Abstract:
It is possible to generate an additionally attenuation pole in a laminate type band pass filter without adding an attenuation circuit and improve the attenuation characteristics of the laminate type band pass filter by independently controlling the frequencies of the attenuation poles. A diplexer is realized by using at least such a filter. The laminate type band pass filter includes a plurality of first resonators adapted to resonate in a predetermined pass band and arranged in a laminate, the first resonators being mutually electromagnetic field coupled, each of the first resonators having a first inductor conductor, a second inductor conductor and a conductor to be capacitive-coupled to a grounding conductor, the second inductor conductor and the conductor to be capacitive-coupled to the grounding conductor forming a second serial resonator in each of the first resonators, the notch frequency of the second serial resonator being set in a frequency band higher than the resonance frequency band of the first resonator.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a laminate type band pass filter to be used for a microwave band and a diplexer using the same. 
     2. Description of the Related Art 
     Structures using via holes as inductor conductors of a resonator have been proposed for filters including a resonator formed by laying a plurality of dielectric layers one on the other have been proposed. 
     More specifically, Patent Document 1 (Japanese Patent No. 3,127,792) proposes an LC filter including a plurality of dielectric layers that are laid one on the other, a plurality of inductors formed by means of via holes running through the plurality of dielectric layers in the layering direction and a plurality of capacitors, each being formed between capacitor electrodes formed among the plurality of dielectric layers, the inductors being arranged in a direction orthogonal relative to the main surfaces of the capacitor electrodes, the plurality of inductors and the plurality of capacitors being respectively connected in parallel, a plurality of LC resonators being formed by the plurality of inductors and the plurality of capacitors, the plurality of inductors of the plurality of LC resonators being electromagnetically coupled. 
     Patent Document 2 (Jpn. Pat. Appln. Laid-Open Publication No. 2003-124769) proposes a laminate type LC filter including an input terminal, an output terminal, at least two LC resonators electrically connected to the input terminal and the output terminal, an input side LC trap circuit electrically connected to between the input terminal and the LC resonators and an output side LC trap circuit electrically connected to between the output terminal and the LC resonators, part of the inductor forming the LC resonator electrically connected to the input terminal being commonly used as part of the inductor forming the input side LC trap circuit, part of the inductor forming the LC resonator electrically connected to the output terminal being commonly used as part of the inductor forming the output side LC trap circuit. The Patent Document 2 discloses that the inductors of the LC resonators and the LC trap circuits are formed by means of via holes running through a plurality of dielectric layers in the layering direction. 
       FIG. 1  of the accompanying drawings is an equivalent electric circuit diagram of a laminate type LC filter  100  disclosed in the Patent Document 2, and  FIG. 2  is an exploded schematic perspective view of the laminate type LC filter that is illustrated in  FIG. 1 . 
     Referring to  FIG. 2 , the laminate type LC filter  100  includes an insulator sheet  103  having a coupling capacitor  110  arranged on the surface thereof, an insulator sheet  104  having resonator capacitors  111  and  112  arranged on the surface thereof, insulator sheets  106 ,  107  respectively having LC trap capacitor conductors  113 ,  114 ,  115  and  116  arranged on the surfaces thereof, insulator sheets  105  and  108  respectively having inductor via holes  117   b,    118   b,    117   e  and  118   e  and insulator sheets  102 ,  109  respectively having grounding conductors  119  and  120  on the surfaces thereof. 
     Inductor via holes  117   a  through  117   e  and inductor via holes  118   a  through  118   e  that operate as resonator coil conductors are successively connected to each other in the layering direction of the insulator sheets  102  through  109  to form resonator inductors L 101  and L 102  substantially having an effective length of λ/4. The axial direction of the resonator inductors L 101  and L 102  are perpendicular to the surfaces of the insulator sheets  102  through  109 . 
     On the insulator sheet  104 , the drawn out part  111   a  of the resonator capacitor conductor  111  is exposed to the left side and connected to the input terminal while the drawn out part  112   a  of the resonator capacitor conductor  112  is exposed to the right side and connected to the output terminal. 
     Referring to  FIG. 2 , the resonator inductor L 101  and the resonator capacitor C 101  form a parallel resonance circuit and hence an LC resonator Q 101 . Similarly, the resonator inductor L 102  and the resonator capacitor C 102  form a parallel resolution circuit and hence an LC resonator Q 102 . The LC resonators Q 101  and Q 102  are electrically connected to each other by way of a coupling capacitor C 103  to form a two-step band pass filter. The part L 101   a  of the resonator inductor L 101  and the LC trap capacitor C 104  form an input side LC trap circuit T 101 . Similarly, the part  102   a  of the resonator inductor L 102  and the LC trap capacitor C 105  form an output side LC trap circuit T 102 . 
     SUMMARY OF THE INVENTION 
     The filters as described in the Patent Documents 1 and 2 have via holes that operate as inductor conductors of resonator. Since the cross sectional area of a via hole is greater than that of a strip line, it is possible to reduce the insertion loss of conductors and improve the insertion loss. 
     However, with a band pass filter formed by means of two resonators according to the Patent Document 1, it is possible to generate an attenuation pole at the low frequency side of the pass band when the coupling between the resonators is capacitive, while it is possible to generate an attenuation pole at the high frequency side of the pass band when the coupling between the resonators is inductive but one or more attenuation circuits need to be added to generate two or more attenuation poles. Therefore, it is necessary to secure space for the additional circuit or circuits, which can baffle the attempt at downsizing. 
