RU2628526C1 - Radar location method with carrier frequency tuning from pulse to pulse - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: radar location method with carrier frequency tuning from pulse to pulse consists in obtaining a signal of carrier frequency by direct heterodyning method of radio pulses of a fixed frequency up in frequency by the frequency value of the heterodyne signal and receiving the reflected signal by return heterodyning method by shifting it down in frequency, followed by filtering of the reflected signal at frequency of radio pulses of a fixed frequency by a frequency-selective device. Carrier frequency tuning is carried out by changing the frequency of the heterodyne signal, in case of direct heterodyning, the response of the frequency-selective device to the ultrashort pulse action is used as the fixed frequency radio pulses, and after return heterodyning, the filtering of the reflected signal is performed by the same frequency-selective device. Direct and return heterodyning are performed by the same device.

EFFECT: ensuring the optimal reception of reflected signals during carrier frequency tuning of the emitted radio pulses from pulse to pulse without requiring long-term stability of the frequency parameters of the incoming devices and with a simpler practical implementation.

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Description

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

A known method of radar with the adjustment of the carrier frequency from pulse to pulse [1], which consists in using simultaneously tunable in frequency of the transmitter and receiver.

The implementation of the method [1] 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 receiver local oscillator are tuned so that the difference frequency always has a constant value equal to the intermediate frequency of the receiver. Optimal filtering of the reflected signals is ensured at an intermediate frequency by a frequency-selective device, the passband of which is consistent with the spectrum of the emitted radio pulse.

The disadvantages of the method [1] 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 frequency-selective device during radar operation.

A known method of radar with the adjustment of the carrier frequency from pulse to pulse [2], which consists in using the automatic frequency control system (AFC) of the receiver local oscillator, which provides coupling of the carrier frequency of the transmitter with the tuning frequency of the receiver.

The implementation of the method [2] 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 enters 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 receiver local oscillator. The frequency of the discriminator of the AFC system, equal to the difference between the carrier frequency of the transmitter and the frequency of the receiver local oscillator, coincides with 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 during the radiation of the radio pulse is adjusted to the carrier frequency of the transmitter, while the passband of the linear part of the receiver is consistent with the spectrum width 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 characteristics (AFC) of the intermediate frequency amplifier (IFA) of the receiver;

- the presence of residual detuning in the AFC system of the local oscillator, which does not allow for full matching of the passband 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 AFC system of the local oscillator.

A known method of radar with the adjustment of the carrier frequency from pulse to pulse [3], which consists in the formation of the emitted radio pulse by transferring the radio pulse of the generator, the frequency of which is fixed and equal to the intermediate frequency of the receiver, to the carrier frequency by the heterodyning method using a frequency tunable continuous heterodyne signal, and receiving the reflected signal by the superheterodyne receiver using the same heterodyne signal. This method is selected for the prototype.

The implementation of the method [3] is as follows.

From the signal U _RI (t) (pos. 1 in Fig. 1) of a fixed-frequency radio pulse source ƒ _RI (pos. 1 in Fig. 2) and the continuous heterodyne signal U of the _IF (t) (pos. 2 in Fig. 1) frequency ƒ the frequency _{response of the} source with frequency tuning (pos. 4 in Fig. 2) by direct heterodyne upward frequency by the first mixer (pos. 2 in Fig. 2) a radio pulse signal U ₀ (t) of the carrier frequency ƒ ₀ (pos. 3 on Fig. 1)

ƒ ₀ = ƒ _RI + ƒ _IFI ,

which, after amplification by a power amplifier (item 3 in FIG. 2), is emitted in the direction of the target.

The signal reflected from the target signal U _OTP (t) (pos. 4 in Fig. 1) after amplification by a low-noise amplifier (pos. 5 in Fig. 2) by the method of return heterodyning by the second mixer (pos. 6 in Fig. 2) is shifted down to the intermediate frequency ƒ _inverter

_IF ƒ = ƒ ₀ -ƒ _HRI,

on which the intermediate frequency signal U of the _inverter (t) (item 5 in Fig. 1) is filtered by a frequency-selective device (CIU) with the passband Δƒ _CIU (item 7 in Fig. 2), which is consistent with the spectrum of the emitted signal S ₀ .

Thus, if the frequency of the source of radio pulses ƒ _{RI is} equal to the intermediate frequency ƒ _IF , at which the filtering is performed,

ƒ _RI = ƒ _IF ,

for any carrier frequency of the emitted signal ƒ ₀ , the receiver will be tuned to this frequency.

