Method for determining radial velocity and acceleration of high-speed manoeuvring target

Abstract

FIELD: radar.SUBSTANCE: invention can be used in radar stations for determining the radial velocity and acceleration of high-speed manoeuvring targets. In the claimed method, the target is illuminated with a continuous linear frequency modulation (LFM) signal, the echo signal is received, demodulated, the demodulated signal is divided in time into two signals of equal duration, equal to half the duration of the illuminating signal, the obtained signals are multiplied after complex conjugation of one of them and the difference frequency signal is extracted. Additionally, the obtained echo difference frequency signal is divided in time into two signals of equal duration, equal to a quarter of the modulation period of the illuminating signal. The obtained signals are multiplied after complex conjugation of one of them. A secondary difference frequency signal is extracted, its spectrum is calculated, and the radial acceleration of the target is determined by the maximum of its fundamental harmonic. A corrective LFM signal with a duration equal to half the modulation period of the illuminating LFM signal is generated. The difference frequency signal is multiplied with the corrective signal, after which the spectrum of the obtained demodulated signal is calculated, the frequency of the fundamental harmonic of the spectrum is determined by its maximum, and taking into account the value of the fundamental harmonic of the spectrum of the secondary difference frequency signal, the target velocity is determined.EFFECT: ensuring invariance to migration of a high-speed manoeuvring target in range channels, measurement of the radial acceleration of the target and elimination of the influence of acceleration on the accuracy of measuring its radial velocity.1 cl, 4 dwg

Description

[0001] The invention relates to radar and can be used in radar stations (RLS) for determining the radial speed and acceleration of high-speed maneuvering targets.

[0002] A known method (analogue) for determining the range and radial velocity of a target in a radar with continuous linear frequency-modulated (LFM) radiation [Ryazantsev L.B., Likhachev V.P., Kupryashkin I.F., Belyaev V.V. A method for digital processing of signals in radar stations with a synthetic aperture of a continuous-wave antenna and a device for implementing it. Russian Federation Patent No. 2624630. Published: 05.07.2017. Bulletin No. 19. - 7 p.]. The disadvantage of the analogue method is that in the presence of target acceleration, after demodulation of the received echo signal, the received beat signal contains information about the speed and acceleration of the target, which leads to the presence of an error in calculating its radial velocity.

[0003] The closest in technical essence to the claimed method (prototype) is the method for determining the acceleration of approach to an air target [Ryazantsev L.B., Likhachev V.P. Probabilistic characteristics of the maneuver indicator of an air target based on the phase-difference assessment of the acceleration of approach. Advances in modern radio electronics. Issue No. 11, 2010. Pp. 10-14]. The method consists of probing the target with a packet of coherent radio pulses of duration T with a high repetition rate F и , receiving a signal packet reflected by a target, dividing it into two sub-apertures of equal duration, multiplying the signals of the two sub-apertures after complex conjugation of the signals of one sub-aperture, finding the maximum of the spectrum of the difference frequency signal obtained as a result of the multiplication, and calculating the target acceleration based on the found value.

[0004] The main limitation of the prototype method is the inadmissibility of target migration along the range and speed channels during its probing time Tз =N пач T, where N пач - the number of packets with different pulse repetition rates F и , which ensures unambiguous measurement of the target range. The duration of the radio pulse packet T with constant F и provides the required radar speed resolution ΔV=λ / (2T), where λ is the wavelength of the probing signal. When observing high-speed maneuvering targets, it is necessary to increase the frequency F и , because F и ≥2V max / λ, where V max - the maximum possible speed of approach of the target to the radar, and, as a consequence, reduce the duration of the probing pulses τ и (to ensure the required duty cycle of the probing pulses Q=1 / (F и τ и )) and increase the duration of the radio pulse packet T=(N-1) / F и , where N is the number of pulses in a packet, which, in turn, leads to the migration of the target along the range and speed channels.

[0005] The technical result of the proposed invention is the measurement of the radial acceleration of a high-speed maneuvering target and the elimination of the influence of acceleration on the accuracy of measuring its radial speed.

[0006] The said technical result is achieved by the fact that in a known method for determining the acceleration of approach to an air target, which consists of probing a target with a signal in the form of a coherent packet of radio pulses, receiving echo signals, dividing them in time into two signals of the same duration (into two sub-apertures) equal to half the duration of the probing signal, complex conjugation of the signals of one sub-aperture, multiplying the received signals, finding the maximum of the spectrum of the difference frequency signal obtained as a result of the multiplication, according to the proposed invention, instead of a packet of pulse signals, a continuous chirp probing signal is emitted and the difference frequency signal is additionally divided into two signals (into two sub-apertures) of the same duration equal to a quarter of the modulation period T / 4 of the chirp probing signal, the signal of one sub-aperture is complex conjugated, the received signals are repeatedly multiplied and a secondary difference frequency signal is isolated,by the frequency of which the radial acceleration of the target is determined and a correction signal is generated, the difference frequency signal is demodulated, its frequency is determined, and, taking into account its value and the frequency value of the secondary difference frequency signal, the radial velocity of the target is calculated.