     The Patent Document 2 proposes addition of one or more new attenuation circuits (trap circuits). According to the Patent Document 2, it is possible to add a trap circuit without increasing the printed conductor layers by using the inductor electrode that forms an LC parallel resonance circuit as part of the inductor electrode for forming a λ/4 resonator and forming the connection electrode for forming the LC parallel resonance circuit in the resonator capacitor forming layer. However, with this arrangement, it is necessary to adjust the “position of electric connection” of the trap circuit electrically connected to the input/output terminal and the resonator in order to adjust the input/output impedance. More specifically, it is necessary to adjust the positions of the drawn out parts  111   a  and  112   a  in the laminating direction in  FIG. 13  and they may not necessarily be optimally arranged in the resonator capacitor forming layer. In other words, another layer for printing a connection electrode may need to be added to baffle the attempt at downsizing. 
     In view of the above-identified circumstances, it is therefore the object of the present invention to provide a laminate type band pass filter in which an additional attenuation pole can be generated without adding an attenuation circuit and whose attenuation characteristics can be improved by independently controlling the frequencies of the attenuation poles and a diplexer using the same. 
     In an aspect of the present invention, the above object is achieved by providing a laminate type band pass filter comprising a plurality of first resonators adapted to resonate in a predetermined pass band and arranged in a laminate body, the first resonators being mutually electromagnetic field coupled, wherein 
     each of the first resonators includes a first inductor conductor, a second inductor conductor and a conductor to be capacitive-coupled to a grounding conductor, 
     each of the first resonators includes a second resonator therein, each of the second serial resonator including the second inductor conductor and the conductor to be capacitive-coupled to the grounding conductor, and 
     each of the second resonators has a notch frequency set in a frequency band higher than a resonance frequency band of the first resonators. 
     In one embodiment of the laminate type band pass filter according to the present invention, the laminate body comprises a plurality of dielectric layers having various thicknesses. 
     Each first resonator may include a capacitor that is connected to the grounding conductor formed on one of the dielectric layers. 
     The first and second inductor conductors may comprise via conductors provided in the selected ones of the dielectric layers. 
     The second inductor conductor and the capacitor in the second resonators may be defined so as to resonate at the high frequency side of the resonance frequency of the first resonators. 
     The resonance frequency of the first resonators may be adjusted by modifying the sizes of the first and second inductor conductors. 
     The resonance frequency of the first resonators may be adjusted by modifying the thickness of the dielectric layers in which the first and second inductor conductors are formed. 
     The resonance frequency of the second resonators may be adjusted by modifying the electrostatic capacitances of the capacitors. 
     The resonance frequency of the second resonators may be adjusted by modifying the sizes of the first and second inductor conductors. 
     In another aspect of the present invention, there is provided a diplexer including filter having a first pass band and a filter having a second pass band, either or both of the two filters being made of a band pass filter as defined above. 
     Thus, as defined above, in the laminate type band pass filter according to the present invention, since the second serial resonator that resonates in a frequency band higher than the resonance frequency of the first resolution to generate an attenuation pole is formed by the second inductor conductor and the conductor to be capacitive-coupled to a grounding conductor of each of the first resonators, it is possible to improve the attenuation characteristics at the high frequency side of a desired pass band without using any additional attenuation circuit. 
     With the above-described arrangement, the resonance frequency of each of the first resonators can be adjusted by modifying the thickness of the laminate and thereby modifying the size of the first inductor and additionally by modifying the magnitude of the capacitive-coupling with the grounding conductor. On the other hand, the resonance frequency of each of the second resonator can be adjusted by modifying the capacitance of the conductor to be capacitive-coupled to the grounding conductor or by modifying the thickness of the laminate and thereby modifying the size of the second inductor. 
     The influence of the first resonator on the resonance frequency given rise to by modifying the capacitance of the conductor to be capacitive-coupled to the grounding conductor can be offset by modifying the size of the first inductor. Therefore, it is possible to independently adjust the resonance frequency of the first resonator and that of the second resonator. Then, the frequencies can be adjusted with ease to enhance the degree of design freedom. 
     Additionally, according to the present invention, there is provided a diplexer including filter having a first pass band and a filter having a second pass band, either or both of the two filters being a band pass filter or band pass filters as defined above, whichever appropriate. Such a diplexer shows excellent attenuation characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an electric equivalent circuit diagram of a known laminate type LC filter  100 ; 
         FIG. 2  is an exploded schematic perspective view of a known laminate type LC filter having the electric equivalent circuit diagram of  FIG. 1 ; 
         FIG. 3  is a schematic circuit diagram of a band pass filter according to the present invention, showing the circuit configuration thereof; 
         FIG. 4  is a schematic perspective view of an embodiment of laminate type band pass filter having the circuit configuration of  FIG. 3 , showing the appearance thereof; 
         FIG. 5  is schematic plan views of the dielectric layers of the band pass filter of  FIG. 4 ; 
         FIG. 6  is an exploded schematic perspective view of the band pass filter of  FIG. 4 ; 
         FIG. 7A  is a graph illustrating the electric characteristics of a known laminate type band pass filter not having any serial resonators for generating an attenuation pole; 
         FIG. 7B  is a graph illustrating the electric characteristics of a laminate type band pass filter according to the present invention and illustrated in  FIGS. 4 through 6 ; 
         FIG. 8  is schematic plan views of the dielectric layers of the second embodiment of laminate type band pass filter having the circuit configuration of  FIG. 3 ; 
         FIG. 9  is an exploded schematic perspective view of the band pass filter of  FIG. 8 ; 
         FIG. 10  is a schematic perspective view of the third embodiment of laminate type band pass filter having the circuit configuration of  FIG. 3 , showing the appearance thereof; 
         FIG. 11  is schematic plan views of the dielectric layers of the band pass filter of  FIG. 10 ; 
         FIG. 12  is an exploded schematic perspective view of the band pass filter of  FIG. 10 ; and 
         FIG. 13  is a graph showing the resonance frequencies that can be obtained when the size of the electrode  42  and that of the electrode  43  of the dielectric layer M 22  are modified in the laminate type band pass filter illustrated in  FIGS. 10 through 12 ; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, the present invention will be described in greater detail by referring to the accompanying drawings that illustrate preferred embodiments of the invention. 
