Abstract:
An antenna element architecture containing a dielectric beamwidth compensation perimeter structure around a radiating element is disclosed. A transmitting and receiving antenna element is provided so as to provide a desired azimuth and elevation radiation pattern in the intended polarization without degrading performance of cross polarization. Both single and dual polarization antenna elements can be employed.

Description:
RELATED APPLICATION INFORMATION 
     The present application claims priority under 35 USC section 119(e) to U.S. provisional patent application Ser. No. 60/964,865 filed Aug. 15, 2007, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to radio communication antenna systems for wireless networks. More particularly, the invention is directed to multi-element antenna arrays. 
     2. Description of the Prior Art and Related Background Information 
     Modern wireless antenna systems generally include a plurality of radiating elements that may be arranged over a ground plane defining a radiated (and received) signal beamwidth and azimuth angle. Antenna beamwidth has been conventionally defined by Half Power Beam Width (HPBW) of the azimuth or elevation beam relative to a bore sight of such antenna element. 
     Real world applications often call for an antenna radiating element with frequency bandwidth, pattern beamwidth and polarization requirements that may not be possible for conventional antenna radiating element designs to achieve due to overall mechanical constraints. In general practice stand alone antenna radiating elements are combined into high performance antenna arrays. Such antenna arrays are typically characterized having a variable or broad beamwidth in the  azimuth plane which necessitates use of antenna radiating element designs capable of azimuth beamwidth optimization to achieve overall antenna performance. 
     Accordingly, a need exists for an improved antenna element architecture which allows optimization of antenna array requirements, such as HPBW, antenna gain, side lobe suppression, F/B ratio, etc., without introducing undesirable tradeoffs, while taking into account cost and complexity of such antenna array.  
     SUMMARY OF THE INVENTION 
     In a first aspect the present invention provides an antenna radiating structure comprising a first generally planar radiating element and a second generally planar radiating element configured above and spaced apart from the first generally planar radiating element in a radiating direction. The second generally planar radiating element is configured generally coplanar with the first generally planar radiating element and has an aperture for radiative coupling thereto. The antenna radiating structure further comprises a ground plane configured below the second generally planar radiating element and a dielectric perimeter structure configured around the edges of the first and second generally planar radiating elements. 
     In a preferred embodiment the antenna radiating structure further comprises an electrically conductive shroud configured on the perimeter of the dielectric perimeter structure. The electrically conductive shroud is preferably configured on the outer vertical surface of the dielectric perimeter structure. The electrically conductive shroud is preferably recessed from the top surface of the dielectric perimeter structure. The antenna radiating structure preferably further comprises a top dielectric substrate coupled to the dielectric perimeter structure and the second generally planar radiating element is configured on the top dielectric substrate. The antenna radiating structure preferably further comprises a second dielectric substrate coupled to the dielectric perimeter structure and the first generally planar radiating element is configured on the second dielectric substrate. The antenna radiating structure preferably further comprises a third dielectric substrate coupled to the dielectric perimeter structure and the ground plane is configured on the third dielectric substrate. The top dielectric substrate and the second dielectric substrate are preferably configured on respective ledges on the inside perimeter edge of the dielectric perimeter structure. The dielectric perimeter structure is preferably configured on top of the ground plane. The dielectric perimeter structure is constructed from a dielectric material having  dielectric constant range E r4 , preferably between 2 to 6. The dielectric perimeter structure preferably has a rectangular fence shape with a wall width between about 0.762 to 3.175 mm chosen for the desired bandwidth of operation of the antenna structure. The antenna structure may be adapted for operation within the UMTS band (1900-2200 MHz) and the dielectric perimeter structure preferably has a width and length of about 75 mm and a height of about 18 to 20 mm. The electrically conductive shroud preferably has a height from about 14 to 20 mm. The electrically conductive shroud is also preferably recessed from the top surface of the dielectric perimeter structure a distance of about 4 mm or less. 
     In another aspect the present invention provides an antenna array. The antenna array comprises a generally planar reflector and a plurality of radiating structures configured in front of the reflector in the radiating direction. Each of the radiating structures comprises first and second coplanar aperture coupled radiating elements and a dielectric fence shaped structure surrounding the radiating elements. 
     In a preferred embodiment of the antenna array each of the plurality of radiating structures further comprises an electrically conductive shroud configured on the perimeter of the dielectric fence shaped structure. Each of the plurality of radiating structures preferably further comprises first and second dielectric substrates, wherein the first and second coplanar aperture coupled radiating elements are configured on the first and second dielectric substrates, respectively. The dielectric fence shaped structure preferably has a wall width between about 0.762 to 3.175 mm, chosen for the desired bandwidth of operation of the antenna array. The dielectric fence shaped structure is constructed from a dielectric material having dielectric constant range E r4 , preferably between 2 to 6. The electrically conductive shroud preferably has a height from about 14 to 20 mm and is recessed from the surface of the dielectric fence shaped structure by about 4 mm or less.  
     Further features and aspects of the invention will be appreciated from the following detailed description of the invention.  
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a single column antenna array incorporating five controlled beamwidth antenna elements. 
         FIG. 2  is a front view of a preferred embodiment of an antenna element in accordance with the present invention. 
         FIG. 3  is a cross section along A-A datum line in Y-view of a preferred embodiment of the antenna element. 
         FIG. 2A  is a front view of the preferred embodiment of the antenna element with first dielectric substrate removed to allow an unobstructed view of the second dielectric substrate. 
         FIG. 3A  is a cross section along A-A datum line, in Y-view, of the preferred embodiment of the antenna element with first dielectric substrate removed. 
         FIG. 2B  is a front view of the preferred embodiment of the antenna element with first and second dielectric substrates removed to allow unobstructed view of the third dielectric substrate. 
         FIG. 3B  is a cross section along A-A datum line, in Y-view, of the preferred embodiment of the antenna element with first and second dielectric substrate removed. 
         FIG. 4  is a cross section detail along A-A datum line, identifying preferred dimensions and distances. 
         FIG. 5  is a representation of HPBW antenna element elevation radiation curves for various dielectric thickness configurations. 
         FIG. 6  presents a typical co-polar and cross-polar radiation patterns in the E-plane. 
