JP4275645B2 - Beam scanning reflector antenna - Google Patents

Description

  The present invention is a reflector antenna that scans a beam in a conical region or a region that shares an axis and is sandwiched between two cones having different apex angles, and is a beam scanning reflector antenna that drives only the main reflector. About.

  Conventionally, there has been a beam scanning reflector antenna of a type that drives only a main reflector as disclosed in Patent Document 1. This beam scanning reflector antenna is intended to be applied to an antenna device used in the ground station of a mobile communication system using a low-orbit satellite, and is set so that the antenna gain is maximized at the lowest operating elevation angle. Yes. In a low-orbit satellite communication system, the propagation loss increases as the satellite elevation angle decreases. Therefore, by setting the antenna gain to the maximum at the minimum operating elevation angle, the elevation angle characteristic of the propagation loss can be compensated by the elevation angle characteristic of the antenna gain. There is an effect that the gain of the entire system including the loss can be maximized.

Japanese Patent No. 3109584

  In mobile satellite communication systems using geostationary satellites and quasi-zenith satellites, unlike low-orbit satellite communication systems, the distance between the satellite and the ground station in the operating state is constant. Is constant. Therefore, in order to maximize the system gain within the beam scanning range during operation, it is necessary to maximize the minimum gain of the antenna within the beam scanning range during operation.

  Conventionally, however, a reflector antenna that scans a conical region or a region that shares an axis and is sandwiched between two cones with different apex angles, and that only drives the main reflector. However, the antenna configuration that maximizes the minimum gain of the antenna within the beam scanning range has not been clarified.

  The present invention has been made to solve the above-described problems, and in the beam scanning reflector antenna of the type that drives only the main reflector, an antenna configuration that maximizes the minimum gain of the antenna within the beam scanning range. The purpose is to obtain.

Beam scanning reflector antenna according to the invention, installed to emit the primary radiation portion including a primary radiator, and a drivable main reflector, the primary radiation pattern vertically downward the primary radiator, the The mirror surface center of the main reflector is installed vertically below the primary radiation section, and the beam is scanned in the azimuth direction by rotating around the vertical axis passing through the phase center of the primary radiation section, and the phase of the primary radiation section In a beam scanning reflector antenna that scans a beam in an elevation angle direction by tilting the main reflector so that the center is included in the symmetry plane of the main reflector , the main reflector is a parabolic reflector, and from its focal point. The incident angle (angle with respect to the normal line) of the light beam to the mirror surface center of the main reflecting mirror is set to an angle that minimizes the maximum gain reduction due to aberration within the beam scanning range, and the phase of the primary radiation section The distance between the mirror center heart and the main reflector, is obtained by the distance that the maximum value of the gain reduction due to the aberration in the beam scanning direction is minimized.

  Since the present invention is configured as described above, in the beam scanning reflector antenna, there is no gain reduction when the beam is scanned in the azimuth direction, and the main factor of the gain reduction is when the beam is scanned in the elevation direction. Occurrence of certain astigmatism can be suppressed, and a decrease in gain can be suppressed.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a schematic configuration of the first embodiment related to the beam scanning reflector antenna of the present invention. In the figure, 1 is a primary radiator constituting the primary radiation section, 2 is a phase center of the primary radiator, 3 is a parabolic reflector which is a main reflector, 4 is a focal point of the parabolic reflector 3, and 5 is a main reflector. The center of the mirror surface of a certain parabolic reflector 3, 6 is the parabolic axis of the parabolic reflector 3, 7 is the beam direction, 8 is the main reflector driving mechanism, and 9 is the azimuth rotation axis.
FIG. 1A shows a case where the phase center 2 of the primary radiator 1 coincides with the focal point 4 of the parabolic reflector 3, and in the case of on-focus, FIG. 1B scans the beam in the Θ ₁ direction where the angle from the zenith is the smallest. In this case, (c) shows the case where the beam is scanned in the Θ ₂ direction where the angle from the zenith is the largest.

