RU2714510C1 - Radar ranging method with carrier frequency variation from pulse to pulse - Google Patents

Abstract

FIELD: radar ranging.SUBSTANCE: invention relates to the field of radar engineering and can be used in the construction of onboard pulsed incoherent radio altimeters. Method of radar ranging consists in generation of emitted signal by direct heterodyning down to intermediate frequency of input intrinsic noise of receiving device, amplification, its subsequent narrow-band filtering at intermediate frequency with a frequency-selective device to obtain quasi-harmonic noise of intermediate frequency, return heterodyne up noise from intermediate frequency to carrier, amplification, limiting amplitude from above, its amplitude-pulse manipulation, amplification to required level of emitted pulse power and subsequent radiation, wherein filtration of reflected signal, amplification and detection is carried out at intermediate frequency.EFFECT: wider range of measured ranges, low power consumption, low level of spurious signals and noise pick-up in power and control circuits.5 cl, 4 dwg

Description

The invention relates to the field of radar technology and can be used to build on-board pulsed incoherent radio altimeters with a change in the carrier frequency from pulse to pulse.

A known method of radar with a change in the carrier frequency from pulse to pulse [Reference radar Volume 1 / ed. M. Skolnik. - M.: “Sov., Radio”, 1976. - P. 8], which consists in the use of a transmitter and a receiver simultaneously tunable in frequency, chosen as an analogue.

The implementation of the analogue method is as follows.

In a frequency-tuned transmitter, emitted radio pulses of a carrier frequency are generated, which are emitted 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 receiver local oscillator are tuned so that the difference frequency always has a constant value equal to the intermediate frequency of the receiver, while filtering the reflected signals is provided at the intermediate frequency by a frequency-selective device (CIU).

The disadvantages of the analogue method are:

- the complexity of coupling 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 long-term stability of the frequency parameters of the master oscillator of the transmitter, local oscillator and CIU during operation of the device.

A known method of radar with a change in the carrier frequency from pulse to pulse [Radio receivers / ed. IN AND. Siforova. - M .: “Owls. radio ”, 1974. - P. 504], which consists in using a system of automatic frequency control (AFC) of the local oscillator of the receiver, which provides the coupling of the carrier frequency of the transmitter with the tuning frequency of the receiver, selected for the analogue.

The implementation of this method is an analogue is as follows.

Carrier frequency pulses are generated in the transmitter and emitted in the direction of the target. Part of the power of the transmitter signal is fed to the AFC system of the receiver local oscillator and for a time equal to the duration of the emitted radio pulse, the AFC system adjusts the frequency of the local oscillator of the receiver, while the frequency of the discriminator of the AFC system is equal to the center frequency of the frequency converter matching the intermediate frequency of the receiver.

The signal reflected from the target enters the receiver, the tuning frequency of which, with the help of the AFC system of the local oscillator, is tuned to the carrier frequency of the transmitter during the radiation of the radio pulse.

The disadvantages of the analogue method 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 characteristics (AFC) of the intermediate frequency amplifier of the receiver;

- the presence of residual mismatch in the AFC system of the local oscillator;

- 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 AFC system of the local oscillator.

A known method of radar with a change in the carrier frequency from pulse to pulse [Patent No. 2628526 of the Russian Federation, IPC G01S 13/24 (2006/01). The method of radar with the adjustment of the carrier frequency from pulse to pulse / Katin S.V., Kashin A.V., Kozlov V.A., Kunilov A.L .; Applicants and patent holders Rosatom State Corporation, Federal State Unitary Enterprise Federal Scientific Research Center for Scientific Research Yu.E. Sedakova. " - No. 2016149715; stated on 12/16/2016; published August 18, 2017, Byul. No. 23], which consists in obtaining a carrier frequency signal by direct heterodyning of fixed frequency pulses up to frequency by the frequency of the local oscillating signal and receiving the reflected signal by the method of return heterodyne by shifting it down in frequency, followed by filtering the reflected signal at a frequency of fixed pulses by a frequency-selective device (CIU), while the tuning of the carrier frequency is carried out by changing the frequency of the local oscillator signal. For direct heterodyning, the response of the CIU to an ultrashort pulse effect is used as fixed frequency pulses, and after the return heterodyning, the reflected signal is filtered by the same CIU, the direct and return heterodyning being carried out by the same device. This method is selected for the prototype.

