JPH061852B2 - Offset antenna - Google Patents

Description

The present invention relates to an aperture plane antenna mainly used for microwave band communication or radar, and more specifically to an improvement of an offset antenna having a circular aperture. .

[Conventional technology]

FIG. 4 is a side view showing a conventional offset antenna disclosed in, for example, Japanese Patent Publication No. 53-31345, and FIG. 5 is a front view.
FIG. 6 is a partial perspective view, in which (1) is a reflection obtained by cutting a paraboloid of revolution having F ₂ as a focal point and AA as a rotation axis at a plane P forming an angle with the rotation axis AA. mirror,
(2) is a sub-reflector of a part of the ellipsoid of revolution having F ₁ and F ₂ as focal points and BB as the axis of rotation, and (3) is, for example, a conical horn primary radiator. The center of the radiated radio wave in (1) coincides with one of the focal points of the sub-reflector (2) F ₁ . (4) is a cylindrical side plate that covers the periphery of the main reflector (1), and (5) is a side plate.
Hole constructed by cutting out part of (4), (6) Primary radiator
A box body that covers (3) and the hole (5) of the side plate (4), (7) is a radome of a dielectric plate that covers the opening of the side plate (4) on the side of the subreflector (2), and (8) is a primary Transmission line for radio waves radiated from radiator (3), (9) is hole (5)
Is the edge of. The conventional offset antenna is constructed as described above, and when it is considered as a transmitting antenna, the radio wave radiated from the primary radiator (3) passes through the transmission line 8 and the phase of the radiated radio wave of the primary radiator (3) is Center, ie focus F ₁
Is radiated as a spherical wave centered at, is reflected by the sub-reflecting mirror (2), passes through the focal point F _2, and is reflected by the main reflecting mirror (1) to become a plane wave, which forms a sharp beam in front of the antenna. If raindrops or snow adheres to the opening of the primary radiator (3), the amplitude distribution and phase distribution of the radio waves radiated from the primary radiator (3) change, which deteriorates the originally sharp beam or causes unnecessary radiation. The radome (7) is the main reflector because radio waves are emitted in the direction.
(1), side plate (4), and box (6) form a sealed structure to prevent rain and snow from entering the inside and adhering to the primary radiator (3). Furthermore, from the primary radiator (3) to the sub-reflector (2),
Holes in the side plate (4) so that radio waves are not blocked on the way of the transmission path (8) from the main reflector (1) to the front of the antenna.
(5) is arranged, and the radome (7) also uses a dielectric thin film that is sufficiently thin compared to the wavelength in order to minimize reflection when radio waves pass. Due to the above considerations, offset antennas are used in high-density communication and sanitary communication as antennas with good characteristics without sidelobe deterioration and gain reduction due to blocking, as compared to parabolic antennas and Cassegrain antennas that inherently have blocking. ing.

[Problems to be solved by the invention]

However, regarding the hole (5) of the side plate (4) required in the conventional offset antenna described above, there are a few points to be considered in terms of electrical characteristics and mechanical strength.

First, in terms of electrical characteristics, when the hole (5) is considered geometrically and optically, its shape is the shape of a cone having the focal point F ₂ as its apex and a wire around the main reflecting mirror (1) and the side plate (4). It should be a through line, but since the wave is actually a radio wave with a wavelength of several cm, the cone formed by this radio wave has a wave-like expansion. Don't Especially in the vicinity of the focal point F ₂ , it is necessary to make it sufficiently large.
As shown in the figure, the hole (5) is usually the same size as the box (6). Furthermore, the hole (5) has an edge between the side plate (4).
(9) is formed, and an edge that is unavoidable as an antenna, that is, the outer periphery of the main reflecting mirror (1) and the sub-reflecting mirror (2), and the edge (9)
Since the side lobe characteristics are deteriorated due to edge diffraction or edge scattering, it is necessary to attach a wave absorber.

Next, in terms of mechanical strength, the hole (5) divides the continuity of the side plate (4) as a cylindrical shell, and further the side plate (4) and the box (6).
Since the curvature and its direction as shells change abruptly at the part to be joined, an out-of-plane bending moment is generated here, so it is necessary to increase the plate thickness or add reinforcement. Also, when a strong wind such as a typhoon acts on the antenna,
Since (6) disturbs the streamline of the wind and increases the wind load, it is necessary to seek a shape with little influence by wind tunnel experiments to reduce the turbulence, and to improve the strength of each part based on the result.

However, these are not the essential problems as an offset antenna, and all are made to prevent deterioration of the original electrical and mechanical characteristics of the offset antenna. The improvement is due to the use of the electromagnetic wave absorber and the plate thickness. The increase in manufacturing costs, such as increase in manufacturing cost, and the large number of experimental elements such as the hole shape, the electromagnetic wave absorber mounting position, and the box shape selection, resulting in difficulty in realizing an inexpensive offset antenna with good characteristics. I was doing.

The present invention has been made to solve the above problems, and an object thereof is to obtain an inexpensive offset antenna that does not cause the above-mentioned characteristic deterioration.

[Means for solving problems]

The offset antenna according to the present invention is such that the inner surface of the side plate is a pyramid having a conducting wire on the outer periphery of the main reflecting mirror and having an apex in the plane including the rotation axis of the main reflecting mirror and having a predetermined relationship with the main reflecting mirror. It includes a subreflector and a primary radiator in the cone or side plate.

