Patent Publication Number: US-9853339-B2

Title: Dielectric waveguide input/output structure and dielectric waveguide filter using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Basic application: Japanese Patent Application No. 2015-050463 filed on Mar. 13, 2015. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an input/output structure of a dielectric waveguide, and, in particular, to an input/output structure suitable for mounting on a printed circuit board, and the like. 
     2. Description of the Related Art 
     There has been used a dielectric waveguide input/output structure comprising an input/output electrode formed on a bottom surface and lateral walls of a dielectric waveguide resonator which performs input and output, as an input/output structure for directly mounting, on a printed circuit board, a dielectric waveguide filter, a dielectric waveguide duplexer, or the like comprising a plurality of dielectric waveguide resonators coupled to each other. 
       FIG. 8  is a lower perspective view illustrating an example of a dielectric waveguide filter comprising a conventional dielectric waveguide input/output structure described in JP 2002-135003A. A dielectric waveguide filter  100  comprises dielectric waveguide resonators  102 ,  102  having a rectangular parallelepiped shape as an outer shape and TE mode as a resonant mode. The dielectric waveguide resonators  102 ,  102  are coupled to each other via a slit  103 . In a bottom surface  102   b  of each of the dielectric waveguide resonators  102 ,  102 , there is provided a band-like input/output electrode  105  that extends from the center on one side of the bottom surface  102   b  to a direction of opposing sides. Each dielectric waveguide resonator  102  is covered with an electrically conductive film, except for opposite sides  106 ,  106  of the input/output electrode  105  and for a lateral opening  107  surrounding the input/output electrode  105  in a lateral surface  102   a  with which the input/output electrode  105  is in contact. 
     BRIEF SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     The dielectric waveguide input/output structure as described above has a strength of coupling which is adjusted by a length of the input/output electrode. However, there is a limitation in an adjustable range of the coupling, which makes it impossible to have an input/output structure with wider bandwidth. 
     Means for Solving the Problem 
     A dielectric waveguide input/output structure of the present invention comprises an input/output point provided near the center on one side of a bottom surface of a rectangular parallelepiped-shaped dielectric body, wherein an outer periphery of the dielectric body is covered with an electrically conductive film, except for an L-shaped lateral part extending along an edge of the bottom surface from opposite sides of the input/output point and for a surrounding part of the input/output point in a lateral surface with which the input/output point is in contact. 
     Effect of the Invention 
     According to the present invention, it becomes possible to provide an input/output structure with wider bandwidth, having wider adjustable range of coupling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an embodiment of a dielectric waveguide filter comprising a dielectric waveguide input/output structure of the present invention. 
         FIG. 1B  illustrates an example of mounting the dielectric waveguide filter in  FIG. 1A  on a substrate. 
         FIG. 2  illustrates a simulation result of an external Q of a conventional dielectric waveguide input/output structure. 
         FIG. 3  illustrates a simulation result of an external Q of the dielectric waveguide input/output structure of the present invention. 
         FIG. 4A  is a diagram for explaining a horizontal axis of  FIG. 2 . 
         FIG. 4B  is a diagram for explaining a horizontal axis of  FIG. 3 . 
         FIG. 5  illustrates a result of simulating a magnetic-field strength distribution inside a resonator. 
         FIG. 6A  schematically illustrates the conventional dielectric waveguide input/output structure. 
         FIG. 6B  schematically illustrates the dielectric waveguide input/output structure of the present invention. 
         FIG. 7  illustrates an alternative embodiment of the dielectric waveguide input/output structure of the present invention. 
         FIG. 8  illustrates an example of the conventional dielectric waveguide input/output structure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1A  illustrates a perspective view for explaining an embodiment of a dielectric waveguide filter comprising a dielectric waveguide input/output structure of the present invention, with a bottom surface up. 
       FIG. 1B  illustrates a perspective view for explaining mounting of the dielectric waveguide filter illustrated in  FIG. 1A  on a substrate. 
     As illustrated in  FIG. 1A , a dielectric waveguide filter  10  comprises dielectric waveguide resonators  20 ,  20 , each consisting of a rectangular parallelepiped-shaped dielectric body, and having TE mode as a resonant mode. The dielectric waveguide resonators  20 ,  20  are coupled to each other via a slit  30 . 
     Each of the dielectric waveguide resonators  20 ,  20  comprises a rectangular input/output electrode  50  defining an input/output point  50   a  near the central region on one side of a bottom surface  40   c,  and is covered with an electrically conductive film  20   a,  except for an L-shaped lateral parts  60 ,  60  extending along an edge of the bottom surface  40   c  from opposite sides of the input/output point  50   a,  and for a lateral opening  70  surrounding the input/output point  50   a  in a lateral surface  40   a  of the dielectric waveguide resonator with which the input/output point  50   a  is in contact. 
