JPH0352307A - Multi-beam antenna - Google Patents

Abstract

PURPOSE:To reduce the deterioration in the aperture phase efficiency by interposing a sub reflecting mirror able to a phase error caused when a radio wave radiates from a main reflecting mirror in advance between the main reflecting mirror and a primary radiator and forming the sub reflecting mirror to be nearly a hyperboloid of revolution. CONSTITUTION:A main reflecting mirror 1 is formed by combining a partial main reflecting mirror 11 being part of a hyperboloid of revolution A and a partial main reflecting mirror 12 being part of a paraboloid of revolution B so that both rotation center axes 41, 42 are crossed with each other. while the shape of the curved face of the partial sub reflecting mirrors 21, 24 of the sub reflecting mirror 2 is selected so that a phase error is corrected when its reflected radio wave radiates via the main reflecting mirrors 11, 12, the shape of the cured face of the middle part 25 is formed with a curved face jointing partial sub reflecting mirrors 22, 23 being part of two different hyperboloids of revolution at a bonding border line 8. Then a primary radiator 31 is provided to a focus Fa' at the projection side in two focii of the hyperboloid of revolution A, and a primary radiator 32 is provided to a focus Fb' at the projection side in two focii of the hyperboloid of revolution B similarly and a radio wave radiates toward the sub reflecting mirror 2. Thus, the deterioration in the aperture phase efficiency is reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a multi-beam antenna that forms antenna beams in two different directions using one antenna. (Prior Art) As a multi-beam antenna that forms antenna beams in two different directions using one antenna, for example, the one shown in FIG. 6 is known. In Figure 6,
Reference numeral 13 denotes a reflecting mirror, and this reflecting mirror 3 is a part of a paraboloid of revolution having a straight line 43 as its central axis of rotation, and is formed by a curved surface at an appropriate portion outside the central axis of rotation 43. And 1
The secondary radiators 3l and 32 are arranged at appropriate distances apart from each other in the vicinity of the focal point F of the paraboloid of revolution that exists on the central axis of rotation 43, and emit radio waves to the reflecting mirror 13, respectively. As a result, radio waves are emitted from the reflecting mirror 13 in two different directions. This type of multi-beam antenna was developed to enable simultaneous communication with two satellites in geostationary orbit, for example. (Problems to be Solved by the Invention) However, the conventional multi-beam antenna shown in FIG. 6 has the following problems. First, in order to increase the deviation of the vinyl radiated from the reflecting mirror 13, it is necessary to widen the arrangement interval between the primary radiators 31 and 32, but this will cause the arrangement positions to move away from the focal point F. Disturbance occurs in the wavefront at the aperture of the reflecting mirror 13, and the antenna gain decreases. In addition, the reflecting mirror 13 is made of a curved surface of a paraboloid of rotation at an appropriate portion with the central axis of rotation 43 removed, and has a primary radiator (31, 32).
is placed near the focal point F on the center axis of rotation 43, so it is an offset antenna type that uses a paraboloid of revolution asymmetrically, as shown in FIG. 7(a). As a result, even if an axially symmetrical beam is emitted from the primary radiator (31, 32), the center axis of the corner (beam center axis>7) that looks from the focal point F to the peripheral end of the reflector l3 is A deviation occurs between the reflected light beam (the central axis of the beam) 6 and the central axis of the aperture (the straight line passing through the center of the outer circle projected by the reflecting mirror 13) 5. Therefore, as shown in FIG. 7(b), The electric field vector at the aperture of the reflecting mirror 13 is bent, and the radio waves emitted from the reflecting mirror 13 include not only the electric field in the y-axis direction (main polarization) but also the electric field in the X-axis direction (cross polarization). As a result, crosstalk will occur in communications using the orthogonal polarization system.The present invention was made in view of this problem, and its purpose is to improve An object of the present invention is to provide a multi-beam antenna that can reduce the decrease in aperture phase efficiency and reduce the bias that occurs in the aperture electric field distribution. (Means for solving the problems) Achieving the above objects. In order to achieve this, the multi-beam antenna of the present invention has the following structure.That is, the multi-beam antenna of the present invention has first and second paraboloids each consisting of a portion of the first and second paraboloids of revolution. one main reflecting mirror in which the partial main reflecting mirrors are joined such that the rotation center axes of the first and second rotation paraboloids intersect; a sub-reflector provided between the first focal point of the object surface and the second focal point of the paraboloid of rotation and the main reflector;
first and second beams that emit radio waves toward the sub-reflector;
a primary radiator; and the main reflecting mirror radiates the reflected radio waves of the sub-reflecting mirror in two different directions. The first partial sub-reflector includes a first partial sub-reflector on the reflecting mirror side, a second partial sub-reflector on the second partial main reflector side, and a central portion connecting the first and second partial reflectors; The curved surface shape of each of the first and second partial sub-reflectors is designed to correct or reduce a phase error when the reflected radio waves of the partial sub-reflector are radiated through the partial main reflector on the side of the partial sub-reflector. On the other hand, the curved surface shape of the central portion is a third curved surface formed of a portion of each of the first and second hyperboloids of revolution, the focal position of one of which coincides with the first and second focal positions, respectively. and a fourth partial sub-reflector; and the first and second primary radiators are formed of the first and second primary radiators existing between the main reflector and the sub-reflector. It is characterized by being placed at the focal point of the other of the hyperboloids of rotation. (Function) Next, the function of the multi-beam antenna of the present invention configured as described above will be explained. For example, the emitted radio waves from the first primary radiator placed at the other focal point of the first rotational hyperboloid illuminate the center of the sub-reflector and the second partial sub-reflector. The central part is the first
