RU2797828C1 - Radar method - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention can be used for radar objects (targets) with the assessment of their coordinates. The technical result is a significant reduction in the power of the transmitter through the use of a narrow-band radio signal and a low bandwidth of the receiver, increased secrecy of radiation; providing the ability to work both at short and long ranges. Said technical result is achieved in that the antenna pattern is switched around the equisignal zone, at one carrier frequency, and signals at the switching frequency are isolated from the received radio signal by amplitude demodulation, which determine the presence of a target in the detection zone. In this case, the radiation is carried out in low-frequency cycles filled with high-frequency pulses, while forming at the output of the receiver two frequency scales of a rough and accurate range estimate, which makes it possible to remove ambiguity in the phase method of ranging.

EFFECT: significant reduction in the power of the transmitter through the use of a narrow-band radio signal and a low bandwidth of the receiver, increased secrecy of radiation; providing the ability to work both at short and long ranges.

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Description

The invention relates to the field of radio engineering and can be used for radar objects (targets) with the assessment of their coordinates.

A known method of radar with the emission and reception of continuous radio signals to transmitters and receivers remote from each other, allowing you to protect the receivers from the powerful radiation of the transmitter.

This method was used at the dawn of radar in the 30s of the last century and was successfully used before the advent of pulse radars, in which the transmitter and receiver worked on the same antenna (the RUS-1 system) (“History of Domestic Radar”, ed. by S.V. Khokhlov , M., table, encyclop, 2015).

Today, the method of pulsed radar is widely used to detect and estimate coordinates at long ranges (“Handbook of radar”, edited by M.I. Skolnik “Technosphere”, M., 2015, book 1).

The disadvantage of this method is the low noise immunity due to the wide bandwidth of the receiver, due to the need to receive pulsed radio signals of short duration, of the order of 1 μs.

Known continuous-wave radars GW radar, which are used to detect moving targets by Doppler frequency shift. However, such radars do not allow measuring range and cannot work on stationary and low-speed targets (History of domestic radar, ed. - S.V. Khokhlova, M., ed. House. Capital Encyclopedia, p. 735).

To work at short ranges less than 1000 m, radars with linear frequency modulation are used, which has found application in radio altimeters.

Known data tracking system, US patent US 2594317 dated 11/21/1942, consisting of a radar with two antennas, one of which is transmitting and the second is receiving, driven by an electromechanical drive, allowing to implement an equisignal zone at the reception and to carry out high-precision reception of angular target coordinates.

This system emits pulse signals and must have a broadband receiver and a transmitter of high pulse power, which significantly reduces the tactical and technical parameters of the radar.

It is also possible to work with narrow-band radiated signals, however, with a high transmitter power, to protect the receiver from its radiation, a spatial spread between the transmitting and receiving antennas is required, as is done in the system in the above-named GW radar system.

There is a Doppler weather radar (international patent application WO 2013/141738 A) containing a narrowband and broadband probing signal generator, a broadband transmitter, an antenna switch with two microwave circulators, a two-frequency generator that generates bursts of short and long pulses, and the outputs of the circulators are connected to two vibrators to horizontal and vertical polarization.

Such a weather radar has an increased accuracy in measuring atmospheric formations, however, since this radar operates in a pulsed mode, it has the same disadvantages as the previous analogue, that is, it does not provide operation in a narrow frequency band, and therefore requires a large radiated transmitter power, does not has stealth and noise immunity.

Known autodyne method of radar with the operation of a radio transmitter and receiver on one antenna (prototype) (Buzykin V.T., Noskov V.Ya. "Autodynes. Scope and development prospects" "Radio engineering systems of the millimeter and submillimeter wave range" Kharkov, Institute of Radiophysics and Electronics of the Academy of Sciences of Ukraine, 1991, pp. 38-47).

However, when working at long ranges, when a large energy of the probing signal is required, this method is not used because of the problematic protection of the radar receiving paths from the powerful radiation of the transmitter.

The proposed method eliminates the disadvantages of pulse radars by significantly reducing the transmitter power through the use of a narrow-band radio signal and a low receiver bandwidth.

Claim 1 The difference between the claimed invention is that the antenna pattern is switched around the equisignal zone, at one carrier frequency, and from the received radio signal, by amplitude demodulation, signals at the switching frequency are isolated, which determine the presence of a target in the detection zone.

P. 2 The method according to P. 1, characterized in that the switching frequency of the antenna is chosen with a wavelength of at least twice the range of the radar.

P. 3. The method according to P. 1, characterized in that the range to the target is determined by measuring the phase difference between the reference signal of the switching frequency and the received signals of this frequency.

P. 4. The method according to P. 1, characterized in that the radiation is carried out in low-frequency cycles filled with high-frequency pulses, while forming two frequency scales of coarse and accurate range estimates at the receiver output.

In FIG. 1 shows a block diagram of a radar that implements the claimed method, where: 1 - frequency synthesizer; 2 - switch; 3, 4 - circulators; 5, 6 - antenna vibrators; 7 - antenna mirror, 8 - equisignal zone; 9 - location object (target); 10 - radiation pattern; 11 - amplitude detector; 12 - bandpass filter; 13 - phase detector; 14 - range indicator (microcontroller); 15 - delay line; 16 - subtraction block.

- грубая сетка измерения дальности;

- точная сетка; r - предельная дальность до цели; Δr - разрешающая способность РЛС по дальности.In FIG. 2 shows time diagrams of antenna switching signals, where:

- coarse range measurement grid;

- accurate grid; r is the maximum range to the target; Δr is the range resolution of the radar.

