RU2296346C2 - Mode of measuring distance in pulse-doppler radar stations - Google Patents

Abstract

FIELD: the invention refers to radiolocation.

SUBSTANCE: the mode of measuring distance in pulse-Doppler radar stations is in that linear-frequency-modulated radio pulses are radiated with a rate providing single-value measuring distance to any flying vehicle being in the limits of the radar station range; according to received signals rough measurement of distance to all detected flying vehicles and their speed is executed, linear-frequency-modulated radio pulses are radiated once more but with a steepness which provides required clearance of the flying vehicles according to distance and speed; according to received signals ambiguous distances to all detected flying vehicles and their speed are accurately measured, using them and rough measured values of distance denotation of distance to each detected flying vehicle is calculated .

EFFECT: increases accuracy of measuring distance to a flying vehicle.

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Description

The invention relates to radar, in particular to pulse-Doppler radar stations (RLS) using linear frequency modulation of the carrier frequency and is intended to accompany the range and speed of aircraft (LA), observed both against the background of free space and against the background of the earth.

The following range measurement methods and methods for eliminating the range measurement ambiguity are known, which solve the range measurement problem: these are patents RU 2145092 C1, 01/27/2000; RU 2010244 C1, March 30, 1994; US 5546088 A, 06/13/1996, EP 1043601 A1, 10/11/2000, WO 020633336 A1, 08/15/2002, 2237265 C1, 05/27/2003; RU 98104808 A, 01/27/2000, EP 0490423 A, 06/17/1992, US 4713664 A, 12/15/1987, FR 2709835 A, 03/17/1995, RU 2221258 C1, 10/01/2004, etc., based on techniques that allow for variable according to a certain law, the repetition frequencies of the emitted radio pulses or the carrier frequency of the radio pulses determine the exact values of the range to the aircraft.

The disadvantages of radar stations using the above methods for measuring ranges include the following:

- the impossibility of measuring the range to slowly flying (having low approach speeds) observed on the background of the earth, aircraft due to the fact that the use of the above methods in the radar does not allow to distinguish radio signals reflected from the aircraft against the background of powerful reflections from the ground;

- the impossibility of resolving aircraft flying at the same speed in the group due to the difficulty of resolving the radio signals reflected from them;

- significant difficulties in the detection and tracking of aircraft flying over a smooth earth or sea surface due to the strong influence of the antipode, causing the fading of the signals reflected from the aircraft.

Of the known technical solutions, the closest (prototype) is a method of measuring the range of several targets with pulse-Doppler radar with an average pulse repetition rate [patent RU 2221258 C1, 01.10.2004], consisting in the following:

- emit radio pulses with linear frequency modulation (LFM) of the carrier frequency and receive radio signals reflected from the aircraft and the earth;

- detect the radio signals reflected from the aircraft and the earth with a multichannel delay time and Doppler frequency receiving device with a chirp local oscillator;

- measure and remember ambiguous delay times and Doppler frequencies in those channels where the radio signals reflected from the aircraft were detected;

- repeat these operations with the same value of the pulse repetition rate (NRF) with the LFM carrier frequency, first with one sign of the increment of the slope of the emitted LFM signal, and then with the opposite sign of the increment of the slope of the emitted LFM signal, and the magnitude of the increments of the slope of the emitted LFM signals is set to so that the total change in the Doppler frequency of the received signal during repeated measurements does not exceed the PI with the LFM carrier frequency minus the length of the blind zone in Doppler frequency even for aircraft, dressing at the maximum range for which this radar is designed;

- according to the magnitude of the increment of the frequency of the received signal, the unequivocal values of the ranges to the detected aircraft are roughly calculated;

- the stored values of the ambiguous delay time and Doppler frequency accurately calculate the range to each detected aircraft.

The disadvantages of the prototype: low accuracy of range measurement due to the low steepness of the emitted chirp signal; the impossibility of measuring the distance to slowly flying aircraft, observed on the background of the earth due to the fact that the method does not provide the allocation of reflected from the aircraft radio signals against powerful reflections from the earth; the impossibility of resolving aircraft flying at the same speeds in the group due to the low resolution of the radio signals reflected from them.

Thus, the object of the invention is to increase the accuracy of measuring the distance to the aircraft, observed from any angle against the background of the earth, and the resolution of the aircraft flying in a dense group with the same speeds.

