Abstract:
[Technical Problem] 
     In a dielectric waveguide input/output structure for performing conversion from a dielectric waveguide through a microstrip to a coaxial line, the conversion is performed once to the microstrip line, and then further to the coaxial line, resulting in a greater loss. Thus, there has been a problem that degradation in performance is unavoidable. Further, the microstrip is required to have a certain level or more of length so as to prevent reduction in size of the printed circuit board. This has been an impediment to downsizing of the input/output structure. 
     [Solution to the Problem] 
     Provided is an input/output structure for a dielectric waveguide, comprising a rectangular-parallelepiped-shaped dielectric block, a plate-shaped dielectric plate, and a feeder line comprising a line-shaped electrically conductive foil sandwiched between the dielectric block and the dielectric plate.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an input/output structure for a dielectric waveguide, and more particularly, to a structure for conversion between the dielectric waveguide and a coaxial line. 
         [0003]    2. Description of the Related Art 
         [0004]    A dielectric waveguide, which is obtained by providing an electrically conductive layer on a surface of a dielectric material, can eliminate the need for using a thick electrically conductive wall and effectively shorten an electromagnetic wave transmitted therethrough by virtue of the dielectric material, thereby to facilitate substantial downsizing of the waveguide device as compared to a traditionally used hollow waveguide. Such a downsized waveguide device is small enough to be directly mounted on a substrate. Thus, an input/output structure has been utilized which employs a structure for conversion between the dielectric waveguide and the microstrip, formed by soldering the dielectric waveguide to a mounted substrate comprising a microstrip line for performing an input/output operation (see, for example, JP 2012-147286A). 
         [0005]      FIG. 9  is an exploded perspective view of a dielectric waveguide filter employing a structure for conversion between the dielectric waveguide and the microstrip, which is a conventional dielectric waveguide input/output structure disclosed in JP 2012-147286A. As illustrated in  FIG. 9 , a dielectric waveguide filter  1  is formed by sequentially coupling dielectric waveguides  1   a,    1   b,    1   c,    1   d  and  1   e  each comprising a rectangular-parallelepiped-shaped dielectric block having an outer periphery covered with an electrically conductive layer. The dielectric waveguide filter  1  comprises:
   a coupling window  4   a  between the dielectric waveguides  1   a  and  1   b;      a coupling window  4   b  between the dielectric waveguides  1   b  and  1   c;      a coupling window  4   c  between the dielectric waveguides  1   c  and  1   d;  and   a coupling window  4   d  between the dielectric waveguides  1   d  and  1   e,  
 
wherein each coupling window allows a dielectric body to be exposed.
   
