RU2598401C1 - Multibeam double-reflector antenna with shifted focal axis - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention is intended for use in radio devices for television, radio broadcast and radio communication through artificial Earth satellites (AES), located in geostationary orbit (GSO), in centimetre and millimetre wave ranges. Disclosed multibeam double-reflector antenna with shifted focal axis consists of a system of radiators, arranged on circular arc, main large mirror-reflector and auxiliary small mirror-convergent mirror, sections of which in plane of arc of irradiators is circles concentric to arc of radiators and having, compared thereto, larger and smaller radii, respectively, wherein each of mirrors consists of two halves symmetrical relative to plane of arc of irradiators, where in plane perpendicular to plane of symmetry of reflector, each half of which has shape of a monotonous part of a parabola with displacement of focal axis relative to plane of symmetry, each half of convergent mirror has shape of a hyperbola, convex towards reflector and positioned so that first focal points of two halves of section of hyperbola are located on arc of arrangement of radiators, and second focal points coincide with focal points of parabolas, forming half of main mirror reflector.

EFFECT: technical result consists in improvement of efficiency of antenna while reducing level of cross-polarisation and creation of a fan-shaped directional pattern.

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Description

The invention is intended for use in the composition of radio devices for television, broadcasting and radio communications through artificial Earth satellites (AES) located in the geostationary orbit (GSO) in the centimeter and millimeter wave ranges.

Known [1, 4] are multi-beam two-mirror toroidal parabolic antennas, consisting of a main reflector mirror in the form of a part of a parabolic torus, an auxiliary counterreflector mirror and a system of irradiators located on an arc of a circle. These antennas allow you to create a fan radiation pattern (LH) for simultaneous radio communication with several satellites on the GSO. The disadvantages of such an antenna include its reduced efficiency, caused by the loss of electromagnetic energy reflected by the main mirror, due to its contact with the counter-reflector, as well as the shadowing of the reflector aperture.

Known [2, 3] are two-mirror antennas with a shifted focal axis, in which the focal axis of the parabola is a generatrix of the main mirror and does not coincide with the axis of axial symmetry of the antenna. The profiles of the main and auxiliary mirrors in antennas with a shifted focal axis were obtained by rotating respectively asymmetric cutouts of the parabola and hyperbola relative to the axis of axial symmetry so that the focus of the parabola is aligned with the first focus of the hyperbola and the irradiator is located in the second focus of the hyperbola. The disadvantage of this antenna is the single-beam radiation pattern. The aim of the invention is to increase the efficiency of the antenna while reducing the level of cross-polarization and the creation of a fan radiation pattern.

For this, a multi-beam two-mirror antenna with an offset focal axis is proposed. It consists of an array of irradiators located on an arc of a circle, a main reflector mirror and an auxiliary counterreflector mirror. The cross sections of the main and auxiliary mirrors in the plane of the irradiator arc are circles concentric to the arc of the irradiator placement and having a larger and smaller radius, respectively. In addition, each of the mirrors consists of two halves symmetric with respect to the plane of the irradiator arc. In a plane perpendicular to the plane of symmetry of the reflector, each of its halves has the shape of a monotonous part of the parabola with a shift of the focal axis relative to the plane of symmetry of the reflector and counterreflector. Each half of the counterreflector in the plane perpendicular to the plane of symmetry of the reflector has the shape of a part of the hyperbola, convex towards the reflector.

The invention is illustrated by drawings, in which:

FIG. 1 is a cross-sectional view of a multi-beam two-mirror antenna with a plane displaced by the focal axis passing through the irradiator placement arc (symmetry plane);

FIG. 2 - section of a multi-beam two-mirror antenna with a plane displaced by the focal axis perpendicular to the plane of symmetry of the antenna.

A multi-beam two-mirror antenna with a shifted focal axis (Fig. 1) contains a grating of irradiators 1 located on an arc of a circle 2, a main large mirror-reflector 3 and an auxiliary small mirror-counter-reflector 10. The cross sections of the main 3 and auxiliary 10 mirrors in the plane of the arc of irradiators 2 are a circle concentric to the arc of the placement of the irradiators 2 and having a larger and smaller radius compared to it, respectively. In this case, each of the mirrors consists of two halves symmetric with respect to the plane of the arc of the placement of irradiators.

The situation is considered for the central feed of the array of feeds 1 on arc 2.

In a plane perpendicular to the plane of symmetry (Fig. 2), each half of the reflector 3 is a surface formed by the monotonous part of the parabola, the focal axis 5-5 ′ of which is offset from the plane of symmetry 6 by parallel transfer. Each half of the counterreflector 10 in the plane perpendicular to the symmetry plane of the counterreflector has the shape of a part of the hyperbola 7, convex towards the reflector 3. In this case, the first focus 8 of the hyperbola 7 is located on the arc of the irradiators 2, and the second focus 9 is on an axis equidistant from the plane of symmetry 6, similar to the axis 5-5 ′, and coincides with the focus of the parabola 3 of the part (upper in the drawing) of the cross section of the main mirror 3.

