RU2408895C2 - Method of localisation of electromagnetic radiation sources of decametre range - Google Patents

Abstract

FIELD: instrument making.

SUBSTANCE: for determining the bearing and angle of radiation source location there used is dependence of mutual correlation of characteristic components of the field, which are determined by means of polarisation discrimination because magnetoionic splitting attributes to the field unique polarisation properties the correlation analysis of which allows improving localisation accuracy of electromagnetic radiation sources of decametre range.

EFFECT: improving localisation accuracy in conditions when the source field is a part of integral natural noise.

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Description

The invention relates to the field of radio engineering and can be used to determine the location of sources of electromagnetic radiation (EMP) decameter range.

Existing methods for localizing electromagnetic radiation sources use, as a rule, an estimate of the amplitude, phase or amplitude-phase characteristics of signals coming from antenna arrays. Improving communication systems using broadband signals of low spectral density, identifying new sources of electromagnetic radiation, such as artificial radio emission of the ionosphere (IRI), makes it necessary to detect and localize sources at a level comparable to natural noise. The fading inherent in the ionospheric channel leads to the need to increase the signal-to-noise ratio to increase the accuracy of localization of the EMR source, which cannot be ensured in the cases listed above.

The presence of the Earth's magnetic field leads to the fact that when an arbitrary polarization wave is incident on the ionosphere at the exit from the ionosphere, we obtain magnetoionic components, in the general case, of elliptical polarization. It is theoretically shown that characteristic waves (CV) have significantly different polarization, called the limiting polarization and defined as [1]

where P _{o, x} is the limiting polarization of the O-ordinary and X-unusual XB,

- гиромагнитная частота, e, m - заряд и масса электрона, с - скорость света, Н₀ - модуль вектора напряженности магнитного поля Земли в ионосфере, ω - циклическая рабочая частота,

, ν - частота соударений между электронами и другими частицами, γ - угол между вектором магнитного поля Земли и волновым вектором.

is the gyromagnetic frequency, e, m is the charge and mass of the electron, s is the speed of light, H ₀ is the magnitude of the Earth’s magnetic field in the ionosphere, ω is the cyclic operating frequency,

, ν is the frequency of collisions between electrons and other particles, γ is the angle between the Earth’s magnetic field vector and the wave vector.

The prototype method is the "Method of localization of radio transmitters" [2]. In this method, in order to increase the accuracy of localization of radio transmitters, the angles of arrival of the ordinary and extraordinary components are simultaneously evaluated. In this case, the polarization characteristics, right-handed and left-handed, are used as a parameter by which the separation into ordinary and extraordinary waves occurs, but localization, as before, is based on an estimate of the amplitude-phase characteristics of the signals coming from the antennas.

The polarization characteristics of the signal themselves are sources of information about how the wave came to the receiving point and in which medium the propagation occurs. It was shown [3] that in the case when the signal is small in magnitude and a partially polarized noise is present, its detection and discrimination is possible by polarization processing. The studies performed by the author [4] showed the presence of elliptical polarization in natural decameter noise, which were previously considered linearly polarized. Therefore, the method shown in [3] can also be applied in the decameter wavelength range.

The technical result of the invention is to improve the accuracy of single-position location of sources of electromagnetic radiation of low spectral density based on the assessment of the mutual correlation of the magnetoionic field components created by these sources along with polarization compensation of natural noise.

This goal is achieved by the fact that the proposed method for determining the location of the source uses polarization signal processing, which consists in isolating a field component with a different antenna device with a different direction of rotation of the electric field vector and their subsequent correlation processing in digital form in a computer.

For elliptical polarization antennas, the wave reception coefficient can be determined by the formula [3]:

where P _{n is the} polarization coefficient of the incident wave;

P _a is the polarization coefficient of the receiving antenna;

the + sign refers to a wave that coincides in polarization with the receiving antenna; - when the direction of rotation of the vectors of the electric field does not match. Thus, the correlation coefficient between two field components with different directions of rotation of the polarization vector depends on the polarization coefficients of the field P _n and the receiving antenna P _a . It was shown above that the ordinary and extraordinary waves have the opposite direction of rotation of the vector, therefore, the degree of selectivity can be defined as:

In the case where P _x = P _a = 1, the correlation coefficient between the envelopes of the magnetoionic components is 0. The correlation coefficient will be 1 (-1) only in the case of linear polarization of the characteristic waves and the receiving antenna.

The author used turnstile antennas as rotating polarization antennas. They are two mutually orthogonal vibrators powered with a 90 ° phase shift. Depending on the connection point of the supply feeder from one antenna, we get two directions of rotation: right and left. We place two such antennas in two mutually orthogonal planes, as shown in figure 1.

In this case, for a wave of arbitrary polarization and an antenna of elliptical polarization, the direction of arrival of the wave in the horizontal plane is determined based on the following algorithm:

- we find the maximum value of the correlation coefficient, let it be R ₁ . Since R ₁ is estimated from the signals received from the north-facing polarization antenna and the eastern-direction polarization antenna, it can be the maximum of the estimated only in the case of the arrival of the wave from the southeast. This follows from an analysis of the behavior of the correlation coefficient upon incidence, for example, of a left-handed polarization wave from different directions;

- based on a comparison of the correlation coefficients R ₂ and R _{4, we} determine the deviation of the direction of arrival of the wave from the bisector of the south-east quadrant. If R ₂ = R ₄ , the wave came from the direction lying in the middle between south and east. Otherwise, the deviation from the bisector is proportional to the difference of the correlation coefficients and can be defined as

- since we determined the direction of arrival from the southeast, the bisector of this quadrant will correspond to an angle of 135 ° and the angle of arrival of the wave can be defined as

the sign in front of Δ is determined by the ratio of R ₂ and R ₄ .