       FIG. 3  is a schematic circuit diagram of an embodiment of band pass filter according to the present invention, showing the circuit configuration thereof. 
     As shown in  FIG. 3 , the band pass filter includes two resonant lines. 
     One of the resonant lines includes a capacitor C 11  and resonance elements L 11  and L 12 , whereas the other resonant line includes a capacitor C 21  and resonance elements L 21  and L 22 . 
     The connection point of the resonance elements L 11  and L 12  of one of the resonant lines is connected to input terminal IN by way of capacitor C 12  and also to the connection point of the resonance elements L 21  and L 22  of the other resonant line by way of capacitor C 31 . The connection point of the resonance elements L 21  and L 22  is also connected to output terminal OUT by way of capacitor C 22 . 
     Both the resonance element L 11  and the capacitor C 11  of the former resonant line are grounded. Similarly, both the resonance element L 21  and the capacitor C 21  of the latter resonant line are grounded. 
     The reference symbols M in  FIG. 3  respectively indicate the inductive coupling between the resonance elements L 11  and L 21  and the inductive coupling between the resonance elements L 12  and L 22 . The magnitude of each of the inductive couplings can be defined by the gap separating the related resonance elements. 
     The band pass filter having the above-described configuration has two first resonators R 1  and R 2  that resonate in a desired pass band and two second serial resonators R 3  and R 4  that generate an attenuation pole at the high frequency side of the above pass band. 
     One of the first resonators, or the first resonator R 1 , that resonates in a desired pass band includes resonance elements L 11  and L 12  and a capacitor C 11 , while the other first resonator R 2  include resonance elements L 21  and L 22  and a capacitor C 21 . 
     One of the second serial resonators, or the second serial resonator R 3 , that generates an attenuation pole at the high frequency side of the resonance frequency of the first resonators is formed by the resonance element L 12  and the capacitor C 11  of the first resonator R 1 , while the other second serial resonator R 4  is formed by the resonance element L 22  and the capacitor C 21  of the first resonator R 2 . 
     With the above-described circuit configuration, the desired pass band for generating resonance is adjusted by means of the elements forming the first resonators R 1  and R 2  and the attenuation pole at the high frequency side of the pass band of the first resonators is adjusted by means of the elements forming the second resonators R 3  and R 4 . 
     While the second resonators R 3  and R 4  that generate an attenuation pole at the high frequency side of a desired pass band for generating resonance are formed by part of the resonance elements, or the resonance elements L 12  and L 22 , and the capacitors C 11  and C 21  of the first resonators R 1  and R 2  that resonate in a desired pass band, the influence of adjustment of the frequency of the attenuation poles at the high frequency side is relatively small on the resonance frequency of the first resonators R 1  and R 2 . Additionally, if necessary, it is possible to adjust the frequencies of the attenuation poles by means of the part of the resonance elements, or the resonance elements L 11  and L 21 , of the first resonators R 1  and R 2 . In this way, it is possible to provide the second resonators that generate an attenuation pole at the high frequency sides of the pass bands of the first resonators so as to make them independently adjustable. Therefore, it is possible to improve the attenuation characteristics of the pass bands of the first resonators at the high frequency side without increasing the size of the filter. 
     Now, specific embodiments of laminate type band pass filter according to the present invention and having the above-described circuit configuration will be described below. 
       FIG. 4  is a schematic perspective view of an embodiment of laminate type band pass filter having the circuit configuration of  FIG. 3 , showing the appearance thereof. 
     The band pass filter is formed by a multilayer substrate prepared by laying a total of six dielectric layers M 1  through M 6  one on the other and has dimensions including a length of about 2.0 mm, a width of about 2.5 mm and a height of about 0.85 mm. 
     In  FIG. 4 , the reference symbols T 1  and T 2  denote respective grounding terminals and the reference symbol IN denotes an input terminal, while the reference symbol OUT denotes an output terminal. 
       FIG. 5  is schematic plan views of the dielectric layers of the band pass filter of  FIG. 4  and  FIG. 6  is an exploded schematic perspective view of the band pass filter of  FIG. 4 . 
     The dielectric layers M 1 , M 3 , M 5  and M 6  are made of a material showing a relatively low dielectric constant (e.g., dielectric constant ∈  7 ), whereas the dielectric layers M 2  and M 4  are made of a material showing a relatively high dielectric constant (e.g., dielectric constant ∈  15 ). 
     A pair of oppositely disposed lateral sides of each of the dielectric layers M 1  through M 6  is provided with three notches at each of the lateral sides. Grounding terminals T 1  and T 2 , an input terminal IN and an output terminal OUT are formed in the notches of each of the dielectric layers. The terminals may alternatively be formed by printing at the lateral sides without forming the notches. 
     Now, the configuration of each of the dielectric layers M 1  through M 6  will be described in greater detail below. 
     A grounding electrode  1  is formed on the lowermost first dielectric layer M 1  and connected to grounding terminals T 1  and T 2 . 
