RU2151407C1 - Radar system - Google Patents

Abstract

FIELD: coast, airport or ship radars for monitoring earth and sea surface and detection objects, in particular, of small size. SUBSTANCE: antenna, which is mounted on mobile base, is driven in horizontal plane. Its electric axis is perpendicular or at angle with respect to direction of movement. When antenna moves, reflected signals are added in each distance element. Coherent addition results in artificial (synthesized) antenna aperture, which is significantly greater than aperture of real antenna. Possibility of coherent addition of received signals is provided by means of compensation of phase alterations in received signal. EFFECT: increased angular resolution in azimuth plane. 5 dwg

Description

где P_с - отраженная мощность сигнала от объекта;
P_ф - мощность собственных шумов приемного канала;
P_a - мощность отражений от подстилающей поверхность.The invention relates to the field of radar and is intended for use in coastal, airfield and ship radar stations for the detection of ground and surface objects,
Known radar stations - coastal, ship or airfield radars, designed to survey the earth and water surface and detect objects located on it, performing a survey by sector-wise swinging the antenna beam in the azimuthal plane. The coverage area of such a radar is a sector with a radius corresponding to the range of the radar. However, their application for the detection of reflected signals from small targets (σ _C <5M ² ) in conditions of reflections from the underlying surface is not effective. The following is a proof of this statement. The main characteristic that determines the possibility of using a radar for detecting or recognizing a ground and sea target against the background of the underlying surface is the resolution. The generalized characteristic of the resolution can be the area of the resolved element on the terrain, within which the goals or elements are not resolved. In this case, the antenna pattern in azimuth determines the linear resolution in azimuth dL. And the width of the spectrum of the probe signal determines the linear resolution in range dz. When detecting land and sea objects against the background of the underlying surface, the detection characteristics depend on the signal-to-noise ratio + background

where P _with - the reflected power of the signal from the object;
P _f - power of the noise floor of the receiving channel;
P _a - power of reflections from the underlying surface.

где σ_ц - эффективная площадь отражений от объекта,
σ_ф - эффективная площадь отражений подстилающей поверхности,
Учитывая, что эффективная площадь отражений подстилающей поверхности определяется
σ_ф= d₁•d₂•σ_o, [1a]
где σ_o - удельное ЭПР подстилающей поверхности, поэтому и характеристики обнаружения объектов на фоне подступающей поверхности будут существенно зависеть от разрешающей способности РЛС.With a low level of the receiver's own noise compared to the background component of the signal P _W <P _f the signal-to-noise + background ratio will be determined

where σ _C is the effective area of reflections from the object,
σ _f - the effective area of reflections of the underlying surface,
Given that the effective area of reflection of the underlying surface is determined
σ _f = d ₁ • d ₂ • σ _o , [1a]
where σ _o is the specific EPR of the underlying surface; therefore, the detection characteristics of objects against the background of the approaching surface will substantially depend on the radar resolution.

Для обеспечения такого углового разрешения размер антенны D в азимутальной плоскости при длине волны λ = 8 мм должен быть

что существенно превышает размер антенного раскрыва.From formulas 1 and 1a it follows that even with a small reflection coefficient σ _{o the} detection of small objects against the background of the sea can be provided only with a very high resolution. So for the detection of an object (boat at sea) with σ _c = 2 m ² against the background of the sea 3-4 points (σ _o = 5 • 10 ^-3 ) with the probability of correct detection of P _by = 0.7, with the probability of false alarm P _lt = 10 ^-6 , the resolved surface element should not exceed 6.6 m ² , which corresponds to a linear resolution in azimuth and range of 2.5 meters. To obtain such a linear azimuth resolution at a distance of D = 5 km, the directivity pattern of the antenna system in the azimuthal plane should not exceed

To ensure such an angular resolution, the size of the antenna D in the azimuthal plane at a wavelength of λ = 8 mm should be

which significantly exceeds the size of the antenna aperture.

 The above shows that existing ground and ship radars are not capable of detecting reflected signals from small targets in conditions of reflection from the underlying surface even of medium intensity.

