Lens antenna apparatus

In a lens antenna apparatus, a guide rail is formed along the outer surface of a hemispherical lens of a hemispherical lens antenna, and a plurality of radiators are positioned and fixed on the guide rail. When the lens antenna apparatus operates, the directivity of radio beams of the radiators is controlled by adjusting an AZ-axis rotating mechanism, an EL-axis rotating mechanism and an xEL-axis rotating mechanism.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-400579, filed Nov. 28, 2003, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens antenna apparatus utilizing a spherical lens that focuses radio beams, which is used in ground stations of a satellite communication system. More particularly, the invention relates to a lens antenna apparatus having a configuration suitable to be mounted on a mobile unit.

2. Description of the Related Art

Conventionally, a lens antenna apparatus utilizing a spherical lens capable of focusing radio beams has been developed. Radiators are arranged in given positions on the lower hemisphere of the spherical lens, and the directivity of the radiators are aligned with the center of the spherical lens to form radio beams in a given direction. The radio beams can be oriented everywhere in the celestial sphere only by freely moving the radiators on the lower hemisphere of the spherical lens. The lens antenna apparatus therefore has the advantage that it need not rotate as a whole unlike a parabolic antenna apparatus and its driving system can easily be downsized.

Under the present circumstances, however, the lens antenna apparatus is difficult to miniaturize further because of constraints of downsizing of the spherical lens in itself. Further, the apparatus is not easy to handle during assembly since it is spherical. To resolve these problems, the following hemispherical lens antenna apparatus is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publications Nos. 2002-232230and 2003-110352. An upper hemispherical lens, which is formed by halving a spherical lens, is placed on a radio reflector to focus radio waves from the celestial sphere, and the reflector reflects the radio waves, thus acquiring the radio waves on the outer surface of the hemispherical lens.

The hemispherical lens antenna apparatus has received attention as one mounted on a mobile unit since it is easy to miniaturize, whereas it needs to communicate with a plurality of stationary satellites on a stationary orbit. It is thus desirable to achieve a multibeam lens antenna apparatus having a simple and stable configuration.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a multibeam lens antenna apparatus having a simple and stable configuration which is suitable to be mounted on a mobile unit.

A lens antenna apparatus according to an aspect of the present invention comprises a fixed base horizontally located in an installation position;

a rotating base mounted on the fixed base rotatably on an azimuth axis, a hemispherical lens antenna mounted on the rotating base and having a radio reflector on which a hemispherical lens is placed, the hemispherical lens being formed by halving a spherical lens that focuses radio beams, a guide rail formed along an outer surface of the hemispherical lens and supported based on an elevation axis perpendicular to the azimuth axis, the azimuth axis passing through a center point of the hemispherical lens, a plurality of radiators arranged opposite to the hemispherical lens in given positions on the guide rail and each having an antenna element that forms radio beams focused by the hemispherical lens, an AZ-axis rotating mechanism which rotates the rotating base on the azimuth axis, an EL-axis rotating mechanism which rotates the guide rail on the elevation axis, and a radiator moving mechanism which moves the radiators along the guide rail with a fixed interval between the radiators, wherein a directivity of radio beams of the radiators is controlled by adjusting the AZ-axis rotating mechanism, the EL-axis rotating mechanism, and the radiator moving mechanism.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A,1B and1C are schematic views showing a basic configuration of a lens antenna apparatus according to an embodiment of the present invention.FIG. 1Ais a perspective view of the lens antenna apparatus viewed obliquely from top,FIG. 1Bis a side view thereof, andFIG. 1Cis a perspective view thereof viewed obliquely from bottom.FIG. 2is a conceptual diagram showing a relationship in connection among respective components of the apparatus shown inFIGS. 1A to 1C. Assume here that the apparatus is mounted on a mobile unit to communicate with each of three communication satellites (not shown but referred to as stationary satellites hereinafter) on a stationary orbit.

The lens antenna apparatus shown inFIGS. 1A to 1Ccomprises an antenna unit100. The antenna unit100includes a radio wave reflector110, a hemispherical lens120, and a guide rail130. The hemispherical lens is placed on the reflector110. The hemispherical lens120is formed by halving a spherical lens called Luneberg. The guide rail130is formed semicircularly along the outer surface of the lens120.

Idealistically, it is desirable that the radio wave reflector110be a plane expanding infinitely. Actually, its size is determined by the tolerance of antenna characteristics (e.g., gain and side lobe).

The spherical lens is also called a spherical dielectric lens. This lens is configured by dielectrics laminated concentrically on a sphere to allow almost parallel radio waves to pass therethrough and focus them on a point. In general, the laminated dielectrics decrease in dielectric constants toward the outer surface of the lens. The hemispherical lens120of the present embodiment is formed by halving the spherical lens equally, and the radio wave reflector110is placed on the flat bottom of the hemispherical lens120. It can thus be treated as a spherical lens in substance.

