RU2038607C1 - Method of measurement of elevation of low-altitude targets - Google Patents

Abstract

FIELD: radiolocation. SUBSTANCE: method provides for radiation and reception of pulse radar signals by two similar antennas polarized in linear symmetry, matching of phase centers of antennas and turning of one of them through 90 deg in plane of aperture. Then measurement of phase shift of received signals of vertical and horizontal polarization is conducted and elevation angle is found by solution of transcendental equation determining relation of this phase shift to elevation angle of target by known parameters of radar and earth surface close to antenna. EFFECT: enhanced authenticity of method. 2 dwg

Description

 The invention relates to radar and can be used in low-altitude ground-based radars for measuring elevation angles of air targets in the sector of small elevation angles above the ground.

 A known method of measuring elevation angles used in the goniometer device of a radar station, which contains the reception of radar signals by three spaced apart antennas and measuring the phase shifts of the received signals [1] The results of the measurement of phase shifts are used to determine the elevation angle of an air target or other source of radio emission.

 However, the antenna system used to implement this method consists of three antennas spaced apart in height and, therefore, is bulky and has a large vertical size.

 There is also a method of determining the altitude or elevation angle used in a radar with a swinging radiation pattern of the antenna, which contains radiation and reception of pulsed radar signals using a transceiver antenna having a narrow elevation radiation pattern and swings in the vertical plane.

 The disadvantage of this method is that when operating in the sector of small elevation angles, the radar antenna receives both direct target echoes and target echoes reflected from the ground. The latter interfere with the operation of the radar, reduce the accuracy of measuring the elevation angle of low-altitude targets, and at very small elevation angles lead to disruption of the radar. In addition, this method contains a technically complex operation of rotating the antenna in elevation.

 Closest to the invention is a method of measuring the elevation angle and tracking targets in the elevation plane, used in a monopulse phase direction finding radar system, which contains the emission and reception of pulsed radar signals using two identical symmetric height-spaced antennas associated with the transmitter during transmission and with two receivers when receiving signals, phase detection of the received signals and the use of the error signal from the output of the phase detector to control I have an electric motor that automatically rotates the antenna system in a vertical plane while tracking the target in elevation [3] In this case, the elevation angle of the target is determined by the current elevation position of the antenna system. The antennas of such a radar system are directed identically and emit radio waves of the same (for example, vertical) polarization. Information about the elevation angle of the target is contained in the phases of the received echo signals. When the axis of the antenna system is precisely aimed at the target, the error signal at the output of the phase detector is zero and the electric motor does not rotate the antenna system. When the target deviates in elevation from the direction of the antenna axis, a mismatch signal appears, which causes the motor and antennas to rotate in elevation until the axis of the antenna system coincides with the direction to the target.

 However, to implement the prototype method, an antenna system of two antennas spaced apart in height is required, which is bulky and has a large vertical size. In addition, this method almost does not allow to measure the elevation angles of low-altitude targets in the sector of small elevation angles from zero to half the elevation width of the antenna pattern. In this case, the measurement of the elevation angle of the target is made with large errors, and with the horizontal direction of the axis of the antennas, measurement of the elevation angle and elevation tracking of the target becomes impossible. This is explained by the fact that in the sector of small elevation angles, radars receive echo signals coming from the target of direct and reflected radio waves from the earth at the same time. The target echoes reflected from the ground distort the phases of the direct echoes and the information contained in these phases about the elevation angle of the target. The disadvantage of the prototype is also the presence of a technically complex operation of rotating the antenna system in elevation.

 The technical objectives of the invention are to reduce the vertical size of the used antenna system by combining the apertures of two antennas, eliminating the complex operation of rotating the antenna system in elevation, and also providing the ability to measure elevation angles of low-altitude targets in the sector of small elevation angles above the ground and improving measurement accuracy in this sector by eliminating the harmful effects of target echoes reflected from the ground and using these signals to achieve a positive effect.