 In order to improve the characteristics, the detection of the development goals of such radars in recent years has been carried out in the direction of increasing the antenna aperture and applying wavelengths in the millimeter wavelength range, however, as shown above, to fulfill the conditions for detecting small targets, it is necessary to use an antenna with an aperture size that is practically impossible.

Currently, radars similar to those used on sea ships are used to review the Russian maritime borders. Therefore, the KCLVINHUQHES, R, SR 1000 river navigation station and MK-3217r electron-Sperry designed to ensure the safety of navigation on rivers and other bodies of water, consisting of an antenna, transmitter, receiver, indicator, and power supply, can be used as an analogue of such radars. These stations have a circular view in azimuth. A distinctive feature is the large opening of the horn antenna L = 2.1 - 2.4 meters with a beam width in azimuth of 0.95 - 1 ^o and a range resolution of Δr = 7.5 meters.

 A ship station of Racul Marine Electronics RACAL-DECCA RM209ВТ, RM2070ВТ is also offered as an analog.

 This radar consists of an antenna, transmitter, receiver, indicator and power supply. To obtain high resolution of this station, antennas with different aperture sizes in the azimuthal plane are used: L = 1.2; 1.8; 2.7 and 3.6 meters using lengths λ = 3 cm and 10 cm.

As a prototype, a shipborne DON type radar can be used (See Ship Shipborne Radars and Their Applications, Volume 3, p. 19. Reference Guide. Authors V.Ya Averyanov et al., Edited by Doctor of Technical Sciences Rakova V.I. Shipbuilding, Leningrad 1970) The radar station "Don" consists of the following units (see figure 1)
1. Antenna (Device A).

 2. Transmitter (Device P).

 3. Receiver (Device P).

 4. Synchronizer (Device I).

 5. Indicator (Device I).

The Don radar has the traditional construction of a pulse station with a magnetron transmitter operating at a radiated wavelength of 3.2 cm. The radar operates with a repetition frequency (F _n 1600-3200) Hz, which determines a unique range. High range resolution is ensured by the emission of short pulses τ _c = (0.1 - 1) μs. Given the focus of the proposed invention, we consider obtaining in the prototype resolution in the azimuthal plane. The relatively high resolution in the azimuthal plane (Δα = 1.1 ^o ) in the prototype is also provided in the traditional way, i.e. due to the large size of the real aperture of the antenna (L = 1.8 m). In this case, the base of the antenna is fixedly mounted, and to provide the necessary viewing area in the azimuthal plane, the antenna rotates at a certain speed around the axis in the center of its base.

As follows from the above, the above analogues and prototype, despite the large size of the antenna system, do not provide the required angular resolution for detecting small objects (σ _c <5m ² ) against the background of the underlying surface.

 The task of the invention is to obtain a high angular resolution in azimuth in the ground, airfield and ship radar. The problem is achieved by the fact that the antenna mounted on a movable base is given movement in a horizontal plane, while its electric axis is installed perpendicular (or at an angle) to the direction of movement and a coherent summation of the reflected signals in each range element is performed.

 For coherent signal processing, the following are introduced: a master oscillator, a signal processor, a data processor, an angle sensor and an antenna speed meter.

 The path of the antenna may have a different configuration. However, to obtain better angular resolution characteristics, it is necessary that the linear portion of the trajectory be maximum.

 During movement, the antenna emits coherent pulses from the transmitter with a real radiation pattern and receives them after reflection from the object. When the antenna moves, by processing and coherently summing the received signals reflected from the object, an artificial (synthesized) antenna opening is created, significantly exceeding the real antenna opening.

The possibility of coherent summation of the received reflected signals during movement is provided by compensating for phase measurements of the received Doppler frequency signals. Compensation of phase changes is carried out on the basis of measuring the speed of the antenna during the entire time the antenna moves along a given path. As a result of coherent summation, an output signal is generated corresponding to the signal received by the synthesized radiation pattern with a width of θ _c substantially less than the width of the radiation pattern of a real antenna θ _p .
The role of the antenna aperture in this case is played by the length of the path of the radar antenna.

The coherent processing time T _c is determined by the speed of the antenna and the path length.

