Abstract:
An antenna system adapted to be mounted on an exterior surface of a mobile platform and having a reduced overall height to reduce aerodynamic drag caused by the antenna system. The antenna system includes a movable platform disposed concentrically within an annular stationary platform. The movable platform includes a slip ring assembly formed on its lower surface which is in physical contact with a brush assembly supported from a lower surface of the stationary platform. By locating the slip ring assembly and the brush assembly adjacent the lower surface of the movable platform, the overall height of the antenna is reduced. Reliability is also improved since contaminants are less likely to accumulate on the slip ring assembly due to its presence on the lower surface of the movable platform.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to the antenna systems, and more particularly to the incorporation of slip rings and brushes for an antenna of the system to facilitate an electrical connection to electrical components associated with the antenna while permitting rotational movement of the antenna, and while reducing the overall height of the system.  
         BACKGROUND OF THE INVENTION  
         [0002]    Any antenna that rotates about an azimuthal axis beyond 360° of rotation requires some means for maintaining electrical contact between the electronic components associated with the antenna and those in the supporting structure on which the antenna is mounted. One form of maintaining such an electrical coupling is through the use of conventional slip rings and brushes. Slip rings and brushes can be used to supply power to the various electrical/electronic components of the antenna such as the azimuthal and elevation drive motors, which allow positioning of the antenna in accordance with desired azimuth and elevation angles. Other electronic components that require electrical power and/or electrical control signals are gyroscopes and encoders that help to control pointing of the antenna.  
           [0003]    Typically, the above-described slip rings and brushes are mounted on a top surface of an antenna base plate. However, such an arrangement serves to increase the overall height of the antenna system. Also, for a system with a large base, this would necessitate that the brushes extend across the base to reach the slip rings. Such a design would inhibit the attachment of other components onto the base because they would interfere with the brush holders as they would rotate. On high speed moving platforms, such as jet aircraft, the additional drag caused by an externally mounted antenna system is of serious concern. The additional drag can significantly reduce fuel economy of the aircraft and thus lead to higher operating costs for the aircraft.  
           [0004]    It is therefore of principal importance that an apparatus used for supporting an antenna and its associated components be formed such that the overall height of the antenna can be kept to a minimum to thereby avoid negatively impacting the performance and cost associated with using an externally mounted antenna on a high speed moving platform such as a jet aircraft.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention is directed to an antenna system apparatus for supporting an antenna which allows 360° rotational movement of the antenna, and which provides a significantly lower height that previously designed antenna support systems. The apparatus of the present invention makes use of a movable platform for mounting an antenna thereon, and a stationary platform mounted adjacent the movable platform. The antenna is mounted on an upper surface of the movable platform and at least one slip ring is formed on a lower surface of the movable platform. More preferably, a plurality of slip rings are formed on the lower surface of the movable platform.  
           [0006]    At least one brush, and more preferably a plurality of brushes, are mounted on a support such that the brushes can be placed in physical contact with the slip rings. A motor operatively associated with the movable platform is used to drive the movable platform rotationally about the stationary platform. In a preferred embodiment, the stationary and movable platforms are disposed generally coplanar to one another and incorporate a bearing assembly therebetween for facilitating smooth rotational movement of the movable platform. This slip ring design is not limited to coplanar mounting plates or the bearings integrated into those plates.  
           [0007]    It is a principal advantage of the present invention that the slip rings and bushes are disposed adjacent the lower surface of the movable platform. This allows the overall height of the apparatus to be minimized by allowing the various electrical and electronic components associated with the antenna to be mounted directly on the upper surface of the movable platform, rather than on other structure disposed above the upper surface, which is common with previous antenna systems This in turn helps to reduce the drag created by the antenna system when it is mounted on an external surface of a high speed mobile platform.  
           [0008]    In a preferred embodiment the apparatus of the present invention comprises a circular movable platform and an annular stationary platform. A bearing assembly is disposed between an outer edge surface of the circular movable platform and an inner edge surface of the annular stationary platform. The bearing assembly facilitates smooth rotational movement of the movable platform.  