The implementation of the prototype method is as follows.

The radio pulse signal of the carrier frequency ƒ ₀ is generated by the mixer 3 (Fig. 1) by direct up-frequency heterodyning from the response of the narrow-band CIU 2 (Fig. 1) to an ultrashort pulse δ (t) (Fig. 2a) of an ultrashort pulse source 1 (Fig. 1) ), having the form of a radio pulse g (t) (Fig. 2b), the duration of which is determined by the passband Δƒ _CIU AFC of this CIU, and the heterodyne signal U of the _IF (t) (Fig. 2c) of the continuous signal source with frequency tuning 7 (Fig. 1 ) The received radio pulse signal of the carrier frequency U ₀ (t) (Fig. 2d) using the "Transmit-Reception" switch 4 (Fig. 1), located in the "Transmission" position, is sent to the power amplifier 5 (Fig. 1) and then through the antenna radiates towards the target.

The signal reflected from the target in the form of a radio pulse U _OTP (t) (Fig. 2e) through a low-noise amplifier 6 (Fig. 1) and a switch 4 (Fig. 1) located in the "Receive" position is sent to the mixer 3 (Fig. 1 ), to which the heterodyne signal U of the _IFR (t) (Fig. 2c) is supplied from a source of a continuous signal with frequency tuning 7 (Fig. 1), the frequency of which does not change after the formation of the carrier pulse of the carrier frequency until the start of the next clock cycle. Next, the intermediate frequency U frequency pulse U of the _inverter (t) (Fig. 2f) passes through the PLL 2 (Fig. 1), whose frequency response in the passband K (ƒ) is consistent with the spectrum S ₀ (() of the emitted radio pulse. In the next clock cycle, the frequency of the continuous signal source with frequency tuning 7 (Fig. 1) changes and the transmitter emits, and the receiver receives a radio pulse with a different carrier frequency.

The disadvantages of the prototype method are:

- the need to use a source of ultrashort video pulses;

- the inability to control the duration of the radio pulse generated in the CIU;

- stringent requirements for the shape of the frequency response of the CIU;

- the inability to optimize the conversion of the radio pulse signal from an intermediate frequency to a carrier (emitted) frequency and from a carrier (received) frequency to an intermediate frequency by direct and return heterodyning using the same device.

The first drawback is due to the technical complexity of creating a source of a video pulse signal with an ultrashort front (τ _Ф ~ 10 ... 100 ps).

The second drawback is related to the dependence of the duration of the CIU radio pulse response to the pulse effect of τ _RI on the pass band of the CIU Δƒ as τ _RI ≈ 1 / Δƒ, where Δƒ is the pass band of the CIU, i.e. an increase in the duration of the radio pulse is possible only with a decrease in the bandwidth of the CIU, which is technically not always feasible [Astaykin A.I. Radiation and reception of ultrashort pulses: Monograph. - Sarov: FSUE RFNC-VNIIEF, 2008. P. 305-309.]. This limits the range of measured ranges.

The third drawback is due to the dependence of the envelope of the radio pulse on the shape of the frequency response of the CIU, in which “tails” and “precursors” may appear in the oscillogram of the generated radio pulse [Ibid.].

The fourth disadvantage is related to the need to use a reciprocal type reciprocal device for direct and return heterodyning based on a diode mixer, the mode of operation of which when receiving reflected radio pulses (operating mode of the receiving mixer) should provide a minimum level of introduced noise, and when generating emitted signals (operating mode of the shift mixer ) is the maximum conversion coefficient, which is technically difficult to implement on a single 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 affects the overall dimensions and reduces the overall efficiency of the transceiver device.

The technical result of the present invention is to expand the range of measured ranges (by expanding the range of durations of emitted radio pulses), reducing power consumption, reducing the level of spurious signals and interference in the power and control circuits.

The technical result is achieved by the fact that in the method of radar with a change in the carrier frequency from pulse to pulse, which consists in the formation of the emitted signal and filtering the reflected signal by one frequency-selective device using the direct and return heterodyning method with changing the carrier frequency by tuning the frequency of the heterodyne signal and detecting the reflected signal at an intermediate frequency, the emitted signal is obtained by direct heterodyning down to the intermediate frequency of the input the noise of the receiving device, by amplification, its subsequent narrow-band filtering at an intermediate frequency by a frequency selective device to obtain quasiharmonic noise of an intermediate frequency, by returning up-quasi-harmonic noise from an intermediate frequency to a carrier frequency, by amplification, by limiting the amplitude above this noise, and its amplitude-pulse manipulation , amplification to the required level of radiated impulse power, followed by radiation from the transmitting antenna.

