JPH04575Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to an improvement of an antenna device used in a microwave relay line or the like.

[Conventional technology]

Conventionally, as shown in FIG. 1, an antenna device includes a primary radiator 1 having a phase center F ₀ , a first sub-reflector sharing the phase center F ₀ of the primary radiator, and further having a focal point F ₁ . 2. A second sub-reflector 3 that shares the focal point F ₁ and further has a focal point F ₂ and the focal point F ₂
Some mirrors are composed of a main reflecting mirror 4 that is a parabolic mirror of revolution that shares the same characteristics.

In the figure, M ₁ , M ₂ , and M are points along the central axis of the primary radiator 1 at which the emitted light ray 5 hits each mirror surface in turn.

As is clear from the configuration diagram in Figure 1, this antenna is designed based on geometric optics, so the frequency range where geometric optics holds true is D/λ (D: mirror aperture diameter, λ: free space wavelength). ) is very large, the aperture efficiency remains constant over a wide band. However, in an antenna that has a small-diameter sub-reflector with an aperture diameter of 10λ or less, the radio waves have a wave-like spread, so F ₁ , which is the common focal point of the first sub-reflector 1 and the second sub-reflector 2, is It can no longer be confocal, and the focal point of the first sub-reflector 1 is apparently F ₁ ', where M ₂ F ₁ '< M ₂ F ₁ (1) holds, and from this focal point F ₁ ', the Radio waves 6 indicated by the dotted line appear to be emitted. Therefore, in the figure, among the radio waves irradiating the first sub-reflector 2, the radio waves 6 in the portion surrounded by the dotted line are reflected by the first sub-reflector 2 and irradiate the entire surface of the second sub-reflector 3. However, among the radio waves that irradiate the first sub-reflector 2, the radio waves that pass outside the dotted line are reflected and travel toward the second sub-reflector 3, but they all become spillover components, causing deterioration of wide-angle radiation characteristics and aperture The drawback was that it resulted in a decrease in efficiency.

Also, the radio wave 6 reflected by the second sub-reflector 3 is focused on the apparent focal point F ₂ ' of the second sub-reflector 3, determined by geometric optics, according to Snell's law, whether it heads toward the main reflector or not. Since a narrower area is irradiated than the area of the main reflecting mirror, the main reflecting mirror is not used effectively, resulting in a reduction in aperture efficiency.

[Summary of the idea]

In order to solve these drawbacks, this invention has a mirror system configured so that the focal points of the first sub-reflector 2 and the second sub-reflector 3 do not become confocal, and will be described in detail below according to the drawings. explain.

[Example of idea]

Figure 2 shows an example of this invention.
1 is a conical horn serving as a primary radiator, 2 is a first sub-reflector consisting of a rotating quadratic curved mirror, 3 is a second sub-reflector consisting of a rotating quadratic curved mirror, and 4 is a main sub-reflector consisting of a rotating parabolic mirror. It is a reflective mirror.

F ₀ and F ₁ ' are the focal points of the first sub-reflector 2, and F ₀ is also the phase center of the conical horn. Furthermore, F ₁ ,
F ₂ is the focus of the second sub-reflector, and F ₂ is also the focus of the main reflector 4. In FIG. 2, when considered from the perspective of geometrical optics, when the points at which the light ray 5 emitted along the central axis of the conical horn 1 hits each reflecting mirror are M ₁ , M ₂ , and M in order, then F ₀ , F ₁ , F ₁ ′, F ₂ ,
It is assumed that M ₁ , M ₂ , and M are on the same plane, and that F ₁ M ₂ → and F ₁ 'M ₂ → are on the same line.

The shape of the first sub-reflector 2 of this antenna is such that the radio wave 6 radiated from the phase center F ₀ of the conical horn 1 is equivalently focused at the focal point F ₁ of the second sub-reflector 3 in consideration of the wave nature of the radio wave. It is determined that the radiation will be emitted from

That is, the focal point F ₁ ' of the first sub-reflector 2 is
It is determined to satisfy equation (2).

F ₁ 'M ₂ -> F ₁ M ₂ - (2) In the antenna device configured as above, the radio wave 6 radiated from the phase center F ₀ of the conical horn 1 passes through the first sub-reflector 2. As a result, the second sub-reflector 3 is efficiently irradiated, so that the spillover component from the second sub-reflector 3 is almost eliminated, making it possible to achieve low side lobes and high efficiency of the antenna. Furthermore, the radio wave 6 radiated from the phase center F ₀ of the conical horn 1 is equivalently transmitted to the second sub-reflector 3.
Since it is radiated from the focal point F ₁ of
focused at confocal _F2 . Therefore, the main reflecting mirror 4 can be efficiently irradiated, and the efficiency of the antenna can be increased.

In the above description, the conical horn 1 is used as the primary radiator, but the present invention is not limited to this, and any primary radiator having a central axis may be used.

Moreover, although the case where the main reflecting mirror 4 is facing downward has been described above, the present invention can be applied even when the main reflecting mirror 4 is facing upward.

[Effect of idea]

As described above, this invention has the advantage that spillover components from the sub-reflector can be reduced and the main reflector can be efficiently irradiated, making it possible to realize an antenna with high efficiency and low side lobes.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional antenna device, and FIG. 2 is a block diagram of an antenna device showing an embodiment of this invention. In the figure, 1 is the primary radiator, 2 is the first sub-reflector, and 3
is a second sub-reflector, 4 is a main reflector, 5 is a light beam, and 6 is a radio wave. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Scope of utility model registration request] In an antenna device configured such that two sub-reflectors are arranged between a primary radiator and a main reflector, and the sub-reflector near the main reflector focuses radio waves on the focal point of the main reflector. , a secondary reflector close to the primary radiator
R ₁ , the other sub-reflector R ₂ , one focal point of the sub-reflector R ₁ that coincides with the phase center of the primary radiator is F ₀ , the other focal point is F ₁ ′, the main reflection of the sub-reflector R ₂ When considering geometric optics with the confocal point with the mirror as F ₂ and the other focal point as F ₁ , the light rays emitted along the central axis of the primary radiator are reflected on the two sub-reflectors R ₁ and R _2. Correct points in order
M ₁ , M ₂ , and if the point corresponding to the main reflecting mirror R is M, then
F ₀ , F ₁ , F ₁ ′, F ₂ , M ₁ , M ₂ , M are in the same plane, and F ₁ M ₂ → and F ₁ ′M ₂ → are on the same line, and F ₁ ′M ₂ -> F ₁ M ₂ - An antenna device characterized by the following.