RU2795755C1 - Method for reducing the noise temperature of multibeam two-mirror antennas with a shifted focal axis - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention relates to radio engineering and serves to reduce the noise temperature of multibeam two-mirror antennas with an offset focal axis. The effect is achieved by the proposed method for reducing the noise temperature of multibeam two-mirror antennas with a displaced focal axis, which consists in installing on the specified antenna, the reflector of which consists of two separate halves, symmetrical to each other with respect to the plane of the feed arc and formed by rotation around the common axis of the corresponding monotonous parts of the parabolas with a shift of the focal axes, a conducting screen in the form of a cutout from a circular cylinder, characterized in that the axis of symmetry of the cylinder coincides with the axis of rotation of the halves of the reflector, the radius of the cylinder is equal to the radius of the inner edges of the halves of the reflector, the angular opening of the cutout in the plane of the arc of the irradiators coincides with the angular opening of the halves of the reflector in the same plane, the notch height is equal to the distance between the inner edges of the reflector halves, and the screen itself is installed in the gap between the reflector halves so that the edges of the screen are aligned with the inner edges of the reflector halves.

EFFECT: increasing the noise quality factor of the receiving system of the satellite earth station by reducing the noise temperature of the receiving antenna.

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Description

The field of technology to which the invention belongs

Currently, satellite communication systems are widely used, especially those using artificial Earth satellites (AES) located in geostationary orbit. Such communication systems are characterized by high (197-215 dB or more) attenuation of the radio wave on the IS3-Earth path [1], in which the waves coming from the satellite to the receiving point slightly exceed natural noise in amplitude.

The potential reception quality is determined by the ratio of the signal power to the noise power at the output of the receiving system, which is directly proportional to the noise quality factor - expressed in decibels, the ratio of the antenna gain to the noise temperature of the receiving system [1].

The present invention relates to the field of radio engineering and is intended to reduce the noise temperature of multibeam two-mirror antennas with a displaced focal axis used as part of earth stations of satellite communication systems with microwave-EHF repeaters located in geostationary orbit.

State of the art

Known multibeam two-mirror antennas with a displaced focal axis [2, 3], which consist of a system of irradiators located on a circular arc, the main (large) mirror (reflector) and the auxiliary (small) mirror (counter-reflector).

The sections of the main and auxiliary mirrors in the plane of the feed arc are circles concentric to the feed arc and having a larger and smaller radius, respectively, in comparison with it. In this case, each of the mirrors consists of two halves, symmetrical with respect to the plane of the feed arc. In a plane perpendicular to the plane of symmetry, each half of the reflector has the shape of a monotonous part of a parabola with the focal axis shifted relative to the plane of symmetry. Each half of the counterreflector in the same plane has the shape of a part of an ellipse or a hyperbola, located so that the first focus is on the feed arc, and the second coincides with the focus of the parabola of the corresponding part of the main mirror.

The disadvantage of multibeam two-mirror antennas with a displaced focal axis is the presence of a diffraction field formed at the inner edges of the reflector halves and the counterreflector break. This field is concentrated in the area (gap) between the halves of the reflector and when the antenna is located above the earth's surface in the receive mode (due to the reciprocity principle) it is a source of additional thermal noise entering the antenna output. As a result, the noise temperature of the antenna increases by 20÷30°K, resulting in a corresponding decrease in the noise quality factor.

There are known ways to reduce the noise temperature of mirror antennas [4-8], which consists in installing conductive screens (blends). These screens are installed on the outer edges of the reflector, counter-reflector or irradiator and do not eliminate the existing disadvantage of multibeam two-mirror antennas with a displaced focal axis.

Disclosure of the essence of the invention

The technical result of the invention is to increase the noise quality factor of the receiving system of the satellite earth station by reducing the noise temperature of the receiving antenna. To do this, a method is proposed to reduce the noise temperature of multibeam two-mirror antennas with a displaced focal axis, which consists in installing on the specified antenna, the reflector of which consists of two separate halves symmetrical to each other with respect to the plane of the feed arc and formed by rotation around a common axis of the corresponding monotonous parts of parabolas with a shift in the focal axes, a conducting screen in the form of a cutout from a circular cylinder. In this case, the axis of symmetry of the cylinder coincides with the axis of rotation of the halves of the reflector, the radius of the cylinder is equal to the radius of the inner edges of the halves of the reflector, the angular opening of the notch in the plane of the arc of the irradiators coincides with the angular opening of the halves of the reflector in the same plane, the height of the notch is equal to the distance between the inner edges of the halves of the reflector, and the screen itself is installed in the area (gap) between the halves of the reflector so that the edges of the screen are aligned with the inner edges of the halves of the reflector.

