JP2007089000A - Strip line filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a strip line filter capable of suppressing variations in coupling capacity caused by layer deviation of a multilayer substrate, being compact while ensuring sufficient coupling capacity, reducing a transmission loss, and further achieving excellent band characteristics. <P>SOLUTION: An input strip line 1 and an output strip line 2 are formed on a first conductor layer of a multilayer substrate, and an input open stab 9 and an output open stab 10 are formed which are disposed proximately while confronting their side surfaces and connected to another end of the input strip line 1 or the output strip line 2 each of which one end corresponds to each other. A first sub input open stab 13 and a first sub output open stab 16 are disposed proximately within a second conductor layer while confronting side surfaces, and a second sub input open stab 14 and a second sub output open stab 17 are disposed proximately within a third conductor layer while confronting side surfaces. The input open stab 9 and the sub input open stabs 13, 14 are conducted through a via hole 15, and the output open stab 10 and the sub output open stabs 16, 17 are conducted through a via hole 18. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stripline filter used as a high frequency filter circuit in a wireless communication module or the like.

  In a radio transceiver, a BPF (band pass filter) having a transmission characteristic of a transmission / reception signal superimposed on a carrier frequency is provided in the next stage of the antenna, and a transmission signal superimposed on the carrier signal is taken out. Such a BPF is generally called a top filter, and its pass characteristic is set to, for example, 5.8 GHz. The BPF is required to have a steep stopband attenuation characteristic and a low transmission loss.

  FIGS. 8A, 8B, and 8C are configuration explanatory views showing a configuration example of a BPF used as a top filter. The BPF 110 shown in the figure has a triplate structure in which resonator conductor patterns 113 and 114 are formed inside a multilayer substrate composed of dielectric substrates 111 and 112. Ground patterns 115 and 116 are formed on the respective surfaces of the dielectric substrates 111 and 112, and are electrically connected to each other through via holes 117 formed on the outer periphery of the substrate. The resonator conductor patterns 113 and 114 have a length M that is ¼ of the pass wavelength λ, and one end of the resonator conductor patterns 113 and 114 is connected to the ground patterns 115 and 116 and the other end is opened in a state of being arranged in parallel to each other. is doing. Input / output patterns 118 and 119 extending laterally are formed in the resonator conductor patterns 113 and 114, respectively.

  FIG. 9 is a circuit configuration diagram showing an equivalent circuit of the BPF 110. As shown in the figure, in the BPF 110, a parallel resonance circuit PR1 including a capacitor C1 and an inductance L1 is formed between the resonator conductor pattern 113 and the ground patterns 115 and 116, and the resonator conductor pattern 114 and the ground pattern 115 are formed. , 116 is formed with a parallel resonant circuit PR2 composed of a capacitor C2 and an inductance L2, and a capacitor C3 is formed between opposing side surfaces of the resonator conductor patterns 113 and 114, and the parallel resonant circuits PR1 and PR2 are This is a capacitively coupled configuration via C3.

  According to the BPF 110, the high-frequency signal having the wavelength λ input from the one resonator conductor pattern 113 is resonated in the band of the passing wavelength λ by the parallel resonance circuits PR1 and PR2, and the high-frequency component outside the band is removed. Is output.

  However, since the BPF 110 forms the capacitor C3 on the opposite side surfaces of the resonator conductor patterns 113 and 114 formed in the same layer, the frequency band is narrow and the transmission loss is large because the capacitance value to be coupled is small. There was a problem. Although it is conceivable to increase the capacitance value of the capacitor C3 by narrowing the distance between the resonator conductor patterns 113 and 114 and increasing the degree of coupling, when trying to realize a desired filter characteristic with such a configuration, When the thickness of the dielectric substrates 111 and 112 is simulated to 125 μm in response to the demand for thinning the product, the pattern interval becomes extremely narrow as about 10 μm, which is not practical from the viewpoint of pattern accuracy.

