Abstract:
A planar dual polarization antenna for receiving and transmitting at least one radio signal includes a first patch plate, a metal grounding plate and a first dielectric layer disposed between the first patch plate and the metal grounding plate. The metal grounding plate includes a first pattern slot and a second pattern slot symmetric with respect to a centerline of the first patch plate. A first rectangle and a second rectangle enclosing an angle constitute a shape of the first pattern slot. The first rectangle and the second rectangle meet at a pivot vertex.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a planar dual polarization antenna and a complex antenna, and more particularly, to a planar dual polarization antenna and a complex antenna of broadband, wide beamwidth, high antenna gain, better common polarization to cross polarization (Co/Cx) value, smaller size, and meeting 45-degree slant polarization requirements. 
     2. Description of the Prior Art 
     Electronic products with wireless communication functionalities, e.g. notebook computers, personal digital assistants, etc., utilize antennas to emit and receive radio waves, to transmit or exchange radio signals, so as to access a wireless communication network. Therefore, to facilitate a user&#39;s access to the wireless communication network, an ideal antenna should maximize its bandwidth within a permitted range, while minimizing physical dimensions to accommodate the trend for smaller-sized electronic products. Additionally, with the advance of wireless communication technology, electronic products may be configured with an increasing number of antennas. For example, a long term evolution (LTE) wireless communication system and a wireless local area network standard IEEE 802.11n both support multi-input multi-output (MIMO) communication technology, i.e. an electronic product is capable of concurrently receiving/transmitting wireless signals via multiple (or multiple sets of) antennas, to vastly increase system throughput and transmission distance without increasing system bandwidth or total transmission power expenditure, thereby effectively enhancing spectral efficiency and transmission rate for the wireless communication system, as well as improving communication quality. Moreover, MIMO communication systems can employ techniques such as spatial multiplexing, beam forming, spatial diversity, pre-coding, etc. to further reduce signal interference and to increase channel capacity. 
     The LTE wireless communication system includes 44 bands which cover from 698 MHz to 3800 MHz. Due to the bands being separated and disordered, a mobile system operator may use multiple bands simultaneously in the same country or area. Under such a situation, conventional dual polarization antennas may not be able to cover all the bands, such that transceivers of the LTE wireless communication system cannot receive and transmit wireless signals of multiple bands. Therefore, it is a common goal in the industry to design antennas that suit both transmission demands, as well as dimension and functionality requirements. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention provides a planar dual polarization antenna to solve current technical narrow-beamwidth problems. 
     An embodiment of the present invention discloses a planar dual polarization antenna, for receiving and transmitting at least one radio signal, comprising a first patch plate; a metal grounding plate comprising a first pattern slot and a second pattern slot, wherein a first rectangle and a second rectangle enclosing an angle constitute a shape of the first pattern slot, the first rectangle and the second rectangle meet at a pivot vertex, and the first pattern slot and the second pattern slot are symmetric with respect to a centerline of the first patch plate; and a first dielectric layer disposed between the first patch plate and the metal grounding plate. 
     An embodiment of the present invention further discloses a complex antenna for receiving and transmitting at least one radio signal, comprising a first planar dual polarization antenna layer comprising a plurality of first patch plates; a metal grounding plate comprising a plurality of rectangular regions, wherein each rectangular region of the plurality of rectangular regions is disposed corresponding to one of the plurality of first patch plates, each rectangular region of the plurality of rectangular regions comprises a first pattern slot and a second pattern slot, a first rectangle and a second rectangle enclosing an angle constitute a shape of the first pattern slot, the first rectangle and the second rectangle meet at a pivot vertex, and the first pattern slot and the second pattern slot are symmetric with respect to a centerline of the first patch plate; and a first dielectric layer disposed between the first planar dual polarization antenna layer and the metal grounding plate. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a top-view schematic diagram illustrating a planar dual polarization antenna according to an embodiment of the present invention. 
         FIG. 1B  is a cross-sectional view diagram of the planar dual polarization antenna taken along a cross-sectional line A-A′ in  FIG. 1A . 
         FIG. 2  is a schematic diagram illustrating a boomerang shape according to an embodiment of the present invention. 
         FIG. 3  is a top-view schematic diagram illustrating a complex antenna according to an embodiment of the present invention. 
         FIG. 4A  is a top-view schematic diagram illustrating a complex antenna according to an embodiment of the present invention. 
         FIG. 4B  is a schematic diagram illustrating a perspective view of the complex antenna shown in  FIG. 4A . 
         FIG. 5A  is a schematic diagram illustrating antenna resonance simulation results of the complex antenna shown in  FIG. 4A . 
         FIGS. 5B to 5E  are schematic diagrams illustrating antenna pattern characteristic simulation results of the complex antenna shown in  FIG. 4A  respectively at 2.3 GHz, 2.4 GHz, 2.496 GHz, 2.69 GHz. 
         FIGS. 6A to 6F  are top-view schematic diagrams illustrating complex antennas according to various embodiments of the present invention. 
         FIG. 7  is a top-view schematic diagram illustrating a complex antenna according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is a top-view schematic diagram illustrating a planar dual polarization antenna  10  according to an embodiment of the present invention.  FIG. 1B  is a cross-sectional view diagram of the planar dual polarization antenna  10  taken along a cross-sectional line A-A′ in  FIG. 1A . The planar dual polarization antenna  10  is utilized to receive and transmit radio signals of a broad band or different frequency bands, such as radio signals in Band  40  and Band  41  of an LTE wireless communication system (Band  40 : substantially 2.3 GHz-2.4 GHz, Band  41 : substantially 2.496 GHz-2.690 GHz). As shown in  FIGS. 1A and 1B , the planar dual polarization antenna  10  is substantially a seven-layered square architecture of reflection symmetry with respect to a symmetry axis axis_y and comprises a feeding transmission line layer  100 , dielectric layers  110 ,  130 ,  150 , a metal grounding plate  120  and patch plates  140 ,  160 . The patch plate  140  is the main radiating body and has a shape substantially conforming to a cross pattern in order to generate electromagnetic waves with linear polarization but not circular polarization. The patch plate  160  is utilized to increase resonance bandwidth of the planar dual polarization antenna  10 , and is electrically isolated from the patch plate  140  by the dielectric layer  150 . In some embodiments, the center of the metal grounding plate  120 , the center of the patch plate  140  and the center of the patch plate  160  are aligned to a centerline CL_ 1  of the patch plate  140 , and the centerline CL_ 1  is disposed perpendicular to the symmetry axis axis_y. The feeding transmission line layer  100  comprises feeding transmission lines  102   a ,  102   b , which are symmetric with respect to the symmetry axis axis_y and orthogonal to feed in radio signals of two polarizations. The metal grounding plate  120  is used for providing a ground and comprises slots  122   a ,  122   b  and pattern slots  124   a ,  124   b . The slots  122   a ,  122   b  are orthogonal to the feeding transmission lines  102   a ,  102   b , respectively. And, they are symmetry to the symmetry axis axis_y so as to generate an orthogonal dual-polarized antenna pattern. 
     Briefly, the length L 1  of the metal grounding plate  120  along the symmetry axis axis_y is longer than the width W 1  of the metal grounding plate  120  along the direction x, thereby increasing 3 dB beamwidth in the horizontal plane. The pattern slots  124   a ,  124   b  of the metal grounding plate  120  is utilized to balance the asymmetry of the length L 1  and the width W 1  and thus improve common polarization to cross polarization (Co/Cx) value. 
     Specifically, to increase the beamwidth in horizontal plane (i.e., the xz plane), the width W 1  of the metal grounding plate  120  along the direction x must be shortened to make the antenna pattern in horizontal plane diverge. It turns out that the length L 1  of the metal grounding plate  120  along the symmetry axis axis_y is longer than the width W 1  of the metal grounding plate  120  along the direction x. Since the length L 1  is not equal to the width W 1 , resonance lengths in the vertical direction and in the horizontal direction will differ. The pattern slots  124   a ,  124   b  of the metal grounding plate  120 , however, could balance the asymmetry due to the uneven quantities between the length L 1  and the width W 1 . The pattern slots  124   a ,  124   b  substantially have a boomerang shape  20 . Please refer to  FIG. 2 .  