Abstract:
A diplexer provides a high degree of design freedom for satisfying the requirements of electric characteristics so as to realize desired characteristics and at the same time can be downsized and a multiplexer is realized by using such a diplexer. The diplexer includes a filter having a first pass band and a filter having a second pass band with a frequency band at least twice as high as the frequency band of the first pass band, the filter having the first pass band being a filter of the lumped constant type, the filter having the second pass band being a filter of the distributed constant type.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a diplexer that can find applications in mobile communication apparatus adapted to operate with microwaves and also to a multiplexer using the same. More particularly, the present invention relates to a diplexer and a multiplexer that have a high-frequency side pass band at or near 5 GHz and are required to secure attenuation in a frequency domain not lower than 10 GHz as in the case of WiFi. WiFi (Wireless Fidelity) is a technology brand invented to improve the consumers&#39; recognition of the “IEEE802.11a/IEEE802.11b” standards for wireless LANs. IEEE802.11a is one of the standards established for LAN technologies by the 802 Committee of IEEE that provides specifications for wireless communications at about 54 Mbps in the 5.2 GHz band. In Japan, 5.15 GHz to 5.25 GHz are assigned to high speed wireless LANs. IEEE802.11b is a standard providing specifications for wireless communications at about 11 Mbps in the 2.4 GHz band. 
         [0003]    2. Description of the Related Art 
         [0004]    There are known separators prepared for band separation in dual band portable phones that can operate for communications by way of two frequency bands and by means of a single potable terminal by integrally laying ceramic insulating layers to produce a laminate and forming therein a first notch circuit having a parallel circuit of an inductance and a capacitance and a second notch circuit also having a parallel circuit of an inductance and a capacitance, the line width of the inductance of the high-frequency side second notch circuit being made grater than the line width of the inductance of the first notch circuit, for the purpose of downsizing, while maintaining the characteristics of the separator (see Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 11-68499). 
         [0005]    Similar separators that can be easily downsized with a small loss and includes a low-frequency side first filter, which is a low pass filter equipped with an attenuation pole, and a high-frequency side second filter, which is a high pass filter also equipped with an attenuation pole, one of the input/output ports of the first and second filters being made to operate as common port, are also known (see Patent Document 2: Jpn. Pat. Appln. Laid-Open Publication No. 11-266133). 
         [0006]    Furthermore, separators including a first filter and a second filter having respective center frequencies that are different from each other, and a separation circuit, where the separation circuit has capacitors respectively connected to the first filter and the second filter in series and inductors respectively connected to the first filter and the second filter in parallel, are known (see Patent Document 3: Japanese Patent No. 3,204,753). 
         [0007]    Separators as described in the above cited Patent Documents 1 and 2 have a functional feature of diplexer by forming an LC circuit element in a multilayer structure. Basically, both of them are provided with a feature of a filter and a feature of matching the high-frequency side with the low-frequency side by combining the function of a low pass filter and that of a high pass filter. Such filters are formed by using an inductor and a capacitor that are lumped constant elements and hence referred to as lumped constant type filters. 
         [0008]    While lumped constant type filters have an advantage that it is not necessary to additionally incorporate a special matching circuit and a relatively high degree of freedom is provided for setting the attenuation pole position because the attenuation pole is produced by an LC resonator, they are accompanied by a disadvantage that resonance peaks appear to reduce the impedance of each lumped constant element to nil in the high-frequency domain where the element gives rise to self resonance to consequently deteriorate the attenuation. Thus, it is necessary to add an attenuation circuit in order to enhance the attenuation characteristic, ending up in an increased number of necessary circuit elements, which by turn obstructs the attempt to downsize the product. Additionally, the number of self resonance peaks increases as the number of circuit elements rises to further deteriorate the attenuation characteristic in the higher harmonic domain. 
         [0009]    Furthermore, from the material point of view, materials showing a relatively low dielectric constant will have to be selected to meet the requirement of forming an ideal inductor. A technique of laying a low dielectric constant material and a high dielectric constant material one on the other to form a laminate has been publicized recently so that an inductor may be formed in a region formed by the low dielectric constant material while a capacitor may be formed in a region formed by the high dielectric constant material for the purpose of achieving improved electric characteristics. 
         [0010]    Meanwhile, according to Patent Document  3 , a filter is formed by using a λ/4 line having a short-circuited side and an open side as resonator and the functional feature of a diplexer is realized by combining two filters and a separator circuit (matching circuit) A filter of the type formed by using a λ/4 line is referred to as distributed constant type filter because it exploits the characteristics attributable to the profiles of the elements. 
         [0011]    While a distributed constant type filter generally can achieve higher electric characteristics particularly in terms of attenuation with an arrangement simpler than a lumped constant type filter, it requires a separator circuit (matching circuit) because a diplexer cannot be realized simply by connecting two filters. 
         [0012]    Additionally, from the material point of view, a material having a higher dielectric constant is preferably employed for the purpose of downsizing because the resonance frequency is determined by the length of the λ/4 line and the dielectric constant of the material. 
         [0013]    As described above, while combinations of lumped constant type elements and those of distributed constant type elements have been proposed to date, no proposal has ever been made to combine a lumped constant type element and a distributed constant type element. The reason for this may apparently be that it is necessary to form a very large resonance element (λ/4 line) in order to reduce the resonance frequency by means of the distributed constant type when a material showing a low dielectric constant is employed, whereas the self resonance frequency of the inductor of the lumped constant type becomes low to consequently narrow the frequency domain necessary for operating as inductor and the attenuation characteristic of higher harmonics is degraded by the self resonance peaks when a material showing a high dielectric constant is employed. 
         [0014]    When combining lumped constant type filters and distributed constant type filters, using the technique of laying different materials, combining a high dielectric constant material and a low dielectric constant material, both the lumped constant type filters and the distributed constant type filters need to be laid to form a laminate so that the thicknesses of sheet allocated to the respective types are relatively reduced to give rise to a problem of a reduced distance separating the ground and the inductor particularly of the lumped constant type to consequently degrade the insertion loss. 
       SUMMARY OF THE INVENTION 
       [0015]    In view of the above-identified problems of the prior art, it is therefore the object of the present invention to provide a diplexer that ensures a high degree of design freedom for satisfying the requirements of electric characteristics so as to realize desired characteristics and at the same time can be downsized and also a multiplexer realized by using such a diplexer. 
         [0016]    In an aspect of the present invention, the above object is achieved by providing a diplexer including: a filter having a first pass band; and a filter having a second pass band with a center frequency at least twice as high as the center frequency of the first pass band; the filter having the first pass band being a filter of the lumped constant type; the filter having the second pass band being a filter of the distributed constant type. 
         [0017]    In the diplexer according to the present invention as defined above, the filter of the lumped constant type having the first pass band may be a band pass filter formed by connecting a low pass filter and a high pass filter in series and the filter of the distributed constant type having the second pass band may be a band pass filter. 
         [0018]    The resonator of the band pass filter of the distributed constant type having the second pass band may include an inductor formed in a multilayer substrate and linking itself to a via conductor formed along the laminating direction of the multilayer substrate and an electrode capacitive-coupled to a grounding electrode. Additionally, the resonator of the band pass filter of the distributed constant type having the second pass band may include an inductor electrode having a bent section. The inductor electrode having a bent section may show a profile at least selected from a spiral profile, a U-shaped profile, a meandering profile and an arc-shaped profile. 
         [0019]    The band pass filter of the distributed constant type having the second pass band may be capacitive-coupled to a common terminal. In another embodiment, the band pass filter of the distributed constant type having the second pass band may be connected to a common terminal by way of an LC parallel resonance circuit. 
