WO2002005385A1

WO2002005385A1 - Reflector antenna

Info

Publication number: WO2002005385A1
Application number: PCT/RU2001/000275
Authority: WO
Inventors: Vadim Anatolyevich Kaloshin
Original assignee: Wavefrontier Co., Ltd
Priority date: 2000-07-10
Filing date: 2001-07-09
Publication date: 2002-01-17
Also published as: AU2001280322A1

Abstract

The invention relates to radio engineering, in particular, to reflector antennas and can be used in systems of communication and satellite television. The tehnical result of the invention is broadening the angle of view. The polyfocal reflector antenna comprises the concave man reflector 10 shaped as a part of a toroidal revolution surface, the feeding device 30 and at least one subreflector 20 shaped as a part of curved surface. The main reflector 10 and the feeding device 30 are located one side from the subreflector 20. The shape of the curved surface of at least one said subreflector are determined from the equation: f (z) = Pm (x, y), Pm (x), y) being a two-dimensional polynomial of the power m: f (z) = Pm (x, O) is the equation of the generatrix of the subreflector, x, y, z - Cartesian coordinates.

Description

REFLECTOR ANTENNA

FIELD OF THE INVENTION

The invention relates to radio engineering, in particular, to reflector antennas and can be used in systems of communication and satellite television.

BACKGROUND OF THE INVENTION

It is widely known that employing multi-mirror antennas, in particular, double reflector multi-beam and scanning ones, enables to provide higher performance than that for single-beam antennas. For scanning or forming multi-beam pattern in a single plane, toroidal-reflector antennas are used. Tore is a body of rotating curved around axis, which does not comply with the axis of symmetry this curved. For example, the multi-beam antenna is known in which phase aberrations of the main toroidal reflector for each beam are compensated for with the aid of a subreflector (see, for example, US patent No 3922682, 25.11.1975; JP patent specification No 57-178402, H01Q 19/19, 02.11.1982.). Subreflectors have the same shape and are located, same as feed elements, symmetrically with respect to the axis of the main reflector. This antenna has two drawbacks. First, it is the low value of the efficiency due to each feed element irradiating a part of the main reflector only. The second drawback is the impossibility to implement two adjacently located beams due to overlaying of subreflectors. The latter drawback has been overcome in the double-reflector antenna comprising two confocal toroidal reflectors (US patent No 3828352, 06.08.1974; JP patent specification No 5-3762, H01Q 19/19, 16.03.1985). Feed elements of this antenna are also located symmetrically with respect to the common axis of toroidal reflectors, their axes being directed towards the axis of toroidal reflectors and each of them irradiating a part of the main reflector only. Due to this and to incomplete compensation of phase aberrations, such an antenna does not provide for efficiency high enough. A multi-beam antenna is known in which shapes of the main and the subreflectors are synthesized basing on condition of minimum phase aberrations for the given number of beams (US patent No 4603334, 29.07.1986). The drawback of this antenna is complexity of the main reflector shape (possessing variable curvature in two planes). A double-reflector bifocal antenna is known with the main reflector having the paraboloid of revolution shape (SU patent description No 1181020, H01Q 19/18, 30.03.1984). The subreflector shape is selected basing on condition of absence of phase aberrations for the two symmetrically located beams. With this, the feed elements are located in the foci located symmetrically, their axes being directed in such a way that the maximums of their patterns, after reflection from the subreflector, enter the central part of the main reflector. The reflector in this case is irradiated completely, the antenna possessing the high value of efficiency with the feed elements located precisely in the foci. The drawback of this antenna is the low number of beams and the narrow angle of view. With increasing the separation of the foci, provided the feed elements being located in these foci, the angular spacing of beams is increasing; however, due to irregular distribution of the field amplitude (amplitude aberrations), efficiency drops down in the aperture of the main reflector. Should the feed elements be located between the foci, the drop in efficiency occurs due to amplitude and phase aberrations.

The closest analogue of the claimed invention is the reflector antenna described in publication: Shishlov AN., Shitikov A.M., Multi-beam offset reflector antenna with wide field of view in one plane, Proc. 27 Sci. Conf on Antenna Theory and Technology,

Moscow, 1994, P. 227 - 230. The antenna comprises the main reflector being a part of paraboloid of revolution, subreflectors and one feed element capable of moving or several fixed feed elements. The shape of the surface of the subreflector is selected from the condition of forming a plane wavefront for two fixed directions of the beam. The outlines of reflectors and location of the feed element are selected in such a way that the mutual shading be avoided; that is, the offset design of the antenna is employed. The free parameters of the subreflector are selected from the condition of maximum efficiency value for these directions. The drawback of this antenna is a narrow angle of view. The present invention is aimed at broadening the angle of view provided retaining of all advantageous features of the antenna. SUMMARY OF THE INVENTION

A polyfocal reflector antenna in accordance with the present invention is disclosed.