FIG. 2  is a schematic diagram illustrating the boomerang shape  20  according to an embodiment of the present invention. Basically, to constitute the boomerang shape  20 , rectangles  210   a ,  210   b  of identical shape and size meet at a pivot vertex P 1  and enclose an angle. To provide a better understanding of the structure of the boomerang shape  20 , one can image the rectangles  210   a ,  210   b  initially align with sides that overlap, and then respectively rotate tilt angles θ 1 , θ 2  in the opposite direction from the symmetry axis axis_y with respect to the pivot vertex P 1 . The tilt angles θ 1 , θ 2  may be 20°, but not limited herein. As shown in  FIG. 1A  and  FIG. 2 , the boomerang shape  20  is symmetric with respect to the symmetry axis axis_y, and the pattern slots  124   a ,  124   b  are disposed symmetrically with respect to the centerline CL_ 1  of the patch plate  140 . Besides, since the dielectric layers  110 ,  130  are disposed to electrically isolate the feeding transmission line layer  100 , the metal grounding plate  120  and the planar dual polarization antenna layer  140  from one another, the feeding transmission lines are coupled to the patch plate  140  by the slots of the metal grounding plate  120 —that is to say, radio signals from the feeding transmission line (e.g., the feeding transmission line  102   a ) are coupled to the slot (e.g., the slot  122   a ), and then coupled to the patch plate  140  when the slot  122  resonates—to increase antenna bandwidth. The resonance direction of the patch plate  140  with a shape substantially conforming to a cross pattern tilts with respect to the metal grounding plate  120 , and this effectively minimizes the dimensions of the planar dual polarization antenna  10  while meeting 45-degree slant polarization requirements. 
     Please note that the planar dual polarization antenna  10  as shown in  FIG. 1A  and  FIG. 1B  is an exemplary embodiment of the invention, and those skilled in the art can make alternations and modifications accordingly. For example, to enhance antenna gain, the planar dual polarization antenna  10  may be arranged to form an array antenna. Please refer to  FIG. 3 .  FIG. 3  is a top-view schematic diagram illustrating a complex antenna  30  according to an embodiment of the present invention. Similar to the planar dual polarization antenna  10 , the complex antenna  30  is a seven-layered square architecture as well and comprises a feeding transmission line layer  300 , three layers of dielectric layers (not shown), a metal grounding plate  320  and planar dual polarization antenna layers  340 ,  360 . However, the planar dual polarization antenna layer  340  of the complex antenna  30  comprises patch plates DPP_ 1 , DPP_ 2  with a shape substantially conforming to a cross pattern. The feeding transmission lines FTL 1   a , FTL —1   b , FTL_ 2   a , FTL_ 2   b  of the feeding transmission line layer  300  are disposed respectively corresponding to the patch plates DPP_ 1 , DPP_ 2  to feed in radio signals of two polarizations. The patch plate UPP_ 1 , UPP_ 2  of the planar dual polarization antenna layer  360  are also disposed respectively corresponding to the patch plates DPP_ 1 , DPP_ 2 . The metal grounding plate  320  can be divided into rectangular regions SC 1 , SC 2 , and slots SL_ 1   a , SL_ 1   b , SL_ 2   a , SL_ 2   b  on the rectangular regions SC 1 , SC 2  are also disposed respectively corresponding to the feeding transmission lines FTL_ 1   a , FTL_ 1   b , FTL_ 2   a , FTL_ 2   b.    
     Technically, because an LTE base station is generally located near the ground, and because of the distance between an LTE base station and a user, the radiation power of the complex antenna  30  should be concentrated in vertical plane (i.e., the yz plane) within plus or minus 10 degrees elevation angle with respect to the horizon. In such a situation, the patch plates DPP_ 1 , DPP_ 2  vertically aligned to form a 1×2 array antenna can ensure that antenna gain meets system requirements. Moreover, the length L 1  of the rectangular regions SC 1 , SC 2  along the symmetry axis axis_y is longer than the width W 1  of the rectangular regions SC 1 , SC 2  along the direction x, thereby increasing 3 dB beamwidth in horizontal plane (i.e., the xz plane). Table 1 is an antenna characteristic table for the complex antenna  30 . As can be seen from Table 1, the complex antenna  30  meets LTE wireless communication system requirements for maximum gain and front-to-back (F/B) ratio. Furthermore, as the width W 1  of the metal grounding plate  320  shrinks from 100 mm to 70 mm, the beamwidth in horizontal plane can increase to 69.5 to 73.0 degrees. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 the total length L 
                 200 
                 200 
                 200 
                 200 
               
               
                 of the metal grounding plate 
               
               
                 (mm) 
               
               
                 the width W1 of the 
                 100 
                  90 
                  80 
                  70 
               
               
                 metal grounding plate (mm) 
               
               
                 maximum gain (dBi) 
                 11.0-11.6 
                 10.9-11.5 
                 10.7-11.3 
                 10.5-11.1 
               
               
                 front-to-back 
                 11.5-12.7 
                 11.4-12.4 
                 11.4-12.7 
                 10.1-11.1 
               
               
                 (F/B) ratio (dB) 
               
               
                 3 dB beamwidth in 
                 62.5°-65.5° 
                 64.0°-68.5° 
                 68.0°-70.5° 
                 69.5°-73.0° 
               
               
                 horizontal plane 
               
               
                 common 
                 19.0-22.0 
                 17.4-20.5 
                 16.0-18.3 
                 13.6-16.8 
               
               
                 polarization to cross 
               
               
                 polarization (Co/Cx) 
               
               
                 value in horizontal plane (dB) 
               
               
                 common 
                 22-29 
                 20-29 
                 18-29 
                 14-28 
               
               
                 polarization to cross 
               
               
                 polarization (Co/Cx) 
               
               
                 value in vertical plane (dB) 
               
               
                   
               
             
          
         
       
     
     To further improve common polarization to cross polarization (Co/Cx) value of the complex antenna  30 , the structure of the metal grounding plate  320  may be modified. Please refer to  FIG. 4A  and  FIG. 4B .  FIG. 4A  is a top-view schematic diagram illustrating a complex antenna  40  according to an embodiment of the present invention.  FIG. 4B  is a schematic diagram illustrating a perspective view of the complex antenna  40 . The complex antenna  40  comprises the feeding transmission line layer  300 , dielectric layers  310 ,  330 ,  350 , a metal grounding plate  420  and the planar dual polarization antenna layers  340 ,  360 . In other words, the structure of the complex antenna  40  is similar to that of the complex antenna  30  shown in  FIG. 3 , and the similar parts are not detailed redundantly. Different from the complex antenna  30 , rectangular regions SC 3 , SC 4  of the metal grounding plate  420  further comprise pattern slots PSL_ 1   a , PSL_ 1   b , PSL_ 2   a , PSL_ 2   b  respectively, which balance the asymmetry due to the uneven quantities between the length L 1  and the width W 1 . The pattern slots PSL_ 1   a , PSL_ 1   b , PSL_ 2   a , PSL_ 2   b  respectively have the shape of the boomerang shape  20  as shown in  FIG. 2 , and are symmetric with respect to the centerline CL_ 1 , CL_ 2  of the patch plates DPP_ 1 , DPP_ 2 , respectively. 
     In other words, with the array antenna structure, antenna gain of the complex antenna  40  increases. And the width W 1  of the rectangular regions SC 3 , SC 4  is shortened to increase beamwidth. In order to balance the asymmetry between the length L 1  and the width W 1 , the rectangular regions SC 3 , SC 4  further respectively comprise the pattern slots PSL_ 1   a , PSL_ 1   b , PSL_ 2   a , PSL_ 2   b  and thus improve common polarization to cross polarization (Co/Cx) value. 
     Simulation and measurement may be employed to determine whether the complex antenna  40  meets system requirements. Specifically,  FIG. 5A  is a schematic diagram illustrating antenna resonance simulation results of the complex antenna  40 . In  FIG. 5A , dotted and solid lines respectively indicate antenna resonance simulation results for a 45-degree slant polarization and a 135-degree slant polarization of the complex antenna  40 , while a dashed line indicates antenna isolation simulation results between a 45-degree slant polarization and a 135-degree slant polarization. It can be seen that, in Band  40  and Band  41 , return losses (S 11 ) of a 45-degree slant polarization and a 135-degree slant polarization of the complex antenna  40  have values below −11.8 dB. Furthermore, isolation between a 45-degree slant polarization and a 135-degree slant polarization of the complex antenna  40  is at least 22.5 dB or above. In addition, Table 2 is an antenna characteristic table for the complex antenna  40 .  FIGS. 5B to 5E  are schematic diagrams illustrating antenna pattern characteristic simulation results of the complex antenna  40  respectively at 2.3 GHz, 2.4 GHz, 2.496 GHz, 2.69 GHz. In  FIGS. 5B to 5E , common polarization radiation pattern of the complex antenna  40  in horizontal plane (i.e., at 0 degrees) is presented by a solid line, common polarization radiation pattern of the complex antenna  40  in vertical plane (i.e., at 90 degrees) is presented by a dotted line, cross polarization radiation pattern of the complex antenna  40  in horizontal plane is presented by a long dashed line, and cross polarization radiation pattern of the complex antenna  40  in vertical plane is presented by a short dashed line.  FIGS. 5B to 5E  and Table 2 show that the beamwidth of the complex antenna  40  in horizontal plane is wide and the complex antenna  40  meets LTE wireless communication system requirements for maximum gain and front-to-back (F/B) ratio. Besides, the common polarization to cross polarization (Co/Cx) value is at least 16.3 dB or above. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
             
               
                   
                 the total length L of the metal 
                 200 
               
               
                   
                 grounding plate (mm) 
               
               
                   
                 the width W1 of the metal grounding 
                  70 
               
               
                   
                 plate (mm) 
               
               
                   
                 maximum gain (dBi) 
                 10.6-11.1 
               
               
                   
                 front-to-back (F/B) ratio (dB) 
                 11.3-11.8 
               
               
                   
                 3 dB beamwidth in horizontal plane 
                 69.5°-74.0° 
               
               
                   
                 common polarization to cross 
                 16.3-17.3 
               
               
                   
                 polarization (Co/Cx) value in 
               
               
                   
                 horizontal plane (dB) 
               
               
                   
                 common polarization to cross 
                 18-29 
               
               
                   
                 polarization (Co/Cx) value in 
               
               
                   
                 vertical plane (dB) 
               
               
                   
                   
               
             
          
         
       
     
     Please note that the planar dual polarization antenna  10  and the complex antenna  30 ,  40  are exemplary embodiments of the invention, and those skilled in the art can make alternations and modifications accordingly. For example, portions of the feeding transmission lines  102   a ,  102   b , FTL_ 1   a , FTL_ 1   b , FTL_ 2   a , FTL_ 2   b  and the slots  122   a ,  122   b , SL_ 1   a , SL_ 1   b , SL_ 2   a , SL_ 2   b  may be modified according to different considerations, which means that degrees of the included angles enclosed by two adjacent portions can be either obtuse or acute angles, length ratios or width ratios may be changed, and the shape and the number of portions may vary. Also, having a shape “substantially conforming to a cross pattern” recited in the present invention relates to the patch plate  140 ,  160 , UPP_ 1 , UPP_ 2 , DPP_ 1 , DPP_ 2  being formed by two overlapping and intercrossing rectangular patch plates. However, the present invention is not limited thereto, and any patch plate having a shape “substantially conforming to a cross pattern” are within the scope of the present invention. For example, a patch plate extends outside a square side plate; alternatively, a patch plate extends outside a saw-tooth shaped side plate; alternatively, a patch plate further extends outside an arc-shaped side plate; alternatively, edges of a patch plate are rounded. The dielectric layers  110 ,  130 ,  150 ,  310 ,  330 ,  350  can be made of various electrically isolation materials such as air. The patch plate  160 , the planar dual polarization antenna layer  360  and the dielectric layer  150 ,  350  in fact depend on bandwidth requirements and may therefore be optional. The complex antennas  30 ,  40  are 1×2 array antennas, but not limited thereto and can be 1×3, 2×4 or m×n array antennas. 
     Besides, the length L 2  of the rectangle  200   a  of the boomerang shape  20  as shown in  FIGS. 2, 4A, 4B  is 25 mm, the width W 2  is 2.5 mm, the distance D between the pivot vertex P 1  of the boomerang shape  20  and the centerline (e.g., the centerline CL_ 1  or the centerline CL_ 2 ) is 47.449 mm; However, the present invention is not limited to this and can be appropriately adjusted according different system requirements. For example, please refer to  FIGS. 6A to 6F  and Table 3.  FIGS. 6A to 6F  are top-view schematic diagrams illustrating complex antennas  61  to  66  according to various embodiments of the present invention. Table 3 is an antenna characteristic table for the complex antennas  61  to  66 . As can be seen from Table 3, by properly adjusting the size of the pattern slot of the complex antennas  61  to  66 , antenna characteristics are changed and common polarization to cross polarization (Co/Cx) value can be greater than 15.8 dB. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 the complex 
                 the complex 
                 the complex 
                 the complex 
                 the complex 
                 the complex 
               