The problem is achieved in that at the first stage:

- they emit LFM radio pulses with a slope that provides a measurement of the unique range to the aircraft with low accuracy; receive radio signals reflected from the aircraft and the earth; measure the frequency values of the received radio signals; the values of the unambiguous ranges to the aircraft are measured with an accuracy determined by the steepness of the LFM carrier frequency of the emitted radio pulses;

- from the measured values of the unambiguous ranges to the detected aircraft determine: the value of the repetition frequency of the emitted radio pulses (IPIR), ensuring that the reflected radio signals from the aircraft in the transparency zone [Merkulov VI, Kanaschenkov AI, Perov AI and others. Estimation of range and speed in radar systems. 4.1. / Ed. A.I. Kanaschenkov and V.I. Merkulov. - M .: Radio engineering, 2004, p. 293]; the ambiguity coefficient for each detected aircraft, corresponding to the above defined CPIR; unambiguous range interval value corresponding to the above defined CPIR;

in the second stage:

- they emit LFM radio pulses with a slope that provides the required resolution of the aircraft in range and speed; receive radio signals reflected from the aircraft and the earth; measure the frequency values of the received radio signals and, using them, measure ambiguous ranges to the detected aircraft; from the values of ambiguous ranges, the values of the coefficients of ambiguity and the value of the interval of unambiguous ranges with high accuracy determine the range to the detected aircraft.

According to the proposed method, the following is performed:

- a priori establish the calculated value of the slope S _{about the} LFM of the carrier frequency of the emitted radio pulses, providing an unambiguous, but rough (with low accuracy) measurement of the range to any, within the range of the radar, aircraft. The calculation of the slope S _o can be performed by the formula:

where Δf _max is the maximum possible frequency tuning range in the radar during the time of emission of radio pulses;

D _max - the range to the maximum remote from the radar detected aircraft;

c ₀ is the speed of light;

- and the calculated value of the slope S _tr LFM carrier frequency of the emitted radio pulses, providing the required radar resolution in range and speed. The calculation of the slope S _tr can be performed by the formula:

where Δf is the passband of the low-pass filter that determines the required radar resolution in speed;

ΔD - the required resolution of the radar range.

The slope value S _tr LFM of the carrier frequency of the emitted radio pulses, calculated by the formula (2), is approximately an order of magnitude greater than the slope value S _о , and therefore, when using it, an unambiguous measurement of the range to the detected aircraft can be provided; however, it makes it possible to significantly increase the accuracy of measuring the range to aircraft when using LFM radio pulses, the dispersion of measurement errors of which is determined by the ratio [Merkulov V.I., Kanaschenkov A.I., Perov A.I. and others. Estimation of range and speed in radar systems. Part 1. / Ed. A.I. Kanaschenkova and V.I. Merkulova. - M .: Radio engineering, 2004, p. 264]

where D _D is the variance of the measurement error range; D _f is the variance of the Doppler frequency shift estimate; c ₀ is the speed of light; S is the slope of the LFM carrier frequency of the emitted radio pulses.

- emit radio pulses with a repetition frequency F _pi and LFM carrier frequency with a slope of S _about . The method does not impose restrictions on the value of the repetition frequency F _{pi of the} emitted radio pulses: it can be any medium or high one used in pulse-Doppler radars;

- receive radio signals reflected from the aircraft and the earth;

- measure the frequency f _pri received radio signals;

- determine the unique value of the range D _oi to each i-th aircraft detected by the value of the frequency f _{pri of the} received radio signals and the slope value S _{of the} LFM of the carrier frequency of the emitted radio pulses by any of the known methods, for example, in accordance with the equation:

where f ₀ is the initial value of the frequency of the emitted radio pulses.

To measure the unique values of the ranges of D _oi can be used used in the prototype multi-channel in time delay and Doppler frequency receiving device with a chirp local oscillator. The measurement of unique ranges in the latter case will be ensured by the slope value S _o LFM of the carrier frequency of the emitted radio pulses used in the proposed method, which allows measuring the unique range to all aircraft located in the radar coverage area.