Therefore, the resonator conductor pattern 113 and the resonator conductor pattern 114 are formed in different layers, and the open stubs (patterns on the non-grounded side of the resonator conductor pattern) are opposed to each other with the dielectric layer interposed therebetween. It is conceivable to increase the capacitance value by securing the facing area for forming the capacitor.
JP 2003-179405 A

  However, the structure in which the resonator conductor patterns are stacked and arranged opposite to each other is arranged opposite to each other due to the difference in expansion / contraction direction of each layer in the process of forming the multilayer substrate when adopting the manufacturing method in which the substrate materials before firing are stacked and then fired. There is a problem in that the gap between the layers of the resonator conductor pattern to be generated occurs and the variation in coupling capacitance increases. Since the variation in the coupling capacitance greatly affects the filter characteristics, it is desired to suppress the variation as much as possible.

  The present invention has been made in view of the above points, and can suppress variation in coupling capacitance due to interlayer displacement of a multilayer substrate, ensure sufficient coupling capacitance, enable downsizing, reduce transmission loss, and It is an object of the present invention to provide a stripline filter that can realize good band characteristics.

  The stripline filter of the present invention includes a multilayer substrate in which a plurality of dielectric layers and a plurality of conductor layers are laminated, an input stripline and an output stripline that are provided on the multilayer substrate and each end of which is grounded, An input open in which the side surfaces of the first conductor layer, which is one of a plurality of conductor layers, are arranged in close proximity to each other, and one end of each is connected to the other end of the corresponding input stripline or the output stripline. A stub and an output open stub and a second conductor layer, which is one of the plurality of conductor layers, are arranged close to each other with their side surfaces facing each other, and are electrically connected to the corresponding input open stub or output open stub. A first sub-input open stub and a first sub-output open stub connected to each other.

  According to this configuration, the coupling capacitance is formed between the opposing side surfaces of the input open stub and the output open stub that are arranged close to each other in the first conductor layer, and in the second conductor layer. Since a coupling capacitance is formed between the opposing side surfaces of the first sub-input open stub and the first sub-output open stub that are arranged close to each other with their side surfaces facing each other, only a pair of input open stubs and output open stubs are coupled. A sufficiently large coupling capacity compared to the capacity can be obtained. In addition, the distance between the opposing side surfaces of the input open stub and the output open stub and the distance between the opposing side surfaces of the first sub-input open stub and the first sub-output open stub hardly change even if an interlayer shift occurs in the firing process. Variations in the coupling capacity can also be suppressed.

  In the stripline filter, the input open stub or the output open stub corresponding to the input open stub or the output open stub corresponding to each other is disposed in the third conductor layer, which is one of the plurality of conductor layers, with the side surfaces facing each other. A second sub-input open stub and a second sub-output open stub that are conductively connected to each other.

  With this configuration, coupling capacitance is also generated on the opposing side surfaces of the second sub-input open stub and the second sub-output open stub that are arranged close to each other with the side surfaces facing each other in the third conductor layer. Capacity can be obtained.

  According to the present invention, in the stripline filter, the input stripline and the output stripline are formed in the same first conductor layer as the input open stub and the output open stub, and the second conductor layer is the first conductor layer. A conductive layer adjacent to the conductive layer is formed, and a ground for grounding one end of the input stripline and the output stripline is formed.

  With this configuration, since the ground for grounding the input stripline and the output stripline and the conductor layer forming the first sub-input open stub and the first sub-output open stub are the same first conductor layer, the conductor layers are increased. The first sub-input open stub and the first sub-output open stub can be arranged without any problem.

  The second conductor layer and the third conductor layer are disposed above and below the first conductor layer, and the first sub input open stub and the second sub input open stub are opposed to the input open stub. It is desirable that the first sub output open stub and the second sub output open stub are arranged opposite to the output open stub.