     One of the electrodes, or electrode  2 , of the capacitor C 11  for forming the resonators R 1  and R 3  and one of the electrodes, or electrode  3 , of the capacitor C 21  for forming the resonators R 2  and R 4  are formed on the second dielectric layer M 2 . 
     The other electrode of the capacitor C 11  and that of the capacitor C 21  are formed respectively at parts  2 ′ and  3 ′ located at corresponding positions of the grounding electrode  1  of the dielectric layer M 1 . 
     One of the electrodes, or electrode  4 , of the capacitor C 12 , one of the electrodes, or electrode  5 , of the capacitor C 22  and one of the electrodes, or electrode  6 , of the capacitor C 31  are formed on the third dielectric layer M 3 . The other electrodes  4 ′,  5 ′ and  6 ′ of the capacitors C 12 , C 22  and C 31  are formed on the fourth dielectric layer M 4 . 
     With the above-described arrangement, the capacitors C 12 , C 22  and C 31  are connected in series. 
     The electrode  4  of the opposite electrodes of the capacitor C 12  on the third dielectric layer M 3  is connected to the input terminal IN. Similarly, the electrode  5  of the opposite electrodes of the capacitor C 22  on the third dielectric layer M 3  is connected to the output terminal OUT. 
     A grounding electrode  7  is formed on the fifth dielectric layer M 5  and connected to the grounding terminals T 1  and T 2 . 
     Via conductors are formed through the dielectric layers M 3 , M 4  and M 5  to produce resonance elements. A via conductor refers to a pillar-shaped conductive path made of an conductive material formed in the through holes (via holes) bored through the dielectric layers or arranged along the inner wall of the through holes in order to electrically connect the dielectric layers. 
     In  FIGS. 5 and 6 , the reference symbols  8  and  9  denote respective via conductors formed in the dielectric layer M 3  and the reference symbols  10  and  11  denote respective via conductors formed in the dielectric layer M 4 , while reference symbols  12  and  13  denote respective via conductors formed in the dielectric layer M 5 . 
     The via conductor  8  formed in the dielectric layer M 3  runs through the dielectric layer M 3  and its upper end is connected to the electrode  6  of the opposite electrodes of the capacitor C 31 , while its lower end is connected to the electrode  2  of the opposite electrodes of the capacitor C 11 . 
     The via conductor  9  formed in the dielectric layer M 3  runs through the dielectric layer M 3  and its lower end is connected to the electrode  3  of the opposite electrodes of the capacitor C 21 . 
     The via conductor  10  formed in the dielectric layer M 4  runs through the dielectric layer M 4  and its upper end is connected to the other electrode  4 ′ of the capacitor C 12 , while its lower end is connected to the via conductor  8  of the dielectric layer M 3  by way of the electrode  6  of the opposite electrodes of the capacitor C 31 . 
     The via conductor  11  formed in the dielectric layer M 4  runs through the dielectric layer M 4  and its upper end is connected to the other electrode  5 ′ of the capacitor C 22  and the other electrode  6 ′ of the capacitor C 31 , while its lower end is connected to the via conductor  9  of the dielectric layer M 3 . 
     The via conductor  12  formed in the dielectric layer M 5  runs through the dielectric layer M 5  and its upper end is connected to the grounding electrode  7 , while its lower end is connected to the via conductor  10  of the dielectric layer M 4  by way of the other electrode  4 ′ of the capacitor C 12 . 
     The via conductor  13  formed in the dielectric layer M 5  runs through the dielectric layer M 5  and its upper end is connected to the grounding electrode  7 , while its lower end is connected to the via conductor  11  of the dielectric layer M 4  by way of the other electrode  5 ′ of the capacitor C 22  and the other electrode  6 ′ of the capacitor C 31 . 
     With the above-described arrangement, the single resonance element L 1  is formed by the via conductors  8 ,  10  and  12  and the electrode  2  of the opposite electrodes of the capacitor C 11 , whereas the single resonance element L 2  is formed by the via conductors  9 ,  11  and  13  and the electrode  3  of the opposite electrodes of the capacitor C 21 . 
     The axial direction of the two resonance elements L 1  and L 2  is perpendicular to the surfaces of the dielectric layers M 1  through M 6  and hence, as an electric current flows through the resonance elements L 1  and L 2 , a magnetic field that runs round on a plane perpendicular to the axial direction of the resonance elements L 1  and L 2  is generated around each of the resonance elements L 1  and L 2 . 
     One of the resonance elements, or the resonance element L 1  that is formed by the via conductors  8  and  10  and the electrode  2  of the opposite electrodes of the capacitor C 11 , has a structure where an intermediate tap is formed between the part of the resonance element L 12  formed by the via conductors  8  and  10  and the part of the resonance element L 11  formed by the via conductor  12  due to the electrodes  4 ,  4 ′ and  6  of the capacitors C 12  and C 31 . 
     On the other hand, the other resonance element L 2  formed by the via conductors  9 ,  11  and  13  and the electrode  3  of the opposite electrodes of the capacitor C 21  has a structure where an intermediate tap is formed between the part of the resonance element L 22  formed by the via conductors  9  and  11  and the part of the resonance element L 21  formed by the via conductor  13  due to the electrodes  5 ,  5 ′ and  6 ′ of the capacitors C 22  and C 31 . 
     With the above-described arrangement of the laminate type band pass filter, the resonance frequency of the first and second resonators R 1  and R 2  can be adjusted by modifying the sizes of the inductors formed by the via holes  8  through  13  bored through the dielectric layers M 3 , M 4  and M 5 . More specifically, the sizes of the inductors can be adjusted by modifying the thickness of the laminate type band pass filter. The resonance frequency can be adjusted by modifying the electrostatic capacitances of the capacitors C 11  and C 21 . More specifically, the electrostatic capacitances of the capacitors C 11  and C 21  can be adjusted by modifying the sizes of the electrodes  2  and  3  of the dielectric layer M 2  or by modifying the thickness of the dielectric layer M 2 . 