         [0020]    The resonator of the band pass filter of the distributed constant type having the second pass band may be connected to a short circuit terminal formed at the side of the surface located vis-à-vis the mounting surface of the multilayer substrate. 
         [0021]    The filter of the lumped constant type having the first pass band may be connected to a common terminal by way of an inductor electrode. 
         [0022]    According to the present invention, there is also provided a multiplexer including at least a lumped constant type filter and a distributed constant type filter and adapted to separate and couple a plurality of bands. 
         [0023]    Thus, since a diplexer according to the present invention includes a filter having a first pass band and a filter having a second pass band with a center frequency at least twice as high as the center frequency of the first pass band, the filter having the first pass band being a filter of the lumped constant type, the filter having the second pass band being a filter of the distributed constant type, it is possible to provide a broader choice of types and a higher degree of design freedom to meet the requirements of electric characteristics. Additionally, since the second pass band is at the higher frequency side relative to the first pass band and the filter having the lower frequency side first pass band is of the lumped constant type, whereas the filter having the higher frequency side second pass band is of the distributed constant type, the length of the resonance element of the distributed constant type filter is determined as a function of its resonance frequency so that it is possible to downsize the diplexer when it is so designed as to be applied to a higher frequency domain. Still additionally, since the center frequency of the second pass band is at least twice as high as the center frequency of the first pass band, it is possible to reduce the length of the resonance element necessary for making a filter of the distributed constant type out of the filter having the second pass band and allowing the use of a low dielectric constant material for it. Then, as a result, it is advantageously possible to form the filter of the lumped constant type having the first pass band in an ideal manner. 
         [0024]    In the diplexer according to the present invention, the filter of the lumped constant type having the first pass band may be a band pass filter formed by connecting a low pass filter and a high pass filter in series and the filter of the distributed constant type having the second bass band may also be a band pass filter. Then, as a result of using such band pass filters, the diplexer according to the present invention provides an advantage of allowing the number of filter elements arranged downstream relative to the diplexer and hence the number of parts of the entire high-frequency side to be reduced so as to pave the way for downsizing. Additionally, when the attenuation of the diplexer is enhanced, it provides an advantage of improving the filter characteristics even if the attenuation of the downstream filters is small. Still additionally, it is possible to eliminate some of the downstream filters and reduce the number of downstream filters by enhancing the attenuation of the diplexer. Then, as a result, it is possible to provide laminate LC parts at low cost. 
         [0025]    In the diplexer according to the present invention, the resonator of the band pass filter of the distributed constant type having the second pass band may include a inductor formed in a multilayer substrate and linking itself to a via conductor formed along the laminating direction of the multilayer substrate and an electrode capacitive-coupled to a grounding electrode. Then, as a result of utilizing the via conductor extending along the laminating direction for the inductor, the diplexer according to the present invention provides an advantage that the magnetic field generated by the inductor is made to extend along a plane that runs in parallel with the dielectric layer without running through the grounding electrode and hence without generating any eddy current. The net result will be that there is no risk of aggravating the insertion loss. 
         [0026]    In the diplexer according to the present invention, the resonator of the band pass filter of the distributed constant type having the second pass band may include a inductor formed in a multilayer substrate and linking itself to a via conductor formed along the laminating direction of the multilayer substrate, an electrode capacitive-coupled to a grounding electrode and an inductor electrode having a bent section. Then, as a result, the frequency can be adjusted more finely not only by adjusting the center frequency by way of the capacitive-coupling relative to the grounding electrode but also adjusting the length of the inductor electrode having the bent section. The inductor electrode having a bent section may show a profile at least selected from a spiral profile, a U-shaped profile, a meandering profile and an arc-shaped profile. When the inductor electrode having the bent section is formed by connecting the opposite ends of the inductor electrodes by way of the via conductor and winding it in the laminating direction of the laminate, it is possible to adjust the length of the inductor electrode without increasing the dimensions of the final product. 
         [0027]    In the diplexer according to the present invention, the band pass filter of the distributed constant type having the second pass band may be capacitive-coupled to a common terminal. Then, as a result, the capacitive-coupled capacitor shows such characteristics that it intercepts signals of the low-frequency domain and passes signals of the high-frequency domain to provide an advantage of matching without requiring an independent separator circuit. 
         [0028]    In the diplexer according to the present invention, the band pass filter of the distributed constant type having the second pass band may be connected to a common terminal by way of an LC parallel resonance circuit. Then, as a result, it is possible to make the resonance frequency of the LC parallel resonance circuit agree with the first frequency and allow the LC parallel resonance circuit to operate as matching circuit. 
         [0029]    In the diplexer according to the present invention, the filter of the lumped constant type having the first pass band may be connected to a common terminal by way of an inductor electrode. Then, as a result, an inductor electrode shows such characteristics that it passes signals of the low-frequency domain and intercepts signals of the high-frequency domain to provide an advantage of matching without requiring an independent separator circuit. 
         [0030]    According to the present invention, it is possible to provide a triplexer or a multiplexer having more than three filters by combining at least one or more than one lumped constant type filters and one or more than one distributed constant type filters. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is a schematic circuit diagram of diplexer according to an embodiment of the present invention, showing the circuit configuration thereof; 
           [0032]      FIG. 2  is a schematic circuit diagram of diplexer according to another embodiment of the present invention, showing the circuit diagram thereof; 
           [0033]      FIG. 3  is a schematic perspective view of a diplexer according to the present embodiment, showing the appearance thereof; 
           [0034]      FIG. 4  is an exploded schematic perspective view of the embodiment of  FIG. 1 ; 
           [0035]      FIG. 5  is a schematic circuit diagram of the equivalent circuit of the diplexer of  FIG. 4 ; 
           [0036]      FIG. 6  is an exploded schematic perspective view of the embodiment of  FIG. 2 ; 
           [0037]      FIG. 7  is a schematic circuit diagram of the equivalent circuit of the diplexer of  FIG. 6 ; 
           [0038]      FIG. 8  is an exploded schematic perspective view of diplexer according to still another embodiment of the present invention; and 
           [0039]      FIG. 9  is a schematic circuit diagram of the equivalent circuit of the diplexer of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Now, the present invention will be described in greater detail below by referring to the accompanying drawings that illustrate preferred embodiments of the invention. 
         [0041]      FIG. 1  is a schematic circuit diagram of an embodiment of diplexer according to the present invention, showing the circuit configuration thereof. In the circuit of  FIG. 1 , reference symbol  10  denotes a low pass filter of the lumped constant type having the first pass band and reference symbol  20  denotes a band pass filter of the distributed constant type having the second pass band. The low pass filter  10  of the lumped constant type includes a parallel resonance circuit of a capacitor  11  and an inductor  12  and the circuit parameters of the resonance circuit are so selected that it resonates in the second pass band. The resonance circuit generates an attenuation pole in the second pass band. One of the opposite ends of the parallel resonance circuit of the capacitor  11  and inductor  12  is connected to low-frequency side terminal LT and grounded by way of a capacitor  13 . The other end of the parallel resonance circuit of the capacitor  11  and the inductor  12  is connected to an antenna terminal, or common terminal ANT, and grounded by way of a capacitor  14 . 
