Patent Publication Number: US-7212169-B2

Title: Lens antenna apparatus

Description:
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. 
   Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
       FIGS. 1A ,  1 B and  1 C are schematic views showing a basic configuration of a lens antenna apparatus according to an embodiment of the present invention. 
       FIG. 2  is a conceptual diagram showing a relationship in connection among respective components of the apparatus shown in  FIGS. 1A ,  1 B and  1 C. 
       FIG. 3  is a schematic, perspective view of three driving mechanisms that rotate on an AZ axis, an EL axis and a xEL axis, respectively in the apparatus shown in  FIGS. 1A ,  1 B and  1 C. 
       FIGS. 4A ,  4 B and  4 C are diagrams showing a wire-type configuration that implements an xEL driving mechanism in the apparatus shown in  FIGS. 1A ,  1 B and  1 C. 
       FIG. 5  is a diagram showing a V roller gear type configuration that implements a xEL driving mechanism in the apparatus shown in  FIGS. 1A ,  1 B and  1 C. 
       FIG. 6  is a perspective view of the apparatus shown in  FIGS. 1A ,  1 B and  1 C which includes radiators each having an X/Y table for fine-tracking. 
       FIG. 7  is a side view of the apparatus shown in  FIGS. 1A ,  1 B and  1 C in which a balance weight mechanism is implemented by a spur gear for the EL driving of a guide rail. 
       FIG. 8  is a side view of the apparatus shown in  FIGS. 1A ,  1 B and  1 C in which a balanced-weight mechanism is implemented by a bevel gear for the EL driving of the guide rail. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of the present invention will be described below with reference to the accompanying drawings. 
     FIGS. 1A ,  1 B and  1 C are schematic views showing a basic configuration of a lens antenna apparatus according to an embodiment of the present invention.  FIG. 1A  is a perspective view of the lens antenna apparatus viewed obliquely from top,  FIG. 1B  is a side view thereof, and  FIG. 1C  is a perspective view thereof viewed obliquely from bottom.  FIG. 2  is a conceptual diagram showing a relationship in connection among respective components of the apparatus shown in  FIGS. 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 in  FIGS. 1A to 1C  comprises an antenna unit  100 . The antenna unit  100  includes a radio wave reflector  110 , a hemispherical lens  120 , and a guide rail  130 . The hemispherical lens is placed on the reflector  110 . The hemispherical lens  120  is formed by halving a spherical lens called Luneberg. The guide rail  130  is formed semicircularly along the outer surface of the lens  120 . 
   Idealistically, it is desirable that the radio wave reflector  110  be 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 lens  120  of the present embodiment is formed by halving the spherical lens equally, and the radio wave reflector  110  is placed on the flat bottom of the hemispherical lens  120 . It can thus be treated as a spherical lens in substance. 
   The antenna unit  100  receives radio waves from stationary satellites through the side surface of the hemispherical lens  120 . 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 reflector  110  in the present embodiment, the radio waves focused on the hemispherical lens  120  are reflected by the reflector  110 , or the flat bottom of the lens  120 . The route of radio waves incident upon the hemispherical lens  120  is diametrically opposed to that of radio waves incident upon a spherical lens with regard to a plane. Radiators  140 ,  150  and  160  are arranged in the focusing positions of radio beams formed on the side surface of the hemispherical lens  120 , namely, the focal points. Thus, the radiators  140 ,  150  and  160  can receive radio waves from three stationary satellites and transmit radio waves thereto. 
   The antenna unit  100  is mounted on a rotating base  210 . The rotating base  210  is placed on a fixed based  200  such that it can freely rotate on an azimuth (AZ) axis. The rotating base  210  has an AZ driving mechanism  220  on its underside. The AZ driving mechanism rotates the rotating base  210  on the AZ axis on the fixed base  200 . 
   Usually, the antenna unit  100  is located almost horizontally and the radiators  140 ,  150  and  160  are 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 lens  120  will become acute and the radiators  140 ,  150  and  160  will block the radio waves. To avoid this, as shown in  FIGS. 1A to 1C , the antenna unit  100  on the rotating base  210  is tilted adequately from the horizontal surface of the fixed base  200 . The radiators  140 ,  150  and  160  can thus be arranged to fall outside the range of a block against the radio waves. 
   The guide rail  130  is formed to extend from the rotating base  210  along the outer surface of the hemispherical lens  120 . 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 lens  120 . An EL driving mechanism  230  is provided at one end of the guide rail  130  in order to rotate the guide rail  130  on the EL axis. 
   The three radiators  140 ,  150  and  160  are provided on the guide rail  130  and each have an antenna element for forming radio beams focused by the hemispherical lens  120 . These radiators are arranged opposed to the hemispherical lens  120  at their respective locations. The locations and polarized axes of the radiators  140 ,  150  and  160  are determined in accordance with the directions of stationary satellites corresponding thereto when the apparatus is initialized. The radiators  140 ,  150  and  160  can be arranged on the same guide rail  130  since their partners for communications are stationary satellites. 
