RU2474839C1 - Method and apparatus for nonlinear radar - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method is realised by creating surveillance nonlinear radar which, at a long range, detects and measures coordinates of controlled explosive devices independently in each range resolution element. Longer detection range is provided due to resonant excitation of the sought objects and use of parametric effects which arise in nonlinear elements of controlled explosive devices when exposed to a powerful electromagnetic field, and measurement of their location is provided by using complex multi-range broadband probe signals with a large base in order to improve range resolution, and by realisation of mono-pulse techniques of measuring angular directions using a discrete set of multi-range receiving antennae.

EFFECT: providing safe remote detection of controlled explosive devices with high range resolution and virtually instantaneous and precise positioning thereof.

2 cl, 6 dwg

Description

The present invention relates to the field of nonlinear radar and is intended for remote detection and accurate measurement of the coordinates of guided explosive devices (IEDs) having selective properties in the frequency range of electromagnetic waves.

The relevance of developing such a method and creating an appropriate device is due to the widespread worldwide use of "explosive" terrorism.

One of the most promising methods for detecting airborne vehicles is the nonlinear radar method. The main results of studies evaluating the possibility of using a nonlinear location to detect engineering mines and explosive devices in various concealment environments are summarized and published in a number of domestic works [1-4]. The implementation of these works ended with the creation in the industry of a portable nonlinear radar INM (non-contact mine finder) [5].

The principle of operation of a nonlinear radar (NRL) is that when an external signal is irradiated, electronic devices containing semiconductor elements (diodes, transistors, microcircuits) re-emit signals at the higher harmonics of the probe signal, which are then received and analyzed by the NRL [6].

Typically, in existing NRLs, the irradiation mode is performed by simple (narrow-band) probing signals (ZS), the base of which is D = Δf · T ~ 1, where Δf is the width of the spectrum of the ZS, and T is the duration of the ZS. There are a large number of search non-linear decimeter wave locators that use simple signals as ES, which solve the problem of finding electronic bookmarks in rooms [7, 8].

Search locators belong to the class of near-location tools, and the use of signals with a small base in them limits the spatial resolution element and makes it difficult to measure the coordinates of the position of search objects when they are remotely detected on the (x, y) plane. Coordinates are measured in search locators by changing the amplitude of the probing signals and the sensitivity of the devices for receiving reflected oscillations of higher harmonics [7, 8]. These operations are performed sequentially in time and therefore require a significant analysis time. Search locators are characterized by a short detection range and resolution, a long analysis time of the reflected signals, which in some cases limits the scope of their application in practical applications, and when detecting UVDs at distances less than 1 m leads to unjustified risk for the operator.

In order to ensure the safety of personnel, it is necessary to implement remote detection of explosive objects and their almost instantly accurate positioning on the ground.

It should be noted that for the tasks in non-linear location, attempts were made to improve resolution and accuracy characteristics in range due to the use of complex signals with the base D >> 1.

It is known that in the usual linear location the use of complex signals allowed to resolve the contradiction between the energy potential and the resolution in range [7].

In a nonlinear location, the use of complex signals has its own characteristics, which are determined by a nonlinear converter in the search objects. In particular, the use of biphasic codes in the extraction of 2nd harmonic oscillations leads to the effect of narrowing the spectrum of oscillations reflected from the UVA, i.e. to deterioration, not improvement, resolution and accuracy of range measurement [8].

The use of complex signals such as linear-frequency modulated oscillations (chirp signals) as probing signals does not change the situation. In fact, the LFM signal at each moment of time is a narrow-band signal, which falls into the passband of the UVD at a finite time interval within the envelope of the LFM signal. As a result, the resolution and range accuracy are determined not by the parameters of the probing signal, but by the parameters of the nonlinear element (NE) in the UVD.

Thus, a simple increase in the base of the probe signal in the case of a nonlinear location does not improve the resolution in range, and the choice of the modulation type of the probe signal in order to improve the resolution for a nonlinear locator is very relevant.

The technical result of the invention is the provision of safe remote detection of UVU with high resolution in range, their instantaneous and accurate positioning on the ground, which is achieved by creating an overview NRL, which at long range detects and measures the coordinates of UVU independently in each element of the resolution in range.

The search did not reveal a description of the method and device close to the claimed, therefore, a prototype of the invention is absent.

An increase in the detection range in the present invention is provided due to the resonant excitation of search objects and the use of parametric effects that arise in nonlinear elements of the UVD when they are irradiated with a powerful electromagnetic field, and their location is measured using complex multi-band wideband probe signals with a large base to improve resolution range, and the implementation of monopulse methods for measuring angular directions using discrete th set of multi-band transmit and receive antennas.