The disadvantages of the method [3] are:

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

- the complexity of the circuit that implements this method.

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

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

The technical result of the invention is the provision of optimal reception of reflected signals when tuning the carrier frequency of the emitted radio pulses from pulse to pulse without requiring long-term stability of the frequency parameters of the input devices and with a simpler practical implementation.

The technical result is achieved by the fact that in the method of radar with the tuning of the carrier frequency from pulse to pulse, which consists in receiving a carrier frequency signal by direct heterodyning of a fixed frequency radio pulse up in frequency by the frequency of the heterodyne signal and receiving the reflected signal by the method of return heterodyning by shifting it down in frequency followed by filtering the reflected signal at a frequency of radio pulses of a fixed frequency by a frequency-selective device, at The carrier frequency is tuned by changing the frequency of the heterodyne signal, with direct heterodyning, the response of the frequency-selective device to ultrashort pulse exposure is used as fixed frequency pulses, and after return heterodyning, the reflected signal is filtered by the same frequency-selective device, with direct and return heterodyning the same device.

The technical result is achieved by the fact that in the method of radar with the adjustment of the carrier frequency from pulse to pulse, a frequency-selective device is used, the response of which to an ultrashort pulse effect has the form of a radio pulse of a given duration and filling frequency.

The method of radar with the adjustment of the carrier frequency from pulse to pulse is explained in the following figures:

Figure 1 explains the method of radar with the adjustment of the carrier frequency from pulse to pulse in the prototype [3]. It shows the voltage diagrams of the following signals: 1 - radio pulse signals U _RI (t) of a fixed frequency ƒ _RI ; 2 - frequency tunable continuous heterodyne signal U _UI (t) with current frequency ƒ _UI ; 3 - emitted radio pulse signals U ₀ (t) of a carrier frequency ƒ ₀ obtained by direct heterodyning; 4 - reflected signals U _OTP (t) of the carrier frequency; ₀ ; 5 - reflected signals U _IF (t) of intermediate frequency ƒ _IF obtained by the method of return heterodyning.

Figure 2 explains the implementation of the radar method with the adjustment of the carrier frequency from pulse to pulse in the prototype [3]. It shows: 1 - a source of radio pulses of a fixed frequency; 2 - the first mixer performing direct heterodyning; 3 - power amplifier; 4 - a source of a continuous signal with frequency tuning; 5 - low noise amplifier; 6 - second mixer, performing reverse heterodyning; 7 - CIU intermediate frequency.

Figure 3 explains the proposed method of radar with the adjustment of the carrier frequency from pulse to pulse. It shows the voltage diagrams of the following signals: 1 - ultrashort pulses δ (t); 2 - radio pulses - responses of the PMI to the influence of ultrashort pulses g (t); 3 - frequency tunable continuous heterodyne signal U of the _IFP (t), 4 - radio-pulse signals of the carrier frequency U ₀ (t) obtained by direct heterodyning from the responses pos. 2 and the signal pos. 3; 5 - reflected signals of the carrier frequency U _OTP (t); 6 - signals of the intermediate frequency U _IF (t) obtained by the method of return heterodyning from the reflected signals pos. 5 and the signal pos. 3.

Figure 4 explains the feasibility of the proposed method of radar with the adjustment of the carrier frequency from pulse to pulse. It shows: 1 - the source of ultrashort pulses; 2 - CIU of intermediate frequency; 3 - mixer, performing direct and return heterodyning; 4 - switch "Transmission-Reception"; 5 - power amplifier; 6 - low noise amplifier; 7 - a source of a continuous signal with frequency tuning.

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

The radio pulse signal U ₀ (t) of the carrier frequency ƒ ₀ (pos. 4 in Fig. 3) is generated by the mixer (pos. 3 in Fig. 4) by direct up-frequency heterodyning from the response of a narrow-band CIU (pos. 2 in Fig. 4) ultra-short pulse δ (t) (pos. 1 in Fig. 3), having the form of a radio pulse g (t) (pos. 2 in Fig. 3), the duration of which is determined by the passband Δƒ _{CHIU of the} frequency response of this CHIU, and of the continuous signal U of the _IFP (t) (pos. 3 in Fig. 3) of a frequency tunable source (pos. 7 in Fig. 4). The received radio pulse signal of the carrier frequency U ₀ (t) using the "Transmit-Reception" switch (pos. 4 in Fig. 4), located in the "Transmission" position, is sent to the power amplifier (pos. 5 in Fig. 4) and then radiates through the antenna towards the target.

