JPH07307616A - Antenna device for mobile earth station - Google Patents

Abstract

PURPOSE:To miniaturize an antenna device for a mobile earth station, to make it light in weight and to track the azimuth of a satellite for all azimuth angles by attaining a structure provided with a rotatable sub-reflection mirror and the main reflection mirror of a tourus shape and providing a tracking mechanism capable of tracking the azimuth of the satellite in an antenna itself. CONSTITUTION:Incident waves from an X-Y direction are reflected at the range P-Q of a part of the circumference of a tourus cross section. Thus, radio waves reflected by the main reflection mirror 1 become spherical waves and advance so as to be gathered at a focus point F which is the middle of the circumference and a center. The radio waves tentatively gathered at the F are spread again and reflected again on the surface P'-Q' of the sub-reflection mirror 2. Since the sub-reflection mirror 2 is a part of a rotating ellipse, similarly to the time of a longitudinal section, the radio waves passed through one of the focus point and reflected by the sub-reflection mirror 2 are gathered at the other focus point F'. When it is defined as the phase center position of a primary radiator 3, all the radio waves reflected by the main reflection mirror 1 and the sub-reflection mirror 2 are gathered at the position of the primary radiator 3. At the time of transmission, only the advancing direction of the radio waves is reversed, complete reversibility is realized and an antenna beam can be turned to all the directions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna device for a mobile earth station mounted on a mobile body such as an automobile or a ship in a mobile satellite communication system.

[0002]

2. Description of the Related Art In an antenna device for a mobile earth station using a directional antenna, it is necessary to always direct the beam of the antenna toward the geostationary satellite and track it. Therefore, conventionally, a technique has been used in which a tracking mechanism capable of separately driving and controlling an elevation angle direction and an azimuth angle direction is provided separately from the antenna body, and an antenna is installed on the tracking mechanism to track a satellite. However, in view of the angular width of the beam width of the antenna, the range of elevation angle change with respect to the geostationary satellite is small, and a moving body with a limited range of movement that can be considered to be almost constant is limited to tracking in the azimuth direction only. The tracking mechanism has been simplified. The tracking mechanism detects the movement of the moving body in the azimuth direction and cancels the movement of the moving body in the azimuth direction by performing the opposite rotational movement to hold the antenna so that it always faces the satellite. In order to prevent the signal line from the antenna from getting entangled with the rotation axis even when the body continues to rotate in one direction,
Conventionally, a rotary joint (a component that allows high-frequency signals to pass through the rotating part) has been used.

[0003]

However, in the conventional structure in which the antenna and the tracking mechanism are separated from each other, the whole antenna device becomes large and complicated, and it is difficult to mount it on a small moving body, and the cost becomes high. was there. In addition, since a precise rotary joint is required for the tracking mechanism, there are problems in terms of reliability and deterioration of signal quality due to passage loss of high frequency signals.

Therefore, according to the present invention, in an antenna of a mobile earth station which does not require tracking in the elevation angle direction, the antenna itself has a tracking mechanism, and further, satellite direction tracking is enabled without using a rotary joint, and the device It is an object of the present invention to provide an antenna device for a mobile earth station, which can be reduced in size, weight, price and reliability.

[0005]

In order to solve the above problems, in a mobile earth station antenna apparatus according to the present invention, a parabola is rotated around a central axis that is perpendicular to the surface of the antenna base and passes through its center. The parabolic surface obtained by
A main reflector with an inner curved surface that approximates the partial shape of the torus surface that is cut into two slices perpendicular to its center axis; and has a surface that is cut out from a part of the spheroid. A sub-reflecting mirror whose rotation axis is installed with a certain inclination from the torus center axis and which rotates around the torus center axis; and an antenna by controlling the amount of rotation of the sub-reflecting mirror. Tracking control means for always matching the beam azimuth angle of the satellite and the azimuth angle of the satellite; and a primary radiator having a structure fixed to the antenna base so as to irradiate the sub-reflecting mirror upward on the central axis of the torus. A structure including;

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of an antenna device for a mobile earth station according to the present invention will be described in detail with reference to the accompanying drawings.

