JPH03149906A - Offset antenna - Google Patents

Abstract

PURPOSE:To obtain an offset antenna without a cause to deterioration in the electric and mechanical characteristic inexpensively by minimizing a hole with a radio wave from a side plate passing therethrough. CONSTITUTION:A part through which a radio wave passes in a side plate 10, that is, a hole 11 may be a point hole or a minute sized ellipse, and the size of the hole is enough to be a radius of a beam waist at a focus F2 even with a consideration in terms of wave taken into account. That is, the hole 11 giving a dominant effect on the electric characteristic of the antenna is minimized. The side plate 10 is structured as an elliptic conical shell and a shell with the same Gaussian curvature zero as that of a cylindrical shell of a side plate of a conventional antenna, then the properties at the standpoint of the strength is nearly the same, but the size of the hole 11 is small enough to be different from that of the conventional antenna an only nearly 10% of the width of the side plate 10 is lost, and the continuity of the shell is sufficiently kept, the strength of the shell is maximized and no reinforcement is required. Since a box 12 is made small, the streamline of wind is less disturbed and the wind load is not almost increased. Thus, the antenna with less cause to the deterioration in the electric and mechanical characteristic is realized inexpensively.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to an aperture antenna mainly used for microwave communication or radar, etc., and more specifically, to an improvement of an off-theft antenna having a circular aperture. .

[Conventional technology]

Fig. 5 is a side view showing a conventional offset antenna disclosed in, for example, Japanese Patent Publication No. 53-31345, Fig. 6 is a front view, and Fig. 7 is a partial perspective view. The main reflecting mirror obtained by cutting a rotating rod body with AA as a focal point and a rotational axis at a plane P forming an angle φ with the rotating wheel AA, (2) is a main reflecting mirror with F, and FO as conjugate focal points, and BB as a rotational axis. The sub-reflector (3), which is a part of the spheroidal surface that is the axis of rotation, is, for example, a primary radiator of a conical horn, and the phase center of the radiated radio wave of this primary radiator (3) is the focal point of the sub-reflector (2). One F is consistent. (4) is a cylindrical side plate that covers the main reflector (1), (5) is a hole made by cutting out a part of the copper plate (4), and (6) is the primary radiator (3) and side plate. (4)
The box body (7) covering the hole (5) is the secondary reflection 1j of the copper plate (4).
radome of dielectric plate covering the opening on the side of lc2), (8)
is the transmission path of radio waves emitted from the primary radiator (3), (9
) is an intersecting line between the cone whose apex is the focal point F and the conductor around the main reflecting mirror (1) and the side plate (4).

A conventional offset antenna is configured as described above, and when considered as a transmitting antenna, the primary radiator (3)
The radio waves radiated from the primary radiator (3) are radiated as a spherical wave centered at the focal point F, which is the phase center of the radiated radio waves of the primary radiator (3), through the transmission path (8).

It is reflected by the sub-reflection 1jl (2), passes through the focal point F2, and is reflected by the main reflecting mirror (1) to become a plane wave, forming a sharp beam in front of the antenna. If raindrops or snow adhere to the aperture of this primary radiator (3), the amplitude distribution and phase distribution of the radio waves emitted from the primary radiator (3) will change, causing the original sharp beam to deteriorate or moving in an unnecessary direction. Since radio waves are emitted to the radome (7), the main reflector (1) and the copper plate (4
), forms a sealed structure together with the box body (6).

This prevents rain and snow from entering the interior and adhering to the primary radiator (3). Additionally, there are holes in the side plate (4) to prevent radio waves from being blocked on the transmission line (8) from the primary radiator (3) to the front of the antenna via the sub-reflector (2) and main reflector (1). (5) is arranged, and the radome (7) also uses a dielectric thin film that is sufficiently thin compared to the wavelength.
The angle formed by the radome (7) and the transmission line (8) is set to an angle φ that is not a right angle to minimize reflection when the radio waves pass through. Due to the above considerations, offset antennas are
Compared to parabolic antennas and Cassegrain antennas, which inherently have blobking, this antenna has no sidelobe degradation or gain reduction due to blobking, and is used in high-density communications and satellite communications as an antenna with good characteristics.

[Problem to be solved by the invention]

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

First of all, in terms of electrical characteristics, if the hole (5) is considered from a geometric optics perspective, its shape should be a mutual line (9), but in reality it is a radio wave with a wavelength of several C-, so the focal point F, Since the cone formed by the radio waves emitted from the hole has a wave-like expansion, the hole (5)
must not be larger than the intersecting line (9). In particular, the hole should be larger than the beam waist radius near the focal point Ft. In practical use, the hole (
5) is usually made to have the same size as the box (6) rather than making a part thicker.

Next, in terms of mechanical strength, the hole (5) separates the continuity of the m-plate (4) as a cylindrical shell, and the part where the side plate (4) and the box body (6) are joined does not function as a shell. Since the curvature and its direction change suddenly, an out-of-plane bending moment is generated here, so measures such as increasing the thickness of the plate or adding reinforcement are necessary.Also, when the antenna is exposed to strong winds such as typhoons, the box Since the body (6) disturbs the flow lines of the wind and increases the wind load, it is necessary to search for a shape with less influence through wind tunnel experiments to reduce the disturbance, and improve the strength of each part based on the results.

All of these are done to prevent deterioration of the original electrical and mechanical characteristics of the offset antenna, but improvements require increased production costs such as an increase in the thickness of the radio wave absorber, and changes in the shape of the hole. This resulted in a development procedure involving a large number of experimental elements, such as the installation position of the radio wave absorber and the selection of the shape of the W body, making it difficult to realize an offset antenna that was inexpensive and had good characteristics.

