JPH0149204B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a satellite communication antenna, and particularly to a satellite communication antenna device for a mobile body that is effective when mounted on a small mobile body.

(Prior Art) Mobile satellite communications, particularly maritime satellite communications that communicate between ships and land and between ships, have been rapidly developing. In such mobile communications, it is necessary to always point the antenna in the direction of the satellite, regardless of rolling, pitching, or other agitation of the mobile body, or movement of the geographical position.
For this purpose, the antenna mounting method and tracking method become problems.

The mounting method is generally Az-El shown in Figure 1a.
2-axis control method using axes, 2-axis control method using X-Y axes shown in b, 3-axis control method using X-Az-El axes shown in c
The axis control system is classified into a four-axis control system using the X-Y-Az-El axes shown in d. Of these, 4 shown in d
The axis control method has been adopted in conventional maritime satellite communications because it has a good perturbation correction accuracy of about 1° to 2°. However, as the number of axes increases in the mounting method, the accuracy of vibration correction improves, but on the other hand, it has drawbacks such as increased weight and size of the system, and increased cost.

On the other hand, tracking methods include a self-tracking method that automatically determines the antenna's tracking direction using incoming radio waves from the satellite, and a program that determines the tracking direction by calculation from the satellite's position information and the moving object's position information. Broadly divided into methods. Among these methods, conventional maritime satellite communication uses a self-tracking method, but the self-tracking method can be applied when the half-power beam width of the antenna used is narrow, and in this case it shows good tracking characteristics. However, it has drawbacks such as the system becoming complicated and expensive.

As mentioned above, conventional maritime satellite communication antenna devices employ a mounting method using four-axis control and a tracking method using self-tracking, and their shape is 1.5 m in height and 1.5 m in diameter (including the radome). The weight is
It weighs around 200Kg. Since such a large and expensive antenna device is required, conventional maritime satellite communication has a major drawback in that it is essentially limited to ships weighing several thousand tons or more, and cannot be used for small ships.

In response, since around 1990, Inmarsat (International Maritime Satellite Communications Organization) has been considering the introduction of a compact system that can be installed on small ships. Such a system is required to be small, lightweight, and inexpensive, and also to have a simple system configuration and easy operation.

A similar antenna device is also required when a mobile body on land or sea receives broadcast radio waves from a broadcasting satellite which will soon be launched in Japan.

(Object of the Invention) The present invention has been made in view of the drawbacks of the prior art described above, and an object of the present invention is to provide a satellite communication antenna device for a mobile object that can be applied to satellite communication by small ships in the future.

(Structure and operation of the invention) The present invention will be described below with reference to illustrated embodiments.

FIG. 2 shows an antenna system according to the present invention, in which 2 is the El axis, 3 is the Az axis, and belts 8, 9
The power of the El drive motor 6 and the Az drive motor 4 is transmitted by this. 5 is an Az angle detector,
Reference numeral 7 denotes an El angle detector, which is used for position information for controlling the drive motors 4 and 6, respectively. Reference numeral 1 denotes the antenna body, which has a structure in which a low noise amplifier 10, a diplexer 11, etc. are arranged on the El axis 2, taking into consideration the weight balance.

The two-axis structure of the Az-El system adopted here is that the arm 15 supporting the El axis 2 has a U-shaped structure as shown in the figure, making it easy to attach the antenna. It is easy to balance the weight even with the antenna, and no balancing weight is required. Therefore, since the load on the Az axis 3 is reduced compared to a normal Az-El mount, the Az axis drive motor 4 can be made smaller, and as a result, the antenna system can be made lighter. or,
In a normal Az[-El mount, due to the shape of the mount, the El axis generally has a driving range from a horizontal state with an elevation angle of 0° to an elevation angle of 90°. It is not possible to drive the pointing direction beyond the zenith direction. With the structure shown in Fig. 2 according to the present invention, the drive range of the El axis can be set up to ±90°, so the El axis 2 can be driven even beyond the zenith direction, and the Az
-It is effective in reducing pointing errors caused by gimbal lock and Az limit, which are common problems with El mounts.

In addition, 12 is a transmitter, 13 is a heat dissipation fin, 1
4 is a radome base. By arranging the heat dissipating fins 13 as shown in the figure, heat can be dissipated from both the radome base 14 and the fins 13, resulting in an efficient configuration.

As the antenna body 1, a parabolic antenna,
A short backfire antenna, a four-element helical antenna, etc. can be used, but as mentioned above, a short backfire antenna and a four-element helical antenna are effective from the viewpoint of reducing size and weight.