 In FIG. 2 shows the X-Y coordinates of the movement of the antenna system. In this example, the antenna moves along the X coordinate.

Фаза траекторного сигнала при такой аппроксимации изменяется по закону

Доплеровская частота траекторного сигнала

Второй член определяет ширину спектра Δf_д доплеровских частот траекторного сигнала. Средняя частота сигнала равна нулю, когда антенна движется перпендикулярно линии визирования на объект.If we restrict ourselves to the quadratic term of the Taylor series expansion, the current distance will be

The phase of the trajectory signal with this approximation changes according to the law

Doppler frequency of the path signal

The second term determines the spectrum width Δf _d Doppler frequencies of the trajectory signal. The average signal frequency is zero when the antenna moves perpendicular to the line of sight of the object.

The maximum signal accumulation time t = T _{with max is} provided when the entire antenna pattern during its movement passes the detection object i.e.

В этом случае ширина спектра доплеровских частот траекторного сигнала будет

где d_а - размер реальной антенны.

In this case, the width of the spectrum of the Doppler frequencies of the trajectory signal will be

where d _a is the size of the real antenna.

При этом ширина спектра доплеровских частот обрабатываемой части траекторного сигнала будет составлять

Из формулы 5 следует, что угловая разрешающая способность соответствует

При движении антенны перпендикулярно линии визирования на объект разрешающая способность Δα будет

Из формулы по аналогии с антенной техникой размер синтезированной апертуры L=U_а•T_с.However, in the present invention, when synthesizing the aperture due to limitations of the real size of the antenna motion section, only a part of the path signal can be used. The synthesis time T _s is selected based on the required angular resolution in azimuth Δα

The width of the spectrum of the Doppler frequencies of the processed part of the trajectory signal will be

From formula 5 it follows that the angular resolution corresponds

When the antenna moves perpendicular to the line of sight on the object, the resolution Δα will be

From the formula, by analogy with the antenna technique, the size of the synthesized aperture is L = U _a • T _s .

 Thus, the radar resolution will be determined by the physical length L of the antenna motion portion. However, it should be noted (see formula 6) that the resolution at the synthesized aperture is two times better than in a real antenna.

 The reality of obtaining the required size of such a synthesized aperture to obtain the required resolution in ground conditions can be confirmed by the following example.

Calculations show that for the detection of small objects σ _c ≤ 5 m ² against the background of reflections from the surface, requiring a linear azimuthal resolution at a distance of R _H = 9000 m - Δτ = 8 m, the angular resolution should be Δα = 3 '.

To obtain such an angular resolution physically, the length of the antenna motion section L (synthesized aperture) must be L = 20 m and is real in ground conditions. As follows from the formula [3]
To implement coherent accumulation, it is necessary to compensate for changes in the phase of the trajectory signal depending on the speed of the angle and range, while ensuring coherence during accumulation.

 Obtaining high azimuth resolution in the proposed radar system is provided using the following processing procedure. The pulsed sounding signal emitted by a moving antenna is reflected from objects and the surface and, with some delay (determined by distance), is received by the same antenna and fed to the receiver input. After conversion to an intermediate frequency, the radio signal is fed to two synchronous phase detectors, the reference signals of which are shifted relative to each other by π / 2. The imaginary and real components of the complex envelope of the signal come from the output of the phase detectors. Since the signal is processed by a digital processor using an analog-to-digital converter, the signal envelope is gated in time (range) and the amplitude is converted to digital form.

где S_вх(τ•α_i) - комплексный сигнал на входе системы обработки, отраженный от объекта, расположенного под углом α_i относительно линии визирования объекта
τ - текущее время на интервале накопления на интервале движения антенны

A(τ,α_i) - амплитуда сигнала;
φ(τ_i;α_i) - фаза сигнала;
h^·(τ) - опорная функция, комплексно сопряженная сигналом, отраженным от объекта;

H(τ) - весовая функция, определяющая заданный уровень боковых лепестков;
U_ar - составляющая скорость движения антенны в направлении на объект V_ar= V_a•Cosα_i;
A_ar - составляющая ускорения движения антенны в направлении на объект