 
         [0010]    Each of the dielectric waveguides  1   a  and  1   e  positioned at either end of the dielectric waveguide filter  1  has a bottom surface having each of island-shaped electrodes  5   a  and  5   e  respectively, which is electrically insulated from the electrically conductive layer. 
         [0011]    A printed circuit board  8  has a front surface having an island-shaped electrode  8   b  and a back surface having a microstrip  8   a.  The printed circuit board  8  also comprises a via-hole  8   c  for coupling the island-shaped electrode  8   b  and the microstrip  8   a  together. The dielectric waveguides la and le are arranged to allow the island-shaped electrodes  5   a  and  5   e  each provided on the respective bottom surface of the dielectric waveguides  1   a  and  1   e  to be opposed to the island-shaped electrodes  8   b  and  8   b  each provided on the respective front surface of the printed circuit boards  8  and  8 , respectively. 
       LIST OF PRIOR ART DOCUMENTS 
     [Patent Documents] 
       [0012]    Patent Document 1: JP 2012-147286A 
         [0013]    Patent Document 2: JP 2003-318614A 
       BRIEF SUMMARY OF THE INVENTION 
     [Technical Problem] 
       [0014]    The inner portion of the dielectric waveguide is filled with the dielectric body. Thus, it is impossible to insert any structure into the dielectric waveguide. Therefore, when it is desired to couple the dielectric waveguide to a coaxial line, it is difficult to use a structure for conversion between a hollow waveguide and a coaxial line that has been used in a hollow waveguide, formed by inserting a probe into the hollow waveguide. For this reason, it is required, as illustrated in  FIG. 9 , to use conversion from the dielectric waveguide through the microstrip to the coaxial line, by which conversion is once performed to the microstrip line  8   a,  and then further to a connector  7  with conversion from the microstrip to the coaxial line, resulting in a greater loss. Thus, there has been a problem that degradation in performance is unavoidable. Further, the microstrip  8   a  is required to have a certain level or more of length so as to prevent reduction in size of the printed circuit board  8 . This has been an impediment to downsizing of the input/output structure. 
       [Means for Solving the Problem] 
       [0015]    According to the present invention, there is provided an input/output structure for a dielectric waveguide having a dielectric body and an electrically conductive layer covering the dielectric body, wherein the dielectric waveguide comprises: a rectangular-parallelepiped-shaped dielectric block, a plate-shaped dielectric plate, and a feeder line comprising a line-shaped electrically conductive foil sandwiched between the dielectric block and the dielectric plate. 
       [Effect of the Invention] 
       [0016]    The dielectric waveguide input/output structure of the present invention makes it possible to achieve an input/output structure with less degradation in performance because it can perform conversion directly between the dielectric waveguide and the coaxial line without performing any conversion to the microstrip. Further, this dielectric waveguide input/output structure makes it possible to achieve a downsized input/output structure because it eliminates the need for using a printed circuit board for the microstrip line. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an exploded perspective view of a dielectric waveguide according to a first embodiment of the present invention. 
           [0018]      FIG. 2  is a cross-sectional view of the dielectric waveguide in  FIG. 1  taken along the line A-A. 
           [0019]      FIG. 3  is an exploded perspective view of a dielectric waveguide according to a second embodiment of the present invention. 
           [0020]      FIG. 4  is a plane view of a dielectric block in  FIG. 3 . 
           [0021]      FIG. 5  is an exploded perspective view of a dielectric waveguide filter according to a third embodiment of the present invention. 
           [0022]      FIG. 6  is a graph illustrating a characteristic of the dielectric waveguide filter according to the third embodiment of the present invention. 
           [0023]      FIG. 7  is a graph illustrating a characteristic of the dielectric waveguide filter according to the third embodiment of the present invention. 
           [0024]      FIG. 8  is a graph illustrating a characteristic of the dielectric waveguide filter according to the third embodiment of the present invention. 
           [0025]      FIG. 9  is an exploded perspective view of a dielectric waveguide filter employing a conventional dielectric waveguide input/output structure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
       [0026]    A first embodiment of the present invention will now be described with reference to the drawings.  FIG. 1  is an exploded perspective view for describing in detail a first embodiment of a dielectric waveguide having a dielectric waveguide input/output structure of the present invention.  FIG. 2  is a cross-sectional view of the dielectric waveguide in  FIG. 1  taken along the line A-A. In  FIG. 1 , the shaded area represents an exposed dielectric portion. 
         [0000]    As illustrated in the figure, the dielectric waveguide  18  comprises a rectangular-parallelepiped-shaped dielectric block  20 , a plate-shaped dielectric plate  30  having a circular through-hole  50  with a diameter φ provided in an approximately central region thereof, and a feeder line  60  comprising a line-shaped electrically conductive foil sandwiched between the dielectric block and the dielectric plate. The dielectric waveguide  18  has an outer periphery including an inside surface  50   a  and a bottom surface  50   b  of the through-hole  50 , which is covered with an electrically conductive layer. The feeder line  60  has an end portion coupled to an island-shaped electrode  90  that is insulated from the electrically conductive layer provided on a side surface of the dielectric waveguide  18 . Thus, the dielectric waveguide  18  is exited from the side surface direction thereof.
 
The dielectric waveguide  18  is coupled to an external device which is not shown via a connector  70  connected to the island-shaped electrode  90 , and is also coupled to another dielectric waveguide via a coupling window  40  allowing a dielectric body to be exposed, provided on the side surface of the dielectric waveguide  18 .
 