It consists of a curved surface that joins the third and fourth partial sub-reflectors, each of which is a part of the second hyperboloid of rotation, but if both can be regarded as approximately equal curved surfaces, it is possible to irradiate the central part. The radio waves are reflected as if they were emitted from one focal point of the first hyperboloid of rotation, that is, the first focal point of the first paraboloid of revolution, toward the first partial main reflecting mirror. Since it reaches the first partial main reflector, the first partial main reflector radiates the incident radio wave in a direction parallel to the center axis of rotation of the first paraboloid of revolution. At this time, all optical path lengths are constant. Furthermore, the radio waves irradiated on the second partial sub-reflector are reflected as if they were emitted from the first focal point toward the second partial main reflector and reach the second partial main reflector; The curved shape of the second partial sub-reflector is set so as to correct or reduce the phase error when the reflected radio waves of the partial sub-reflector are radiated via the second partial main reflector, that is, Since the optical path length is set to be constant,
The reflected radio waves from the second partial main reflecting mirror are radiated in a direction parallel to the central axis of rotation of the first paraboloid of revolution without reducing the aperture phase efficiency due to phase error as in the conventional case. ．． The above also applies to the second primary radiator placed at the other focal point of the second hyperboloid of rotation (in this case, the central part and the first partial sub-reflector are targeted). The light is emitted from the main reflecting mirror in a direction parallel to the second rotation center axis. What should be noted here is that although the central part is shared by two primary radiators, no phase error occurs here even though it is a hyperboloid of rotation. In other words, the sub-reflector simultaneously corrects the phase error that occurs in the main reflector in the two radio wave emission directions. In addition, since the sub-reflector is generally a hyperboloid of rotation, the deviation of the beam center axis due to this cancels out the deviation of the beam center axis due to the paraboloid of revolution, that is,
It is possible to correct the bias in the aperture electric field distribution and improve the cross-polarization characteristics of the antenna. As described above, according to the multi-beam antenna of the present invention, since the sub-reflector that is approximately a rotational hyperboloid is interposed, the decrease in aperture phase efficiency can be reduced or improved, and cross-polarization characteristics can be improved. be able to. <<Example>> Hereinafter, an example of the present invention will be described with reference to the attached drawings. Figures 1 and 2 show a multi-beam antenna according to an embodiment of the present invention. This multi-beam antenna includes a main reflector 1, two primary radiators 31 and 32, and one sub-reflector 2. The main reflecting mirror 1 rotates a partial main reflecting mirror 11 made up of a part of a paraboloid of revolution A and a partial main reflecting mirror 12 made of a part of a paraboloid of revolution B about the central axis of rotation 41 of the paraboloid of revolution A. Is it joined along the joining boundary line 14 so that the rotation center axis 42 of the paraboloid B intersects? It is. The sub-reflector 2 is a partial sub-reflector 21 of the partial main reflector 12@
And, partial principal reflex! It consists of a partial sub-reflector 24 on the ilill side and a central part 25 that connects both. Each of the partial sub-reflectors 21 and 24 has a curved surface shape set as described below. Moreover, the curved surface shape of the central portion 25 consists of two different partial sub-reflectors 22 and 23, which are made up of parts of a hyperboloid of rotation A and a hyperboloid of rotation B, with the convex side being the main reflector it'l! It consists of a curved surface joined by a joining boundary line 8 toward l. Of the two focal points of the hyperboloid of revolution A, the position of the focal point on the concave side (i.e., one focal point) coincides with the focal position F of the paraboloid of revolution A, and the focal point on the convex side (
That is, the first primary radiator 3 is placed at the position of F1' (the other focal point).
1 is provided, and radiates radio waves toward the sub-reflector 2. Similarly, of the two focal points of the hyperboloid of revolution B, the position of the focal point on the concave side (i.e., one focal point) coincides with the focal point position Fb of the paraboloid of rotation B, and the focal point on the convex side (i.e., the other focus of) F
A second primary radiator 32 is provided at the position l,' and emits radio waves toward the sub-reflector 2. next,
The method for determining the curved shape of the sub-reflector 2 will be explained with reference to FIGS. 3 and 4. First, FIG. 3 shows a portion of the sub-reflection a2 that receives radio wave radiation from the primary radiator 3l (referred to as sub-reflection fl2'). Now, assume that the entire part (sub-reflector 2') is a hyperboloid of revolution A with F. as the concave focal point and F1' as the convex focal point. Then, the light emitted from the focal point F.' When considering a large number of rays, after these rays are reflected by the sub-reflector 2', they proceed as if they were being emitted from the focal point F. Then, among these rays, partial main reflection #
] (Paraboloid of revolution A) 11 All rays of light incident on the partial main reflecting mirror (paraboloid of revolution A) 11 become parallel rays parallel to the rotation center axis 41, and from the focal point F,' to the secondary The distances from the reflecting mirror (hyperboloid of rotation A) 2' to the plane perpendicular to the rotation center axis 41 are equal. On the other hand, focus F. Among the rays virtually emitted from the rays, the rays incident on the partial main reflecting mirror (paraboloid of revolution B) 12 are reflected by the partial main reflecting mirror (paraboloid of revolution B) 12, and then are approximately aligned with the central axis of rotation. However, the distance from the focal point F&' to the plane perpendicular to the rotation center 141 via the subreflector (hyperboloid of rotation A) 2 is not constant, resulting in a slight error. Therefore, the portion 26 corresponding to the partial main reflecting mirror 11 is the central portion 25, and the curved surface shape of this portion 26 is determined to be a hyperboloid of revolution A. In addition, partial main reflecting mirror 1
The portion 21 corresponding to No. 2 becomes the partial sub-reflector 21, and the curved shape of this portion 2l is a predetermined curved shape slightly displaced from the hyperboloid of rotation A.

That is, the light is emitted from the focal point F1, is reflected by the partial sub-reflector 21, is reflected by the partial main reflector 12, and is reflected by the rotation center axis 41.
The optical path length of each ray to the plane perpendicular to is made equal for each ray. As a result, efficiency degradation due to phase errors based on the paraboloid of revolution B can be reduced. Next, FIG. 4 shows the part of the sub-reflector 2 that receives radio wave radiation from the primary radiator 32 (referred to as the sub-reflector 2''). but,
Hyperboloid of revolution B with Fb as the concave focus and Fb as the convex focus
Assume that Then, the path of the light beam emitted from the focal point Fb' and radiated in the direction of the rotation center axis 42 can be explained in the same way as in FIG. Part 2 corresponding to 12
7 is the central portion 25, and the curved surface shape of this portion 27 is determined to be a hyperboloid of revolution B. Further, the portion 24 corresponding to the partial main reflecting mirror 11 becomes the partial sub-reflecting mirror 24, and the curved shape of this portion 24 is made into a predetermined curved shape slightly displaced from the hyperboloid of rotation B. Then, one sub-reflector 2 is determined from the sub-reflector 2' and the same 2'' determined in this way. That is, it corresponds to the partial main reflector 11 in the sub-reflector 2' shown in FIG. The portion 26 corresponding to the partial main reflecting mirror 12 in the sub-reflecting mirror 2″ shown in FIG. It is cut along the joining boundary line 8 corresponding to l4, and the cut ends are joined together. Partial main reflector 1
The remaining portion of the portion 26 corresponding to the partial main reflecting mirror 12 becomes the partial sub-reflecting mirror 22, and the remaining portion 26 corresponding to the partial main reflecting mirror 12
It can be seen that the remaining portion of 7 becomes the partial sub-reflector 23. Here, the hyperboloids of rotation A and B have different curved shapes, but the inclination angle β (
(Fig. 2) can be appropriately selected, the two rotation hyperboloids can be made into approximately equal curved surfaces within the range of the partial sub-reflector 22 and the same 23, and one sub-reflector can be aligned in the two beam radiation directions. This means that it can be shared with other users. Next, the principle of cross-polarization suppression will be explained with reference to FIG. In FIG. 5(a), the beam center of the beam reflected by the sub-reflector 2 is the central axis 61 of the beam emitted from the focal point F1 (the central axis of the angle 2θ1 looking into the sub-reflector 2 from the focus F,' in the figure). Axis 62 is the focal point F. In the same figure, it opens upward from the central axis 52 of the angle 2θ2 from which the main reflecting mirror 1 is viewed.
That is, in the same figure, θ,〉θ4. As can be seen by comparing this with Figure 7, the axis deviation (θ, −θ4
) is opposite to the direction of axis deviation due to the paraboloid of revolution shown in Figure 7. Therefore, the axis deviation can be reduced, and the beam center axis 63 of the light reflected by the main reflecting mirror 1 of the beam center axis 62 can be made to coincide with the center axis 53 of the aperture. As a result, the aperture electric field distribution of the main reflecting mirror 1 becomes as shown in Fig. 5(b), the curvature of the electric field vector (see Fig. 7(b)) is corrected, and the cross-polarization characteristics are improved. That will happen. In the multi-beam antenna according to the present invention, the main reflecting mirror 1 is a paraboloid of revolution, and the sub-reflecting mirror 2 is approximately a hyperboloid of rotation, so the positional relationship between the main reflecting mirror 1 and the sub-reflecting mirror 2 must be made appropriate. It can be seen that cross-polarization characteristics can be improved by (Effects of the Invention) As explained above, according to the multi-beam antenna of the present invention, the sub-reflector that can pre-correct the phase error that occurs when the main reflector emits radio waves is connected to the main reflector and the primary radiator. Since it is interposed between the aperture surface and the aperture surface, the decrease in aperture phase efficiency can be reduced or improved. In addition, since the sub-reflector is approximately a rotational hyperboloid, the bias in the aperture distribution caused by the main reflector can be corrected, and a multi-beam antenna with less cross-polarization generation can be realized.