     On the other hand, each of the elements of the second resonators R 3  and R 4  is defined so as to resonate at the high frequency side of the resonance frequency of the first resonators R 1  and R 2  and the resonance frequency can be adjusted by modifying the electrostatic capacitances of the capacitors C 11  and C 21 . More specifically, the electrostatic capacitances of the capacitors C 11  and C 21  can be adjusted by modifying the sizes of the electrodes  2  and  3  of the dielectric layer M 2  or by modifying the thickness of the dielectric layer M 2 . Additionally, they can also be adjusted by modifying the sizes of the inductors formed by the via holes  8  through  11  bored through the dielectric layers M 3  and M 5 . More specifically, the sizes of the inductors can be adjusted by modifying the thicknesses of the dielectric layers M 3  and M 4 . 
     Since the influence of adjusting the sizes of the electrodes  2  and  3  of the dielectric layer M 2  and modifying the thicknesses of the dielectric layers M 3  and M 4  on the resonance frequency of the first resonators R 1  and R 2  is smaller than the influence on the resonance frequency of the second resonators R 3  and R 4 , the influence of adjusting the resonance frequency of the second resonators R 3  and R 4  on the resonance frequency of the first resonators R 1  and R 2  is small and insignificant. Additionally, since the resonance frequency of the first resonators R 1  and R 2  can be adjusted, if necessary, by modifying the thickness of the dielectric layer M 5 , it is possible to adjust the resonance frequency of the first resonators R 1  and R 2  and that of the second resonators R 3  and R 4  independently. 
     In the embodiment of  FIGS. 4 through 6 , the dielectric layers M 1 , M 2 , M 3 , M 4 , M 5  and M 6  respectively have thicknesses of 0.06 mm, 0.019 mm, 0.03 mm, 0.019 mm, 0.549 mm and 0.03 mm. 
       FIG. 7A  is a graph illustrating the electric characteristics of a known laminate type band pass filter not having any serial resonators for generating an attenuation pole and  FIG. 7B  is a graph illustrating the characteristics of a laminate type band pass filter according to the present invention and illustrated in  FIGS. 4 through 6 . 
     As shown in  FIG. 7A , an attenuation pole is generated only in the frequency band of 8 GHz of the known band pass filter. 
     On the other hand, in the laminate type band pass filter according to the present invention, an attenuation pole is generated in the frequency band of 8 GHz due to the coupling of the first resonators R 1  and R 2  and another attenuation pole is generated in the frequency band of 12 GHz that is located at the higher frequency side of the former frequency band due to the second resonators R 3  and R 4  as seen from  FIG. 7B . 
     Now, the second embodiment of laminate type band pass filter having a circuit configuration as shown in  FIG. 3  will be described below by referring to  FIGS. 8 and 9 . 
       FIG. 8  is schematic plan views of the dielectric layers of the second embodiment of laminate type band pass filter having the circuit configuration of  FIG. 3 .  FIG. 9  is an exploded schematic perspective view of the band pass filter of  FIG. 8 . 
     The band pass filter includes a total of seven dielectric layers M 11  through M 17 . 
     The dielectric layers M 11 , M 13 , M 16  and M 17  are made of a material showing a relatively low dielectric constant (e.g., dielectric constant ∈  7 ), whereas the dielectric layers M 12 , M 14  and M 15  are made of a material showing a relatively high dielectric constant (e.g., dielectric constant ∈  15 ). 
     The dielectric layers M 11 , M 12 , M 13 , M 14 , M 15 , M 16  and M 17  respectively have thicknesses of 0.06 mm, 0.019 mm, 0.03 mm, 0.019 mm, 0.019 mm, 0.50 mm and 0.03 mm. 
     A pair of oppositely disposed lateral sides of each of the dielectric layers M 11  through M 17  is provided with three notches at each of the lateral sides. Grounding terminals T 21 , T 22  and T 23 , an input terminal IN and an output terminal OUT are formed in the notches of each of the dielectric layers. Note that the terminals may alternatively be formed by printing at the lateral sides without forming the notches. 
     Now, the configuration of each of the dielectric layers M 11  through M 17  will be described in greater detail below. 
     A grounding electrode  21  is formed on the lowermost first dielectric layer M 11  and connected to grounding terminals T 21 , T 22  and T 23 . 
     One of the electrodes, or electrode  22 , of the capacitor C 11  for forming the resonators R 1  and R 3  and one of the electrodes, or electrode  23 , of the capacitor C 21  for forming the resonators R 2  and R 4  are formed on the second dielectric layer M 12 . 
     The other electrode of the capacitor C 11  and that of the capacitor C 21  are formed respectively at parts  22 ′ and  23 ′ located at corresponding positions of the grounding electrode  21  of the dielectric layer M 11 . 
     One of the electrodes, or electrode  24 , of the capacitor C 12  and one of the electrodes, or electrode  25 , of the capacitor C 22  are formed on the third dielectric layer M 13 . The other electrodes  24 ′ and  25 ′ of the capacitors C 12  and C 22  are formed on the fourth dielectric layer M 14 . 
     The electrode  24  of the opposite electrodes of the capacitor C 12  on the third dielectric layer M 13  is connected to the input terminal IN. Similarly, the electrode  25  of the opposite electrodes of the capacitor C 22  on the third dielectric layer M 13  is connected to the output terminal OUT. 