The primary radiator 1 constituting the primary radiation section is installed so as to radiate a primary radiation pattern vertically downward. The parabolic reflector 3, which is the main reflector, is installed so that its mirror surface center 5 is vertically below the primary radiator 1, and the incident angle of light rays from the focal point 4 to the mirror surface center 5 (angle with respect to the normal line n). ) Is θ ₀ . The azimuth rotation axis 9 is a vertical axis that passes through the phase center 2 and the mirror center 5 of the primary radiator 1.

Next, a schematic operation of beam scanning will be described with reference to FIG. For convenience of explanation, the case of transmission will be described as an example, but it is obvious that the antenna operates in the same manner also in the case of reception because the antenna is reversible. First, with reference to FIG. 1A, the case of on-focus where the phase center 2 of the primary radiator 1 is at the focal point 4 of the parabolic reflector 3 will be described. The radio wave radiated vertically downward from the primary radiator 1 operating as the primary radiating unit is reflected by the parabolic reflector 3 operating as the main reflecting mirror, and radiates a beam in the direction of the parabolic axis 6. At this time, due to symmetry, the parabolic reflector 3 can be scanned on a conical surface having a half apex angle 2θ ₀ without rotating by rotating the parabolic reflector 3 about the azimuth rotation axis 9.

Next, a case where the beam elevation angle is scanned in the zenith direction from the case of on-focus and the beam scanning angle from the zenith is set to the minimum value Θ ₁ will be described with reference to FIG. At this time, the main reflector driving mechanism 8 includes the parabolic reflector 3 in which the mirror center 5 is vertically below the phase center 2 of the primary radiator 1 and the phase center 2 is included on the symmetry plane of the parabolic reflector 3. To drive.

  In general, in an antenna that scans a beam by driving only the main reflecting mirror as the main reflecting mirror, the parabolic reflecting mirror is defocused and fed during beam scanning, so that aberration occurs and the gain decreases. Gain reduction when a parabolic reflector is defocused is described in the literature “Naito, et al.,“ Single-reflector-type large beam separation angle multi-beam antenna ”, Science theory (B-II), vol. J77-B- II, no. 10, pp. 528-538, Oct. 1994 ”. From this document, it can be seen that astigmatism, which is the main cause of gain reduction, is minimized when power is supplied from within the plane of symmetry of the parabolic reflector. In FIG. 1B, the parabolic reflector 3 is driven so that the phase center 2 of the primary radiator 1 is included on the symmetry plane of the parabolic reflector 3, so that power is fed from within the symmetry plane of the parabolic reflector 3. Gain reduction during scanning can be minimized. When the beam is scanned in the azimuth direction, the parabolic reflector 3 is rotated about the azimuth rotation axis 9 as in the case of the on-focus in FIG. The beam can be scanned without any performance degradation due to the above.

As shown in FIG. 1C, when the beam elevation angle is scanned in the horizontal direction from the on-focus case and the scanning angle from the zenith is set to the maximum value Θ ₂ , the operation is the same as in FIG. It is obvious to do.

In addition, the parabolic reflector 3 has an incident angle (an angle with respect to the normal n) θ ₀ of the light beam from the focal point 4 to the mirror center 5 so that the maximum value of gain reduction due to aberration within the beam scanning range is minimized. The distance l (small L) between the phase center 2 and the mirror surface center 5 is set according to the beam scanning direction so that the gain reduction due to aberration is minimized.