The polyfocal reflector antenna comprising: the concave main reflector shaped as a part of a toroidal surface; the feeding device having at least one feed element; at least one subreflector shaped as a part of curved surface; said main reflector, said feeding device and at least one subreflector being installed in such a way that said main reflector and the feeding device are located one side from at least one said subreflector; the shape of the surface of at least one said subreflector is determined from the equation / (z) = P_m (x, y),

P_m (x, y) being a two-dimensional polynomial of the power m; f (z) = P_m (x, 0) is the equation of the generatrix of the subreflector; x, y, z - Cartesian coordinates; the shape of the surface of at least one subreflector, location of feed elements of the feeding device and directions of their axes are determined in the result of optimization basing on the requirement of the maximum value of the efficiency at least for the two directions of beams of the given type of pattern.

The antenna can be characterized by the fact that said main reflector, at least one of subreflectors and the feeding device are arranged according to the offset scheme.

The antenna can be further characterized by the fact that said toroidal shape of surface of said main reflector is formed by rotation of a parabola around an axis being orthogonal to the main axis of said parabola, and the cross-section of at least one said subreflector in the plane of symmetry of the main reflector is an ellipse.

The antenna can be further characterized by the fact that the shape of the surface of at least one subreflector is a toroidal surface, and the axis of at least one feed element of said feeding device intersects the plane of symmetry of the antenna in the point located between the surface of at least one said subreflector and its axis. The antenna can be further characterized by the fact that at least one said subreflector has the concave-convex shape.

The antenna can be further characterized by the fact that said main reflector has the edge fringed as a planar curve. The antenna can be further characterized by the fact that said feeding device is equipped with a means for mechanical displacement of at least one feed element.

The antenna can be further characterized by the fact that wherein said feeding device is embodied as an array of feed elements.

The antenna can be further characterized by the fact that the polyfocal reflector antenna additionally comprises the aberration compensator embodied as at least one lens and/or reflector.

The antenna can be further characterized by the fact that the shape of the surface of one of said subreflectors is determined from the condition of formation of planar wavefront. The antenna can be further characterized by the fact that the shape of the surface of at least one of said subreflectors is determined from the condition of formation of cylindrical wavefront.

BRIEF DESCRIPTION OF THE INVENTION

The invention is disclosed in the following detailed description and accompanying drawings, wherein:

Figure 1 presents the general view of the antenna in compliance with the invention; Figure 2 is the general view of the antenna with the flat edge of the main reflector;

Figure 3 is the view in the plane ZX for the example of the embodiment of the antenna shown in Figure 2;

Figure 4 is the same as Figure 3 in the plane XY;

Figure 5 is efficiency versus scanning angle for the closest analogue and for the example of the embodiment of the antenna shown in Figure 3 and Figure 4; Figure 6 presents the antenna with the correcting lens; Figure 7 is the antenna with two separate subreflectors; Figure 8 is the antenna with three integrated subreflectors; Figure 9 is the antenna with two separate subreflectors synthesized for a single beam and a group of beams.

DETAILED DESCRIPTION OF THE INVENTION

The invention is based on the following prerequisites and considerations.

The claimed design of the antenna employs a toroidal reflector as a main reflector, which is the feature well known in the reflector antenna engineering, as it has been shown above. However, in the state-of-the-art multi-beam and scanning antennas, the scanning of the beam is implemented through rotation of the feed element or the feeding device (the feed element with the subreflector) around the torus axis. With this, the axes of feed elements are directed towards the rotation axis, and, taking into consideration the axial symmetry of the torus, no change of the antenna gain occurs in the course of scanning. With this, the feed element in each particular position irradiates only a part of the main reflector surface, so the efficiency of such systems proves to be not high. In the claimed invention, it is suggested to employ the toroidal reflector as a main reflector of a polyfocal, in particular, a bifocal system. This feature, provided the following recommended choice of the subreflector shape, enables to broaden the scanning sector of polyfocal systems with the main reflector shaped as a paraboloid of revolution with retaining the high efficiency value. The shape of the subreflector is selected in this case basing on the condition of the minimum phase and amplitude aberrations, that is, the least difference of the actual amplitude and phase distribution within the main reflector aperture from that required for implementation of the maximum value of efficiency for two or more positions of the feed element for the given shape of pattern. This means that in the course of optimization it is possible to introduce the restrictions for the level of the lateral radiation, the deviation of the fan pattern from the desired fan pattern in the vertical plane (the plane orthogonal to the scanning plane), etc. The generatrix of the main reflector described by the equation x = F(z), and the generatrix of the subreflector described by the equation

P_m (x, 0) = f(z), Pm (x, y) being a two-dimensional polynomial of the power m, can be selected in a multitude of ways, for example, basing on the technological considerations, on the requirement of implementation of a certain mapping (correspondence) function for beam fronts at antenna inputs and outputs in the vertical plane (y — 0), determining, in particular, the amplitude distribution in the aperture for a synphase antenna, and hence, the lateral radiation of the antenna and the scanning properties in the vertical plane.

