JPH10276005A - Filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polarized filter with built-in multi-layer board having a narrow band pass characteristic and low in insertion loss. SOLUTION: This filter has a 1st attenuation pole in the vicinity of the pass band and a 2nd attenuation pole at a higher frequency than the pass band frequency. In the inside of a dielectric board consisting of a plurality of dielectric layers 61 (61a-61h) inserted between a couple of ground electrodes 62a and 62b, as to resonators A1 -A3 consisting of tip short circuit strip lines 65 (65a, 65b), 69 and tip open strip lines 64 (64a, 64b), 66 (66a, 66b), 68, 70, the two resonators A1 , A3 and the resonator A2 are placed in different layers and coupled electromagnetically in a direction of the length of the lines, connected to input output terminals 63 (63a, 63b), the length of the tip open strip lines 65, 69 is selected to be about 1/4 of a wavelength of the 2nd attenuation pole or the length of the tip short circuit strip lines 64, 66, 68, 70 is selected to be about 1/2 of the wavelength of the 2nd attenuation pole. Thus, the polarized filter of the multi-layer board built-in filter with the steep narrow band pass characteristic and the low insertion loss is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter built in a multilayer substrate used for a communication device or the like, and more particularly to a bandpass filter.

[0002]

2. Description of the Related Art In recent years, a filter used in a communication device such as a radio telephone has been mounted with a filter component such as a coaxial dielectric type on a wiring board in accordance with a demand for thinner and smaller communication devices. From surface mount type
It has been developed into a filter of a planar lamination type, and further to a built-in substrate type configured by embedding a resonance electrode in a wiring substrate made of a dielectric.

[0003] As such a conventional planar laminated filter, for example, Japanese Patent Application Laid-Open No. 5-95202 proposes a filter having a structure shown in an exploded perspective view in FIG.

In FIG. 5, reference numerals 1a and 1b denote dielectric layers, 1c
1g are dielectric sheets having a smaller thickness than those, and a strip line resonator electrode 2a is provided on the dielectric sheet 1c.
2b is a second electrode 3a, a third electrode 3b, and a fourth electrode 3c of the parallel plate capacitor on the dielectric sheet 1d.
3d, a shield electrode 4a on the dielectric sheet 1e,
A shield electrode 4b is formed on each of the dielectric sheets 1f. Stripline resonator electrodes 2a and 2
b, the resonator length of the strip line resonator is substantially a quarter wavelength, and the line width on the short-circuit side of the strip line resonator electrodes 2a and 2b is changed from a wide portion to a narrow portion in the middle of the strip line. The size is reduced by reducing the size. Then, the dielectric layers 1a and 1b, the dielectric sheets 1c to 1f, and the dielectric sheet 1g for protecting the shield electrode 4b are all stacked to form a laminated structure. · Side electrodes 5a and 5b respectively connected to 3d, and shield electrodes 4a and 4b
To form side electrodes 6a to 6c connected respectively.

According to the planar laminated filter having such a structure, the strip line resonator electrodes 2a and 2b and the second to fourth electrodes 3a to 3d opposed thereto constitute a parallel plate capacitor therebetween. I do. The second electrode 3a of such a parallel plate capacitor is an interstage coupling capacitor, the third electrode 3b is a parallel capacitor for lowering the resonance frequency of the stripline resonator, and the fourth electrodes 3c and 3d are input / output coupling. Functions as a capacitor. Further, the fourth electrodes 3c and 3d are connected to the side electrodes 5a and 5b and used as input / output terminals.
4b is connected by side electrodes 6a to 6c and used as a ground terminal.

FIG. 6 shows an equivalent circuit of the planar laminated filter. In FIG. 6, the strip line resonator 11a
11b corresponds to the stripline resonator electrodes 2a and 2b, and the capacitors 12a and 12b correspond to capacitors formed between the third electrode 3b and the stripline resonator electrodes 2a and 2b. Corresponds to a capacitor formed between the second electrode 3a and the stripline resonator electrodes 2a and 2b, and the capacitors 14a and 14b
Corresponds to a capacitor formed between the fourth electrodes 3c and 3d and the stripline resonator electrodes 2a and 2b.

