RU2244939C1 - Device for measuring effective scattering cross-section of object - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: device for measuring effective scattering cross-section of radio-location objects has receiving-transmitting unit, registrar, stand mounted for rotation and provided with fixing unit which is used for mounting test object oriented in such a manner that normal to flat front of electromagnet wave radiated by receiving-transmitting unit belongs to preset plane of rotation of object. Precision inspection of measurement of angular diagram of effective scattering cross-section of objects provided due to the fact that radio-transparent envelope is rigidly fixed on the surface of object in parallel with preset plane of rotation of object. Radio-transparent envelope is made in form of thin straight cylinder of preset size. Cavity of envelope is partially filled with e4lectrically conducting liquid. Measured maximal level of effective scattering cross-section of main lobe of radio-transparent cylinder allows to find angle of inclination of plane of rotation of object.

EFFECT: improved precision of inspection.

7 dwg

Description

The invention relates to radio engineering and can be used to measure the effective scattering area (EPR) of various objects of radar.

A known method of measuring the EPR using a pulse location, including placing the investigated object in a field emitted by a pulse locator, measuring the dissipated power and comparing it with the power dissipated by the reference reflector / 1 /. The closest technical solution to the present invention is a device that implements this method / 2 / and containing (Fig. 1) a transceiver unit 1, a recorder 2, a rotary stand 3 with a mount, which serves to install the measurement object 4, oriented so that the plane of rotation object 5, normal to the flat front of the emitted transceiver waves lie in the same plane. A significant disadvantage of this device is the uncontrolled accuracy of measuring the angular EPR diagram of the object due to the possible inclination of the plane of rotation of the object.

Let us explain this statement. With the circular rotation of the object during the measurement of the EPR angular diagram, it is possible to tilt the plane of rotation 5 (Fig. 1) relative to the horizon by an angle α caused by a number of factors, for example, such as:

wrong choice of the attachment point of the vertical cord with a horizontal support / 3 /;

the center of mass of the object displaced relative to the axis of rotation;

uneven tension of the cords of the mount, connecting the object with a rotary stand.

Such factors do not allow the correct measurement of the EPR of objects in the horizontal plane of rotation, and also make it impossible to control the angle of inclination specially set for the object within fractions and units of degrees. Most susceptible to this are objects having dimensions much greater than the wavelength of the measuring installation. For such objects, a strongly rugged EPR diagram with a width of petals not exceeding a fraction of degrees / 4 / is characteristic. Figure 2 shows the EPR diagrams of a metal rectangular plate with dimensions 5λx80 ° in the sector of location angles 0 ± 15 ° relative to the normal to its surface:

c - the plate rotated in a horizontal plane around a small axis, the angle of inclination α≅0 °;

d - the plate rotated in a plane with an inclination angle α of up to 1 °. An analysis of the given EPR diagrams shows that the inclination of the plane of rotation of the object even within one degree leads to a decrease in the maximum EPR value of the main lobe of the plate (f) to 10 dB or more. Such uncontrolled errors are especially unacceptable during the calibration and adjustment of the measuring installation, when long metal cylinders and plates can be used as reference reflectors. Thus, the urgent task is to accurately control the angular position of the plane of rotation of the object when measuring its EPR diagram.

The purpose of the invention is the control of the accuracy of measuring the angular diagram of the EPR of the object.

This goal is achieved by the fact that in the device for measuring the EPR of radar objects, which contains a transceiver unit, a recorder, a rotary stand with a mounting unit that serves to install the measurement object, oriented so that the normal to the plane front of the electromagnetic wave emitted by the transceiver lies in the plane of rotation of the object, on the surface of an object parallel to a given plane of its rotation, a radiolucent shell (RPO) in the form of a long thin straight circular cylinder (RPO-qi) is rigidly fixed Indra) (6, 1), a cavity which is partially filled with electrically conducting liquid. In this case, the dimensions of the cavity of the RPO cylinder and the level of the electrically conductive liquid are selected from the relations (Fig. 3)

b / a≥100; h≤0,2a; a≤0,5λ,

where b is the length of the generatrix of the cylinder,

a is the diameter of the base of the cylinder,

h - level evenly distributed along the entire length of the cylinder of the conductive fluid,

λ is the wavelength of the measurement setup.