         [0027]    The dielectric block  20  and the dielectric plate  30  are coupled together using a joining glass, and the external electrically conductive layer, the island-shaped electrode  90  and the feeder line  60  are formed by printing a silver paste followed by sintering. 
         [0028]    The dielectric waveguide  18  as described above exhibits less degradation in performance because it can perform conversion directly between the dielectric waveguide and the coaxial line. Further, the dielectric waveguide  18  can provide a downsized dielectric waveguide input/output structure because it eliminates the need for using a printed circuit board for the microstrip line. 
         [0029]    This type of structure having a convex portion in the resonator, which is referred to as a re-entrant structure, is known to reduce the length in the axial direction of the dielectric waveguide to decrease the area occupied by the dielectric waveguide, and to be capable of suppressing a third harmonic that is not easy to be suppressed. If the dielectric waveguide  18  does not have the through-hole  50 , it cannot be successfully oscillated by feeding from the side surface direction. Thus, providing the through-hole  50  has an effect that the dielectric waveguide  18  can be operated in a successful manner, that the length of the waveguide can be reduced, and that the third harmonic can be suppressed. Further, the dielectric waveguide  18  also has an effect of reducing unwanted radiations because it has a conversion section not exposed to the outside but located in the dielectric body. 
         [0030]    In the re-entrant structure, the bottom surface  50   a  of the through-hole  50  has less influence on the characteristic of the structure even when it allows the dielectric body to be exposed. Thus, it may be possible to provide no electrically conductive layer on the bottom surface  50   a  of the through-hole  50 . 
         [0031]    Further, it is considered that the dielectric block  20  is operating in a mode close to a TE mode, while the dielectric plate  30  is operating in a mode close to a TEM mode. Thus, it is considered that the dielectric block  20  and the dielectric plate  30  are operating in different operation modes. Therefore, the boundary between the dielectric block  20  and the dielectric plate  30  has a small influence on the characteristic of the structure, and it has a small influence on the characteristic even in the presence of a gap caused by the joining glass between the dielectric block  20  and the dielectric plate  30 . Preferably, the joining glass has a relative permittivity close to those of the dielectric block  20  and the dielectric plate  30 . 
         [0032]    Further, the relative permittivities of the dielectric block  20  and the dielectric plate  30  may be varied. The dielectric material having higher relative permittivity is expensive. Thus, it may be possible to restrain the cost of the dielectric waveguide input/output structure by, for example, employing for the dielectric plate  30  a less expansive dielectric material with lower relative permittivity than the dielectric block  20 . 
       Second Embodiment 
       [0033]      FIG. 3  is an exploded perspective view for describing in detail a second embodiment of a dielectric waveguide having a dielectric waveguide input/output structure of the present invention.  FIG. 4  is a plain view of the dielectric block for describing in detail a feeder line in  FIG. 3 . In  FIGS. 3 to 4 , like numerals refer to the same parts as those described in  FIGS. 1 to 2  and any overlapping description will be omitted. A dielectric waveguide  19  according to the second embodiment has approximately the same structure as the dielectric waveguide illustrated in the first embodiment except for the shape of the feeder line  60 . 
         [0034]    As illustrated in  FIG. 3 , the feeder line  61  has a distal end having a width y 1  that is thicker than a width y 0  of a root portion thereof (y 1 &gt;y 0 ), and the distal end of the feeder line  61  is spaced away from the through-hole  50  by a distance d. Further, the feeder line  61  has an approximately quarter wavelength open stub  61   a  provided on each of opposite sides at a position spaced away from a distal end thereof by an approximately quarter wavelength. 
         [0035]    By providing the open stub  61   a,  it becomes possible to suppress the second harmonic. Further, by forming the feeder line  61  to have the distal end having a width y 1  that is thicker than a width y 0  of the root portion thereof, it becomes possible to improve the power durability by locating the distal end at a distance from the through-hole, and to achieve a larger bandwidth of the input/output structure by keeping the external Q at low level. 
         [0036]    The dielectric waveguide  19  as described above can have an input/output structure with capability of suppressing the second harmonic, improved power durability and larger bandwidth by only changing the shape of the feeder line of the dielectric waveguide illustrated in the first embodiment. 
       Third Embodiment 
       [0037]      FIG. 5  is an exploded perspective view of a third embodiment which the dielectric waveguide illustrated in the second embodiment is applied to a dielectric waveguide filter. As illustrated in  FIG. 5 , a dielectric waveguide filter  100  is formed by sequentially coupling rectangular-parallelepiped-shaped dielectric waveguides  11  to  15  each having an outer periphery covered with an electrically conductive layer. The dielectric waveguide filter  100  comprises:
   a coupling window w 41  between the dielectric waveguides  11  and  12 ;   a coupling window w 42  between the dielectric waveguides  12  and  13 ;   a coupling window w 43  between the dielectric waveguides  13  and  14 ; and   a coupling window w 44  between the dielectric waveguides  14  and  15 ,
 
wherein each coupling window allows a dielectric body to be exposed.
   