[Brief explanation of drawings]

Fig. 1 is a conceptual configuration diagram of a multi-beam antenna according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of the multi-beam antenna of the embodiment, and Figs. 3 and 4 are methods for determining the curved shape of the sub-reflector. 5 is an explanatory diagram of the principle of the cross-polarization suppression effect, FIG. 6 is a conceptual diagram of a conventional multi-beam antenna, and FIG. 7 is an explanatory diagram of generation of cross-polarized waves in a conventional antenna. ．．

Claims (1)

[Claims] A first and second partial main reflecting mirrors each formed of a part of the first and second paraboloids of revolution are joined together so that the central axes of rotation of the first and second paraboloids of revolution intersect with each other.
a focal point (first focal point) position of a first paraboloid of revolution and a focal point (second focal point) position of a second paraboloid of revolution existing on the respective rotational central axes; a sub-reflector provided between the main reflector; and first and second primary radiators that emit radio waves toward the sub-reflector; A multi-beam antenna configured to radiate radio waves in two different directions; the sub-reflector includes a first partial sub-reflector on the first partial main reflector side and a second partial main reflector on the side of the first partial main reflector; It consists of a second partial sub-reflector on the mirror side and a central part that connects the first and second partial sub-reflectors, and the curved shape of each of the first and second partial sub-reflectors is the same as that of the partial sub-reflector. It is set to correct or reduce the phase error when the reflected radio wave is emitted through the partial main reflector on the side of the partial sub-reflector, while the curved shape of the central part is set to adjust the focal position of each of the is a curved surface joined to third and fourth partial sub-reflectors each made of a portion of each of the first and second hyperboloids of revolution that coincide with the first and second focal positions, respectively; and
the first and second primary radiators are respectively arranged at the other focal position of the first and second hyperboloids of rotation that exist between the main reflecting mirror and the sub-reflecting mirror; A multi-beam antenna featuring