Further, M is a strip line resonator 11a.
This represents the magnetic field coupling between 11b and the filter is configured as described above.

[0008] According to the filter having such a configuration, the size reduction and the shield can be realized with a simple structure by performing the lamination, and the variation in the filter characteristics can be suppressed because the electrode printing process is reduced. In addition, it is possible to reduce the coupling between resonators and realize a small and flat dielectric filter having good narrow band pass characteristics.

The planar filter having such a configuration can be of a similar configuration and can be of a built-in substrate type.

Next, as a conventional filter with a built-in substrate, Japanese Patent Application Laid-Open No. 4-284606 proposes a filter having a structure shown in an exploded perspective view in FIG. FIG.
(A) and (b) are XY cross-sectional view and ST cross-sectional view, and FIG. 9 is an equivalent circuit diagram of a band-pass filter in which this is mounted on a multilayer substrate.

7 to 9, 21 to 26 are dielectric layers,
27, 31, and 35 are ground electrodes, 28, 30, 32, 34, and 36 are coils,
29 and 33 are capacitor electrodes, 37 and 38 are blind through-holes (through holes filled with conductors), 39 to 49 are capacitors, 50 to 52 are coils, 53
Denotes an input terminal, and M denotes a mutual inductance. Ground electrodes 27, 31, 35, coils 28, 30, 32, 34, 36,
Capacitor electrodes 29 and 33, through holes 37 and 38, input terminals
53 are each formed by a thick film printing pattern.

As a result, as shown in FIG.
45 and coil 50, capacitor 46 and coil 51, capacitor 47
And the coil 52 constitute an LC resonator which is a parallel resonance circuit. Also, the capacitors 43, 44, 48, and 49 are coupling capacitors, respectively. In the circuit of FIG. 9, only a part of the circuit is shown although N LC resonators are connected in parallel, and FIGS. In this circuit, only the mounting diagrams of the capacitors 43, 44, 45, 46 and the coils 50, 51 are shown.

When such a circuit is mounted on a multilayer substrate, the coils of adjacent LC resonators, ie, between the coils 50 and 51, between the coils 51 and 52, are magnetically coupled. And a filter with a built-in substrate is configured as described above.

According to the built-in board type filter having such a configuration, it is not necessary to newly add a coil to improve the pass band characteristic of the band-pass filter, so that the number of coils mounted on the multilayer board is reduced. It is possible to reduce the size of the filter element and to improve the pass band characteristics at the same time.

One of the characteristics required for such a filter is to selectively pass only a predetermined frequency band. For this purpose, it is necessary that the pass band has a narrow band, has a frequency pass characteristic such that it has a steep attenuation pole near the pass band, and has a small insertion loss of the filter.

Further, in order to form a steep attenuation pole near the pass band, it is necessary to increase electromagnetic field coupling between strip line resonators, that is, to increase mutual admittance.

Further, in order to reduce the insertion loss in the pass band, it is necessary to reduce the wiring resistance of the strip line or the coil pattern.

[0018]

However, in the conventional filter as shown in FIGS. 5 and 6, in the coupling between the strip line resonators 11a and 11b, the tip short-circuited between the strip line resonator electrodes 2a and 2b. Has a problem that the mutual admittance of the side coupling becomes too small and a steep attenuation pole cannot be obtained in the vicinity of the pass band.

The strip line resonators 11a and 11b
Is defined as a resonator length of about a quarter wavelength, and therefore, there is a problem that the demand for further miniaturization cannot be sufficiently satisfied.

On the other hand, even in the conventional filters as shown in FIGS. 7 to 9, since the coil pattern is used as the circuit element, the length of the coil becomes larger than the line width of the coil. Therefore, since the resistance of the coil is increased, there is a problem that the reduction of the loss of the bandpass filter cannot be sufficiently satisfied.

The present invention has been devised to solve the above problems, and an object of the present invention is to reduce the size and thickness of the band-pass filter so as to realize good polarized narrow-band passband characteristics. An object of the present invention is to provide a filter with a built-in multilayer substrate, which can sufficiently meet the requirements and has low insertion loss.