In general, the above-mentioned document “Naito, et al.,“ Single-reflector-type large beam separation angle multi-beam antenna ”, Theological theory (B-II), vol. J77-B-II, no. 10, pp. 528-538, Oct. 1994 ", the main causes of gain reduction during beam scanning are astigmatism and field curvature. Astigmatism is determined independently by angle θ ₀ and field curvature by distance l. Is done. Therefore, the angle θ ₀ is designed so as to minimize the maximum amount of astigmatism generated within the beam scanning range, and the distance l is set so that the curvature of field is minimized according to the beam scanning direction. be able to. However, in reality, aberrations other than astigmatism and field curvature occur, resulting in a decrease in gain. Therefore, at an angle θ ₀ and a distance l designed only considering astigmatism and field curvature, Deviation from the value that minimizes the gain drop occurs. This deviation is about 5 degrees at the maximum at the angle θ ₀ and about 5% at the distance l. Therefore, the angle θ ₀ and the distance l designed in consideration of only astigmatism and field curvature are set as initial values, and the angle θ ₀ and the distance l are changed within the predicted range of deviation, thereby reducing the gain due to the aberration. The optimum value that minimizes is determined.

The angle that minimizes astigmatism within the beam scanning range, which is the initial design value of the angle θ ₀ , is given as follows. FIG. 2 shows the literature “Naito, et al.,“ Single-reflector type large beam separation angle multi-beam antenna ”, the theory of theory (B-II), vol. J77-B-II, no. 10, pp.528-538, Oct. 1994 "is a diagram showing a coordinate system and parameters when a parabolic reflector is defocused. From this document, when the defocus angle is constant, astigmatism, which is a main factor of gain reduction, is minimized when power is supplied from within the symmetry plane of the parabolic reflector.

Now, θ is changed over an angle range of θ ₁ to θ ₂ corresponding to the beam scan of the elevation angle. In this case, the maximum value of the coefficient C ₂ astigmatism be minimized, thereby maximizing the minimum gain in the beam scanning range. This condition is given by the following equation.

ここで、αはビーム偏向係数（beam deviation factor）で、幾何光学的なビーム偏向方向と実際のビーム偏向方向との比を与える係数で、例えば図４に引用した、文献「Y.T. Lo, "On the Beam Deviation Factor of a Parabolic Reflector," IRETrans. AP−8, 3, pp.347−349」に記載されているように、鏡面構成によって決まる0.6〜1.0の間の定数である。 Next, the relationship between the primary radiator 1 angle of incidence angle from the phase center 2 to the mirror center 5 θ (θ1~θ ₂₎ a beam scanning angle angle theta from the zenith (theta ₁ through? _2), 3 Will be described. In the figure, 1 to 9 are the same as those shown in FIG. 1 and function in the same manner. θ ₀ is an incident angle from the focal point 4 of the parabolic reflector 3 to the mirror surface center 5, and n is a normal vector at the mirror surface center 5. From the figure, the beam scanning angle Θ from the zenith is the incident angle θ from the phase center 2 of the primary radiator 1 to the mirror center 5, the angle θ ₀ between the normal vector at the mirror center 5 and the parabolic axis 6, the parabolic axis 6 and the angle α (θ−θ ₀ ) between the beam direction 7 and Θ = θ + θ ₀ + α (θ−θ ₀ ). Therefore, θ is given by the following equation using the beam scanning angle Θ from the zenith.

Here, α is a beam deviation factor, which is a coefficient that gives a ratio between the geometric optical beam deflection direction and the actual beam deflection direction. For example, reference “YT Lo,“ On ”cited in FIG. As described in the Beam Deviation Factor of a Parabolic Reflector, “IRETrans. AP-8, 3, pp.347-349”, it is a constant between 0.6 and 1.0 determined by the mirror configuration.