         [0042]    The band pass filter  20  of the distributed constant type has two resonant lines. One of the resonant lines is formed by a capacitor  21   a  and resonance elements  22   a ,  23   a , whereas the other resonant line is formed by a capacitor  21   b  and resonance elements  22   b ,  23   b . The connection point of the resonance elements  22   a ,  23   a  of one of the resonant lines is connected to the common terminal ANT by way of a capacitor  24  and also to the connection point of the resonance elements  22   b ,  23   b  of the other resonant line by way of a capacitor  25 , the latter connection point being connected to high-frequency side terminal HT by way of a capacitor  26 . The resonance element  23   a  of the former resonant line is grounded. Similarly, the resonance element  23   b  of the other resonance line is grounded. The band pass filter  20  of the distributed constant type has two serial resonance circuits and one of the serial resonance circuits is formed by the capacitor  21   a  and the resonance element  22   a , whereas the other serial resonance circuit is formed by the capacitor  21   b  and the resonance element  22   b . The serial resonance circuits operate to generate an attenuation pole at the high-frequency side of the pass band. The reference symbols M in  FIG. 1  respectively indicate the inductive coupling between the resonance elements  22   a ,  22   b  and the inductive coupling between the resonance elements  23   a ,  23   b . The magnitude of each of the inductive couplings can be defined by the gap separating the related resonance elements. 
         [0043]      FIG. 2  is a schematic circuit diagram of another embodiment of diplexer according to the present invention, showing the circuit diagram thereof. In  FIG. 2 , the circuit components similar to those of  FIG. 1  are denoted respectively by the same reference symbols. 
         [0044]    In the circuit of  FIG. 2 , reference symbol  30  denotes a band pass filter of the lumped constant type having the first pass band and is formed by a low pass filter  10  of the lumped constant type and a high pass filter  40  of the lumped constant type. The high pass filter  40  of the lumped constant type includes a serial resonance circuit of an inductor  41  and a capacitor  42 . One of the opposite ends of the serial resonance circuit is grounded by way of the capacitor  42 , while the other end thereof is connected to low-frequency side terminal LT by way of a capacitor  43  and also to one of the opposite ends of the parallel resonance circuit of the capacitor  11  and the inductor  12  of the low pass filter  10  of the lumped constant type by way of a capacitor  44 . The other end of the parallel resonance circuit is connected to common terminal ANT. The low pass filter  10  of the lumped constant type having the first pass band has a circuit configuration same as its counterpart of  FIG. 1 . In other words, the low pass filter  10  of the lumped constant type includes the parallel resonance circuit of the capacitor  11  and the inductor  12  and the circuit parameters of the resonance circuit are so selected that it resonates in the second pass band. The resonance circuit generates an attenuation pole in the second pass band. 
         [0045]    The band pass filter  20  of the distributed constant type has a circuit configuration similar to its counterpart of  FIG. 1 . In other words, the band pass filter  20  of the distributed constant type has two resonant lines. One of the resonant lines is formed by a capacitor  21   a  and resonance elements  22   a ,  23   a , whereas the other resonant line is formed by a capacitor  21   b  and resonance elements  22   b ,  23   b . The connection point of the resonance elements  22   a ,  23   a  of one of the resonant lines is connected to the common terminal ANT by way of a capacitor  24  and also to the connection point of the resonance elements  22   b ,  23   b  of the other resonant line byway of a capacitor  25 , the latter connection point being connected to high-frequency side terminal HT by way of a capacitor  26 . The resonance element  23   a  of the former resonant line is grounded. Similarly, the resonance element  23   b  of the other resonance line is grounded. The band pass filter  20  of the distributed constant type has to two serial resonance circuits and one of the serial resonance circuits is formed by the capacitor  21   a  and the resonance element  22   a , whereas the other serial resonance circuit is formed by the capacitor  21   b  and the resonance element  22   b . The serial resonance circuits operate to generate an attenuation pole at the high-frequency side of the pass band. 
         [0046]      FIG. 3  is a schematic perspective view of a diplexer according to the present invention, showing the appearance thereof. Referring to  FIG. 3 , the diplexer  1  (or  2  or  3 ) is formed by a multilayer substrate prepared by laying a total of fourteen dielectric layers 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. The diplexer has grounding terminals T 1  through T 3 , a low-frequency side terminal T 4 , a high-frequency side terminal T 5  and an antenna terminal, or common terminal T 6 .  FIGS. 4 and 5  illustrate the embodiment of diplexer  1  of  FIG. 1 . The illustrated diplexer  1  is formed by a multilayer substrate that is prepared by laying a plurality of dielectric layers (fourteen in the case of the illustrated embodiment) including dielectric layers M 1 , M 2 , M 3 , M 4 , M 5 , M 6 , M 7 , M 8 , M 9 , M 10 , M 11 , M 12 , M 13  and M 14 . The dielectric layers M 1 , M 2 , M 3 , M 6 , M 7 , M 8 , M 9 , M 10 , M 11 , M 12  and M 14  are made of a material showing a relatively low dielectric constant (e.g., dielectric constant ε 7), whereas the dielectric layers M 4 , M 5  and M 13  are made of a material showing a relatively high dielectric constant (e.g., dielectric constant ε 15). A pair of oppositely disposed lateral sides of each of the dielectric layers M 1  through M 14  is provided with three notches at each of the lateral sides. Grounding terminals T 1  through T 3 , a low-frequency side terminal T 4 , a high-frequency side terminal T 5  and an antenna terminal, or common terminal T 6 , are formed respectively 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. 
         [0047]    A grounding electrode G 1  is formed on the lowermost first dielectric layer M 1  so as to include in the right half area thereof sites to be located respectively vis-à-vis the corresponding ones of the paired electrodes of capacitor C 1  and capacitor C 5  of a band pass filter of the lumped constant type having the first pass band that is formed on the right half of the second dielectric layer M 2 . On the other hand, the grounding electrode G 1  formed on the lowermost first dielectric layer M 1  includes in the left half area thereof sites to be located vis-à-vis the respective ones of the paired electrodes of capacitor C 7  and capacitor C 9  of a band pass filter of the distributed constant type having the second pass band that is formed on the left half of the second dielectric layer M 2 . The sites of those ones of the paired electrodes of the capacitors on the grounding electrode G 1  also operate as capacitors. Additionally, the grounding electrode G 1  is also connected to the grounding terminals T 1 , T 2 , T 3  so as to operate as grounding electrode. It will be appreciated as a matter of course that the elements of the band pass filter of the lumped constant type and those of the band pass filter of the distributed constant type may be arranged inversely in terms of right and left. 
         [0048]    The other electrode of the capacitor C 1  and that of the capacitor C 5  of the band pass filter of the lumped constant type having the first pass band are arranged in the right half area on the second dielectric layer M 2  at respective positions located vis-à-vis the grounding electrode G 1  formed on the first dielectric layer M 1  with the dielectric layer interposed between them and the other electrode of the capacitor C 7  and that of the capacitor C 9  of the band pass filter of the distributed constant type having the second pass band are arranged in the left half area on the second dielectric layer M 2  at respective positions located vis-à-vis the grounding electrode G 1  formed on the first dielectric layer M 1  with the dielectric layer interposed between them. A via conductor (which refers herein to a pillar-shaped conductive path formed in the through holes (via holes) bored through the respective dielectric layers in order to electrically connect the dielectric layers) V 2 - 1  is formed on the second dielectric layer M 2 . The via conductor V 2 - 1  is connected to site P 1 - 1  in the grounding electrode G 1  formed on the first dielectric layer M 1 . 
         [0049]    One of the opposite electrodes of the capacitor C 6  and one of the opposite electrodes of the capacitor C 10  of the band pass filter of the distributed constant type having the second pass band are formed on the left half of the third dielectric layer M 3 . Those electrodes are connected respectively to the common terminal T 6  and the high-frequency side terminal T 5 . Additionally, a via conductor V 3 - 1  is formed on the third dielectric layer M 3  at a position corresponding to the via conductor V 2 - 1  formed in the second dielectric layer M 2 , while via conductors V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  are also formed on the third dielectric layer M 3  at respective positions located vis-à-vis the sites P 2 - 2 , P 2 - 3 , P 2 - 4  and P 2 - 5  on the electrodes of the capacitor C 1 , the capacitor C 5 , the capacitor C 9  and the capacitor C 7  formed on the second dielectric layer M 2 . Note that the electrodes of the capacitor C 6  and the capacitor C 10  on the third dielectric layer M 3  are electrically isolated from all the via conductors formed on the third dielectric layer M 3 . 
