Method for forming adaptive threshold level of radar detector in under high pulse repetition frequency of probing signal

Abstract

FIELD: radar.SUBSTANCE: invention can be used in pulse-Doppler (PD) radar stations (RS) of ground or surface basing to solve the problem of selecting a group of moving air objects under narrow-band passive interference (PI), primarily against a background of intense reflections from the underlying earth or water surface, local objects and slow-moving meteorological formations. The claimed method involves forming an adaptive threshold level of a radar detector in a high pulse repetition frequency mode of a probing signal. To do this, a probing signal is generated, emitted, an echo signal is received, and its optimal processing is carried out by heterodyning the echo signals and integrating the obtained results. The interference power is measured in the analysed range resolution elements and a threshold level is formed as the average value of these measurements. In addition, a probing linear frequency-modulated (LFM) signal is formed, and with optimal processing of echo signals, they are demodulated by multiplying them with a heterodyne signal of the same modulation as the probing signal, converting the quasi-continuous signal into a continuous one and its Fourier transform.EFFECT: improving the quality of detection of targets with small components of radial velocities in PD RS under PI.1 cl, 5 dwg

Description

[0001] Field of technology to which the invention relates

[0002] The invention relates to the field of radar and can be used in pulse-Doppler (PD) radar stations (RLS) of ground (surface) basing to solve the problem of detecting low-speed and (or) stationary air objects against the background of narrow-band passive interference (PI) and, first of all, against the background of intense reflections from the underlying earth (water) surface, local objects and slow-moving meteorological formations.

[0003] Technology Level

[0004] Detecting useful signals against a background of PP is one of the most important radar problems, which is most often solved by frequency (speed) selection methods using quasi-continuous signals in the high repetition rate mode [1]. When observing low-speed and / or stationary objects, the frequency differences between the useful signal and interference are so minimal that the principles of speed selection do not allow the implementation of the principles of speed selection. In this case, the detection problem is performed in the resolution element by comparing the result of processing the input realization with a certain threshold level determined by a given probability of false alarm, as well as the power of intrinsic noise and external interference [2]. Since the intensity of the latter in several resolution elements may vary, an adaptive threshold level is used.

[0005] A method for calculating the adaptive threshold is known based on the method of order statistics [3]. However, it is applicable to pulsed signals, and in the case of quasi-continuous radiation, several pulses reflected from different resolution elements, the range to which is a multiple of the distance between adjacent probing pulses, will simultaneously arrive at the radar receiver, which will distort the true interference level in the analyzed range element.

[0006] A known method for forming an adaptive threshold level of a radar detector is based on the analysis of the interference power in the current resolution element and its neighboring elements [4, pp. 3-19, 48-96], adopted as a prototype. The essence of this method is as follows (see Fig. 1):

[0007] 1) Formation of a probing signal (block 1.1), its emission and reception of echo signals (blocks 1.2);

[0008] 2) Optimal echo signal processing:

[0009] - heterodyning (block 1.3);

[0010] - integration (block 1.4);

[0011] 3) Formation of the threshold level z0 based on measurements of the interference power in the analyzed resolution elements (block 1.5):

[0012]

[0013] where - echo signal, - impulse response of the matched processing device, - duration of the probing signal, - time; - interference power in the i-th resolution element, k - number of analyzed resolution elements.

[0014] The following can be pointed out as disadvantages of the prototype under consideration. When forming the adaptive threshold level z0, interference samples (1) obtained in several resolution elements with different angular coordinates and / or time delays, as a rule, adjacent to the element k being tested, are used. Analysis of the interference intensity at different angular positions of the antenna pattern beam does not present difficulties; however, it is not always possible to correctly measure the interference level (1) in several resolution elements by range. This problem arises only with probing quasi-continuous signals (QCS). This is explained by the fact that with quasi-continuous radiation, several pulses reflected from different resolution elements, the range to which is a multiple of the distance between adjacent probing pulses, will simultaneously arrive at the radar receiver (Fig. 2).An additive mixture of received echo signals will distort the true interference level in the analyzed range element, and the threshold (2) calculated in this case will not provide the potential detection performance. For comparison, it should be noted that in pulsed radar mode, there are no difficulties in accurately assessing the level of interference reflections at any range segment, because echo signals reflected from different range elements always differ in delay time (Fig. 2).

[0015] Disclosure of the essence of the invention

[0016] The technical problem solved by the developed method is to improve the quality of detection in the ID radar of targets with small components of radial velocities against the background of the PP.