  As a result, the first sub-input open stub, the first sub-output open stub, the second sub-input open stub and the second sub-output open stub can be arranged without increasing the conductor layer, and the three-layer opposed arrangement structure is provided. The occupied volume on the open stub side can be reduced, and the entire filter can be reduced in size.

  In addition, it is good also as a structure which provides the land for mounting an electronic component while forming a circuit pattern in the conductor layer used as the uppermost layer or the lowest layer of the said multilayer substrate.

  According to the present invention, it is possible to suppress variations in coupling capacitance due to interlayer displacement of the multilayer substrate, to secure a sufficient coupling capacitance and to reduce the size, to reduce transmission loss, and to realize good band characteristics.

  Hereinafter, details of a stripline filter according to an embodiment of the present invention will be described with reference to the accompanying drawings. The stripline filter according to the present embodiment is used in, for example, a BPF that constitutes an antenna input / output unit of a wireless transmission / reception apparatus (not shown), and has a transmission characteristic of transmission / reception signals superimposed on, for example, a 5.8 GHz carrier frequency transmitted / received by an antenna. Have.

  FIG. 1 is a perspective view in which strip lines, open stubs, via holes, and the like constituting the strip line filter according to the present embodiment are extracted, and FIGS. 2 (a), 2 (b), and 2 (c) are strip lines shown in FIG. It is the schematic side view which looked at each from each direction of a, b, and c. The stripline filter according to the present embodiment includes the first to fourth dielectric layers and the first to fifth conductor layers, but the present invention is limited to such a multilayer substrate. is not.

  As shown in FIG. 1, in the first conductor layer, two strip lines 1 and 2 each having a rectangular conductor pattern are formed in parallel with a predetermined distance therebetween. One end of each of the strip lines 1 and 2 is connected to a ground formed in a second conductor layer and a third conductor layer, which will be described later, via via holes 3 and 4. An input end 5 made of a conductor pattern provided in the fourth conductor layer is electrically connected to the other end of one strip line 1 through a via hole 6, and a fourth conductor layer is connected to the other end of the other strip line 2. The output end 7 made of a conductor pattern provided in the conductor is conductive through the via hole 8. That is, one strip line 1 constitutes an input strip line which is a short-circuited short-circuit line (short stub) in which one end is connected to the input end 5 and the other end is connected to the ground. Further, the other strip line 2 constitutes an output strip line which is a short-circuited line (short stub) having one end connected to the output end 7 and the other end connected to the ground.

  The first conductor layer is formed with an input open stub 9 and an output open stub 10 each having a rectangular shape and comprising a conductor pattern. One end of the input open stub 9 is electrically connected to the input end 5 through the connecting portion 11 and the via hole 6 (the end facing the ground end in the stripline 1). One end of the output open stub 10 is electrically connected to the output end 7 via the connecting portion 12 and the via hole 8 (the end facing the ground end in the strip line 2). As shown in FIGS. 2B and 2C, the input open stub 9 and the output open stub 10 are opposed to each other in the same layer with their side surfaces separated by a predetermined distance W1. It is desirable that the input open stub 9 and the output open stub 10 are close to each other in order to increase the capacitance value of the coupling capacitance, but the coupling between the side surfaces of the input open stub 9 and the output open stub 10 alone is preferable. There is a limit.

  In the present embodiment, the first sub input open stub 13 made of a conductor pattern having substantially the same shape as the input open stub 9 is disposed opposite to the second conductor layer on the upper layer side of the input open stub 9. Further, a second sub input open stub 14 made of a conductor pattern having substantially the same shape as the input open stub 9 is disposed opposite to the third conductor layer on the lower layer side of the input open stub 9. The first sub input open stub 13, the input open stub 9, and the second sub input open stub 14 are electrically connected through via holes 15 at a plurality of locations. Similarly, a first sub output open stub 16 made of a conductor pattern having substantially the same shape as the output open stub 10 is disposed opposite to the second conductor layer on the upper layer side of the output open stub 10. Further, a second sub output open stub 17 made of a conductor pattern having substantially the same shape as the output open stub 10 is disposed opposite to the third conductor layer on the lower layer side of the output open stub 10. The first sub output open stub 16, the output open stub 10, and the second sub output open stub 17 are electrically connected by via holes 18 at a plurality of locations.