Figures 3a and 3b show an example of a short-backfire antenna. In the figure, 30 is a main reflecting plate, 31 is a sub-reflecting plate, 32 is a cross dipole feeding element, and 33 is a cylindrical rim. The radio waves exhibit sharp directivity in the antenna axis direction due to multiple reflections between the two reflecting plates 30 and 31. In particular, by providing a concave portion 34 with a diameter D ₂ and a depth h _s in the main reflecting plate 30 with a diameter D ₁ as shown in the figure, a high gain can be achieved and miniaturization can be achieved.

Further, FIG. 4 shows a four-element helical antenna. The feature of this antenna is that each antenna element 36 is individually housed in a metal cylinder (rim) 37, and by adjusting the height of this rim 37, mutual coupling between the antenna elements 36 is suppressed.
It has improved characteristics. Note that 38 is a matching circuit, and 39 is a combining circuit.

Next, control of the antenna mount axis will be explained with reference to FIG. 5. In Figure 5, 1
2 is the antenna body shown in FIG. 2, 4 and 6 are Az-axis drive motors and El-axis drive motors, respectively, and 21 is a gyro which outputs information regarding the direction of travel of the ship. Reference numerals 22 and 23 are a rolling angle detector and a pitching angle detector, respectively, which are the oscillations of the ship, and output angle information corresponding to the oscillation of the ship. Reference numeral 34 denotes a position information output device that outputs changes in position information due to navigation of the ship, and corresponds to NNSS or the like. In current systems, satellite tracking is performed by self-tracking using a step track, but as mentioned earlier, applying this method to a small antenna system is problematic from a technical, economic, and structural perspective. . Therefore, by obtaining accurate position information of the ship from NNSS, etc., and specifying which satellite it is pointing to in advance, we can know the satellite elevation angle and satellite direction when the ship is not moving. The information and signals from the gyro 21, the rolling angle detector 22, and the pitching angle detector 23 are sent to the computing unit 20.
The drive angles of the Az and El axes required to accurately point the antenna toward the satellite are calculated, and the respective drive motors 4 and 6 are controlled based on the commands.

Note that the rotation angles α' and β' of the Az axis 3 and El axis 2 are given by the following equations, respectively.

α′=sin ^-1 {−sinPcosγcosαcosβ +sinγcosαsinβ +cosγcosPsinα} β′=tan ^-1 {sinPsinγcosαcosβ＋cosαsinβco
sγ−sinαsinγcosP／cosPcosαcosβ＋sinPsinα} Where α: Satellite azimuth angle β: Satellite elevation angle P: Pitching angle γ: Rolling angle With recent advances in microcomputer technology, the computing unit 20
We are now able to provide high-speed and low-cost products,
As a result, the small antenna device shown in FIG. 2 can be easily realized.

(Effects) As explained in detail above, according to the present invention, U
The use of a letter-shaped arm makes it easy to mount the antenna and balance the weight against the El axis, eliminating the need for a balancing weight. Furthermore, Az supporting the U-shaped arm
The load on the shaft is also reduced. Also, from a control point of view, since a U-shaped arm is used, the rotation angle of the El axis can be expanded beyond the zenith, and pointing errors due to gimbal lock can be improved.
[High speed] Precise control is possible. Therefore, the antenna device of the present invention is small in size and has high performance, and is suitable for use on ships, but it is also extremely suitable when installed on aircraft and land-based mobile objects for satellite communication including broadcast reception. It has a very effective effect.

[Brief explanation of drawings]

Fig. 1 a, b, c, and d are control axis configuration diagrams for explaining the control of a conventional antenna device, Fig. 2 is a front view showing an example of the structure of the antenna of the present invention, and Fig. 3 a, b are FIGS. 4a and 4b are a perspective view and a front view showing an example of the antenna used in the present invention; FIGS.
The figure is a block diagram showing an example of an antenna control system used in the present invention. 1...Antenna body, 2...El axis, 3...Az
Axis, 4...Az drive motor, 5...Az angle detector,
6...El axis drive motor, 7...El angle detector, 8,
9...Belt, 10...Low noise amplifier, 11...
Diplexer, 12...Transmitter, 13...Radiation fin, 14...Radome base, 15...Arm, 20...Arithmetic unit, 21...Gyroscope, 22...
...Rolling angle detector, 23...Pitching angle detector, 24...Position information output device, 30...Main reflector, 31...Sub-reflector, 32...Cross dipole feeding element, 33, 37...Rim , 34... recess, 36... antenna element, 38... matching circuit,
39...Synthesis circuit.

Claims (1)

[Claims] 1 Equipped with an Az-El 2-axis mount in which the El axis is supported by a U-shaped arm and the El axis is brought closer to the antenna center axis, and the antenna is directed toward the satellite based on the position information of the moving object and the motion information of the moving object. 1. A satellite communication antenna device for a mobile object, comprising a control function for driving and controlling the El axis and the Az axis to direct the antenna to the antenna.