Abstract:
A directional coupler for the directional transmission of high-frequency signals provides at least three lines and at least three ports. Two lines of the three lines are connected in a conductive manner at least at their ends. A third line is arranged between the two first lines and coupled to the latter in an electromagnetic manner. In this context, the high-frequency signal is transmitted from the third line to the first line and second line. The coupling is implemented via a coupling gap.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a directional coupler with directional transmission of high-frequency signals. 
     2. Related Technology 
     Coupled lines are conventionally used in directional couplers. In this context, reference is made, for example, to U.S. Pat. No. 5,689,217. However, with a conventional single-layer structure on a printed circuit board, only a low sharpness of directivity can be achieved. With the conventional structure, a sharpness of directivity of more than 30 dB can be achieved only with a structure of at least three layers or with a mechanically very complex structure or with an explicit optimization during manufacture of the sharpness of directivity of each individual directional coupler. 
     SUMMARY OF THE INVENTION 
     The invention provides a directional coupler, which provides a high sharpness of directivity within a required frequency range at low cost and with compact dimensions of the circuit structure. 
     Accordingly, the invention provides a directional coupler with at least three lines and at least three ports for the directional transmission of high-freguency signals, wherein a first line and a second line are connected in a conductive manner at least at their two ends, wherein a third line is arranged between the first line and the second line, wherein the third line is coupled in an electromagnetic manner to the first line and to the second line, so that the high-freguency signal is transmitted from the first and second line to the third line, wherein the coupling of the third line to the first line and the second line is implemented via at least one coupling gap. 
     The directional coupler according to the invention provides at least three lines and at least three ports. Two of the three lines are connected in a conductive manner at least at their ends. A first line is arranged between the first and second line and coupled electromagnetically to the latter. In this context, the high-frequency signal is transmitted from the third line to the first line and the second line. The coupling is implemented across a coupling gap. The coupling area increased by the three coupled lines allows a compact construction of the circuit with a good sharpness of directivity. 
     The directional coupler is advantageously constructed using stripline technology. A structure using widely-available stripline technology ensures compatibility with other circuits constructed using this technology within the respective application of the same substrate. Furthermore, this technology is characterized by a low cost for the circuit structure. 
     The frequency response of the sharpness of directivity is advantageously determined by selecting the width of the lines and/or of the coupling gap. Accordingly, a simple adjustability of the frequency-dependent sharpness of directivity is possible during the design process. 
     The first and the second line advantageously provide at least one common port. The first line advantageously provides at least two ports. This structure allows the signals to be impressed and picked up. 
     The transmission of signals from at least one first port of the third line to at least one port of the first and second line is advantageously, at most, weakly attenuated. The transmission of signals from at least one second port of the third line to at least one port of the first and second line is advantageously strongly attenuated. A high sharpness of directivity can be achieved in this manner. 
     By preference, the third line is connected in a conductive manner to a fourth line and a fifth line at least at their ends. In this context, the fourth and fifth line are preferably arranged parallel and outside of the first and second line. The fourth and fifth line are advantageously separated from the first and second line by coupling gaps. An increase in the number of lines increases the coupling area. This significantly increases the sharpness of directivity with a cost and space requirement for the circuit structure, which is not significantly increased. 
     The first and second line are advantageously connected in a conductive manner to several further lines at least at their ends. The first line is also advantageously connected in a conductive manner to several further lines at least at their ends. By preference, the several further lines extend parallel and outside of the first and second lines and are each separated by coupling gaps. A line connected to the first and second line and a line connected to the third line are advantageously positioned in an alternating manner at the side of the first and second line facing away from the third line. An arbitrary number of further coupling lines further increases the sharpness of directivity without significantly increasing the cost and space requirement of the circuit structure. 
     The directional coupler is advantageously constructed on the front side of the substrate. The rear side of the substrate is advantageously metallized and provides a reference potential. All lines connected to the third line are advantageously connected via through-contacts to the rear side of the substrate, wherein the metallization is interrupted around the connections of the through-contacts. By connecting the lines on the rear side of the substrate, a more costly manufacturing process is avoided. This structure allows a high sharpness of directivity at low cost and with small dimensions of the structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described by way of example below with reference to the drawings, in which an advantageous exemplary embodiment of the invention is illustrated. The drawings are as follows: 
         FIG. 1  shows an exemplary presentation of the front side of the first exemplary embodiment of the directional coupler according to the invention; 
         FIG. 2  shows an exemplary presentation of the rear side of the first exemplary embodiment of the directional coupler according to the invention; 
         FIG. 3  shows an exemplary presentation of details of the front side of the first exemplary embodiment of the directional coupler according to the invention; 
         FIG. 4  shows an exemplary presentation of the front side of a second exemplary embodiment of the directional coupler according to the invention; 
         FIG. 5  shows an exemplary presentation of the rear side of the second exemplary embodiment of the directional coupler according to the invention; 
         FIG. 6  shows an exemplary presentation of details of the front side of the second exemplary embodiment of the directional coupler according to the invention; and 
         FIG. 7  shows an exemplary three-dimensional presentation of the second exemplary embodiment of the directional coupler according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The circuit-technology structure and function of the directional coupler according to the invention is explained with reference to  FIGS. 1-7 . In some cases, the presentation and description of identical elements has not been repeated in similar drawings. 