In addition, at the time of formation of the emitted signal, the receiving device is introduced into the mode of increased values of the noise figure.

In addition, by direct heterodyning the input intrinsic noise of the receiving device down to the intermediate frequency, a minimum noise figure is provided, and by returning heterodyning of quasi-harmonic noise from the intermediate frequency up to the carrier frequency, the maximum conversion coefficient is provided.

In addition, the threshold limit of the amplitude above the quasi-harmonic noise of the carrier frequency is selected according to a given ratio of the average number of radio pulses with full energy content to the total number of radio pulses in the emitted sequence from the relation

где

Where

U ₀ is the threshold for limiting the amplitude of quasi-harmonic noise,

σ is the effective value of quasi-harmonic noise,

N is the ratio of the average number of radio pulses with full energy content to the total number of radio pulses in the emitted sequence.

In addition, the duration of the emitted radio pulse is set regardless of the bandwidth of the frequency selective device.

The prototype method of radar with a change in the carrier frequency from pulse to pulse is illustrated in figure 1 and figure 2.

The figure 1 shows a functional diagram explaining the prototype method of radar with a change in the carrier frequency from pulse to pulse. It shows: 1 - the source of ultrashort pulses (ISKI); 2 - frequency-selective device of intermediate frequency (CIU); 3 - mixer (SM), performing direct and return heterodyning; 4 - switch "Transmission-Reception" (Switch); 5 - power amplifier (PA); 6 - low noise amplifier (LNA); 7 - a source of a continuous signal with frequency tuning (ANN).

The figure 2 shows the plot of the voltage of the signals explaining the prototype method of radar with a change in the carrier frequency from pulse to pulse, where:

a - ultrashort pulses δ (t);

b - radio pulses - responses of the PMI to the influence of ultrashort pulses g (t);

in - frequency-tunable heterodyne signal U _IFP (t);

g - radio pulse signals of a carrier frequency U ₀ (t) obtained by direct heterodyning from the responses δ (t) and the U signal of the _IFP (t);

d - reflected signals of the carrier frequency U _OTP (t);

e - intermediate frequency signals U _IF (t) obtained by the method of return heterodyning from the reflected signals U _OTP (t) and the signal U _IFR (t).

The proposed method of radar with a change in the carrier frequency from pulse to pulse is illustrated in figure 3 and figure 4.

The figure 3 shows a functional diagram explaining the proposed method of radar with a change in the carrier frequency from pulse to pulse. It shows: 8 - receiver switch (OP); 9 - input amplifier of the receiver (OPS) with a controlled noise figure; 10 - mixer (SM); 11 - frequency-tunable local oscillator (Get); 12 - a preliminary amplifier of an intermediate frequency (PCB); 13 - CIU in the form of a band-pass filter of intermediate frequency (PPF); 14 - intermediate frequency amplifier (UPCH); 15 - first directional coupler (HO1); 16 - the first amplitude detector (AD1); 17 - shear mixer (CMC); 18 - amplifier-limiter (UO); 19 - amplitude-pulse manipulator (AIM); 20 - second directional coupler (HO2); 21 - output power amplifier (VUM); 22 - second amplitude detector (AD2), 23 - quantizer (KB).

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

a - broadband noise of the input stages of the receiving device u (t) during radiation (1) and reception (2);

b - quasi-harmonic noise of an intermediate frequency at the output of the CIU s (t) obtained by direct heterodyning of the broadband noise of the input stages of the receiving device;

в - frequency tunable continuous heterodyne signal U _ГЕТ (t);

d - quasi-harmonic noise of the carrier frequency U ₀ (t) obtained by the method of return heterodyning from signal s (t) and signal U _ГЕТ (t);

d - limited quasi-harmonic noise of the carrier frequency U _OGR (t);

e - emitted radio pulse quasiharmonic signal U _RI (t);

g - reflected radio pulse signal U _OTP (t);

C is the reflected signal of the intermediate frequency U _IF (t);

and - envelope of the reflected signal U _ОГ (t).

