RU2210789C2 - Procedure measuring effective scattering surface of objects - Google Patents

Abstract

FIELD: measurement of radar characteristics of objects, study of scattering properties of detection and ranging objects. SUBSTANCE: procedure measuring effective scattering surface includes formation of radiation field in working space of radar measurement complex, measurement and calibration of scattered power against basic standard. Reference reflector comprising two omnidirectional reflectors is used in compliance with invention. Diagrams of their effective scattering surfaces are employed to establish positions and relative intensity of noise sources induced along propagation path of electromagnetic waves which are eliminated or minimized in the long run by one of standard methods. Proposed procedure measuring effective scattering surfaces of objects makes it possible to increase precision of determination of diagrams of backward scattering of objects in maxima of 0.5-2.0 dB and in relative minima up to 10.0 dB. Advantage of this approach of measurement of radar characteristics lies in simplicity of its realization achieved by way of expansion and updating of traditional procedures do not requiring additional expenditure of materials and research. EFFECT: increased precision of measurement of radar characteristics of objects due to improved technical parameters of radiation field. 6 dwg

Description

 The invention relates to radio engineering, in particular to radar, and can be used to measure the radar characteristics (RLH) of objects in the ranges of millimeter, centimeter and decimeter radio waves at open and closed ranges.

 Known methods for measuring the effective scattering surface (EPR) of objects, including the formation of the target irradiation field with different polarizations, measuring and standardizing the scattered field, as well as determining the modulus and phase difference of the reflection coefficients for the main and cross base polarizations. [1. Konareikin D.B. et al. Polarization of radar signals. M.: Sov. Radio, 1966, pp. 280-288, as well as 2. UK application 148064 for IPC G 01 S 13/00, 1979].

 A common drawback of these methods is the low accuracy of the EPR measurement because their use does not identify the location and does not control the intensity of the sources of residual background reflections on the propagation path of electromagnetic waves (EMW), as well as re-reflection between the individual elements of the radar measuring complex (RIC) ), therefore, as a rule, measurements are carried out at a relatively high level of interfering reflections.

 A more accurate method is known for measuring the EPR of ground objects with a low reflection level (Russia, AS 843556, IPC G 01 S 13/00, 1979), which consists in forming an irradiation field in the working volume of the RIC, placing in the range of the RIC additionally gated by range a reflector rigidly mounted on a movable platform and moving in such a way that, at a certain position of the reflector, the vector sum of the radar signals induced in the transceiver antenna in the absence of an object is zero.

 However, the known method is inherently identical to the compensation of residual reflections produced in the receiver RIC in the absence of a target in the working volume, which, as you know, is not enough. In addition, the compensation of background reflections (without an object) does not exclude the influence of interfering signal sources on the total irradiation field and the measured values of the EPR of objects.

 There is also a method of increasing the accuracy of EPR measurements [Russia, a.s. 1083776, IPC G 01 R 29/00, 1981], based on the irradiation of an equidistant lattice with a certain step, made up of identically oriented objects, and the reception of a signal scattered across it, which is used to judge the EPR of an individual object, and the number of elements making up the lattice choose on the basis of exceeding the "useful" signal due to scattering by the grating over the background.

 The main disadvantage of this method is that the amplitude-phase distortion of the irradiation field and the re-reflection of the object — the design elements of the RIC are thus not eliminated for any number of objects making up the equidistant array, and thus high measurement accuracy is not ensured.

 The closest in technical essence to the proposed method is a method for measuring the EPR of objects, including the formation of an irradiation field in the working volume of the RIC, placing the object under study in it, measuring the power dissipation and standardizing the levels of reflected radar signals [5. Rat Scat complex for measuring radar cross-section of targets, TIIER, vol. 53 8, 1965, pp. 1085-1094]. The disadvantage of this method, as well as analogues, is the low accuracy of measuring the EPR of objects due to the lack of data on the true distribution of local sources (LI) of secondary radiation on the propagation path of electromagnetic waves. The indicated method of measuring the EPR, due to significant fluctuations in the background reflections, does not ensure the constancy of the parameters of the irradiation field in the working volume of the RIC and the control of the accuracy of the EPR measurements, especially at a low level of reflected radar signals. That is, there is a lack of effectiveness of traditional methods of forming the irradiation field in the working volume of the RIC.