×
× e

+e

2arg

e

+ e

Δφ 0, (1) где ε σ и h_н относительная диэлектрическая проницаемость, проводимость и средняя высота мелкомасштабных неровностей земной поверхности соответственно;
λ длина волны;
h высота подъема фазового центра антенны над землей;
arg обозначение операции вычисления аргумента комплексного числа.To do this, in the method for measuring the elevation angle of low-altitude targets, containing radiation and receiving pulsed radar signals using two identical symmetric horizontally directed linearly polarized antennas connected to the transmitter during transmission and two receivers when receiving signals, the phase centers of the antennas are combined and one of them is rotated 90 in the plane ^of the aperture, measured phase shift Δ φ of the received signals vertical and horizontal polarization at the output of the receivers, and the target elevation angle θ is determined by p sheniya following transcendental equation:
2arg

×
× e

+ e

2arg

e

+ e

Δφ 0, (1) where ε σ and h _{n are the} relative permittivity, conductivity and average height of small-scale irregularities of the earth’s surface, respectively;
λ wavelength;
h the height of the phase center of the antenna above the ground;
arg designates the operation of computing the argument of a complex number.

 In FIG. 1 shows a simplified block diagram of a device implementing the method; in FIG. 2 the dependence of the phase shift Δ φ on the elevation angle of the target θ in the working sector of the radar.

,

на выходе приемников 5 и 6 сигналов вертикальной и горизонтальной поляризации соответственно, и спецвычислитель 8, определяющий по измеренному сдвигу фаз Δ φ угол места цели θ путем решения трансцендентного уравнения (1) на интервале угломестного рабочего сектора РЛС. При этом полагается, что входящие в уравнение (1) длина волны λ высота h подъема над землей фазового центра антенн, относительная диэлектрическая проницаемость ε, проводимость σ и средняя высота h_н мелкомасштабных неровностей земной поверхности (высота травяного покрова, кустарника, волн на море и т.п.) вблизи РЛС известны или заранее измерены каким-либо известным способом. Антенная система рассматриваемой РЛС может быть выполнена в виде антенной решетки из симметричных вертикальных и горизонтальных вибраторов (на фиг. 1 показаны один вертикальный и один горизонтальный вибраторы). Приемники 5 и 6 должны иметь идентичные фазовые характеристики. Возможность практической реализации предложенного способа подтверждается тем, что показанные на фиг. 1 используемые элементы РЛС: передатчик 4, приемники 5, 6 и фазометр 7 представляют собой обычные известные устройства, серийно выпускаемые отечественной промышленностью, а в качестве спецвычислителя 8 можно использовать обычную микроЭВМ.Implementing the proposed radar method includes vertical 1 and horizontal 2 polarization antennas, the phase centers of which coincide, an antenna switch 3 connecting the antennas to the transmitter 4 when transmitting sounding signals and to the corresponding vertical 5 and horizontal 6 polarization receivers when receiving target echoes, phase meter 7 measuring phase shift Δ φ of stress

,

at the output of the receivers 5 and 6 of the signals of vertical and horizontal polarization, respectively, and a special calculator 8, which determines the angle of the target θ from the measured phase shift Δ φ by solving the transcendental equation (1) on the interval of the elevation working sector of the radar. It is assumed that the wavelength λ included in Eq. (1) is the height h of the antenna phase center above the ground, the relative permittivity ε, the conductivity σ and the average height h _{n of} small _- scale irregularities of the earth’s surface (the height of the grass cover, shrub, waves at sea and etc.) near the radar station are known or previously measured in any known manner. The antenna system of the considered radar can be made in the form of an antenna array of symmetrical vertical and horizontal vibrators (in Fig. 1 shows one vertical and one horizontal vibrators). Receivers 5 and 6 should have identical phase characteristics. The possibility of practical implementation of the proposed method is confirmed by the fact that shown in FIG. 1 used radar elements: transmitter 4, receivers 5, 6 and phase meter 7 are conventional known devices commercially available from the domestic industry, and as a special calculator 8 you can use a conventional microcomputer.