It should be noted that in the non-linear survey remote sensing locator, the locator must perform UVD detection regardless of their frequency range and measure the range and angular directions in a given detection zone, that is, in fact, the processing of received vibrations in the overview NRL should be at least two-dimensional.

In addition, it should be borne in mind that the specific applications of the NRL impose restrictions on its overall dimensions, which must be acceptable for installation on any vehicle, including being suitable for manual use.

Given the above limitations, it is most expedient to use monopulse location methods [9] for the implementation of a survey radar radar [9], which allow an almost instantaneous survey of a given area of space using a limited number of multi-band antennas that allow radiation and reception of a multi-band wideband signal. A limited number of antennas minimizes the overall dimensions of the survey radar.

In principle, the viewing time of a given area of space cannot be instantaneous and is determined by the accumulation (averaging) time of the received oscillations, i.e. filtering time of received signals against the background of noise and external interference, which, as a rule, does not have practical value in real conditions when making decisions based on the results of detection of air-conditioners, and in this sense is carried out almost instantly in real time. The viewing time in the frequency range of the UVD should also be instantaneous, which is ensured by the use of multi-band wideband sounding signals that provide “backlight” and detection of the UVD in the entire frequency range of their operation and, thus, provide two-dimensional processing.

This approach eliminates sequential scanning operations by angular and frequency parameters and implements non-search detection methods, which will significantly reduce the viewing time of a given area. The basis of non-search two-dimensional detection methods (in space and frequency) is the use of multi-band wideband probing signals, the width of the spectrum of which should cover the entire frequency range of operation of the UVU.

A typical UHF frequency range corresponds to the frequency range of connected radio stations, which are often used as radio control channels, and occupies a frequency band from 30 MHz to 3000 MHz.

In the survey NRL with the frequency-searchless method for detecting UHF responses at higher harmonics, the multiband probing NRL signal should have a discrete frequency structure. A discrete frequency structure of the multiband sounding signal is necessary to ensure the sensitivity of the reception of the UVC responses at higher harmonics, which should be detected against the background of the intrinsic noise of the NRL receivers, i.e. in this frequency range, the spectral components of the multiband sounding signal must strictly be equal to zero.

On the other hand, the spectrum of the probing signals must occupy a continuous frequency band in order to satisfy the conditions for the resonant excitation of the receiving channels of the UVD in their entire frequency range. Taking into account the parametric effects arising in the nonlinear elements of the UVD [6], a compromise solution for ensuring the optimal structure of the probing signals in the frequency domain is the emission of a continuous spectrum in discrete zones.

The width of the spectrum of each of the discrete zones is comparable with their center frequency. The arrangement of the central frequencies of the discrete zones of broadband signals is commensurate with their spectrum width. Signals emitted in such discrete zones belong to the class of multi-band wideband signals.

The width of the spectrum of the discrete zones of a broadband multi-band signal is determined by the expression

where m is the number of higher harmonics,

n is the serial number of the discrete zone of the multi-band signal,

ω ₀ - the smallest cutoff frequency of the frequency range of the UVU.

In practical applications, the second harmonic of the ES in the reflected signal is of greatest importance. Therefore, we consider the structure of a multi-band ZS, designed to detect the responses of the UVD at the second harmonic.

To detect reflected signals at the 2nd harmonic, the spectrum of the probing signals in each of the discrete zones should have an octave structure. The number of octave zones that overlap the frequency range of the available and promising UVUs does not exceed 3–4. A typical view of the CS in the spectral region is shown in FIG.

Coherent filtering of broadband complex sounding signals in each n discrete zone allows you to localize the location of different IEDs in range with a resolution element of ~ 4 ÷ 5 m, starting with a discrete octave zone, the boundary of which starts at 30 MHz. The implementation of such a resolution element is commensurate with the spatial step of a typical installation of mines on the x, y plane. This circumstance is a sufficient condition for the application of monopulse location methods for accurate determination of the location of the air-blast devices in their entire possible frequency range. Indeed, the measurement methods in monopulse location are based on the assumption that the detection object is localized in space and does not exceed the range resolution element [9].

For the formation of the necessary range resolution element, it is fundamental to use in the NRL a probe signal in the form of broadband noise with a uniform spectral density in each of the n zones. A limit on the spectral width of each discrete zone is a necessary condition for highlighting higher-order harmonics against the background of the fundamental harmonic.