         [0050]    The other electrode of the capacitor C 6  and the electrode of the capacitor C 10  of the band pass filter of the distributed constant type having the second pass band are formed on the left half of the fourth dielectric layer M 4 . Additionally, via conductors V 4 - 1 , V 4 - 2 , V 4 - 3 , V 4 - 4  and V 4 - 5  are formed on the fourth dielectric layer M 4  at respective positions located vis-à-vis the via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3  and electrically connected to the respective via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3 . As illustrated in  FIG. 4 , the electrodes of the capacitor C 6  and the capacitor C 10  are respectively electrically connected to the via conductors V 4 - 5  and V 4 - 4 . 
         [0051]    Electrode C 8  that is a component of the electrode pattern that forms capacitor C 8  in the equivalent circuit of the band pass filter of the distributed constant type having the second pass band is formed on the left half of the fifth dielectric layer M 5 , while via conductors V 5 - 1 , V 5 - 2 , V 5 - 3 , V 5 - 4  and V 5 - 5  are also formed on the fifth dielectric layer M 5  at respective positions located vis-à-vis the via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3 . While the capacitor C 8  in the equivalent circuit is shown as a single capacitor C 8  for the sake of convenience, it is formed by the electrodes C 6 , C 8  and C 10  in  FIG. 4  (also in  FIGS. 6 and 8 ). More specifically, the first capacitor is formed by the electrode C 6  formed on the fourth dielectric layer M 4  and the electrode C 8  formed on the fifth dielectric layer M 5  and the second capacitor is formed by the electrode C 10  formed on the fourth dielectric layer M 4  and the electrode C 8  formed on the fifth dielectric layer M 5  and the capacitor C 8  is formed by connecting the capacitors in series to form the capacitor C 8  in the equivalent circuit. 
         [0052]    The capacitors L 1  through L 4  of the band pass filter of the lumped constant type having the first pass band are partly formed on the right half of each of the sixth through ninth dielectric layers M 6  through M 9 . The inductors L 1 , L 2  and L 4  of the band pass filter of the lumped constant type having the first pass band are partly formed on the right half of each of the tenth and eleventh dielectric layers M 10  and M 11 . Additionally, via conductors V 6 - 1  through V 6 - 5  are formed on the sixth dielectric layer M 6  at respective positions located vis-à-vis the via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3 . 
         [0053]    One of the opposite ends of the part of the inductor L 1  formed on the sixth dielectric layer M 6  is connected to the via conductor V 6 - 2  and hence to the site P 2 - 2  of the electrode of the capacitor C 1  formed on the second dielectric layer M 2  by way of the corresponding via conductors V 5 - 2 , V 4 - 2  and V 3 - 2 . Additionally, the mutually linked via conductors also operate as inductor. The other end of the part of the inductor L 1  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 1  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 6  also formed on the seventh dielectric layer M 7 , while the other end of the part of the inductor L 1  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 1  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 6  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 1  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 1  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 6  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 1  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the inductor L 1  formed on the tenth dielectric layer M 10  by way of the via conductor V 10 - 6  also formed on the tenth dielectric layer M 10 , while the other end of the part of the inductor L 1  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 1  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 6  also formed on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 1  formed on the eleventh dielectric layer M 11  is connected to the low-frequency side terminal T 4 . 
         [0054]    One of the opposite ends of the part of the inductor L 2  formed on the sixth dielectric layer M 6  is connected to the via conductor V 6 - 1  and then to the site P 1 - 1  of the grounding electrode G 1  formed on the first dielectric layer M 1  by way of the corresponding via conductors V 5 - 1 , V 4 - 1 , V 3 - 1  and V 2 - 1 . Additionally, the mutually linked via conductors also operate as inductor. The other end of the part of the inductor L 2  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 2  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 7  also formed on the seventh dielectric layer M 7 , while the other end of the part of the inductor L 2  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 2  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 7  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 2  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 2  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 7  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 2  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the inductor L 2  formed on the tenth dielectric layer M 10  by way of the via conductor V 10 - 7  also formed on the tenth dielectric layer M 10 , while the other end of the part of the inductor L 2  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 2  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 7  also formed on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 2  formed on the eleventh dielectric layer M 11  is connected to the corresponding electrode of the capacitor C 3  formed on the twelfth dielectric layer M 12  by way of the via conductor V 12 - 7  also formed on the twelfth dielectric layer M 12 . 
         [0055]    One of the opposite ends of each of the inductors L 3  and L 4  formed on the sixth dielectric layer M 6  is connected to the via conductor V 6 - 3  and the other end of the inductor L 3  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 3  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 8  also formed on the seventh dielectric layer M 7 . The other end of the part of the inductor L 3  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 3  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 8  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 3  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 3  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 8  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 3  formed on the ninth dielectric layer M 9  is connected to the capacitor C 4  formed on the thirteenth dielectric layer M 13  byway of the via conductor V 10 - 8 , the via conductor V 11 - 8 , the via conductor V 12 - 8  and the via conductor V 13 - 8  formed respectively on the tenth dielectric layer M 10 , the eleventh dielectric layer M 11 , the twelfth dielectric layer M 12  and the thirteenth dielectric layer M 13 . 
         [0056]    The other end of the inductor L 4  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 4  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 9  also formed on the seventh dielectric layer M 7 . The other end of the part of the inductor L 4  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 4  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 9  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 4  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 4  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 9  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 4  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the part of the inductor L 4  formed on the tenth dielectric layer M 10  by way of the via conductor M 10 - 9  also formed on the tenth dielectric layer M 10 . The other end of the part of the inductor L 4  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 4  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 9  also formed on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 4  formed on the eleventh dielectric layer M 11  is connected to the common terminal T 6 . 
         [0057]    The capacitors C 2 , C 3  and C 4  of the band pass filter of the lumped constant type having the first pass band are formed on the right half of the twelfth dielectric layer M 12  and also on the right half of the thirteenth dielectric layer M 13 . One of the electrodes of the capacitor C 2  and the corresponding one of the electrodes of the capacitor C 3 , the capacitors C 2  and C 3  being formed on the twelfth dielectric layer M 12 , are connected to each other so as to operate as a single electrode. The electrode of the capacitor C 4  formed on the twelfth dielectric layer M 12  is connected to the connection point of the inductors L 3  and L 4  formed on the sixth dielectric layer M 6  byway of the via conductors V 12 - 3 , V 11 - 3 , V 10 - 3 , V 9 - 3 , V 8 - 3  and V 7 - 3  and also to the site P 2 - 3  of the electrode of the capacitor C 5  formed on the second dielectric layer M 2  by way of the via conductors V 6 - 3 , V 5 - 3 , V 4 - 3  and V 3 - 3 . Additionally, the mutually linked via conductors also operate as inductor. The other electrode of the capacitor C 2  formed on the thirteenth dielectric layer M 13  is connected to the low-frequency side terminal T 4  and the other electrodes of the capacitors C 3  and C 4  formed on the thirteenth dielectric layer M 13  are connected to each other. 
         [0058]    As shown in  FIG. 4 , a grounding electrode G 13  is formed on the left half of the thirteenth dielectric layer M 13  in a region that contains the via conductors V 13 - 4  and V 13 - 5  and connected to the grounding terminals T 1  and T 3 . 
         [0059]    A conductive material is arranged in the through holes (via holes) formed in the dielectric layers to form via conductors that operate as conductive paths electrically connecting the dielectric layers. The via conductors V 3 - 5  through V 13 - 5  form resonance elements R 11  and R 12  of the band pass filter of the distributed constant type having the second pass band, while the via conductors V 3 - 4  through V 13 - 4  form resonance elements R 21  and R 22  of the band pass filter of the distributed constant type having the second pass band. 
         [0060]      FIG. 5  is an equivalent circuit of the diplexer having the above described configuration. In  FIG. 5 , M denotes the inductive coupling of the resonance elements R 11  and R 21  and that of the resonance elements R 12  and R 22 , the magnitude of which can be defined by the gap separating the resonance elements. The circuit including the inductor L 2  in the band pass filter of the lumped constant type can be formed as series resonator. Additionally, the circuit including the capacitor C 6  in the band pass filter of the distributed constant type can be formed as parallel resonator. Furthermore, the circuit including the capacitor C 10  can also be formed as parallel resonator. 
         [0061]      FIGS. 6 and 7  illustrate another embodiment of diplexer according to the present invention. In  FIGS. 6 and 7 , the components similar to those of  FIGS. 4 and 5  are denoted respectively by the same reference symbols. 
         [0062]      FIG. 6  is an exploded schematic perspective view of the embodiment. Referring to  FIG. 6 , the illustrated diplexer  2  is formed by a multilayer substrate that is prepared by laying a plurality of dielectric layers (fourteen in the case of the illustrated embodiment) including dielectric layers M 1 , M 2 , M 3 , M 4 , M 5 , M 6 , M 7 , M 8 , M 9 , M 10 , M 11 , M 12 , M 13  and M 14 . The dielectric layers M 1 , M 2 , M 3 , M 6 , M 7 , M 8 , M 9 , M 10 , M 11 , M 12  and M 14  are made of a material showing a relatively low dielectric constant (e.g., dielectric constant ε 7), whereas the dielectric layers M 4 , M 5  and M 13  are made of a material showing a relatively high dielectric constant (e.g., dielectric constant ε 15). A pair of oppositely disposed lateral sides of each of the dielectric layers M 1  through M 14  is provided with three notches at each of the lateral sides. Grounding terminals T 1  through T 3 , a low-frequency side terminal T 4 , a high-frequency side terminal T 5  and an antenna terminal, or common terminal T 6 , are formed respectively 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. 
         [0063]    A grounding electrode G 1  is formed on the lowermost first dielectric layer M 1  so as to include in the right half area thereof sites to be located respectively vis-à-vis the corresponding ones of the paired electrodes of capacitor C 1  and capacitor C 5  of a band pass filter of the lumped constant type having the first pass band that is formed on the right half of the second dielectric member M 2 . On the other hand, the grounding electrode G 1  formed on the lowermost first dielectric layer M 1  includes in the left half area thereof sites to be located vis-à-vis the respective ones of the paired electrodes of capacitor C 7  and capacitor C 9  of a band pass filter of the distributed constant type having the second pass band that is formed on the left half of the second dielectric member M 2 . The sites of those ones of the paired electrodes of the capacitors on the grounding electrode G 1  also operate as capacitors. Additionally, the grounding electrode G 1  is also connected to the grounding terminals T 1 , T 2  and T 3  so as to operate as grounding electrode. It will be appreciated as a matter of course that the elements of the band pass filter of the lumped constant type and those of the band pass filter of the distributed constant type may be arranged inversely in terms of right and left. 
         [0064]    The other electrode of the capacitor C 1  and that of the capacitor C 5  of the band pass filter of the lumped constant type having the first pass band are arranged in the right half area on the second dielectric layer M 2  at respective positions located vis-à-vis the grounding electrode G 1  formed on the first dielectric layer M 1  with the right half of the dielectric layer M 2  interposed between them and the other electrode of the capacitor C 7  and that of the capacitor C 9  of the band pass filter of the distributed constant type having the second pass band are arranged in the left half area on the second dielectric layer M 2  at respective positions located vis-à-vis the grounding electrode G 1  formed on the first dielectric layer M 1  with the left half of the dielectric layer M 2  interposed between them. A via conductor V 2 - 1  is formed in the second dielectric layer M 2 . The via conductor V 2 - 1  is connected to site P 1 - 1  in the grounding electrode G 1  formed on the first dielectric layer M 1 . 
         [0065]    One of the opposite electrodes of the capacitor C 6  and one of the opposite electrodes of the capacitor C 10  of the band pass filter of the distributed constant type having the second pass band are formed on the left half of the third dielectric layer M 3 . Those electrodes are connected respectively to the common terminal T 6  and the high-frequency side terminal T 5 . Additionally, a via conductor V 3 - 1  is formed in the third dielectric layer M 3  at a position corresponding to the via conductor V 2 - 1  formed in the second dielectric layer M 2 , while via conductors V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  are also formed in the third dielectric layer M 3  at respective positions located vis-à-vis the sites P 2 - 2 , P 2 - 3 , P 2 - 4  and P 2 - 5  on the electrodes of the capacitor C 1 , the capacitor C 5 , the capacitor C 9  and the capacitor C 7  formed on the second dielectric layer M 2 . Note that the electrodes of the capacitor C 6  and the capacitor C 10  on the third dielectric layer M 3  are electrically isolated from all the via conductors formed on the third dielectric layer M 3 . 
         [0066]    The other electrode of the capacitor C 6  and the electrode of the capacitor C 10  of the band pass filter of the distributed constant type having the second pass band are formed on the left half of the fourth dielectric layer M 4 . Additionally, via conductors V 4 - 1 , V 4 - 2 , V 4 - 3 , V 4 - 4  and V 4 - 5  are formed on the fourth dielectric layer M 4  at respective positions located vis-à-vis the via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3  and electrically connected to the respective via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3 . As illustrated, the electrodes of the capacitor C 6  and the capacitor C 10  are respectively electrically connected to the via conductors V 4 - 5  and V 4 - 4 . 
         [0067]    Electrode C 8  that is a component of the electrode pattern that forms capacitor C 8  in the equivalent circuit of the band pass filter of the distributed constant type having the second pass band is formed on the left half of the fifth dielectric layer MS, while via conductors VS- 1 , V 5 - 2 , V 5 - 3 , V 5 - 4  and V 5 - 5  are also formed in the fifth dielectric layer M 5  at respective positions located vis-à-vis the via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3 . While the capacitor C 8  in the equivalent circuit is shown as a single capacitor C 8  for the sake of convenience, it is formed by the electrodes C 6 , C 8  and C 10  in  FIG. 6  (also in  FIGS. 4 and 8 ) . More specifically, the first capacitor is formed by the electrode C 6  formed on the fourth dielectric layer M 4  and the electrode C 8  formed on the fifth dielectric layer M 5  and the second capacitor is formed by the electrode C 10  formed on the fourth dielectric layer M 4  and the electrode C 8  formed on the fifth dielectric layer M 5  and the capacitor C 8  is formed by connecting the capacitors in series to form the capacitor C 8  in the equivalent circuit. 
         [0068]    The inductors L 1  through L 4  of the band pass filter of the lumped constant type having the first pass band are partly formed on the right half of each of the sixth through ninth dielectric layers M 6  through M 9 . The inductors L 1 , L 2  and L 4  of the band pass filter of the lumped constant type having the first pass band are partly formed on the right half of each of the tenth and eleventh dielectric layers M 10  and M 11 . Additionally, via conductors V 6 - 1  through V 6 - 5  are formed on the sixth dielectric layer M 6  at respective positions located vis-à-vis the via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3 . 