Brief description of the drawings

The invention is illustrated by drawings, in which:

- fig. 1 - multibeam two-mirror antenna with a displaced focal axis and an additional screen (section by a plane passing through the arc of the irradiators);

- fig. 2 - multibeam two-mirror antenna with a displaced focal axis and an additional screen (section by a plane perpendicular to the plane of the feed arc).

The drawings indicate:

1 - reflector;

2, 2' - upper and lower halves of the reflector, respectively;

3 - counter-reflector;

4 - arc of irradiators;

5 - plane of the irradiator arc;

6 - irradiator;

7 - axis of rotation;

8, 8' - focal axis of the parabola forming half of the reflector 2;

9 - additional cylindrical screen.

Implementation of the invention

When connected to the irradiator 6 and similar high-frequency oscillation generator, the specified irradiator emits a spherical wave towards the counter-reflector 3, a spherical wave, which, reflected from the counter-reflector, is directed towards the upper 2 and lower 2' halves of the reflector 1, symmetrical to each other relative to the plane of the arc of the irradiators 5 and formed by rotation around a common axis 7 of the corresponding monotone parts of the parabolas with a shift of the focal axes 8-8'. After reflection from the counter-reflector 3 and further from the reflector 1, the initial spherical wave front is transformed into a flat one, forming a highly directed radiation of the antenna with a maximum lying in the plane of the irradiator arc 5.

At the same time, at the edges of the reflector and counter-reflector, as well as at the break in the middle of the counter-reflector, so-called edge currents [9] are formed, the amplitude of which depends on the level of irradiation of the indicated edges and the break, as well as on the break angle. Edge currents, in turn, form diffraction radiation, the maxima of which are oriented symmetrically with respect to the plane tangent to the edge of the reflector (counter-reflector), at some angle to it. The diffraction radiation of the inner (closest to each other) edges of the upper 2 and lower 2' halves of the reflector 1, as well as the break of the counter-reflector 3, is directed mainly into the free gap between the halves of the reflector 2 and 2'.

To provide radio communication through satellites, multibeam reflector antennas are inclined relative to the earth's surface so that the maxima of the radiation patterns of the feeds located on the arc 4 are directed towards the corresponding satellites. In this case, the gap between the halves of the reflector 2 and 2' and the diffraction radiation arising in it turns out to be directed towards the earth's surface. By virtue of the reciprocity principle, due to the specified diffraction radiation, the noise of the earth's surface enters the feed 6 and the like, the magnitude of which significantly exceeds the noise of the atmosphere that enters the feed through the main lobe of the antenna pattern [10]. Due to this, the noise temperature of the antenna increases and, accordingly, the noise quality factor decreases.

When installed in the gap between the halves of the reflector 2 and 2' of the conductive screen 9 in the form of a cutout from a circular cylinder, the symmetry axis of which coincides with the axis of rotation of the halves of the reflector 7, the radius is equal to the radius of the inner edges of the halves 2, 2' of the reflector 1, the angular opening of the cutout in the plane the arc of the irradiators 5 coincides with the angular opening of the halves of the reflector 2, 2' in the same plane, and the height of the notch is equal to the distance between the inner edges of the halves of the reflector 2, 2', and the alignment of the edges of the screen 9 with the inner edges of the halves of the reflector 2, 2' at the junction screen 9 and halves of the reflector 2, 2' instead of the edge (rib) forms a continuous reflective surface with a break angle close to 180°. As is known [9], at such a break angle, the edge currents and the corresponding diffraction radiation will be minimal. In addition, the specified radiation will be directed towards the counter-reflector 3, that is, towards the atmosphere. The diffraction radiation of the break of the counter-reflector 3 itself, when the screen 9 is installed, will be reflected from the specified screen also towards the atmosphere. Thus, the additional screen 9 will partially eliminate diffraction radiation and redirect it towards the atmosphere, which creates less noise than the earth's surface. With this in mind, a decrease in the noise temperature of the antenna and, consequently, the entire receiving system, as well as an increase in its noise quality factor, will be achieved.