[0017] The technical result is achieved in that in the method for forming an adaptive threshold level of a radar detector in the mode of a high pulse repetition frequency of a probing signal, which consists of forming a probing signal, emitting it, receiving echo signals, optimally processing by heterodyning the echo signals and integrating the results obtained, measuring the interference power in the analyzed range resolution elements and forming a threshold level as the average value of these measurements, according to the invention, a probing linear frequency-modulated (LFM) signal is formed, and with optimal processing of echo signals, they are demodulated by multiplying with a local oscillator signal of the same modulation as the probing signal, converting a quasi-continuous signal into a continuous one and its Fourier transform.

[0018] The physical essence of the proposed method is as follows. According to the method, the analysis of interference intensity in the range resolution elements is performed in the frequency domain. To maximize the separation of the spectral components of signals reflected from different range resolution elements, the first step involves introducing linear frequency modulation into the probing SNS with a slope p, selected as proposed in [5,6]:

[0019]

[0020] where - pulse repetition frequency of the probing KNS, - deviation of the probing signal frequency; - signal duration, - time; - amplitude of the probing signal; - pulse number; - the number of pulses in the signal; - pulse repetition period; - carrier frequency; - initial phase.

[0021] The next stage consists of emitting probing signals and receiving signals reflected from targets.

[0022] At the third stage, the received signal is converted to an intermediate frequency and demodulated - the chirp structure is removed as a result of multiplication with a local oscillator signal with the same modulation as the probing signal:

[0023]

[0024] The next step is to transform the KNS into a continuous signal using a classic synchronous storage circuit in which the delay line is tuned to time equal to the difference in the pulse repetition period and the duration of one pulse (Fig. 5):

[0025]

[0026] It is known that a continuous signal has a single-peak spectral structure, and the introduced chirp of the probing SNS provides a frequency shift of the echo signal relative to the emitted one, proportional to the range from the radar to the secondary radiation object:

[0027]

[0028] where - frequency deviation of the probing KNS, - distance to the secondary radiation object, - the speed of propagation of radio waves, - signal duration.

[0029] Then, spectral analysis of the signal transformed using the delay line (6) will allow us to unambiguously estimate the power of the PP in any of the analyzed range resolution elements (Fig. 3). Therefore, at the next stage, a Fourier transform of the received continuous signal is performed to estimate the interference power:

[0030]

[0031] where - converted signal, - frequency, - time.

[0032] At the final stage, the threshold level is calculated in accordance with the expression:

[0033]

[0034] Brief description of drawings

[0035] The invention is explained by the drawings presented in Fig. 1-5, which reveal the essence and principles of forming an adaptive threshold level in the mode of a high repetition frequency of the pulses of the probing signal.

[0036] Figure 1 shows a block diagram of a prototype method for forming an adaptive threshold level:

[0037] 1.1. Block for generating and forming a probing signal (heterodyne voltage);

[0038] 1.2. Transmitting and receiving antenna;

[0039] 1.3. Mixer;

[0040] 1.4. Integrator;

[0041] 1.5. Threshold level generation block.

[0042] Figure 2 shows the behavior of interference in pulsed and quasi-continuous mode. For the former, a characteristic decrease in interference power is observed with increasing distance from the transceiver to the signal reflector. In contrast, with quasi-continuous mode, as the surface being detected moves away from the radar, a false (inflated) interference level is observed.

[0043] Figure 3 shows the behavior of interference in quasi-continuous mode using the proposed method. A characteristic decrease in the interference power level is observed with increasing distance from the reflecting element.

[0044] Figure 4 shows a block diagram of a device implementing the proposed method for generating an adaptive threshold level for a radar detector in the high-pulse repetition rate mode of the probing signal. The following notations are used in Figure 4:

[0045] 4.1. Block for generating and forming a probing signal (heterodyne voltage);

[0046] 4.2. Transmitting and receiving antenna;

[0047] 4.3. Mixer;

[0048] 4.4. Summation block;

[0049] 4.5. Pulse sequence delay block;

[0050] 4.6. Fourier Transform Block;

[0051] 4.7. Threshold level generation block.

[0052] Figure 5 shows a comparative analysis of the behavior of the interference power and the calculated values ​​of the adaptive detection threshold according to the Neumann-Pearson criterion with an increase in the distance of the reflection surface from the radar for the proposed method and the prototype method.

[0053] Implementation of the invention

[0054] The invention can be implemented using the block diagram shown in Fig. 4 and consists of the sequential execution of the following operations:

[0055] - formation of a probing KNS with a chirp (3) with a modulation slope calculated in accordance with (4), carried out by block 4.1;

[0056] - radiation of the formed probing KNS with chirp and reception of echo signals, carried out by block 4.2;

[0057] - demodulation of the echo signal by multiplying it on the mixer with the reference (heterodyne) signal (5), carried out by block 4.3;

[0058] - conversion of the KNS into continuous in a synchronous storage device (block 4.4, 4.5) with a time delay line (6);

[0059] - transfer of the received continuous signal to the frequency domain using the Fourier transform, carried out by block 4.6;

[0060] - calculation of the interference power in the frequency domain (8), and calculation of the threshold level (9), carried out by block 4.7.