           [0009]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0011]    [0011]FIG. 1 is a simplified plan view of an antenna system  10  in accordance with a preferred embodiment of the present invention:  
         [0012]    [0012]FIG. 2 is a cross-sectional view of a portion of the apparatus of FIG. 1 taken in accordance with section line  2 - 2  in FIG. 1;  
         [0013]    [0013]FIG. 3 is a cross-sectional view of a different portion of the apparatus of FIG. 1 taken in accordance with section line  3 - 3  in FIG. 1; and  
         [0014]    [0014]FIG. 4 is a plan view of the lower surface of the movable platform.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0016]    Referring to FIG. 1, there is shown an antenna system  10  in accordance with a preferred embodiment of the present invention. The antenna system  10  is shown mounted on an external surface  12  of a mobile platform  14 . The mobile platform 14  may comprise any form of mobile platform such as a land vehicle, a ship or an aircraft. It is anticipated that the antenna system 10  will find particular utility in connection with high speed commercial and military aircraft. In such applications, it will be appreciated that an extremely important consideration is minimizing drag created by the antenna system  10 . To this end, minimizing the overall height of the antenna system  10  is of paramount importance. The present invention accomplishes this goal through a unique arrangement of electrical coupling elements, which will be described below momentarily.  
         [0017]    With further reference to FIG. 1, the antenna system  10  includes a movable circular platform  16  and a stationary annular platform  18 . The movable platform  16  has mounted thereon a reflector antenna  20  for receiving and/or transmitting radio frequency signals. While the antenna  20  is shown as reflector antenna, it will be appreciated that the movable platform  16  is capable of supporting a planar, phased array antenna or virtually any other form of antenna. The movable platform  16  rotates the antenna  20  about an azimuthal axis  22  so that the antenna  20  can be pointed at any desired azimuth scanning angle.  
         [0018]    For moving the movable platform  16 , a support bracket  24  is fixedly coupled to an upper surface  26  of the platform  16 . The support bracket  24  carries a motor  28 , which may comprise any form of motor but one preferred form comprises a stepper motor. The motor  28  is carried at an outermost end of the support bracket  24 . The antenna  20  is further rotatable about an elevation axis  30  via a motor  32  mounted on the supper surface  26  or on a suitable bracket supported on the upper surface  26  of the movable platform  16 . Accordingly, the antenna can also be pointed at any desired elevation scanning angle.  
         [0019]    Referring to FIG. 2, the azimuth motor  28  includes a gear, which is shown as a pinion gear  34 . The pinion gear  34  is driven via an output shaft  36  of the motor  28  and engages a toothed exterior edge surface  38  of the stationary platform  18 . An outer edge surface  40  of the movable platform  16  is disposed generally coplanar with an inner edge surface  42  of the stationary platform  18  and a bearing assembly  44  is interposed between the surfaces  40  and  42 . The bearing assembly  44  allows the movable platform  16  to move smoothly rotationally about the azimuthal axis  22  when the pinion gear  34  is driven by the motor  26 . Thus, it will be appreciated that the support bracket  24 , the motor  28  and the pinion gear  34  all move concurrently with the movable platform  16  during rotational movement of the platform  16 . Similarly, the elevation motor  32  rotates with the movable platform 16 . It will be appreciated, however, that other bearings and/or drive arrangements could just as easily be implemented and, that the above-described arrangement is meant to merely illustrate one suitable driving arrangement for the movable platform  16 . One preferred form of drive mechanism is disclosed in co-pending U.S. application Ser. No. 09/975,858, filed Aug. 12, 2001, assigned to the Boeing Co., and hereby incorporated by reference.  
         [0020]    Referring to FIG. 3, the stationary platform  18  can also be seen to include a lower surface  46  to which a support bracket  48  is fixedly secured. The movable platform 16  also includes a lower surface  50  having an annular cavity  52  within which is formed a slip ring assembly  54 . The support bracket  48  has a length sufficient to extend underneath the slip ring assembly  54  and an outer most end  56  which supports a brush assembly  58  thereon. The brush assembly  58  includes a plurality of independent electrical brushes  58   a . The brushes  58   a  of the brush assembly  58  are in contact with the slip ring assembly  54  to thus form a path through which electrical signals can be transmitted between the brush assembly  58  and the slip ring assembly  54 . In this regard, it will be appreciated that electrical conductors leading to the elevation motor  32  and the azimuth motor  28  extend into contact with the slip ring assembly  54  such that electrical signals transmitted to the assembly  54  can be further transmitted to the motors  28  and  32 , as well as other electrical components mounted on the movable platform  16 . For convenience, these additional conductors have not been shown, but it will be appreciated that additional holes may be formed in the movable platform  16  through which the additional conductors can be coupled to the slip ring assembly  54 . It will also be appreciated that the brush assembly  58  includes a cable assembly  60  which can be used to communicate electrical signals to and from the brush assembly  58 . The cable assembly  60  may be formed to extend through an interior assembly (not shown) in the support bracket  48  or could be supported along an outer surface of the support bracket  48 .  