The antenna unit100receives radio waves from stationary satellites through the side surface of the hemispherical lens120. If a spherical lens is used, radio waves are focused inside the lens. Since the hemispherical lens is used and placed on the radio wave reflector110in the present embodiment, the radio waves focused on the hemispherical lens120are reflected by the reflector110, or the flat bottom of the lens120. The route of radio waves incident upon the hemispherical lens120is diametrically opposed to that of radio waves incident upon a spherical lens with regard to a plane. Radiators140,150and160are arranged in the focusing positions of radio beams formed on the side surface of the hemispherical lens120, namely, the focal points. Thus, the radiators140,150and160can receive radio waves from three stationary satellites and transmit radio waves thereto.

The antenna unit100is mounted on a rotating base210. The rotating base210is placed on a fixed based200such that it can freely rotate on an azimuth (AZ) axis. The rotating base210has an AZ driving mechanism220on its underside. The AZ driving mechanism rotates the rotating base210on the AZ axis on the fixed base200.

Usually, the antenna unit100is located almost horizontally and the radiators140,150and160are arranged thereon in conformity with the direction and elevation angle of the stationary satellites for communications with the lens antenna apparatus. If, however, the apparatus is used near the equator, on a sloping ground in an intermontane region, etc., the incident and outgoing angles of radio waves on and from the hemispherical lens120will become acute and the radiators140,150and160will block the radio waves. To avoid this, as shown inFIGS. 1A to 1C, the antenna unit100on the rotating base210is tilted adequately from the horizontal surface of the fixed base200. The radiators140,150and160can thus be arranged to fall outside the range of a block against the radio waves.

The guide rail130is formed to extend from the rotating base210along the outer surface of the hemispherical lens120. It freely rotates on an elevation (EL) axis that is perpendicular to the azimuth (AZ) axis that passes through the center point of the hemispherical lens120. An EL driving mechanism230is provided at one end of the guide rail130in order to rotate the guide rail130on the EL axis.

The three radiators140,150and160are provided on the guide rail130and each have an antenna element for forming radio beams focused by the hemispherical lens120. These radiators are arranged opposed to the hemispherical lens120at their respective locations. The locations and polarized axes of the radiators140,150and160are determined in accordance with the directions of stationary satellites corresponding thereto when the apparatus is initialized. The radiators140,150and160can be arranged on the same guide rail130since their partners for communications are stationary satellites.

The guide rail130includes a mechanism240for controlling the movement of the radiators140,150and160along the guide rail130with their locations maintained for tracking the satellites. This mechanism will be referred to as a cross elevation (xEL) driving mechanism hereinafter.

In the forgoing lens antenna apparatus, as shown inFIG. 3, the locations of the radiators140,150and160can freely be adjusted along the outer surface of the hemispherical lens120while keeping the interval between the radiators by the three AZ, EL and xEL driving mechanisms. Thus, the radiators140,150and160can always track the three stationary satellites.

Since the radiators140,150and160and xEL driving mechanism240applies an excessive weight to the support portion of the guide rail130, the guide rail130is difficult to adjust finely when rotating on the EL axis. It is thus desirable to provide a balance weight mechanism250close to the EL axis of the guide rail130to reduce the above weight applied to the guide rail130.

The rotating base210includes a control unit300for automatically controlling the directivity of radio beams so as to track the satellites for communications with the antenna apparatus by adjusting the AZ-axis rotating mechanism220, EL driving mechanism230, and xEL driving mechanism240, as illustrated inFIG. 1C.

FIGS. 4A,4B and4C show a wire-type configuration that implements the xEL driving mechanism240described above.FIG. 4Ais a schematic perspective view of the configuration,FIG. 4Bis a detailed perspective and partly sectional view thereof, andFIG. 4Cis a sectional view thereof. In the wire-type configuration, the guide rail130is hollowed. A loop-shaped wire241passes through the hollow of the guide rail130and is put on pulleys242and243at both ends of the guide rail130. One (242) of the pulleys is rotated in a forward or backward direction by a motor244with a reducer. Thus, the wire241moves back and forth, and the radiators140,150and160are fixed on one side of the wire241.

As shown inFIG. 4A, the guide rail130has an opening toward the surface of the hemispherical lens120and guide frames131and132on its both sides. Each of the radiators (e.g., the radiator140shown inFIG. 4A) has pulleys142and143at its proximal end141. These pulleys142and143are fitted to the guide frames131and132, respectively. The radiator140also has a projected piece144in its middle. The projected piece144is inserted into the opening of the guide rail130and connected to the wire241therein. With this configuration, the radiators140,150and160can move together smoothly along the guide rail130as the wire241moves.