[0061] The declared technical result is confirmed by the results obtained by the simulation modeling method in the MATLAB application package.

[0062] Initial data for simulation:

[0063] 1. Type of probing signal: quasi-continuous signal with chirp;

[0064] 2. Probing signal duration: Tс =5 ms;

[0065] 3. Signal pulse duration: T c =0.66 µs;

[0066] 4. Duty cycle Q=15;

[0067] 5. Noise type: white Gaussian noise with unit variance and zero mathematical expectation;

[0068] 6. Voltage signal-to-noise ratio: q=11dB;

[0069] 7. The passive interference model is defined as an additive mixture of copies of the probing signal, shifted relative to each other by the value of the time delay resolution interval, with a random initial phase and amplitude, the mathematical expectation of which decreases proportionally to the increase in range.

[0070] Next, the dependence of the interference power level was investigated and the adaptive detection threshold values ​​were calculated using the Neyman-Pearson criterion with increasing distance of the reflection surface from the radar for the proposed and prototype methods. For this purpose, the additive mixture of noise and passive interference was processed by the proposed and prototype methods using a specially developed and state-registered computer program [7]. As a result of processing by the prototype method, the interference power level and the detection threshold level do not change with increasing range, which will negatively affect the quality indicators of radar target detection. As a result of processing by the proposed method, the interference power level and the detection threshold level decrease with increasing range to 30 km to -20 dB, which will increase the conditional probability of correct target detection with a fixed conditional probability of false alarm.

[0071] Thus, the developed method for forming an adaptive threshold level of a radar detector in the mode of a high repetition rate of probing signal pulses provides the ability, inaccessible to analogs and the prototype, to effectively detect targets with small components of radial velocities in an ID radar against the background of passive interference with a locally concentrated energy spectrum, and above all, under the influence of intense masking reflections from the underlying surface, local objects and slow-moving meteorological formations, which achieves the stated technical result.

[0072] List of used literature

[0073] 1. Bakulev P.A., Stepin V.M. Methods and devices for selecting moving targets. - M: Radio and Communications, 1986. - 288 p.

[0074] 2. Radar signals and their application / A.A. Trukhachev. - M .: Voenizdat.2005. - 234 p.

[0075] 3. Estimation of signal detection losses by a receiver with an adaptive threshold based on the method of order statistics / Orlov I. Ya., Fitasov E.S.-M.: News of universities. Radiophysics. - Vol. LXI, No. 7. - 2018. - P.596-604.

[0076] 4. Adaptive threshold levels in radar signal detection devices / A.A. Trukhachev. - M .: NPO Almaz, 2017. - 344 p: ill.

[0077] 5. Method for unambiguous primary ranging of a group of targets against a background of narrow-band passive interference in the mode of high pulse repetition frequency of the probing signal: patent for invention / S.A. Zaitsev, A.

[0078] M. Lavrentiev, P.V. Pustozerov, K. E. Kuznetsov, Yu.V. Denishchik. - No. 2756034 dated 09 / 24 / 2021.

[0079] 6. Method for selecting moving targets in the high-repetition-rate mode of a probing linear-frequency-modulated signal with a low duty cycle: patent for invention / S.A. Zaitsev, A.M. Lavrentyev, A.A. Kirichenko. - No. 2802367 dated 08 / 28 / 2023.

[0080] 7. Simulation model of a radar signal detector with an adaptive threshold level: certificate of state registration of computer programs / A. M. Lavrentyev, R. V. Zimnovich, N. A. Nemkin, I. A. Smolev S. A. Zaytsev applicants and copyright holder S. A. Zaytsev. - No. 2024612550; declared 19.01.2024; registered 01.02.2024.

Claims

A method for forming an adaptive threshold level of a radar detector in the mode of a high pulse repetition frequency of a probing signal, which consists of forming a probing signal, emitting it, receiving echo signals, optimally processing it by heterodyning the echo signals and integrating the results obtained, measuring the interference power in the analyzed range resolution elements and forming a threshold level as an average value of these measurements, characterized in that a probing linear frequency-modulated signal is formed, and during optimal processing of the echo signals, they are demodulated by multiplying them with a local oscillator signal of the same modulation as the probing signal, converting the quasi-continuous signal into a continuous one and its Fourier transform.

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