,

принимаемых эхо-сигналов цели на выходах приемников 5 и 6 определяются следующими формулами:

F $\genfrac{}{}{0ex}{}{\text{2}}{\text{в}}$ (θ)

×
×

e

+ e

^×
×

(2) на выходе приемника вертикальной поляризации 5 и

F $\genfrac{}{}{0ex}{}{\text{2}}{\text{г}}$ (θ)

×
×

e

+ e

^×
×

(3) на выходе приемника горизонтальной поляризации 6, где

,

комплексные коэффициенты усиления приемников 5 и 6 (приемники одинаковы);
λ длина волны;
G_мв, G_мг -максимальные коэффициенты усиления антенн вертикальной и горизонтальной поляризации;
r наклонная дальность от точки расположения антенной системы на поверхности земли до цели;
Р мощность передатчика;
R_пв, R_пг входные сопротивления приемников 5 и 6;
σ_цв, σ_цг эффективные отражающие поверхности цели для радиоволн вертикальной и горизонтальной поляризации соответственно;
θ угол места цели;
F_в (θ),F_г (θ) нормированные диаграммы направленности в вертикальной плоскости в свободном пространстве симметричных антенн 1 и 2;
φ_ов, φ_ог изменения фаз радиоволн вертикальной и горизонтальной поляризации при отражении от цели;
h высота подъема над землей фазового центра антенн;
ε σ, h_н относительная диэлектрическая проницаемость, проводимость и средняя высота мелкомасштабных неровностей земной поверхности на площадке вблизи антенны РЛС.The radar antenna system emits and receives both direct and vertically and horizontally polarized radio waves reflected from the ground. In this case, targets reflected from the ground of the echo signal interfering with the operation of the prototype are fundamentally necessary in this case and are used to achieve a positive effect. Complex stress amplitudes

,

the received echo signals of the target at the outputs of the receivers 5 and 6 are determined by the following formulas:

F $\genfrac{}{}{0ex}{}{\text{2}}{\text{in}}$ (θ)

×
×

e

+ e

^×
×

(2) at the output of the vertical polarization receiver 5, and

F $\genfrac{}{}{0ex}{}{\text{2}}{\text{g}}$ (θ)

×
×

e

+ e

^×
×

(3) at the output of the horizontal polarization receiver 6, where

,

complex gain of receivers 5 and 6 (the receivers are the same);
λ wavelength;
G _mv , G _{mg -} maximum gain of antennas of vertical and horizontal polarization;
r the inclined distance from the location of the antenna system on the earth's surface to the target;
P transmitter power;
R _pv , R _pg input resistance of the receivers 5 and 6;
σ _cv, σ _{cg are the} effective reflective surfaces of the target for vertical and horizontal polarization waves, respectively;
θ target elevation angle;
F _in (θ), F _g (θ) normalized radiation patterns in the vertical plane in the free space of the symmetrical antennas 1 and 2;
φ _s , φ _og changes in the phases of radio waves of vertical and horizontal polarization upon reflection from the target;
h the elevation above the ground of the phase center of the antennas;
ε σ, h _{n the} relative dielectric constant, conductivity and average height of small-scale irregularities of the earth's surface at the site near the radar antenna.

и

с учетом приведенных выше замечаний, получим трансцендентное уравнение (1) для определения угла места цели θ.It is known that when vertical and horizontal polarization radio waves are reflected from balloons, warheads, missiles and other simple-to-form targets with approximately axial symmetry, the changes in the phase of the radio wave φ _s and φ _og will be approximately the same for both polarizations, i.e. φ _s ≈φ _og. The proposed method is intended for measuring elevation angles of such targets. Calculating from formulas (2) and (3) the phase shift of the complex stress amplitudes

and

taking into account the above remarks, we obtain the transcendental equation (1) to determine the target elevation angle θ.

 Thus, the above distinguishing features are essential and fundamentally necessary for the implementation of the proposed method.