[Action]

In the present invention, since the side plate can cover the transmission line without dividing or blocking the radio wave radiated from the primary radiator, the side plate does not need a hole for passing the radio wave, and the side lobe characteristic caused by the edge of the hole is eliminated. No deterioration or deterioration of mechanical strength around the hole. Further, since the side plate of the present invention also serves as the box body covering the sub-reflector, the primary radiator and the hole, the number of parts constituting the offset antenna is reduced.

〔Example〕

FIG. 1 is a side view showing an embodiment of the present invention, FIG. 2 is a front view, and in the figure, (1) is a reflecting mirror, (2) is a sub-reflecting mirror,
(3) is the primary radiator, (7) is the radome, and (8) is the transmission line, which are the same as above. Reference numeral (10) is a side plate, which is perpendicular to the plane of symmetry of the reflecting mirror (1), that is, the plane formed by the outer periphery of the main reflecting mirror (1), that is, perpendicular to the plane P and on the plane Q which the rotation axis AA includes (in FIG. Is a cone having a vertex T on the plane parallel to and on the plane including the focal point F ₂ and having the outer circumference of the main reflecting mirror (1) as a conductor has an inner surface shape. This cone, that is, the side plate (10) The angle θ formed by the rotation axis AA and the generatrix on the rotation axis AA side on the plane Q of the cone is determined so that the sub-reflecting mirror (2) and the primary radiator (3) are included inside, and this angle θ, The apex angle 2α (half apex angle α) on the plane Q of the cone and the plane P is the rotation axis AA.
And the angle φ formed by satisfying the following relationship.

The cone having the point on the plane Q as the apex and the outer circumference (ellipse) of the main reflecting mirror (1) as the conducting wire is an elliptical cone and is not generally rotationally symmetric, but the angles θ, α, and φ are expressed by the formula (1 ), The elliptical cone becomes a rotationally symmetric cone. That is, an ellipse formed by a cone having a half-vertical angle α on the plane P, that is, the outer circumference of the side plate (10) on the side of the main reflecting mirror (1) and the outer circumference (oval) of the main reflecting mirror (1) can be matched. it can.

In the offset antenna configured as above,
The radio wave radiated from the primary radiator (3) to the sub-reflector (2) and the main reflector 1 propagates through the transmission line (8) as in the conventional device and forms a sharp beam in front of the antenna. Since the eggplant cone is included in the side plate (10), the holes and the edges due to the holes which are present in the conventional device are unnecessary, and the side plate (10) does not divide or block the transmission line (8). In other words, the edge that causes the deterioration of electrical characteristics is only the unavoidable edge of the antenna, that is, the outer circumference of the main reflector (1) and the sub-reflector (2), and the side lobe degradation due to the wave behavior of radio waves is minimal. It becomes a thing.

Mechanically, the side plate (10) is a conical shell and has the same Gaussian curvature 0 as the cylindrical shell of the side plate (4) of the conventional device, so the strength properties are almost the same. Unlike the device, since there is no hole, the continuity of the shell is maintained,
The strength of the shell can be maximized and no reinforcement measures are required. Since the side plate (10) of the present invention also serves as the box body (6) of the conventional device, the box body (6) is unnecessary, the number of parts is reduced, and the streamline of the wind becomes smooth and the wind load is also high. Does not increase.

Furthermore, this side plate (10) has a Gaussian curvature of 0 as described above.
Since it is a shell that can be expanded, the side plate (10) can be manufactured by sheet metal processing, so an offset antenna can be constructed at extremely low cost, and a manufacturing method other than sheet metal processing, for example, when molding glass fiber reinforced plastic Also in the case of manufacturing, there is an advantage that the inner surface shape of the side plate is conical or can be sufficiently processed by a general-purpose machine such as a vertical lathe. Fig. 3 shows an example (1/2 part) of the developed shape when the side plate (10) is manufactured by sheet metal working.

〔effect〕

As described above, the present invention has an effect that it is possible to inexpensively realize the offset antenna without causing the deterioration of the electromechanical characteristics by forming the side plate of the offset antenna with a predetermined cone.

[Brief description of drawings]

1 is a side view showing an embodiment of the present invention, FIG. 2 is a front view, FIG. 3 is a side plate development view, FIG. 4 is a side view showing a conventional offset antenna, and FIG. 5 is a front view. , FIG. 6 is a partial perspective view. In the figure, (1) is a main reflecting mirror, (2) is a sub-reflecting mirror, (3) is a primary radiator, (4) is a side plate, (5) is a hole, (6) is a box, and (7) is The radome, (8) is the transmission line, (9) is the edge, and (10) is the side plate. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A main reflecting mirror obtained by cutting a paraboloid of revolution along a plane that forms an angle with a rotation axis, a side plate attached to the outer periphery of the main reflecting mirror, and a focal point which is the focal point of the main reflecting mirror. One sub-reflecting mirror of the spheroidal surface, and a primary radiator whose radio wave phase center is the focal point of the other sub-reflecting mirror.
In an offset antenna composed of a radome covering the opening side of the side plate, a side plate having an inner surface of a cone having an apex in the plane of symmetry of the main reflector and having the outer circumference of the main reflector as a conductor is provided. The sub-reflecting mirror and the primary radiator are provided inside the side plate, and among the generatrixes on the symmetry plane of the cone, the angle θ at which the generatrix on the rotation axis side of the paraboloid of revolution serves as the rotation axis, the cone The half apex angle α on the plane of symmetry of the body and the angle φ for cutting the main reflecting mirror are The offset antenna is characterized by the following relationship.