Possible correlations of the measured correlation coefficients are summarized in the table shown in figure 1, and allow you to determine the direction of arrival of the wave from any direction in the horizontal plane.

Similarly, the angle of arrival of the wave in the vertical plane is determined, but the degree of correlation of the signals from the other outputs of the antennas is estimated, as shown in figure 2.

To implement the antenna device of the proposed method, the author used a non-standard solution, which consists in using a reinforced concrete administrative building as an element of the antenna structure (Fig. 3). The manufacture of an antenna device based on symmetrical vibrators, the right side of figure 2, makes it necessary to place them at a height of 15 meters on a free-standing mast. Such a design will be difficult to implement and expensive. It is known [4] that for the decameter wavelength range, the underlying surface is semi-conductive and using this property it is possible to obtain elliptical polarization based on a single vibrator located in a special way above this surface. But at the same time, the elliptical polarization is obtained in a narrow solid angle and its parameters are not constant. If you place two mutually orthogonal asymmetric vibrators above the conductive surface with which they form an angle of 45 °, then they and their mirror image will create a turnstile antenna. The roof of any reinforced concrete building can serve as such a conductive surface, since the size of metal cells is much smaller than the wavelength and for this wavelength range it will be equivalent to a solid one. By selecting the size and height of the building, you can get the necessary polarization characteristics. A schematically similar antenna device is shown on the left side of FIG. It consists of four antenna antennas APS-6-3, mounted on a special support structure and located in the middle of a three-story office building.

To implement the proposed method, the author used a hardware complex containing (figure 4):

- an antenna device including two mutually orthogonal turnstile antennas with an orientation of north-south and east-west - 1;

- a recording device, including:

- switching device, consisting of splitters - 2 and switches - 3,

- radio receivers - 4;

- a control and calibration device, including a two-beam oscilloscope - 5 and measuring instruments - 7;

- computer - 6.

The device switching signals through the use of splitters 2 provides a constant level of signals received at the inputs of radio receivers with various combinations of antenna outputs. The control and calibration device allows you to maintain the same signal level from radio receivers, since the automatic gain control of the RPU is disabled during measurements. The signal level from the RPU is set based on the dynamic range of the computer's sound card. These special measures have been taken to eliminate the influence of complex devices on the degree of correlation of signals from antennas.

The signals from the antennas 1 pass through the splitters 2 and are switched by switches 3 to the radio receivers 4, the low-frequency outputs of which are connected to the computer 6. By appropriate selection of the position of the switches, low-frequency signals of all possible combinations of polarizations are shown in the tables in Fig. 1 and figure 2, with their subsequent translation into digital form. Then, the obtained information is translated into a text format, on the basis of which the correlation coefficients are calculated. The direction of arrival in both planes is determined by the previously described algorithm.

The localization of the electromagnetic radiation source is determined by the bearing in the horizontal plane and the distance, determined by the angle of elevation in the vertical plane based on the calculation, using ionograms of a vertical sounding station or ionosphere model, for example, IRI (International Reference Ionosphere). In conditions when the level of the source of electromagnetic radiation is comparable with natural noise, it is necessary to take into account their influence on the accuracy of localization. For this purpose, at the time of absence of radiation, a control measurement of the direction of arrival of natural noise is made, and on this basis, an adjustment is made to the calculated azimuth and elevation angle.

When localizing artificial ionospheric radiation, it is necessary to take into account the fact that the source is at an altitude of 80 to 300 kilometers and the standard approach is not applicable here. When modifying the ionosphere to increase the impact efficiency, as a rule, harmonics of the gyromagnetic frequency are used as the pump wave. It is known that the gyromagnetic frequency is a function of two arguments: altitude and geomagnetic latitude [5]:

where f ₁ ≈ 0.8 MHz;

r _o is the radius of the Earth;

r is the distance from the center of the earth to the point in question;

φ is the geomagnetic latitude of this point.

The author has shown [6] that, based on the characteristics of the IRI, it is possible to determine the height of the impact, and the combination of height - gyromagnetic frequency - geomagnetic latitude determines the geomagnetic parallel along which a similar effect is possible. The intersection of the bearing and the geomagnetic parallel determines the location of the source of artificial ionospheric radiation.

The method was tested in the direction of Sovetskaya Gavan - Petropavlovsk-Kamchatsky (an ionospheric-wave service transmitter was used) and at broadcasting stations of various locations, as well as for localizing IRI [6].

Information sources

1. C. Davis. Radio waves in the ionosphere. - World, 1973. - 504 p.

2. "The method of localization of radio transmitters." RU 2154836 C2, 08.20.2000 (prototype).

3. Pozdnyak S.I., Melititsky V.A. Introduction to the statistical theory of polarization of radio waves. - Soviet Radio, 1974.- 478 p.

4. Sivokon V.P. Short wave polarization in the ionosphere communication channel. // Telecommunications. - 2007 - No. 7. - S. 55-58.

5. Gershman B.N. and others. Wave phenomena in the ionosphere and space plasma. - Science, 1984. - 391 p.

6. Sivokon V.P. HF noise variations as a result of ionosphere modification. // Telecommunications. - 2009 - No. 1. - S. 52-56.

Claims (1)

A method for localizing decameter range electromagnetic radiation sources, using the magnetoionic splitting effect in the ionosphere, characterized in that the location of the decameter range electromagnetic radiation source emitter is determined based on polarization selection of the magnetoionic field components and estimating their mutual correlation by the ratio of measured correlation coefficients of received signals for all possible combinations of polarizations of these signals with the possibility ensuring the determination of the direction of their arrival from any direction in the horizontal and vertical planes.

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