         FIG. 7  is a front view of a preferred embodiment of an antenna element in accordance with the present invention.  
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It is an object of the present invention to provide optimization for a compact antenna radiating element while providing preferred beamwidth performance and without degrading performance in the cross-polarization radiation. In a preferred embodiment of the present invention, a dual polarization antenna element is provided comprising a co-planar aperture-coupled patch with dielectric perimeter compensation structure having dimensions adapted for the specific application, further circumferenced by a partially recessed or fully recessed, electrically conductive perimeter shroud on the outward vertical surface of the dielectric. 
     The antenna element preferably includes a top dielectric substrate which includes a top side patch having the appropriate shape and size. The top dielectric substrate with radiating metallization is placed above a pre-shaped ground plane disposed on a second dielectric substrate or a suitably constructed spacing element. A third (bottom) dielectric substrate is provided which contains pass through aperture coupling slots and feed lines disposed on the back side of the third dielectric. In an aperture-coupled patch radiator the excitation signals pass through a pair of slots arranged orthogonally at their centers. Each slot excites a corresponding mode within the antenna element. Teachings related to aperture-coupled antenna elements previously disclosed in U.S. Pat. No. 6,018,319 (Lindmark) may be employed herein and the disclosure of such patent is incorporated herein by reference. 
     Reference will now be made to the accompanying drawings, which assist in illustrating the various pertinent features of the present invention. 
       FIG. 1  shows a front view of an antenna array,  100 , according to an exemplary implementation, which utilizes a conventionally disposed reflector  105  plane. Reflector,  105  is oriented in a vertical orientation (Y-dimension) of the antenna array. The reflector,  105 , may, for example, consist of electrically conductive  plate suitable for use with Radio Frequency (RF) signals. Further, reflector  105 , plane is shown as a featureless rectangle, but in actual practice additional features (not shown) may be added to aid reflector performance as to enhance overall antenna array performance. 
     The antenna array,  100 , contains a plurality of antenna elements, also referred to as RF radiators ( 110 ,  120 ,  130 ,  140 ,  150 ) arranged vertically and preferably proximate to the vertical center axis P 0  of the reflector  105 , plane and are vertically offset from one another. In the illustrative non-limiting implementation shown, the plurality of RF radiators ( 110 ,  120 ,  130 ,  140 ,  150 ) arranged as shown on reflector  105  plane form an antenna array useful for RF signal transmission and reception. However, it shall be understood that an alternative number and/or type of radiating elements, such as taper slot antenna, horn, folded dipole, and etc, can be used as well. 
     Conventionally, an antenna array for a wireless network may include signal divider and combiner networks, as well as other circuits and subsystems that together provide useful performance aspects of an antenna array. Detailed descriptions covering these aspects of the antenna array are omitted from this disclosure since they are well known to those skilled in the art. Such antenna array can be connected to an RF transceiver for use in a wireless network with suitably constructed radio frequency guides such as coaxial cable. 
     With reference to  FIG. 2  a top view (while viewing into a negative Z direction) of a stacked aperture-coupled patch (ACP) antenna element  110  is presented. A perspective view is shown in  FIG. 7 . Construction details are provided in  FIGS. 2A-4 . 
     Referring to the above noted figures, antenna element  110  is constructed using three separate dielectric substrates or layers. The top most dielectric substrate  111  is provided for secondary radiating patch  112  that is disposed on the outward  facing side of the first dielectric substrate  111 . By definition an outward facing side is oriented in positive Z direction as denoted by the coordinate system reference. The top most dielectric substrate  111  is preferably securely mounted to the top ledge of the four sided dielectric fence ( 115   a - d ). A small recess grove (or other means) can be used to maintain proper orientation of the top most dielectric substrate  111  relative to the aperture structure  118  below. Furthermore, secondary radiating patch  112  is centrally disposed on the outward facing side of the first dielectric substrate  111 , however, alternative orientations are also possible. 
     Middle dielectric substrate  116 , also referred to as dielectric substrate # 2 , is disposed bellow first dielectric substrate  111 . Main radiating  117  patch is disposed on the outward facing side of the middle dielectric substrate  116 . Depending on the thickness of the middle dielectric substrate  116  main radiating  117  patch can be positioned on the inward facing side of the middle dielectric substrate  116 . Preferably, middle dielectric substrate  116  is secured to the four sided dielectric fence ( 115   a - d ) via perimeter slot cut into dielectric fence ( 115   a - d ) or through other mechanical means known in the art. 
     Bottom dielectric substrate  119 , also referred to as dielectric substrate # 3 , is disposed bellow dielectric substrate # 2  and mounted flash below through opening  212  in the reflector plane  105 . The outward facing side of the dielectric substrate ( 119 ) # 3  (facing toward dielectric substrate # 2 ) is covered with conductive material, for example copper. The top side of the dielectric substrate  119  provides a ground plane for main radiating  117  patch and secondary radiating patch  112 . The radio frequency (RF) energy from feed lines (not shown) disposed on the bottom side of the 3 rd  dielectric substrate  119  and orthogonal to aperture  118  cross arms is coupled to main radiating  117  patch and to a lesser extent to secondary radiating patch  112 . The backside of the through opening  212  in the reflector plane  105  where RF feed lines are disposed is shielded with RF shield  210  to prevent back side RF radiation.  
     The beamwidth of a conventionally constructed aperture-coupled patch (ACP) antenna is typically between 60 and 70 degrees. A conventionally constructed ACP can not be readily adapted for broader beamwidth over wider operating frequency band. The present invention allows increases in HPBW without loss of operating frequency bandwith or by degrading cross polarization performance by employing a combination of predetermined thickness (DF dimension) in dielectric fence ( 115   a - d ) and electrically conductive shroud  114 . 
     Dielectric fence ( 115   a - d ) can be constructed utilizing dielectric material having dielectric constant range E r4 , preferably between 2 to 6. In the preferred embodiment dielectric fence ( 115   a - d ) is shown as a square; however, the geometric shape of the fence structure is dictated by the radiating element electromagnetic properties and thus alternative shapes can be used instead. A wider width (DF) dielectric fence ( 115   a - d ) results in wider HPBW. Illustrative performance curves and radiation patterns are shown in  FIGS. 5 and 6  respectively. 
     Preferred dimensions of the dielectric structures and conductive structures will vary with the specific application. In a preferred embodiment, adapted for operation within UMTS band (1900-2200 MHz), dielectric fence ( 115   a - d ) preferably has the following dimensions: 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Dimension 
                 Value Range 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 d1 
                 75 
                 mm 
               