The method works as follows. The frequency synthesizer 1 is turned on, generating a carrier frequency signal ƒ of the radar and a control signal of the switch 2 operating at a low frequency F _to . The carrier frequency signal ƒ comes from the switch 2 to the circulators 3, 4, the outputs of which are connected, respectively, to the vibrators of the antennas 5, 6 located at the focus of the mirror 7, displaced from the focus center.

As a result, an equisignal zone 8 is formed in the radiation direction.

In this zone, the space is scanned in height and azimuth, so that when the target enters the radiation pattern, it reflects a radio signal modulated at the switching frequency F _to =F _c .

The reflected useful signal F _c from the target through the circulators 3 and 4 is fed to the amplitude detector 11 and through the bandpass filter 12, tuned to the frequency F _c , enters the phase detector 13. In the microcontroller 14, this signal in the form of an envelope is converted into a digital code and displayed on range indicator.

The range to the target is determined by the phase difference between the reference signal at the switching frequency F _K and the received useful signal F _c . To improve the accuracy of determining the range to the target, the radiation is carried out in periodic cycles.

Compensation for reflections from local objects is carried out by subtracting signals in block 16 after a period of the switching frequency formed by delay line 15.

Let us give a comparative assessment of the energy parameters of the pulsed technology and the narrow-band quasi-continuous technology claimed by this patent.

The radar transmit pulse power is estimated as:

- длина волны; с - скорость света; ƒ - несущая частота;

- коэффициент направленного действия антенны; А_эф=k⋅S_A - эффективная площадь антенны; k - коэффициент использования антенны; S_A - площадь раскрыва антенны;

- требуемое отношения сигнал/шум на входе приемника; Р_ш=K⋅Т⁰⋅Δƒ - мощность собственных шумов приемника;

- постоянная Больцмана; Т⁰=300°K - температура входных цепей приемника по Кельвину; Δƒ - полоса пропускания приемника.where: r - distance to the target; α is the absorption coefficient of radio waves in the atmosphere; (R _w + R _p ) - the total power of noise and interference at the input of the receiver; σ _c - effective target scattering area (EPR);

- wavelength; c is the speed of light; ƒ - carrier frequency;

- coefficient of directional action of the antenna; A _eff =k⋅S _A - effective area of the antenna; k - antenna utilization factor; S _A - antenna opening area;

- required signal-to-noise ratio at the receiver input; Р _w =K⋅Т ⁰ ⋅Δƒ - receiver intrinsic noise power;

- Boltzmann's constant; T ⁰ =300°K - temperature of the input circuits of the receiver in Kelvin; Δƒ - receiver bandwidth.

Substitution of the following numerical values of the parameters for the impulsive mode, at a distance of r=300 km; e ^-2αr =0.1; R _p \u003d 10⋅R _w ; p=10; σ _c \u003d 1 m ² ; G _A =1250; A _eff \u003d 1 m ² ; ƒ=10 GHz; Δƒ=1 MHz, when performing calculations gives P _i =50 kW, P _cf =150 W, and at a distance of r=600 km, P _i =32 MW, P _cf =10 kW.

In the case of narrow-band quasi-continuous technology according to the claimed method, the average transmitter power at a distance of r=300 km, with a receiver bandwidth of Δƒ=10 Hz, will decrease to P _cf =0.5 W, and the energy gain will be 10 ⁵ times.

Thus, in the narrowband mode, an extremely low transmitter power is obtained, which makes it possible to implement a microwave transceiver and antenna using modern stripline technology in a portable version. The disadvantage of the claimed method is the problem of estimating the range to the target. In pulse technology, it is measured by the delay time of the radio signal, and in narrowband, by determining the phase difference between the reference signal of the switching frequency and the received one.

составит Δr_Г=1700 м. На точной шкале, при F_К=500 кГц, величина Δr_T=170 м.So, on a coarse scale, with a phase difference measurement accuracy of 1 °, the range estimation error, at a distance of 300 km and a switching frequency

will be Δr _G \u003d 1700 m. On an accurate scale, at F _K \u003d 500 kHz, the value of Δr _T \u003d 170 m.

For the same parameters in the impulse technology Δr _And =700 m.

Despite this, there are many applications where narrowband technology is justified and brings tangible benefits.

The main ones are high noise immunity and secrecy of the radar; low transmitter power; the ability to work at short and long ranges, small size, with the exception of the dimensions of the antenna, which determine the accuracy of estimating the angular coordinates of targets.

Of the applied areas of using the new technology, the application is especially interesting: in over-the-horizon radar at ranges of more than 1000 km; subsurface, to search for explosives; flaw detection of main pipelines and railway rails; high-precision measurement of distances, in particular, the displacement of geophysical alignments of high-rise dams; detection of ultra-small targets, such as unmanned vehicles EPR less than 0.1 m ² , a task that is not subject to pulsed radar.

For high-speed targets that spread the reflected signal bandwidth, an appropriate filter must be installed at the demodulator output at the receiver.

Claims (2)

1. Radar method, which consists in the emission and reception of electromagnetic narrow-band radio signals on one antenna, characterized in that an equisignal zone is formed in the direction of radiation by emitting a carrier frequency signal ƒ coming from the switch to circulators connected to antenna vibrators located at the focus of the mirror , the space of the equisignal zone is scanned in height and azimuth, the antenna pattern is switched around the equisignal zone, while the switching frequency F _k of the antenna is selected with a wavelength not less than twice the range of the radar station (RLS), and when the target hits useful radio signal F _c is reflected from the target, modulated at the switching frequency, and from the received reflected radio signal, by amplitude demodulation, signals with a switching frequency are isolated, which determine the presence of a target in the detection zone and determine the range to the target, while determining the range is carried out by the phase difference between the reference signal at the switching frequency F _k and the received useful signal F _c . 2. The radar method according to claim 1, characterized in that the determination of the range to the radiation target is carried out in periodic cycles.

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