The signal reflected from the target in the form of a radio pulse U _OTP (t) (pos. 5 in Fig. 3) through a low-noise amplifier (pos. 6 in Fig. 4) and a Transmit-Receive switch (pos. 4 in Fig. 4), located in the "Receive" position, is sent to the mixer (item 3 in Fig. 4), which receives a continuous signal U _IFP (t) from a source of a continuous signal with frequency tuning (item 7 in Fig. 4), the frequency of which after the formation of the carrier frequency radio pulse does not change until the start of the next clock cycle. Next, the intermediate frequency pulse U of the _inverter (t) passes through the CIU (item 2 in Fig. 4), the frequency response of which in the passband K (ƒ) is consistent with the spectrum S ₀ (ƒ) of the emitted radio pulse. In the next clock cycle, the frequency of the continuous signal source with frequency tuning ƒ the _IFR changes and the transmitter emits, and the receiver receives a radio pulse with a different carrier frequency.

Theoretically, the possibility of implementing the proposed method of radar with the tuning of the carrier frequency from pulse to pulse is due to the fact that with an ultra-short pulse action in the form of a δ (t) function, the spectrum of which N (ω) is uniform in the entire frequency band, the response of the frequency-selective device g ( t) has a spectrum S (ω) repeating its amplitude-frequency characteristic K (ω), i.e.

S (ω) ~ NK (ω),

[4]:the temporary response form g (t) is the inverse Fourier transform of the amplitude-frequency characteristics of the frequency-selective device

[four]:

Thus, the amplitude-frequency characteristic of the CIU K (ω) is proportional to the spectrum S (ω) of both the emitted and reflected signals

K (ω) = k ₀ S (ω),

which allows consistent filtering of the reflected signal, i.e. its optimal reception.

In the practical implementation of the radar method with tuning of the carrier frequency from pulse to pulse, the CIU can be made in the form of a band-pass filter, the passband of which Δƒ is determined by the duration of the emitted radio pulse τ _RI [5]:

Δƒ≈1 / τ _RI ,

at the same time, for the formation of this radio pulse - a response to an ultrashort pulse action - the shape of the frequency response of a band-pass filter should be one-humped.

As a result, the proposed method of radar with the adjustment of the carrier frequency from pulse to pulse allows for optimal reception of the reflected signal through the use of a single CIU, which provides both the formation of the spectrum of the emitted signal and consistent filtering of the reflected signal.

It should be noted that for the proposed method of radar with the adjustment of the carrier frequency from pulse to pulse, strict requirements for the frequency stability of the devices implementing it under the conditions of destabilizing factors and aging are not imposed.

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

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

- the formation of the emitted signal and the reception of the reflected signal to carry out direct and return heterodyning using a single device, which will reduce energy costs and simplify the practical implementation of this method;

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

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

Literature

1. Reference radar. Ed. M. Skolnik. Volume 1. M., Sov. radio, 1976, p. 8.

2. Radio receivers. Ed. IN AND. Siforova. M., Sov. radio, 1974, p. 504.

3. Soloviev N.A. The use of a signal with spectrum synthesis for constructing a long-range portrait and inverse synthesis of aperture // Science and Education: Scientific and Technical Edition: 77-30569 / 249869. Scientific publication of MSTU N.E. Bauman, November 2011.

4. Finkelstein M.I. Basics of radar. M., Sov. radio, 1973, p. 195-200.

5. Radio receivers. Ed. A.P. Zhukovsky. M, Higher. school., 1989, p. 244.

Claims (2)

1. The method of radar with the adjustment of the carrier frequency from pulse to pulse, which consists in receiving a carrier signal by direct heterodyning of a fixed frequency radio pulses up to the frequency of the heterodyne signal and receiving the reflected signal by the method of return heterodyning by shifting it downward in frequency with subsequent filtering of the reflected signal at a frequency of radio pulses of a fixed frequency by a frequency-selective device, while the carrier frequency is tuned by changing the frequency of the heterodyne signal, characterized in that for direct heterodyning, the response of the frequency-selective device to an ultrashort pulse effect is used as fixed frequency pulses, and after return heterodyning, the reflected signal is filtered by the same frequency-selective device, with direct and return heterodyning being performed by one and the same device. 2. The method of radar with the adjustment of the carrier frequency from pulse to pulse according to claim 1, characterized in that they use a frequency-selective device, the response of which to ultra-short pulse exposure has the form of a radio pulse of a given duration and frequency of filling.

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