First, the principle of the antenna device of the present invention is shown in FIG.
~ It demonstrates by FIG. FIG. 1 is a schematic perspective view of an antenna structure including a main reflecting mirror 1, a sub-reflecting mirror 2 and a primary radiator 3, in which radio waves from the satellite direction pass through the main reflecting mirror 1 and the sub-reflecting mirror 2 and the primary radiator is shown. It shows that the focus is on 3. This basic principle can be easily understood by grasping the reflection state of radio waves in a vertical section including the central axis of the torus and a horizontal section orthogonal to the central axis of the torus. These longitudinal section and transverse section are shown in FIGS. 2 and 3, respectively.

FIG. 2 is a geometrical optical drawing of how a radio wave travels on a vertical section including the central axis of the torus. Since the source of the radio wave from the satellite is far, it becomes a plane wave and enters from the XY directions. Since the cross section of the main reflecting mirror is a parabola, it is reflected by the surface PQ of the main reflecting mirror, and the reflected wave becomes a spherical wave and proceeds so as to be focused on the focal point F. The parabola is set so that the position of the focal point F is located at the center of the main reflecting mirror surface and the central axis of the torus, and the inclination of the parabola axis matches the satellite elevation angle. The radio waves once gathered at F spread again,
It is reflected again on the surface P'-Q 'of the sub-reflecting mirror. The sub-reflector is part of a spheroid and its longitudinal section is elliptical.
It is well known in geometric optics that an ellipse has two focal points, and light emitted from one focal point is focused on the other focal point. Therefore, make one focus of the ellipse coincident with F,
If the other focus is an ellipse that is placed on the central axis of the torus, the radio waves reflected by the sub-reflecting mirror will be collected at the second focus F ′. If this is taken as the phase center position of the primary radiator, it can be used as an offset Gregorian antenna (a double-reflector antenna with a real focal point between the main reflector and the subreflector, and the central axes of the two reflectors do not match). Will be equivalent.

Next, FIG. 3 is a geometrical-optical drawing of a cross-section orthogonal to the central axis of the torus and a projection of the propagation of radio waves on the cross-section. As described above, the plane wave enters from the XY directions. In this case, the cross section of the main reflecting mirror is a circle, but it is well known from geometrical optics that the area where the circumference is not large approximates a parabola, and its focus is in the center of the circumference and its center. Widely applied to reflection telescopes. The incident wave from the XY direction is reflected in a partial range PQ of the circumference of the torus cross section. Therefore,
The radio wave reflected by the main reflecting mirror becomes a spherical wave, and proceeds so as to be focused on a focal point F in the center between the circumference and the center. The radio waves once gathered at F spread again and the surface P'- of the subreflector
It is reflected again at Q '. Since the sub-reflecting mirror is a part of the spheroid, the radio waves passing through one focus and reflected by the sub-reflecting mirror are focused on the other focus F ′ as in the case of the longitudinal section. If this is set as the phase center position of the primary radiator, all the radio waves reflected by the main reflecting mirror and the sub-reflecting mirror gather at the position of the primary radiator.

The above has described how the radio waves travel when this antenna receives radio waves from a satellite. However, at the time of transmission, only the traveling directions of the radio waves are reversed, and perfect reversibility is established. With such a structure, when only the sub-reflecting mirror is rotated around the central axis of the torus, the antenna beam can be directed in all azimuth directions.

In the above explanation, it was considered that a part of the circle which is not large at the time of the cross section is approximated to a parabola.
It is necessary to estimate in what size range this approximation can be used. Therefore, the path difference (unit: mm) when the light is reflected at an arbitrary point P on the main reflecting mirror and reaches the focus F and when it is reflected at the reference point R and reaches the focus F is calculated. The parameters used for the calculation are shown in FIG. 4, and the table of the calculation results is shown in Table 1.