- determine the new value of IPIR F _pi , ensuring that radio signals reflected from the detected aircraft enter the transparency zones, and the value of the ambiguity coefficient K _ni for each i-th detected aircraft, which is stored. The determination of the IPIR values F _pi and the coefficient K _{n of} ambiguity is possible by any of the known methods, for example, given in [patent RU No. 2219558, G 01 S 13/12, 03/27/2002] or in [Merkulov V.I., Kanaschenkov A.I. ., Perov A.I. and others. Estimation of range and speed in radar systems. Part 1. / Ed. A.I. Kanaschenkov and V.I. Merkulov. - M .: Radio engineering, 2004, p. 298]. In accordance with the method described in the literature, the values of the coefficient K _{ni of} ambiguity and IPIR F _pi can be found as follows:

- using the found unique value of the range D _oi to each 1-st detected aircraft for each j-th, of all possible in the radar, the values of the repetition period T _pj calculate the relative delay of the received signal

where Θ _ij is the relative delay of the received signal from the i-th detected aircraft for the j-th repetition period T _pj ;

- for each i-th detected aircraft calculate the value of the coefficient K _ni ambiguity by the formula

where the notation int [·] means the operation of taking the integer part of the number in square brackets;

- setting an ambiguous relative delay Θ _{0j by the} condition that the signal from the i-th target must reach a certain point in the transparency zone, for example, in its middle, for each j-th repetition period T _pj calculate the difference

in this case, the repetition period T _pj , for which this difference will be the smallest, is used to calculate the CPIR according to the formula

- find the value of the interval of unique range ΔD _about = s ₀ / F _pi , corresponding to the above-defined value IPIR F _pi . The value of the interval of unambiguous range ΔD _about remember;

- they emit LFM radio pulses with a new PNIR F _pi and a slope value S _tr LFM of the carrier frequency of the emitted radio pulses, providing the required radar resolution in range and speed;

- receive the radio signals reflected from the aircraft and the earth and measure the frequencies f _{pri of the} received radio signals;

- determine the ambiguous values of the range of D _ni to each i-th detected aircraft by the value of the frequencies f _{pri of the} received radio signals and the value of the slope S _tr LFM carrier frequency of the emitted radio pulses. The determination of the values of ambiguous ranges D _{ni is} possible by any of the known methods, for example, in accordance with the equation:

to measure the ambiguous values of the ranges of D _{ni, a} multi-channel receiving device with a LFM local oscillator used in the prototype for the delay time and Doppler frequency can be used;

- find the unique value of the range D ′ _oi to each i-th aircraft detected by the measured values of the ambiguous ranges of D _ni , the values of the coefficients K _{ni of the} ambiguity and the value of the interval of the unambiguous range Δ Д _about by the formula:

The unique values of the ranges D _oi and D ′ _oi calculated by formulas (3) and (5), respectively, differ only in the accuracy of determining the range to the detected aircraft.

For a better understanding of the proposed method as a process of performing actions on a material object using material means and confirming the possibility of carrying out the claimed invention, the drawing shows a structural diagram of a pulse-Doppler radar with a range measurement method implemented in it, where:

1 - antenna;

2 - antenna switch (AP);

3 - receiving device (PFP);

4 - analog-to-digital Converter (ADC);

5 - on-board digital computer (BTsVM);

6 - storage device (memory);

7 - transmitting device (PRD);

8 - synchronizer;

9 - local oscillator.

Antenna 1 is connected to the AP 2, the input of which is connected to the output of the PRD 7, the first input of which is connected to the first output of the synchronizer 8. The output of the AP 2 is connected to the first input of the PRM 3, the second input of which is connected to the second output of the synchronizer 8, the input of which is connected to the first the output of the digital computer 5. The output of the PRM 3 is connected to the first input of the ADC 4, the output of which is connected to the first input of the digital computer 5, the third output of which, which is also its third input, is connected to the first input, which is also the first output, memory 6, through the second input whose cc DYT original data. The third output of the synchronizer 8 is connected to the second input of the ADC 4, and the fourth output to the second inputs of the local oscillator 9 and the digital computer 5. The second output of the digital computer 5 is connected to the first input of the local oscillator 9, the output of which is connected to the second input of the PRD 7.

The pulse-Doppler radar cited as an example of implementation with the range measurement method implemented in it operates as follows.