   The guide rail  130  includes a mechanism  240  for controlling the movement of the radiators  140 ,  150  and  160  along the guide rail  130  with 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 in  FIG. 3 , the locations of the radiators  140 ,  150  and  160  can freely be adjusted along the outer surface of the hemispherical lens  120  while keeping the interval between the radiators by the three AZ, EL and xEL driving mechanisms. Thus, the radiators  140 ,  150  and  160  can always track the three stationary satellites. 
   Since the radiators  140 ,  150  and  160  and xEL driving mechanism  240  applies an excessive weight to the support portion of the guide rail  130 , the guide rail  130  is difficult to adjust finely when rotating on the EL axis. It is thus desirable to provide a balance weight mechanism  250  close to the EL axis of the guide rail  130  to reduce the above weight applied to the guide rail  130 . 
   The rotating base  210  includes a control unit  300  for 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 mechanism  220 , EL driving mechanism  230 , and xEL driving mechanism  240 , as illustrated in  FIG. 1C . 
     FIGS. 4A ,  4 B and  4 C show a wire-type configuration that implements the xEL driving mechanism  240  described above.  FIG. 4A  is a schematic perspective view of the configuration,  FIG. 4B  is a detailed perspective and partly sectional view thereof, and  FIG. 4C  is a sectional view thereof. In the wire-type configuration, the guide rail  130  is hollowed. A loop-shaped wire  241  passes through the hollow of the guide rail  130  and is put on pulleys  242  and  243  at both ends of the guide rail  130 . One ( 242 ) of the pulleys is rotated in a forward or backward direction by a motor  244  with a reducer. Thus, the wire  241  moves back and forth, and the radiators  140 ,  150  and  160  are fixed on one side of the wire  241 . 
   As shown in  FIG. 4A , the guide rail  130  has an opening toward the surface of the hemispherical lens  120  and guide frames  131  and  132  on its both sides. Each of the radiators (e.g., the radiator  140  shown in  FIG. 4A ) has pulleys  142  and  143  at its proximal end  141 . These pulleys  142  and  143  are fitted to the guide frames  131  and  132 , respectively. The radiator  140  also has a projected piece  144  in its middle. The projected piece  144  is inserted into the opening of the guide rail  130  and connected to the wire  241  therein. With this configuration, the radiators  140 ,  150  and  160  can move together smoothly along the guide rail  130  as the wire  241  moves. 
     FIG. 5  shows a V roller gear type configuration as another type of the xEL driving mechanism  240  described above. In this configuration, the guide rail  130  is lengthened more than half the circumference of a virtual circle to be formed by the guide rail. One end of the guide rail  130  has 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 base  210  and below the EL axis, the inner and outer surfaces of one end of the guide rail  130  are supported slidably by three V rollers  245 A,  245 B and  245 C and the inner surface of the other end thereof is supported by two V rollers  246 A and  246 B. A gear  247  is fitted into the gear groove, and a driving motor  248  to which the gear  247  is coupled is rotated forward or backward. Since the entire guide rail can rotate along the outer surface of the hemispherical lens  120 , the radiators  140 ,  150  and  160  have only to be fixed directly to the guide rail  130 . 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 rail  130  lowers. 
   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 tables  140 A,  150 A and  160 A can be provided on their respective support portions of the radiators  140 ,  150  and  160 . 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 in  FIG. 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 in  FIG. 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. 7  shows a configuration of the balance weight mechanism  250  that is implemented by a spur gear for the EL driving of the guide rail  130 . In this configuration, a large-diameter first gear  251  is fitted to the guide rail  130  to rotate on the EL axis, and a small-diameter second gear  252  is engaged with the first gear  251  and fixed to the rotating base  210 . A balance weight  253  is attached to the second gear  252  in a predetermined direction. 
   The balance weight  253  can almost cancel an imbalance caused around the EL axis of the guide rail  130  located at an angle close to 45 degrees while the guide rail  130  is located at an angle ranging from 30 degrees to 60 degrees. When the guide rail  130  is located at an angle of almost 45 degrees, the balance weight  253  is located at an angle of 45 degrees, thereby almost keeping a counterbalance. In this case, the weight of the balance weight  253  is 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 rail  130  and balance weight  253  is 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. 8  shows another configuration of the balance weight mechanism  250  that is implemented by a bevel gear. In this configuration, a first bevel gear  245 A is fitted to the guide rail  130  to rotate on the EL axis. A second bevel gear  245 B is engaged with the first bevel gear  254 A. A fourth bevel gear  245 D is engaged with a large-diameter third bevel gear  254 C that is coaxial with the second bevel gear  245 B. A balance weight  255  is attached to the fourth bevel gear  245 D and extended in a direction perpendicular to the rotating axis of the gear  245 D. In this configuration, too, the balance weight  255  can almost cancel an imbalance caused around the EL axis of the guide rail  130 . 
   In the embodiment described above, the algorithm for tracking stationary satellites rotates the guide rail  130  on 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. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.