AU687278B2

AU687278B2 - Mobile earth station antenna apparatus

Info

Publication number: AU687278B2
Application number: AU40298/95A
Authority: AU
Inventors: Yoshihiro Hase; Ryutaro Suzuki
Original assignee: Communications Research Laboratory
Current assignee: National Institute of Information and Communications Technology
Priority date: 1994-12-07
Filing date: 1995-12-07
Publication date: 1998-02-19
Anticipated expiration: 2015-12-07
Also published as: JPH08162833A; AU4029895A; JP2642889B2; CA2164545A1

Description

P/00/011 Regulation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

TO BE COMPLETED BY APPLICANT Name of Applicant: COMMUNICATIONS RESEARCH LABORATORY, MINISTRY OF POSTS AND TELECOMMUNICATIONS Actual Inventor(s): Yoshihiro HASE; Ryutaro SUZUKI Address for Service: CALLINAN LAWRIE, 278 High Street, Kew, 3101, Victoria, Australia Invention Title: "MOBILE EARTH STATION ANTENNA APPARATUS" The following statement is a full description of this invention, including the best method of performing it known to me:- _1_1 MOBILE EARTH STATION ANTENNA APPARATUS The present invention relates to a mobile earth station antenna apparatus that includes a directional antenna and a satellite tracking system, for a mobile satellite communications system mounted in a mobile unit such as a car or marine vessel.

In the case of a mobile earth station having a directional antenna, in order to constantly track a satellite the antenna has to be moved to compensate for variations in the attitude of the mobile unit.

Conventionally the following technology has been used as the tracking mechanism of a mobile earth station antenna.

*i *To enable the antenna to be oriented in any direction of all hemisphere, the antenna is usually provided with a combination of two mutually perpendicular axes of rotation in a vertical plane, which are the azimuth e and elevation (hereinafter referred to as "Az-EI axes"), or two mutually perpendicular axes in the horizontal plane (hereinafter referred to as "X-Y axes"), with each axis having its own motor drive.

A feature of the Az-EI axes drive is that it can be made light and compact, especially when the mobile unit concerned has a small range of movement, such as a car on land or a coastal marine vessel. The reason why this is possible is that since the elevation angle of the satellite is substantially constant within the range of movement, the elevation axis drive can be dispensed with, and just an azimuth axis drive used.

A feature of the X-Y axes drive is that it does not require an RF (radio frequency) rotary joint which is a special rotary joint permitting passage of RF signals therethrough, since there is no azimuthal rotation of the antenna relative to the antenna base. This makes it I ~s C CI

I

2 possible to use ordinary coaxial cable to feed an RF signal to the antenna.

For keeping the antenna beam oriented toward the satellite, a tracking control apparatus can be used in which the direction of the antenna beam is obtained by using sensors to measure the azimuth angle in the direction of progress of the mobile unit and the angle of inclination relative to the horizontal plane of the mobile unit.

Another way is to use trial-and-error control to orient the beam so that the signal received from' the satellite is always maintained at its maximum strength. Alternatively, a combination of the above two methods can be used.

*However, while in the case of an Az-El axes drive only one motor is required, thereby reducing the size of the apparatus, the continuous rotation of the antenna in the one direction means that it is not feasible to use a coaxial cable or other such means of directly connecting the antenna to the base to feed an RF signal to the antenna. Instead, it is necessary to employ an RF rotary joint through which an RF signal can be transmitted. Such an arrangement can adversely affect the reliability of the apparatus, degrade the performance owing to signal loss, and increase the cost. The X-Y axes drive does not require an RF rotary joint, since there is no azimuthal rotation of the antenna relative to the base. ic.;ever, even in cases in which the satellite elevation iz monxoe or less constant and therefore elevational tracking is not required, two motors are still required, which increases the size and cost of the apparatus. Thus, in neither the Az-El axes drive or the X-Y axes drive arrangement has been possible to dispense with the need for an RF rotary joint while at the same time achieving a small, light apparatus.