Before starting work in the memory 6 from external systems enter: N _chpir (from 3 to 5) values IRP F _pi providing a given radar potential (while to ensure a given potential radar NPIR are such that an unambiguous range measurement is not provided); f ₀ is the initial value of the frequency of the emitted radio pulses; c ₀ is the value of the speed of light; Δf is the value of the passband used in the radar low-pass filters that determine the resolution of the radar speed; ΔD is the radar resolution range. In addition, according to formulas (1) and (2), they are calculated and entered into memory 6: S _о is the slope value of the LFM carrier frequency of the emitted radio pulses, which provides an unambiguous but crude measurement of the distance to aircraft located in the radar coverage area; S _Tr - the value of the slope of the LFM carrier frequency of the emitted radio pulses, providing the required radar resolution in range and speed.

The digital computer 5, depending on the operating mode of the radar, reads from the memory 6 one of the IPIR values F _pi stored in it, as well as the slope value S _{of the} LFM of the carrier frequency of the emitted radio pulses, providing an unambiguous range measurement. The value of CPIR F _pi BCVM 5 through the first output is issued to the synchronizer 8, and the value of the slope S _o through the second output to the local oscillator 9.

The synchronizer 8 in accordance with the obtained value of the PFIN F _pi generates: start pulses of the transmitter (ITP), which through the first output feeds to the first input of the PRD 7; receiver locking pulses, which through the second output feed to the second input of the PFP 3; pulses of the beginning of radiation, which through the fourth output feeds to the second inputs of the local oscillator 9 and the digital computer 5; clock pulses, which through the third output delivers to the second input of the ADC 4.

The local oscillator 9 generates a linearly changing frequency signal, which from its output goes to the second input of the PRD 7.

PRD 7, in accordance with the obtained IPP, generates radio pulses, the modulation of which in frequency is carried out by a local oscillator signal 9.

The claimed method does not impose any restrictions on the procedures for generating a signal linearly varying in frequency and generating LFM of emitted radio pulses; therefore, local oscillators and PRD of modern radar systems can be used as local oscillator 9 and Tx 7.

Formed by the LFM radio pulses from the output of the PRD 7 through AP 2 enter the antenna 1 and are emitted into space.

The radio signals reflected from the aircraft and the earth are received by the antenna 1 and, after amplification in it, are fed through the AP 2 to the input of the PFM 3, which selects, amplifies, and converts it to an intermediate frequency.

The claimed method does not impose any restrictions on the procedures of selection, amplification and conversion of received radio signals, whereby any modern radar receiver can be used as a PFP 3.

The radio signals converted to the intermediate frequency from the output of the PFP 3 are fed to the first input of the ADC 4, which, in accordance with the clock pulses coming from the synchronizer 8, converts them into digital form by time and level quantization.

From the output of the ADC 4, the radio signals in digital form are fed to the first input of the digital computer 5, which, using pulses of the start of radiation, one of the known methods, for example, used in the prototype, performs multi-channel processing of the received radio signals in terms of delay time and Doppler frequency, the result of which is frequency f _pri of the radio signals reflected from these aircraft, where i is the number of the detected aircraft.

Then, the digital computer 5 reads from the memory 6 the initial value of the frequency of the emitted radio pulses f ₀ , the speed of light c ₀ and the slope value S _{of the} LFM of the carrier frequency of the emitted radio pulses, and using the measured values of the frequencies f _{pri of the} received radio signals, calculates the unique ranges D _oi to all detected aircraft, which through the third output transfers to memory 6, which remembers them.

After this, the computer 5:

- using the calculated unambiguous ranges D _oi to the detected aircraft by one of the known methods, for example, given in [patent RU No. 2219558, G 01 S 13/12, 03/27/2002], calculates the CPIR value F _pi , which ensures that radio signals reflected from the detected aircraft are hit in the transparency zone, and the coefficient K _{ni of} ambiguity for each i-th detected aircraft. The values of the coefficients K _{ni of the} ambiguity of the computer 5 through the third output gives in the memory 6, which remembers them. The value of CPIR F _pi BCVM 5 through the first output produces in the synchronizer 8;

- according to the formula (4) calculates the value of the interval of the unique range Δ Д _о corresponding to the calculated value of the CPIR F _pi , and through the third output gives it to the memory 6, which remembers it;

- reads from the memory 6 the value of the slope S _tr LFM carrier frequency of the emitted radio pulses, providing the required radar resolution in range and speed, and through the second output feeds it to the first input of the local oscillator 9.