λ - длина излучаемой волны
Для представления этих зависимостей при цифровой обработке сигнала следует произвести переход к дискретной форме.Signal processing is carried out by the method of harmonic spectral analysis. In this case, the signals of the radar image of one gated range strip at the output of the processing system in analog form can be described

where S _in (τ • α _i ) is a complex signal at the input of the processing system reflected from an object located at an angle α _i relative to the line of sight of the object
τ is the current time in the accumulation interval in the interval of the antenna

A (τ, α _i ) is the signal amplitude;
φ (τ _i ; α _i ) is the phase of the signal;
h ^· (τ) is the reference function, complex conjugate to the signal reflected from the object;

H (τ) is a weight function that determines a given level of side lobes;
U _ar - component velocity of the antenna in the direction of the object V _ar = V _a • Cosα _i ;
A _ar - component of the acceleration of the antenna in the direction of the object

λ is the wavelength
To represent these dependencies in digital signal processing, a transition to a discrete form should be made.

In this case, τ is replaced by K • T, ω by 2π • l / NT, and integration is replaced by summation over K,
where K is the reference number of the input signals and the reference function on the accumulation interval.

l - reference number of the output signal (spectrum)
T is the sampling period of the input signals and the reference function
N is the number of samples in the accumulation interval.

B соответствии с вышеизложенным признаки и преимущества предлагаемой paдиoлoкaциoнной системы приводятся ниже в описании предложенного варианта предполагаемого изобретения.N = T _H / T
Given these changes, the radar image signal at the output of the digital processing system will

In accordance with the foregoing, the features and advantages of the proposed radar system are given below in the description of the proposed variant of the alleged invention.

 In FIG. 1-5 are drawings explaining the description of the proposed radar. In FIG. 1 shows a block diagram of a conventional prototype radar system.

 In FIG. 2 is a drawing explaining the presence of Doppler and phase changes during the movement of the antenna, making it possible to synthesize the aperture of the antenna.

 In FIG. 3 presents a block diagram of the proposed radar, corresponding to the claims.

 In FIG. 4 on two sheets (Fig. 4-1 and Fig. 4-2) presents a detailed block diagram of the proposed in Fig. 3 radar, which details the process of generating and processing signals in each of the units and in the radar as a whole.

 The connection of the bonds between the sheets is indicated by the letters from n to l.

 In FIG. 5 is a drawing of a possible embodiment of the movement of the antenna along the guides.

In FIG. 3 presents a block diagram of the proposed radar system, where:
- block 1 - antenna
- block 2 - transmitter
- block 3 - receiver
- block 4 - frequency synthesizer
- block 5 - indicator
- block 6 - circulator
- block 7 - angle sensor
- block 8 - speed meter
- block 9 - signal processor
- block 10 - data processor
- block 11 - master oscillator
In the proposed radar, the antenna is mounted on a movable base and the antenna is set to translate back and forth along the guides in a horizontal plane, while its electric axis is installed perpendicular (or at an angle) to the direction of movement. The configuration of the antenna trajectory can be different (including circular).

 However, for simplicity of signal processing, the preferred configuration of the trajectory of movement, which provides the greatest length of the linear section.

 In FIG. 5 shows an embodiment of the movement of the antenna along the rails and the placement of the antenna on a moving base. The movement of the base along the guides is carried out using the engine. The design of the antenna, the movable base, the construction of the guides is determined by the specific requirements and conditions of use of the radar. The implementation of this design is carried out by traditional engineering methods using well-known materials and structures, including standard ones.

 In FIG. 4 (1-2) presents a detailed structural diagram of a radar system in accordance with this proposal (Fig. 3).