     One of the electrodes, or electrode  26 , of the capacitor C 31  is formed on the fifth dielectric layer M 15  and a grounding electrode  27  is formed on the sixth dielectric layer M 16  and connected to the grounding terminals T 21  and T 22 . 
     The other electrode of the capacitor C 31  is formed by the other electrodes  24 ′ and  25 ′ of the capacitors C 12  and C 22  formed on the dielectric layer M 14 . With the above-described arrangement, the capacitors C 12 , C 22  and C 31  are connected in series. 
     Via conductors are formed through the dielectric layers M 13 , M 14 , M 15  and M 16  to produce resonance elements. 
     In  FIGS. 8 and 9 , the reference symbols  28  and  29  denote respective via conductors formed in the dielectric layer M 13  and the reference symbols  30  and  31  denote respective via conductors formed in the dielectric layer M 14 , while reference symbols  32  and  33  denote respective via conductors formed in the dielectric layer M 15  and reference symbols  34  and  35  denote respective via conductors formed in the dielectric layer M 16 . 
     The via conductor  28  formed in the dielectric layer M 13  runs through the dielectric layer M 13  and its lower end is connected to the electrode  22  of the opposite electrodes of the capacitor C 11 . 
     The via conductor  29  formed in the dielectric layer M 13  runs through the dielectric layer M 13  and its lower end is connected to the electrode  23  of the opposite electrodes of the capacitor C 21 . 
     The via conductor  30  formed in the dielectric layer M 14  runs through the dielectric layer M 14  and its upper end is connected to the other electrode  24 ′ of the capacitor C 12 , while its lower end is connected to the via conductor  28  of the dielectric layer M 13 . 
     The via conductor  31  formed in the dielectric layer M 14  runs through the dielectric layer M 14  and its upper end is connected to the other electrode  25 ′ of the capacitor C 22 , while its lower end is connected to the via conductor  29  of the dielectric layer M 13 . 
     The via conductor  32  formed in the dielectric layer M 15  runs through the dielectric layer M 15  and its lower end is connected to the via conductor  30  of the dielectric layer M 14  by way of the other electrode  24 ′ of the capacitor C 12 . 
     The via conductor  33  formed in the dielectric layer M 15  runs through the dielectric layer M 15  and its lower end is connected to the via conductor  31  of the dielectric layer M 14  by way of the other electrode  25 ′ of the capacitor C 22 . 
     The via conductor  34  formed in the dielectric layer M 16  runs through the dielectric layer M 16  and its upper end is connected to the grounding electrode  27 , while its lower end is connected to the via conductor  32  of the dielectric layer M 15 . 
     The via conductor  35  formed in the dielectric layer M 16  runs through the dielectric layer M 16  and its upper end is connected to the grounding electrode  27 , while its lower end is connected to the via conductor  33  of the dielectric layer M 15 . 
     With the above-described arrangement, the single resonance element L 1  is formed by the via conductors  28 ,  30 ,  32  and  34  and the electrode  22  of the opposite electrodes of the capacitor C 11 , whereas the single resonance element L 2  is formed by the via conductors  29 ,  31 ,  33  and  35  and the electrode  23  of the opposite electrodes of the capacitor C 21 . 
     The axial direction of the two resonance elements L 1  and L 2  is perpendicular to the surfaces of the dielectric layers M 11  through M 17  and hence, as an electric current flows through the resonance elements L 1  and L 2 , a magnetic field that runs round on a plane perpendicular to the axial direction of the resonance elements L 1  and L 2  is generated around each of the resonance elements L 1  and L 2 . 
     One of the resonance elements, or the resonance element L 1  that is formed by the via conductors  28 ,  30 ,  32  and  34  and the electrode  22  of the opposite electrodes of the capacitor C 11 , has a structure where an intermediate tap is formed between the part of the resonance element L 12  formed by the via conductors  28  and  30  and the part of the resonance element L 11  formed by the via conductors  32  and  34  due to the electrodes  24 ,  24 ′ and  26  of the capacitors C 12  and C 31 . 
     On the other hand, the other resonance element L 2  formed by the via conductors  29 ,  31 ,  33  and  35  and the electrode  23  of the opposite electrodes of the capacitor C 21  has a structure where an intermediate tap is formed between the part of the resonance element L 22  formed by the via conductors  29  and  31  and the part of the resonance element L 21  formed by the via conductors  33  and  35  due to the electrodes  25 ,  25 ′ and  26  of the capacitors C 22  and C 31 . 
     With the above-described arrangement of the laminate type band pass filter, the resonance frequency of the first and second resonators R 1  and R 2  can be adjusted by modifying the sizes of the inductors formed by the via holes  28  through  35  bored through the dielectric layers M 13 , M 14 , M 15  and M 16 . More specifically, the sizes of the inductors can be adjusted by modifying the thickness of the laminate type band pass filter. The resonance frequency can be adjusted by modifying the electrostatic capacitances of the capacitors C 11  and C 21 . More specifically, the electrostatic capacitances of the capacitors C 11  and C 21  can be adjusted by modifying the sizes of the electrodes  22  and  23  of the dielectric layer M 12  or by modifying the thickness of the dielectric layer M 12 . 
