RU2245562C2 - Carrier-tuning and mti-mode radar system - Google Patents

Abstract

FIELD: radar engineering.

SUBSTANCE: proposed noise-immune radar system that incorporates provision for maintaining its serviceability in complex electromagnetic situations and intensive background returns from passive noise, local objects, and meteorological formations, as well as for measuring radial speed of target by Doppler frequency shift has tunable microwave oscillator, two gating stages, two gate-pulse generators, synchronizer, τ pulse length delay line, adder, transmitter, transmit-receive switch, transceiving antenna, pulse modulator, high-frequency amplifier, two band filters, two mixers, two intermediate-frequency amplifiers, three phase detectors, two switching circuits, processor, and repetition rate delay line.

EFFECT: enhanced immunity to active noise and facilitated measurement of target radial speed.

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Description

The present invention relates to the field of radar and can find application in the development of noise-resistant radar systems that maintain performance in a complex electromagnetic environment and in the presence of intense interfering reflections from passive interference, local objects and meteorological conditions.

Known radar with the tuning of the carrier frequency and the regime of SDS according to US patent No. 4155088 US MKI ² G 01 S 9/42, NCI 343-7.7, 343-18, 1979. The probe signal used in it is a sequence of composite pulses. Each composite pulse consists of two partial pulses of the same duration of different carrier frequencies. It is fundamental for the implementation of the SDC mode that the carrier frequencies of two partial pulses located at the same position in any two sequentially emitted composite pulses are equal.

In each subsequent composite pulse, the carrier frequencies of the other partial pulse are randomly selected from a given set of frequencies. Therefore, the SDC mode is ensured by processing in the compensation scheme pairs of partial pulses of the same frequency, which are at the same positions in two consecutive composite pulses. At each subsequent probe cycle, the positions of the partial pulses change in accordance with the change in their carrier frequencies.

The operation of the prototype of the proposed radar with the adjustment of the carrier frequency and the mode of the SEC is illustrated by the drawings, presented in figure 1, 2.

Figure 1 - Diagram of changes in the carrier frequency of the probing composite pulses of the prototype.

Figure 2 - Electrical functional diagram of the prototype:

1 - tunable microwave generator;

2 - the first strobe cascade;

3 - second strobe cascade;

4 - the first strobe generator;

5 - second strobe generator;

6 - a sync generator;

7 - delay line for the duration τ;

8 - adder;

9 - transmitter;

10 - receive-transmit switch;

11 - transceiver antenna;

12 - pulse modulator;

13 - high frequency amplifier;

14 - the first band-pass filter;

15 - second band-pass filter;

16 - the first mixer;

17 - the second mixer;

18 is a first intermediate frequency amplifier;

19 is a second intermediate frequency amplifier;

20 is a first phase detector;

21 is a second phase detector;

22 is a first switching diagram;

23 - processor;

24 is a subtraction scheme;

25 - delay line for the repetition period Tp;

26 is a second switching circuit.

The operation of this radar can be explained by a functional diagram. Frequency tunable microwave generator 1 generates continuous microwave oscillations whose frequencies are fm, fn, fm + fnh, fn + fnh, fnh, where fnh is the intermediate frequency of the radar receiver. The frequencies fm and fn are the carrier frequencies of the partial pulses. The frequencies fm + fnh and fn + fnh are heterodyning to lower the frequency of the reflected signal to an intermediate one.

The frequencies fm, fn, fm + fnh and fn + fnh are obtained by multiplying the reference oscillation fnh, which ensures the coherence of all oscillations.

Continuous oscillations with frequencies fm and fn arrive at the first and second strobe stages 2 and 3, respectively, which are controlled by pulses of duration τ generated by the first and second strobe generators 4 and 5, respectively. The synchronization of their start is carried out by pulses generated by the synchro-generator 6. The second strobe generator 5 is launched with a delay of time τ relative to the moment the first strobe pulse generator is started 4. This is ensured by the delay of the synchronization pulses by time τ in LZ 7.

As a result, at the outputs of the first and second strobe stages 2 and 3, partial microwave pulses of duration τ of different carrier frequencies fm and fn and shifted one relative to the other by time τ are formed. After combining them in the adder 8, a composite probing pulse with a duration of 2τ is formed, consisting of two partial pulses of different frequencies. The composite pulse amplified in the transmitter 9 passes through the transmit-receive switch 10 and is radiated through the transmit-receive antenna 11. The transmitter 9 is gated by a pulse modulator 12, the pulse duration of which is selected slightly more than 2τ to eliminate phase distortions that occur when the transmitter is turned on. The signals received from the target are fed to the high-frequency amplifier 13 of the radar receiver. After amplification, partial pulses of different frequencies are selected in the first and second bandpass filters 14 and 15, the passband of which corresponds to parts of the frequency range within which random selection of frequencies fm and fn occurs.

