RU2799999C1 - Radiolocation method with carrier frequency tuning from pulse to pulse - Google Patents

Abstract

FIELD: radar technology.

SUBSTANCE: probing and heterodyne radio pulses are received by impact on the RF generator by a sequence of paired pulses, forming during each radio pulse coherent frequencies of the triggering oscillation pulses, which are shifted relative to each other by the value of the intermediate frequency. The probing radio pulses of each pair are emitted, the reflected radio pulses are received and mixed in the mixer with the oscillations of the RF generator during the formation of heterodyne radio pulses of each pair, the reflected radio signals at an intermediate frequency are isolated with subsequent filtering. The frequencies of the probing and heterodyne radio pulses are tuned from clock to clock by changing the natural frequency of the RF generator resonator while maintaining in each clock the difference in the frequencies of the radio pulses equal to the intermediate frequency.

EFFECT: ensuring optimal reception of reflected signals when changing the carrier frequency of emitted radio pulses from pulse to pulse without imposing requirements for long-term stability of the frequency parameters of the input devices and with a simpler practical implementation.

2 cl, 4 dwg

Description

The invention relates to the field of radar engineering and can be used in the construction of airborne radar stations with carrier frequency tuning from pulse to pulse.

A known method of radar with carrier frequency tunability from pulse to pulse (see p. 8, Fig. 1, [1]), which consists in the use of simultaneously tunable transmitter and receiver.

The implementation of the method [1] is as follows.

In a frequency agile transmitter, radiated radio pulses of a carrier frequency are generated, which are radiated in the direction of the target. The reflected signals are received by the receiver, in which the tuning frequency is changed using a frequency-tunable local oscillator. The frequencies of the transmitter and the local oscillator of the receiver are tuned in such a way that the difference frequency always has a constant value equal to the intermediate frequency of the receiver. Optimal filtering of the reflected signals is provided at the intermediate frequency by a frequency selective device (FID), the bandwidth of which is matched to the spectrum of the emitted radio pulse.

The disadvantages of the method [1] are:

- the complexity of pairing the frequencies of the transmitter and the local oscillator of the receiver when they are tuned in the operating frequency range;

– the need to ensure the long-term stability of the frequency parameters of the transmitter master oscillator, local oscillator and frequency-selective device during the operation of the radar.

There is a known method of radar with carrier frequency tuning from pulse to pulse (see pp. 503–506, Fig. 13.4, [2]), which consists in using an automatic frequency control (AFC) system of the receiver local oscillator, which provides conjugation of the carrier frequency of the transmitter with the tuning frequency of the receiver.

The implementation of the method [2] is as follows.

The transmitter generates radio pulses of the carrier frequency, which are emitted in the direction of the target. Part of the transmitter signal power enters the AFC system of the receiver local oscillator and in a time equal to the duration of the emitted radio pulse, the AFC system adjusts the frequency of the receiver local oscillator. The discriminator frequency of the AFC system, equal to the difference between the carrier frequency of the transmitter and the frequency of the local oscillator of the receiver, coincides with the intermediate frequency of the receiver.

The signal reflected from the target enters the receiver, the tuning frequency of which, using the AFC system of the local oscillator during the emission of the radio pulse, is tuned to the carrier frequency of the transmitter, while the bandwidth of the linear part of the receiver is matched to the width of the spectrum of the radio pulse of the transmitter. This equality provides the condition for optimal reception of the reflected signal.

The disadvantages of the method [2] are:

– the need to ensure the stability of the frequency characteristics of the discriminator of the AFC system of the local oscillator and the amplitude-frequency characteristic (AFC) of the intermediate frequency amplifier (IF) of the receiver;

– the presence of a residual mismatch in the AFC system of the local oscillator, which does not allow for full matching of the bandwidth of the linear part of the receiver with the width of the spectrum of the radio pulse of the transmitter, i.e. its optimality;

– the presence of restrictions on the duration of the emitted radio pulses during the tuning of their carrier frequency due to the inertia of the local oscillator AFC system.

