Abstract:
A coupler for use in wireless communications systems that is particularly useful in broadband applications includes a pair of coupling elements that are mounted on the interior and exterior surfaces of a vehicle, such as a rear window. Both coupling elements have dielectric substrates mounted within housings and each of the substrates includes a dual “bowtie” arrangement. This arrangement includes a first bowtie that is etched onto the substrate to remove the conductive upper layer and a second bowtie formed of conductive material and positioned within the first bowtie and spaced apart from its boundaries so as to define a slot separating the two.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to portable wireless communications systems, and more particularly to an improved coupling device used with such communication systems. 
     Wireless communications systems are in wide use. These systems are used to transmit both voice and data over cellular and other communications systems. The first cellular telephone systems were analog systems that operated in a frequency band from around 800 MHz to 960 MHz. Newer, digital communication systems operate in PCN or PCS networks at higher frequency bands of between about 1500 to about 2400 MHz. The frequency bands have been expanded for currently, the cellular frequencies for most North American cellular systems include two frequency bands: 824-894 MHz for the AMPS band and 1.85-1.99 GHz for the PCS band. In Europe these two bands are slightly different and include 890-960 MHz for GSM and 1.71-1.88 GHz for the PCN band, with some communication frequencies being as high as 2.17 GHz. 
     Systems that operate in both these bands are preferred so that communication can be supplied to a system user regardless of the equipment the user or system operates. In order to complement the operation of the system, it is desirable to efficiently couple a system antenna to the telephone or other apparatus. A coupler is a device that is used to couple radio-frequency (RF) signals between two components of a system, such as in a mobile telephone system, the exterior antenna and the interior coaxial cable and vice-versa. The couplers permit window mounting, and are mounted on opposite sides of a mounting surface which is typically a portion of one of the windows of a vehicle. 
     Typically, these couplers are structured to operate only in a single narrow frequency band. Other couplers, such as that described in U.S. Pat. No. 6,069,588, issued May 30, 2000 are complex in structure because they utilize multiple electronic components as part of the coupler. Still other couplers, like that described in U.S. Pat. No. 5,995,821 issued Nov. 30, 1999 uses multi-part coupling elements that must be oriented at desired angles and distances to each other in order to efficiently operate. In order to accommodate cellular and mobile telephones that operate in multiple cellular bands, a coupler itself must be capable of transferring RF signals through the medium upon which it is mounted with minimal signal loss. 
     A need therefore exists for an improved coupler that operates efficiently in multiple frequency bands with a simple structure, and which has minimal signal loss in operation. The present invention is directed to such a coupler. 
     SUMMARY OF THE INVENTION 
     It is therefore a general object of the present invention to provide an improved coupler that operates within dual frequency bands of wireless communication systems. 
     It is another object of the present invention to provide a simple and inexpensive coupler that efficiently couples RF signals in a wide bandwidth of from about 800 to about 2000 MHz. 
     It is yet another object of the present invention to provide an improved coupler for use with wireless telecommunication systems that includes a bowtie slot formed within a layer of conductive material on the surface of a circuit board and which is fed from a feedline on the opposite side of the circuit board, the feeding occurring at the apex of the bowtie. 
     Still another object of the present invention is to provide an improved dual band-operative coupler of small size that encompasses all present bands of cellular communication frequencies and that includes a pair of dielectric bases adapted for respective attachment to opposite sides of a glass surface of either a vehicle or building, the bases having opposing first and second sides, the second sides of the bases each including a layer of conductive material disposed thereon, and, a pair of bowtie slots formed thereon in alignment with each other so that one bowtie slot is located within the other bowtie slot, the two bowtie slots being separated from each other by an intervening layer of conductive material, each base further including a feed point that provides a feed point providing a feed connection through the dielectric stratum to the apexes of the two bowties. 
     Yet a still further object of the present invention is to provide a coupler incorporating a pair of bowtie-shaped slots of the structure set forth above and further including a tuning network extending along an opposite surface of the support and connecting to the bowtie element(s) at an associated apex portion thereof. 
     The present invention accomplishes these objects and advantages through its novel and unique structure. In one principal aspect of the present invention, a coupling element is provided for attachment to an interior surface of a vehicle or building, preferably a window. The coupler includes a housing, a coaxial transmission line and a dielectric support board disposed within the housing. One side of the board that faces toward the interior surface of the window has a layer of conductive material formed thereupon. A pair of slots are formed in the conductive material, in the form of inner and outer slots. The outer slot has the shape of a bowtie in which a pair of triangular-shaped members are joined together at their apexes. The inner slot also has the shape of a bowtie and the inner slot is separated from the outer slot by an extent of conductive material. The two bowtie slots are preferably oriented along common axes, and the intervening conductive layer that separates them from each other also has a bowtie shape, or a shape that approximates an angled lemniscate. The first and second bowties are separated at their apexes by the opening. The other side of the dielectric board supports the transmission line which is terminated to the coupler by way of a passage, or via, that extends through the board and which communicates with the apex of the bowtie. 
     In another principal aspect of the present invention, the transmission line may be terminated to a conductive tuning network disposed on the opposite side of the dielectric board. This network may include a serpentine pattern of conductive material, such as foil that may be arranged to provide the desired frequency. The bowtie pattern can be easily formed on the dielectric boards by etching the conductive material disposed on the surfaces thereof. Conventional circuit board material may be used for the substrate such as phenolic, copper-clad or laminated sheets or epoxy-based or fiberglass fabric sheets coated with a conductive layer. 
     These and other objects, features and advantages of the present invention will be clearly understood through consideration of the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the course of the following detailed description, reference will be frequently made to the accompanying drawings in which: 
     FIG. 1 is a schematic diagram illustrating a vehicle environment in which the present invention finds utility; 
     FIG. 2 is a partial exploded perspective view looking at the exterior antenna mount through a glass interface at the interior coupler member of the coupler of the present invention; 
     FIG. 3 is the same view as FIG. 2, but from the interior side of the glass interface illustrating the coupler member used with the exterior antenna mount; 
     FIG. 4 is a diagrammatic, sectional view of a coupler assembly of the present invention mounted on a glass window and terminated to a radiating element on the exterior and to a coaxial transmission line on the interior; 
     FIG. 5 is a perspective, diagrammatic view of one of the two coupler members of the present invention illustrating the structural relationship and dimensions thereof; 
     FIG. 6 is a plan view of the internal coupling element of the invention illustrating the geometric relationship of the bowtie portions of the coupling elements; and, 
     FIG. 7 is a schematic view of another embodiment of the invention, utilizing a “rounded” bowtie-slot design. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Known couplers that have been used in the telecommunications field are typically small in size and are mostly capable of performance in a tight range of frequencies. They do not operate well in wide frequency ranges. The present invention performs well across all frequencies from 824 MHz to about 2 Ghz, which includes the AMPS (824-894 MHz), GSM (890-960 MHz), PCN (1710-1880 MHz) and PCS (1850-1990 MHz) bands. The present invention provides a coupler that effectively transmits radio frequency (“RF”) signals through a window, or other dielectric across a wide bandwidth ranging from about 829 MHz to about 2 to 3 GHz. It is contemplated that the present invention will perform as well for future communication systems, such as the European UMTS with a maximum frequency of 2.17 GHz and even up to anticipated frequencies of 3 GHz. 
     In its most useful application, that of mobile communications, as illustrated in FIG. 1, a typical mobile communications system is seen to include a wireless telephone, or receiver,  20  that is disposed within the vehicle  21 , an antenna  22  and a transmission line  23  interconnecting the two. The antenna  22  may include a module  29  having a swivel mount  30  that is attached to a plate or dielectric board  31  and which supports a radiating element  33 . The radiating element  33  may have its own particular structure that may be detachably mounted by way of a screw base  34  that permits the radiating element  33  to be selectively rotated back and forth between two flanges  36 . The swivel mount  30  and its supporting board  31  are typically mounted in a housing  35  that protects the board  31  and any circuitry thereon, from the environment. An adhesive layer, using a pressure-sensitive adhesive or the like covers the underside  36  of the board  31  and serves to attach the entire assembly to an exterior surface  25  of the vehicle  21 , such as the rear window  26 . 
     In order to effectively pass RF signals through the vehicle&#39;s exterior surface  25  (typically a glass window), a coupler assembly  40 , is provided. It will be understood that the present invention refers to a coupling assembly which passes signals through an interface, such as a vehicle window  26 , as opposed to an antenna that actually receives and transmits RF signals. The coupler assembly  40  is attached to a separate antenna radiating element  33 , as shown in FIGS. 1,  2  and  4 . FIG. 4 diagrammatically illustrates the use of couplers of the present invention and they can be seen to include an external coupling element  82  that is affixed to a vehicle exterior surface, preferably a glass window  26 , and an internal coupling element  81  that is affixed to a vehicle interior surface. The external coupling element  82  supports and is connected to an antenna radiating element  33 , while the internal coupling element  81  is connected to and supports a transmission line, such as a coaxial cable  72 , having an inner signal conductor  74  surrounded by a dielectric cover, which in turn is surrounded by a conductive outer shield  73 . The two coupling elements  31 ,  41  are typically housed in respective housings  35  and  43 . 
     FIG. 2 illustrates the face of the internal coupling element  81  best, while FIG. 3 illustrates the face of the external coupling element  82 . These two faces oppose each other in installation, as shown in FIG.  4 . The internal coupling element  81  of the coupler assembly  40  includes a dielectric support board  41  with two, opposite surfaces  44 ,  45 , a coaxial transmission line to board connector  42  that is mounted to the surface  45  of the board  41 . A housing  43 , shown in phantom in FIG. 4, may be provided that encloses the board and the connector  41  two components. Similarly, the external coupling element  82  includes a dielectric board  31  and an antenna radiating element support structure  30 , all of which are typically enclosed within a housing  35 , shown in phantom in FIGS. 2 and 4. In use, the internal coupling element  81  is mounted on the interior surface of the vehicle glass  26  as illustrated in alignment with the external coupling element  82 . 
     It has been discovered that the use of a particular slot pattern on the dielectric support boards  31 ,  41  permits the coupler to effectively pass, or transmit, RF signals over a wide band of frequencies that range from about 800 MHz to about 2.0 GHz through the glass of the vehicle. This coupler permits the use of a multi-band antenna on the vehicle without drilling through the body of the vehicle to connect the external antenna radiating element  33  to the internal transmission line  72 . Each coupling element  81 ,  82  includes a dielectric board with two surfaces. The internal coupling element support board  41  has two opposing surfaces  44 ,  45 , with the former surface  44  being referred to herein as the “inner” surface in that it faces and abuts the window glass  26  of the vehicle window, and the latter surface  45  being referred to herein as the “outer” surface of the internal coupling element  81  in that it faces outwardly with respect to the window glass. Similar terminology holds for the exterior coupler module that also supports the antenna  33 , with the “inner” surface  60  thereof facing the window interior surface, or the plane of the paper in FIG.  2  and the “outer” surface  61  facing away from the window. 
     Each of the two coupler members has a unique pattern that imparts the unexpected coupling in a wide frequency band. As shown in FIGS. 2 &amp; 4, and particularly, FIG. 4, the internal coupling element support board  41  can be seen to include a first layer of conductive material  47  applied to its inner surface  44 . This and other conductive material used on the support board  41  is shaded in FIG. 4 for clarity. This layer  47  is preferably formed as a continuous layer on the inner surface  44  of the support board  41  as would normally be found on a copper-clad circuit board, and it preferably extends to or near the edge  70  of the support board  41 . This conductive material may include thin films, foils or plates formed from copper, brass, gold, steel, alloys thereof or any conductive material. A non-conductive area is formed in the conductive layer  47  by removing a selected amount and extent of the first conductive layer  47  in order to define a non-conductive “slot”, or “aperture”,  48  within the first conductive layer  47 . This slot  48 , as illustrated best in FIG. 6, is formed from two areas  49  that are illustrated as triangular-shaped and which are oriented thereon so that their respective apexes  49   a  either meet or intersect together in the central part of the board  41  as illustrated. Both triangular shapes are preferably the same size so that the slot  48  is symmetrical about a longitudinal axis L of the support board  41 , shown in FIG. 2, as well as a transverse axis T of the support board  41 , shown in FIG.  6 . These two axes may be considered as axes of symmetry insofar as the conductive layers and non-conductive slots are concerned. The mating of these two triangular areas  49  cooperatively provide an overall bowtie-shaped configuration of the slot  48 . This slot  48  defines the lower end of frequency bandwidth in which the coupler assembly  40  operates. The intersection of the two triangular-shaped areas  49  serve also to define two apexes  53   a  of two generally triangular-shaped conductive areas  53  that are offset with respect to the non-conductive areas  49  and which are oriented along the longitudinal axis of symmetry L of FIG.  2 . Although triangular-shaped slots are illustrated in the drawings, it will be understood that the slots need not be exact triangles. For example, the corners thereof may be rounded, rather than being formed of two intersecting lines, as illustrated in FIG.  7 . 