A multi-beam two-mirror antenna with a shifted focal axis operates as follows. Any of the array of irradiators 1 located on the arc 2, being connected to a generator of high-frequency electromagnetic waves (not shown in the drawings), is a source of primary electromagnetic waves. These waves are alternately reflected first from the counterreflector 4, then from the reflector 3. In the approximation of geometric optics, the rays emanating from the irradiator 1 (shown in Fig. 2 by lines with arrows), after successive reflections from the counterreflector 10 and reflector 3 due to their relative position, as well as the properties of second-order curves (hyperbola and parabola) will be parallel to each other. Moreover, the lengths of these rays from the arc of the irradiators 2 to the aperture plane of the antenna 11 will be equal. If in this case the phase center of the irradiator is located on the arc of the irradiators 2, then in the aperture of the antenna 11 there will be a common-mode distribution of the field, forming a beam with the main maximum lying in the plane of symmetry of the antenna. Due to the geometrical properties of hyperbola 7, the rays of the main lobe of the bottom beam of the irradiator of the highest intensity, after reflection from the counterreflector 10, fall on the central part of the reflector 3, the rays of lower intensity fall on the edges of the reflector 3. Since the path lengths of the rays falling into the center of the reflector 3 are less than for rays falling on its edges, the amplitude distribution of the field will form in the aperture of the antenna, which will intensively decline to the edges. Due to this, the antenna will have a lower level of the side lobes of the beam and, as a result, an increased isolation between adjacent beams.

Since the halves of the reflector 3 are shifted relative to the plane of symmetry, the field reflected from them will not fall onto the counterreflector 10. Therefore, the proposed antenna eliminates the shadowing of the field reflected from the reflector by the counterreflector, which increases the antenna efficiency.

Since the rays reflected from the symmetric halves of the counterreflector 10 are directed only towards the corresponding halves of the reflector 3, then after reflection from it, they do not fall onto the counterreflector and, moreover, into the irradiator. Therefore, in the antenna there is no reaction of the field reflected from the reflector to the irradiator.

In antennas with an asymmetric reflector, the currents induced on it have spurious field components orthogonal to the main polarization and lead to the appearance of cross-polarized radiation orthogonal to the main polarization. In the proposed antenna, the reflector 3 and the counter-reflector 10 are composed of symmetrical halves. The spurious, orthogonal to the main components of the currents induced on these halves are opposite, will compensate each other and the corresponding radiation field. As a result, a multi-beam antenna with a shifted focal axis will have a reduced level of cross-polarization.

When placing one irradiator from the array of irradiators 1 in another position on the arc 2 (Fig. 1), a beam is formed with the main lobe deflected in the plane of this arc. When several irradiators are placed on the arc 2, a fan pattern with independent partial diagrams is formed, i.e. (rays) by the number of irradiators.

Thus, the proposed multi-beam two-mirror antenna with a displaced focal axis has a fan beam with increased overall efficiency and a low level of cross-polarization.

LITERATURE

1. Somov A.M. Propagation of radio waves and antennas of satellite communication systems: Textbook for universities. - M .: Hot line - Telecom, 2015 .-- 456 p.: Ill.

2. Improvements in or relating to Microwave Aerials: Patent GB 973583: IPC H01Q 17/00; H01Q 19/10; H01Q 19/19. / I.L. Lee Application GB 19620014057 dated 04/11/1962; Publ. 10/28/1964

3. Eisenberg G.Z., Yampolsky V.G., Tereshin O.N. VHF antennas. / Ed. G.Z. Eisenberg: In the 2nd part of Part 2 - M., Communication, 1977 .-- 288 pp., Ill.

4. Frolov O.P., Wald V.P. Mirror antennas for satellite earth stations. - M .: Hot line - Telecom, 2008 .-- 496 p .: ill.

Claims (1)

A multi-beam two-mirror antenna with a displaced focal axis, consisting of a system of irradiators located on an arc of a circle, a main large reflector mirror and an auxiliary small mirror-counter-reflector, the sections of which in the plane of the irradiator arc are circles, concentric to the irradiator arc and having a larger and a smaller radius, respectively, characterized in that each of the mirrors consists of two halves symmetric with respect to the plane of the irradiator arc, and in the plane, perpendicular to the plane of symmetry of the reflector, each half of which has the shape of a monotonous part of the parabola with the focal axis shifted relative to this plane of symmetry, each half of the reflector is shaped as part of the hyperbola, convex towards the reflector and located so that the first foci of the two halves of the hyperbola section are located on the arc of the irradiators and the second tricks coincide with the foci of the parabolas, which form half of the main reflector mirror.

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