[0012]

[Table 1]

In FIG. 4, a plane S is a virtual plane orthogonal to a virtual line connecting the antenna and the satellite, and all phases of radio waves are aligned on this plane. Radio waves are assumed to be incident from the elevation angle of 45 °. A point Q is an intersection of a line passing through the focal point F and orthogonal to the central axis of the torus and the torus surface, and this point is a reflection reference point. Point P is an arbitrary reflection point on the torus surface,
The position is displayed in polar coordinates viewed from the point O. That is,
The angle in the vertical direction of the point P is θ, and the angle in the horizontal direction is φ. The calculation result in the table shows that the difference between the path X-PF and the path Z-RF is mm when the radius OR of the circle passing through the reference point R on the surface of the torus and orthogonal to the central axis of the torus is 100 mm.
It is expressed in units, and is the result of calculating θ and φ every 2 °. If the path difference is about 1/10 of the wavelength, it can be said to be a practically acceptable range.

From this table, for example, assuming that the radius to the central axis of the torus is 100 mm and the frequency of the radio wave is 30 GH.
It can be seen that when z (wavelength 10 mm), θ and φ are in the range of −30 ° to 30 ° and −12 ° to 12 °, respectively, it is sufficiently practical. When the frequency is higher, the path difference becomes larger than the wavelength. Therefore, by slightly modifying the mirror surface of the sub-reflecting mirror from the spheroid, the path difference that is practically acceptable can be accommodated. Such a mirror surface correction technique has already been put to practical use in various reflector antennas. In addition, the shape of the inner curved surface that is the reflecting surface of the main reflecting mirror 1 does not necessarily have to be a paraboloid of revolution, and even if the shape is made to exactly match the partial shape of the torus surface obtained by rotating the arc, the path difference It can be practically used in a small range.

Next, a specific embodiment of the present invention shown in FIG. 5 will be described. In the figure, 1 is a torus-shaped main reflecting mirror. The width of the torus in the vertical direction is set so that the amount of transmitted radio waves emitted from the primary radiator 3 and reflected by the sub-reflecting mirror 2 toward the main reflecting mirror 1 leaks to the outside sufficiently. If this width is large, the gain of the antenna is large but the beam width in the elevation direction is narrowed. If it is small, the gain is small but the beam width in the elevation direction is large. In the case of a vehicle-mounted mobile earth station, the inclination of the main road is within 5 °, so it is considered appropriate to set the beam width in the elevation direction to about 10 °.

Reference numeral 2 in the drawing denotes a sub-reflecting mirror having a shape obtained by cutting a part of a spheroid. The primary radiator 3 is installed with an appropriate inclination so as to reflect the transmitted radio waves so as to enter the upper and lower widths of the main reflecting mirror 1. Since the directivity of the primary radiator 3 needs to be rotationally symmetric with respect to the central axis, cutting the ellipsoid into a circular shape when viewed from directly above is a wasteless shape.

The edge of the sub-reflecting mirror 2 is supported by a column and is fixed to a rotating ring 4 mounted on an antenna base 6. Although the pillar is rod-shaped in the figure, it may be a cylindrical one in which only the portion through which radio waves pass is hollowed out. In the case of a cylinder, the part can be manufactured integrally with the rotating ring. The rotary ring 4 is rotated by a drive motor 5 about the central axis of the torus. Therefore, the sub-reflecting mirror 2 also rotates around the central axis of the torus by this rotating mechanism. Although the drive mechanism shown in this drawing is configured to directly transmit the rotational force of the drive motor 5 to the rotary ring 4 to rotate the rotary ring 4 as a follower, the drive mechanism is not limited to this. For example, the rotary shaft of the drive motor 5 may be installed parallel to the central axis of the torus, and the rotary ring 4 may be indirectly driven by the power transmission means such as a pulley and a belt.