  In this way, the open stub side has a three-layer structure and does not form a capacitor portion between the layers, but the opposite side surfaces of the first sub input open stub 13 and the first sub output open stub 16, the input open stub 9 and the output open. Capacitance portions are formed for the same layer such as the opposite side surface of the stub 10 and the opposite side surface of the second sub-input open stub 14 and the second sub-output open stub 17.

  FIG. 3 is a top view of the stripline filter of the present embodiment. FIG. 4 is a cross-sectional view taken along line AA shown in FIG. 3 along the strip line and the open stub on the input side, and shows a side cross-sectional structure of the strip line filter 20. In FIG. 4, each conductor layer is exaggerated and is actually formed with a sufficiently smaller thickness than the dielectric layer. The cross-sectional structure along the strip line and the open stub on the output side is not shown, but is the same as that on the input side.

  The stripline filter 20 is constructed on a multilayer substrate whose outer shape is rectangular. The stripline filter 20 includes a multilayer substrate composed of first to fourth dielectric layers 31 to 34 and first to fifth conductor layers 35 to 39. A fourth conductor layer 38 is formed on the upper surface of the first dielectric layer 31. The fourth conductor layer 38 is formed with a conductor pattern that forms the input end 5. Various circuit patterns are formed on the fourth conductor layer 38 and lands on which various electronic components are placed are provided.

  A second conductor layer 36 is formed between the first dielectric layer 31 and the second dielectric layer 32. FIG. 5A is a plan view of the second conductor layer 36. The second conductor layer 36 forms a ground made of a conductor pattern having a size corresponding to the outer shape of the substrate. In the central portion of the second conductor layer 36, circular openings 41 and 42 having a diameter larger than the diameter of the via holes 6 and 8 are formed concentrically with the region where the via holes 6 and 8 are formed. That is, the via holes 6 and 8 are passed through the circular openings 41 and 42 so that the via holes 6 and 8 and the ground (second conductor layer 36) do not conduct. In addition, a rectangular opening 43 is formed adjacent to the circular openings 41, 42. The first sub input open stub 13 and the first sub are separated from the inner periphery of the opening 43 in the opening 43. An output open stub 16 is arranged. The opposing side surfaces of the first sub input open stub 13 and the first sub output open stub 16 are filled with a dielectric material that is a part of the first dielectric layer 21. A plurality of via holes 44 are formed in the extended portion of the second conductor layer 36 so as to be electrically connected to the ground, which will be described later, of the fourth conductor layer 38.

  A first conductor layer 35 is formed between the second dielectric layer 32 and the third dielectric layer 33. FIG. 5B is a plan view of the first conductor layer 35. In the first conductor layer 35, a pair of strip lines 1, 2 extend in parallel on one side with the input / output ends (via holes 6, 8) as the center, and a pair of open stubs 9, 10 on the other side. It extends in parallel. An annular ground pattern 45 is formed so as to surround the strip lines 1 and 2 and the open stubs 9 and 10. The ground pattern 45 is electrically connected to the upper and lower second conductor layers 36 and the third conductor layer 37 through the via holes 44. The input open stub 9 and the output open stub 10 have the same rectangular shape, and are arranged in parallel by being separated by a predetermined distance W1. It is desirable to make the distance W1 as small as possible. The opposing open side surfaces of the input open stub 9 and the output open stub 10 are filled with a dielectric material that is a part of the second dielectric layer 32.