Next, the effect of the first embodiment configured using the relationship described above will be described with reference to FIGS. FIG. 5 is a diagram showing astigmatism during beam scanning and the amount of gain reduction due to astigmatism in the first embodiment. Here, Θ ₁ = 30 °, Θ ₂ = 60 °, l ₀ (Small L Zero) = 250 mm, and the beam deflection coefficient α = 0.9. Gain reduction is evaluated at a frequency of 12 GHz. Θ ₀ obtained by the present invention with a solid line is θ ₀ = 23.9195 deg. For comparison, the characteristics B, C, and D when θ ₀ different from that of the present invention are indicated by broken lines. It can be seen that by setting θ ₀ according to the present invention, the maximum value of the amount of astigmatism generated within the beam scanning range is minimized, and the worst value of gain reduction due to astigmatism is minimized. Since FIG. 5 is evaluated in consideration of only astigmatism, as described above, θ ₀ shifts by about 5 degrees at the maximum when other aberrations occur.

FIG. 6 is a diagram showing another example of astigmatism and gain reduction during beam scanning related to the beam scanning reflector antenna of the present invention. Here, Θ ₁ = 0 °, Θ ₂ = 30 °, l ₀ = 250 mm, and the beam deflection coefficient α = 0.9 are designed. Gain reduction is evaluated at a frequency of 12 GHz. Θ ₀ obtained by the present invention with a solid line is θ ₀ = 10.795 deg. For comparison, the characteristics B, C, and D when θ ₀ different from that of the present invention are indicated by broken lines. It can be seen that by setting θ ₀ according to the present invention, the maximum value of the astigmatism generation amount within the beam scanning range can be minimized and the worst value of gain reduction can be minimized. Since FIG. 6 is evaluated only considering astigmatism, as described above, θ ₀ shifts by about 5 degrees at the maximum when other aberrations occur.

Embodiment 2. FIG.
FIG. 7 is a diagram showing a schematic configuration of the second embodiment related to the beam scanning reflector antenna of the present invention. In the figure, 1 to 9 are the same as those shown in FIG. 1 and function in the same manner. Reference numeral 10 denotes an elevation angle rotation axis of the main mirror, which is an axis that passes through the mirror center 5 of the parabolic reflector 3 that is the main reflecting mirror and is perpendicular to the symmetry plane of the parabolic reflector 3. In this embodiment, the distance between the phase center 2 of the primary radiator 1 and the mirror surface center 5 of the parabolic reflector 3 is set to a constant value ₁₀ and the parabolic reflector 3 is driven in the elevation direction with the elevation rotation axis 10 as the center. Therefore, the main reflector driving mechanism 8 can be simplified.

Next, it will be described with reference to FIG. 8 that even if the distance between the phase center 2 of the primary radiator 1 and the mirror surface center 5 of the parabolic reflector 3 is set to a constant value _10, there is substantially no inconvenience. FIG. 8 shows the distance l (small L) between the phase center 2 of the primary radiator 1 and the mirror surface center 5 of the parabolic reflector 3 in Embodiment 1 between the focal point 4 and the mirror surface center 5 of the parabolic reflector 3. the distance l ₀ a normalized value is a graph showing with respect to the beam scanning angle from the zenith. From this graph, in the beam scanning range of angles 30 to 60 ° from the zenith, the difference from the distance l ₀ of the distance l is very small and less than 0.2% and substantially the distance l as the constant value l ₀ It turns out that there is no inconvenience.

Embodiment 3 FIG.
FIG. 9 is a diagram showing a schematic configuration of the third embodiment related to the beam scanning reflector antenna of the present invention. In the figure, 2 to 9 are the same as those shown in FIG. 1 and function in the same manner. 11 is a backfire primary radiator which comprises a primary radiation part. In this embodiment, since the self-supporting backfire primary radiator 11 that does not require a support structure is used as the primary radiation portion, a support structure portion that is indispensable for a normal primary radiator such as a horn becomes unnecessary. The configuration of the antenna can be simplified.

Embodiment 4 FIG.
FIG. 10 is a diagram showing a schematic configuration of the fourth embodiment related to the beam scanning reflector antenna of the present invention. In the figure, 3 to 9 are the same as those shown in FIG. 1 and function in the same manner. Reference numeral 1 denotes a primary radiator that radiates vertically upward, and reference numeral 12 denotes a rotating hyperboloid mirror that operates as a sub-reflecting mirror. The primary radiator 1 and the rotating hyperboloid mirror 12 constitute a Cassegrain type primary radiation section. 2 is the phase center of the primary radiation part of the Cassegrain type. In this embodiment, the height of the antenna can be reduced by configuring such a Cassegrain type primary radiation section.