[0022]

According to the present invention, there is provided a filter comprising a frequency band having a first attenuation pole near a pass band and a second attenuation pole having a higher frequency than the first attenuation pole on a high frequency side. A filter having characteristics, inside a dielectric substrate composed of a plurality of dielectric layers sandwiched between a pair of ground electrodes,
Three resonators each including a short-circuited strip line having one end connected to the ground electrode and an open-ended strip line connected to the other end of the short-circuited short-circuit line are provided. The resonators are located in a different layer from the other set of resonators, each resonator is electromagnetically coupled in the line length direction, and the two sets of resonators have a short-circuited strip line and an open end. An input / output terminal is connected to a connection point with the strip line via a capacitor, and a line length of the open end strip line is set to approximately one quarter of a wavelength of the second attenuation pole or the end shorted strip. The line length of the line is approximately one half of the wavelength of the second attenuation pole.

In the filter according to the present invention, the two sets of resonators are disposed so as to face the tip short-circuit strip line and the upper and lower layers of the tip short-circuit strip line, respectively. And a capacitor electrode of a capacitor connected to the input / output terminal is sandwiched between the two open-ended striplines connected by the through conductor. It is characterized by the following.

According to the filter of the present invention, a part of the electrodes of two sets of resonators forming a set at both ends of the circuit among the three sets of stripline resonators, and the two sets of resonators The dielectric layer is sandwiched so that a part of another set of electrodes, which is located in a different layer from the circuit and located in the center in the circuit, has a coupling state close to a so-called side coupling. Are arranged so as to be electromagnetically coupled in the line length direction, so that the mutual admittance Y ₁₃ · Y ₃₅ of the above-mentioned coupling between the open-end strip lines and the mutual admittance Y ₂₄ of the above-mentioned coupling between the tip short-circuit strip lines It is possible to make Y ₄₆ sufficiently large, so that when a band-pass filter is configured, it is possible to have a steep attenuation pole near the low frequency side or high frequency side of the pass band,
Steep attenuation characteristics can be provided.

Further, since a pair of ground electrodes sandwiching the dielectric substrate are also arranged so as to sandwich a part of the electrodes of the stripline resonator and the dielectric layer, the open-end stripline or the short-circuited tip of each resonator is provided. The self-admittance of the strip line can be increased, and the passband can be narrowed at the same time.

Further, each of the resonators passes through the line length L ₁ of the open end strip line, approximately one quarter of the wavelength of the second attenuation pole on the high-frequency side of the pass band, or the line length L ₂ of the short-circuit end strip line. Since the wavelength is set to approximately one half of the wavelength of the second attenuation pole on the high frequency side of the band, the second attenuation pole useful in the frequency band characteristics can be stably set to a desired frequency. Therefore, by setting the second attenuation pole to a frequency that is desired to be blocked outside the pass band, such as the second harmonic or the third harmonic of the center frequency of the pass band, a band pass filter having good pass band characteristics is provided. Can be obtained.

Further, according to the filter of the present invention, the length of the strip line resonator constituting the band-pass filter is made shorter than a quarter wavelength of the center frequency of the pass band, so that the substrate built-in type can be obtained. The filter can sufficiently cope with the demand for miniaturization and thinning. Further, by appropriately setting the admittance value of each stripline resonator within a structurally permissible range as a built-in substrate type, further downsizing can be achieved.

Furthermore, according to the filter of the present invention, it is possible to reduce the resistance of the line length 1 ₂ of the tip shorting strip line for the line width W ₂ by fastening within 2-3 fold Thus, a smooth flow of the resonance current can be ensured, and the insertion loss with respect to the pass band can be reduced. Furthermore, by setting the width of the connection portion to be approximately equal to the line width at the connection portion between the open-end stripline and the short-circuited stripline, a smoother flow of the resonance current can be secured. The insertion loss with respect to the pass band can be further reduced.

As described above, according to the filter of the present invention,
It is possible to provide a filter with a built-in multilayer substrate with a low insertion loss, which can realize good polarized narrow band passband characteristics as a bandpass filter, can sufficiently cope with demands for miniaturization and thickness reduction. .