усредненная по серии n измерений диаграмма обратного рассеяния (ДОР) по мощности эталонных отражателей; х, у, z - текущие координаты точки наблюдения на трассе; r = [x-x₁(s)]²+[y-y₁(s)]²+[z-z₁(s)]², x₁(s), y₁(s), z₁(s) - параметрические уравнения траектории L перемещения подвижного отражателя в рабочем объеме; h_s - коэффициенты Ламе траектории; р - вещественный параметр изменяющийся в пределах 3. . . 10; k = 2π/λ, λ - рабочая длина волны РИК; зависимость от времени принята в виде exp(iωt), а фазу φ(s) в интеграле (1) выбирают исходя из условия комплексного сопряжения с полем передающей антенны (в случае антенны с изотропной диаграммой направленности φ(s)=kr_a, где r_a - расстояние от фазового центра антенны до точки расположения подвижного отражателя). Далее стандартными методами минимизируют вклад помеховых радиолокационных сигналов, улучшая параметры поля облучения антенной системы (АС) и повышая тем самым точность измерений ЭПР.The technical task of this invention is to improve the accuracy of measurements of the EPR of objects by improving the parameters of the radiation field of the RIC. This is achieved by the fact that in the known method of measuring the EPR, based on the formation of the irradiation field in the working volume of the RIC, placing the test object in the field created by the pulse locator, measuring the power of the reflected signal and subsequent standardization, the EPR diagram of two omnidirectional reference reflectors when moving one of them by a specified law within the working volume meter produces a theoretical estimate diagram I ₀ (s) EPR same reflector in the free space of e radiation antenna complex and the difference graph, by computer simulation, determine the geometric position and the relative intensity of residual sources of reflection by the formula EMW

averaged over a series of n measurements, the backscatter diagram (DOR) for the power of the reference reflectors; x, y, z - current coordinates of the observation point on the track; r = [xx ₁ (s)] ² + [yy ₁ (s)] ² + [zz ₁ (s)] ² , x ₁ (s), y ₁ (s), z ₁ (s) are the parametric equations of the trajectory L moving the movable reflector in the working volume; h _s are the Lame coefficients of the trajectory; p is a material parameter varying within 3.. . 10; k = 2π / λ, λ is the working wavelength of the RIC; the time dependence is taken in the form exp (iωt), and the phase φ (s) in the integral (1) is selected based on the condition of complex conjugation with the field of the transmitting antenna (in the case of an antenna with an isotropic radiation pattern φ (s) = kr _a , where r _a is the distance from the phase center of the antenna to the location of the movable reflector). Then, by standard methods, they minimize the contribution of interfering radar signals, improving the parameters of the radiation field of the antenna system (AS) and thereby increasing the accuracy of EPR measurements.

 A comparative analysis of the claimed solution with the prototype shows that the proposed method differs from the known one by the presence of new features: firstly, new actions - measurement of the EPR of two reference omnidirectional reflectors in a real RIC field and a theoretical assessment of the EPR diagram of the same reflectors in free space in the radiation field antennas and, secondly, of new principles - by determining the geometric position and relative intensity of interfering signals induced by speakers on the propagation path of electromagnetic waves, by calculating the curvilinear integral (1) of the difference between the measured and theoretically calculated EPR diagrams of two omnidirectional reference reflectors (radio image inversion).