       FIG. 1  shows an exemplary presentation of the front side of a first exemplary embodiment of the directional coupler according to the invention. The lines  16 ,  18  and  19  are applied to a substrate  10  using stripline technology. In this context, the line  16  is connected to the coaxial ports  12  and  13 , as described in greater detail with reference to  FIG. 2 . The lines  18  and  19  are also connected to one another in a conductive manner. Accordingly, on the upper side of the substrate  10 , a non-metallized window is formed, which is surrounded on all sides by the lines  18  and  19 , and in which the first line  16  is arranged in such a manner that it nowhere touches the first line  18  and the second line  19  on the upper side. 
     The lines  18  and  19  provide the two common coaxial ports  11  and  14 . The desired coupling direction of the directional coupler in this context extends from coaxial port  11  to coaxial port  12  and from coaxial port  14  to coaxial port  13 . The function of the directional coupler is described in greater detail with reference to  FIG. 3 . 
     In  FIG. 2 , an exemplary presentation of the rear side of the first exemplary embodiment of the directional coupler according to the invention is presented. The rear side of the substrate  10  named with reference to  FIG. 1  is metallized over the entire surface. The line  16  from  FIG. 1  is guided by means of through-contacts to the rear side  30  of the substrate  10 . Here, the through-contacts are connected in a conductive manner to through-contacts of the coaxial ports  32  and  33  within regions  35  and  36  insulated from the metallization. 
       FIG. 3  shows an exemplary presentation of details of the front side of the first exemplary embodiment of the directional coupler according to the invention. The conductor  58  is connected in a conductive manner to the contacts  52  and  54 . The lines and  51  and  59  are also connected in a conductive manner. The contacts  50 ,  52 ,  54  and  57  lead to the coaxial ports  11 ,  12 ,  13  and  14  described with reference to  FIG. 1 . The named lines  51 ,  58  and  59  are separated from one another by the coupling gap  56 . The frequency response of the sharpness of directivity of the directional coupler is adjusted by specifying the width of the coupling gap  56  and/or the width of the lines  51 ,  58  and  59 . Because of the large available coupling area through the several lines  51 ,  58  and  59 , a high sharpness of directivity can be achieved with a compact structure of the directional coupler on only one substrate layer. 
       FIG. 4  shows an exemplary presentation of the front side of a second exemplary embodiment of the directional coupler according to the invention. The lines  75 ,  76 ,  77 ,  78  and  79  are applied to a substrate  70  using stripline technology. In this context, the lines  75 ,  76  and  77  are connected to the coaxial ports  72  and  73  as described in greater detail with reference to  FIG. 5 . The lines  78  and  79  are also connected to one another in a conductive manner. The lines  78  and  79  provide the two common coaxial ports  71  and  74 . The desired coupling direction of the directional coupler extends in this context from coaxial port  71  to coaxial port  72  and from coaxial port  74  to coaxial port  73 . The function of the directional coupler is described in greater detail with reference to  FIG. 6 . 
     In  FIG. 5 , an exemplary presentation of the rear side of the second exemplary embodiment of the directional coupler according to the invention is presented. The rear side  80  of the substrate  70  named with reference to  FIG. 4  is metallized over the entire surface. The lines  75 ,  76  and  77  from  FIG. 3  are guided by means of through-contacts to the rear side  80  of the substrate  70 . Here, the through-contacts are connected to one another in a conductive manner and connected to through-contacts of the coaxial ports  82  and  83  within regions  85  and  86  insulated from the metallization. 
       FIG. 6  shows an exemplary presentation of details of the front side of the second exemplary embodiment of the directional coupler according to the invention. The lines  110 ,  113  and  118  are connected in a conductive manner to the contacts  112  and  114 . The lines  111  and  119  are also connected in a conductive manner. The contacts  110 ,  112 ,  114  and  117  lead to the coaxial ports  71 ,  72 ,  73  and  74  described with reference to  FIG. 4 . The named lines  110 ,  113  and  118  are separated by coupling gaps  115 ,  116  and  120  from the lines  111  and  119 . The frequency response of the sharpness of directivity of the directional coupler is adjusted by specifying the width of the coupling gaps  115 ,  116  and  120  and/or the width of the lines  110 ,  111 ,  113 ,  118  and  119 . Because of the large coupling area available through the several lines  110 ,  111 ,  113 ,  118  and  119 , a high sharpness of directivity can be achieved with a compact structure of the directional coupler on only one substrate layer. 
     In  FIG. 7 , an exemplary three-dimensional presentation of the second exemplary embodiment of the directional coupler according to the invention is presented. In this context, the scaling of the axes does not correspond to the scaling of the preceding presentations. In particular, in  FIG. 7 , the vertical dimension is considerably stretched by comparison with the horizontal dimensions in the plane of the substrate, so that the through-contacts  90  are more readily recognizable. The striplines  92 ,  96  and  97  are connected in a conductive manner via the through-contacts  90  and the connection  100  on the rear side of the substrate to one another and to the contacts  94  and  98 . The striplines  91  and  95  are connected on the front side of the substrate to one another and to the contacts  93  and  99 . The coupling is implemented from port  93  to port  94  and from port  99  to port  98 . 
     The invention is not restricted to the exemplary embodiment presented. For example, further different components influencing the frequency response of the sharpness of directivity can be used. A use of the structure in multi-layer printed circuit boards is also conceivable. A further increase in the number of lines used for the coupling is also possible. All of the features described above or features illustrated in the drawings can be combined with one another as required within the framework of the invention.