 
         [0042]    Each of the dielectric waveguides  11  and  15  positioned at either side of the dielectric waveguide filter  100  comprises a rectangular-parallelepiped-shaped dielectric block  20 , a plate-shaped dielectric plate  30  having a circular through-hole  50  with a diameter φ in an approximately central region thereof, and a feeder line  60  comprising a line-shaped electrically conductive foil sandwiched between the dielectric block and the dielectric plate. The feeder line  60  has an end portion coupled to an island-shaped electrode  90  that is insulated from the electrically conductive layer provided on a side surface of the dielectric waveguide  18 . 
         [0000]    Each of the dielectric waveguides  11  and  15  is coupled to an external device which is not shown, via a connector  70  connected to the island-shaped electrode  90 .
 
The feeder line  61  has a distal end having a width that is thicker than a width of a root portion thereof. Further, the feeder line  61  has an approximately quarter wavelength open stub  61   a  provided on each of opposite sides at a position spaced away from a distal end thereof by an approximately quarter wavelength.
 
         [0043]    The dielectric waveguide filter  100  as described above has an input/output structure with less degradation in performance because it employs a dielectric waveguide input/output structure that can perform conversion directly from the dielectric waveguide to the coaxial line. Further, this dielectric waveguide  100  can provide a downsized dielectric waveguide filter because it eliminates the need for using a printed circuit board for the microstrip line. 
         [0044]      FIGS. 6 to 8  are graphs illustrating a comparison result between the dielectric waveguide filter  100  according to the third embodiment of the present invention illustrated in  FIG. 5  and the conventional dielectric waveguide filter  1  illustrated in  FIG. 9 .  FIG. 6  is a graph illustrating a return loss (S 11 ) and an insertion loss (S 21 ) around a passband.  FIG. 7  is a graph illustrating an insertion loss (S 21 ) around a frequency band of double the passband.  FIG. 8  is a graph illustrating an insertion loss (S 21 ) around a frequency band of triple the passband. 
         [0000]    In each figure, frequency f [GHz] is shown on a horizontal axis, [dB] is shown on a vertical axis, characteristic of the dielectric waveguide filter  100  is depicted in solid line, and characteristic of the dielectric waveguide filter  1  is depicted in dotted line. 
         [0045]    Each of the dielectric waveguide filters  1  and  100  is designed to have a center frequency of the passband f 0 =2.12 [GHz] and a bandwidth fw=40 [MHz]. 
         [0000]    In the dielectric waveguide filter  100 , each component has the following dimensions:
   the dielectric block  20 : a 20 ×b 20 ×L 20 =24.0 mm×8.0 mm×15.00 mm;   the dielectric plate  30 : a 30 ×b 30 ×L 30 =24.0 mm×4.1 mm×15.00 mm;   the dielectric waveguide  12 : a 22 ×b 22 ×L 22 =24.0 mm×8.0 mm×20.14 mm;   the dielectric waveguide  13 : a 23 ×b 23 ×L 23 =24.0 mm×8.0 mm×20.39 mm;   the dielectric waveguide  14 : a 24 ×b 24 ×L 24 =24.0 mm×8.0 mm×20.14 mm;   the coupling window  41 : w 41 ×h 41 =6.59 mm×3.0 mm;   the coupling window  42 : w 42 ×h 42 =5.11 mm×3.0 mm;   the coupling window  43 : w 43 ×h 43 =5.11 mm×3.0 mm;   the coupling window  44 : w 44 ×h 44 =6.59 mm×3.0 mm;   in the feeder line  60 , the distal end width y 1  is 1.6 mm, and the root portion width y o  is 0.5 mm;   the through-hole  50  has a φ=3.8 mm; and   the distance d between the through-hole  50  and the feeder line  60  is 1.73 mm.
 