In case of forming of pencil-beam pattern it is necessary to form the plane wavefront (synphase aperture). The generatrix of the subreflector provided the given shape of the main reflector generatrix being determined from the condition of plane wavefront formation (see Kaloshin, V.A., Venetsky, A.S., Synthesis of multi-beam and multilobe antennas, Proc. 28 Moscow Int. Conf. on Antenna Theory and Technology, Moscow, 1998, P. 380-383). Should it prove necessary to implement a given mapping function in the vertical plane, the generatrix of both reflectors are determined simultaneously by solving of the respective two-dimensional problem (see Kaloshin, N.A., The method of key problems is asymptotic theory of wave-guiding and emitting systems with edges. - Dr. Sci. Thesis, Moscow, IRE of Russian Academy of Science, 1989). It is possible to select generatrix of the main and subreflectors with the purpose of ensuring the high scanning properties of the antenna in the vertical plane. To this end, either the mapping function in this plane should satisfy the anaplantism condition, i.e. the Abbe sines condition (see Zelkin, Ye.G., Petrova, R.A. Lens antennas. - Moscow, Sovetskoye Radio, 1974. - 280 pages), or generatrix of the main reflector and subreflectors should be selected from the condition of polyfocal system formation in this plane (see said publ: Kaloshin, N.A., Venetsky, A.S.).

In case of fan pattern embodiment in the vertical plane, the wavefront is cylindrical rather than plane (curved in the vertical plane). The initial approximation for optimization process purposed for determining the shape of the subreflector can be found in this case through solution of the integro-differential equation (see Kaloshin, V.A., Dr. Sci. Thesis). Given the shape of the main reflector generatrix, it is possible to implement various shapes of the fan pattern in the vertical plane through the corresponding choice of the subreflector shape. In selection of the main reflector generatrix, it is possible to implement a given amplitude distribution in the main reflector aperture (in the vertical plane), and respectively, the given level of deviation of the fan pattern shape from the shape of synthesized fan-type pattern and the level of the lateral radiation. In the case of the fan-type pattern, a known iteration procedure (see monography: Andriychuk, M.M. et al., Synthesis of antennas by the amplitude patterns. - Kiyev, Naukova Dumka, 1993. - 255 pages) can be employed for this. The process of the optimization while forming the fan pattern for achieving the maximum efficiency value is carried out using the condition of the required deviation of the pattern in the vertical plane from the preset one.

Thus, initially the sought-for shape of the main and subreflectors generatrix is determined, that is, functions F(z) and f(z), after which, through optimization process, the parameters of the main reflector (the curvature radius in the horizontal plane, the aperture shape) and the shape of the subreflector are found. With this, generally, optimization of feed element locations (focal line) and directions of their axes are carried out. It is possible to carry out the optimization process without preliminary determination of generatrix of reflectors. In this case, the functions F(z) and f(z) are determined simultaneously with calculation of polynomial P_m (x, y).

Figure 1 presents the general view of the antenna in compliance with the invention, with the rectangular aperture and the main reflector edge fringed as a non- planar curve, while Figure 2 shows the same with the main reflector edge fringed as a planar curve formed by intersection of torus surface with the plane.

The antenna comprises the main reflector 10 embodied as a part of the toroidal surface, the subreflector 20 and the feeding device 30. The components 10 and 20 of the device are rigidly bound to each other by means of one or more rods 15; with this, depending on the type of the antenna, the survey of the space is carried out either through mechanical displacement of the feed element 32 in the feeding device 30 (the scanning mode of antenna operation), or the feeding device is embodied as an array of fixed feed elements 32, for example, of the horn type (multi-beam regime of antenna operation). The design implementation of the feeding device 30 is not considered in the present application, as it is not relevant for the essence of the invention.