(фиг.4) пропорционально углу наклона РПО-цилиндра α_i. Таким образом, каждому конкретному углу наклона (α_i) РПО-цилиндр с электропроводной жидкостью как радиолокационный отражатель будет подобен “проводящим проводам” разной длины

со средним диаметром q_i. При этом длина этих “проводов” равна многим длинам волн, а диаметр составляет лишь долю длины волны /5/. В данном случае точность контроля за наклоном плоскости вращения определяется по измеренному уровню максимального значения ЭПР главного лепестка m (σ_m) электропроводной жидкости (“провода”) при облучении ее по нормали, когда θ=0°, где θ - угол локации (фиг.5). Измеренное значение ЭПР характеризует угол наклона РПО-цилиндра и, соответственно, наклон плоскости вращения объекта.The device operates as follows. During the measurement of the EPR diagram, the possible tilt of the object with the RPO cylinder 6 fixed on it leads to the flow of the electrically conductive fluid k towards the tilt with a corresponding decrease in the length of the extended fluid volume

(figure 4) is proportional to the angle of inclination of the RPO cylinder α _i . Thus, for each specific tilt angle (α _i ), the RPO cylinder with the electrically conductive liquid as a radar reflector will be similar to “conductive wires” of different lengths

with an average diameter q _i . Moreover, the length of these “wires” is equal to many wavelengths, and the diameter is only a fraction of the wavelength / 5 /. In this case, the accuracy of monitoring the inclination of the plane of rotation is determined by the measured level of the maximum EPR value of the main lobe m (σ _m ) of the electrically conductive liquid (“wire”) when it is irradiated normally, when θ = 0 °, where θ is the location angle (Fig. 5). The measured value of the EPR characterizes the angle of inclination of the RPO cylinder and, accordingly, the inclination of the plane of rotation of the object.

A relatively simple calculation formula for determining the EPR level of the main lobe of an electrically conductive liquid (“wire”) for the case θ = 0 °, which gives good agreement with the experiment, is the modified formula Chu / 5 /

- длина протяженного объема (длина “провода”) электропроводной жидкости при заданном угле наклона α_i;Where

- the length of the extended volume (length of the “wire”) of the electrically conductive fluid at a given angle of inclination α _i ;

q _i is the average width of the volume (diameter of the “wire”) of the conductive fluid (figure 4);

i = 1, 2, 3, ...;

γ = 1.78 ..., n = 3.1415926 ...;

λ is the wavelength of the measuring setup, provided that the direction of polarization coincides with the generatrix of the RPO cylinder.

Over a wide range of changes in the EPR values, the value of σ _m weakly depends on q / λ; therefore, we have

then it follows from (1) that

It is not difficult to establish the relationship between the maximum EPR value of the main lobe (σ _m ) of the electrically conductive fluid (“wires”) and the inclination of the RPO cylinder α (Fig. 5), representing the volume of the electrically conductive fluid in the projection A (when the RPO cylinder is tilted) in the form of a right triangle shaded in FIG. 4. The triangle in the projection is obtained after tilting at a certain angle α ', which determines the angular sensitivity of the device, when tilted at which the projection from the quadrangular is converted into the shape of a rectangular triangle. Moreover, the value of the “angle of sensitivity” can be selected based on the ratio

α ’= arctan (2h / b).

The decrease in the large leg of the triangle 1 _i with an increase in the angle α _i at a constant volume of the electrically conductive fluid is associated with the value of σ _m and, according to relation (2), it is possible to construct the dependence shown in Fig.6. An analysis of this dependence allows us to conclude that the use of a RPO cylinder in practice will make it possible to control the angle of inclination of the object's rotation plane with high accuracy (up to tenths of a degree), thereby eliminating possible errors in measuring the angular EPR diagram. Thus, the RPO cylinder rigidly fixed on the object when measuring its EPR diagram will allow determining the angle of inclination of the object’s rotation plane by the maximum EPR value of the main lobe and, if necessary, adjusting its angular position by any available means.