         [0069]    One of the opposite ends of the part of the inductor L 1  formed on the sixth dielectric layer M 6  is connected to the via conductor V 6 - 2  and hence to the site P 2 - 2  of the electrode of the capacitor C 1  formed on the second dielectric layer M 2  by way of the corresponding via conductors V 5 - 2 , V 4 - 2  and V 3 - 2 . Additionally, the mutually linked via conductors also operate as inductor. The other end of the part of the inductor L 1  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 1  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 6  also formed on the seventh dielectric layer M 7 , while the other end of the part of the inductor L 1  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 1  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 6  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 1  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 1  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 6  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 1  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the inductor L 1  formed on the tenth dielectric layer M 10  by way of the via conductor V 10 - 6  also formed on the tenth dielectric layer M 10 , while the other end of the part of the inductor L 1  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 1  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 6  also formed on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 1  formed on the eleventh dielectric layer M 11  is connected to the low-frequency side terminal T 4 . 
         [0070]    One of the opposite ends of the part of the inductor L 2  formed on the sixth dielectric layer M 6  is connected to the site P 1 - 1  of the corresponding electrode of the capacitor C 5  formed on the first dielectric layer M 1  by way of the corresponding via conductors VS- 1 , V 4 - 1 , V 3 - 1  and V 2 - 1 . Additionally, the mutually linked via conductors also operate as inductor. The other end of the part of the inductor L 2  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 2  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 7  also formed on the seventh dielectric layer M 7 , while the other end of the part of the inductor L 2  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 2  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 7  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 2  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 2  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 7  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 2  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the part of the inductor L 2  formed on the tenth dielectric layer M 10  by way of the via conductor V 10 - 7  also formed on the tenth dielectric layer M 10 , while the other end of the part of the inductor L 2  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 2  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 7  also formed on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 2  formed on the eleventh dielectric layer M 11  is connected to the corresponding electrode of the capacitor C 3  formed on the twelfth dielectric layer M 12  by way of the via conductor V 12 - 7  also formed on the twelfth dielectric layer M 12 . 
         [0071]    One of the opposite ends of each of the inductors L 3  and L 4  formed on the sixth dielectric layer M 6  is connected to the via conductor V 6 - 3  and the other end of the inductor L 3  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 3  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 8  also formed on the seventh dielectric layer M 7 . The other end of the part of the inductor L 3  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 3  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 8  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 3  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 3  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 8  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 3  formed on the ninth dielectric layer M 9  is connected to the corresponding electrode of the capacitor C 4  formed on the thirteenth dielectric layer  13  by way of the via conductor V 10 - 8 , the via conductor V 11 - 8 , the via conductor V 12 - 8  and the via conductor V 13 - 8  formed respectively on the tenth dielectric layer M 10 , the eleventh dielectric layer M 11 , the twelfth dielectric layer M 12  and the thirteenth dielectric layer M 13 . 
         [0072]    The other end of the part of the inductor L 4  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 4  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 9  also formed on the seventh dielectric layer M 7 . The other end of the part of the inductor L 4  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 4  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 9  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 4  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 4  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 9  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 4  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the part of the inductor L 4  formed on the tenth dielectric layer M 10  by way of the via conductor M 10 - 9  also formed on the tenth dielectric layer M 10 . The other end of the part of the inductor L 4  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 4  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 9  also formed on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 4  formed on the eleventh dielectric layer M 11  is connected to the common terminal T 6 . 
         [0073]    The capacitors C 2 , C 3  and C 4  of the band pass filter of the lumped constant type having the first pass band are formed on the right half of the twelfth dielectric layer M 12  and also on the right half of the thirteenth dielectric layer M 13 . One of the electrodes of the capacitor C 2  and the corresponding one of the electrodes of the capacitor C 3 , the capacitors C 2  and C 3  being formed on the twelfth dielectric layer M 12 , are commonly connected. The electrode of the capacitor C 4  formed on the twelfth dielectric layer M 12  is connected to the connection point of the inductors L 3  and L 4  formed on the sixth dielectric layer M 6  by way of the via conductors V 12 - 3 , V 11 - 3 , V 10 - 3 , V 9 - 3 , V 8 - 3  and V 7 - 3  and also to the site P 2 - 3  of the electrode of the capacitor C 5  formed on the second dielectric layer M 2 . Additionally, the mutually linked via conductors also operate as inductor. The other electrode of the capacitor C 2  formed on the thirteenth dielectric layer M 13  is connected to the low-frequency side terminal T 4  and the other electrodes of the capacitors C 3  and C 4  formed on the thirteenth dielectric layer M 13  are connected to each other. 
         [0074]    In this embodiment, inductor L 6  is formed on the left halves of the eighth dielectric layer M 8  through the eleventh dielectric layer M 11  and connected to the two resonance elements R 11  and R 12  that are by turn connected in series to the capacitor C 7  of the band pass filter of the distributed constant type having the second pass band. More specifically, an L-shaped element that takes part of the inductor L 6  is formed on each of the eighth dielectric layer M 8  through the eleventh dielectric layer M 11  and one of the opposite ends of the part of the inductor L 6  formed on the eighth dielectric layer M 8  is connected to the via conductor V 8 - 5 , while the other end thereof is connected to one of the opposite ends of the part of the inductor L 6  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 11  formed also on the ninth dielectric layer M 9 . The other end of the part of the inductor L 6  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the part of the inductor L 6  formed on the tenth dielectric layer M 10  by way of the via conductor V 10 - 5  formed also on the tenth dielectric layer M 10 . The other end of the part of the inductor L 6  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 6  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 11  formed also on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 6  formed on the eleventh dielectric layer M 11  is connected to the via conductor V 12 - 5  formed on the twelfth dielectric layer M 12 . An inductor L 6  showing a spiral profile is formed in this way. The inductor L 6  may alternatively be made to have a bent section showing a U-shaped profile, a meandering profile or an arc-shaped profile instead of a spiral profile. 
         [0075]    As shown in  FIG. 6 , electrode G 13  is formed on the left half of the thirteenth dielectric layer M 13  in a region containing the via conductors V 13 - 4  and V 13 - 5 . The electrode G 13  is connected to the grounding terminal T 3 . 
         [0076]    A conductive material is arranged in the through holes (via holes) formed in the dielectric layers to form via conductors that operate as conductive paths electrically connecting the dielectric layers. The via conductors V 3 - 5  through V 8 - 5  form resonance element R 12  of the band pass filter of the distributed constant type having the second pass band, while the via conductors V 11 - 5  through  13 - 5  form resonance element R 11  of the band pass filter of the distributed constant type having the second pass band, the inductor L 6  showing a spiral profile being connected between the resonance elements R 11  and R 12 . On the other hand, the via conductors V 3 - 5  through V 8 - 5  form resonance element R 22  of the band pass filter of the distributed constant type having the second pass band, while the via conductors V 3 - 4  through V 13 - 4  form resonance element R 21  of the band pass filter of the distributed constant type having the second pass band. 
         [0077]      FIG. 7  is an equivalent circuit of the diplexer having the above-described configuration. In  FIG. 7 , M denotes the inductive coupling of the resonance elements R 11  and R 21  and that of the resonance elements R 12  and R 22 , the magnitude of which can be defined by means of the gap separating the resonance elements. The magnitude can also be defined by means of the profile and the winding direction of the inductor L 6 . The circuit including the inductor L 2  in the band pass filter of the lumped constant type can be formed as series resonator. Additionally, the circuit including the capacitor C 6  in the band pass filter of the distributed constant type can be formed as parallel resonator. Furthermore, the circuit including the capacitor C 10  can also be formed as parallel resonator. 