     As illustrated in  FIG. 1B , the dielectric waveguide filter  10  is mounted on a printed circuit board  80  which comprises lines  90   a,    90   b  each having a distal end formed in an approximately the same shape as the input/output electrode  50 , and a ground pattern  90   c.  In this case, the distal end of each of the lines  90   a,    90   b  is connected to respective one of the input/output electrodes  50 ,  50 , and the electrically conductive film  20   a  is connected to the ground pattern  90   c.  The lines  90   a,    90   b  are, for example, microstrip lines or coplanar lines. 
       FIG. 2  illustrates a graph of a result of simulating a dielectric waveguide filter comprising a conventional dielectric waveguide input/output structure. 
       FIG. 3  illustrates a graph of a result of simulating a dielectric waveguide filter comprising the dielectric waveguide input/output structure of the present invention. 
     In  FIG. 2 , the horizontal axis represents a relative length between lateral parts A′ and B′ in the illustration of  FIG. 4A , and the vertical axis represents an external Q. 
     In  FIG. 3 , the horizontal axis represents a relative length between lateral parts A and B in the illustration of  FIG. 4B , and the vertical axis represents an external Q. It is noted that the external Q is a reciprocal of coupling. 
     It can be seen from the results of  FIGS. 2 and 3  that the dielectric waveguide input/output structure of the present invention has a lower minimum value of external Q as compared to the conventional dielectric waveguide input/output structure, and that the external Q becomes minimum when a distal end of edge is near the central portion of adjacent side. 
     This is considered to occur for the following reason. 
       FIG. 5  illustrates a result of simulating a magnetic-field strength distribution inside a resonator. As illustrated in the simulation of  FIG. 5 , the magnetic field is strongest in lateral sides near the center of the resonator, and weakest in the center and corners of the resonator. 
       FIG. 6A  schematically illustrates the conventional dielectric waveguide input/output structure, and  FIG. 6B  schematically illustrates the dielectric waveguide input/output structure of the present invention. In  FIGS. 6A and 6B , dashed lines indicate locations with the largest magnetic field in the result of  FIG. 5 . 
     The conventional dielectric waveguide input/output structure illustrated in  FIG. 6A  intersects with the lateral part at only one location of the locations with largest magnetic field in the dielectric resonator, whereas the dielectric waveguide input/output structure of the present invention illustrated in  FIG. 6B  intersects with the lateral part at three locations of the locations with largest magnetic field in the dielectric resonator. 
     For this reason, it is possible for the latter to have a smaller external Q. 
     Since the dielectric waveguide input/output structure of the present invention enables the adjustable range of coupling to be wider than the conventional dielectric waveguide input/output structure in this way, it becomes possible to have an input/output structure with wider bandwidth. 
     It is noted that when the dielectric waveguide is mounted on a substrate, the electromagnetic field is likely to leak from a small gap between a lateral surface and a bottom surface of the dielectric waveguide, making the coupling strength reduced. A fillet formed by a solder between the substrate and the lateral surface of the dielectric waveguide can easily prevent the leakage of the electromagnetic field. 
       FIG. 7  is a perspective view illustrating an alternative embodiment of a dielectric waveguide filter comprising the dielectric waveguide input/output structure of the present invention, with a bottom surface up. 
     As illustrated in  FIG. 7 , a dielectric waveguide filter  11  comprises rectangular parallelepiped-shaped dielectric waveguide resonators  21 ,  22  and a rectangular parallelepiped-shaped dielectric block  23  that is smaller than the dielectric waveguide resonators  21 ,  22 , which are serially connected via a slit  31 . 
     An input/output point  51   a  provided on one side of a bottom surface of the dielectric waveguide resonator  21  is extended across the bottom surface to an end surface  23   a  of the adjacently-disposed dielectric block  23 . 
     By having such a structure, the leakage of the electromagnetic field at the input/output point can be prevented. 
     It is noted that the dielectric waveguide input/output structure is not necessarily required to be provided in the resonators positioned at either end of the dielectric waveguide filter. 
     If other dielectric waveguide resonators are located on opposite sides of a dielectric waveguide resonator, it may have an input/output point provided on one side of the bottom surface thereof that is not adjacent to the other dielectric waveguide resonators. 
     EXPLANATION OF CODES 
     
         
           10 ,  11 ,  12 ,  13 ,  100 : dielectric waveguide filter 
           20 ,  21 ,  22   a  to  22   f,    23   a  to  23   f,    102 : dielectric waveguide resonator 
           30 ,  31 ,  103 : slit 
           40   a,    40   b,    41   a,    41   b,    102   a:  lateral surface 
           40   c,    102   b:  bottom surface 
           50 ,  51 ,  105 : input/output electrode 
           50   a,    51   a:  input/output point 
           60 ,  61 ,  106 : lateral part 
           70 ,  71 ,  107 : lateral opening 
           80 ,  81 ,  82 ,  83 : printed circuit board 
           90   a,    90   b,    91   a,    91   b,    92   a,    92   b,    93   a,    93 : line 
           90   c:  ground pattern