 In the study of other well-known technical solutions in the art, the specified set of features that distinguish the invention from the prototype was not identified. The proposed measurement sequence, namely: first, record the EPR diagram of two reference reflectors in the real radiation field of the RIC and make a theoretical estimate of the EPR in free space in the radiation field of the antenna, restore the geometric position and relative intensity of the secondary sources, and on this basis, or eliminate interference signals completely, or reduce their contribution to the irradiation field to acceptable levels with the help of radar absorbing materials (RPM) and coatings, it allows improving the field parameters o walks in the working volume of the RIC, not limited to the heuristic approach as in the prototype, and only to the section of the route that is essential for the propagation of electromagnetic waves. [6. Black B.F. Propagation of radio waves. M .: Sov. radio, 1962, p. 28-37].

 The implementation of new principles for correcting the irradiation field in the working volume of the RIC, which consists in first determining the induced sources of interfering reflections, and then gradually decreasing their effect on the primary field of the AS, allows improving the main parameters of the irradiation field in the working volume of the RIC in the direction of their approach to the primary field of the transmitter antenna in free space. That is, the proposed method for measuring the ESR of objects while maintaining the technical feasibility of the method allows to increase the accuracy of measuring the radar characteristics of objects with effective control of the constancy of the amplitude and phase parameters of the radiation field of the RIC.

 In FIG. 1 shows a structural diagram of a device that implements the proposed method for measuring ESR diagrams of objects. Figure 2 shows the geometry of the polygon and the propagation path of EMW, explaining the essence of the proposed method. Figure 3 shows fragments of the EPR diagrams of the reference reflectors in the field of the AS of the transmitter in free space (dashed curve) and in the presence of a given intensity and position of the sources of interfering signals (solid curve). Figure 4 illustrates fragments of the restored relative intensities of secondary radiation sources.

 A device that implements the claimed method for measuring the EPR of objects and is shown in FIG. 1, contains a series-connected recorder - 1, a receiver unit - 2, an antenna switch - 3, a pulse transmitter - 4, a transceiver antenna - 5, a slewing rotary device (OPU) - 6, designed to accommodate reference reflectors and studied objects - 7, a remote control with a rotation angle sensor - 8. In the device that implements the proposed method, typical nodes and elements are used, made at the modern level development of radio engineering [7. Mayzels E.N. Measuring the dispersion characteristics of radar targets. M .: Sov. radio, 1972].

 In FIG. 2 shows a transceiver antenna - 5, OGTU - 6, reference and reflectors moving according to a given law - 7, local heterogeneity that creates interference reflections - 9.

где f(θ,φ) - угловая зависимость амплитудной диаграммы направленности антенны РИК; θ₀,φ₀;θ₁,φ₁ и θ_s,φ_s - углы, определяющие направление из фазового центра антенны на опорный отражатель, подвижный отражатель и ЛИ соответственно; S(θ_s,φ_s;α,β) - относительный коэффициент бистатического рассеяния вторичного источника в направлениях на опорный и подвижный отражатели, характеризуемых из точки ЛИ соответственно углами

расстояние между фазовым центром антенны с координатами x_а, y_а, z_a и ЛИ с координатами x_s, y_s, z_s;

расстояние между ЛИ и опорным отражателем;

расстояние между ЛИ и подвижным отражателем;

расстояние между фазовым центром антенны и опорным отражателем;

расстояние между фазовым центром антенны и подвижным отражателем. Для приведенных на фиг.3 диаграмм принято, что x_а=800 м, y_а=0, z_a=2,5 м; х_s=100 м, z_s= 5 м. Подвижный отражатель перемещался по цилиндрической равномерной спирали радиуса r_sp= 10 м в пределах z=0...6 м. Подстилающая поверхность была горизонтальной и имела уровень z=-1 м. Количество витков спирали составляло 60, а длина волны λ=10 см. Диаметр равноамплитудно и синфазно возбуждаемого круглого раскрыва антенны d=19 м, а максимум ДН антенны был направлен в центр рабочего объема РИК на высоте z=3 м. Относительный коэффициент бистатического рассеяния вторичного источника был выбран таким, что мощность поля, рассеянного ЛИ, в центре рабочего объема по отношению к мощности поля излучения антенны составляла -25 дБ.In FIG. 3 in relative units presents fragments of DOR I ₀ (dashed curve) and I _m (solid curve) reference reflectors obtained by computer simulation according to the following formulas:

where f (θ, φ) is the angular dependence of the amplitude radiation pattern of the RIC antenna; θ ₀ , φ ₀ ; θ ₁ , φ ₁ and θ _s , φ _s are the angles that determine the direction from the phase center of the antenna to the reference reflector, movable reflector, and LI, respectively; S (θ _s , φ _s ; α, β) is the relative coefficient of bistatic scattering of the secondary source in the directions to the reference and movable reflectors, characterized by angles from the LI point, respectively

the distance between the phase center of the antenna with coordinates x _a , y _a , z _a and LI with coordinates x _s , y _s , z _s ;

the distance between the LI and the reference reflector;

the distance between the LI and the movable reflector;

the distance between the phase center of the antenna and the reference reflector;

the distance between the phase center of the antenna and the movable reflector. For the diagrams shown in FIG. 3, it is assumed that x _a = 800 m, y _a = 0, z _a = 2.5 m; x _s = 100 m, z _s = 5 m. The movable reflector moved along a cylindrical uniform spiral of radius r _sp = 10 m within z = 0 ... 6 m. The underlying surface was horizontal and had a level z = -1 m. the spiral turns was 60 and the wavelength λ = 10 cm. The diameter of the equally-amplitude and in-phase excited circular aperture of the antenna was d = 19 m, and the maximum of the antenna beam was directed to the center of the RIC working volume at a height of z = 3 m. The relative coefficient of bistatic scattering of the secondary source was chosen so that the power of the field scattered by LI in the center Static preparation volume to the power antenna radiation field was -25 dB.

 Figure 4 presents the results of evaluating the relative intensity of the sources depending on the coordinates x, y, z are fixed), y, x, z are fixed), z, x, y are fixed). The data shown by the solid curve correspond to the sections covering the LI, and the dashed curve correspond to the sections in which the LI are absent, and upon receipt, it was believed that y = 10 m, z = 5 m in Fig. 4a; x = 100 m, y = 10 m in Fig. 4b, x = 100 m, y = 10 m in Fig. 4c. All the above results were obtained under the assumption that there are no re-reflections of electromagnetic waves from the underlying surface, although they can also be taken into account if necessary.

, на порядок и более превосходил собственные шумы приемопередающей аппаратуры и фоновых отражений с учетом дальности R до ОПУ. Излучаемые блоком 5 радиоволны рассеиваются на составном эталонном отражателе 7 и через приемный блок 2, запоминаются регистратором 1 (формируется экспериментальная диаграмма ЭПР - I_m(s)). Далее составляется разность между измеренными значениями I_m(s) и диаграммой ЭПР I_o(s) тех же отражателей, рассчитываемой теоретически для свободного пространства в поле излучения антенны комплекса, либо уже содержащейся в банке данных ЭВМ. Рассчитывается функция источников F(x, y,z) по формуле (1). При этом в восстановленном изображении источников - функции F(x,y,z) появляются пики, связанные с помеховыми сигналами, в случае наличия при определенных х, у и z наведенных источников излучения на трассе распространения ЭМВ. Для лучшего выделения ("поднятия") выбросов помеховых сигналов из общего фона показатель степени р в (1) целесообразно варьировать в пределах 3...10. Далее выявленные помеховые источники минимизируются до приемлемых уровней, после чего РИК считается подготовленным к измерению РЛХ объектов. Существо предложенного способа измерения ЭПР объектов на РИК любого типа состоит в следующем. Для реального поля облучения, определяемого геометрией РИК, измеряют ДОР двух всенаправленных эталонных отражателей устанавливаемых на ОПУ измерителя, причем один из отражателей выполняет роль опорного, а второй перемещается в пределах рабочего объема по определенному закону, например, вращается по цилиндрической спирали радиуса r_sр так, чтобы получаемая интерференционная картина суммарных отражений ЭМВ охватывала максимально возможную апертуру рабочего объема. По соотношению (1) вычисляют функцию F(x,y,z), восстанавливая распределение вторичных источников по трассе распространения ЭМВ и известными приемами уменьшают их воздействие на поле облучения РИК. При необходимости процесс корректировки амплитудных и фазовых параметров поля облучения может производиться методом последовательных приближенный вплоть до полного совпадения его с полем излучения антенны РИК в свободном пространстве.A device that implements the proposed method works as follows. Traditional measures are being taken to reduce the background level due to reflections from the elements of the RIC, inhomogeneities in the propagation path of electromagnetic waves, and local objects. Reflections from a portion of the path that enters the region essential for the propagation of radio waves [6] are preliminarily attenuated to a predetermined level using a specially sized in space and coated with RPM metal screen with certain dimensions. When measuring the DOR of a diffuser made up of reflectors 7, they are placed on the basis of the OPA-6, with one reference reflector being placed on the axis of rotation of the OPU, and the second moving according to a given law L (x, y, z), for example, in a spiral within the working range volume, in vertical steps Δh ~ λ. If spheres are selected as reference reflectors, then the value of their radius a is chosen so that the level of reflections specified by the value of the EPR

