JPH01305704A - Offset antenna - Google Patents

Abstract

PURPOSE:To generate an offset antenna without a deterioration factor in electrical and mechanical characteristics by setting the side board of the antenna to be the decided enveloping body of a cone. CONSTITUTION:The cone in which the outer periphery of a main reflecting mirror 1 is made by a conductor and in which one point on the outer periphery of a radome 11 is set to be an apex is an oval cone. When the apex makes a round of the outer periphery of the radome 11, the enveloping body is generated as the set of the cone. The shape of the enveloping body is unequivocally decided with respect to the reflecting mirror 1 when the radius of the radome 11 and the relative position of the main reflecting mirror 1 and the radome 11 are decided. Consequently, the radius and the position are decided in such a way that an auxiliary reflecting mirror 2 and a primary radiator 3 are enveloped in the internal part of the enveloping body and the correlation line of the radome 11 and a transmission line 8 is enveloped in the radome 11. Thus, the shape of the side board 10 is decided. The side board 10 does not interrupt or block the transmission line 8, and respective small parts of the side board 10 are continuously and smoothly constituted along a circle, whereby the characteristics are prevented from being electrically and mechanically deteriorated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates primarily to an aperture antenna used for microwave fluorescent communication or radar, etc., 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.

Fig. 5 is a front view, and Fig. 6 is a partial perspective view. (1) is a plane P in which a paraboloid of revolution with a focal point of 72 f and an axis of rotation AA forms an angle φ with the axis of rotation AA. (2) is a sub-reflector that is part of an ellipsoid of revolution with both Fl and F2 as focal points and BB as the rotation axis; (3) is a primary radiator of a conical horn, for example. The phase center of the radiated radio wave of this primary radiator (3) coincides with one of the focal points Fl of the sub-reflector (2). (4) is the main reflector (1)
A cylindrical side plate that covers the periphery.

(5) is a hole formed by cutting out a part of the side plate (4);
(6) is a box that covers the primary radiator (3) and the hole (5) in the side plate (4), and (7) is a dielectric plate that covers the opening f on the sub-reflector (2) side of the side plate (4). Radome, C81 is the primary radiator (3
), and (9) is the edge of the hole (5). The conventional offset antenna is configured as described above, and when considered as a transmitting antenna, the radio waves radiated from the primary radiator (3) are transmitted through the transmission path f81,
The radiation from the '-primary radiator 3) is emitted as a spherical body centered at the wave phase center, that is, the focal point F1, reflected by the sub-reflector (2), passes through the focal point F2, and becomes the main reflection fi (11
It is reflected as a plane wave and forms 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. Since radio waves are emitted in the following directions, the radome () has a main reflector (11, nr plate (4), 1 box body (
6) to form a sealed structure, which prevents rain and snow from entering the interior and adhering to the primary radiator (3).Furthermore, from the primary radiator (3) to the sub-reflector (j; Q, main reflector) The holes (5) in the side plate (4) are arranged so that the radio waves are not blocked on the way to the transmission path (8) that passes through the mirror (1) and reaches the front of the antenna. A sufficiently thin dielectric film is used, and the angle formed by the radome (7) and the transmission path 181 is not a right angle to minimize reflection when the radio waves pass through.

Due to the above considerations, offset antennas are used in high-density communications and satellite communications as antennas with good characteristics, without side rope deterioration or gain reduction due to blocking, compared to parabolic antennas and Cassegrain antennas, which inherently have blocking. ing.

[Problem to be solved by the invention]

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

First, in terms of electrical characteristics, when considering the hole (5) from a geometrical optical perspective, its shape is a conical line with the focal point F2 as the apex and the main reflecting mirror (with a conducting wire around it) and the side plate (4). However, since the radio waves are actually radio waves with a wavelength of several α, the cone formed by these radio waves has a wave-like expansion, so the hole (5
) must be larger than the above correlation line. In particular, it is necessary to make the hole (5) sufficiently large near the focal point F2, and in practical use, the hole (5) is usually made to have the same size as the box (6) as shown in FIG. Furthermore, the hole (5) forms an edge (9) between it and the side plate (4), and an edge (9) is formed between the hole (5) and the side plate (4). 9) It is necessary to have
Since edge diffraction or edge scattering increases the deterioration of sidelobe characteristics, it is necessary to install a radio wave absorber.

Next, in terms of mechanical strength, the hole (5) separates the continuity of the side plate (4) as a cylindrical shell, and the part where the side plate (5) and the box body (6) are joined has a curvature as a shell. This sudden change in direction causes an out-of-plane bending moment, which requires measures such as thickening the plate and adding reinforcement. In addition, when strong winds such as typhoons act on the antenna, the single box body (6) disturbs the wind flow layer and increases the wind load, so in order to reduce the disturbance, we conducted wind tunnel experiments to find a shape that has less impact on the wind. Based on the results, it is necessary to improve the strength of each part. Furthermore, the shape of the radome (7) is elliptical because it is obtained by cutting a cylinder diagonally, but since the radome (7) is a thin film, this elliptical shape tends to change to a circular shape when strong winds act on it. As a result, the side plate (4)
Not only does secondary stress occur in the antenna, but the entire antenna is deformed, resulting in a change in beam direction.

However, these are not essential issues for offset antennas; they are all done to prevent deterioration of the original electrical and mechanical characteristics of offset antennas, but improvements can be made by using radio wave absorbers and reducing plate thickness. This leads to an increase in manufacturing costs, such as the increase in the number of antennas, and a development procedure that requires a large amount of experimental elements, such as selecting the shape of the hole and the shape of the box body where the radio wave absorber is installed.As a result, it becomes difficult to realize an offset antenna that is inexpensive and has good characteristics. was.