[0007] The essence of the method is as follows. Instead of a coherent burst of radio pulses, a continuous chirp signal of the same duration is emitted; the range and radial velocity of the target are determined based on the analysis of the frequency parameters of the beat signal, formed by demodulating the received signal, carried out by multiplying the received echo signal with a copy of the probing signal. For a radar with a continuous chirp probing signal, the complex representation of the beat signal in a separate modulation period is described by the expression [Kupryashkin I.F., Likhachev V.P., Ryazantsev L.B. Small-sized multifunctional radars with continuous frequency-modulated radiation. Monograph. Moscow: "Radio Engineering", 2020, 280 p. Pp. 58-59]

[0008]

[0009] where t∈[0, T]; A б - amplitude of the beat signal; j - imaginary unit; R ц (t) is the law of change in the range to the target, c is the speed of light in a vacuum; f0, μ=Δf / T, Δf and T are the initial frequency, the rate of change of frequency (steepness) of the chirp, the width of the spectrum and the modulation period of the probing signal, respectively.

[0010] A maneuvering target is characterized by the presence of acceleration. Taking into account that during the modulation of the probing signal, the acceleration of the maneuvering target is constant and, representing the law of range change as a function of time, where R0,V ц and a ц - the initial range to the target, its radial velocity and acceleration, respectively, then the signal (1) will take the form

[0011]

[0012] where f RД =f R +f Д ; - Doppler, - long-range frequency,

[0013]

[0014] The presence of target acceleration leads to additional nonlinear frequency modulation of the beat signal and, as a consequence, to an expansion of its spectrum, which reduces the accuracy of determining the radial velocity and range of the target.

[0015] Compensation for nonlinear modulation in signal (2) is carried out using the phase-difference method [Kondratenkov G.S., Frolov A.Yu. Radiovision. Radar Systems for Remote Sensing of the Earth. Moscow: “Radiotekhnika”, 2005, 368 p. Pp. 221-223; Ryazantsev L.B., Likhachev V.P. Probabilistic Characteristics of an Air Target Maneuver Indicator Based on a Phase-Difference Estimate of Approach Acceleration. Advances in Modern Radio Electronics. Issue No. 11, 2010. Pp. 10-14]. For this purpose, signal S б (t) of duration T is divided in time into two signals S1(t)=S б (tT / 2) and S2(t)=S б (t+T / 2) of duration T / 2 (Fig. 1). Then the complex conjugate signal is multiplied with the signal S2(t). The result of the multiplication is the difference frequency signal, the normalized expression for which, without taking into account the amplitude component and the initial phase, has the form

[0016]

[0017] where t∈[0, T / 2].

[0018] Signal (5) is a chirp oscillation, the demodulation of which is carried out by repeated phase-difference processing. That is, the signal SΔ1(t) of duration T / 2 is divided in time into two signals S3(t)=SΔ1(tT / 4) and S3(t)=SΔ1(t+T / 4) of duration T / 4, after which the obtained signals are multiplied and the secondary difference frequency signal SΔ2(t) is isolated, which, without taking into account the initial phase and amplitude component, has the form:

[0019]

[0020] where t∈[0, T / 4].

[0021] The signal SΔ2(t) describes a harmonic oscillation with a frequency fΔ2=a μ T 2 / 8, which, in accordance with (4), is proportional to the acceleration of the target.

[0022] To obtain an estimate of the magnitude calculate the signal spectrum (6) and determine the frequency of the fundamental harmonic based on its maximum amplitude

[0023]

[0024] where F{⋅} is the Fourier transform operator.

[0025] Next, based on the assessment received calculate the acceleration of the target according to the expression

[0026]

[0027] and generate a correction signal required to demodulate the SΔ1(t) signal and calculate the exact target speed, in accordance with the expression

[0028]

[0029] The target speed is calculated by estimating the parameter μ2 of the signal (2), which is reduced to determining the fundamental harmonic of the signal spectrum obtained by multiplying the signal SΔ1(t) with the correction signal S к (t) in accordance with

[0030]

[0031] By found values calculate an estimate of the target's radial velocity

[0032]

[0033] Thus, unlike the prototype, in the proposed method, target probing is carried out by a continuous chirp signal, the phase-difference processing of the beat signal is repeated, the target acceleration is calculated, based on the value of which a correction signal is generated, which is used to demodulate the difference frequency signal, which ensures the receipt of an estimate of the radial acceleration and eliminates the error (increases the accuracy) in calculating the radial velocity of a high-speed maneuvering target.

[0034] Fig. 2 and 3 show structural diagrams of a device for implementing a method for determining the radial velocity and acceleration of a high-speed maneuvering target.

[0035] The device consists of a frequency modulator 1, a high-frequency generator 2, a transmitting antenna 3, a receiving antenna 4, a receiving device 5, a first random access memory (RAM) 6.1, a second RAM 6.2, a first phase-difference processing device 7.1, a second phase-difference processing device 7.2, a multiplier 8, a first spectrum analyzer 9.1, a second spectrum analyzer 9.2, a correction signal generator 10, a speed calculator 11, an acceleration calculator 12, and a synchronization device 13.

[0036] Phase-difference processing device 7.1 (7.2) is designed to separate the input signal into two signals of the same duration by time, multiply the received signals and extract the difference frequency signal.

[0037] The phase-difference processing device 7.1 (7.2) can be implemented, for example, in accordance with the diagram shown in Fig. 3, and contains a signal divider 14, a digital complex conjugator 15, and a digital complex multiplier 16.

[0038] Phase-difference processing unit 7.1 (7.2) operates as follows. An input digital signal with N samples is fed to the input of divider 14, where it is split into two signals. The first N / 2 samples are fed to the first input of digital complex multiplier 16, the second N / 2 samples are fed to the input of digital complex conjugator 15, the result of which is fed to the second input of digital complex multiplier 16. As a result of complex multiplication, a digital difference frequency signal is formed at the output of the phase-difference processing unit.

[0039] The embodiment of the device shown in Fig. 2, which implements the proposed method for determining the radial speed and acceleration of a high-speed maneuvering target, functions as follows.

[0040] At the beginning of each modulation period T of the probing signal, the frequency modulator 1, in response to a signal from the synchronization device 13, generates a chirp signal, which, after being converted to a high frequency by the high-frequency generator 2, is emitted into space by the transmitting antenna 3. The receiving antenna 4 receives the signal reflected from the target, which is fed to the input of the receiving device 5, where it is multiplied with a copy of the probing signal, resulting in the formation of a beat signal, which is converted into a discrete complex signal and recorded in RAM 6.1. At the end of the modulation period, in response to a signal from the synchronization device 13, RAM 6.1 outputs the stored signal to the phase-difference processing device 7.1, resulting in the formation of a difference frequency signal, which is stored in RAM 6.2. The signal from the output of RAM 6.2 is fed to the second phase-difference processing device 7.2, at the output a secondary difference frequency signal fΔ2 is formed, which is fed to the first spectrum analyzer 9.1, where the spectrum of the received signal and its fundamental harmonic are calculated. (Fig. 4). The obtained value is fed to the input of the correction signal generator 10 and the speed calculator 11, and is also used to calculate the target acceleration in the acceleration calculator 12. The correction signal generator 10, at the end of each modulation period of the probing signal, generates a correction signal in accordance with the expression

[0041]

[0042] which is fed to the first input of multiplier 8, the second input of which receives the signal recorded in RAM 6.2. As a result, a harmonic oscillation is obtained at the output of multiplier 8, the frequency value which is determined in the spectrum analyzer 9.2. Based on the calculated value in the speed calculator 11 taking into account the value calculate the target's speed.

Claims

A method for determining the radial velocity and acceleration of a target in a radar station (RLS), which consists of probing the target, receiving an echo signal, demodulating it, dividing the demodulated signal in time into two signals of the same duration, equal to half the duration of the probing signal, multiplying the received signals after complex conjugation of one of them, and isolating the difference frequency signal f Δ1 , characterized in that a continuous linear frequency-modulated (LFM) probing signal is formed, the received echo signal of the difference frequency is divided in time into two signals of the same duration, equal to a quarter of the modulation period of the probing signal T, the received signals are multiplied after complex conjugation of one of them, the secondary difference frequency signal is isolated, its spectrum is calculated based on the maximum of the fundamental harmonic of the received spectrum determine the radial acceleration of the target where Δf is the spectrum width of the probing chirp signal, c is the speed of light in a vacuum, a correcting chirp signal is formed with a duration equal to half the modulation period of the probing chirp signal, the difference frequency signal is multiplied with the correcting signal, after which the spectrum of the received demodulated signal is calculated, the maximum of which is used to determine the frequency of the fundamental harmonic of the spectrum , and taking into account the value determine the target's speed where f0 is the initial frequency of the probing chirp signal.

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