               
                   
                 antenna 61 
                 antenna 62 
                 antenna 63 
                 antenna 64 
                 antenna 65 
                 antenna 66 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
               
               
                   
                 70 
                 70 
                 70 
                 70 
                 70 
                 70 
               
               
                   
                 25 
                 20 
                 20 
                 20 
                 15 
                 20 
               
               
                   
                 5 
                 7.5 
                 10 
                 12.5 
                 15 
                 17.5 
               
               
                   
                 47.449 
                 44.975 
                 44.975 
                 44.975 
                 42.483 
                 44.975 
               
               
                   
                 10.5-11.1 
                 10.5-11.2 
                 10.5-11.1 
                 10.5-11.1 
                 10.6-11.0 
                 10.4-10.9 
               
               
                   
                 11.5-12.3 
                 11.0-11.7 
                 11.2-11.8 
                 11.4-12.0 
                 11.2-11.7 
                 11.2-12.6 
               
               
                   
                 70.5°-75.0° 
                 69.5°-74.0° 
                 69.5°-73.5° 
                 69.5°-75.0° 
                 69.5°-73.5° 
                 69.5°-74.0° 
               
               
                 common polarization 
                 15.8-18.7 
                 16.4-17.6 
                 16.6-17.8 
                 16.1-19.2 
                 16.1-16.8 
                 16.4-21.7 
               
               
                 to cross polarization 
               
               
                 (Co/Cx) value in 
               
               
                 horizontal plane (dB) 
               
               
                 common polarization 
                 23-35 
                 19-31 
                 20-31 
                 23-31 
                 18-27 
                 24-31 
               
               
                 to cross polarization 
               
               
                 (Co/Cx) value in 
               
               
                 vertical plane (dB) 
               
               
                   
               
             
          
         
       
     
     On the other hand, to reduce the beamwidth in horizontal plane (i.e., the xz plane), the width of the metal grounding plate along the direction x may be enlarged.  FIG. 7  is a top-view schematic diagram illustrating a complex antenna  70  according to an embodiment of the present invention. The structure of the complex antenna  70  is substantially similar to that of the complex antenna  40 , and the similar parts are not detailed redundantly. Different from the complex antenna  40 , the width W 7  of the metal grounding plate  720  along the direction x increases to make the antenna pattern in horizontal plane converge. Therefore, the length L 7  of rectangular regions SC 5 , SC 6  of the metal grounding plate  720  along the symmetry axis axis_y is less than the width W 7  of rectangular regions SC 5 , SC 6  along the direction x. The rectangular regions SC 5 , SC 6  of the metal grounding plate  720  further comprises pattern slots PSL_ 5   a , PSL_ 5   b , PSL_ 6   a , PSL_ 6   b  to balance the asymmetry of the length L 7  and the width W 7 . 
     To sum up, by adjusting the ratio of the length to the width of the rectangular regions of the metal grounding plate, beamwidth increases. In order to balance the asymmetry of the length and the width, the metal grounding plate comprises pattern slots, which improves common polarization to cross polarization (Co/Cx) value. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.