It should be noted that during the irradiation of the NE ZS, forced oscillations arise in it. In the case when the resonance circuit of the UVA coincides with the spectrum of the discrete zones of the CS, resonant oscillations arise in the input circuit of the UVA, the amplitude of which increases linearly. Resonant oscillations also occur at multiple harmonics. To excite resonant oscillations at multiple harmonics, it is required to introduce an external signal with higher energy into the circuit. The required increase in energy is minimal for harmonics with the lowest magnification, for example, for the second harmonic.

The occurrence of resonant oscillations in the input circuit of the UVU leads, at sufficiently large amplitudes, to modulation according to the periodic law of the input resistance of the UVU receiver. As a result, the input loop of the UVU turns into a loop with variable parameters and starts working as a parametric amplifier, which leads to an increase in the response of the probe signal reflected from the NE and to the expansion of the passband of the loop of the UVU [10]. The enhancement of the response occurs due to the use of the energy of an external ES or the energy of a NE power source.

, где K=1, 2, 3, ... - целое число.The expansion of the bandwidth of the UVU loop occurs not only at the fundamental harmonic, but also at least on the set of harmonic components

, where K = 1, 2, 3, ... is an integer.

The frequency data set describes resonant vibrations in an oscillatory system, the parameters of which vary according to a sinusoidal law. These resonant vibrations are called “generalized” resonance [11].

Combining the conditions of "generalized" resonance with the discrete radiation of the probing signals, we find that each of the n zones of the probing signal excites a set of harmonic components K = 2 · m ^-n . Of greatest interest are the zones that are adjacent to the n discrete zone of the probing signal, because in these zones, the least energy is required to excite the parametric amplification of the input oscillations. In the case of the 2nd harmonic excitation, this corresponds to the appearance of oscillations at a frequency of 2ω ₀ and a subharmonic frequency

The presence of generalized resonance justifies the sufficiency of the structure of a multi-band probing signal, consisting of a set of discrete zones for detecting NEs in the entire expected range of electromagnetic waves. It should be noted that with a sufficiently large pulsed radiation power, the requirements for the number of discrete zones in the frequency domain of a multi-band probing signal are reduced.

The considered oscillation mechanism in NE caused by the use of broadband probing signals determines to a large extent the energy potential of the locator.

The appearance of a “transparency” window at a frequency of 2ω ₀ due to the presence of a generalized resonance causes the passage of oscillations at the second harmonic with virtually no attenuation in the input circuits of the UVU.

In the general case, the range of the NRL is determined by the range equation appropriate for non-linear radar. Under the condition of excitation of parametric oscillations in the NE, an increase in the detection range occurs, compared with nonresonant (nonparametric) response excitation. An increase in the detection range occurs due to the parametric amplification of the response at the fundamental harmonic and the appearance of a “transparency” window at higher harmonics, for example, the second, and amounts to about 10–30 times as compared to nonresonant excitation of the NE.

Let us consider in more detail the procedure for detecting and measuring coordinates in the NRL. The main factor that distinguishes NRL from classical linear radar is the presence of nonlinear transformations of the ES in NE, which leads to the appearance of higher harmonics.

The occurrence of harmonic oscillations at a frequency of 2ω ₀ can be caused by two phenomena. One of them is the nonlinear conversion of oscillations in the nonlinear elements of the UVD, and the other is the conversion (heterodyning) of the received oscillations in the UVD at a frequency of 2ω ₀ , due to their multiplication by the time-variable conductivity of the UVU circuit. Both of these mechanisms lead to the appearance of a constant component in the circuits of the input circuit of the UVU with a nonlinear element, which leads to a displacement of its operating point and, accordingly, to an increase in the nonlinear distortion of the probe signal.

The stimulated parametric amplification mode in a UVU with a resonant oscillatory circuit belongs to the class of non-degenerate parametric amplifiers. In a non-degenerate parametric amplifier, a quadratic nonlinear element is especially important for practice, because it, in contrast to higher degrees, leads to amplification without distortion [12].

This circumstance makes it possible to realize cross-correlation processing of signals reflected at the 2nd harmonic from non-linear elements of the UVD and the probe signal of a transmitter previously subjected to non-linear quadratic transformation. The minimization of arising distortions in the structure of a complex signal during non-linear transformation can be achieved by choosing the type of modulation of the probe signal. Obviously, the instantaneous spectrum of such a probe signal should be broadband, and the modulation parameter will be determined by time-position coding. These conditions are satisfied by white Gaussian noise with a limited passband (for the second harmonic, the width of the spectrum of the probe signal is equal to an octave).