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a filter according to the present invention will be described in detail with reference to the accompanying drawings. 1A to 1H are exploded plan views showing an example of an embodiment of a filter according to the present invention, and FIGS. 2A and 2B are AA ′ of the filter shown in FIG. It is sectional drawing and BB 'sectional drawing.
FIG. 3 is an equivalent circuit diagram of this filter.

In these figures, 61a to 61h are dielectric layers, 62a and 62b are ground electrodes formed on dielectric layers 61a and 61h, respectively, and 63a and 63b are ground electrodes 62a on dielectric layer 61a. This is the derived input / output terminal electrode.

64a and 64b are open-end stripline electrodes (open-end striplines) formed on the dielectric layer 61b, and 65a and 65b are open-circuit stripline electrodes (open-end short-circuit strips) formed on the dielectric layer 61c. Lines), 66a and 66b are open-end stripline electrodes (open-end stripline) formed on the dielectric layer 61d, and these are open-end stripline electrodes 64.
a.66a and 64b.66b are connected in parallel via a large number of via holes (through conductors) 67a.67b arranged around the periphery. In this way, the open end strip line electrodes 64a and 66a and the open end strip line electrodes 64b and 66b are connected via the via holes 67a and 67b, respectively, and one side in the width direction thereof is connected to the shorted end strip line electrodes 65a and 67a by the via holes 67a and 67b. 65b, each of which is connected to one side in the width direction of 65b.
By another side in the width direction of b is connected via a ground electrode 62a · 62b and via-hole 74, the side of the other end non-grounded side of the tip shorting strip line Y ₂ consisting of a short-circuit end strip line electrode 65a Are not connected to the ground side of the strip line resonator set A ₁ connected to the open end strip line Y ₁ composed of open end strip line electrodes 64 a and 66 a, and the short-circuited strip line Y ₆ composed of the short-circuited strip line electrode 65 b. constitute a set a ₃ stripline resonator end open strip line Y ₅ consisting of a top end open strip line electrodes 64b and 66b on the other end side is connected.

Reference numeral 68 denotes an open-end stripline electrode (open-end stripline) formed on the dielectric layer 61e;
Represents a tip short-circuited strip line electrode (tip short-circuited strip line) formed on the dielectric layer 61f, and 70 represents a dielectric layer 61g.
The open-end stripline electrodes (open-end stripline) formed above are connected in parallel via a number of via holes 71 provided around the open-end stripline electrodes 68 and 70, respectively. As a result, the strip line resonator sets A ₁ and A ₃
Similarly, the tip shorting strip consisting line electrodes 69 short-circuited end strip line Y ₄ of consisting of an open end strip line electrodes 68 and 70a on the side of the other end non-ground side end open strip line Y ₃ is connected to the strip line and constitute a set a ₂ of the resonator.

Then, as shown in FIGS. 2A and 2B and FIG. 3, the filter of the present invention has a ground electrode 62.
a and 62b, and the ground electrode 62
a and 62b are connected by a large number of via holes (through conductors) 74. As a result, the strip line resonator sets A ₁ and A ₃ are located at both ends of the circuit of the filter, and the strip line resonator set A ₂ is located at the center of the circuit. A _1-
A ₃ are each open-end strip lines Y ₁ and an open end strip line Y ₃ called by bonding state close to the side coupled line length direction electromagnetic coupling between Y _13, the open-end strip lines Y ₃ and top end open strip Line Y
₅ and line length direction of the electromagnetic field coupling Y _35, as well as the leading-end short strip line Y ₂ and the tip shorting strip line Y ₄ line length direction of the electromagnetic field coupling Y ₂₄ and a distal end short-circuit strip line Y ₄ the line length direction of the electromagnetic field coupling Y ₄₆ of the tip shorting strip line Y _6, is electromagnetically coupled.

Reference numerals 72a and 72b denote via holes on the dielectric layer 61c above the short-circuited strip line electrodes 65a and 65b.
Capacitor electrodes 73a and 73b are provided so as to be surrounded by 67a and 67b.
This is a via hole for connecting b to the input / output terminal electrodes 63a and 63b. Capacitor electrodes 72a forms a capacitor C ₁ between the configured end open strip line electrodes 64a · 66a so as to sandwich the electrode 72a via the dielectric layer 61b · 61c, the capacitor electrode 72b is a dielectric layer 61b · 61c through to form a capacitor C ₂ between the configured end open strip line electrodes 64b · 66b so as to sandwich the electrode 72b.