The present invention has been made to solve this problem, and its purpose is to obtain an inexpensive offset antenna that does not have the above-mentioned characteristics deterioration factors.

[Means to solve the problem]

The off-theft antenna according to the present invention has an inner surface shape of the side plate that is arranged on an axis parallel to the axis of rotation of the main reflector, passing through the farthest point from the focal point F on the outer periphery of the main reflector, using the outer periphery of the main reflector as a conductor. It is a cone having an apex at , and forming a predetermined relationship with the main reflecting mirror.

[Effect]

In this invention, since the number of holes in the side plate through which radio waves pass is minimized, there is less deterioration of mechanical strength around the holes, and the shape of the box body is minimized.

〔Example〕

Fig. 1 is a side view showing an embodiment of the present invention, Fig. 2 is a front view, and Fig. 3 is a partial perspective view.
is the main reflector, (2) is the sub-reflector, (3) is the primary radiator,
(7) is a radome, and (8) is a transmission line, which are the same as the above-mentioned conventional device. (10) is a side plate, (11) is a hole formed by cutting out a part of the copper plate (10), (12)
is a box that covers the sub-reflector (2), the primary radiator (3), and the hole (11) in the side plate (l◎). This copper plate (10) is connected to a plane Q that is perpendicular to the plane P formed by the outer periphery of the main reflecting mirror (1) and includes the rotation axis AA (in Fig. 1, a plane that is parallel to the plane of the paper and includes the focal point FO) and the main reflection! The main reflecting mirror (1) passes through the point on the far side from the focal point F of the two intersections formed by the outer circumference of
The inner surface is a cone with the outer periphery of 1) as a conducting wire, and this generatrix is set so that the branch line between the cone and the plane Q, that is, the generatrix of the rotation axis AA of the two generatrixes passes near the focal point F. The angle θ formed by the rotation axis AA and the rotation axis AA is determined. This cone is an elliptical cone, and its shape is uniquely determined when the position of the apex T is determined from the angle 0.

In the offset antenna configured as above,
From primary radiator (3) to sub-reflector (2), main reflector (1)
The radio waves radiated to the antenna propagate through the transmission path (8) and form a sharp beam in front of the antenna in the same way as in the conventional device, but the part where the radio waves pass through the side plate (10), that is, the hole (II), is may be a point or a minute ellipse, and even if wave considerations are taken into account, the size of the beam waist radius at F is sufficient. In other words, the holes (11
) is the smallest. Mechanically, this copper plate (10) is an elliptic conical shell with a Gaussian curvature of 0, which is the same as the cylindrical shell of the side plate (4) of the conventional device, so its strength properties are is almost the same, but unlike the conventional device, the hole (11)
Since this is small and only a fraction of the width of the side plate (10) is missing, the continuity of the shell is sufficiently maintained, the strength of the shell can be maximized, and no reinforcing measures are required. Since the box body (12) of the present invention is much smaller than the box body (6) of the conventional device, it does not disturb the calm streamlines and the wind load hardly increases.

As described above, this copper plate (10) is a shell with a Gaussian curvature O, so it has a developable curved surface, and since it can be manufactured by sheet metal processing, an offset antenna can be constructed at an extremely low cost. The development example of copper plate (10) <112 part) is the third
As shown in the figure.

〔Effect of the invention〕

As explained above, the present invention has the effect that by forming the side plate of the offset antenna into a certain cone shape, it is possible to realize an offset antenna at a low cost without causing deterioration of electrical and mechanical characteristics.

[Brief explanation of the drawing]

Fig. 1 is a side view showing an embodiment of the present invention, Fig. 2 is a front view, Fig. 3 is a partial perspective view, Fig. 4 is an open view of the side plate,
FIG. 5 is a side view showing a conventional off-theft antenna, FIG. 6 is a front view, and FIG. 7 is a partial perspective view. In the figure, (1) is the main reflector, (2) is the sub-reflector, (
3) is the primary radiator, (4) is the side plate, (5) is the hole, (6)
is a box, (7) is a radome, (8) is a transmission line, (9) is an interconnect line, (10) is a hole in a copper plate (11), and (12) is a box. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A side plate attached to the outer periphery of the main reflecting mirror obtained by cutting the rotating parapet surface with a plane, a sub-reflecting mirror of a part of the spheroidal surface whose focal point of the main reflecting mirror is one of the conjugate focal points, and the other of the above-mentioned sub-reflecting mirrors. In an offset antenna consisting of a primary radiator whose radio wave phase center is at the conjugate focal point and a radome covering the opening side of the side plate, the main reflector is perpendicular to the plane of symmetry of the main reflector, that is, the plane that cuts the main reflector. On an axis parallel to the rotation axis of the main reflection mirror that passes through the point on the side far from the focal point of the main reflection mirror among the two intersections formed by the plane containing the rotation axis of the reflection mirror and the outer periphery of the main reflection mirror. A side plate having an inner surface shaped like a cone having an apex and the outer periphery of the main reflecting mirror as a conducting wire is provided, and the sub-reflecting mirror and the primary radiator are disposed outside the side plate, and the sub-reflecting mirror and the primary radiator are disposed outside the side plate. A branch line of the plane of symmetry between the cone and the main reflecting mirror, that is, a generating line on the rotation axis side of the main reflecting mirror among the two generating lines is the main reflecting mirror. The offset antenna is characterized in that the side plate is provided with a hole having a predetermined radius that does not interfere with radio waves from the sub-reflector, passing near the focal point of the antenna.