There is a known method of radar with a change in the carrier frequency from pulse to pulse [3], which consists in the formation of the emitted signal and filtering the reflected signal by one CFD using the method of direct and return heterodyning with changing the carrier frequency by tuning the frequency of the heterodyne signal and detecting the reflected signal at an intermediate frequency, and the emitted signal is obtained by direct heterodyning down to the intermediate frequency of the input intrinsic noise of the receiving device, amplification, its subsequent narrow-band filtering at the intermediate frequency of the CID with obtaining quasi harmonic noise of the intermediate frequency, reverse upward heterodyning of quasi-harmonic noise from the intermediate frequency to the carrier frequency, amplification, limiting the amplitude from above this noise, its amplitude-pulse manipulation, amplification to the required level of the radiated pulse power, followed by radiation by the transmitting antenna.

The main disadvantage of the method [3] is a weak degree of coherence of the oscillations of the generated radio pulses due to the use of the quasi-harmonic noise of the receiving device as a reference signal source. This is the reason that limits the maximum range of pulse-Doppler radars. In addition, the method [3] differs in the complexity of its implementation.

There is a method of radar with carrier frequency tuning from pulse to pulse [4], which consists in obtaining a carrier frequency signal by direct heterodyning of radio pulses of a fixed frequency up in frequency by the frequency of the heterodyne signal and receiving the reflected signal by reverse heterodyning by shifting it down in frequency, followed by filtering the reflected signal in the CIA at the frequency of radio pulses of a fixed frequency, while the carrier frequency is tuned by changing the frequency of the heterodyne signal, with direct heterodyning as a radio pulse fixed-frequency pulses use the CFD response to an ultrashort pulse action, and after return heterodyning, the reflected signal is filtered by the same CFD, with direct and return heterodyning carried out by the same device.

The disadvantages of the method [4] are:

– the inability to control the duration of the radio pulse generated in the CRM;

– stringent requirements for the form of frequency response of CRI;

– the inability to optimize the radio signal conversion mode from the intermediate frequency to the carrier (radiated) frequency and from the carrier (received) frequency to the intermediate frequency by the method of direct and return heterodyning when using the same device;

- high current consumption in the power circuit;

– the presence of radiation leakage from a continuous signal source with frequency tunability complicates the solution of the problem of electromagnetic compatibility and secrecy of work in the conditions of an increased number of radio facilities.

The first drawback is related to the dependence of the duration of the radio-pulse response of the CID on the impulse action ( ps) from strip passing CIA as , Where is the CFD bandwidth, i.e. an increase in the duration of a radio pulse is possible only with a decrease in the bandwidth of the CID, which is technically not always feasible (see pp. 303–311, [5]). This leads to a limitation of the range of measured ranges.

The second disadvantage is due to the dependence of the radio pulse envelope on the shape of the frequency response of the FID, in which the appearance of “tails” and “harbingers” in the oscillogram of the generated radio pulse is possible (see pp. 305–307, Fig. 5.30, 5.31, [5]).

The third drawback is associated with the need to use a reciprocal-type converting device based on a diode mixer for direct and return heterodyning, the operating mode of which, when receiving reflected radio pulses (receiving mixer operating mode), should provide a minimum level of introduced noise, and when generating radiated signals (shift mixer operating mode) - the maximum conversion coefficient, which is technically difficult to implement on one device. Thus, the non-optimality of direct and return heterodyning using the same device leads to the need to introduce additional stages in the power amplifier, which worsens the weight and size characteristics and reduces the overall efficiency of the transceiver.

The fourth and fifth disadvantages are due to the constancy of the operating mode of the continuous signal source with frequency agility.