With such a configuration, as shown in FIG. 3, the capacitor C connected in series to the connection between the open-end strip line Y ₁ and the short-circuit strip line Y _2.
One input-output terminal electrodes 63a through a ₁ is connected, the other via a capacitor C ₂ connected in series to the connection portion between the distal end opening strip line Y ₅ and the tip shorting strip line Y ₆ of the input and output terminal electrodes 63b Is connected.

These capacitors C ₁ and C ₂ are provided to prevent the input / output terminals of the filter from being grounded in a DC manner.
With this configuration, the capacitors C ₁ and C ₂
The stray capacitance generated between the capacitor and the ground electrode 62a can be almost eliminated, an ideal series capacitor can be realized, and stable filter characteristics can be obtained. Also, by adjusting the capacitance of these capacitors C ₁ and C ₂ ,
The input / output impedance of the filter can also be adjusted.

According to such a configuration, the ground electrode 62a
When 62b and inputs an input signal with, for example, input and output terminal electrodes 63a connected to the ground potential, the input signal is input to the set A ₁ of the strip line resonator via holes 73a · capacitor electrode 72a, the stripline resonator signal having a predetermined frequency of the set a ₁ the input signal of the vessel undergoes a selective resonance, the set of the strip line resonator energy of the resonance by the electromagnetic coupling between the set a ₂ of the strip line resonator is transmitted to a _2,
In the set A ₂ of the strip line resonator occurs resonance for a given frequency, more resonance energy stripline resonator pairs A ₃ and is transmitted by electromagnetic coupling to the set A ₃ of the strip line resonator of the strip lines in the set a ₃ of the resonator occurs resonance for a given frequency, which by the output from the output terminal electrode 63b via the via-hole 73b · capacitor electrode 72b, it is possible to selectively passes only a predetermined frequency.

At this time, a set A _{1 of} strip line resonators
Since the set A ₂ and the set A ₂ and the set A ₃ are located in different layers and vertically opposed across the dielectric layer,
The mutual admittance between the resonators can be increased by increasing the area of the electrodes of each resonator facing each other. As a result, the filter of the present invention has a narrow pass band and a low pass band. of which has a steep first attenuation pole in the vicinity of the high frequency side or low frequency side, the wavelength of the desired second attenuation pole on the high frequency side of the pass band the line length L ₁ of each resonator of the open-end strip lines by substantially quarter, or the tip is short-circuited strip line of the line length L ₂ 1 a of the passband of the desired wavelength of the second attenuation pole on the high-frequency side substantially half useful in the frequency band characteristic The second attenuation pole can be set stably at its desired frequency.

Generally, in order to narrow the pass band of the band pass filter, each of the strip lines Y _{1 to} Y ₆
Must be increased, or the mutual admittance between the strip lines Y _{1 to} Y ₆ needs to be reduced. However, in order to move the attenuation pole f ₁ near the narrow band pass band closer to the pass frequency band, it is necessary to reduce the self admittance or increase the mutual admittance, which contradicts the narrow band. There is a tendency.

On the other hand, in order to secure a necessary pass band and to realize a narrow band having an attenuation pole in the vicinity thereof, both the mutual admittance and the self admittance of each of the strip lines Y _{1 to} Y ₆ are large. The size may be sufficiently larger than the input / output impedance of the filter circuit.

According to the filter of the [0042] present invention, the mutual admittance Y ₁₃ between pairs A ₁ and set A ₂ of the strip line resonator is open ended stripline electrode 66a and the tip opening of the via dielectric layer 61d Overlap width with strip line electrode 68, distance between electrodes (thickness of dielectric layer 61d), and dielectric layer
It is determined by the dielectric constant of 61d. To increase the self-admittance Y ₁ and Y ₃ of the strip line pairs A ₁ and set A ₂ of each strip line resonator, increasing the width of the open-end strip line electrodes 64a, 66a and 68, 70 or, they electrode and can be achieved by structural configuration so that such shortening the distance between the ground electrode 62a · 62b, in order to increase the mutual admittance Y ₁₃ is open ended stripline electrodes 66a and top end open strip line electrode 68
Can be achieved by a structural setting such as increasing the width of overlap with the above or reducing the distance between the electrodes.