     In an important aspect of the present invention, a second conductive layer of material  51  is disposed on the internal coupling element support board  41 . The term “second” is used herein to describe this layer  51  only in the sense that it is separated from the first layer  47  of conductive material by the bowtie slot  48 . Both the first and second layers  47 ,  51  may be part of the original conductive facing on the board  41 , portions of which may be removed in a conventional manner, such as photo-etching, in order to form the bowtie slot  48 . This second conductive layer  51  may be considered as an insert that is placed within the slot  48  and thus it may be formed by applying a second conductive layer to the support board separate from the first conductive layer  51 . 
     The second conductive layer  51  also has the configuration of a bowtie as illustrated, but this second bowtie  51  is smaller in dimension than the bowtie non-conductive slot  48  so that the second conductive area  51  lies entirely within, or is encompassed by, the non-conductive slot  48 . The slot  48  itself may also be considered as having a general bowtie shape, or at least in outline, and may further be considered as having the configuration of an angled partial lemniscate (the mathematical symbol used to represent infinity and which is similar to a figure-eight), similar to what is illustrated in FIG.  7 . The internal coupling element  81  thus presents two conductive areas that are separated by an intervening dielectric slot. 
     The inner coupling element transmission line, or coaxial cable  72 , is terminated to the inner surface  44  of the internal coupling element  81 . As illustrated in FIG. 3, the coaxial connector  42  has a center opening  64  that is adapted to receive the center conductor  74  of the coaxial transmission cable  72  and which is surrounded by a dielectric material, which in turn, is surrounded by a conductive threaded collar  65 . The collar  65  mates with a coupling attached to the cable and terminated to the cable inner shield  73 . In order to terminate or connect this grounded shield of the cable to the internal coupling element  81 , the internal coupling element  81  has a series of vias, or passages,  66  through which conductive material, such as solder, may extend to provide an electrical connection between the cable grounding shield and the first conductive layer  47 , near the edge  70  of the support board  41 . 
     The signal conductor of the coaxial cable  72  is also terminated to the first conductive layer  47 , but in an area spaced apart from the location of connection of the cable grounding shield  73 . This is effected by way of another via  67  that is located near the apex of one of the triangles formed by the first conductive layer  47 . This termination acts as a feed port for the coupler assembly and in order to provide the most effective feeding, it is desired to locate this termination near the apex of the triangles but across a gap formed by the non-conductive slot  48  of the support board  41 . The feedline that extends to the via  67  may utilize a conductive stripline  68  as shown in FIG. 3 that extends from the coaxial connector  42  near the edge  70  of the internal coupling element  81  across the gap “G” (FIG. 2) formed by the intersection of the two triangles  49  that cooperatively form the bowtie slot  48 . The stripline  68  may incorporate a serpentine pattern as shown to “tune” the feedline by matching the impedance of the antenna radiating element  33 . The termination of the feedline from the coaxial cable  72  may be considered as occurring near the convergence of the apexes  49   a  of the triangular-shaped areas  49  that make up the bowtie slot, and near the convergence of the apexes  53   a  of the triangular-shaped areas  53  of the first conductive layer  47 . 
     A similar structural arrangement occurs on the support board  31  of the external coupling element  82  in that the inner surface  60  thereof includes a first conductive layer  90  that encompasses a non-conductive slot  91 , also having a bowtie shape. The external coupling element  82  further includes a conductive insert, or second layer  92  that is contained within the non-conductive slot  91 . In order to obtain optimum performance, the second layer of conductive material  92  is also preferably separated from the first conductive layer  90  by the intervening slot  91 . The second support board  31  also has a via  95  (FIGS. 2 &amp; 3) by which the antenna radiating element  33  is terminated to the first conductive layer  90 , by way of soldering or the like. This termination also occurs near the gap “G” between the apexes of the first conductive layer  90  and the intersection of the apexes of the two non-conductive triangles that cooperatively form the bowtie non-conductive slot  91  of the second coupling element. 
     It has been found that the bowtie slots  48  and  91 , provide a means for coupling RF signals at the low end of the desired operational frequency bandwidth extending from between about 800 MHz to about 1000 MHz (1 GHz) which will cover the AMPS frequency band in North America and the GSM frequency band in Europe. The inner conductive bowties  51 ,  92  provide a means of tuning the coupler and serves to extend, or broaden, the frequency bandwidth of the coupler assembly  40 . The first conductive layers  47 ,  90  act as groundplanes for their respective coupling elements. 
     For the coupler element shown in FIG. 4, the following dimensions have been determined to provide operation that encompasses both the AMPS bandwidth of 824-894 MHz and the PCS bandwidth of 1850-1990 MHz: 
     