 To uniquely determine the elevation angle of the target, it is necessary to ensure that the transcendental equation (1) has a unique solution on the interval of the elevational working sector of the radar. The calculations showed that this requirement is satisfied within the lower interference lobe of the antenna patterns taking into account the influence of the earth. To meet this requirement, it is necessary that the angular width of the antenna patterns in free space does not exceed twice the width of the lower interference lobe, i.e., it is necessary to use antennas low-lying above the ground. This is a significant drawback of the proposed method. It should be noted that a similar drawback is inherent in the prototype, which can unambiguously measure the angular coordinate only within the same interference lobe of the radiation pattern of the diversity antenna system. In addition, the prototype is practically not operational in the sector of small elevation angles above the ground.

To confirm the feasibility of practical implementation of the proposed method in FIG. Figure 2 shows the calculated dependence of the phase shift Δ φ of the received echoes of vertical and horizontal polarization on the elevation angle of the target θ within the lower interference lobe of the antenna patterns taking into account the influence of the underlying surface. This graph is calculated by formula (1) for radars with a wavelength of λ 1.8 m and a height of the antenna phase center h 11.5 m above the excited sea with an average wave height h _n 0.5 m. The angular width of the lower interference lobe in this the case is 4.5 ^o , while it is necessary to use antennas with an elevation beam width of 9 ^o . As seen in FIG. 2, in this case, the elevation radar operating sector equal to the upper half of the main lobe antenna pattern, the equation (1) has a unique solution and method provides an unambiguous definition of the elevation angle in the working sector of low- purposes from 0 to ^about 4.5.

 Thus, the proposed method can be practically implemented.

 A radar that implements the proposed method works as follows.

The radar antenna system is preformed so that the phase centers of the antennas are aligned and one of the antennas is rotated 90 ^° in the plane of the aperture, so one of the antennas has vertical polarization and the other horizontal. The transmitter 4 generates a high-frequency pulse sounding signal. Antenna switch 3 during transmission connects both antennas in parallel to the output of the transmitter 4. Antennas 1 and 2 emit radio waves of vertical and horizontal polarization, respectively. Radio waves bounce off the air target and arrive at the radar antennas. Each of the antennas receives signals of the corresponding polarization. When receiving an antenna switch 3 connects the antenna 1 to the input of the receiver 5 of the vertical polarization signal, and the antenna 2 to the input of the receiver 6 of the horizontal polarization signal. Receivers 5 and 6 amplify the signals and convert them to an intermediate frequency. The phasometer 7 measures the phase shift Δ φ of the output voltages of the receivers 5 and 6 at the intermediate frequency of the receivers. The result of measuring the phase shift Δφ is supplied to a special calculator 8, which determines the elevation angle of the target θ by solving the transcendental equation (1). At the same time, the known values of the parameters λ h ε σ, h, h _{н are} introduced in advance into the work program of special calculator 8.

 Thus, the proposed method is practically feasible, has significant distinguishing features, eliminates all the above disadvantages of the prototype and provides an unambiguous definition of the elevation angles of low-altitude targets in the sector of small elevation angles above the ground.

Claims (1)

METHOD FOR MEASURING AN ANGLE AREA OF LOW-TARGET OBJECTIVES, which consists in emitting and receiving pulsed radar signals using two identical symmetrical horizontally directed antennas connected to a transmitter and two receivers, characterized in that the radiation and reception of pulsed radar signals is carried out using linearly polarized antennas , phase centers of which are aligned and one of them is rotated by 90 ^o in the aperture plane so that one horizontal polarization antenna radiates signals another vertical polarization measured phase shift Δφ of the received signals the horizontal and vertical polarizations at the output of the receivers, and the elevation angle q is determined by the formula

where Δφ is the phase shift of the received signals of vertical and horizontal polarization;

relative permittivity, conductivity and average height of small-scale irregularities of the earth’s surface, respectively;
λ wavelength;
h the height of the phase center of the antenna above the ground.

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