         [0021]    With further reference to FIGS. 3 and 4, the slip ring assembly  54  will be described in greater detail. With brief reference to FIG. 4, it will be noted that the slip ring assembly  54  forms an annular shape concentric with the azimuth pivot axis  22  (FIG. 1). The slip ring assembly  54  is formed by first machining the movable platform  16  such that the lower surface  46  is flat. Next, the cavity  52  is formed by removing a suitable amount of material from the lower surface  46 . Preferably, the movable platform  16  is made of stainless steel to provide a suitable surface against which the bearing assembly  44  can contact. Stainless steel also provides protection against corrosion and thermal contraction/expansion problems.  
         [0022]    The cavity  52  is preferably formed such that tapered edges  62  are formed at the center and at opposite ends of the cavity  52 . Once the cavity  52  is formed, an appropriate plastic insulating material, possibly phenolic or epoxy, is injection molded into the cavity to form an insulated base  64 . Next, a plurality of grooves  66  are machined into the insulated base  64 . Alternatively, the grooves  66  may be formed during the injection molding process provided the molding tool used can be constructed with suitable circular, concentric circular portions to form the grooves  66 .  
         [0023]    Once the grooves  66  are formed, the insulated base  64  is electro-plated with a standard series of metallic coatings terminating in a final electro-plated filling of gold. These conductive fillings are denoted by reference numeral  68  and form independent slip rings. The final step is again machining the lower surface  46  of the movable platform  16  to remove the excess over-plating of gold and thereby provide a uniform, flat surface for the entire lower surface  46 .  
         [0024]    The brush assembly  58  comprises a number of brushes  58   a  which correspond to the number of conductive slip rings  68  formed on the movable platform  16 . The slip ring brushes  58   a  are preferably formed as gold plated, beryllium copper, spring-like devices that slide over the slip rings  68  as the movable platform  16  rotates. It will also be appreciated that the brushes  58   a  of the brush assembly  58  are preferably designed so as to be curved in accordance with the curvature of the slip rings  68 .  
         [0025]    A principle advantage of forming the slip rings  68  on the lower surface  46  of the movable platform  16  is that any moisture that reaches the surface of the slip ring  68  will readily run-off. The slip rings  68  are also much less likely to become contaminated with miscellaneous debris that might fall onto the slip rings during use of the antenna system  10 .  
         [0026]    Still another positive feature of the movable platform  16  is that it is possible to embed an electrical heating wire (or wires) into the insulated base  64  during manufacture of the movable platform  16 . Electric current can then be supplied to the heating wire (or wires) in a controlled manner to generate a controlled degree of heat to avoid formation of ice on the slip rings  68  and the movable platform  16 .  
         [0027]    To further increase reliability of the antenna system  10 , a redundant set of brushes of the brush assembly  58  could be mounted on the support bracket  48  or on another suitable support bracket. In this manner, the mean time between failures (MTBF) could be increased for the antenna system  10 . Increasing the MTBF effectively reduces the cost of service and maintaining the antenna system  10  over a given period of time.  
         [0028]    The antenna system  10  of the present invention thus provides a means for reducing the overall height of an antenna that is to be secured to an exterior surface of a mobile platform. Importantly, this allows the drag associated with the antenna system 10  to be minimized when the mobile platform to which it is mounted is moving at a high rate of speed. The antenna system  10  further is constructed in a manner which improves reliability by placing the slip ring on the lower surface of the movable platform  16 , in contrast to previously developed movable platforms where the slip rings are located on the upper surface.  
         [0029]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.