Abstract:
The invention provides a dielectric filter, comprising: a dielectric block including a first surface and a second surface opposite to each other; a resonator hole extending between the first surface and second surface of the dielectric block, said resonator hole including a large-sectional area portion, a small-sectional area portion and a step portion between the large-sectional area portion and the small-sectional area portion; an inner conductor provided on the inner surface of the resonator hole; an outer conductor provided on the outer surface of the dielectric block; the inner conductor being electrically left unconnected to the outer conductor at the first surface of the dielectric block and being electrically connected to the outer conductor at the second surface of the dielectric block; and a seat portion provided on the first surface of the dielectric block such that the first surface serves as a mounting surface of the dielectric filter.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dielectric filter, a dielectric duplexer, a mounting structure having the same, and a communication device. 
     2. Description of the Related Art 
     In recent years, radio wave communication equipment, such as portable telephones and the like, of small in size, light in weight, and thin types have been spread widely and rapidly. With the spread, it has been more intensively needed to develop dielectric filters and dielectric duplexers, to be mounted on the equipment of the above-mentioned type, which are small in size, light in weight, and low in height. 
     Conventionally, a dielectric filter of the above-mentioned type, shown in FIG. 11, has been known. A dielectric filter  8  comprises a plurality of resonator holes  3  provided in a single dielectric block  2  which has an outer conductor  1  provided on the surface thereof. An inner conductor  4  is provided on the inner surface of each resonator hole  3 . The inner conductor  4  is electrically connected to the outer conductor  1 , at the side surface  2   b  of the dielectric block  2 , shown as the back-face of the dielectric filter  8  in FIG. 11, and is electrically left unconnected to the outer conductor  1  at the side surface  2   a  shown as the front-face in FIG.  11 . 
     Ordinarily, the dielectric filter  8  is so mounted onto a circuit board  6  that the axes of the resonator holes  3  are in parallel to the circuit board  6 . To reduce the height of the dielectric filter  8  having the above-described mounting form, the method may be supposed by which the diameters of the resonator holes  3  are decreased in order that the height h of the dielectric block  2  is reduced. However, it is difficult to form the dielectric block  2  by means of a metallic mould, due to the resonator holes  3  having a reduced diameter. In general, the dielectric filter  8  has a high Q 0 . To obtain the high Q 0 , it is necessary to assure the optimum height h with respect to the diameter of each resonator hole  3 . For this reason, it is problematic to reduce the height of the dielectric filter  8 . In some cases, an electromagnetic field leaking from the side surface  2   a , which is an open-circuited surface, exerts a hazardous influence over the characteristics of other electronic components mounted onto a circuit board  6 . Similarly, in some cases, an electromagnetic field leaking from the other electronic components unfavorably affects the characteristics of the dielectric filter  8 . 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a dielectric filter, a dielectric duplexer, a mounting structure having the same, and a communication device each of which is small in size, low in height, and has good characteristics. 
     To achieve the above object, the present invention provides a dielectric filter comprising: a dielectric block including a first surface and a second surface opposite to each other; a resonator hole extending between the first surface and second surface of the dielectric block, said resonator hole including a large-sectional area portion, a small-sectional area portion and a step portion between the large-sectional area portion and the small-sectional area portion; an inner conductor provided on the inner surface of the resonator hole; an outer conductor provided on the outer surface of the dielectric block; the inner conductor being electrically left unconnected to the outer conductor at the first surface of the dielectric block and being electrically connected to the outer conductor at the second surface of the dielectric block; and a seat portion provided on the first surface of the dielectric block to allow the first surface to serve as a mounting surface of the dielectric filter. 
     The present invention also provides a dielectric duplexer comprising the above described dielectric filter, wherein a plurality of said resonator holes are provided, at least one of which constituting a transmitting filter and at least the other one of which constituting a receiving filter. 
     According to the above described structure and arrangement, the dielectric filter or the dielectric duplexer is so mounted to a circuit board or the like that the axes of the resonator holes are substantially perpendicular to the circuit board or the like. In each resonator hole, the step portion is formed between the large-sectional area portion and the small-sectional area portion. The conductor path of the inner conductor is extended to lie on the surface of the step. Thus, the conductor path is longer by an amount corresponding to the step portion. Accordingly, the size of the dielectric filter or the dielectric duplexer can be reduced in the axial direction of the resonator hole, compared with the filter or duplexer which does not have such a step portion. Thus, the mounting height of the dielectric filter or the dielectric duplexer can be reduced. Further, a gap is formed between the first surface of the dielectric block which serves as the mounting surface, and the circuit board or the like, due to the seat portion provided on the first surface of the dielectric block. With the gap, a stray capacitance, produced between the first surface of the dielectric block and the circuit board, is reduced. In addition, since the first surface, which is the open-circuited surface, is opposed to the circuit board, an electromagnetic field leaking from the first surface can be inhibited from exerting an unfavorable influence over other electronic components mounted on the circuit board. Similarly, an electromagnetic field leaking from the other electronic components can be inhibited from affecting the dielectric filter or the dielectric duplexer. 