         [0078]    As shown in  FIG. 6 , electrode G 13  is formed on the left half of the thirteenth dielectric layer M 13  in a region containing the via conductors V 13 - 4  and V 13 - 5 . The grounding electrode G 13  is connected to the grounding terminal T 1  and T 3 . 
         [0079]      FIGS. 8 and 9  illustrate still another embodiment of diplexer according to the present invention. In  FIGS. 8 and 9 , the components similar to those of  FIGS. 4 and 5  are denoted respectively by the same reference symbols. 
         [0080]      FIG. 8  is an exploded schematic perspective view of the embodiment. Referring to  FIG. 8 , the illustrated diplexer  3  is formed by a multilayer substrate that is prepared by laying a plurality of dielectric layers (fourteen in the case of the illustrated embodiment) including dielectric layers M 1 , M 2 , M 3 , M 4 , MS, M 6 , M 7 , M 8 , M 9 , M 10 , M 11 , M 12 , M 13  and M 14 . The dielectric layers M 1 , M 2 , M 3 , M 6 , M 7 , M 8 , M 9 , M 10 , M 11 , M 12  and M 14  are made of a material showing a relatively low dielectric constant (e.g., dielectric constant ε 7), whereas the dielectric layers M 4 , M 5  and M 13  are made of a material showing a relatively high dielectric constant (e.g., dielectric constant ε 15). A pair of oppositely disposed lateral sides of each of the dielectric layers M 1  through M 14  is provided with three notches at each of the lateral sides. Grounding terminals T 1  through T 3 , a low-frequency side terminal T 4 , a high-frequency side terminal T 5  and an antenna terminal, or common terminal T 6 , are formed respectively in the notches of each of the dielectric layers. Note that, in this embodiment again, the terminals may alternatively be formed by printing at the lateral sides without forming the notches. 
         [0081]    A grounding electrode G 1  is formed on the lowermost first dielectric layer M 1  so as to include in the right half area thereof sites to be located respectively vis-à-vis the corresponding ones of the paired electrodes of capacitor C 1  and capacitor C 9  of a band pass filter of the lumped constant type having the first pass band that is formed on the right half of the second dielectric member M 2 . On the other hand, the grounding electrode G 1  formed on the lowermost first dielectric layer M 1  includes in the left half area thereof sites to be located vis-à-vis the respective ones of the paired electrodes of capacitor C 7  and capacitor C 9  of a band pass filter of the distributed constant type having the second pass band that is formed on the left half of the second dielectric member M 2 . The sites of those ones of the paired electrodes of the capacitors on the grounding electrode G 1  also operate as capacitors. Additionally, the grounding electrode G 1  is also connected to the grounding terminals T 1 , T 2  and T 3  so as to operate as grounding electrode. It will be appreciated as a matter of course that the elements of the band pass filter of the lumped constant type and those of the band pass filter of the distributed constant type may be arranged inversely in terms of right and left. 
         [0082]    The other electrode of the capacitor C 1  and that of the capacitor C 5  of the band pass filter of the lumped constant type having the first pass band are arranged in the right half area on the second dielectric layer M 2  at respective positions located vis-à-vis the grounding electrode G 1  formed on the first dielectric layer M 1  with the right half of the dielectric layer M 2  interposed between them and the other electrode of the capacitor C 7  and that of the capacitor C 9  of the band pass filter of the distributed constant type having the second pass band are arranged in the left half area on the second dielectric layer M 2  at respective positions located vis-à-vis the grounding electrode G 1  formed on the first dielectric layer M 1  with the left half of the dielectric layer M 2  interposed between them. A via conductor V 2 - 1  is formed in the second dielectric layer M 2 . The via conductor V 2 - 1  is connected to site P 1 - 1  in the grounding electrode G 1  formed on the first dielectric layer M 1 . 
         [0083]    One of the opposite electrodes of the capacitor C 6  and one of the opposite electrodes of the capacitor C 10  of the band pass filter of the distributed constant type having the second pass band are formed on the left half of the third dielectric layer M 3 . Those electrodes are connected respectively to the common terminal T 6  and the high-frequency side terminal T 5 . Additionally, a via conductor V 3 - 1  is formed in the third dielectric layer M 3  at a position corresponding to the via conductor V 2 - 1  formed in the second dielectric layer M 2 , while via conductors V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  are also formed in the third dielectric layer M 3  at respective positions located vis-à-vis the sites P 2 - 2 , P 2 - 3 , P 2 - 4  and P 2 - 5  on the electrodes of the capacitor C 1 , the capacitor C 5 , the capacitor C 9  and the capacitor C 7  formed on the second dielectric layer M 2 . Note that the electrodes of the capacitor C 6  and the capacitor C 10  on the third dielectric layer M 3  are electrically isolated from all the via conductors formed on the third dielectric layer M 3 . 
         [0084]    The other electrode of the capacitor C 6  and the electrode of the capacitor C 10  of the band pass filter of the distributed constant type having the second pass band are formed on the left half of the fourth dielectric layer M 4 . Additionally, via conductors V 4 - 1 , V 4 - 2 , V 4 - 3 , V 4 - 4  and V 4 - 5  are formed on the fourth dielectric layer M 4  at respective positions located vis-à-vis the via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3  and electrically connected to the respective via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3 . As illustrated in  FIG. 8 , the electrodes of the capacitor C 6  and the capacitor C 10  are respectively electrically connected to the via conductors V 4 - 5  and V 4 - 4 . 
         [0085]    Electrode C 8  that is a component of the electrode pattern that forms capacitor C 8  in the equivalent circuit of the band pass filter of the distributed constant type having the second pass band is formed on the left half of the fifth dielectric layer MS, while via conductors V 5 - 1 , V 5 - 2 , VS- 3 , VS- 4  and V 5 - 5  are also formed in the fifth dielectric layer MS at respective positions located vis-à-vis the via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3 . While the capacitor C 8  in the equivalent circuit is shown as a single capacitor C 8  for the sake of convenience, it is formed by the electrodes C 6 , C 8  and C 10  in  FIG. 8  (also in  FIGS. 4 and 6 ). More specifically, the first capacitor is formed by the electrode C 6  formed on the fourth dielectric layer M 4  and the electrode C 8  formed on the fifth dielectric layer MS and the second capacitor is formed by the electrode C 10  formed on the fourth dielectric layer M 4  and the electrode C 8  formed on the fifth dielectric layer MS and the capacitor C 8  is formed by connecting the capacitors in series to form the capacitor C 8  in the equivalent circuit. 
         [0086]    The inductors L 1  through L 4  of the band pass filter of the lumped constant type having the first pass band are partly formed on the right half of each of the sixth through ninth dielectric layers M 6  through M 9 . The inductors L 1 , L 2  and L 4  of the band pass filter of the lumped constant type having the first pass band are partly formed on the right half of each of the tenth and eleventh dielectric layers M 10  and M 11 . Additionally, via conductors V 6 - 1  through V 6 - 5  are formed on the sixth dielectric layer M 6  at respective positions located vis-à-vis the via conductors V 3 - 1 , V 3 - 2 , V 3 - 3 , V 3 - 4  and V 3 - 5  formed on the third dielectric layer M 3 . 