An experimental verification of the possibility of compressing complex noise signals reflected at the 2nd harmonic of the surroundings confirms the correctness of the considered model of NRL functioning. Figure 2 (a) presents a noise sounding signal with a base of D ~ 1000. Figure 2 (b) shows the signal at the output of the receiver of the 2nd harmonic of the surroundings, which contains 2 components - the intrinsic noise of the receiver and noise oscillations of the surroundings, reflected from the VUU at the 2nd harmonic. Figure 2 (c) presents the result of the compression of the AP after cross-correlation processing at the output of the receiving device.

Figure 2 (g) presents a similar result in the range of ranges of interest for the NRL.

From the obtained data it can be seen that the signal at the output of the 2nd harmonic receiver after cross-correlation processing with the probing signal subjected to non-linear transformation is shortened by about 1000 times, i.e., in proportion to the base of the probing signal (see Fig. 2 (d)).

In fact, this means that the considered mechanism of the NRL functioning provides lanerization of the received oscillations in the transmitter circuit (1st harmonic) - NE - receiver (2nd harmonic), which makes it possible to reasonably apply the well-known methods of linear filtering of complex signals for selected type of modulation (noise or time coding) of the probe signal.

It should be noted that the measurements of angular coordinates performed in each element of the resolution in range are a prerequisite for the application of single-pulse methods for measuring angular directions.

Angular directions in 2 orthogonal planes can be measured using various methods that are widely tested in monopulse systems [9].

Measurement of the angular directions of the electromagnetic wave reflected from the NE in 2 orthogonal planes, azimuthal and elevation, or the use of triangulation measurement methods in the same plane, using the movement of the NRL in this plane, make it possible to unambiguously assess its location.

The use for this purpose of data on estimating the delay of reflected oscillations from NEs is ineffective, because the time from the delay is determined by the linear chains of the UVU τ _L.Ts. (antenna, input circuit, etc.), and the excitation of parametric effects requires a certain time τ _PAR to pump energy into the circuit. As a result, the delay of oscillations at the output of the receiver is defined as

,

,

- запаздывание, которое соответствует истинному положению УВУ.Where

- delay, which corresponds to the true position of the UVU.

Since τ _L.Ts. and τ _PAR are the characteristics of a specific UVU

нельзя использовать для оценки местоположения УВУ.and a priori unknown, then the estimate

cannot be used to estimate the location of the OOD.

Note that the duration of the envelope of the probe signal should provide temporary parameters of energy pumping into the NE circuit. In fact, this condition determines the value of the base of a complex broadband sounding signal, which is necessary for the excitation of the parametric amplification mode in the NE. It is known [13] that parametric oscillations develop over a duration of τ _pairs = 0.2–0.3 μs.

Given this circumstance, the value of the base of a complex broadband sounding signal in each n discrete zone with an unchanged structure during non-linear transformation is

D≈m ⁿ · τ · ω _{0 pairs}

and amounts to at least 30 for the meter wavelength range, which is quite sufficient to isolate resonant stimulated oscillations reflected from a nonlinear element against the background of the intrinsic noise of the NRL receiver.

The structural diagram of the survey non-linear radar that implements the method described above in the local detection zone in azimuth is shown in Fig. 3, where it is indicated: 1 - transmitter, 2 - bandpass filter for extracting fundamental harmonics and suppressing higher harmonics, 3 - directional coupler, 4 - transmitting antenna, 5 - chronizer, 6 - driver of the reference voltage for the correlator, 7 - display device, 8 - meter of parameters of the received signals, 9 _{1 ... N} - receivers tuned to the harmonic components of the reflected signal, 10 _{1 ... N} - harmonic filters, 11 _{1 ... N} - receiving antennas, N - number of channels.

Survey non-linear radar remotely detects UVA and measures their position in space. An important factor is the time of formation of the position of the air defense system, which determines the feasibility of using a surveillance radar in real practical applications. These circumstances determine the functioning and structural diagram of the survey non-linear radar, presented in figure 3.

