RU2598399C1 - Multibeam double-reflector antenna with shifted focal axis - Google Patents

Abstract

FIELD: antennae.

SUBSTANCE: multibeam double-reflector antenna with shifted focal axis consists of a system of radiators arranged on a circular arc, main large mirror-reflector and auxiliary small mirror-convergent mirror. Section of main and auxiliary mirrors in plane of arc irradiators represents a circle. Each of mirrors consists of two halves symmetrical relative to plane of arc of radiators. In plane perpendicular to plane of symmetry, each half of reflector has shape of parabola. Each half of convergent mirror has shape of ellipse concave towards reflector. First foci of symmetrical sections of ellipse are located on arc of arrangement of radiators, and second foci coincide with focal points of parabola, corresponding to half cross-section of main mirror.

EFFECT: technical effect consists in increased efficiency of antenna while reducing level of polarisation and maintaining fan-shaped directional pattern.

1 cl, 2 dwg

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 the shadowing of its counterreflector.

To eliminate shadowing by the counter-reflector of the field reflected from the reflector, as well as the reaction of the field reflected by the counter-reflector to the irradiator, toroidal parabolic antennas are performed, as a rule, according to an asymmetric scheme with a remote irradiator (of the "offset" type). The disadvantage of this implementation is the increased level of cross-polarization.

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 are obtained by rotating, respectively, asymmetric notches of the parabola and ellipse located on opposite sides of the focal axis of the parabola relative to the axis of axial symmetry so that the focus of the parabola is aligned with the first focus of the ellipse and the second focus of the ellipse lies on focal axis of the parabola. 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 a system 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 half of it has the form of a monotonous part of the parabola with a shift of the focal axis relative to the plane of symmetry. Each half of the counterreflector in the same plane has the shape of a part of the ellipse concave towards the reflector and located so that the first focus of the ellipse is located on the arc of the irradiator array, and the second coincides with the focus of the parabola forming the main mirror.

The invention is illustrated by drawings, in which:

- FIG. 1 is a cross section of a multi-beam two-mirror antenna with a displaced focal axis by a plane passing through the arc of irradiators;

- 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 system 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 sections of the main and auxiliary mirrors in the plane of the arc of the irradiators are circles, concentric arc irradiators and having a larger and smaller radius, respectively. In this case, each of the mirrors consists of two halves symmetric with respect to the plane of the arc of the array of irradiators.

In the plane perpendicular to the plane of symmetry (figure 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 relative to the plane of symmetry 6 by parallel transfer. Each half of the counterreflector 10 in the plane perpendicular to the plane of symmetry has the shape of a part of the ellipse 7 concave toward the reflector 3. Moreover, the first focus 8 of the ellipse 7 is located on the arc of the irradiators 2, and the second focus 9 is on the focal axis 5-5 ′ and coincides with the focus of the parabola of the corresponding part of the main mirror 3. Circle 4 represents the geometric location of the points of placement of the foci of the parabola, combined with the second foci of 9 ellipses 7. Circle 2 represents the geometric location of the points first foci 8 of ellipses 7 and irradiators 1.

A multi-beam two-mirror antenna with a shifted focal axis operates as follows. Any of the 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 10, then from the reflector 3.

In the approximation of geometric optics, the rays emanating from the irradiator (shown in Fig. 2 by lines with arrows), after successive reflections from the counterreflector 4 and reflector 3, due to their relative position, as well as the properties of the second-order curves (ellipse 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 geometric properties of the ellipse, the rays corresponding to the maximum of the main lobe of the beam of the irradiator and having the highest intensity, reflected from the central part 6 of the counterreflector 10, fall on the edge of the reflector 3. Rays that fall on the periphery of the counterreflector 10 and have a lower intensity irradiate the middle part of the reflector 3. The path length from the irradiator 1 to the edge of the reflector 3 is greater than to its middle part. Therefore, the amplitude distribution of the field along the radius of the aperture of the antenna in comparison with conventional two-mirror antennas will be more uniform, which will lead to an increase in the utilization of the area of the aperture of the antenna.

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

Since the waves reflected from the counterreflector 10 are directed only towards the corresponding halves of the reflector 3, they do not fall back into the irradiator. Therefore, in the antenna there is no reaction of the field reflected by the counterreflector 10 to the irradiator 1.

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

When moving one of the irradiator system 1 to another position along arc 2 (Fig. 1), the main lobe of the deflector deviates in the plane of this arc. If several irradiators are placed on arc 2, a fan pattern with independent partial diagrams (rays) by the number of irradiators will be formed

Thus, the proposed multi-beam two-mirror antenna with a shifted 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 mirror-reflector and an auxiliary small mirror-counterreflector, the sections of which in the plane of the arc of placement of the irradiators are circles, concentric to the location of the irradiators and having compared to a larger and smaller radius, respectively, characterized in that each of the mirrors consists of two halves symmetrical with respect to the plane of the irradiator arc d, moreover, in the plane perpendicular to the antenna symmetry plane, each half of the reflector has the shape of a monotonous part of the parabola with the focal axis offset relative to the antenna symmetry plane, each half of the reflector has the shape of a part of the ellipse concave towards the reflector and located so that the first foci of the symmetrical sections of the ellipse located on the arc of the irradiators, and the latter coincide with the foci of the parabola, corresponding to half the cross section of the main mirror.

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