  A third conductor layer 37 is formed between the third dielectric layer 33 and the fourth dielectric layer 34. FIG. 5C is a plan view of the third conductor layer 37. The third conductor layer 37 forms a ground made of a conductor pattern having a size corresponding to the outer shape of the substrate. An opening 46 having the same shape is formed in a region facing the opening 43 of the second conductor layer 36. The second sub input open stub 14 and the second sub output open stub 17 are disposed in the opening 46 so as to be separated from the inner peripheral edge of the opening 46. A space between the opposing side surfaces of the second sub-input open stub 14 and the second sub-output open stub 17 is filled with a part of the third dielectric layer 33. A plurality of via holes 44 that communicate with the ground of the second conductor layer 36 through the ground pattern 45 of the first conductor layer 35 are formed in the outer extending portion of the third conductor layer 37.

  The first sub input / output open stubs 13, 16, the input / output open stubs 9, 10, and the second sub input / output open stubs 14, 17 are precisely positioned so as to face each other in the stacking direction. Is done. However, a certain amount of interlayer displacement occurs as in the prior art due to differences in expansion and contraction of each layer during the firing process.

  FIG. 6A shows a configuration example of circuit patterns and lands formed on the upper surface of the first dielectric layer 31. FIG. 6B shows a configuration example of circuit patterns and lands formed on the lower surface of the fourth dielectric layer 34.

  The stripline filter 20 configured as described above is equivalent to the equivalent circuit shown in FIG. 9 in the same manner as the top filter shown in FIG. That is, in the stripline filter 20, when a high frequency signal is input from the input end 5, the stripline 1 on the input side and the stripline 2 on the output side are electromagnetically coupled. A capacitor C1 and an inductance L1 are formed between the second conductor layer 36 and the third conductor layer 37, which are grounds disposed opposite to each other via the dielectric layers 32 and 33 above and below the strip line 1 on the input side. A parallel resonant circuit PR1 is formed. In addition, a capacitor C2 and an inductance L2 are provided between the second conductor layer 36 and the third conductor layer 37, which are grounded to be opposed to each other via the dielectric layers 32 and 33 above and below the strip line 2 on the output side. A parallel resonant circuit PR2 is formed.

  On the other hand, a capacitor C3 that capacitively couples the parallel resonant circuit PR1 and the parallel resonant circuit PR2 is formed on the open stub side that is electrically connected to the input terminal 5 to which the high-frequency signal is input. That is, in the first conductor layer 35, the input open stub 9 and the output open stub 10 are arranged close to each other with a distance W1 therebetween, and the length and thickness of each open stub 9, 10 and the distance W1 etc. The coupling capacitance C3-a determined according to the above is generated. In the present embodiment, also in the second conductor layer 36, the first sub-input open stub 13 and the first sub-output open stub 16 are arranged close to each other with a distance W1 therebetween, and the first sub-input open stub 16 is disposed. A coupling capacitance C3-b determined according to the distance W1 or the like is generated between the stub 13 and the first sub-output open stub 16. Further, also in the third conductor layer 37, the second sub-input open stub 14 and the second sub-output open stub 17 are arranged close to each other with a distance W1 therebetween, and the second sub-input open stub 14 and A coupling capacitance C3-c determined according to the distance W1 and the like is generated between the second sub-output open stub 17 and the like. A capacitor C3 that capacitively couples the parallel resonant circuit PR1 and the parallel resonant circuit PR2 illustrated in FIG. 9 includes a coupling capacitance C3-a obtained by the second conductor layer 36 and a coupling capacitance C3-b obtained by the first conductor layer 35. And the total capacitance of the coupling capacitance C3-c obtained in the third conductor layer 37.

  Here, as a manufacturing method of the stripline filter 20 according to the present embodiment, after the lamination work is completed by stacking a green sheet or the like to be a conductor layer having the conductor pattern on the dielectric layer, the whole is fired. A method of obtaining a multilayer substrate composed of first to fourth dielectric layers 31 to 34 and first to fifth conductive layers 35 to 39 is used.