               
                   
                 d2 
                 75 
                 mm 
               
               
                   
                 HD 
                 18 to 20 
                 mm 
               
               
                   
                 DF 
                 0.762 to 3.175 
                 mm 
               
               
                   
                 E r4   
                 ~2.2 to 4.6 
               
               
                   
                   
               
             
          
         
       
     
     Electrically conductive shroud  114  provides cross polarization decoupling between antenna array radiating elements as well as partial HPBW enhancement. Conductive shroud  114  is positioned directly on the top surface of reflector  105  plane. A low resistance path between conductive shroud  114  and the top surface of reflector  105  plane is required to achieve desired antenna element  110  performance. 
     In a preferred embodiment, for example for the noted UMTS band, the electrically conductive shroud  114  preferably has the following dimensions: 
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Dimension 
                 Value Range 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 HM 
                 14 to 20 
                 mm 
               
               
                   
                 d1 
                 75 
                 mm 
               
               
                   
                 d2 
                 75 
                 mm 
               
             
          
           
               
                   
                 Material 
                 Copper 
               
               
                   
                   
               
             
          
         
       
     
     The present invention has been described primarily in solving aforementioned problems relating to use of dielectric perimeter fence together with a conductive shroud to increase 3 dB HPBW without degrading radiation in the cross-polarized field component. In this regard, the foregoing description of an antenna element based on the aperture-coupled patch (ACP) radiator is presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Accordingly, variants and modifications consistent with the following teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain modes known for practicing the invention disclosed herewith and to enable others skilled in the art to utilize the invention in equivalent, or alternative embodiments and with various modifications considered necessary by the particular application(s) or use(s) of the present invention.