An object of the present invention is to provide, in a mobile earth station in which elevational tracking is not required, a mobile earth station antenna apparatus .I which can perform azimuthal satellite tracking without using costly RF rotary joints and which is light, compact, low-cost, and highly reliable.

To attain the above object, the present invention provides a mobile earth station antenna apparatus, comprising a base located on a virtual horizontal plane surface, a rotary member located on the base, the rotary member having a surface inclined at a satellite elevation angle relative to the virtual horizontal plane, a first hollow rotary joint that rotatably connects the rotary member to the base and has a rotation axis perpendicular to the base, an antenna located on the inclined surface of the rotary member with a feed point at the center of the antenna, a second hollow rotary joint having an axis of rotation inclined to a satellite elevation angle, the second hollow rotary joint rotatably connecting the antenna e to the inclined surface of the rotary member, an RF signal eo cable that passes through hollow portions of the first and second hollow rotary joints and is connected at the leading end thereof to the antenna feed point, a drive unit 0 provided on the base for rotating the rotary member, and a satellite tracking apparatus that transmits drive control signals to the drive unit to orient an antenna beam toward a satellite.

When the mobile earth station antenna apparatus thus configured according to this invention is mounted on a mobile unit with respect to which the satellite azimuth angle changes with the movement of the mobile unit, the rotary member is rotated by control signals from the satellite tracking system to orient the axis of the second hollow rotary joint toward the satellite. This brings the orientation of the beam of the antenna, which has a directional pattern that is axially symmetrical with respect to the axis of rotation, into alignment with the direction in which the satellite is located. Furthermore, the rotary member can rotate with respect to the base by means of the first hollow rotary joint, and the rotary member and antenna can rotate relative to each other by means of the second hollow rotary joint, in addition to which the end of the RF signal cable running through the hollow portions of the first and second rotary joints is in contact with the antenna feed point. Thus, even if the movement of the mobile unit causes the rotary member to rotate in the same direction, since the antenna does not rotate along with the rotation of the rotary member, the contact between the RF signal cable and the antenna is not affected, nor does the RF signal cable become twisted.

Since the antenna apparatus of this invention .*uses one drive motor and does not use a costly RF rotary joint for RF signal transmission, it can be made light, e small, and highly reliable, at a low cost.

Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description of the invention.

Figure 1 is a perspective view of an ernmodiment of the antenna apparatus of the invention; FFigure 2 is a side view of the antenna apparatus

S

of Figure 1; Figure -3 is an enlarged sectional view of the principal portions of the antenna apparatus; and 0.60 Figure 4 is an enlarged view of the principal portions of another embodiment of the antenna apparatus of the invention.

As shown in the drawings, the mobile earth station antenna apparatus according to the present invention comprises a base 6 affixed on a virtual horizontal plane surface of a mobile unit 10 such as an automobile, a rotary member 2 located on the base 6, the rotary member 2 having a surface 2a inclined, relative to I II the virtual horizontal plane, at a satellite elevation angle, a first hollow rotary joint 4 having an axis of rotation normal to the base 6 and connecting the rotary member 2 rotatably to the base 6, an antenna 1 located on the inclined surface 2a, an RF signal feed point 8 arranged at the center of the antenna 1, a second hollow rotary joint 3 connecting the antenna 1 rotatably to the inclined surface 2a and having an axis of rotation inclined to the satellite elevation angle, an RF signal cable 7 that is connected at the leading end thereof to the feed point 8 via the hollow portions of the rotary joints 3 and 4, a drive unit 5 located on the base 6 that rotates the rotary member 2, and a satellite tracking apparatus 11 that transmits drive control signals to the drive unit S to a.

direct the beam of the antenna 1 toward the satellite as the mobile unit 10 moves.

~The base 6 may for example be attached to the Ci..

mobile unit 10 roof forming the virtual horizontal surface.