In practice, the RPO cylinder can be attached to the measurement object in such a way as to guarantee the observation of its main lobe against the background of the EPR diagram of the object itself. In the case when it is necessary to exclude the possible influence of reflections of the RPO cylinder on the EPR diagram of the object, after checking the accuracy of the installation of the plane of rotation of the measurement object, the RPO cylinder is dismantled, and the measurement of the EPR diagram of the object can be continued without it.

This device has been tested in the conditions of the Reference radar measuring complex / 6 /. As a measurement object, a reference reflector was used to calibrate measuring installations in the form of a metal cylinder with a length of 125 λ and a base diameter of 37.5 λ. The RPO cylinder was deployed relative to the generatrix of the reference reflector by 30 ° and was rigidly fixed at the point through which the axis of rotation of the measurement object passes , while it had dimensions respectively b = 188λ, a = 0.5λ, and the level (h) uniformly distributed along the entire length of the cylinder of the electrically conductive liquid corresponded to 0.1λ.

The tests were carried out as follows. Two EPR diagrams of an object with a RPO cylinder were successively measured. In both cases, the object rotated uniformly in a plane that coincided with the normal to the plane front emitted by the electromagnetic wave transceiver (λ = 0.8 cm). The reflected signal in the form of an EPR diagram was recorded by the analyzer. In the first measurement, the plane of rotation of the object was set, if possible, parallel to the horizon, in the second, the plane was given a certain angle of inclination. On figr presents an EPR diagram of the first measurement, on figr - the second. An analysis of the EPR diagrams thus measured allows one to draw the following conclusions: the maximum EPR level of the main lobe of the RPO cylinder (m) in the first measurement allows, according to the dependence (Fig. 6), to determine that the angle of inclination of the plane of rotation lies in the range 0 ... 0.05 degrees (0.05 ° corresponds to the "angle of sensitivity"). In the second measurement, the angle of inclination according to the same dependence corresponds to 0.75 °. Thus, it provides control over the measurement of the angular diagram of the EPR of the object with an accuracy of tenths or hundredths of a degree.

The advantage of the proposed device is the simplicity of its implementation by a slight upgrade of the known device.

Sources of information

1. Mayzels E.N., Torgovanov V.A. Measuring the dispersion characteristics of radar targets.

2. A device for measuring the effective scattering area of objects according to A.S. USSR No. 491111, IPC G 01 R 29/10, 1975 (prototype).

3. Blacksmith, Hyatt, Mac. An introduction to radar target cross-section measurement methods. TIIER, 1965, t. 53, No. 8, p. 1044.

4. Kobak V.O. Radar reflectors. M .: Sov. Radio, 1975, p. 214-217.

5. Crispin, Muffett. Evaluation of the radar cross section of bodies of simple shape. TIIER, 1965, vol. 53, No. 8, pp. 969-970.

6. Sumin A.S. and others. Control for “invisible”. AVIA panorama. No. 6, 1997. P.30.

Claims (1)

A device for measuring the effective scattering area of objects, containing a transceiver unit, a recorder, a rotary stand with a mount, used to install the measurement object, oriented so that the normal to the flat front of the electromagnetic wave emitted by the transceiver lies in a given plane of rotation of the object, characterized in that the surface of an object parallel to a given plane of its rotation, a radiolucent shell in the form of a straight circular cylinder, the cavity of which is partially filled with conductive fluid, while the dimensions of the cylinder and the level of conductive fluid in its cavity are selected from the ratio b / a≥100; h≤0,2a; a≤0.5λ, where b is the length of the generatrix of the cylinder;  a is the diameter of the base of the cylinder;  h is the level of the electrically conductive liquid evenly distributed along the entire length of the cylinder;  λ is the wavelength of the measurement setup.

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