     A depression may be provided on the step portion between the large-sectional area portion and the small-sectional area portion of each resonator hole, and the conductor path of the inner conductor is extended to lie on the surface of the depression on the step. Thus, the conductor path is longer by an amount corresponding to the depression. Accordingly, the size of the dielectric filter or the dielectric duplexer can be further reduced in the axial direction of the resonator hole. 
     Furthermore, a slot may be provided on the first surface of the dielectric block. Depending on the size and shape of the slot, it is possible to change the resonator length of each dielectric resonator composed of one of the resonator holes, the outer conductor, and the dielectric block, and moreover, the coupling coefficients of the capacitive coupling and the inductive coupling between adjacent resonators. 
     Further, the mounting structure and the communication device of the present invention, equipped with at least one of the dielectric filters and the dielectric duplexer, can meet flexibly the requirement that the device should be reduced in height. 
    
    
     Other features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention which refers to the accompanying drawings, wherein like reference numerals indicate like elements to avoid duplicative description. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a dielectric filter according to a first preferred embodiment of the present invention. 
     FIG. 2 is a perspective view of the dielectric filter shown in FIG.  1 . 
     FIG. 3 is a cross-sectional view of the dielectric filter shown in FIG.  1 . 
     FIG. 4 is a perspective view of a dielectric filter according to a second preferred embodiment of the present invention. 
     FIG. 5 is a perspective view of a dielectric duplexer according to a third preferred embodiment of the present invention. 
     FIG. 6 is a perspective view of a dielectric filter according to a fourth preferred embodiment of the present invention. 
     FIG. 7 is a plan view of the dielectric duplexer shown in FIG.  6 . 
     FIG. 8 is a cross sectional view taken along line VIII—VIII of FIG.  6 . 
     FIG. 9 is a cross-sectional view taken along line IX—IX. 
     FIG. 10 is a block diagram of a communication device according to a fifth preferred embodiment of the present invention. 
     FIG. 11 is a perspective view of a conventional dielectric filter. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Preferred Embodiment, FIGS.  1  through  3   
     As shown in FIG. 1, a dielectric filter  11  comprises a single dielectric block  12  having a substantially rectangular parallelepiped shape. The dielectric block  12  has two resonator holes  13  and  14  which extend between the first and second surfaces  12   a ,  12   b  thereof opposite to each other. The resonator holes  13 ,  14  are so arranged in the single dielectric block  12  that their axes are in parallel to each other. 
     The resonator holes  13 ,  14  are composed of a large-sectional area portion  13   a  and a small-sectional area portion  13   b  having a circular cross-section and in communication with the large-sectional area portion  13   a , and a large-sectional area portion  14   a  and a small-sectional area portion  14   b  having a circular cross-section and in communication with the large-sectional area portion  14   a , respectively. In step portions  15  in the boundary areas between the large-sectional area portion  13   a  and the small-sectional area portion  13   b  and between the large-sectional area portion  14   a  and the small-sectional area portion  14   b , depressions  18  are formed at a predetermined distance to the small-sectional area portions  13   b ,  14   b , respectively. More particularly, the depressions  18  are so formed along the inner surfaces of the large-sectional area portions  13   a ,  14   a  excluding the parts of the inner walls thereof which are adjacent to each other as to surround about three-fourths of the circumferences of the small-sectional area portions  13   b ,  14   b , respectively. The opposite ends  18   a  of each depression  18  are projected outwardly, so that the opposed areas of the adjacent parts of the resonator holes  13 ,  14  are increased. Thus, the coupling degree of the resonator holes  13 ,  14  can be enhanced. 