The real-time non-linear survey radar determines the coordinates of all the air-defense devices located in the field of view. The device operates as follows. Using transmitter 5, a powerful multi-band wideband complex signal is generated in transmitter 1, which is filtered in block 2, where the main harmonic is extracted in each of the n≥2 ranges of the probe signal and the higher harmonics are suppressed. Further, the generated signal through the first output of the directional coupler 3 enters the transmitting antenna 4 and irradiates the NE of the UVU. As a result of the parametric effect, due to the expansion of the Δf bands in the VLF, the signal response is received at the Nth harmonic (N≥2n) at the receiving antennas 11 ₁ ... 11 _N and, passing through the harmonics filters 10 _{1 ... N} , is fed to the first inputs of the receivers 9 _{1 ... N.} In the receivers 9 _{1 ... N,} these signals are subjected to correlation processing with the reference signal of the transmitter supplied to the second inputs of the receivers 9 _{1 ... N} from the second output of the directional coupler 3 through the voltage driver 6, and compression. At the outputs of the receivers 9 _{1 ... N} , the signal is separated (for example, by a threshold device) against the background of noise and interference, and the spatial resolution of the range is solved.

The outputs of the receivers 9 _{1 ... N} go to the inputs of block 8, where they measure the distance to the air-blast and, using single-pulse methods [9, p. 21, 71, 100], the angular directions of the arrival of signals reflected from the NE of the air-blast. The processed information in block 8 provides the location of NE NEOs, after which the results are displayed in block 7.

Thus, the use of complex broadband, frequency-discrete, multi-band probing signals in the NRL is a necessary and sufficient condition for providing excitation of parametric amplification mode in nonlinear elements of search objects with subsequent nonlinear conversion of the reflected oscillations up and down in frequency into frequency zones free of the spectral components of the discrete by the frequency of a multi-range probing signal. In order to cover the entire frequency range of connected radio stations used to undermine the airborne UVD, the number of discrete frequency ranges of the multi-band probing signal should be at least 2-3, the number of channels in frequency in each receiver should be 2 times larger, taking into account the conversion of reflected oscillations up and down in frequency. To determine the angular directions to search objects, it is necessary to implement a single-pulse method for measuring angular directions using an N-channel receiving system. The number of receiving channels is determined by the ratio of the total viewing area in the angular coordinate to the bottom width of the elementary emitters.

Literature

1. Non-linear radar. Digest of articles. Part 2. / Under. ed. A.A. Gorbacheva, A.P. Koldanova, A.A. Potapova, E.P. Chigina - A.A. Gorbachev, E.P. Chigin. The interaction of electromagnetic waves with nonlinear objects. M .: Radio engineering, 2006, p.6-13.

2. VB Steinshleger. On the theory of scattering of electromagnetic waves by a vibrator with a nonlinear contact. Radio engineering and electronics, 1978, v.23, No. 7, p.1329-1338.

3. A.A. Gorbachev, S.V. Lartsov, S.P. Tarakankov, E.P. Chigin. Amplitude characteristics of nonlinear scatterers. Radio engineering and electronics, 1996, t. 41, No. 5, p. 588-562.

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Claims (2)

1. The method of nonlinear radar, which consists in the formation of powerful multi-band wideband complex signals with a base D >> l and a limited spectrum in each of n≥2 ranges, which, after extracting the main ones and suppressing the higher harmonics of each range, radiate into space in as sounding signals (ZS), exciting resonant parametric oscillations in the search objects and amplification of the signals reflected from them at the highest harmonics of the ZS arriving at N≥2n receiving frequency channels in which they produce multi-correlation processing of reflected signals with a probing signal previously subjected to nonlinear conversion, compression and extraction of reflected signals against a background of noise, providing spatial resolution in range and using monopulse measurement methods, determining angular directions in a given viewing area. 2. A nonlinear radar device containing a transmitter that generates powerful multi-band wideband complex sounding signals with a base D >> l and a limited spectrum in each of n≥2 ranges, connected in series with a band-pass filter that selects the main and suppresses the higher harmonics of the transmitter signal directed by the coupler and a transmitting antenna, a chronizer, a voltage driver, the first input of which is connected to the second output of the directional coupler, a display device, a pair meter of meters of received signals and N≥2n receiving frequency channels, each of which is tuned to one of the harmonic components of the reflected signal and consists of a series-connected receiving antenna, a harmonic filter and a receiver providing signal correlation with the correlation signal, compressing and isolating the signal against noise , the second inputs of the receivers are connected to the output of the reference voltage driver, and the outputs are connected to the N inputs of the meter of parameters of the received signals, where the distance mono-pulse methods - measuring the angular directions of arrival of the reflected signals, the output of the received signal parameter meter is connected to the first input of the display device, the second input of which, as well as the transmitter input and the second input of the voltage driver, is connected to the third, first and second outputs of the chronizer, respectively .

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