The closest analogue (prototype) of the proposed method is the method of radar with carrier frequency tunability from pulse to pulse (Soloviev N.A. Using a signal with spectrum synthesis to build a range portrait and inverse aperture synthesis // Science and Education: scientific and technical edition: 77-30569/249869. Scientific publication of MSTU named after N.E. Bauman, November, 2011 [6 ]), which consists in the formation of an emitted radio pulse by transferring the radio pulse signal of the generator, the frequency of which is fixed and equal to the intermediate frequency of the receiver, to the carrier frequency by the method of heterodyning using a continuous heterodyne signal tunable in frequency, and receiving the reflected signal by a superheterodyne receiver using the same heterodyne signal.

The implementation of the prototype method is as follows.

From signal (see pos. 1 in Fig. 1) a source of radio pulses of a fixed frequency (see diagram " a " in Fig. 2) and a continuous heterodyne signal (see pos. 2 in Fig. 1) with a frequency frequency tunable source (see diagram “ b ” in Fig. 2) by direct heterodyning up in frequency, the first mixer (see pos. 2 in Fig. 1) generates a radio pulse signal carrier frequency (see diagram " in " in Fig. 2) , which, after being amplified by a power amplifier (see item 3 in Fig. 1), is radiated towards the target.

The radio signal reflected from the target (see diagram “ d ” in Fig. 2) after amplification with a low-noise amplifier (see pos. 5 in fig. 1) by the method of reverse heterodyning by a second mixer (see pos. 6 in fig. 1) is shifted down to an intermediate frequency , at which the intermediate frequency signal (see diagram " e " in Fig. 2) is filtered consistent with the spectrum of the emitted signal CIA (see pos. 7 in Fig. 1) with a bandwidth .

Thus, if the frequency of the source of radio pulses is equal intermediate frequency , on which the filtering is carried out, , for any carrier frequency of the emitted signal the receiver will be tuned to that frequency.

The disadvantages of the prototype method [6] are:

– the need to maintain in operation the equality of the frequencies of the source of radio pulses of the transmitter to the tuning frequency of the CFD of the receiver;

– the complexity of the scheme that implements this method;

- high current consumption in the power circuit;

– the presence of radiation leakage from a continuous signal source with frequency tunability complicates the solution of the problem of electromagnetic compatibility and secrecy of work in the conditions of an increased number of radio facilities.

The first drawback is due to the difficulty of ensuring the long-term stability of the frequency parameters of the transmitter and the CFD of the receiver during aging and destabilizing environmental factors.

The second drawback is due to the presence of two mixers, of which the first (shift mixer) generates a carrier frequency signal in the transmitter by direct heterodyning, the second in the receiver converts the reflected carrier frequency signal into an intermediate frequency signal by reverse heterodyning.

The third and fourth disadvantages are due to the constancy of the operating mode of the continuous signal source with frequency agility.

Thus, the technical problem to be solved by the claimed invention consists in the need to ensure optimal reception of reflected signals when the carrier frequency of the emitted radio pulses is tuned from pulse to pulse without imposing requirements on the long-term stability of the frequency parameters of the incoming devices and with a simpler practical implementation, as well as reducing power consumption, reducing the level of spurious signals and interference in the power and control circuits.

The solution to this problem is achieved by the proposed method of radar with carrier frequency tuning from pulse to pulse, which consists in the fact that a high-frequency (HF) generator is impacted by a sequence of paired trigger pulses with steep fronts, while forming coherent oscillations relative to the trigger pulses during each radio pulse, and the oscillation frequencies of the radio pulses of each pair are shifted relative to each other by the value of the intermediate frequency, the first radio pulses of each pair are probing, and the second are the local oscillator Probing radio pulses of each pair formed in the RF generator radiate into the controlled space, receive reflected radio pulses from the target located in this space and mix them in the mixer with oscillations of the RF generator during the formation of heterodyne radio pulses of each pair, select the reflected radio signals at an intermediate frequency with subsequent filtering, while the frequencies of the probing and heterodyne radio pulses are tuned from cycle to cycle by changing the natural frequency of the RF generator resonator with preservation in each cycle frequency difference of radio pulses equal to the intermediate frequency.