In the dielectric waveguide filter  1 , each component has the following dimensions:
   the dielectric waveguide  1   a : a 1 ×b 1 ×L 1 =24.0 mm×8.0 mm×22.86 mm;   the dielectric waveguide  1   b : a 2 ×b 2 ×L 2 =24.0 mm×8.0 mm×19.78 mm;   the dielectric waveguide  1   c : a 3 ×b 3 ×L 3 =24.0 mm×8.0 mm×19.91 mm;   the dielectric waveguide  1   d : a 4 ×b 4 ×L 4 =24.0 mm×8.0 mm×19.78 mm;   the dielectric waveguide  1   e : a 5 ×b 5 ×L 5 =24.0 mm×8.0 mm×22.86 mm;   the coupling window  4   a : w 1 ×h 1 =6.59 mm×3.0 mm;   the coupling window  4   b : w 2 ×h 2 =5.11 mm×3.0 mm;   the coupling window  4   c : w 3 ×h 3 =5.11 mm×3.0 mm; and   the coupling window  4   d : w 4 ×h 4 =6.59 mm×3.0 mm.
 
All the relative permittivities c of the dielectric block and the dielectric plate are 20.0.
   
 
         [0067]    The result in  FIG. 6  shows that the dielectric waveguide filter  100  of the present invention and the conventional dielectric waveguide filter  1  have approximately the same insertion loss (S 11 ) and return loss (S 21 ) around the passband. 
         [0068]    Further, the result in  FIG. 7  shows that the dielectric waveguide filter  100  of the present invention has a lower return loss (S 21 ) than the conventional dielectric waveguide filter  1  around a frequency band of double the passband. 
         [0069]    Moreover, the result in  FIG. 8  shows that the dielectric waveguide filter  100  of the present invention has a lower return loss (S 21 ) than the conventional dielectric waveguide filter  1  around a frequency band of triple the passband. 
         [0070]    Thus, the dielectric waveguide filter  100  of the present invention can exhibit less degradation in performance and can eliminate the need for using a printed circuit board for the microstrip line because it can perform conversion directly from the dielectric waveguide to the coaxial line without any conversion to the microstrip. Further, the dielectric waveguide filter  100  can provide a downsized dielectric waveguide input/output structure because the axial length of the dielectric waveguide can be shortened by having a re-entrant structure. 
         [0071]    Further, the dielectric waveguide filter  100  makes it possible to suppress the second harmonic by having an open stub, and even to suppress the third harmonic, that is not easy to be suppressed, by having a re-entrant structure. Thus, a dielectric waveguide filter with lower harmonic generation can be achieved. As a result, it is not required to alternatively use a low-pass filter for suppressing the harmonic components. Furthermore, the dielectric waveguide filter  100  also makes it possible to suppress unwanted radiations at the input/output conversion section because the feeder line and the open stub provided therewith are located within the waveguide and are not exposed to the outside. 
         [0072]    The feeder line is pulled out to the direction orthogonal to the coupling direction of the dielectric waveguide. Alternatively, it may be pulled out to any direction. If the feeder line is pulled out to the longitudinal direction of the dielectric block, it is subject to less dimensional restriction than the case of being pulled out to the short-side direction, so that the distance between the distal end of the feeder line and the through-hole, for example, may be increased. This makes it possible to improve the power durability of the feeder line. 
         [0073]    The dielectric waveguide input/output structure of the present invention is not limited to the input/output structure for the dielectric waveguide filter, but is applicable to various types of dielectric waveguide device having a connection to external devices. 
       EXPLANATION OF CODES 
       [0000]    
       
           1   a  to  1   e,    10  to  15 ,  18 ,  19 : dielectric waveguide 
           20 : dielectric block 
           30 : dielectric plate 
           4   a  to  4   d,    40  to  44 : coupling window 
           50 : through-hole 
           60 ,  61 : feeder line 
           61   a : open stub 
           7 ,  70 : connector 
           8 : printed circuit board 
           8   a : microstrip 
           8   c : via-hole 
           5   a,    5   e,    8   b,    90 : island-shaped electrode 
           1 ,  100 : dielectric waveguide filter