[0043] Also transadmittance Y ₂₄ between pairs A ₁ and set A ₂ of the strip line resonators are dielectric layer 61c
.Strip line electrode with short-circuited tip through 61d and 61e
It is determined by the overlapping width of 65a and the short-circuited strip line electrode 69, the distance between the electrodes (thickness of the dielectric layers 61c, 61d, 61e) and the dielectric constant of the dielectric layers 61c, 61d, 61e.

In order to increase the self-admittances Y ₂ and Y ₄ of the strip lines of the sets A ₁ and A ₂ of each strip line resonator, the width of the tip short-circuit strip line electrodes 65 a and 69 is increased or the width thereof is increased. electrode and can be achieved by structural configuration so that such shortening the distance between the ground electrode 62a · 62b, in order to increase the mutual admittance Y ₂₄ overlaps with the tip short-circuit strip line electrode 65a and the leading-end short strip line electrode 69 This can be achieved by a structural setting such as increasing the width or reducing the distance between the electrodes.

The above is the same for self-admittance Y ₅ · Y ₆ and mutual admittance Y ₃₅ · Y ₄₆ pairs A ₂ and set A ₃ other strip line resonator.

Further, according to the filter of the present invention, the high-frequency side of the pass band, a second attenuation pole f ₄ whose frequency is higher than the first attenuation pole near the pass band. The position of the second attenuation pole f ₄ is open ended stripline Y ₁ · Y ₃
· Y ₅ of dependent resonator length L ₁ or short-circuited end resonator length L ₂ of the strip line _{Y 2 · Y 4 · Y 6} , in between these resonator length and the wavelength lambda ₄ attenuation poles f ₄ There is the following relationship. When 2L ₁ ≧ L _2, when _{L 1 = λ 4/4 2L} 1 ≦ L 2, L 2 = λ 4/2 end open strip line Y ₁ · Y ₃ · Y ₅ and the tip shorting strip line Y ₂ · The impedance at the connection portion between Y ₄ and Y ₆ becomes 0 if either of the strip lines satisfies these conditional expressions, so that an attenuation pole f ₄ is formed on the frequency as a filter characteristic.

The center frequency of the pass band is determined by appropriately setting the self and mutual admittance values of each strip line.

The frequency characteristic as shown in FIG. 4 can be obtained by the filter of the present invention having the above-described circuit configuration. FIG.
(A) and (b) are diagrams showing characteristics of insertion loss S ₂₁ (dB) with respect to frequency (GHz).

[0049] According to the filter of Figure 4 (a) and (b) from seen present invention, the low-frequency side near or in the high frequency side near the narrow-band pass band f ₂ -f ₃ as described above (the A sharp attenuation pole f near the low frequency side in the figure)
_{With one} .

According to the circuit configuration and structure of the filter of the present invention as described above, the input / output impedance (the reciprocal of the input / output admittance) of the filter can be arbitrarily set in a certain region.

Generally, a discrete filter component for high frequency has an input / output impedance set to 50Ω on both the input side and the output side. However, such components and ICs (integrated circuits) such as switches and amplifiers for high-frequency circuits
In many cases, components such as a chip inductor and a chip capacitor for impedance matching are required between them. The reason is that the input / output impedance of the connected partner is not always 50Ω.

On the other hand, according to the filter of the present invention, the input / output impedance can be easily changed by changing the admittance value of each strip line and the capacitance value (capacitance) of the capacitors C ₁ and C _2. it can. Therefore, ICs for switches and ICs for amplifiers
If the filter of the present invention is used as a high-frequency filter connected to the filter, the number of components such as a chip inductor and a chip capacitor for impedance matching can be reduced, and the isolation characteristics caused by those components can be reduced. Degradation and an increase in loss can be prevented, and a high-frequency circuit having good high-frequency characteristics can be realized.

