Patent Publication Number: US-2005128147-A1

Title: Antenna system

Description:
RELATED APPLICATIONS  
      The present invention claims priority on provisional patent application Ser. No. 60/529,851, filed on Dec. 15, 2003, entitled “High Gain Antenna”. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates generally to the field of antennas and more particularly to an antenna system.  
     BACKGROUND OF THE INVENTION  
      Wireless networks which includes Wireless Local Area Networks (WLAN), Wireless Wide Area Networks (WWAN), Cellular Networks and satellite communication (SATCOM) are becoming popular. The typical antennas used in these networks are omni directional antennas or bulky dish type directional antennas. Omni directional antennas have low gain and therefore require greater power levels than directional antennas for the same coverage area. In addition, since omni directional antennas transmit in all directions it makes it easy for hackers and ease droppers to listen in on the network or even gain access to the network. Directional antennas have higher gain, but normally there radiation patterns are fixed. As a result, these antennas are more difficult to install and use in a a field or enterprise applications for proper coverage and reduce nulls and blind spots.  
      Thus there exists a need for antenna system wherein the radiation pattern is not fixed but is adjustable either in the factory or in the field for optimal coverage and gains. At the same time, antenna system should be of lower cost for mass deployment.  
     SUMMARY OF INVENTION  
      A flexible aperture antenna that overcomes these and other problems has a high dielectric substrate with a first surface and a second surface. The first surface is used for reflection and the second surface as a radiator. A reflective material is deposited on the first surface of the high dielectric material. A radiator design is deposited on the second surface of the high dielectric material. The high dielectric material may be of foam or any other polymeric flexible material. A reflection pattern of the antenna remains substantially uniform and proportional as the high dielectric flexible foam is flexed either in the horizontal or vertical axis. A number of radiator designs arrays are deposited on the second surface of the high dielectric flexible foam. The multiple of arrays form a high gain far field pattern. The antenna assembly is held by two vertical bars which are used to flex the antenna by moving them in or out. The assembly can be flexed manually or by use of a servo motor with automatic feed back for proper adjustment of radiation pattern.  
      In one embodiment, a flexible antenna system has a flexible film antenna. A frame has a pair of bars attached to a pair of sides of the flexible antenna and capable of translating in a plane of the frame. A gain of the flexible film antenna may remains essentially uniform as the flexible film antenna is flexed. The flexible film antenna may have a high dielectric flexible foam with a first surface and a second surface. A reflective material is deposited on the first surface of the high dielectric material. A radiator design is deposited on the second surface of the high dielectric flexible foam. The radiator design may have a number of emitters and a number of signal feeds. A change in an impedance of each of the emitters is equal to the change of an impedance of each of the signal feeds as the radiator design is flexed. A motor may control a position of the pair of bars. A wireless controller may be coupled to the motor.  