A method of obtaining a radiated signal is as follows.

When the input of the receiving device is turned off using the switch of the receiver 8 (Fig. 3), the intrinsic noise of the input amplifier of the receiver 9 (Fig. 3) u (t) (Fig. 4a) is at the maximum level by direct heterodyning using the mixer 10 (Fig. 3) and the continuous heterodyne signal U _ГЕТ (t) (Fig. 4c) from the output of the local oscillator 11 (Fig. 3) is lowered to the intermediate frequency and after amplification in the preliminary amplifier of the intermediate frequency 12 (Fig. 3), narrow-band filtering in PPF 13 (Fig. 3) ) and amplifications in the intermediate frequency amplifier 14 (Fig. 3) are converted into quasi-harmo matic noise intermediate frequency s (t) (FIG. 4b). Then, by returning heterodyne up to quasi-harmonic noise from the intermediate frequency to the carrier frequency using a shift mixer 17 (Fig. 3) and a continuous signal U _ГЕТ (t) (Fig. 4c) from the output of the local oscillator 11 (Fig. 3), the quasi-harmonic noise of the carrier frequency is amplified and limit the amplitude from above in the amplifier-limiter 18 (Fig. 3) and from the received signal in the form of a limited amplitude above the quasi-harmonic noise of the carrier frequency U _OGR (t) (Fig. 4e) pulse-amplitude manipulation using the amplitude-pulse manipulator 19 (Fig. 3) form a radio-pulse quasi-harmonic signal U _RI (t) (Fig. 4e) and after amplification in the output power amplifier 21 (Fig. 3) emit a transmitting antenna.

To form a start pulse for measuring the delay of the reflected radio pulse relative to the emitted, a small part of the latter is transmitted to the second amplitude detector 22 (Fig. 3) using the second directional coupler 22 (Fig. 3), the selected envelope of the radio pulse is quantized by quantizer 23 (Fig. 3) and the resulting the video pulse as a start pulse is supplied to the processing unit (not shown in FIG. 3).

The method of receiving the reflected signal is as follows.

The reflected radio pulse signal U _OTP (t) (Fig. 4g) is amplified by the input amplifier of the receiver 9 (Fig. 3), which is in the mode of the minimum noise figure, by direct heterodyning, it is converted into an intermediate frequency signal U _IF (t) (Fig. 4h) using mixer 10 (Fig. 3) and local oscillator 11 (Fig. 3). After amplification in the preliminary amplifier of the intermediate frequency 12 (Fig. 3), filtering in the PPF 13 (Fig. 3), the reflected signal of the intermediate frequency is amplified by the intermediate frequency amplifier 14 (Fig. 3) and detected through the first directional coupler 15 (Fig. 3) the first amplitude detector 16, (Fig. 3), at the output of which the envelope of the reflected signal U _ОГ (t) (Fig. 4i) is isolated, while the pulse-amplitude manipulator 19 (Fig. 3) is locked.

Thus, when the transceiver device maintains a constant frequency of the local oscillator signal for one clock cycle, the carrier frequency of the emitted signal completely coincides with the receiver tuning frequency.

At the time of formation of the emitted signal, the receiving device is introduced into the mode of increased noise figure.

When implementing the input amplifier of the receiver on microwave transistors, its maximum noise figure is achieved at the maximum power gain, which is optimal for the "Transmission" mode. The transition of the input amplifier of the receiver to the state of the minimum noise figure (for the "Reception" mode) can be ensured by the mismatch of the input impedance of the microwave transistor with the output impedance of the signal source while changing the mode of the microwave transistor in direct current [Radio receivers / ed. A.P. Zhukovsky. - M .: “Higher. school. ", 1989. S. 41].

Direct heterodyning of the input noise of the receiving device down to the intermediate frequency is carried out by the mixer 10 (Fig. 3), which provides the minimum noise figure, and the return heterodyning of quasi-harmonic noise from the intermediate frequency up to the carrier frequency is carried out by the shift mixer 17 (Fig. 3), which ensures the maximum coefficient transformations.

The duration of the emitted radio pulse is set by the amplitude-pulse manipulator, regardless of the bandwidth of the frequency-selective device.