Reference numeral 3 in the drawing is a primary radiator, and since the antenna gain and beam shape are the same no matter which direction the sub-reflecting mirror 2 faces, its directivity is symmetrical with respect to the central axis. It must have a pencil-type directional pattern. Specifically, any antenna element having a pencil type directional characteristic such as a horn antenna or a patch antenna may be used. In the case of a horn antenna, there is an advantage that a wide bandwidth can be obtained, but the height of the entire antenna becomes large due to the long and thin shape. In the case of a patch antenna, the height of the whole antenna can be reduced because it is very thin, but since the bandwidth becomes narrow, it may be difficult to perform both transmission and reception when the frequency difference between transmission and reception is large.

Reference numeral 6 in the drawing denotes a base, which supports the whole and is fixed to the surface of the moving body, for example, the roof of the automobile. In the figure, the size is larger than the main reflecting mirror 1 for the sake of easy understanding, but in actuality, it is sufficient if the size is large enough to support the main reflecting mirror.

Although not shown here, in order to operate as a mobile earth station antenna device, a tracking device serving as tracking control means is required inside the moving body. The tracking device uses a drive signal so that the azimuth of the beam of the antenna always matches the azimuth direction of the satellite by using the received signal from the antenna, the signal from the sensor that detects the traveling direction of the moving body, or both signals. 5 is a device for controlling 5.

In addition, in order to perform communication as a mobile earth station, it is necessary to have a transmitter / receiver inside the mobile unit. Further, this device can be used not only as a communication antenna device for both transmission and reception but also as a reception-only antenna device such as a satellite broadcasting receiver.

[0022]

As described above, according to the antenna apparatus for a mobile earth station of the present invention, since the rotatable sub-reflecting mirror and the torus-shaped main reflecting mirror are provided, the satellite azimuth tracking is possible. The antenna itself can have a unique tracking mechanism, and no rotary joint is required. Therefore, the antenna device for a mobile earth station can be made smaller, lighter, less expensive, and more reliable.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing the basic principle of an antenna device for a mobile earth station according to the present invention.

FIG. 2 is a diagram showing paths of radio waves on a cross section including a central axis, which shows a basic principle of an antenna device for a mobile earth station according to the present invention.

FIG. 3 is a cross-sectional view showing a basic principle of the antenna device for a mobile earth station according to the present invention, the cross-section being perpendicular to the central axis, and a radio wave path projected on the cross-section.

FIG. 4 is a diagram for explaining parameters when calculating a path difference between a path of a radio wave reflected at an arbitrary point on the main reflector of the antenna apparatus for a mobile earth station according to the present invention and a reference path. .

FIG. 5 is a perspective view showing an embodiment of the present invention.

[Explanation of symbols]

 1 main reflecting mirror 2 sub-reflecting mirror 3 primary radiator 4 rotating ring 5 drive motor 6 base

Claims (1)

[Claims] 1. An antenna device for a mobile earth station, comprising a tracking mechanism for making the beam direction of an antenna always coincide with a satellite direction, and carrying out communication with a geostationary satellite when mounted on a mobile body on land or on water, Partial shape of a torus surface obtained by cutting a paraboloid of revolution obtained by rotating a parabola around a central axis perpendicular to the surface of the antenna base and passing through its center into two planes perpendicular to the central axis. It has a main reflecting mirror with an inner curved surface that approximates to, and a surface of a spheroid with a part cut off, and its rotation axis is installed with a certain inclination from the center axis of the torus. A sub-reflecting mirror having a structure for rotating the sub-reflecting mirror, and tracking control means for always matching the azimuth of the beam direction of the antenna with the azimuth of the satellite by controlling the amount of rotation of the sub-reflecting mirror. An antenna device for a mobile earth station, comprising: a primary radiator having a structure fixed to an antenna base so as to irradiate a sub-reflecting mirror upward on a central axis of a torus.