      In one embodiment a flexible antenna system has a high dielectric substrate. A radiator design is deposited on a first surface of the high dielectric substrate. The radiator design may have a number of emitters. The high dielectric substrate may have a reflective second surface. The antenna may be capable of flexing and maintaining an essentially undistorted far field gain pattern. A frame may have a pair of bars attached to a pair of edges of the high dielectric material. The pair of bars may be capable of translating in a plane of the frame. A gain of the antenna is greater than an omni-directional antenna when the antenna is essentially flat.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exploded cross sectional view of a flexible antenna in accordance with one embodiment of the invention;  
       FIG. 2  is a top left perspective view of a frame for holding a flexible antenna in accordance with one embodiment of the invention;  
       FIG. 3  is cross sectional schematic diagram of the flexible antenna in a flat and a flexed position in accordance with one embodiment of the invention;  
       FIG. 4  is a radiator design in accordance with one embodiment of the invention;  
       FIG. 5  is a gain plot of the antenna design using the radiator of  FIG. 4  in a flat position in accordance with one embodiment of the invention;  
       FIG. 6  is a gain plot of the antenna design using the radiator of  FIG. 4  in a flexed position in accordance with one embodiment of the invention;  
       FIG. 7  is a gain plot of the antenna design using the radiator of  FIG. 4  in an even more flexed position in accordance with one embodiment of the invention;  
       FIG. 8  is a schematic diagram of an antenna system in accordance with one embodiment of the invention; and  
       FIG. 9  is a bottom left perspective of a frame for holding a flexible antenna in accordance with one embodiment of the invention;  
       FIG. 10  is a side view of the frame for holding a flexible antenna of  FIG. 9  in accordance with one embodiment of the invention;  
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      The antenna system described herein is inexpensive to manufacture, has a high gain and has a flexible substrate that when flexed changes its gain. The antenna system has a high dielectric flexible foam or polymeric material as a substrate and metallic surfaces deposited on both sides for the for the radiator and reflector functions of the antenna system. A reflective layer is deposited on one surface of the flexible foam. An antenna system is deposited (screen print, sputtered, vapor deposition, etc) on the other surface of the flexible foam. The antenna system may have a number of emitters and a number signal feed paths. The input signal is applied to the signal feed path system and radiator design  20  and the ground or negative input of the input signal is applied to the reflector  18 . By designing the emitters and the signal feed paths so that the impedance changes for the emitters are essentially the same as the impedance changes for the feed paths as the antenna system is flexed, it is possible to maintain a substantially uniform and proportional far field gain pattern. A frame and motor are used to flex the antenna. This allows the antenna to have a broader beam width lower gain in one position and a higher gain narrower beam width in a second position. Thus a single antenna can replace multiple antenna designs and shift its gain pattern for the particularly circumstance. An alternate to direct deposition on the foam/polymeric surface is use of polymeric film with metal deposition on both sides.  
       FIG. 1  is an exploded cross sectional view of a flexible antenna  10  in accordance with one embodiment of the invention. The antenna  10  has a high dielectric substrate  12 . In one embodiment, the substrate is a high dielectric flexible foam that has a dielectric constant as close to air as possible. Thus “high” as used herein is near or above the dielectric constant of air or a vacuum. The substrate has a first surface  14  and a second surface  16 . A reflective material  18  is deposited onto the first surface  14 . In one embodiment, the reflective surface  18  is copper or other conductive material. The copper may be deposited by screen printed, sputtered, vapor deposition or any other method. The second surface  16  is deposited with a radiator design  20 . The radiator design  20  is also made of a highly conductive material and may be deposited with any known method or may be etched from a solid layer of the conductor. Since, both the reflector  18  and the radiator design  20  are formed on the substrate  12  by automated procedures this is an extremely inexpensive and labor saving method of forming an antenna. In addition, by correctly forming the radiator design  20  the antenna  10  may be flexed and change its gain and beam width characteristics.  
      In another embodiment, the foam  12  is replaced with an air gap. In this case the reflector  18  and the radiator  20  may be formed on a thin flexible substrate such as a polymeric material. The foam  12  is replaced with spacers that may also be made of foam. The spacers  12 , in one embodiment, are small pieces of foam that are used to create the gap  12  between the reflector  18  and the radiator  20 .  
      In another embodiment, the flexible antenna  10  does not have a reflector  18 . In this case the radiator  20  may be formed on a thin flexible substrate of the foam  12 .  
       FIG. 2  is a top left perspective view of a frame  30  for holding a flexible antenna in accordance with one embodiment of the invention. The frame  30  has a base  32  and four sides  34 ,  36 ,  38 ,  40 . In the top and bottom sides  34  &amp;  40  are placed a pair of moveable bars  42  &amp;  44 . The pair of bars  42  &amp;  44  attach to the sides of the antenna. The bars  42  &amp;  44  can move along the slots  46 ,  48 ,  50 ,  52 . When the bars are moved along the slots  46 ,  48 ,  50 ,  52 , the antenna is flexed and its gain profile is changed.  