         [0087]    One of the opposite ends of the part of the inductor L 1  formed on the sixth dielectric layer M 6  is connected to the via conductor V 6 - 2  and hence to the site P 2 - 2  of the electrode of the capacitor C 1  formed on the second dielectric layer M 2  by way of the corresponding via conductors V 5 - 2 , V 4 - 2  and V 3 - 2 . Additionally, the mutually linked via conductors also operate as inductor. The other end of the part of the inductor L 1  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 1  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 6  also formed on the seventh dielectric layer M 7 , while the other end of the part of the inductor L 1  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 1  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 6  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 1  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 1  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 6  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 1  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the inductor L 1  formed on the tenth dielectric layer M 10  by way of the via conductor V 10 - 6  also formed on the tenth dielectric layer M 10 , while the other end of the part of the inductor L 1  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 1  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 6  also formed on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 1  formed on the eleventh dielectric layer M 11  is connected to the low-frequency side terminal T 4  of the eleventh dielectric layer M 11 . 
         [0088]    One of the opposite ends of the part of the inductor L 2  formed on the sixth dielectric layer M 6  is connected to the via conductor V 6 - 1  and hence to the site P 1 - 1  of the grounding electrode G 1  formed on the first dielectric layer M 1  by way of the corresponding via conductors V 5 - 1 , V 4 - 1 , V 3 - 1  and V 2 - 1 . Additionally, the mutually linked via conductors also operate as inductor. The other end of the part of the inductor L 2  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 2  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 7  also formed on the seventh dielectric layer M 7 , while the other end of the part of the inductor L 2  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 2  formed on the eighth dielectric layer M 8  by way of the via conductor V 8 - 7  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 2  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 2  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 7  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 2  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the inductor L 2  formed on the tenth dielectric layer M 10  by way of the via conductor V 10 - 7  also formed on the tenth dielectric layer M 10 , while the other end of the part of the inductor L 2  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 2  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 7  also formed on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 2  formed on the eleventh dielectric layer M 11  is connected to the corresponding electrode of the capacitor C 3  formed on the twelfth dielectric layer M 12  by way of the via conductor V 12 - 7  also formed on the twelfth dielectric layer M 12 . 
         [0089]    One of the opposite ends of each of the inductors L 3  and L 4  formed on the sixth dielectric layer M 6  is connected to the via conductor V 6 - 3  and the other end of the inductor L 3  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 3  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 8  also formed on the seventh dielectric layer M 7 . The other end of the part of the inductor L 3  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 3  formed on the eighth dielectric layer M 8  by way of via conductor V 8 - 8  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 3  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 3  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 8  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 3  formed on the ninth dielectric layer M 9  is connected to the electrode of the capacitor C 4  formed on the thirteenth dielectric layer M 13  by way of the via conductors V 10 - 8 , the via conductor V 11 - 8 , the via conductor V 12 - 8  and the via conductor V 13 - 8  formed respectively on the tenth dielectric layer M 10 , the eleventh dielectric layer M 11 , the twelfth dielectric layer M 12  and the thirteenth dielectric layer M 13 . 
         [0090]    The other end of the inductor L 4  formed on the sixth dielectric layer M 6  is connected to one of the opposite ends of the part of the inductor L 4  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 9  also formed on the seventh dielectric layer M 7 . The other end of the part of the inductor L 4  formed on the seventh dielectric layer M 7  is connected to one of the opposite ends of the part of the inductor L 4  formed on the eighth dielectric layer M 8  by way of the via conductor V 8 - 9  also formed on the eighth dielectric layer M 8 . The other end of the part of the inductor L 4  formed on the eighth dielectric layer M 8  is connected to one of the opposite ends of the part of the inductor L 4  formed on the ninth dielectric layer M 9  by way of the via conductor V 9 - 9  also formed on the ninth dielectric layer M 9 . The other end of the part of the inductor L 4  formed on the ninth dielectric layer M 9  is connected to one of the opposite ends of the part of the inductor L 4  formed on the tenth dielectric layer M 10  by way of the via conductor M 10 - 9  also formed on the tenth dielectric layer M 10 . The other end of the part of the inductor L 4  formed on the tenth dielectric layer M 10  is connected to one of the opposite ends of the part of the inductor L 4  formed on the eleventh dielectric layer M 11  by way of the via conductor V 11 - 9  also formed on the eleventh dielectric layer M 11 . The other end of the part of the inductor L 4  formed on the eleventh dielectric layer M 11  is connected to the common terminal T 6 . 
         [0091]    The capacitors C 2 , C 3  and C 4  of the band pass filter of the lumped constant type having the first pass band are formed on the right half of the twelfth dielectric layer M 12  and also on the right half of the thirteenth dielectric layer M 13 . One of the electrodes of the capacitor C 2  and the corresponding one of the electrodes of the capacitor C 3 , the capacitors C 2  and C 3  being formed on the twelfth dielectric layer M 12 , are commonly connected. The electrode of the capacitor C 4  formed on the twelfth dielectric layer M 12  is connected to the connection point of the inductors L 3  and L 4  formed on the sixth dielectric layer M 6  by way of the via conductors V 12 - 3 , V 11 - 3 , V 10 - 3 , V 9 - 3 , V 8 - 3  and V 7 - 3  and also to the site P 2 - 3  of the electrode of the capacitor C 5  formed on the second dielectric layer M 2  by way of the via conductors V 6 - 3 , V 5 - 3 , V 4 - 3  and V 3 - 3 . The other electrode of the capacitor C 2  formed on the thirteenth dielectric layer M 13  is connected to the low-frequency side terminal T 4  and the other electrodes of the capacitors C 3  and C 4  formed on the thirteenth dielectric layer M 13  are connected to each other. 
         [0092]    In this embodiment, an inductor L 7  is formed on the left halves of the sixth dielectric layer M 6  and the seventh dielectric layer M 7  to by turn form parallel resonator along with the capacitor C 6  of the band pass filter of the distributed constant type having the second pass band. More specifically, a U-shaped element that takes part of the inductor L 7  is formed on each of the sixth dielectric layer M 6  and the seventh dielectric layer M 7  and one of the opposite ends of the part of the inductor L 7  formed on the sixth dielectric layer M 6  is connected to the common terminal T 6 , while the other end thereof is connected to one of the opposite ends of the part of the inductor L 7  formed on the seventh dielectric layer M 7  by way of the via conductor V 7 - 12  formed on the seventh dielectric layer M 7 . The other end of the part of the inductor L 7  formed on the seventh dielectric layer M 7  is connected to the via conductor V 7 - 5  formed also on the seventh dielectric layer M 7 . The inductor L 7  that forms a parallel resonator with the capacitor C 6  is formed in this way. The inductor L 7  may alternatively be made to have a bent section showing a U-shaped profile, a meandering profile or an arc-shaped profile instead of a spiral profile. 
         [0093]    As shown in  FIG. 8 , a grounding electrode G 13  is formed on the left half of the thirteenth dielectric layer M 13  in a region that contains the via conductors V 13 - 4  and V 13 - 5  and connected to the grounding terminals T 1  and T 3 . 
         [0094]    A conductive material is arranged in the through holes (via holes) formed in the dielectric layers to form via conductors that operate as conductive paths electrically connecting the dielectric layers. The via conductors V 3 - 5  through V 13 - 5  form resonance elements R 11  and R 12  of the band pass filter of the distributed constant type having the second pass band, while the via conductors V 3 - 4  through V 13 - 4  form resonance elements R 21  and R 22  of the band pass filter of the distributed constant type having the second pass band. 
         [0095]      FIG. 9  illustrates an equivalent circuit of the diplexer having the above-described configuration. In  FIG. 9 , M denotes the inductive coupling of the resonance elements R 11  and R 21  and that of the resonance elements R 12  and R 22 , the magnitude of which can be defined by the gap separating the resonance elements. In this embodiment again, the circuit including the inductor L 2  in the band pass filter of the lumped constant type can be formed as series resonator. Additionally, the circuit including the capacitor C 10  can be formed as parallel resonator.