Partial pulses are converted to an intermediate frequency in the first and second mixers 16 and 17, to the heterodyne inputs of which signals fm + fnch and fn + fnch are supplied from the outputs of the microwave generator 1. Partial pulses amplified in the first and second amplifiers of intermediate frequency 18 and 19 are received to the first and second phase detectors 20 and 21, respectively. As a reference signal, fnch oscillations coming from the output of the microwave generator 1 are used. At the outputs of the first and second phase detectors 20 and 21, partial video pulses of the composite signal received from the target are generated.

Video pulses are fed to the first switching circuit 22, which has two signal inputs and outputs.

The second output of the first switching circuit 22 is connected to the first input of the subtraction circuit 24, and the first output, through the delay line 25 for one repetition period, is connected to the second input of the subtraction circuit 24. Video pulses are generated at the output of the subtraction circuit 24 in case of reflections from a moving target. In the case of reflections from local objects and meteorological events, video pulses from the outputs of the first and second phase detectors are mutually compensated and there is no signal at the output of the subtraction circuit 24.

Management of switching schemes and time cycles of the entire radar is carried out by the processor 23.

Due to the fact that the same carrier frequencies are formed at the same positions of the partial pulses, it is necessary to synchronize the start signal of the SDC display. For this, a second switching circuit 26 is used, connected to the synchronizer 6 and the output of the LZ 7, which provides a delay in the start of alternating periods for a time τ.

This radar with the tuning of the carrier frequency and the SDS mode is closest to the proposed one.

However, this radar is characterized by a number of serious drawbacks. The use of partial pulses allows coherent processing between only two partial pulses having the same frequency, but coherence between partial pulses with different carrier frequencies is not ensured. Therefore, the envelope of the video pulses at the output of the subtraction circuit will be random. Accordingly, measuring the radial velocity of a target by Doppler frequency offset is not possible.

Relatively low radar noise immunity in relation to active interference, as The carrier frequency of the partial pulses located at the same positions is repeated, therefore, it can be opened by the REP reconnaissance receiver and suppressed.

The present invention solves the problem of increasing noise immunity with respect to active interference and measuring the radial velocity of the target by Doppler frequency offset.

To achieve the specified technical result in a radar with a tunable carrier frequency and an SDC mode containing a tunable microwave generator, the first and second outputs of which are connected to the first inputs of the first and second strobe stages, respectively, the second inputs of which are connected to the outputs of the first and second strobe generators pulses respectively. The input of the second strobe pulse generator is connected to the output of the delay line for the pulse duration τ. The outputs of the first and second strobe stages are connected to the first and second inputs of the adder, the output of which is connected to the first input of the transmitter, the second input of the transmitter is connected to the output of the pulse modulator, the output of the transmitter is connected to the input of the receive-transmit switch, the input-output of which is connected to the input- the output of the transceiver antenna, and the output of the receive-transmit switch is connected to the input of the high-frequency amplifier. The output of the high-frequency amplifier is connected to the inputs of the first and second bandpass filters. The bandpass filters are connected in series with the first mixer, the first intermediate frequency amplifier, the first phase detector and the second mixer, the second intermediate frequency amplifier, and the second phase detector, respectively. The second inputs of the first and second mixers are connected to the third and fourth outputs of the tunable microwave generator, the second inputs of the first and second phase detectors are connected to the fifth output of the tunable microwave generator. The outputs of the first and second phase detectors are connected to the first and second inputs of the first switching circuit. The first output of the first switching circuit is connected to the first input of the delay line for the repetition period, the second output of the delay line for the repetition period is connected to the input of the sync generator, the output of the sync generator is connected to the second input of the delay line for the repetition period, to the input of the processor, to the input of the first strobe generator , to the input of the delay line for the duration of the pulse τ, to the input of the pulse modulator, to the first input of the second switching circuit, while the second input of the second switching circuit is connected to the output of the delay line and for the pulse duration τ, the first output of the processor is connected to the third input of the first switching circuit, the second output of the processor is connected to the input of the tunable microwave generator, the third output is connected to the third input of the second switching circuit, and also an additional third phase detector, the first input of which is connected with the second output of the first switching circuit, and the second input is connected to the first output of the delay line for a repetition period. In this case, an output of the SDC signal is generated.

It is fundamental to ensure coherent processing that the carrier frequencies of two partial pulses located at the same position in any two sequentially emitted composite pulses differ by a fixed frequency Δf.

In each subsequent composite pulse, the carrier frequency of another partial pulse is randomly selected from a given frequency range.

Due to the presence of distinctive features at the output of the third phase detector, when the signals are reflected from a moving target, video pulses are formed whose amplitude is modulated by the Doppler difference frequency. The Doppler difference frequency depends on the choice of a fixed value of the offset of the carrier frequency Δf

ΔFdop = Fdop2-Fdop1 = 2Vp (f1 + Δf) / s-2Vpf1 / s = 2VpΔf / s,

where Vp is the radial velocity of the target, f1 is the carrier frequency of the first partial probe pulse in the pair, and c is the speed of light.