  In this case, due to the expansion and contraction of the dielectric material or the conductor layer material in the firing process, for example, the second conductor layer 36 is entirely shifted in the direction of arrow B in FIG. It is assumed that the shift is in the direction of arrow C in FIG.

  If the input open stub and the output open stub are simply arranged so as to face each other and the capacitor C3 is formed between them, the coupling capacitance changes due to interlayer displacement, but in this embodiment, the coupling capacitance changes due to interlayer displacement. Is greatly suppressed.

  This is because the interval W1 between the first sub-input open stub 13 and the first sub-output open stub 16 is maintained without change even if the second conductor layer 36 is entirely shifted in the direction of arrow B. Is. The coupling capacitor C3-a formed between the first sub-input open stub 13 and the first sub-output open stub 16 in the second conductor layer 36 has the first sub-input open stub 13 and the first sub-input as described above. It depends on the interval W1 with the output open stub 16. Even if the second conductor layer 36 is entirely shifted in the direction of the arrow B, the first sub-input open stub 13 and the first sub-output open stub 16 are shifted by substantially the same distance in the same direction (B direction). Therefore, the distance W1 between the first sub input open stub 13 and the first sub output open stub 16 is also maintained. Further, since the sub-open stubs 13 and 16 where the interlayer displacement occurs and the open stubs 9 and 10 are conducted through the via holes 15 and 18, the coupling capacitance is formed in the stacking direction where the interlayer displacement occurs. Is not generated, the coupling capacitance does not change due to interlayer displacement.

  Even in the first conductor layer 35, even if the first conductor layer 35 is entirely shifted in the direction of the arrow C, the interval W1 between the input open stub 9 and the output open stub 10 is maintained in the same manner as described above. The coupling capacitance C3-b formed between the stub 9 and the output open stub 10 hardly changes. Even in the third conductor layer 37, even if the third conductor layer 37 is shifted in any direction as a whole, the interval W1 between the second sub-input open stub 9 and the output open stub 10 is maintained as described above. Therefore, the distance W1 between the second sub input open stub 14 and the second sub output open stub 17 hardly changes, and the coupling capacitance C3-c hardly changes. Therefore, the capacitor C3 that capacitively couples the parallel resonant circuit PR1 and the parallel resonant circuit PR2 in the equivalent circuit of FIG. 9 hardly changes even when an interlayer shift occurs.

  As described above, the parallel resonant circuit PR1 formed by the input-side stripline 1 and the parallel resonant circuit PR2 formed by the output-side stripline 2 are combined with the coupling capacitance C3- of the input / output open stubs 9 and 10. Capacitance coupling is performed by a capacitor C3 in which b is combined with the coupling capacitance C3-a of the first input / output sub-open stubs 13 and 16 and the coupling capacitance C3-c of the second input / output sub-open stubs 14 and 17.

  A high frequency signal in a predetermined frequency band is selected and output from the output terminal 7 connected to the strip line 2 on the output side. As a result of setting a predetermined numerical value to the stripline filter 20 having the above-described structure and simulating the filter characteristics, the filter characteristics shown in FIG. 7 were obtained. As shown in the figure, good filter characteristics are obtained that fall sharply in the high-frequency stop band.

  As described above, according to the present embodiment, the open stub for forming the coupling capacitor has a multilayer structure, and the coupling capacitor is formed with the side surfaces facing each other in the same layer, and the lamination direction is made conductive by the via holes 15 and 18. As compared with the case of only the input open stub 9 and the output open stub 10, a sufficiently large coupling capacity can be obtained. In addition, even if interlayer misalignment occurs in the firing process, the coupling capacity of each layer hardly changes, so that variation in coupling capacity can be suppressed.

  Further, according to the present embodiment, the ground and the first input / output sub-open stubs 13 and 16 are formed in the same layer in the second conductor layer 36, and the ground and the first input / output sub-open stubs 13 and 16 are formed in the same layer in the third conductor layer 37. Since the two input / output sub-open stubs 14 and 17 were formed, the sub-open stubs could be stacked without increasing the conductor layers.