, an order of magnitude or more superior to the intrinsic noise of the transceiver equipment and background reflections, taking into account the distance R to the GPR. The radio waves emitted by block 5 are scattered on the composite reference reflector 7 and through the receiving block 2 are stored by the recorder 1 (an experimental EPR diagram is formed - I _m (s)). Next, the difference between the measured values of I _m (s) and the EPR diagram I _o (s) of the same reflectors is compiled, theoretically calculated for free space in the radiation field of the antenna of the complex, or already contained in the computer database. The source function F (x, y, z) is calculated by the formula (1). In this case, peaks associated with interfering signals appear in the reconstructed image of the sources — functions F (x, y, z), if, for certain x, y, and z, there are induced radiation sources on the electromagnetic propagation path. In order to better distinguish (“raise”) the emissions of interfering signals from the general background, the exponent p in (1) should be varied within 3 ... 10. Further, the identified interference sources are minimized to acceptable levels, after which the RIC is considered prepared for the measurement of radar objects. The essence of the proposed method for measuring the EPR of objects on a RIC of any type is as follows. For the real field of radiation, determined by the geometry of the RIC, the DOR of two omnidirectional reference reflectors installed on the meter is measured, with one of the reflectors acting as a reference and the second moving within the working volume according to a certain law, for example, it rotates in a cylindrical spiral of radius r _sp so so that the resulting interference pattern of the total reflections of the EMW covers the maximum possible aperture of the working volume. Using the relation (1), the function F (x, y, z) is calculated, restoring the distribution of secondary sources along the EMW propagation path and using known techniques, reduce their effect on the radiation field of the RIC. If necessary, the process of adjusting the amplitude and phase parameters of the irradiation field can be carried out by the method of successive approximations up to its full coincidence with the radiation field of the RIK antenna in free space.

 Thus, the proposed solution has a new property, which consists in measuring the real radiation field of the RIC and theoretical estimation in free space in the radiation field of the antenna of the complex of EGTR diagrams of the composite reference reflector and restoring the sources of interference signals, which optimizes the characteristics of the radiation field of the RIC by minimizing the contribution interfering reflections, which does not coincide with the properties of known solutions and leads to the achievement of a positive effect, which consists in correcting and the irradiation field in the working volume of the RIC and increasing the accuracy of measurements of the EPR diagrams of objects.

 To evaluate the technical result of the proposed method for correcting the parameters of the radiation field in comparison with the prototype, the following considerations can be given. In the known method, the measurement of RLH is performed using the properties of the screening plane, the limiting case of which is the mirror plane. At the same time, the interfering effect of both local objects and the numerous re-reflections of electromagnetic waves between the speakers, the control system, the location object and the track surface are not fully taken into account and controlled. That is, we can conclude that the effectiveness of the measures used in the known method for forming the irradiation field in the working volume of the RIC is limited and especially when measuring the EPR of objects of large electrical dimensions with a low level of visibility is insufficient. The proposed method is aimed at improving and monitoring the parameters of the irradiation field in the working volume of the measuring complexes. The latter is achieved by restoring all possible interfering sources of secondary radiation, and by reducing their influence on the parameters of the irradiation field in the working volume, the accuracy of measuring the EPR diagrams of real objects is improved.