The dielectric layers 61a to 61h constituting the dielectric substrate
Is made of an electrically insulating material such as glass ceramics or alumina / mullite.

The dielectric layers 61a to 61h are made of, for example, 18 to 24% by weight of alumina, 8 to 17% by weight of quartz, cordierite.
13 to 25% by weight, the balance being formed of glass ceramics of borosilicate glass, 72 to 76% by weight of silicon oxide, 15 to 17%
By weight, boron oxide, 2-4% by weight alumina, 1.5% by weight or less of magnesium oxide, 1.1-1.4% by weight of zirconium oxide, 2-3% by weight of lithium oxide / potassium oxide / sodium oxide 18-24% by weight of alumina powder, 8-17% by weight of quartz powder, 13-25% by weight of cordierite powder and a suitable organic binder, solvent, plasticizer, dispersant, etc. are added to the mixed silicate glass powder and mixed. A green sheet (raw sheet) is obtained by forming the slurry into a sheet by employing a doctor blade method or a calender roll method, which is well known in the art, and then appropriately punching a predetermined green sheet. And stacking a plurality of sheets up and down to form a green sheet laminate.
It is manufactured by firing at a temperature of 0 ° C.

The ground electrodes 62a and 62b and the input / output terminal electrodes 63a
・ 63b, open end stripline electrode 64a ・ 64b ・ 66
a ・ 66b ・ 68 ・ 70 、 Strip line electrode 65a
・ 65b ・ 69, capacitor electrode 72a ・ 72b, via hole 67
a ・ 67b ・ 71 ・ 72 ・ 73a ・ 73b ・ 74 are made of a metal material such as copper or silver / silver-palladium alloy, and when made of copper, an organic binder / solvent etc. suitable for copper powder Are added and mixed, and the dielectric paste is applied to each of the dielectric layers 61a to 61h.
By forming a predetermined pattern on the upper and lower surfaces and inside of the dielectric substrate by printing and applying a predetermined pattern on the upper and lower surfaces and through holes of the green sheet in advance using a thick film method such as a screen printing method. Will be arranged.

It should be noted that the present invention is not limited to the above example, and that changes and improvements may be made without departing from the spirit of the present invention. For example, in the above-described example, the ground electrode 62a is provided on the upper surface of the dielectric substrate and is exposed to the outside. However, a dielectric layer may be further laminated thereon and provided inside the dielectric substrate. it may be arranged so as to interrupt the a ₂ between the resonator a ₁ and a _3.

[0057]

According to the filter of the present invention, a part of the electrodes of the two sets of resonators forming the sets at both ends of the circuit among the three sets of stripline resonators, and the two sets of the electrodes are used. The dielectric layer is positioned so that a part of another set of electrodes which is located in a different layer from the resonator and forms a set at the center of the circuit is in a coupling state close to a so-called side coupling. because it is arranged so as to electromagnetically coupled to interposed therebetween line length direction, and the coupling of the mutual admittance Y ₂₄ between the coupling of mutual admittance Y ₁₃ and the tip shorting strip line between the open-end strip lines When a band-pass filter is configured, it is necessary to have a sharp attenuation pole near the low frequency side or high frequency side of the pass band while securing the necessary pass band. Can do Can, it is possible to provide a bandpass filter having a narrow band characteristic having a steep attenuation characteristic.

According to the filter of the present invention, a pair of ground electrodes sandwiching the dielectric substrate are also arranged with a part of the electrodes of the stripline resonator sandwiching the dielectric layer. The self-admittance of the open-end stripline and the short-circuited stripline can be increased, and the passband can be narrowed easily.

Further, according to the filter of the present invention, the line length L ₁ of the open strip line at the end of each resonator is set to approximately one quarter of the wavelength of the second attenuation pole on the high frequency side of the pass band, or the end is short-circuited. from what has been stripline line length 1 substantially half of the wavelength of the second attenuation pole L ₂ a pass band of the high frequency side, the second attenuation pole are useful in a frequency band characteristic stable to the desired frequency Can be set. Therefore, by setting the second attenuation pole to a frequency that is desired to be blocked outside the pass band, such as the second harmonic or the third harmonic of the center frequency of the pass band, a band pass filter having good pass band characteristics is provided. Could be obtained.