The shape of the surface of the subreflector is determined from the equation f (z) =P_m (x, y),

P m (x, y) being the two-dimensional polynomial of the power m. The power of the polynomial and its coefficients are the free parameters for optimization of the antenna with respect to the maximum value of efficiency for two or more points of location of the feed element coordinates, and axes directions of those are also found as a result of optimization. Another way to determine the shape of a single subreflector is specification of its shape in a certain class of functions and determining optimum values of free parameters employing, similar to the above case, one of the known methods of multidimensional optimization (see Aoki, M. Introduction into methods of functionals optimization. - Moscow, Nauka, 1976). In this case, the power m and some of the coefficients of the polynomial P_m (x,y) are specified prior to launching the optimization process. Parameters of the main reflector or locations of feed elements could also be specified initially.

Figures 3 and 4 present the example of embodiment of the antenna with the planar edge of the main reflector, in vertical (ZX) and horizontal (YX) planes, respectively. The main reflector 10 is a non-axial-symmetrical cutting of a parabolic torus, the axis 34 of which is shown in Figure 3 as a chain line. The lowest point 102 of the reflector 10 lies at the X axis (parabola axis).

The generatrix of the main reflector is determined by the equation: x = A -z²/B,

A and B being the free geometric parameters of the main reflector.

From the requirement of formation of the plane wavefront, the generatrix of the subreflector in the ZX plane is selected as an ellipse with one focus coinciding with the parabola focus, and the other focus is selected in the point coinciding with the lowest point 102 of the main reflector. The equation of the subreflector cross-section takes on the form x = a- b (l - (z/c)²)^1/2 a, b, c being the free geometric parameters of the subreflector.

The free geometric parameters of main and subreflectors, as well as directions and location of feed element axes were calculated as a result of optimization in respect to the maximum value of efficiency for two beams spaced by the 10 degrees angle. After this, the optimization resulted in determining the shape of the focal curve 40 (for other feed element locations) shown in Figure 4 with asterisks. With this, the, optimization of the subreflector shape was carried out in the class of toroidal surfaces. In this case, P _m (^χ, y) = ^χ2 + y².

The free geometric parameters of the subreflector were found in the process of optimization and constituted (all values hereinafter are specified in millimeters): α = 5043, b = 1411, c = 1152 .

As a result, the subreflector 10 has the concave-convex surface and is an asymmetrical, in the ZX plane, cutting of the elliptic torus with the axis 36 coinciding with the Z axis (see Figures 3, 4). Simultaneously, the free geometric parameters of the antenna main reflector having the shape of parabolic torus were found: A = 6652, B = 6519.

The resulting equation of the main reflector surface takes on the form:

(x + Δ)² + V² = (6652 - z²/6519)² , Δ = 794 being the spacing between axes of main and subreflectors. In case of embodiment of the claimed antenna with the movable feed element 32, the displacement of the latter is carried out along the focal curve 40, which approximates the circle with the radius 3930. In case of employing several feed elements 32, these are also located on the curve 40. The axes of feed elements are directed towards the axis located in the XZ plane parallel to the subreflector axis and displaced from the latter towards the reflector by the distance 2560. With this, the feed elements form the beams spaced in a broad angular sector in the XY plane.

The main and subreflectors have the common plane of symmetry ZX. The main reflector aperture is equal to the area of the circle of diameter 3000. The area of the subreflector 20 constitutes ca. 0.33 of the main reflector area. The width of the pattern of feed elements on 10 dB level constitutes 30 degrees; with this, the value of the radius of the main reflector in the plane XY constitutes 6652, that of the subreflector 3632, the spacing of their axes being 794. The boundary of the main reflector 10 is planar and is formed by intersection of the plane determined by the equation 2557 (x+A) + z = 17009 with the surface of the parabolic torus. The boundary of the subreflector 20 is determined from the condition of interception of beams reflected from the main reflector 10 in case of incidence of the flat wavefront at various angles in the specified angular sector (in the described example, 20 degrees). The reflectors are located according to the offset scheme and do not shade each other.

Figure 5 shows efficiency versus scanning angle for the bifocal antenna (see cited work by Shishlov AN., Shitikov A.M.) calculated in compliance with the physical optics method - with solid line (curve 1), and that for the above example of the claimed antenna - with dotted line (curve 2). It can be seen that the complete coverage sector of the bifocal antenna (Shishlov AN., Shitikov A.M.) for the efficiency level 0.6 constitutes ca. 9° (± 4,5°), while for the claimed antenna it exceeds 20° ( ± 10°).

To further increase the coverage sector, it is possible to employ a reflector antenna with aberrations compensator 60, which compensates for aberrations not eliminated by the subreflector 20 (Figure 6). There can be several such compensators 60 in the form of lenses and/or reflectors installed in front of each of the feed elements 32. The shapes of surfaces of such lenses or reflectors can be found using the method (see cited work by Kaloshin, N.A., Venetsky, A.S.).