     On the other hand, each of the elements of the second resonators R 3  and R 4  is defined so as to resonate at the high frequency side of the resonance frequency of the first resonators R 1  and R 2  and the resonance frequency can be adjusted by modifying the electrostatic capacitances of the capacitors C 11  and C 21 . More specifically, the electrostatic capacitances of the capacitors C 11  and C 21  can be adjusted by modifying the sizes of the electrodes  22  and  23  of the dielectric layer M 12  or by modifying the thickness of the dielectric layer M 12 . Additionally, they can also be adjusted by modifying the sizes of the inductors formed by the via holes  28  through  31  bored through the dielectric layers M 13  and M 14 . More specifically, the sizes of the inductors can be adjusted by modifying the thicknesses of the dielectric layers M 13  and M 14 . 
     Since the influence of adjusting the sizes of the electrodes  22  and  23  of the dielectric layer M 2  and modifying the thicknesses of the dielectric layers M 13  and M 14  on the resonance frequency of the first resonators R 1  and R 2  is smaller than the influence on the resonance frequency of the second resonators R 3  and R 4 , the influence of adjusting the resonance frequency of the second resonators R 3  and R 4  on the resonance frequency of the first resonators R 1  and R 2  is small and insignificant. Additionally, since the resonance frequency of the first resonators R 1  and R 2  can be adjusted, if necessary, by modifying the thickness of the dielectric layers M 15  and M 16 , it is possible to adjust the resonance frequency of the first resonators R 1  and R 2  and that of the second resonators R 3  and R 4  independently. 
     Now, the third embodiment of laminate type band pass filter having a circuit configuration as shown in  FIG. 1  will be described below by referring to  FIGS. 10 through 12 . 
       FIG. 10  is a schematic perspective view of the third embodiment of laminate type band pass filter having the circuit configuration of  FIG. 3 , showing the appearance thereof.  FIG. 11  is schematic plan views of the dielectric layers of the third embodiment of laminate type band pass filter.  FIG. 12  is an exploded schematic perspective view of the band pass filter of  FIG. 10 . 
     As shown in  FIGS. 10 ,  11  and  12 , the laminate type band pass filter includes a total of seven dielectric layers M 21  through M 27 . 
     The dielectric layers M 21 , M 23 , M 26  and M 27  are made of a material showing a relatively low dielectric constant (e.g., dielectric constant ∈  7 ), whereas the dielectric layers M 22 , M 24  and M 25  are made of a material showing a relatively high dielectric constant (e.g., dielectric constant ∈  15 ). 
     The dielectric layers M 21 , M 22 , M 23 , M 24 , M 25 , M 26  and M 27  respectively have thicknesses of 0.06 mm, 0.019 mm, 0.03 mm, 0.019 mm, 0.019 mm, 0.526 mm and 0.03 mm. 
     A pair of oppositely disposed major lateral sides of each of the dielectric layers M 21  through M 27  is provided at each of the lateral sides with three grounding terminals T 31 , T 32 , T 33 , T 34 , T 35  and T 36  that are formed by printing. A pair of oppositely disposed minor lateral sides of each of the dielectric layers M 21  through M 27 , an input terminal IN and an output terminal OUT is provided respectively with an input terminal IN and an output terminal OUT that are formed by printing. 
     Now, the configuration of each of the dielectric layers M 21  through M 27  will be described in greater detail below. 
     A grounding electrode  41  is formed on the lowermost first dielectric layer M 21  and connected to grounding terminals T 31  through T 36 . 
     One of the electrodes, or electrode  42 , of the capacitor C 11  for forming the resonators R 1  and R 3  and one of the electrodes, or electrode  43 , of the capacitor C 21  for forming the resonators R 2  and R 4  are formed on the second dielectric layer M 22 . 
     The other electrode of the capacitor C 11  and that of the capacitor C 21  are formed respectively at parts  42 ′ and  43 ′ located at corresponding positions of the grounding electrode  41  of the dielectric layer M 21 . 
     One of the electrodes, or electrode  44 , of the capacitor C 12  and one of the electrodes, or electrode  45 , of the capacitor C 22  are formed on the third dielectric layer M 23 . The other electrodes  44 ′ and  45 ′ of the capacitors C 12  and C 22  are formed on the fourth dielectric layer M 14 . 
     The electrode  44  of the opposite electrodes of the capacitor C 12  on the third dielectric layer M 23  is connected to the input terminal IN. Similarly, the electrode  45  of the opposite electrodes of the capacitor C 22  on the third dielectric layer M 23  is connected to the output terminal OUT. 
     One of the electrodes, or electrode  46 , of the capacitor C 31  is formed on the fifth dielectric layer M 25  and a grounding electrode  47  is formed on the sixth dielectric layer M 26  and connected to the grounding terminals T 31  through T 36 . 
     The other electrode of the capacitor C 31  is formed by the other electrodes  44 ′ and  45 ′ of the capacitors C 12  and C 22  formed on the dielectric layer M 24 . With the above-described arrangement, the capacitors C 12 , C 22  and C 31  are connected in series. 
     Via conductors are formed through the dielectric layers M 23 , M 24 , M 25  and M 26  to produce resonance elements. 
     In  FIGS. 11 and 12 , the reference symbols  48  and  49  denote respective via conductors formed in the dielectric layer M 23  and the reference symbols  50  and  51  denote respective via conductors formed in the dielectric layer M 24 , while reference symbols  52  and  53  denote respective via conductors formed in the dielectric layer M 25  and reference symbols  54  and  55  denote respective via conductors formed in the dielectric layer M 26 . 
     The via conductor  48  formed in the dielectric layer M 23  runs through the dielectric layer M 23  and its lower end is connected to the electrode  42  of the opposite electrodes of the capacitor C 11 . 
     The via conductor  49  formed in the dielectric layer M 23  runs through the dielectric layer M 23  and its lower end is connected to the electrode  43  of the opposite electrodes of the capacitor C 21 . 