The synchronizer 8, in accordance with the new value CPIR F _pi , again generates the above-mentioned pulses and issues them to the same destinations.

The local oscillator 9 generates a linearly varying frequency signal, but with a new slope value, which from its output goes to the second input of the PRD 7.

PRD 7, AP 2, antenna 1, PRM 3, ADC 4, BTsVM 5 again, as described above, carry out: generation of LFM radio pulses and their radiation, reception of radio signals reflected from the aircraft and the earth, their selection, amplification, conversion to an intermediate frequency, digitalization and measurement of the frequencies f _pri of the radio signals reflected from these aircraft.

After that, the digital computer 5, using formula (5), calculates the ambiguous values of the ranges Д _нi to all detected aircraft and reads from the memory 6 the stored values of the ambiguity coefficients К _нi for all detected aircraft and the value of the unique range interval ΔД _о , which, using formula (6), calculates the exact value of the range D _oi to each i-th aircraft.

The proposed method for measuring range in pulse-Doppler radars has a fundamental difference from the known methods, which consists in high accuracy of measuring range to aircraft, including slowly flying ones, and their resolution in the group even if their speeds are equal, since the value is used to calculate the range the slope of the LFM carrier frequency of the emitted radio pulses, providing the required radar resolution in range and speed (see formula (2)). Moreover, the inventive method does not impose restrictions on the value of the slope of the chirp signal, which will ensure high resolution radar range and speed.

The effectiveness of the proposed method of measuring range was checked using mathematical modeling. The model included all the blocks shown in figure 1. The accuracy of the range measurement was estimated by statistical processing of a series of random results obtained by mathematical modeling of the signal processing process. The results showed that the measurement of the range to the aircraft is provided with a standard deviation of units of meters.

Claims (1)

The method of measuring range in pulse-Doppler radar stations (radar), based on the emission of radio pulses with a given repetition rate (PIIR) F _pi and linear frequency modulation (LFM) of the carrier frequency and the reception of radio signals reflected from aircraft (aircraft) and the earth, characterized in that a priori establish the calculated value of the slope S _{about the} LFM of the carrier frequency of the emitted radio pulses, providing an unambiguous, but rough measurement of the range to any, within the range of the radar, aircraft according to the formula

where Δf _max is the maximum possible frequency tuning range in the radar during the time of emission of radio pulses; D _max - the range to the maximum remote from the radar detected aircraft; c ₀ is the speed of light, and the calculated value of the slope S _tr LFM carrier frequency of the emitted radio pulses, providing the required radar resolution in range and speed, in accordance with the formula

where Δf is the passband of the low-pass filter that determines the required radar resolution in speed; ΔD is the required radar resolution in range, emit radio pulses with a repetition frequency F _pi and LFM carrier frequency with a slope of S _about receive radio signals reflected from the aircraft and the earth, measure the frequency f _pri received radio signals, determine the unique value of the range D _oi to each i-th detected aircraft by the value of the frequency f _{pri of the} received radio signals and the slope value S _{of the} LFM of the carrier frequency of the emitted radio pulses, using the calculated unambiguous ranges of D _oi to the detected aircraft, determine the new value of the PIIR F _pi , providing hit reflected from the detected LA radio signals in the transparency window, and the value of the coefficient K _ni ambiguity for each i-th detected LA, which is stored, find and remember the value of the interval of unique range ΔD _about = c ₀ / F _pi corresponding to the value found above IPIR F _pi , emit LFM radio pulses with a new PIIR F _pi and a slope value S _tr LFM of the carrier frequency of the emitted radio pulses, providing the required radar resolution in range and speed, receive the radio signals reflected from the aircraft and the earth and measure the frequencies f _{pri of the} received radio signals, the value of the frequencies f _{pri of the} received radio signals and the value of the slope S _tp LFM of the carrier frequency of the emitted radio pulses determine the ambiguous value of the range of D _ni to each i-th detected aircraft, according to the measured values of the ambiguous ranges of D _ni , the values of the coefficients K _{ni of the} ambiguity and the value of the interval of the unique range Δ Д _о in accordance with the expression

find a unique value of the range D _oi to each i-th detected aircraft.