     An outer conductor  17  and a pair of input and output electrodes  21 ,  22  are provided on the outer surface of the dielectric block  12 . Inner conductors  16  are provided on the inner surfaces of the resonator holes  13 ,  14 , respectively. The outer conductor  17  is provided on the outer surface of the dielectric block  12  excluding the area where the input and output electrodes  21 ,  22  and the open-circuited first surface  12   a  where the large-sectional area portion portions  13   a,    14   a  are open-circuited (hereinafter, referred to as an open-circuited surface  12   a ). A pair of the input and output electrodes  21 ,  22  are provided, not connected to the outer conductor  17 . Moreover, one ends of the input and output electrodes  21 ,  22  are connected directly to the inner conductor  16 , and the other ends are extended to lie on the inner surface of concave portions with a substantially semi-circular cross-section  19  which are provided in the side surfaces of the dielectric block  12 , respectively. 
     In the open-circuited surface  12   a , the inner conductors  16  are electrically left unconnected to the outer conductor  17  and connected to the inner and outer electrodes  21 ,  22 , respectively. In the second surface  12   b  on the side where the small-sectional area portions  13   b ,  14   b  are short-circuited (hereinafter, referred to as a short-circuited surface  12   b ), the inner conductors  16  are electrically connected to the outer conductor  17 . Thus, dielectric resonators R 1 , R 2  are formed of the inner conductors  16  in the resonator holes  13 ,  14 , and the outer conductor  17 , respectively, provided in the single dielectric block  12 . 
     Seat portions  23   a ,  23   b ,  23   c , and  23   d  are provided in the four corners of the open-circuited surface  12   a  of the dielectric block  12 , and seat portions  23   e ,  23   f  in the right- and left-hand edges thereof, respectively. The outer conductor  17  is extended to lie on the surfaces of the seat portions  23   a  through  23   d , and the input and output electrodes  21 ,  22  are formed on the surfaces of the seat portions  23   e ,  23   f , respectively. 
     As shown in FIGS. 2 and 3, the dielectric filter  11  having the above configuration is mounted to a circuit board  50  or the like of a communication device in its stable state by use of the seat portions  23   a  through  23   f  and the open-circuited surface  12   a  as the mounting face. That is, the filter  11  is so mounted by soldering or the like that the axes of the resonator holes  13 ,  14  are perpendicular to the circuit board  50 . On the upper side of the circuit board  50 , signal patterns  51  and  52  are provided in opposition to each other. Ground patterns  53  are provided on the opposite sides of the signal patterns  51  and  52 , and have a bridge at a position between the signal patterns  51  and  52 . The outer conductor  17  is extended to lie on the surfaces of the seat portions  23   a  through  23   d  to be electrically connected to the ground patterns  53  on the circuit board  50 , respectively. The input and output electrodes  21 ,  22  provided on the surfaces of the seat portions  23   e ,  23   f  are electrically connected to the signal patterns  51 ,  52  on the circuit board  50 , respectively. 
     The open-circuited surface  12   a  is so disposed that a gap (an air layer) is assured between the open-circuited surface  12   a  and the circuit board  50  by means of the seat portions  23   a  through  23   f , not in direct contact with the circuit board  50 . If the open-circuited surface  12   a  were in direct contact with the circuit board  50 , a high stray capacitance would be produced between the open sides of the dielectric resonators R 1 , R 2  and the ground pattern  53  of the circuit board  50 , due to the high dielectric constant of the dielectric block  12 . This high stray capacitance would unfavorably influence the characteristics of the dielectric filter. On the contrary, in the first embodiment, since the gap (air layer) is formed between the open-circuited surface  12   a  and the ground pattern  53  on the circuit board  50 , the stray capacitance produced between the open sides of the dielectric resonators R 1 , R 2  and the ground pattern  53  on the circuit board  50  can be reduced, due to the low dielectric constant of air. Thus, in the dielectric filter  11 , influences with the stray capacitance can be inhibited. That is, the resonant frequencies of the dielectric resonators R 1 , R 2  and the coupling coefficients of the capacitive coupling and the inductive coupling between the dielectric resonators R 1 , R 2  can be stabilized. Moreover, the resonant frequencies of the dielectric resonators R 1 , R 2  can be controlled by changing the heights d of the seat portions  23   a  through  23   f.    
     The open-circuited surface  12   a  is opposed to the circuit board  50 , not opposed to the other electronic components (not shown) mounted onto the circuit board  50 . This is effective in preventing an electromagnetic field, leaking from the open-circuited surface  12   a , from affecting the other electronic components. Similarly, this can inhibit an electromagnetic field, leaking from the other electronic components, from influencing the dielectric filter  11 . 
     Further, in the resonator holes  13 ,  14 , the step portions  15  are provided in the boundary areas between the large-sectional area portion  13   a  and the small-sectional area portion  13   b  and between the large-sectional area portion  14   a  and the small-sectional area portion  14   b , respectively. The conductor paths of the inner conductors  16  are extended to lie on the surface of the steps  15 , and thereby, are longer by an amount corresponding to the surfaces of the steps  15 . Furthermore, the depressions  18  are provided in the steps  15 , respectively. Therefore, the conductor path of each inner conductor  16  is longer as compared with the conventional dielectric filter not provided with the depressions  18 . If the conductor path of the inner conductor  16  is longer, the center frequency of the dielectric filter  11  is lower. Accordingly, on condition that the center frequency is constant, the lengths in the axial direction of the resonator holes  13 ,  14  of the dielectric filter  11  can be reduced, as compared with the conventional dielectric filter. As a result, the mounting height H of the dielectric filter  11  can be reduced without reduction in the size of the resonator holes  13 ,  14 . 
     Second Preferred Embodiment, FIG.  4   
     As shown in FIG. 4, a dielectric filter  11  a is the same as the dielectric filter  11  described in reference to FIG. 1, except for a slot  26  provided in the open-circuited surface  12   a  of the dielectric block  12 . The slot  26  is so formed between the resonator holes  13 ,  14  that the slot  26  and a part of the respective resonator holes  13 ,  14  are overlapped each other. 
     The dielectric filter  11   a , having the same advantages as those of the dielectric filter  11  of the first preferred embodiment, is further advantageous in that the coupling coefficients of the capacitive coupling and the inductive coupling between the adjacent dielectric resonators R 1 , R 2  can be desirably controlled in correspondence to the depth and the shape and size of the slot  26 , and thereby, the band width of the dielectric filter  11   a  can be easily controlled. 
     Third Preferred Embodiment, FIG.  5   
     As shown in FIG. 5, a dielectric filter  11  b is the same as the dielectric filter  11  described in reference to FIG. 1 except for slots  27 ,  28 , and  29  provided in the open-circuited surface  12   a  of the dielectric block  12 . The slot  27  is so formed between the resonator holes  13 ,  14  that the slot  27  and a part of the resonator holes  13 ,  14  are overlapped each other. The slot  28  is formed near to the input and output electrode  21 , with one end thereof in contact with the resonator hole  13 . The slot  29  is formed near to the input and output electrode  22 , with one end thereof in contact with the resonator hole  14 . The depths of the slots  27  through  29  are set in conformity to the specifications of the dielectric filter  11   b.    
     The dielectric filter  11   b , having the same advantages as those of the dielectric filter  11  of the first preferred embodiment, is further advantageous in that the coupling coefficients of the capacitive coupling and the inductive coupling between the adjacent dielectric resonators R 1 , R 2  can be desirably controlled in correspondence to the depth and the shape and size of the slot  27 , and thereby, the band width of the dielectric filter  11   b  can be easily adjusted. In addition, advantageously, the resonator lengths of the dielectric resonators R 1 , R 2  can be adjusted by changing the shape and size and the depth of the slots  28 ,  29 , and thereby, the filter frequency of the dielectric filter  11   b  can be easily adjusted. 
     Fourth Preferred Embodiment, FIGS.  6  through  9   
     FIGS. 6,  7 ,  8 , and  9  are a perspective view of a dielectric duplexer according to a sixth preferred embodiment of the present invention, a plan view thereof, a cross sectional view taken along line VIII—VIII of FIG. 6, and cross-sectional view taken along line IX—IX of FIG.6, respectively. A dielectric duplexer  31  includes a single dielectric block  32  having a rectangular parallelepiped shape, and seven resonator holes  34   1  through  34   7  extending between the first and second surfaces  32   a  and  32   b  of the dielectric block which are opposed to each other. The resonator holes  34   1  through  34   7  are so arranged with the axes thereof in parallel to each other as to form one line in the dielectric block  32 . 
     The resonator holes  34   1  through  34   7  each comprises a large-sectional area portion  34   a  having a rectangular cross-section and a small-sectional area portion  34   b  in communication with the large-sectional area portion  34   a  (see FIG.  8 ). In a step portion  35  in the boundary area between the large-sectional area portion  34   a  and the small-sectional area portion  34   b , depressions  38  are formed at the opposite ends of the large-sectional area portion  34   a , respectively (see FIG.  9 ). The size of the resonator holes  34   1  through  34   1  and the size and depth of the depressions  38  are so set individually that the duplexer  31  has required electric characteristics. That is, the shape and size of each of the resonator holes  34   1 ,  34   3 ,  34   4 , and  34   7  is set large, while that of each of the resonator holes  34   5 ,  34   6  are set small. The resonator hole  34   2  is so set as to have a size and shape which is intermediate between those of the resonator holes  34   1 ,  34   6 . Further, the mutual distances between the resonator holes  34   5 , through  34   7  are set to conform to the specifications of the dielectric duplexer. 
     The four resonator holes  34   1  through  34   4  arranged in the area of the duplexer  31  which lies in one half of thereof on the left-hand side are electromagnetically coupled with each other to constitute a transmission side filter  33   t.  Similarly, the four resonator holes  34   4  through  34   7  arranged in the area of the duplexer  31  which lies in one half thereof on the right-hand side are electromagnetically coupled with each other to constitute a reception side filter  33   r.    
     An outer conductor  37 , a transmission electrode  41 , an antenna electrode  42 , and a reception electrode  43  are formed on the outside of the dielectric block  32 . Inner conductors  36  are formed on the inner surfaces of the resonator holes  34   1  through  34   7 , respectively. The outer conductor  37  is formed on the outside of the dielectric block  32  excluding the area where the electrodes  41  through  43  are provided and the first surface  32   a  on the side where the large-sectional area portions  34   a  open (hereinafter, referred to as the open-circuited surface  32   a ). The transmission electrode  41  is connected directly to the inner conductor  36  of the resonator hole  34 ,. The antenna electrode  42  is connected directly to the inner conductor  36  of the resonator hole  34   4 . The reception electrode  43  is connected directly to the inner conductor  36  of the resonator hole  34   7 . 
     Each inner conductor  36  is electrically left unconnected to the outer conductor  37  at the open-circuited surface  32   a , and is short-circuited (electrically connected) to the outer conductor  37  at the surface on the side where the small-sectional area portions  34   b  open (hereinafter, referred to as a short-circuiting side surface  32   b ). Thus, the dielectric resonators each are formed of the dielectric block  32 , each inner conductor  36  of the resonator holes  34   1  through  34   7 , and the outer conductor  37 , respectively. 
     Seat portions  45   a  through  45   p  are provided in the peripheral area of the open-circuited surface  32   a  of the dielectric block  32 . The outer conductor  37  is extended to lie on the surfaces of the seat portions  45   a ,  45   b ,  45   d ,  45   f , and  45   h  through  45   p . The transmission electrode  41  is formed on the surface of the seat portion  45   c , the antenna electrode  42  on the surface of the seat portion  45   e , and the reception electrode  43  on the surface of the seat portion  45   g.    
     The dielectric duplexer  31 , having the above described configuration, is mounted, with the open-circuited surface  32   a  used as the mounting surface, onto a circuit board or the like in its stable state by use of the seat portions  45   a  through  45   p.  That is, the duplexer  31  is so mounted onto the circuit board that the axes of the resonator holes  34   1  through  34   7  are substantially perpendicular to the circuit board. When the duplexer is mounted, the open-circuited surface  32   a  is so disposed as to assure a gap (air layer) between the open-circuited surface  32   a  and the circuit board, by means of the seat portions  45   a  through  45   p , avoiding the direct contact with the circuit board. Accordingly, stray capacitance between the open side surfaces of the dielectric resonators contained in the dielectric duplexer  31  and a ground pattern of the circuit board can be reduced. Thus, in the dielectric duplexer  31 , the stray capacitance can be inhibited from exerting an influence. The resonant frequencies of the respective dielectric resonators and the coupling coefficients of the capacitive coupling and the inductive coupling between the mutual dielectric resonators can be stabilized. In addition, the resonant frequencies of the dielectric resonators can be adjusted by changing the height of the seat portions  45   a  through  45   p.    
     The open-circuited surface  32   a  is opposed to the circuit board, not opposed to the other electronic components mounted onto the circuit board. This is effective in preventing an electromagnetic field, leaking from the open-circuited surface  32   a , from affecting other electronic components. Similarly, this can inhibit an electromagnetic field, leaking from the other electronic components, from exerting an influence over the dielectric duplexer  31 . 
     Further, in each of the resonator holes  34   1  through  34   7 , the step portion  35  is formed in the boundary area between the large-sectional area portion  34   a  and the small-sectional area portion  34   b . The conductor path of the inner conductor  36 , which is extended to lie on the surface of the step  35 , is longer by an amount corresponding to the surface of the step  35 . Furthermore, the depression  38  is provided in the step  35 . Therefore, the conductor path of the inner conductor  36  is longer as compared with the conventional dielectric filter not provided with the depressions  38 . If the conductor length of the inner conductors  36  is longer, the center frequencies of the dielectric resonators contained in the dielectric duplexer  31  is longer. The conductor length of the inner conductors  36  is lengthened. Accordingly, on condition that the center frequency is constant, the length in the axial direction of the resonators  34 , through  34   7  of the dielectric duplexer  31  can be made shorter than the conventional dielectric duplexer. As a result, the mounting height of the dielectric duplexer  31  can be reduced without reduction in the size of the resonator holes  34   1  through  34   7 . 
     Fifth Preferred Embodiment, FIG.  10   
     A communication device embodying the present invention will be described in the following fifth preferred embodiment taking a portable telephone for an example. 
     FIG. 10 is an electric circuit block diagram showing the RF section of a portable telephone  120 . In FIG. 10, there are indicated an antenna element by reference numeral  122 , a filter (duplexer) for use with the antenna by  123 , a transmission side isolator by  131 , a transmission side amplifier by  132 , a transmission-side interstage band-pass filter by  133 , a transmission side mixer  134 , a reception side amplifier by  135 , a reception side interstage band-pass filter by  136 , a reception side mixer by  137 , a voltage controlling oscillation device (VCO) by  138 , and a local band-pass filter by  139 . 
     In the above configuration, as the filter (duplexer) for use with the antenna  123 , is available, for example, the dielectric duplexer  31  of the above-described fourth embodiment. Further, as the transmission side interstage band-pass filter  133 , the reception side interstage band-pass filter  136 , and the local band-pass filter  139 , can be used, for example, the dielectric filters  11 ,  11   a , and  11   b  of the first, the second, and the third preferred embodiment. The RF section can be reduced in height by mounting the dielectric duplexer  31  and the dielectric filters  11 ,  11   a , and  11   b . Thus, the portable telephone of a thin type can be realized. 
     Other Preferred Embodiments 
     The dielectric filter, the dielectric duplexer, the structure having the same mounted therein, and the communication device of the present invention may be modified in all respects without departing from the scope of the invention, not restricted to the above-described embodiments. For example, in the dielectric duplexer  31  of the fourth embodiment, the open-circuited surface  32   a  may be provided with a slot. The large-sectional area portions and the small-sectional area portions provided in the dielectric filter and the dielectric duplexer may have an optional shape and size in their cross-sections. The shape and size of the depressions may be optionally changed in correspondence to the shape and size of the cross-sections. 
     As apparently understood in the above description, according to the present invention, the size of the dielectric filter or dielectric duplexer can be reduced in the axial direction of the resonator holes, and the mounting height can be decreased without changes in the conductor path of the inner conductor, due to the steps formed in the boundary areas between the large-sectional area portions and the small-sectional area portions of the resonator holes. When the dielectric filter or the dielectric duplexer is mounted onto the circuit board, the gap is formed between the first surface of the dielectric block, which is the mounting face of the filter or the duplexer, and the circuit board or the like, due to the seat portions provided on the first surface of the dielectric block. With the gap, the stray capacitance to be produced between the first surface of the dielectric block and the circuit board can be reduced. 
     Moreover, the first surface, which is the open-circuited surface, is opposed to the circuit board. This inhibits an electromagnetic field leaking from the first surface from affecting the other electronic components mounted onto the circuit board. Similarly, this inhibits an electromagnetic filed, leaking from the other electronic components, from exerting an influence over the dielectric filter or the dielectric duplexer. Further, the seat portions provided on the first surface are effective in mounting the dielectric filter or the dielectric duplexer on the circuit board in its stable state. Moreover, the depressions provided in the steps between the large-sectional area portions and the small-sectional area portions enable the size of the dielectric filter or the dielectric filter to be further reduced in the axial direction of the resonator holes. As a result, the mounting height of the dielectric filter or the dielectric duplexer can be further reduced. 
     The coupling coefficients of the capacitive coupling and the inductive coupling between of adjacent resonator holes, and moreover, the resonator length of the dielectric resonators can be changed by providing the slot in the first surface of the dielectric block and changing the depth and shape of the slot. 
     The communication device and the mounting structure of the present invention, as it is equipped with at least one of the dielectric filter or the dielectric duplexer having the above-stated characteristics, can flexibly satisfy the requirement of the thin type communication device. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the forgoing and other changes in form and details may be made therein without departing from the spirit of the invention.