By the value of the frequency of the envelopes of the video pulses at the output of the third phase detector, it becomes possible to determine the radial velocity of the target.

If the carrier frequency of the first partial pulse in the pair is randomly selected and the carrier frequency Δf is fixed for the second partial pulse in the pair, the value of the carrier frequencies of the entire sequence of composite probe pulses will be presented to the reconnaissance receiver of the electronic suppression system with a random sequence. This greatly complicates the formulation of active interference and, therefore, will increase the noise immunity of the proposed radar.

The proposed radar with the adjustment of the carrier frequency and the mode of the SDC is illustrated by the drawings presented in figure 3, 4.

Figure 3 - Diagram of changes in the carrier frequency of the probing composite pulses.

Figure 4 - Electric functional diagram, where:

1 - tunable microwave generator;

2 - the first strobe cascade;

3 - second strobe cascade;

4 - the first strobe generator;

5 - second strobe generator;

6 - synchronizer;

7 - delay line for the pulse duration τ;

8 - adder;

9 - transmitter;

10 - receive-transmit switch;

11 - transceiver antenna;

12 - pulse modulator;

13 - high frequency amplifier;

14 - the first band-pass filter;

15 - second band-pass filter;

16 - the first mixer;

17 - the second mixer;

18 is a first intermediate frequency amplifier;

19 is a second intermediate frequency amplifier;

20 is a first phase detector;

21 is a second phase detector;

22 is a first switching diagram;

23 - processor;

25 - delay line for the repetition period Tp;

26 - the second switching circuit;

27 - the third phase detector.

The radar with the tuning of the carrier frequency and the SDC mode contains a tunable microwave generator 1, the first and second outputs of which are connected to the first inputs of the first and second strobe stages 2, 3, respectively. The second inputs of strobe stages 2, 3 are connected to the outputs of the first and second strobe generators 4, 5, respectively. The input of the strobe pulse generator 5 is connected to the output of the delay line for a pulse duration of τ 7. The outputs of the strobe stages 2 and 3 are connected to the first and second inputs of the adder 8, the output of which is connected to the first input of the transmitter 9, the second input of the transmitter 9 is connected to the pulse output modulator 12. The output of the transmitter 9 is connected to the input of the transmit-receive switch 10, the input-output of which is connected to the input-output of the transceiver antenna 11, and the output to the input of the high-frequency amplifier 13. The output of the high-frequency amplifier 13 is connected to the inputs the first and second bandpass filters 14, 15. The outputs of the bandpass filters 14, 15 are connected to the first inputs of the first and second mixers 16, 17, respectively. The second inputs of the first and second mixers 16, 17 are connected to the third and fourth outputs of the tunable microwave generator 1, respectively. The outputs of the first and second mixers 16, 17 are connected to the inputs of the first and second amplifiers of intermediate frequency 18, 19, respectively. The outputs of the first and second intermediate frequency amplifiers 18, 19 are connected to the first inputs of the first and second phase detectors 20, 21, respectively. The second inputs of the phase detectors 20, 21 are connected to the fifth output of the tunable microwave generator 1. The outputs of the first and second phase detectors 20, 21 are connected to the first and second inputs of the first switching circuit 22, respectively, the second output of which is connected to the first input of the third phase detector 27, and the first output is to the first input of the delay line for the repetition period Tp 25. The first output of the delay line 25 is connected to the second input of the third phase detector 27.

The time control of the radar is carried out by a sync generator 6, the output of which is connected to the inputs of the processor 23, the first strobe pulse generator 4, the delay line for the pulse duration τ 7, the first input of the second switching circuit 26, the input of the pulse modulator 12 and the second input of the delay line 25.

The input of the clock 6 is connected to the second output of the delay line 25. The output of the delay line 7 is also connected to the second input of the second switching circuit 26. The first, second and third outputs of the processor 23 are connected respectively to the third input of the first switching circuit 22, the input of the tunable microwave generator 1 and to the third input of the second switching circuit 26.

The inventive radar system operates as follows.