  In the above embodiment, the open stub side has a three-layer structure. However, for example, the coupling capacitor C3-b by the open stubs 9 and 10 and the coupling capacitor C3-a by the first sub-open stubs 13 and 16 have a capacitor C3. As long as a sufficient capacitance value can be secured, the second sub-open stubs 14 and 17 are not necessarily required. Alternatively, the first sub-open stubs 13 and 16 may be left without the second sub-open stubs 14 and 17. In order to secure a larger coupling capacity, the open stub side may be provided with four or more layers and the third and fourth sub-open stubs may be provided. Further, the strip lines 1 and 2 are not necessarily arranged in the same layer.

  The present invention is applicable to a high frequency filter circuit of a small electronic device such as a wireless communication module.

The perspective view which extracted the stripline and open stub in the stripline filter which concerns on one Embodiment (A) Side view of stripline filter as viewed from direction a in FIG. 1, (b) Right front view of stripline filter as viewed from direction b in FIG. 1, (b) Stripline as viewed from direction c in FIG. Left front view of filter Top view of stripline filter according to the above embodiment 3 is a cross-sectional view taken along line AA in FIG. (A) Plan view of the second conductor layer shown in FIG. 4, (b) Plan view of the first conductor layer shown in FIG. 4, (c) Plan view of the third conductor layer shown in FIG. (A) Plan view of the fourth conductor layer shown in FIG. 4, (b) Plan view of the fifth conductor layer shown in FIG. Filter characteristic diagram of stripline filter according to the above embodiment Configuration diagram of a conventional top filter Equivalent circuit diagram of the top filter shown in FIG.

Explanation of symbols

1, 2 Strip line 3, 4, 6, 8, 15, 18, 44 Via hole 5 Input terminal 7 Output terminal 9 Input open stub 10 Output open stub 11, 12 Connecting part 13 First sub input open stub 14 Second sub input Open stub 16 1st sub output open stub 17 2nd sub output open stub 20 Stripline filter 31-34 1st-4th dielectric layer 35-39 1st-5th conductor layer

Claims (5)

A multilayer substrate in which a plurality of dielectric layers and a plurality of conductor layers are laminated;
An input strip line and an output strip line provided on the multilayer substrate, each end of which is grounded;
Inputs that are arranged close to each other in the first conductor layer, which is one of the plurality of conductor layers, with their side surfaces facing each other, and each one end of which is connected to the other end of the corresponding input strip line or the output strip line Open stub and output open stub,
First sub-inputs that are arranged close to each other in the second conductor layer, which is one of the plurality of conductor layers, with their side surfaces facing each other, and are electrically connected to the corresponding input open stub or output open stub, respectively. An open stub and a first sub-output open stub;
A stripline filter comprising:   Second sub-inputs that are arranged close to each other in the third conductor layer, which is one of the plurality of conductor layers, with their side surfaces facing each other, and are electrically connected to the corresponding input open stub or output open stub. The stripline filter according to claim 1, further comprising an open stub and a second sub-output open stub.   The input strip line and the output strip line are formed in the same first conductor layer as the input open stub and the output open stub, and the second conductor layer includes a conductor layer adjacent to the first conductor layer, 2. The stripline filter according to claim 1, wherein a ground for grounding one end of the input stripline and the output stripline is formed.   The second conductor layer and the third conductor layer are disposed above and below the first conductor layer, and the first sub input open stub and the second sub input open stub are disposed opposite to the input open stub. 3. The stripline filter according to claim 2, wherein the first sub-output open stub and the second sub-output open stub are disposed opposite to the output open stub. 5. The land according to claim 1, wherein a circuit pattern is formed on a conductor layer which is an uppermost layer or a lowermost layer of the multilayer substrate and a land for placing an electronic component is provided. Stripline filter.

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