The radar system includes:
antenna - 1
transmitter - 2
receiver - 3
frequency synthesizer - 4
indicator - 5
circulator - 6
angle sensor - 7
speed meter - 8
signal processor - 9
data processor -10
master oscillator - 11
power amplifier - 12
modulator - 13
Microwave receiver - 14
intermediate frequency amplifier - 15
-16 phase detector
phase detector -17
ADC - 18
ADC - 19
memory - 20
memory - 21
multiplier - 22
multiplier - 23
multiplier - 24
multiplier - 25
difference node - 26
knot of the sum - 27
FFT processor - 28
calculator - 29
Cos α module assembly - 30
multiplier - 31
multiplier - 32
multiplier - 33
multiplier - 34
multiplier - 35
knot of the sum - 36
knot of the sum - 37
node Sin Δφ - 38
Cos Δφ - 39 node
memory - 40
memory - 41
multiplier - 42
multiplier - 43
multiplier - 44
node Sin ² α _i - 45
data setter - 46
The radar operates as follows:
During the movement of the antenna (1), the power amplifier (12) amplifies the high-frequency pulses arriving at it from the modulator (13) and transfers it to the antenna (1) through the circulator (6). By the antenna (1), these pulses are emitted into space and propagate in the direction of the selected region.

The coherence of the signal is determined by the master oscillator (11). The modulator (13) modulates the high-frequency signal f and generates pulses supplied to the power amplifier having a given duration (τ) and a repetition period (T _p ), determined by a unique range.

 A high-frequency signal (f) is generated by a frequency synthesizer (4) developed by well-known design methods and manufactured using a well-known element base.

From the master quartz oscillator (II), a signal with an input frequency f _r enters the frequency synthesizer (4), multiplies to a higher frequency f and is used as the carrier frequency of the radar signal emitted by the antenna. Also in the process of movement, the reflected signals from objects and the surface are received by the antenna and through the circulator (6) enter the microwave receiver (14). In the microwave receiver (14), these signals in the receiver mixer are mixed with the synthesizer signal f _s , resulting in the formation of intermediate frequency signals f _op . The intermediate frequency signals in the intermediate frequency amplifier of the amplifier (15) are amplified and fed to phase detectors (16) and (17), to which a signal with a frequency f _pr equal to the intermediate frequency f _pr is received from the synthesizer. Moreover, to one of the phase detectors, the synthesizer signal f _pr arrives with a shift of π / 2.

Due to the movement of the antenna (1) at the outputs of the phase detectors, in-phase "1" and quadrature "Q" Doppler frequency signals are formed. Further, both signals "1" and "Q" using an analog-to-digital Converter (18) and (19), controlled by a clock signal f _c'a , are converted to digital form. From the ADC outputs (18) and (19), an array of two quadrature signals entering the processor (9), synchronized by the signal f _cn from block 4, is accumulated in memory (20) and (21) for each range element and each repetition period. Simultaneously, in the process of moving the antenna, to compensate for phase changes, in the data processor (10) with a synchronized signal f _p α, from the block (4), a support function is formed that is complex conjugate with the signal reflected from the object in accordance with the formula [7]. For this, a linear term of the phase change Δφ _{l of the} support function and its quadratic term Δφ _{q are formed} .
To form a linear term from the angle sensor (7), the value of the angle α _i enters the cosα node and from it goes to the multiplier (31). At the same multiplier (31), a speed value U _{a is} received from the speed meter. The product V _a cosα _{i is} supplied to the multiplier (32), where it is multiplied by the value a = 4π • τ _and / λ coming from the data master (46). The product (4π • τ _and / λ) • V _a Cosα is supplied to the multiplier (34), where it is multiplied by the number of the range element ε coming from the data pickup (46). As a result, at the output of the multiplier (34), a specific phase change is formed for each element of the range in the repetition period T _p - (4π • τ _and • ε / λ) • V _a • Cosα _i
In the multiplier (33) and (35), a phase change from period to period "T _p " is formed for all range elements. For this, from the multiplier (31), the value of V _a • Cosα _{i is} successively multiplied in the multipliers (33) and (35) first by the coefficient b = (4π / λ) • T _p , and then by the coefficient "K" equal to the period number " T _p ", resulting in the output of the multiplier (35) will be (4π • k • T _p / λ) • V _a Cosα.
In the node of the sum (36), a linear term of the phase change is formed
for each element of the range for the "K" - th repetition period.