The modeling performed by the authors as applied to a specific RIC (R≈800 m, z _a ≈3 m, d≈2 m) showed the possibility of reproducing the irradiation field compared to the field in free space within the width of the main antenna lobe with the decay level at the edges an amplitude of ~ 3 dB and a phase incidence of ~ π / 8 with an error of -0.2 dB in amplitude and 5 ... 6 ⁰ in phase, which ensures the accuracy of measuring the EPR diagrams of objects at least 0.5 dB at relative maximums.

и по дальности более

с интенсивностью более 0,1% от мощности первичного излучения в рабочем объеме, при отсутствии посторонних шумов и помех вполне разрешаются. Этого достаточно, для целенаправленного воздействия на источники помеховых сигналов. В известных способах измерения РЛХ и у прототипа подобная коррекция параметров облучающего объект поля отсутствует.As a measure of the effectiveness of the proposed method, we take the assessment of the location of the induced radiation sources on the measuring path. In known methods, possible sources of interference are identified intuitively, based on practical experience. In the proposed method, the location and relative intensity of the interfering signals are calculated by evaluating the function F (x, y, z) according to (1). The effectiveness of the proposed method was modeled on the example of a RIC with round aperture antennas with a diameter of d ~ 0.5 ... 2 m, placed at a height of z _a = 2. . .6 m and ranges R = 200 ... 1000 m for the absence of interfering reflections and provided that the power of the interference reflections is ~ 0.01 ... 50% of the power of the direct wave. It turned out that secondary sources induced on the propagation path, when they are spaced in the transverse direction, are more

and in range more

with an intensity of more than 0.1% of the power of the primary radiation in the working volume, in the absence of extraneous noise and interference are completely resolved. This is enough for a targeted effect on the sources of interfering signals. In the known methods of measuring radar and prototype such a correction of the parameters of the field irradiating the object is absent.

 Summarizing the arguments presented and taking into account the known limit estimates of the measurement errors of the EPR diagrams of objects [7], we can conclude that the accuracy of determining the DOR of the objects of the proposed method in comparison with the known technical solutions can be increased at the maximum of the DOR by 0.5. ..2 dB, and in relative minima up to 10 dB.

 The advantage of the proposed method for measuring radar retreatment is the simplicity of its implementation, achieved by expanding and improving the known measurement procedures that do not require additional material costs and scientific research.

Claims (1)

A method for measuring the effective scattering surface of objects, including the formation of an irradiation field in the working volume of a radar measuring complex (RIC), placing an object under study in it, measuring the dissipated power and standardizing the levels of reflected radar signals, characterized in that they additionally measure the effective I _m (s) diagram scattering surface (EPR) of two omnidirectional reference reflectors, one of which is mounted motionless, and the other is moved within the working volume of the RIC a path defined by a parameter s, produce a theoretical estimate diagram I ₀ (s) ESR of the reflector in the free space in the antenna complex radiation and evaluate the location and relative intensities of the sources of jamming signals from the values of the function F (x, y, z) , calculated according to the formula

where x, y, Z are the current coordinates of the observation point on the track;

x ₁ (s), y ₁ (s), z ₁ (s) - parametric equations of the trajectory L of the moving reflector in the working volume;
h _s are the Lame coefficients of the trajectory;
p is a real parameter lying within 3.. . 10;
k = 2π / λ, λ is the working wavelength;
i is the imaginary unit;
the time dependence for the incident and scattered electromagnetic waves is taken in the form exp (+ iωt), and the phase φ (s) in the integral determining F (x, y, z) is chosen based on the condition of coupling with the field of the transmitting antenna.

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