Further, according to the filter of the present invention, the length of the strip line resonator constituting the band-pass filter is made shorter than a quarter wavelength of the center frequency of the pass band, so that the built-in substrate type is realized. The filter was able to respond sufficiently to the demand for miniaturization and thinning. By appropriately setting the admittance value of each of these stripline resonators within a range that is structurally permitted as a built-in substrate type, further miniaturization can be achieved.

Further, according to the filter of the present invention, the resistance of the strip line can be reduced by keeping the length L ₂ of the short-circuited strip line at the end within ₂ to 3 times the line width W ₂ . As a result, a smooth flow of the resonance current can be secured, and the insertion loss with respect to the pass band can be reduced. Furthermore, by setting the width of the connection portion to be approximately equal to the line width at the connection portion between the open-end stripline and the short-circuited stripline, a smoother flow of the resonance current can be secured. The insertion loss with respect to the pass band can be further reduced.

As described above, according to the filter of the present invention,
It is possible to provide a filter with a built-in multilayer substrate with a low insertion loss, which can realize good polarized narrow-band passband characteristics as a bandpass filter, sufficiently cope with demands for miniaturization and thinning. Was.

[Brief description of the drawings]

FIGS. 1A to 1H are exploded plan views each showing an example of an embodiment of a filter according to the present invention.

FIGS. 2A and 2B are a sectional view taken along the line AA ′ and a sectional view taken along the line BB ′ of the filter shown in FIG. 1, respectively.

FIG. 3 is an equivalent circuit diagram of the filter of the present invention shown in FIGS. 1 and 2.

4 (a) and 4 (b) are diagrams showing frequency characteristics of the filter of the present invention shown in FIGS. 1 to 3, respectively.

FIG. 5 is an exploded perspective view showing an example of a conventional planar laminated filter.

FIG. 6 is an equivalent circuit diagram of the planar multilayer filter of FIG. 5;

FIG. 7 is an exploded perspective view showing an example of a conventional filter with a built-in substrate.

8A is a sectional view taken along the line XY of FIG. 7, and FIG. 8B is a sectional view taken along the line ST of FIG.

9 is an equivalent circuit diagram of the filter with a built-in substrate shown in FIG. 7;

[Explanation of symbols]

61a to 61h: dielectric layers 62a, 62b: ground electrodes 64a, 64b, 66a, 66b, 68, 70 ················································································································································································· , 73a, 73b, 74 ··· Via holes (through conductors) 72a, 72b ······· Capacitor electrodes A ₁ , A ₂ , A ₃ , ·········・ Stripline resonator set C ₁ , C ₂・ ・ ・ Capacitor L ₁・ ・ ・ ・ ・ ・ Open end strip line line length f ₁ of the line length L ₂ · · · · · · · · tip shorting strip line · · · · · · · · No. Attenuation pole f ₄ · · · · · · · · second attenuation pole

Claims (2)

[Claims] 1. A filter having a frequency band characteristic having a first attenuation pole near a pass band and a second attenuation pole having a higher frequency than the first attenuation pole on a high frequency side. Inside a dielectric substrate composed of a plurality of dielectric layers sandwiched between ground electrodes, a tip short-circuit stripline having one end connected to the ground electrode and a tip open-circuit connected to the other end of the tip short-circuit stripline Three resonators each composed of a strip line are disposed, and two of the resonators are located in a different layer from the other resonator, and each resonator is placed in an electromagnetic field direction in the line length direction. And 2
An input / output terminal is connected via a capacitor to a connection point between the tip short-circuited stripline and the open-ended stripline of the pair of resonators, and the line length of the open-ended stripline is set to the second attenuation pole. A filter characterized in that the wavelength is approximately one-quarter of the wavelength or the line length of the short-circuited strip line is approximately one-half of the wavelength of the second attenuation pole. 2. The two sets of resonators are disposed so as to face the tip short-circuit stripline and the upper and lower layers of the tip short-circuit stripline, respectively, and are connected by a through conductor. 2. An open strip line, wherein a capacitor electrode of a capacitor connected to the input / output terminal is sandwiched between two open end strip lines connected by the through conductor. Filter.