       FIG. 3  is cross sectional schematic diagram of the flexible antenna in a flat  60  and a flexed position  62  in accordance with one embodiment of the invention. The section  64  represents the emitters of the antenna. The bars  42  &amp;  44  of  FIG. 2  are used to move the flexible antenna between these two positions. Note that the antenna is continuously flexible between these positions. In other embodiments the antenna is allowed to from a tube and have an essentially omni directional gain pattern.  
       FIG. 4  is a radiator design  70  in accordance with one embodiment of the invention. The radiator design has four identical emitters  72 . A signal feed system  74  branches into two arms  76 . The two arms  76  connect to four signal traces  78 . The four signal traces  78  are coupled to impedance matching traces  80  that apply the signal to the emitters  72 . The input signal is applied to the center between the arms  76 . The radiator design  70  is designed to flex along the axis  82 .  
       FIG. 5  is a gain plot  90  of the antenna design using the radiator of  FIG. 4  in a flat position in accordance with one embodiment of the invention. The plot  90  shows three traces; one for a gain cross section along the x-axis  92 , one for a gain cross section along the y-axis (axis  82  in  FIG. 4 ) and one for a gain cross section along the beam axis  94 . Note that the section along the beam axis is almost exactly the same as the section along the y-axis for all three  FIGS. 5-7 . The flat antenna has a beam width of about 36 degrees (slightly larger for the y-axis) and a gain of about 14 dB.  FIG. 6  is a gain plot  100  of the antenna design using the radiator of  FIG. 4  in a flexed position in accordance with one embodiment of the invention. Note that the x-axis gain  92  has essentially the same profile as in  FIG. 5 . This makes sense since the antenna is not flexed along the x-axis and therefore the geometrical configuration of the antenna in this axis is essentially undisturbed by the flexing. The beam axis  94  however has been significantly broadened by the flexing of the antenna. The beam width in this example on the beam axis is about 47 degrees and the gain is about 12 dB. As a result, of flexing the antenna the beam width has been expanded about 11 degrees.  FIG. 7  is a gain plot  102  of the antenna design using the radiator of  FIG. 4  in an even more flexed position in accordance with one embodiment of the invention. In this case the beam width for the on beam axis is about 90 degrees and the gain is about 10 dB. The overall shape of the plot is very similar to that found in  FIG. 6 . This plots show that the overall gain pattern remains substantially proportional and uniform as the antenna is flexed. In the flat position the antenna is a high gain antenna with a narrow beam width. This reduces the power required by the transmitter and decreases the probability that a hacker can intercept the signal. The antenna also has very high front to back rejection ratio, so very little signal leaks out the backside of the antenna. This also reduces the chance that a hacker can intercept a signal from the antenna.  
       FIG. 8  is a schematic diagram of an antenna system  110  in accordance with one embodiment of the invention. The system  110  has a flexible antenna  112  held by a frame  114 . The frame  114  has adjustable bars  116 ,  118  that are moved by a motor  120 . The motor  120  is coupled to a wireless controller  122 . This allows the antenna shape and gain profile to be adjustable remotely.  
       FIG. 9  is a bottom left perspective of a frame for holding a flexible antenna  130  in accordance with one embodiment of the invention. The frame  132  is a pivoting cylinder. A pair of posts  134 ,  136  hold the edges of the flexible antenna  138 . The posts  134 ,  136  may be manually moved towards each other to cause the antenna  138  to flex.  FIG. 10  is a side view of the frame for holding a flexible antenna of  FIG. 9  in accordance with one embodiment of the invention. This view shows that the antenna sytem  130  may be rotated about the cylinder  132 . In one embodiment the rotation of the antenna  138  in the cylinder  132  has a plurality of set positions. The positions may be spaced every 20 degrees in one embodiment.  
      Thus there has been described an antenna that is very inexpensive to manufacture. By selecting the correct antenna design, the antenna may be flexed to obtain a different gain profile. The antenna provides a higher gain than the present omni directional antennas used in wireless networks. As a result, the power required by the transmitter is reduced and there is a low probability of intercept by hacker or eavesdroppers.  
      While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alterations, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alterations, modifications, and variations in the appended claims.