       
         
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 A = 50 mm 
               
               
                   
                 B = 42 mm 
               
               
                   
                 C = 33 mm 
               
               
                   
                 D = 50 mm 
               
               
                   
                 E = 42 mm 
               
               
                   
                 F = 30 mm 
               
               
                   
                   
               
             
          
         
       
     
     Although other shapes are believed to operate in a similar manner, it is believed that the triangular shape illustrated offers best performance. In order to tune the performance of the coupler, the dimensions of the non-conductive slots  48 ,  91  may be adjusted (i.e., the depth and width thereof) to gain the most efficient performance of the coupling assembly  40 . 
     A second slot  100 ,  100 ′ may be provided for the system in the center areas of the conductive bowtie inserts  51 ,  92  that extends within the boundaries thereof in order to add a reactive load to the input impedance of the coaxial transmission line  72 . This second slot may be rectangular as illustrated in FIGS. 2,  3  &amp;  5 , or it may have a slight bowtie configuration as illustrated in FIG.  6 . 
     FIG. 7 illustrates another embodiment of a coupler element  300  in which the angled edges or corners of the slots have been rounded. The conductive layer  147  has a rounded slot  149  formed therein, and that in turn has a rounded conductive insert  151 , with its own corresponding rounded slot  200 . The apexes  153  of the conductive layer  147  are likewise rounded. Similar performance is believed to be attained using such an embodiment. 
     While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended claims. For example, the bowtie configuration may be modified to reduce its dimensions, increase its dimensions or to change its overall configuration, provided that a second conductive layer or insert is maintained within the slot and isolated from the first conductive layer.