If it is necessary to form several broadly spaced groups of beams, or groups of beams and separate beams, an antenna can be used with several subreflectors, separate ones 202, 204 (Figure 7) or 204, 206 (Figure 8), or integrated to a single component 208,

210, 212 (Figure 9) with respective exciting elements.

In case of forming a beam group (several closely located beams), or of continuous scanning, it is necessary to employ an subreflector 206 (Figure 8) synthesized similarly to the above example. To form a separate beam, the shape of respective reflector can be found from the condition of formation of a planar wavefront (for a pencil-beam pattern) or a cylindrical wavefront (linear in the horizontal plane) for the fan pattern provided a given beam direction according to the known formulae (see work by Kaloshin, N.A.,

Venetsky, A.S.). Operation of the antenna device in the multi-beam regime is carried out as follows. The radiation from one of the feed elements 32 comes to the subreflector 20 (Figure 1), is reflected from it and comes to the main reflector 10. The electromagnetic field reflected from the main reflector 10, having the wavefront actually linear in the horizontal plane, is emitted into the space forming the antenna pattern. The radiation from the other feed element comes to the subreflector 20 at another angle in the horizontal plane and forms its own pattern, the maximum of which in the horizontal plane is deflected from the maximum of the previous pattern by the angle depending on the relative position of feed elements in the feeding device. With this, the axes of feed elements are located in such a way that the maximum of the pattern after reflection from the subreflector would fall into the central part of the main reflector. In case of such an orientation of feed elements, the main reflector is illuminated completely, and, provided compensation of phase distortions due to the corresponding shape of the subreflector, the high value of efficiency is ensured. In the receive regime, the antenna operates in the same manner, but in the reverse order, in compliance with the reciprocity principle.

In the scanning regime, variation of location of the antenna beam in the space is carried out through displacement of the feed element (in the transmission regime) or the receiving component (in the receive regime).

INDUSTRIAL APPLICABILITY

The invention can be embodied using the modern component base and various means of processing of materials, e.g. punching. Materials used for manufacturing of main and subreflectors could be aluminum or its alloys, steels with corrosion-resistant surfacing, metallized plastics and other materials.

Claims

THE CLAIMS

1. The polyfocal reflector antenna comprising: the concave main reflector shaped as a part of a toroidal surface; the feeding device having at least one feed element; at least one subreflector shaped as a part of curved surface; said main reflector, said feeding device and at least one subreflector being installed in such a way that said main reflector and the feeding device are located one side from. at least one said subreflector; the shape of the surface of at least one said subreflector is determined from the equation

/ (z) = P_m (x, y),

Pm (x, y) being a two-dimensional polynomial of the power m; f (z) = P_m (x, 0) is the equation of the generatrix of the subreflector; x, y, z - Cartesian coordinates; the shape of the surface of at least one subreflector, location of feed elements of the feeding device and directions of their axes are determined in the result of optimization basing on the requirement of the maximum value of the efficiency at least for the two directions of beams of the given type of pattern.

2. The device as claimed in claim 1, wherein said main reflector, at least one of subreflectors and the feeding device are arranged according to the offset scheme.

.

3. The device as claimed in claim 1 or 2, wherein said toroidal shape of surface of said main reflector is formed by rotation of a parabola around an axis being orthogonal to the main axis of said parabola, and the cross-section of at least one said subreflector in the plane of symmetry of the main reflector is an ellipse.

4. The device as claimed in any preceding claim, wherein the shape of the surface of at least one subreflector is a toroidal surface, and the axis of at least one feed element of said feeding device intersects the plane of symmetry of the antenna in the point located between the surface of at least one said subreflector and its axis.

5. The device as claimed in any preceding claim, wherein at least one said subreflector has the concave-convex shape.

6. The device as claimed in any preceding claim, wherein said main reflector has the edge fringed as a planar curve.

7. The device as claimed in any preceding claim 1 - 6, wherein said feeding device is equipped with a means for mechanical displacement of at least one feed element.

8. The device as claimed in any preceding claim 1 - 6, wherein said feeding device is embodied as an array of feed elements.

9. The device as claimed in any preceding claim, wherein the polyfocal reflector antenna additionally comprises the aberration compensator embodied as at least one lens and/or reflector.

10. The device as claimed in any preceding claim 1 - 9, wherein the shape of the surface of one of said subreflectors is determined from the condition of formation of planar wavefront.

11. The device as claimed in any preceding claim 1 - 9, wherein the shape of the surface of at least one of said subreflectors is determined from the condition of formation of cylindrical wavefront.