:In shape, the rotary member 2 is a cylinder the upper part of which has been cut an angle to form the inclined surface e. 0 2a. The rotary member 2 is rotatably affixed by means of the hollow rotary joint 3, the rotation axis of which is i perpendicular to the base. The inclined surface 2a is inclined by the angle of satellite elevation, relative to the virtual horizontal plane. The disc-shaped antenna 1 on the inclined surface 2a is rotatably affixed by means of the hollow rotary joint 3, the rotation axis of which is inclined by the angle of satellite elevation. Thus, the antenna 1 is rotated about the rotation axis 4a of the hollow rotary joint 4 with the antenna 1 inclined to the angle of satellite elevation, relative to the virtual horizontal plane.

For the purpose of this invention, the antenna 1 may be a thin, circular microstrip patch antenna, or a parabolic antenna, a helical antenna or other such antenna i II having an axially symmetrical directional pattern. An antenna that lacks sufficient strength can be attached, as shown, in the enLdiment of Figure 3, by bonding an antenna element la onto a disc-shaped baseplate 9, and attaching the baseplate 9 via the second hollow rotary joint 3.

If an antenna is used that is not flat, such as for example a helical array antenna, as shown in Figure 4, antenna elements la can be attached to multiple locations on the baseplate 9 and the feed point 8 connected to the RF signal cable 7 can be connected to each antenna element la via a divider 12. Since only circularly polarized waves can be used with the apparatus of this invention, the antenna elements used will also be for a circularly polarizing antenna. In the embodiment shown in Figures 1 and 2, the base 6 is depicted as being larger than the antenna i, but in practice the base 6 only needs to be .o large enough to support the antenna.

~The edge of the bottom 2b of the rotary member 2 is provided with a contrate gear that is in meshed engagement with a gear wheel 5a fixed to the end of the drive shaft of a drive unit 5 such as a motor provided on the base 6. The antenna 1 is oriented to the prescribed azimuth by rotating the drive shaft to rotate the rotary member 2. That is, with the antenna 1 attached at an angle that matches the angle of satellite elevation, the beam of ***the antenna 1 is directed toward the satellite by the drive unit 5 under the control of the satellite tracking apparatus 11. In this way, the satellite orientation of the antenna beam is maintained no matter what the direction of mobile unit movement. In the configuration shown in Figure 1 the turning force generated by the drive unit 5 is directly transmitted to rotate the rotary member 2.

However, the drive mechanism is not limited to this arrangement. For example, the drive shaft of the drive unit 5 could be arranged parallel with the axis of the rotary member 2 and a belt-and-pulley type indirect transmission used to transmit the driving force to the rotary member 2.

As shown in Figure 3, the hollow rotary joint 3 that rotatably connects the inclined surface 2a of the rotary member 2 with the antenna 1 or baseplate 9 is for mutually rotating two planes perpendicular to the axis of rotation. Thus, the hollow rotary joint 3 may for example be constituted as a ball bearing having an inner rotating ring 3a and an outer rotating ring 3b separated by balls 3c that allow such rotation, in which the inner ring 3a is affixed to the inclined surface 2a, the outer ring 3b is affixed to the rear surface of the baseplate 9, and a hollow portion 3d constitutes the rotating axis of the Sjoint. The same ball bearing arrangement may also be used e* to constitute the hollow rotary joint 4.

Ordinary, inexpensive coaxial cable can be used for the RF signal cable 7 connecting the antenna 1 with a transceiving apparatus (not shown). Thus, the RF signal cable 7 is connected at one end to the transceiving apparatus, and the other end is fed through the hollow portions of the rotary joints used to connect the antenna g* to the rotary member and the rotary member to the base, and is connected to the feed point 8 of the antenna. Since the edge of the antenna 1 that is at the top is not set but depends on the azimuthal orientation, the antenna 1 has to have an axially symmetrical directional pattern with respect to an imaginary line perpendicular to the plane of the aperture.