In practical implementation, the frequency-selective device is implemented in the form of a PPF with the most steep slopes of the frequency response with maximum out-of-band attenuation.

The level of restriction in the amplifier-limiter is determined by the given probability of exceeding the envelope of quasiharmonic noise of a fixed threshold (by analogy with the determination of the detection threshold by the given probability of false alarm for normal noise in the absence of a signal) in accordance with the ratio [Optimal filters and pulse signal storage devices / S. . Lezin. - M .: “Owls. Radio ”, 1963. - S. 192]

Where

F is the probability of exceeding the envelope of the threshold (the probability of false alarm in the absence of a signal),

U ₀ is the limit threshold,

u is the noise voltage,

σ is the effective value of the noise,

- значение порога ограничения, нормированное на эффективное значение шума.

- the value of the limit threshold, normalized to the effective value of the noise.

The false alarm probability F can be considered as the average number of radio pulses with full energy content n ₁ , referred to the total number of radio pulses in the sequence n ₀ , i.e. when n ₁ / n ₀ = N

F = N [Characteristics of detection / M.S. Katsenbogen. - M .: “Owls. Radio ”, 1965. - S. 25].

Hence, the limit threshold U ₀ can be determined using relation (1) as

Thus, the proposed method of radar with a change in the carrier frequency from pulse to pulse allows you to match the carrier frequency of the emitted radio pulse signals with the tuning frequency of the receiving device through the use of a single CIU, which provides both the formation of the emitted signal and filtering the reflected signal, with stringent requirements the frequency stability of the devices implementing it under the conditions of destabilizing factors and aging are not presented.

It should be noted that the formation of a start pulse is also possible for radio pulses with incomplete energy filling with a decrease in the quantization threshold, which, under the conditions of reflection of these radio pulses from a reflecting surface with low losses or the presence of a sufficient supply of energy potential, can ensure their full reception.

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

- expand the range of measured ranges (by expanding the range of durations of the emitted radio pulses);

- reduce the requirements for CIU in the form of frequency response and bandwidth;

- optimize the operating modes of devices that carry out direct and return heterodyning signals;

- increase the overall efficiency due to the exclusion of the second (video-pulse) generator from the circuit;

- reduce the level of spurious signals and pickups on the power and control circuits due to the presence in the device circuit of only one generating device with a narrow-band spectrum - a local oscillator tunable in frequency.

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

Claims (9)

1. The method of radar with a change in the carrier frequency from pulse to pulse, which consists in generating the emitted signal and filtering the reflected signal with one frequency selective device using the direct and return heterodyning method with changing the carrier frequency by tuning the frequency of the local oscillator signal and detecting the reflected signal at an intermediate frequency, characterized in that the emitted signal is obtained by direct heterodyning down to the intermediate frequency of the input intrinsic noise of the receiving of a device, by amplification, its subsequent narrow-band filtering at an intermediate frequency by a frequency selective device to obtain quasiharmonic noise of an intermediate frequency, by returning heterodyne up to quasi-harmonic noise from an intermediate frequency to a carrier frequency, by amplification, limiting the amplitude from above this noise, its amplitude-pulse manipulation, amplification to the desired level of radiated impulse power, followed by radiation from the transmitting antenna. 2. The method according to p. 1, characterized in that at the time of formation of the emitted signal, the receiving device is entered into a mode of increased noise figure. 3. The method according to p. 1, characterized in that the direct heterodyning of the input intrinsic noise of the receiving device down to the intermediate frequency provides a minimum noise figure, and the return heterodyning of the quasi-harmonic noise from the intermediate frequency up to the carrier frequency provides the maximum conversion coefficient. 4. The method of radar with a change in the carrier frequency from pulse to pulse according to claim 1, characterized in that the threshold limit of the amplitude above the quasi-harmonic noise of the carrier frequency is selected according to a given ratio of the average number of radio pulses with full energy content to the total number of radio pulses in the emitted sequence from the relation

Where U ₀ is the threshold for limiting the amplitude of quasi-harmonic noise, σ is the effective value of quasi-harmonic noise, N is the ratio of the average number of radio pulses with full energy content to the total number of radio pulses in the emitted sequence. 5. The method according to p. 1, characterized in that the duration of the emitted radio pulse is set regardless of the bandwidth of the frequency-selective device.

Images