Для формирования квадратичного изменения фазы Δφ_кв опорной функции используются умножители (42), (43), (44), a также узел Sin²α_i. B умножителе (42) значение скорости V_a с измерителя скорости (8) вначале умножается само на себя, а затем умножается на (КТ_n)², поступающий из задатчика данных, (46) затем величина V_a ²(КТ_n)² поступает на умножитель (43), куда поступают коэффициент C = 2π/λ и коэффициент 1/R из задатчика данных (46). Затем эта величина поступает в умножитель (44), где умножается на значение Sin²α , поступающее из узла Sin²α_i(45).
С выхода умножителя (44) квадратичный член изменения фазы

поступает на узел суммы, где суммируется с линейным членом каждого элемента дальности в каждом периоде T_п. С выхода узла суммы изменение фазы опорной функции Δφ = Δφ_λ+Δφ_кв для каждого элемента дальности ε в каждом периоде повторения T_п поступают в узлы SinΔφ и CosΔφ и накапливаются в памяти для каждого элемента дальности и каждого периода повторения.

To form a quadratic phase change Δφ _{kv of the} support function, multipliers (42), (43), (44) are used, as well as the node Sin ² α _i . In the multiplier (42), the value of the velocity V _a from the speed meter (8) is first multiplied by itself, and then multiplied by (CT _n ) ² coming from the data collector, (46) then the value V _a ² (CT _n ) ^{2 is} received to the multiplier (43), where the coefficient C = 2π / λ and the coefficient 1 / R from the data setter (46) arrive. Then this quantity goes to the multiplier (44), where it is multiplied by the value of Sin ² α coming from the node Sin ² α _i (45).
From the output of the multiplier (44), the quadratic term of the phase change

arrives at the node of the sum, where it is summed with the linear term of each element of range in each period T _p . From the output of the sum node, the phase change of the support function Δφ = Δφ _λ + Δφ _kv for each element of the range ε in each repetition period T _p comes to the nodes SinΔφ and CosΔφ and is accumulated in the memory for each element of the range and each repetition period.

 At the end of the movement of the antenna along the trajectory, the signal samples of each range element of each period from the memory 20, 21 are multiplied in the multipliers 22, 23, 24, and 25 with the samples for each element of the range and the repetition period of the reference function coming from the memory (40) and (41 ) From the outputs of the nodes of the difference (26) and the sum (27), the signals of two quadratures are fed to the FFT processor, where they are subjected to harmonic analysis using the fast Fourier transform algorithm.

 The result of the conversion of signals from the time domain to the frequency domain is the azimuthal readings of two quadratures of radar information in each range element. Then the readings of the two quadratures arrive at node 29, where a module is formed from them. Next, the signals enter the display system 5.

Technical efficiency
The technical effect of the invention is to increase the angular azimuthal resolution of the radar system.

где θ_d,θ - угловое разрешение РЛС,
L - линейный размер,
K_обуж - коэффициент обужения реальной диаграммы.Depending on the realized size of the antenna trajectory, an increase in the angular resolution of the proposed radar in comparison with the prototype will be

where θ _d , θ is the angular resolution of the radar,
L is the linear size,
K _shoelaces - coefficient of shoelaces of a real diagram.

Depending on the application _obuzh coefficient K may be greater than 10.

Claims (1)

Radar system consisting of an antenna, transmitter, circulator, receiver, frequency synthesizer and indicator, while the antenna input-output through the circulator is connected to the receiver input and transmitter output, the first output of the frequency synthesizer is connected to the first input of the receiver, characterized in that the antenna is installed on a movable base, moved in a horizontal plane, installed perpendicularly or at an angle to the direction of movement of the electrical axis of the antenna, as well as the fact that a signal processor is introduced into the system, a data processor, a speed meter, an angle sensor and a master oscillator, from which the signal with the input frequency f _r enters the frequency synthesizer, is multiplied to a higher frequency and used as the carrier frequency of the radar signal emitted by the antenna, while the second output of the frequency synthesizer is connected to the second input of the receiver, the third output - with the third input of the receiver, the fourth output - with the first input of the signal processor, the second input of which is connected to the output of the receiver, the third input - with the output of the data processor, and in stroke - to the input of the indicator, the second data processor input coupled to the output speed detector, and the third input - to the output angle sensor, wherein the data processor synchronizes signal f _pα of the frequency synthesizer forms the support function of the complex conjugate of the signal reflected from object.

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