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 offset antenna according to the present invention has a radome with a circular outer circumferential shape, and the inner surface of the gil plate with a conical envelope whose vertices are each point on the outer cylinder of the radome, with the outer circumference of the main reflecting mirror serving as a conductor. , the sub-reflector and the primary radiator are included in the envelope of the reflector, that is, the side plate.

[Effect]

In this invention, since the side plate can cover the transmission path without dividing or blocking the radio waves radiated from the primary radiator, there is no need for a hole for passing Km waves in the side plate, and the side rope characteristic due to the edge of the hole can be avoided. There is no deterioration or deterioration of mechanical strength around the hole. Furthermore, since the side plate of the present invention also serves as the sub-reflector, the primary radiator, and the box covering 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, and FIG. 2 is a front view. In FIG. 1, (1) is a main reflecting mirror.

(2) is a sub-reflector, (3) is a primary radiator, (81 is a transmission line, and these are the same as the conventional device described above.・a・ is a side plate,
Qll is a radome with a circular outer circumference. The shape of the side plate Q is determined as follows. The cone whose apex is a point on the outer circumference of the radome αD with the outer periphery of the main reflecting mirror +11 as a conductor is an elliptic cone and is defined in terms of sea definition. As the apex moves around the outer periphery of the radome αυ, the cone is determined accordingly, but when the apex goes around the outer periphery of the radome αB, an envelope is formed as a collection of these cones. The shape of this envelope is uniquely determined with respect to the main reflection fi (11) once the large diameter or radius of the radome (111) and the relative position between the main reflection mirror (1) and the radome αυ are determined. The sub-reflector (2) and the primary radiator (3) are included inside the radome αD, and the intersecting line between the radome αB and the transmission line (81 is included inside the radome (111).
Determine the radius of and its location.

When the outer peripheral shape of the radome is determined as described above, the envelope is uniquely defined, and the side plate αω with this as the inner shape
The shape of is determined. The surface of this side plate Q1 is generally not a developable curved surface, but as shown in FIG. 3, it equally divides the outer periphery of each of the main reflecting mirror (1) and the radome α9.

Numerical approximation can be developed as a triangular cumulative shape from the actual length between each point.

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 line +81, similar to the conventional device, and form a sharp beam in front of the antenna.

The cone formed by this radio wave is included in the side plate αα.

There is no need for holes or edges created by holes that existed in conventional equipment.
The side plate a does not divide or block the transmission path (8). The edge that causes the deterioration of the negative characteristic of the tab is an unavoidable edge as an antenna, that is, the main reflector Tl.
+ and the outer periphery of the sub-reflector (2) only.

Sidelobe degradation due to the wave-like behavior of radio waves is minimized.

Mechanically, each small part of the side plate α is an elliptic conical shell that is continuous and smooth along the circumference, so it is a shell with a Gaussian curvature of 0, which is the same as the cylindrical shell of the side plate (4) of the conventional device. Approximate to 2, the strength properties are the same, and since there are no holes unlike conventional equipment, the continuity of the shell is maintained, so the strength of the shell can be maximized, and reinforcement measures are not required. Not necessary. Since the box (Gl) of the conventional device also serves as the side plate Ql of the present invention, two boxes (6) are unnecessary, the number of parts is reduced, and the streamline of the wind becomes smooth, so that the wind load does not increase. Furthermore, the outer circumferential shape of the radome αυ is circular, and the joint rigidity with the side plate α is continuous and smooth along the circumference, while secondary stress and changes in the beam direction are small.

This side plate a can be numerically approximated as described above, and can be manufactured by sheet metal processing, so that an offset antenna can be constructed at an extremely low cost.

Therefore, an offset antenna without any characteristic deterioration factors can be realized at an extremely low cost.

〔Effect of the invention〕

The present invention has the effect of realizing the above-described side plate of an offset antenna at a low cost without causing deterioration of electrical and mechanical characteristics by forming the side plate of the offset antenna into a predetermined pyramidal envelope. be.

[Brief explanation of the drawing]

W, Fig. 1 is a side view showing one embodiment of the present invention, Fig. 2 is a front view thereof, Fig. 3 is a developed view of the side plate according to the invention, Fig. 4 is a side view showing a conventional offset antenna, and Fig. 4 is a side view showing an embodiment of the present invention. FIG. 5 is a front view thereof, and FIG. 6 is a partial perspective view of the conventional antenna. In the figure, CI) is the main reflector, +21Vi sub-reflector, (3) is the primary radiator, (4) is the side plate, (5) is the hole, (
6) is a box body, (71 is a radome, f81 is a transmission line, (9
) is the edge, αG is the side plate. αD is a radome. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A main reflecting mirror obtained by cutting a paraboloid of revolution with a plane, a side plate attached to the outer circumference of the main and sub-reflecting mirror, and a sub-reflecting part of the ellipsoid of revolution whose focal point is the focal point of the main reflecting mirror. mirror and
In an offset antenna comprising a primary radiator whose radio wave phase center is at the other focal point of the sub-reflector, and a radome covering the opening side of the side plate, a radome with a circular outer circumferential shape is provided, and the main reflector is A side plate is provided, the inner surface of which is a pyramidal envelope with the outer periphery of the mirror as a conducting wire and each point on the outer periphery of the radome as the apex, and the sub-reflector and the primary radiator are provided inside this side plate. An offset antenna characterized by: