Dielectric resonator apparatus comprising connection conductors extending between resonators and external surfaces
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dielectric resonator apparatus, and in particular, to a dielectric resonator apparatus comprising at least one dielectric resonator coaxial resonator and having connection conductors for external couplings, wherein the dielectric resonator apparatus is preferably used as a dielectric filter. 
     2. Description of the Prior Art 
     FIG. 4A is a perspective view of an appearance of a conventional comb-line type dielectric resonator apparatus having a rectangular-parallelepiped-shaped dielectric block 1, FIG. 4B is a cross-sectional view along a line IVB--IVB&#39; of FIG. 4A, and FIG. 4C is a cross-sectional view along a line IVC--IVC&#39; of FIG. 4A. 
     Referring to FIGS. 4A, 4B and 4C, three circular cylindrical resonator holes 2a, 2b and 2c are arranged in parallel to each other in the dielectric block 1 so as to penetrate the dielectric block 1 between a pair of first end second end surfaces which are disposed oppose to each other, so that each of the resonator holes 2a to 2c has an opening on the first end surface 1a, and has another opening on the second end surface 1b as seen in FIG. 4C. Further, an outer electric conductor 5 is formed on all the surfaces of the dielectric block 1 as seen in FIG. 4A. In the specification, an electric conductor is referred to as a conductor hereinafter. Inner conductors 3a, 3b and 3c shown in FIGS. 4A and 4B are formed respectively on the inner peripheral surfaces of the resonator holes 2a, 2b and 2c, so that a conductor-non-formed portion or gap 30 shown in FIG. 4C, where each of the inner conductors 3a to 3c is not formed, is formed in the vicinity of the first end surface 1a and also another end of each of the inner conductors 3a to 3c located on the side of the second end surface 1b is electrically connected to the outer conductor 5, as shown in FIG. 4C. The longitudinal length of each of the inner conductors 3a to 3c is set to a quarter of the guide-wavelength λg/4. Furthermore, a pair of input and output electrodes 14a and 14b shown in FIG. 4A is formed respectively on a predetermined side surface 1c of the dielectric block 1 so as to be electrically insulated from the outer conductor 5 and so as to be close to one ends of the inner conductors 3a and 3c located in the side of the second end surface 1b of the dielectric block 1. 
     In the conventional dielectric resonator apparatus having such a structure, three quarter-wavelength dielectric coaxial resonators are constituted corresponding to the inner conductors 3a to 3c, and as shown in FIGS. 4B and 4C, an external coupling capacitance Ce shown in FIG. 4B and 4C is formed between the input electrode 14a and the inner conductor 3a, and another external coupling capacitance Ce shown in FIG. 4B is formed between the output electrode 14b and the inner conductor 3c. In the conventional dielectric resonator apparatus, the above-mentioned external coupling capacitances Ce can be changed by adjusting the areas of a pair of input and output electrodes 14a and 14b, or by adjusting the distance between the input electrode 14a and the inner conductor 3a and the distance between the output electrode 14b and the inner conductor 3b. 
     In the case where the above-mentioned external coupling capacitances Ce are changed by adjusting the areas of a pair of input and output electrodes 14a and 14b, when the external coupling capacitances Ce are increased by increasing the areas of a pair of input and output electrodes 14a and 14b, this results in a decrease in the unloaded Q (Q 0 ) of the conventional dielectric resonator apparatus. 
     On the other hand, in the case where the above-mentioned external coupling capacitances Ce are changed by adjusting the distance between the input electrode 14a and the inner conductor 3a and the distance between the output electrode 14b and the inner conductor 3b, it is necessary change the sizes of the dielectric resonator apparatus such as the sizes of the dielectric block 1, the sizes of the resonator holes 2a to 2c or the like. 
     Accordingly, it is difficult to obtain a predetermined desirable optimum unloaded Q (Q 0 ) in the electric characteristics of the conventional dielectric resonator apparatus. On the other hand, in order to manufacture various kinds of dielectric resonator apparatuses having various kinds of electric characteristics, it is necessary to manufacture many dielectric resonator apparatuses having different sizes corresponding to the respective electric characteristics. This results in increase in the manufacturing cost and the managing cost. 
     Further, when the external coupling capacitances Ce are increased by increasing the inner diameters of the resonator holes 2a to 2c, the mechanical strength of the dielectric block 1 decreases. 
     SUMMARY OF THE INVENTION 
     One object of the preferred embodiments of the present invention is therefore to provide a dielectric resonator apparatus comprising at least one dielectric coaxial resonator, capable of easily obtaining predetermined desirable optimum external couplings without changing the sizes of the dielectric resonator apparatus and without decreasing the unloaded Q (Q 0 ). 
     In order to achieve the aforementioned objective, according to one aspect of the preferred embodiments of the present invention, there is provided a dielectric resonator apparatus comprising: 
     a dielectric block of a dielectric material having first and second end surfaces, and a plurality of side surfaces located between the first end surface and the second end surface; 
     at least one cylindrical resonator hole formed so as to penetrate an inner portion of said dielectric block, the resonator hole having opening on the first end surface of the dielectric block and another opening on the second end surface of the dielectric block; 
     an outer conductor formed on at least the first end surface and the plurality of side surfaces of the dielectric block; 
     at least one inner conductor formed on an inner portion of the resonator hole so that one end thereof located on the side of the first end surface of the dielectric block is electrically connected to the outer conductor and another end thereof located on the side of second end surface of the dielectric block is electrically insulated from the outer conductor, thereby constituting at least one dielectric coaxial resonator; 
     a pair of input and output electrodes formed on at least one predetermined side surface of the dielectric block so as to be electrically insulated from the outer conductor and so as to be close to one end of the inner conductor located on the side of the first end surface of the dielectric block; 
     two penetrating holes formed so as to penetrate an inner portion of the dielectric block between the pair of input and output electrodes and the inner conductor, respectively; and 
     two connection conductors for electrically connecting the pair of input and output electrodes to the inner conductor, respectively, the two connection conductors being formed on inner portions of the penetrating holes. 
     In the above-mentioned dielectric resonator apparatus, the pair of input and output electrodes is preferably formed so as to extend from the predetermined side surface of the dielectric block to the first end surface thereof. 
     In the above-mentioned dielectric resonator apparatus, the two penetrating holes are preferably formed so as to penetrate the inner portion of the dielectric block between the first end surface of the dielectric block to the inner conductor. 
     In the above-mentioned dielectric resonator apparatus, the pair of input and output electrodes is preferably formed so as to extend from the predetermined side surface of the dielectric block to the other side surfaces thereof, respectively. 
     In the above-mentioned dielectric resonator apparatus, the two penetrating holes are preferably formed so as to penetrate the inner portion of the dielectric block between the predetermined side surface of the dielectric block to the inner conductor. 
     In the above-mentioned dielectric resonator apparatus, the apparatus preferably comprises a plurality of resonator holes and a plurality of inner conductors, thereby comprising a plurality of dielectric coaxial resonators, 
     the pair of input and output electrodes is formed so as to be close to said two inner conductors located at both ends of the plurality of inner conductors, respectively, 
     the two penetrating holes are formed so as to penetrate the inner portion of the dielectric block between the pair of input and output electrodes and the two inner conductors located at both ends of the plurality of inner conductors, respectively, and 
     the two connection conductors electrically connect the pair of input and output electrodes to said two inner conductors located at both ends of the plurality of inner conductors, respectively. 
     According to the preferred embodiments of the present invention, predetermined desirable optimum external couplings can be obtained without changing the sizes of the dielectric resonator apparatus and without lowering the unloaded Q (Q 0 ) thereof by changing in a direction substantially parallel to the axes of the resonator hole, the forming positions of the connection conductors for electrically connecting a pair of input and output electrodes with the inner conductor corresponding thereto or the forming positions of the penetrating holes. Accordingly, the dielectric block can be used in common with a plurality of dielectric resonator apparatuses, and can be standardized, resulting in decrease in the manufacturing cost and the managing cost. Then the inexpensive dielectric resonator apparatus having a higher unloaded Q (Q 0 ) and predetermined desirable optimum external couplings can be obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the preferred embodiments of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings throughout which like parts are designated by like reference numerals, and in which: 
     FIG. 1A is a perspective view of an appearance of a comb-line type dielectric resonator apparatus according to a first preferred embodiment of the present invention; 
     FIG. 1B is a cross-sectional view along a line IB--IB&#39; of FIG. 1A; 
     FIG. 1C is a cross-sectional view along a line IC--IC&#39; of FIG. 1A; 
     FIG. 2A is a perspective view of an appearance of a comb-line type dielectric resonator apparatus according to a second preferred embodiment of the present invention; 
     FIG. 2B is a cross-sectional view along a line IIB--IIB&#39; of FIG. 2A; 
     FIG. 2C is a cross-sectional view along a line IIC--IIC&#39; of FIG. 2A; 
     FIG. 3 is a perspective view of an appearance of a comb-line type dielectric resonator apparatus according to a third preferred embodiment of the present invention; 
     FIG. 4A is a perspective view of an appearance of a conventional comb-line type dielectric resonator apparatus; 
     FIG. 4B is a cross-sectional view along a line IVB--IVB&#39; of FIG. 4A; and 
     FIG. 4C is a cross-sectional view along a line IVC--IVC&#39; of FIG. 4A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments according to the present invention will be described below with reference to the attached drawings where like parts in different drawings are designated by like reference numerals which may be described in detail in some of the drawings. 
     FIRST PREFERRED EMBODIMENT 
     FIG. 1A is a perspective view of an appearance of a comb-line type dielectric resonator apparatus according to a first preferred embodiment of the present invention, FIG. 1B is a cross-sectional view along a line IB--IB&#39; of FIG. 1A, and FIG. 1C is a cross-sectional view along a line IC--IC&#39; of FIG. 1A. 
     Referring to FIGS. 1A, 1B and 1C, the dielectric resonator apparatus comprises a substantially rectangular-parallelepiped-shaped dielectric block 1 having first and second end surfaces 1a and 1b, and four side surfaces 1c, 1d, 1e and if located between the first and second surfaces 1a and wherein the first and second end surfaces 1a and 1b are disposed to each other, the side surfaces 1c and 1f are disposed opposite to each other, and the side surfaces 1d and 1e are disposed opposite to each other. Three circular cylindrical resonator holes 2a, 2b and 2c are formed substantially in parallel to each other in the dielectric block 1 so as to penetrate the dielectric block 1 between a pair of the first end second end surfaces 1a and 1b which are disposed opposite to each other, so that each of the resonator holes 2a to 2c has an opening on the first end surface 1a, and has another opening on the second end surface 1b. 
     Further, an outer conductor 5 is formed on all the surfaces 1a to 1f of the dielectric block 1, and inner conductors 3a, 3b and 3c are formed respectively on the inner peripheral surfaces of the resonator holes 2a, 2b and 2c, so that a conductor-non-formed portion or gap 40 (see FIG. 1C), where each of the inner conductors 3a to 3c is not formed, is formed in the vicinity of the second end surface 1b and also one end of each of the inner conductors 3a to 3c located on the side of the first end surface 1a is electrically connected to the outer conductor 5, as shown in FIG. 1C. The longitudinal length of each of the inner conductors 3a to 3c is set to a quarter of the guide-wavelength λg/4. Accordingly, since the one ends of the inner conductors 3a to 3c located on the side of the first end surface 1a of the dielectric block 1 are electrically connected to the outer conductor 5, the first end surface 1a of the dielectric block 1 becomes a short-circuit surface. On the other hand, since the other ends of the inner conductors 3a to 3c located on the side of the second end surface 1b of the dielectric block 1 are electrically insulated from the outer conductor 5, the second end surface 1b of the dielectric block 1 becomes an open-circuit surface. 
     Furthermore, a pair of rectangular input and output electrodes 4a and 4b is formed respectively on the predetermined side surface 1c of the dielectric block 1 located between the first and second end surfaces 1a and 1b so as to be electrically insulated from the outer conductor 5 and so as to be close to one ends of the inner conductors 3a and 3c located on the side of the first end surface 1a of the dielectric block 1, wherein the predetermined side surface 1c of the dielectric block 1 is the top surface thereof shown in FIG. 1A. 
     As shown in FIGS. 1B and 1C, a penetrating hole 6a is formed so as to penetrate the dielectric block 1 between the resonator hole 2a and a part of the side surface 1c on which the input electrode 4a is formed, in a direction parallel to the first and second end surfaces 1a and 1b or perpendicular to the axial directions of the resonators holes 2a to 2c, and so as to be close to the first end surface 1a, wherein the part of the side surface 1c on which the input electrode 4a is formed is located apart from the first end surface 1a by a predetermined length L which is smaller than half the longitudinal length of the dielectric coaxial resonators. Further, a connection conductor 7a is formed on the inner peripheral surface of the penetrating hole 6a so that one end of the connection conductor 7a is electrically connected to the input electrode 4a and the other end of the connection electrode 7a is electrically connected to the inner connector 3a. Then, the input electrode 4a is electrically connected through the connection conductor 7a to the inner conductor 3a. 
     Furthermore, another penetrating hole 6b is formed so as to penetrate the dielectric block 1 between the resonator hole 2c and another part of the side surface 1c on which the output electrode 4b is formed, in a direction parallel to the first and second end surfaces 1a and 1b or perpendicular to the axial direction of the resonator holes 2a to 2c, and so as to be close to the first end surface 1a, wherein another part of the side surface 1c on which the output electrode 4b is formed is located apart from the first end surface 1a by a predetermined length L (shown in FIG. 1C) which is less than half the longitudinal length of the dielectric coaxial resonators. Further, another connection conductor 7b is formed on the inner peripheral surface of the penetrating hole 6b so that one end of the connection conductor 7b is electrically connected to the output electrode 4b and another end of the connection electrode 7b is electrically connected to the inner connector 3c. Then, the output electrode 4b is electrically connected through the connection conductor 7b to the inner conductor 3c. 
     As a result, the penetrating hole 6a is formed so as to penetrate between the input electrode 4a and the inner conductor 3a, and the penetrating hole 6b is formed so as to penetrate between the input electrode 4b and the inner conductor 3c. 
     In the dielectric resonator apparatus having the above-mentioned structure, three comb-line type quarter-wavelength dielectric coaxial resonators are constituted by the inner conductors 3a to 3c. Generally speaking, the dielectric resonator apparatus is preferably mounted on a printed circuit board (not shown) so that the side surface 1c which is the top surface of FIG. 1A is in contact with a top surface of the printed circuit board. 
     In the dielectric resonator apparatus of the present preferred embodiment, since a pair of input and output electrodes 4a and 4b is electrically connected through the connection conductors 7a and 7b to the inner conductors 3a and 3c, respectively, the dielectric resonator apparatus having external couplings formed by the connection conductors 7a and 7b can be obtained without any external coupling capacitance Ce. 
     It is to be noted that a pair of input and output electrodes 14a and 14b is formed on the side surface 1c so as to be close to the second end surface 1b of the open-circuit surface in the conventional dielectric resonator apparatus shown in FIGS. 4A, 4B and 4C, whereas a pair of input and output electrodes 4a and 4b is formed on the side surface 1c so as to be close to the first end surface 1a of the short-circuit surface in the dielectric resonator apparatus of the present preferred embodiment shown in FIGS. 1A, 1B and 1C. 
     According to such a structure of the dielectric resonator apparatus of the present preferred embodiment, the strengths of the external couplings respectively between a pair of input and output electrodes 4a and 4b and the dielectric coaxial resonators located at both ends of the three dielectric coaxial resonators can be changed by changing in a direction substantially parallel to the axes of the resonator holes 2a to 2c, the forming positions of the connection conductors 7a and 7b for electrically connecting a pair of input and output electrodes 4a and 4b to the inner conductors 3a and 3c, respectively, thereby changing the forming positions of the penetrating holes 6a and 6b in this direction. In other words, the strengths of the external couplings can be changed by increasing the lengths L shown in FIG. 1C between the penetrating hole 6a and the first end surface 1a of the short-circuit surface and between the penetrating hole 6b and the first end surface 1a of the short-circuit surface since the electric field strength of each dielectric coaxial resonator on the side of the second end surface 1b is stronger than that on the side of the first end surface 1a. 
     Accordingly, desirable optimum external couplings can be obtained without changing the sizes of the dielectric resonator apparatus such as the sizes of the dielectric block 1, the sizes of the resonator holes 2a to 2c or the like, and without lowering the unloaded Q (Q 0 ) of the dielectric resonator apparatus. In this case, it is not necessary to provide many dielectric resonator apparatuses having different sizes corresponding to various kinds of electric characteristics. Then one dielectric block 1 having a single standard uniform size can be used in common with a plurality of dielectric resonator apparatuses, and the dielectric block 1 can be standardized. This results in a remarkable decrease in both the manufacturing cost and the managing cost. 
     In the present preferred embodiment, a pair of input and output electrodes 4a and 4b is formed on the side surface 1c of the dielectric block 1 so as to be close to the first end surface 1a of the short-circuit surface, however, the present invention is not limited to this. The present invention includes the following second and third preferred embodiments. 
     SECOND PREFERRED EMBODIMENT 
     FIG. 2A is a perspective view of an appearance of a comb-line type dielectric resonator apparatus according to a second preferred embodiment of the present invention, and FIG. 2B is a cross-sectional view along a line IIB--IIB&#39; of FIG. 2A and FIG. 2C is a cross sectional view along a line IIC--IIC&#39; of FIG. 2A. The differences between the first and second preferred embodiments are as follows. 
     Referring to FIG. 2A, a pair of input and output electrodes 4aa and 4ba is formed at two areas so as to be electrically insulated from the outer conductor 5 and so as to be close to the inner conductors 3a and 3c, respectively, wherein each area is located so as to extend from the side surface 1c to the first end surface 1a of the short-circuit surface. In the present preferred embodiment, penetrating holes 6aa and 6ba are formed in a direction inclined from the axial direction of each of the resonator holes 2a to 2c so as to penetrate the dielectric block 1 between the first end surface 1a and each of the inner conductors 3a and 3c, respectively, and then, referring now to FIGS. 2B and 2C, connection conductors 7aa and 7ba are formed on the inner peripheral surfaces of the penetrating holes 6aa and 6ba, respectively. Then the input electrode 4aa is electrically connected through the connection conductor 7aa to the inner conductor 3a, and the output electrode 4ba is electrically connected through the connection conductor 7ba to the inner conductor 3c. 
     THIRD PREFERRED EMBODIMENT 
     FIG. 3 is a perspective view of an appearance of a comb-line type dielectric resonator apparatus comprising two dielectric coaxial resonators, according to a third preferred embodiment of the present invention. The differences between the first and third preferred embodiments are as follows. 
     Referring to FIG. 3, a pair of input and output electrodes 4ab and 4bb is formed at two areas so as to be electrically insulated from the outer conductor 5 and so as to be close to the inner conductors 3a and 3b, respectively, wherein one area is located so as to extend from the side surface 1c to the side surface 1d, and another area is located so as to extend from the side surface 1c to the side surface 1e. In the present preferred embodiment, penetrating holes 6ab and 6bb are formed so as to penetrate the dielectric block 1 between the side surface 1c and each of the inner conductors 3a and 3c, respectively, and then connection conductors (not shown) are formed on the inner peripheral surfaces of the penetrating holes 6ab and 6bb, respectively. Then the input electrode 4ab is electrically connected through the connection conductor to the inner conductor 3a, and the output electrode 4bb is electrically connected through the connection conductor to the inner conductor 3b. 
     OTHER PREFERRED EMBODIMENTS 
     In the above-mentioned first and second preferred embodiments, the dielectric resonator apparatus comprising the three dielectric coaxial resonators is described. In the above-mentioned third preferred embodiment, the dielectric resonator apparatus comprising the two dielectric coaxial resonators is described. However, the present invention is not limited to this. The dielectric resonator apparatus may comprise one, four, or more than four dielectric coaxial resonators. 
     In the above-mentioned preferred embodiments, the circular cylindrical resonator holes 2a to 2c are formed in the dielectric block 1, however, the present invention is not limited to this. Resonator holes each having the other shape such as a rectangular cylindrical shape, a hexagonal prism, or the like may be formed in the dielectric block 1. 
     In the above-mentioned preferred embodiments, the gap 40 is formed in the vicinity of the second end surface 1b of the open-circuit surface, however, the present invention is not limited to this. The gap 40 may be formed in each of the resonator holes 2a to 2c so as to be apart from the second end surface 1b of the open-circuit surface by a predetermined distance. 
     A gap for electrically insulating each of the inner conductors 3a to 3c from the outer conductor 5 may be formed by forming a gap, where the outer conductor 5 is not formed, in the vicinity of the openings of the resonator holes 2a to 2c which are located on the second end surface 1b. This gap may be formed on the whole second surface 1b. In other words, the outer conductor 5 is not formed on the second surface 1b. 
     In each of the above-mentioned preferred embodiments, the comb-line type dielectric resonator apparatus comprising a plurality of quarter-wavelength dielectric coaxial resonators is described. However, the present invention is not limited to this. The present invention can apply to a comb-line type dielectric resonator apparatus comprising a plurality of half-wavelength dielectric coaxial resonators, an interdigital type dielectric resonator apparatus comprising a plurality of quarter-wavelength dielectric coaxial resonators, and an interdigital type dielectric resonator apparatus comprising a plurality of half-wavelength dielectric coaxial resonators- In the interdigital type dielectric resonator apparatus comprising a plurality of dielectric coaxial resonators, the gaps 40 are formed alternately in the vicinity of the first and second end surfaces 1a and 1b in the resonator holes 2a to 2c. For example, in the first preferred embodiment shown in FIGS. 1A, 1B and 1C, the gap 40 of the inner conductor 3a is formed in the vicinity of the second end surface 1b, the gap 40 of the inner conductor 3b is formed in the vicinity of the first end surface 1a, and the gap 40 of the inner conductor 3c is formed in the vicinity of the second end surface 1b. 
     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.