FIG. 5shows a V roller gear type configuration as another type of the xEL driving mechanism240described above. In this configuration, the guide rail130is lengthened more than half the circumference of a virtual circle to be formed by the guide rail. One end of the guide rail130has recesses on its inner and outer surfaces, whereas the other end thereof has a recess on its inner surface and a gear groove on its outer surface. Above the rotating base210and below the EL axis, the inner and outer surfaces of one end of the guide rail130are supported slidably by three V rollers245A,245B and245C and the inner surface of the other end thereof is supported by two V rollers246A and246B. A gear247is fitted into the gear groove, and a driving motor248to which the gear247is coupled is rotated forward or backward. Since the entire guide rail can rotate along the outer surface of the hemispherical lens120, the radiators140,150and160have only to be fixed directly to the guide rail130. Though the wire-type configuration is complicated, a relatively stable EL driving operation can be expected because the center of gravity of the entire guide rail130lowers.

If the aperture of the antenna apparatus increases and the angle of the beams becomes acute to reduce the precision of tracking at the AZ, EL and xEL axes, X/Y tables140A,150A and160A can be provided on their respective support portions of the radiators140,150and160. These support sections are located on a partial sphere and at a fixed distance from the center of the lens or on the plane perpendicular to the beams that form a quasi-sphere, as shown inFIG. 6. In the V roller gear type configuration, coarse adjustment (low frequency, large amplitude) is performed by the AZ, EL and xEL axes, while fine adjustment (high frequency, small amplitude) is done by the X/Y tables to track the stationary satellites with reliability. Originally, three axes are required even for the fine adjustment, namely, two axes of X/Y tables plus one axis in the direction of polarized axis. In the configuration shown inFIG. 6, however, only the driving mechanism of the polarized axis, which is not so sensitive in terms of tracking, is not synthesized with but can be separated from the other two axes. The driving mechanism can thus be omitted.

FIG. 7shows a configuration of the balance weight mechanism250that is implemented by a spur gear for the EL driving of the guide rail130. In this configuration, a large-diameter first gear251is fitted to the guide rail130to rotate on the EL axis, and a small-diameter second gear252is engaged with the first gear251and fixed to the rotating base210. A balance weight253is attached to the second gear252in a predetermined direction.

The balance weight253can almost cancel an imbalance caused around the EL axis of the guide rail130located at an angle close to 45 degrees while the guide rail130is located at an angle ranging from 30 degrees to 60 degrees. When the guide rail130is located at an angle of almost 45 degrees, the balance weight253is located at an angle of 45 degrees, thereby almost keeping a counterbalance. In this case, the weight of the balance weight253is based on the axle ratio and the mass of the whole balance weight is reduced by the reducer on the EL axis. A balance between the guide rail130and balance weight253is kept on the EL axis to minimize the influence of a disturbance (translational vibration) on the torque of a motor. It is desirable that the reducer be free of backlash and the structural elements have adequate stiffness against control frequency.

FIG. 8shows another configuration of the balance weight mechanism250that is implemented by a bevel gear. In this configuration, a first bevel gear245A is fitted to the guide rail130to rotate on the EL axis. A second bevel gear245B is engaged with the first bevel gear254A. A fourth bevel gear245D is engaged with a large-diameter third bevel gear254C that is coaxial with the second bevel gear245B. A balance weight255is attached to the fourth bevel gear245D and extended in a direction perpendicular to the rotating axis of the gear245D. In this configuration, too, the balance weight255can almost cancel an imbalance caused around the EL axis of the guide rail130.

In the embodiment described above, the algorithm for tracking stationary satellites rotates the guide rail130on the AZ and EL axes to coincide with the celestial equator (simply referred to as the equator hereinafter) and controls the antenna apparatus such that its directivity coincides with the satellites on the equator. The interval between satellites on the equator is fixed, as is the polarization angle of the satellites to the equator. Multibeams can thus be transmitted to all the satellites at once only by the above control.

It is assumed that the lens antenna apparatus will be subjected to a great disturbance in inoperative mode. It is thus desirable that the axis driving mechanisms each have a retreat mode in which a stall lock or a non-energization brake prevents the disturbance from being applied to the driving unit and structural element.

When the lens antenna apparatus uses multibeams, if its antenna aperture is used for some of the multibeams only to be received, the apparatus has an adequate gain. As for an antenna apparatus that can be decreased in beam tracking precision, its radiators can be displaced from the focal point of a lens to broaden the range of beams, with the result that a driving mechanism for fine adjustment can be omitted.