RU2037839C1 - Device for measuring angles of elevation of low-height targets - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: device has three symmetrical receiving aerials 1-3 which are oriented at horizontal direction and moved apart in height, three receivers 4-6, low-height target angle of elevation calculator 7. EFFECT: improved precision of measurement. 2 dwg

Description

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

 The aim of the invention is the ability to measure the elevation angles of low-altitude targets in the sector of small elevation angles above ground.

 In FIG. 1 shows a simplified structural diagram of the device, conventionally shows the location of the antennas above ground and their radiation patterns.

 The structure of the device includes the following elements: three symmetrical horizontally directed receiving antennas spaced apart in height 1, 2, 3, receivers 4, 5, 6 and a position angle calculator θ of the low-altitude target.

 The angled working sector is defined by the upper half of the main lobe of the radiation pattern of one of the antennas 1, 2, 3, in which the width of the radiation pattern in the vertical plane is narrower.

e^-jkz[F(θ)e^jkhsinθ+F(-θ)

e^-jkhsinθ] (1) где θ угол места цели;
r наклонная дальность от точки расположения антенн на поверхности земли до цели;

- комплексный коэффициент усиления приемного канала;
h высота подъема антенны над землей;
К 2 π / λ волновое число;
λ длина волны;
F( θ) нормированная диаграмма направленности антенны в вертикальной плоскости в свободном пространстве;

комплексный коэффициент, зависящий от характеристик передающей системы РЛС и цели, одинаковый для обоих антенн;

комплексный коэффициент отражения радиоволн от земной поверхности при вертикальной или горизонтальной поляризации.The complex amplitude of the voltage of the echo signal at the output of one of the receiving channels is presented in the following form:

e ^-jkz [F (θ) e ^jkhsinθ + F (-θ)

e ^-jkhsinθ ] (1) where θ is the elevation angle of the target;
r the slant range from the location of the antennas on the earth's surface to the target;

- complex gain of the receiving channel;
h the height of the antenna above the ground;
K 2 π / λ wave number;
λ wavelength;
F (θ) is the normalized antenna pattern in the vertical plane in free space;

a complex coefficient depending on the characteristics of the radar transmitting system and the target, the same for both antennas;

complex coefficient of reflection of radio waves from the earth's surface with vertical or horizontal polarization.

 We assume that the shape of the radiation pattern F (θ) is symmetric in the vertical plane, then F (θ) F (- θ).

-1 при любой поляризации радиоволн и любых реальных характеристиках земной поверхности. С учетом этого формулу (1) можно упростить и записать в следующем виде:

e^-jkr[F(θ)2e^jπ/2sin(kh sinθ) (2)
Эта формула справедлива и для другого приемного канала, антенна которого установлена на другой высоте над землей. Нижняя и верхняя антенны и их приемники одинаковы. Из формулы (2) видно, что в секторе малых углов места сдвиг фаз эхо-сигналов на выходе приемных каналов верхней и нижней антенн практически не зависит от угла места цели и напряжение рассогласования на выходе фазового детектора близко к нулю. Следовательно, рассматриваемый аналог не может измерять углы места маловысотных целей и сопровождать такие цели в секторе малых углов места над землей.It is known that at small slip angles θ the complex reflection coefficient of radio waves from the earth

-1 for any polarization of radio waves and any real characteristics of the earth's surface. With this in mind, formula (1) can be simplified and written as follows:

e ^-jkr [F (θ) 2e ^{jπ / 2} sin (kh sinθ) (2)
This formula is also valid for another receiving channel, the antenna of which is mounted at a different height above the ground. The lower and upper antennas and their receivers are the same. It can be seen from formula (2) that in the sector of small elevation angles, the phase shift of the echo signals at the output of the receiving channels of the upper and lower antennas is practically independent of the elevation angle of the target and the mismatch voltage at the output of the phase detector is close to zero. Therefore, the considered analogue cannot measure the elevation angles of low-altitude targets and accompany such targets in the sector of small elevation angles above the ground.

0, (3)

0, где Gm₁, Gm₂, Gm₃ максимальные коэффициенты усиления нижней, средней и верхней антенн соответственно;
К₁, К₂, К₃ коэффициенты усиления приемников, связанных с соответствующими антеннами;
λ длина волны;
F₁( θ), F₂( θ), F₃( θ)- нормированные диаграммы направленности соответствующих антенн в вертикальной плоскости в свободном пространстве;
h₁, h₂, h₃ высоты подъема соответствующих антенн над землей;
U₁, U₂, U₃ амплитуды напряжений эхо-сигналов.This goal is achieved due to the joint solution of the system of two transcendental equations with one unknown θ in the interval of the elevational working sector of the device

0, (3)

0, where Gm ₁ , Gm ₂ , Gm _{3 are the} maximum gains of the lower, middle and upper antennas, respectively;
K ₁ , K ₂ , K ₃ the gain of the receivers associated with the respective antennas;
λ wavelength;
F ₁ (θ), F ₂ (θ), F ₃ (θ) - normalized radiation patterns of the respective antennas in a vertical plane in free space;
h ₁ , h ₂ , h _{3 the} height of the corresponding antennas above the ground;
U ₁ , U ₂ , U _{3 the} amplitude of the voltage of the echo signals.

The principle of operation of the proposed device is illustrated by the following: we can write the following expression for the complex amplitudes of the voltages U ₁ , U ₂ , U ₃ echo signals at the outputs of the receivers of the lower, middle and upper antennas.