It is a schematic block diagram of the beam scanning reflector antenna by Embodiment 1 of this invention. FIG. 3 is a reference diagram from a literature showing a coordinate system and parameters when a parabolic reflector is defocused to explain the beam scanning characteristics of the beam scanning reflector antenna according to the first embodiment of the present invention. It is a figure explaining the relationship between the incident angle of the light ray from the phase center of the primary radiator of the beam scanning reflector antenna by Embodiment 1 of this invention to the mirror surface center, and the beam scanning angle from a zenith. It is a reference figure from literature explaining the beam deflection coefficient of the beam scanning reflector antenna according to the first embodiment of the present invention. It is a figure which shows the astigmatism at the time of beam scanning, and the gain fall by this by the beam scanning reflector antenna by Embodiment 1 of this invention. It is a figure which shows the other example of the astigmatism at the time of beam scanning and the gain fall by this of the beam scanning reflector antenna by Embodiment 1 of this invention. It is a schematic block diagram of the beam scanning reflector antenna by Embodiment 2 of this invention. FIG. 6 is a diagram for explaining that there is substantially no inconvenience even when the distance between the phase center of the primary radiator and the center of the parabolic reflector of the beam scanning reflector antenna according to the second embodiment of the present invention is set to a constant value l ₀ . is there. It is a schematic block diagram of the beam scanning reflector antenna by Embodiment 3 of this invention. It is a schematic block diagram of the beam scanning reflector antenna by Embodiment 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary radiator 2 Phase center 3 Parabola reflector 4 Focus 5 Mirror surface center 6 Parabola axis 7 Beam direction 8 Main reflector drive mechanism 9 Azimuth rotation axis 10 Elevation angle rotation axis 11 Backfire primary radiator 12 Rotating hyperboloid mirror

Claims (5)

A primary radiator including a primary radiator and a drivable main reflector ;
The primary radiation part is installed so as to emit a primary radiation pattern vertically downward,
The mirror surface center of the main reflecting mirror is installed vertically below the primary radiation part,
Scanning the beam in the azimuth direction by rotating around the vertical axis passing through the phase center of the primary radiation section,
In a beam scanning reflector antenna that scans a beam in an elevation angle direction by tilting the main reflector so that the phase center of the primary radiation portion is included in a symmetry plane of the main reflector ,
The main reflector is a parabolic reflector, and the incident angle of light rays from the focal point to the center of the mirror surface of the main reflector (the angle with respect to the normal line) is minimized within the beam scanning range. Angle and
The beam scanning reflection characterized in that the distance between the phase center of the primary radiating portion and the mirror surface center of the main reflecting mirror is a distance that minimizes the maximum gain reduction due to aberration in the beam scanning direction. Mirror antenna. The rotation center of the mirror surface of the elevation direction, passes through the center of the main reflector, claim 1 Symbol mounting beam scanning reflector antenna is characterized in that the axis perpendicular to the plane of symmetry of the main reflector. Claim, characterized in that the beam scanning range, and a region sandwiched between cone cone and half apex angle theta ₂ half apex angle theta ₁ from the zenith _{(0 ≦ Θ 1 <Θ 2} ) 1 or 2 A beam scanning reflector antenna as described. 4. The beam scanning reflector antenna according to claim 3 , wherein a half apex angle Θ ₁ = 0 and the beam scanning range is a conical region having a half apex angle Θ ₂ . The beam scanning reflector antenna according to any one of claims 1 to 4 , wherein the primary radiating section includes a primary radiator and a rotating hyperboloid mirror.

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