Obtaining the best result in frequency multiplication is achieved by the fact that in the method of radar with frequency tunability from pulse to pulse, the duration of the shock pulse front is chosen such that it is equal to half the oscillation period of the RF generator, and the amplitude of the pulses is at least an order of magnitude higher than the level of intrinsic noise of the RF generator.

The pulse-to-pulse hopping radar method is illustrated by the following figures.

The figure 1 shows a functional diagram explaining the prototype method of radar with changing the carrier frequency from pulse to pulse. It shows: 1 - a source of radio pulses (RES) of a fixed frequency; 2 – the first mixer (Sm-1) performing direct heterodyning; 3 – power amplifier (PA); 4 - source of a continuous signal with frequency agility (FC); 5 – low noise amplifier (LNA); 6 – the second mixer (Sm-2) performing reverse heterodyning; 7 - CIA intermediate frequency.

The figure 2 shows signal voltage diagrams that explain the prototype method of radar with a change in carrier frequency from pulse to pulse, where:

" a " - radio pulse signals fixed frequency ;

" b " - frequency-tunable continuous heterodyne signal with current frequency ;

" in " - emitted radio pulse signals carrier frequency , obtained by direct heterodyning;

" g " - reflected signals carrier frequency ;

" d " - reflected signals intermediate frequency obtained by the reverse heterodyning method.

The proposed method of radar with changing the carrier frequency from pulse to pulse is explained by the following figures.

The figure 3 shows a functional diagram explaining the proposed method of radar with changing the carrier frequency from pulse to pulse. It shows: 1 - shock pulse generator (SIUV) with a steep front; 2 - RF generator (HFG), made with the possibility of frequency control; 3 – power amplifier (PA); 4 – low noise amplifier (LNA); 5 - mixer (cm); 6 – frequency-selective device (FSM) of intermediate frequency.

The figure 4 shows signal voltage diagrams explaining the proposed method of radar with a change in carrier frequency from pulse to pulse, where:

" a " - the output voltage of the pulse generator shock impact;

" b " - output fluctuations RF generator during the formation of pairs of radio pulses on the first and second frequencies, respectively;

" in " - fluctuations radio pulses reflected from the target;

" g " - converted vibrations frequencies at the outlet of the mixer;

" d " - signals intermediate frequency obtained at the output of the frequency-selective device CIA.

The proposed radar method with carrier frequency tuning from pulse to pulse and optimal reception of reflected signals is carried out as follows.

The high-frequency (HFG) generator (see item 2 in Fig. 3) is shocked a sequence of paired trigger pulses with steep fronts (see diagram " a " in Fig. 4), which are formed in the SIUV (see pos. 1 in Fig. 3). Provided that the duration of the front of the trigger pulses is approximately equal to half the oscillation period of the RF generator, and the amplitude of the pulses is not less than an order of magnitude higher than the level of the intrinsic noise of the RF generator, the so-called shock oscillations at the natural frequency of the RF generator resonator are most effectively excited in it (see Section 5.6. "Approximate procedure for designing and calculating the RFC", pp. 103–108, book [7]). Shock oscillations in the RF generator impose the initial phase [8] of the oscillations of each radio pulse and ensure their coherence with respect to frequency trigger pulses [9, 10].

When tuning the natural frequency of the resonator of the RF generator from the frequency per frequency in the process of formation of the first and second radio pulses of each pair, coherent oscillations are obtained radio pulses at frequencies, respectively And , multiples of the trigger pulse frequency , Where , are the frequency multiplication factors of the first and second radio pulses (see diagram " b " in Fig. 4). Frequency difference And is chosen equal to the intermediate frequency by choosing coefficients And multiplication.

The first radio pulses (probing) of each pair at a frequency arrive at the heterodyne input of the mixer (see pos. 5 in Fig. 3) and at the input of the power amplifier (see pos. 3 in Fig. 3). From the output of the last sounding radio pulses further through the transmitting antenna emitted into the radar-controlled space in the direction of the target.

Radio pulses reflected from a target located in a controlled space at frequency (see diagram " c " in Fig. 4) through the receiving antenna and a low-noise LNA amplifier (see pos. 4 in Fig. 3) are sent to the mixer Сm (see pos. 5 in Fig. 3), the heterodyne input of which receives heterodyne radio pulses of each pair, generated by an RF generator at a frequency (see diagram " b " in Fig. 4). Further from the output of the mixer See radio pulses (see diagram " g " in Fig. 4) intermediate frequency pass through the CIA (see pos. 6 in Fig. 3) in the form of a signal (see diagram " e " in Fig. 4). CFD frequency response over bandwidth matched with the spectrum received radio pulses, which ensures their optimal reception.

From cycle to cycle of formation, emission of probing and reception of reflected radio pulses, the natural frequency of the resonator of the RF generator is tuned while maintaining for each cycle the condition of equality of the frequency difference And intermediate frequency: . This achieves a change in the carrier frequency of the probing radio pulses from pulse to pulse and the reception of radio signals reflected from the target at the radiation frequency. To reduce spurious radiation into space, it is advisable to turn off the PA power amplifier in the "Receive" mode, and in the "Transmit" mode, it is desirable to turn off the LNA to eliminate its possible overload.

In the practical implementation of the radar method with carrier frequency tunability from pulse to pulse, the CID can be made in the form of a bandpass filter, the bandwidth of which is determined by the duration of the probing radio pulse (see p. 244, [11]): .

It should be noted that for the proposed method of radar with carrier frequency tuning from pulse to pulse, there are no strict requirements for the frequency stability of the devices implementing it under the action of destabilizing factors and aging.

The proposed method of radar tunable carrier frequency from pulse to pulse allows in comparison with the prototype:

– maintain in operation the equality of the frequencies of the source of radio pulses of the transmitter to the tuning frequency of the CFD of the receiver;

– to ensure optimal reception of the reflected signal in the entire range of tuning of the carrier frequency of probing radio pulse signals;

– to reduce the requirements for CFD in terms of frequency response and bandwidth;

– independent choice of parameters of the duration of radio pulses, the delay time between the probing and heterodyne radio pulses, respectively, to expand the range of measured ranges (by expanding the range of durations of the probing radio pulses) to the target, as well as the repetition period of paired radio pulses;

– the formation of probing and heterodyne radio pulses using the same device - an RF generator operating in a pulsed mode, which reduces energy costs and simplifies the practical implementation of this method, as well as reduces the level of spurious signals and interference in the power and control circuits;

– reduce the requirements for long-term stability of the frequency parameters of the devices implementing this method.

Thus, the proposed method of radar has significant advantages over the prototype and analogues.

Claims (2)

1. A radar method with carrier frequency tunability from pulse to pulse, which consists in the fact that probing radio pulses are emitted into a controlled space, reflected radio pulses are received from a target located in this space, the oscillations of the reflected radio pulses are mixed with the heterodyne oscillations of a high-frequency (HF) generator in the mixer, then the reflected radio pulses are isolated at the mixer output, followed by filtering the reflected radio pulses at an intermediate frequency, characterized in that the probing and heterodyne radio pulses are received by a shock effect on the RF generator by a sequence of paired trigger pulses with steep fronts, while forming pairs of radio pulses in the RF generator, in which the first are probing, the second are heterodyne, and their oscillations are coherent with respect to the trigger pulses, their frequencies are shifted relative to each other by an intermediate frequency, and the frequencies of the probing and heterodyne radio pulses are tuned from clock to clock by changing the natural frequency of the RF generator resonator while maintaining the frequency difference of the radio pulses in each cycle, equal to the intermediate frequency. 2. The method according to claim 1, characterized in that the duration of the front of the shock pulses is chosen such that it is equal to half the oscillation period of the RF generator, and the amplitude of the pulses is at least an order of magnitude higher than the level of intrinsic noise of the RF generator.