The tunable microwave generator 1 generates continuous microwave oscillations of the frequency fnch, fm, fn, fm + fnch, fn + fnch. Oscillations of the carrier frequencies fm, fn arrive at the first and second strobe stages 2 and 3, which are controlled by pulses of duration τ generated by the first and second strobe generators 4 and 5. Synchronization of their start is carried out by synchronization pulses generated by the sync generator 6. Start of the second generator the strobe pulses 5 are delayed for a time τ relative to the start of the first strobe pulse generator 4. This is achieved by delaying the synchronization pulses by time t in the delay line for a duration s pulse τ 7. As a result, the outputs of the first and second gating stages 2 and 3 are formed by partial microwave pulses τ and carrier frequencies fm and fn. In this case, the partial pulses are shifted relative to each other by time τ. The obtained partial pulses are combined in the adder 8, forming a composite radio pulse with a duration of 2τ, consisting of frequencies fm and fn. The composite pulse is amplified in the transmitter 9 and through the receive-transmit switch 10 enters the transceiver system 11, which emits the pulse into space. In this case, the transmitter 9 is gated by a pulse modulator 12, the pulse duration of which is selected slightly more than 2τ to eliminate phase distortions that occur when the transmitter is turned on.

The signals reflected from the target are received by the transceiver antenna 11 and through the receive-transmit switch 10 enter the high-frequency amplifier 13 of the radar receiver. After preliminary amplification, the signals are fed to the first 14 and second 15 bandpass filters, where the signals are separated by the frequencies fm + fdop1 and fn + fdop2, where fdop1, fdop2 is the Doppler frequency shift at the carrier frequencies of the radar fm and fn, respectively.

The conversion of the divided partial pulses to an intermediate frequency is carried out in the first and second mixers 16, 17, the heterodyne inputs of which receive a continuous oscillation with the frequency fm + fnch, fn + fnch from the 3rd and 4th outputs of the tunable microwave generator 1. Amplified in the first and the second intermediate frequency amplifiers 18, 19, partial pulses are fed to the first inputs of the first and second phase detectors 20, 21, the second inputs of which receive the reference voltage fnch from the 5th output of the tunable microwave generator 1. At the outputs of the first second phase detectors 20, 21 is formed corresponding to the Doppler frequency signal and fdop1 fdop2. These signals are fed to the first and second inputs of the first switching circuit 22. The first partial pulse in the pair is delayed in the delay line for the repetition period Tp 25 and is fed to the second input of the third phase detector 27, the first input of which receives an undetected second partial pulse in the pair. At the output of the third phase detector 27, video pulses are formed with an envelope frequency equal to the Doppler difference frequency

Δfdop = fdop2-fdop1 = 2VpΔf / c

The switching circuits 22 and 26 are controlled by the signals of the processor 23. When one of the outputs of the first switching circuit is connected to the delay line for a repetition period Tp 25, the other of its outputs is directly connected to the input of the third phase detector. At the output of the third phase detector 27, an SDC signal is formed by joint processing of partial pulses with a fixed detuning of two sequentially following composite probe pulses.

Due to the fact that the carrier frequencies with a fixed detuning are formed at the same positions of the partial pulses, it is necessary to synchronize the start signal of the SDC display. For this, a second switching circuit 26 is used, connected to the clock 6 and the output of the delay line 7, which provides a delay in the start of alternating periods for a time τ.

Claims (1)

A radar with a tunable carrier frequency and an SDC mode, containing a tunable microwave generator, the first and second outputs of which are connected to the first inputs of the first and second strobe stages, respectively, the second inputs of which are connected to the outputs of the first and second strobe generators, respectively, while the input the second strobe generator is connected to the output of the delay line for the pulse duration τ, the outputs of the first and second strobe stages are connected to the first and second inputs of the adder, the output of which is connected to the first during the transmitter, the second input of the transmitter is connected to the output of the pulse modulator, the output of the transmitter is connected to the input of the receive-transmit switch, the input-output of which is connected to the input-output of the transceiver antenna, the output of the receive-transmit switch is connected to the input of the high-frequency amplifier, the output of the high-frequency amplifier connected to the inputs of the first and second bandpass filters, which are connected in series with the first mixer, the first intermediate frequency amplifier, the first phase detector and the second mix a second intermediate-frequency amplifier, a second phase detector, respectively, while the second inputs of the first and second mixers are connected to the third and fourth outputs of the tunable microwave generator, the second inputs of the first and second phase detectors are connected to the fifth output of the tunable microwave generator, the outputs of the first and second phase detectors are connected to the first and second inputs of the first switching circuit, the first output of the first switching circuit is connected to the first input of the delay line for a repetition period, the second the output of the delay line for the repetition period is connected to the input of the sync generator, the output of the sync generator is connected to the second input of the delay line for the period of repetition, to the input of the processor, to the input of the first generator of strobe pulses, to the input of the delay line for the duration of the pulse τ, to the input of the pulse modulator, to the first input of the second switching circuit, while the second input of the second switching circuit is connected to the output of the delay line for the pulse duration τ, the first output of the processor is connected to the third input of the first switching circuit, in the second processor output is connected to the input of the tunable microwave generator, the third output is connected to the third input of the second switching circuit, characterized in that it also has a third phase detector, the first input of which is connected to the second output of the first switching circuit, the second input is connected to the first output of the line delays for the repetition period.

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