δω ₀ = N (Ω ₀₂ - Ω ₀₁ ). The generated probe signal through the low-pass filter 7 is fed to the input of the transmitting antenna 8.

Power amplifiers 5.1 and 5.2 can be made according to the linear amplifier circuit and matched with the spectrum width of the probing signal (7).

Directional couplers 14.1 and 14.2 are designed to generate the first and second local oscillator chirp voltages, the frequencies of which f _Г1 (t) and f _Г2 (t) are respectively supplied to the second inputs of the mixers 10.1 and 10.2.

The search for objects with nonlinear elements begins from the moment of transmitting antenna radiation of 8 probing LFM signals (7).

In the signal supplied to the input of the receiving antenna 9, along with the signal (7) reflected from objects with nonlinear scatterers, there is a signal (5) that is absent in the spectrum of the irradiating field.

The passband of the bandpass filter 4.3 is consistent mainly with the second term of expression (5). The useful signal and interference from the output of the band-pass filter 4.3 are fed through a high-frequency amplifier 16 to the mixer 10.1, where they are mixed with the signal of the first LFM local oscillator:

At the output of the mixer 10.1, signals of the first angular intermediate frequency (ω _IF1 ) are formed:

where ω _C (t-τ) = ω _{PROBE. 1} (t-τ) + ω _{PROBE. 2} (t-τ);

i = 1, 2;

ω _{POM. 1} (t-τ) = 2ω _{PROBE. 1} (t-τ); ω _{POM. 2} (t-τ) = 2ω _{PROBE. 2} (t-τ).

и часть спектра поThe passband of the bandpass filter 4.4 is consistent mainly with the first term of expression (9). Useful signal

and part of the spectrum by

where they mix with the second LFM local oscillator signal

At the output of the mixer 10.2, signals of the second angular intermediate frequency are formed (ω _ПЧ2 )

и помехи

приведены на фиг.5.Amplitude-frequency spectra of a useful signal

and interference

are shown in figure 5.

Signals (11) are input to the bandpass filter 4.5. The bandwidth of the bandpass filter 4.5 Δω _PF4.5 defines the non-linear radar _{field of} view.

на входе приемника 11 приведен на фиг.6.View of the amplitude-frequency spectrum of the useful signal

at the input of the receiver 11 is shown in Fig.6.

In the receiver 11 there is an amplification and conversion of the useful signal to a form convenient for observation on the indicator device 12.

Thus, the introduction of new blocks and communication lines into the nonlinear radar not only reduces the influence of the harmonics of the probe signal arriving at the receiver input, both from the transmitting antenna and reflected from the underlying surface, but also provides frequency selection of the useful signal from interference in the absence of time differences between them, which ensures the detection of electronic devices in the near search zone.

To implement a technical solution, standard industrial equipment can be used. So, for example, the reference generator 1 is a generator with quartz stabilization, made, for example, on a chip of the K564LN2 series [V.N. Veniaminov, O.N. Lebedev, A.I. Miroshnichenko. Chips and their application: Ref. Allowance. - 3rd ed., Revised. and add. - M.: Radio and Communications, 1989, 240 pp., P. 210, Fig. 7.10, d].

Frequency divider 2 can be performed, for example, on a chip series KM155IE8 [Perelman BL, Shevelev V.I. Domestic microcircuits and foreign analogues. Handbook, "Scientific and Technical Center Mikrotekh", 2000 - 375 pp., Ill., Pp. 129, 81].

The LFM generator 3 is, for example, a circuit of a digital synthesizer of the LFM signal [Kochemasov V.N., Belov L.A., Okoneshnikov V.S. Formation of signals with linear frequency modulation. - M.: Radio and Communications, 1983. - 192 p., Ill., P. 55, Fig. 4.12].

The low-pass filter 7, bandpass filters 4.1, 4.2, 4.3, 4.4 and 4.5 can be performed, for example, according to the bandpass filter [Radio transmitting devices. / M.V. Balakirev, Yu.S. Vokhmyakov, A.V. Zhurikov, and others; Ed. O.A. Chelnokova. - M .: Radio and communications, 1982. - 256 p., Ill., P. 94, fig. 4.12].

Mixers 10.1 and 10.2 are, for example, diode frequency converters made according to the balanced circuit [M.S. Shumilin, V. B. Kozyrev, V. A. Vlasov. Design of transistor cascades of transmitters. Textbook for technical schools. - M.: Radio and Communications, 1987. - 320 p.: Ill., P. 178, Fig. 2.77].

Blocks 5.1 and 5.2 of the formation of the probing LFM signals can be performed according to the PLL with multiplying the input reference LFM signal Ω ₀₁ (Ω ₀₁ ) (see Fig. 4) N times [MV Halperin Practical circuitry in industrial automation. - M .: 1987. - 320 p .: ill., See p. 183, fig. 4.18, b].

The proposed technical solution is new, since non-linear radar is not known from publicly available information, which provides frequency selection of the useful signal from interference in the absence of time differences between them. This is achieved through the use of a sounding signal with double linear frequency modulation.

Claims (1)

A nonlinear radar for detecting eavesdropping devices, comprising a reference oscillator, a frequency divider, a linear frequency-modulated oscillator, the second input of which is connected to the output of the reference oscillator and two band-pass filters, the inputs of which are connected to the output of the linear frequency-modulated oscillator, connected in series to the first block a probing linear frequency-modulated signal and a first power amplifier, as well as a low-pass filter, the output of which is connected to To the receiving antenna, the receiving antenna is connected to the input of the third bandpass filter, in addition, the first mixer, the fourth bandpass filter, the second mixer and the fifth bandpass filter, as well as a receiver whose output is connected to the first input of the indicator device, the second input of which is connected to the output a frequency divider, characterized in that the first valve, the first directional coupler and the power addition unit, the output of which is connected to the input of the low-pass filter, are introduced in series connected in series to the second block for generating a probing linear frequency-modulated signal, a second power amplifier, a second gate and a second directional coupler, the output of which is connected to the second input of the power addition unit, while the outputs of the first and second bandpass filters are connected to the inputs of the first and second blocks of formation probing linear frequency-modulated signal, respectively, the output of the first power amplifier is connected to the input of the first valve, the second outputs of the first and second of the directional couplers are connected to second inputs of the first and second mixers, respectively, and a high-frequency amplifier whose output is connected to the input of the first mixer and the input - with the output of the third bandpass filter, the output of the fifth bandpass filter coupled to the receiver input.

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