The satellite tracking apparatus of this invention may be a known apparatus that includes a sensor for detecting received signal levels, a gyroscope for detecting rotation in the direction of movement of the mobile unit, and a signal processing circuit for control purposes. Such an apparatus uses signals from the antenna or signals from a sensor that detects the direction of movement of the mobile unit, or both signals, to transmit drive rotation signals to the drive unit 5 to keep the antenna beam directed toward the satellite.

The mobile earth station antenna apparatus configured as described above is mounted on a mobile unit, on the roof of a car, for example. If necessary, the antenna apparatus can be covered with a radome to protect it from the weather. The mobile unit may also have an onboard transceiving apparatus (not shown) to which one end of the RF signal cable 7 is connected. Thus, the antenna apparatus may be used for two-way communications purposes, 4 or just for receiving satellite broadcasts.

When the satellite azimuth changes as a result of 44 movement by the mobile unit, the satellite tracking apparatus 11 causes the rotary member 2 to be rotated relative to the base 6, to orient the rotation axis of the hollow rotary joint 3 toward the satellite. This therefore brings the orientation of the beam of the antenna 1, which has a directional pattern that is axially symmetrical with respect to the axis of rotation, into alignment with the direction in which the satellite is located. Furthermore, :the rotary member 2 can rotate with respect to the base 6 by means of the first hollow rotary joint 4, and the rotary member 2 and the antenna 1 can rotate relative to each *4 other by means of the second hollow rotary joint 3, and the RF signal cable 7 connecting the antenna 1 passes through the hollow centers of the two rotary joints. This rotary connection between the rotary member 2 and the rotary joint 3 means that rotation of the antenna 1 is suppressed by the coaxial cable 7, so that the antenna 1 does not necessarily rotate with the rotation of the rotary member 2. As a result, the antenna 1 can be turned for alignment with the satellite while maintaining the set elevation, with no twisting relative to the base 6, without affecting the antenna connection of the RF signal cable 7 to the feed point 8.

With the angle of elevation thus fixed, a single motor can be used to rotate the antenna to align the beam along the required azimuth without the antenna being twisted relative to the axis of rotation. Thus, azimuthal satelli'e tracking can be performec< ithout using costly RF rotary joints, and the apparatus cai be made light, small, and highly reliable, ,et a low cost. In addition to two-way satellite-based commrnications, the antenna apparatus of this invention can therefore be readily utilized for carmounted reception of satellite broadcasts, and can therefore be manufactured as a compact, low-cost apparatus for private car applications.

oe 06 a a 4 91 r 66 ft i I

Claims

2. The antenna apparatus according to claim 1, wherein the antenna is supported by a baseplate.
3. A mobile earth station antenna apparatus substantially as hereinbefore described with reference to the accompanying drawings. DATED this 7th day of December 1995. COMMUNICATIONS RESEARCH LABORATORY, MINISTRY OF POSTS AND TELECOMMUNICATIONS By their Patent Attorneys; CALLINAN LAWRIE ^S ABSTRACT A mobile earth station antenna apparatus includes a base located on a virtual horizontal plane surface, a rotary member located on the base the rotary member having a surface (2a) inclined at a satellite elevation angle relative to the virtual horizontal plane, a first hollow rotary joint that rotatably connects the rotary member to the base and has a rotation axis perpendicular to the base, an antenna located on the inclined surface (2a) of the rotary member a second hollow rotary joint having an axis of rotation inclined to a satellite elevation angle, the second hollow rotary joint rotatably connecting the antenna to the inclined surface (2a) of the rotary member an RF signal cable that passes through hollow portions of the first and second hollow rotary joints 4) and is connected to the antenna, a drive unit provided on the base for rotating the rotary member and a satellite tracking apparatus (11) that transmits drive control signals to the drive unit to orient an antenna beam toward a satellite. *0 9 9 999o