K

e^-jkrF_n(θ)sin

sin

, (4) где n 1, 2, 3. Находя из формулы (4) отношения амплитуд напряжений U₃/U₂ и U₂/U₁ эхо-сигналов на выходах приемников верхней, средней и нижней антенн, получим систему трансцендентных уравнений (3) для определения угла места цели θ.U _n = j2

K

e ^-jkr F _n (θ) sin

sin

, (4) where n 1, 2, 3. Finding from the formula (4) the ratio of the amplitudes of the voltage U ₃ / U ₂ and U ₂ / U _{1 of the} echo signals at the outputs of the receivers of the upper, middle and lower antennas, we obtain a system of transcendental equations ( 3) to determine the elevation angle of the target θ.

 In the elevated working sector, each of the equations of this system has many roots. From this set, choose the root that is the same for the first and second equations of system (3).

 However, there may be such particular constructions of the antenna system when among the many roots of the first and second equations of system (3) in the elevated working sector there are several identical ones. In such cases, the solution to system (3) is ambiguous and the proposed device cannot work. Therefore, special measures should be taken when constructing the antenna system so that such ambiguity does not exist in the elevated working sector of the device.

There will be no ambiguity if the elevation height above the ground of the upper antenna h _{3 is} not a multiple of the elevation heights h ₂ , h _{1 of the} other two antennas. There will also be ambiguity when the radiation pattern of the upper antenna is relatively narrow compared to other antennas and covers only a relatively small (no more than 5-7) number of interference lobes of the lower antenna arising from the influence of radio waves reflected from the earth's surface.

и

от аргумента

h₁sinθ для а) правильного построения антенной системы (а) и б) неправильного построения антенной системы (б). Для заданного направления цели, которое помечено стрелкой, на этих графиках крестиками помечены корни первого и второго уравнений системы (3), а крестиками в кружках корни, одинаковые для первого и второго уравнений. При этом в обоих случаях высоты подъема антенн над землей были выбраны так, чтобы h₂ 2h₁ и h₃ Uh₁. Кроме того, нижняя 1 и средняя 2 антенны одинаковы, все приемники также одинаковы, т. е. К₁ К₂= К₃. В случае (а) диаграмма направленности верхней антенны 3 в вертикальной плоскости была в четыре раза уже, чем антенн 1, 2 и охватывала примерно 5 интерференционных лепестков нижней антенны, а в случае (б) все три антенны были одинаковыми с нижней антенной. Как видно из графиков (см. фиг. 2), при правильном построении антенной системы возможно однозначное определение угла места цели, а при неправильном уравнения системы 3 имеют несколько одинаковых корней и однозначное определение угла места цели становится невозможно.In FIG. 2 shows the calculated dependences of the signal voltage ratios

and

from argument

h ₁ sinθ for a) the correct construction of the antenna system (a) and b) the incorrect construction of the antenna system (b). For a given direction of the target, which is marked by an arrow, the roots of the first and second equations of the system (3) are marked with crosses in these graphs, and the roots with the crosses in the circles are the same for the first and second equations. Moreover, in both cases, the antenna heights above the ground were chosen so that h ₂ 2h ₁ and h ₃ Uh ₁ . In addition, the lower 1 and middle 2 antennas are the same, all receivers are also the same, i.e., K ₁ K ₂ = K ₃ . In case (a), the directivity pattern of the upper antenna 3 in the vertical plane was four times narrower than that of antennas 1, 2 and covered about 5 interference lobes of the lower antenna, and in case (b) all three antennas were the same as the lower antenna. As can be seen from the graphs (see Fig. 2), with the correct construction of the antenna system, it is possible to uniquely determine the elevation angle of the target, and if incorrect, the equations of the system 3 have several identical roots and unambiguous determination of the elevation angle of the target becomes impossible.

 Elements of the structural diagram of the proposed device is as follows.

 As antennas 1, 2, 3, you can use symmetric horizontally directed antennas (for example, mirrored or horn). Receivers 4, 5, 6 are made according to the usual superheterodyne circuit. Limiting the amplitude of the signals in the receiver path is unacceptable. The identity of the amplitude and phase characteristics of these receivers is not required. Special computer 7 is made in digital form and is a specialized computer for jointly solving a system of two transcendental equations (3) with one unknown and choosing from the set of roots of these equations one identical for both equations.

 The dynamics of the proposed device is as follows.

Receiving antennas 1, 2, 3 receive echoes of a low-altitude target, arriving at the antenna as a direct radio wave or a radio wave reflected from the ground. Receivers 4, 5, 6 amplify the echo signals, convert and, at an intermediate frequency, and detect. The output voltages U ₁ , U ₂ , U _{3 of the} receivers at the video frequency are supplied to the calculator 7, where they are converted to digital form. The computer 7 determines the elevation angle of the low-altitude target by jointly solving the system of equations (3) on the interval of the elevational working sector of the device.

Claims (1)

DEVICE FOR MEASURING ANGLES OF LOW-TARGET AIMS, containing three symmetric horizontal directional, spaced-apart receiving antennas, each of which is connected to respective receivers, characterized in that a low-altitude target angle calculator θ is introduced, the first, second and third inputs of which are connected to the outputs the corresponding receivers, and the output is the output of the device, and the calculation of the angle q is performed according to the following formulas:

where U ₁ , U ₂ , U _{3 the} amplitude of the voltage of the echo signals at the outputs of the receivers of the lower, middle and upper antennas, respectively,

maximum gains of the lower, middle and upper antennas, respectively;
K ₁ , K ₂ , K ₃ receiver gains;
λ wavelength;
F ₁ (θ), F ₂ (θ), F ₃ (θ) normalized radiation patterns of the respective antennas in a vertical plane in free space;
h ₁ , h ₂ , h _{3 the} height of the corresponding antennas above the ground.

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