Table 1 shows the results of calculating the characteristics of a variant of a multibeam two-mirror antenna with a displaced focal axis and a hyperbolic generatrix of the counterreflector with and without an additional screen. At the same time, all the geometric parameters of the antenna, as well as the parameters of its location relative to the earth's surface, as well as the parameters of the earth's surface and atmosphere, remained unchanged. The height of the counter-reflector was 2.5 meters, the elevation angle of the main lobe of the radiation pattern was 9.6 degrees. The calculation was carried out for the Ku range by the method of physical optics, refined by the method of edge waves.

As can be seen from the presented data, the installation of a cylindrical screen 9 allows you to achieve the claimed technical result.

LITERATURE

1. Energy characteristics of space radio links. / Ed. O.A. Zenkevich. - M.: Sov. radio, 1972. - 436 p.

2. Multibeam two-mirror antenna with an offset focal axis: Patent RU 2598399: IPC H01Q 19/19. / R.V. Kabetov, A.M. Somov; Application 2015115130/28 dated 04/22/2015; Published 09/27/2016.

3. Multibeam two-mirror antenna with a shifted focal axis: Patent RU 2598401: IPC H01Q5/00. / R.V. Kabetov, A.M. Somov; Application 2015115131/28 dated 04/22/2015; Published 09/27/2016.

4. Aizenberg G.Z., Yampolsky V.G., Tereshin O.N. VHF antennas. / Ed. G.Z. Aizenberg: In 2 hours. Part 1. - M., Svyaz, 1977. - 384 p.: ill.

5. AC SU 1022247 A1: IPC H01Q 19/18. /B.M. Avdeenko, I.F. Oleksenko, B.B. Sakhoshko, N.P. Tokovenko, Yu.A. Erukhimovich, V.G. Yampolsky; Published 06/07/1983.

6. Axisymmetric reflector antenna: Patent RU 2420840: IPC H01Q15/14. / A.M. Somov, P.A. Titovets; Application 2009118272/07 dated May 15, 2009; Published 06/10/2011.

7. Axisymmetric two-mirror antenna: Patent RU 2420841: IPC H01Q19/18. / A.M. Somov, P.A. Titovets; Application 2010111549/07 dated 03/26/2010; Published 06/10/2011.

8. Axisymmetric reflector antenna (options): Patent RU 2426203: IPC H01Q 19/00. / A.M. Somov, P.A. Titovets; Application 2010108978/07 dated 03/12/2010; Published 08/10/2011.

9. Ufimtsev P.Ya. Theory of diffraction edge waves in electrodynamics. Introduction to the physical theory of diffraction. / Per. from English. - 2nd ed., corrected. and additional - M.: BINOM. Knowledge Laboratory, 2012. - 372 p., ill.

10. Somov A.M. Fragmentation method for calculating the noise temperature of antennas. - M.: Hotline-Telecom, 2008. - 208 p.: ill.

Claims (1)

A method for reducing the noise temperature of multibeam two-mirror antennas with a displaced focal axis, which consists in installing on a multibeam two-mirror antenna with a displaced focal axis, the reflector of which consists of two separate halves symmetrical to each other with respect to the plane of the feed arc and formed by rotation around a common axis of the corresponding monotonous parts of parabolas with displacement of the focal axes of the conducting screen in the form of a cutout from a circular cylinder, characterized in that the axis of symmetry of the cylinder coincides with the axis of rotation of the halves of the reflector, the radius of the cylinder is equal to the radius of the inner edges of the halves of the reflector, the angular opening of the cutout in the plane of the arc of the irradiators coincides with the angular opening of the halves of the reflector in the same plane, the height of the notch is equal to the distance between the inner edges of the halves of the reflector, and the screen itself is installed in the gap between the halves of the reflector so that the edges of the screen are aligned with the inner edges of the halves of the reflector.

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