     The via conductor  50  formed in the dielectric layer M 24  runs through the dielectric layer M 24  and its upper end is connected to the other electrode  44 ′ of the capacitor C 12 , while its lower end is connected to the via conductor  48  of the dielectric layer M 23 . 
     The via conductor  51  formed in the dielectric layer M 24  runs through the dielectric layer M 24  and its upper end is connected to the other electrode  45 ′ of the capacitor C 22 , while its lower end is connected to the via conductor  49  of the dielectric layer M 23 . 
     The via conductor  52  formed in the dielectric layer M 25  runs through the dielectric layer M 25  and its lower end is connected to the via conductor  50  of the dielectric layer M 24  by way of the other electrode  44 ′ of the capacitor C 12 . 
     The via conductor  53  formed in the dielectric layer M 25  runs through the dielectric layer M 25  and its lower end is connected to the via conductor  51  of the dielectric layer M 24  by way of the other electrode  45 ′ of the capacitor C 22 . 
     The via conductor  54  formed in the dielectric layer M 26  runs through the dielectric layer M 26  and its upper end is connected to the grounding electrode  47 , while its lower end is connected to the via conductor  52  of the dielectric layer M 25 . 
     The via conductor  55  formed in the dielectric layer M 26  runs through the dielectric layer M 26  and its upper end is connected to the grounding electrode  47 , while its lower end is connected to the via conductor  53  of the dielectric layer M 25 . 
     With the above-described arrangement, the single resonance element L 1  is formed by the via conductors  48 ,  50 ,  52  and  54  and the electrode  42  of the opposite electrodes of the capacitor C 11 , whereas the single resonance element L 2  is formed by the via conductors  49 ,  51 ,  53  and  55  and the electrode  43  of the opposite electrodes of the capacitor C 21 . 
     The axial direction of the two resonance elements L 1  and L 2  is perpendicular to the surfaces of the dielectric layers M 21  through M 27  and hence, as an electric current flows through the resonance elements L 1  and L 2 , a magnetic field that runs round on a plane perpendicular to the axial direction of the resonance elements L 1  and L 2  is generated around each of the elements. 
     One of the resonance elements, or the resonance element L 1  that is formed by the via conductors  48 ,  50 ,  52  and  54  and the electrode  42  of the opposite electrodes of the capacitor C 11 , has a structure where an intermediate tap is formed between the part of the resonance element L 12  formed by the via conductors  48  and  50  and the part of the resonance element L 11  formed by the via conductors  52  and  54  due to the electrodes  44 ,  44 ′ and  46  of the capacitors C 12  and C 31 . 
     On the other hand, the other resonance element L 2  formed by the via conductors  49 ,  51 ,  53  and  55  and the electrode  43  of the opposite electrodes of the capacitor C 21  has a structure where an intermediate tap is formed between the part of the resonance element L 22  formed by the via conductors  49  and  51  and the part of the resonance element L 21  formed by the via conductors  53  and  55  due to the electrodes  45 ,  45 ′ and  46  of the capacitors C 22  and C 31 . 
     With the above-described arrangement of the laminate type band pass filter, the resonance frequency of the first and second resonators R 1  and R 2  can be adjusted by modifying the sizes of the inductors formed by the via holes  48  through  55  bored through the dielectric layers M 23 , M 24 , M 25  and M 26 . More specifically, the sizes of the inductors can be adjusted by modifying the thickness of the laminate type band pass filter. The resonance frequency can be adjusted by modifying the electrostatic capacitances of the capacitors C 11  and C 21 . More specifically, the electrostatic capacitances of the capacitors C 11  and C 21  can be adjusted by modifying the sizes of the electrodes  42  and  43  of the dielectric layer M 22  or by modifying the thickness of the dielectric layer M 22 . 
     On the other hand, each of the elements of the second resonators R 3  and R 4  is defined so as to resonate at the high frequency side of the resonance frequency of the first resonators R 1  and R 2  and the resonance frequency can be adjusted by modifying the electrostatic capacitances of the capacitors C 11  and C 21 . More specifically, the electrostatic capacitances of the capacitors C 11  and C 21  can be adjusted by modifying the sizes of the electrodes  42  and  43  of the dielectric layer M 22  or by modifying the thickness of the dielectric layer M 22 . Additionally, they can also be adjusted by modifying the sizes of the inductors formed by the via holes  48  through  51  bored through the dielectric layers M 23  and M 24 . More specifically, the sizes of the inductors can be adjusted by modifying the thicknesses of the dielectric layers M 23  and M 24 . 
       FIG. 13  is a graph showing the frequency characteristics of the laminate type band pass filter that can be obtained when the size of the electrode  42  and that of the electrode  43  are modified from 0.5 mm to 0.7 mm at a step of 0.05 mm in the direction of the arrow in  FIG. 13 . 
     From  FIG. 13 , it will be seen that the resonance frequency of the second resonators R 3  and R 4  is shifted toward the high frequency side as the sizes of the electrodes  42  and  43  are reduced. 
     The above-described embodiments are so many laminate type band pass filters having a single pass band. The present invention can also provide a diplexer that shows excellent attenuation characteristics at the high frequency side and is formed by using a band pass filter having a first pass band and a band pass filter having a second pass band when either or both of them are band pass filters according to the present invention. 
     For example, in a diplexer according to the present invention, both the band pass filter having a first pass band and the band pass filter having a second pass band may be of the distributed constant type as described above by way of the embodiments. 
     In a diplexer according to the present invention, the band pass filter having a first pass band may be of the distributed constant type and the band pass filter having a second pass band may be of the lumped constant type.