JP2021002779A - Waveguide filter - Google Patents

Abstract

To provide a waveguide filter capable of improving blocking characteristics on both sides of a pass band and reducing the size.SOLUTION: A waveguide filter includes a plurality of resonators which are connected in multiple stages via iris and resonate in a TE101 mode. The plurality of resonators have a pair of conductor layers opposite to each other across a dielectric body. A conductor wall with which two resonators adjacent to each other are partitioned without interposition of the iris among the plurality of resonators, and slots for intersecting with each other in a plan view are provided. The slot is formed in only one of the pair of conductor layers.SELECTED DRAWING: Figure 1

Description

The present invention relates to a waveguide filter.

Conventionally, there is known a polar bandpass filter in which four stages of waveguides are connected and a first-stage waveguide and a fourth-stage waveguide are jump-coupled via an iris (for example). , Patent Document 1). In this filter, the first, third, and fourth stages of the waveguide function as a TE101 mode resonator, and the second stage waveguide functions as a higher-order mode resonator of the TE102 mode or higher. As a result, the directions of the magnetic fields generated in the jump-coupled waveguides of the first and fourth stages are opposite, and the coupling coefficient of the waveguides of the first and fourth stages becomes negative, so that the pass band is low. It is possible to have a filter characteristic in which an attenuation pole appears on the region side and the high region side.

Japanese Unexamined Patent Publication No. 2009-11163

However, since the waveguide that functions as a resonator in the higher-order mode of TE102 mode or higher has a larger shape than the waveguide that functions as a resonator in TE101 mode, the size of the entire filter becomes larger.

Therefore, the present disclosure provides a waveguide filter capable of improving the cutoff characteristics on both sides of the pass band and reducing the size.

This disclosure is
It is equipped with multiple resonators that are connected in multiple stages via an iris and resonate in TE101 mode.
The plurality of resonators have a pair of conductor layers facing each other with a dielectric interposed therebetween.
A slot that intersects in a plan view with a conductor wall that separates two adjacent resonators among the plurality of resonators without the intervention of an iris is provided.
The slot provides a waveguide filter formed in only one of the pair of conductor layers.

According to the technique of the present disclosure, it is possible to provide a waveguide filter capable of improving the cutoff characteristics on both sides of the pass band and reducing the size.

It is a perspective view of the waveguide filter in the 1st configuration example. It is a top view of the waveguide filter in the 1st configuration example. It is a top view which shows typically the waveguide filter in the 1st configuration example. It is a figure which shows typically the magnetic flow direction generated in each resonator in a pass band. It is a figure which shows typically the magnetic flow direction generated in each resonator outside the pass band. It is a top view of the waveguide filter in the 2nd configuration example. It is an enlarged view of the slot of the waveguide filter in the 2nd configuration example. It is a top view of the waveguide filter in the 3rd configuration example. It is an enlarged view of the slot of the waveguide filter in the 3rd configuration example. It is a perspective view of the waveguide filter in the 4th configuration example. It is a top view of the waveguide filter in the 4th configuration example. It is a top view of the waveguide filter in the 5th configuration example. It is a top view of the waveguide filter in the 6th configuration example. It is a figure which shows the modification of a slot. It is a figure which shows an example of the simulation result of the filter characteristic of the four types of waveguide filters in which four resonators R1 to R4 are connected in multiple stages. It is a figure which shows an example of the simulation result of the filter characteristic of the four types of waveguide filters in which six resonators R1 to R6 are connected in multiple stages.

Hereinafter, modes for carrying out the present invention will be described. In the following description, the X-axis direction, the Y-axis direction, and the Z-axis direction represent a direction parallel to the X-axis, a direction parallel to the Y-axis, and a direction parallel to the Z-axis, respectively. The X-axis direction, the Y-axis direction, and the Z-axis direction are orthogonal to each other. The XY plane, YZ plane, and ZX plane are a virtual plane parallel to the X-axis direction and the Y-axis direction, a virtual plane parallel to the Y-axis direction and the Z-axis direction, and a virtual plane parallel to the Z-axis direction and the X-axis direction, respectively. Represents.

The waveguide filter according to the present disclosure is a filter provided with a waveguide formed in a dielectric surrounded by a conductor, and filters high-frequency signals in a high-frequency band such as microwaves and millimeter waves (for example, 0.3 GHz to 300 GHz). To do. The waveguide filter according to the present disclosure is suitable for filtering high frequency signals corresponding to radio waves transmitted or received by an antenna in, for example, a 5th generation mobile communication system (so-called 5G) or an in-vehicle radar system. is there.

FIG. 1 is a perspective view of the waveguide filter in the first configuration example. The filter 101 shown in FIG. 1 is a waveguide filter having a SIW (Substrate Integrated Waveguide) structure. The SIW structure includes a first conductor layer 21, a second conductor layer 22, a dielectric 23 sandwiched between the first conductor layer 21 and the second conductor layer 22, and a pair of conductor layers 21, It has a conductor wall 24 formed by an array of a plurality of conductive pillars that connect 22 to each other and penetrate the dielectric 23. The filter 101 passes a high frequency signal in a predetermined frequency band and blocks a high frequency signal in a frequency band other than the frequency band. That is, the filter 101 is a bandpass filter having a pass band through which a high frequency signal of a predetermined frequency band (for example, a frequency band including 28 GHz) is passed.

The filter 101 includes a plurality of resonators R1 to R4 connected in multiple stages via irises 31 to 33, an input unit 11 connected to the input side of the first first stage resonator R1, and the final four stages. It includes an output unit 12 connected to the output side of the resonator R4 of the eye. The resonators R1 to R4, the input unit 11 and the output unit 12 are formed in a plane and integrally along the ZX plane. The input unit 11 and the resonator R1 are connected via the iris 36, and the output unit 12 and the resonator R4 are connected via the iris 37.

The resonators R1 to R4, the input unit 11 and the output unit 12 are located between the pair of conductor layers 21 and 22 and the dielectric 23 sandwiched between the pair of conductor layers 21 and 22 and the pair of conductor layers 21 and 22. It has a conductor wall 24 and a conductor wall 24 for conductively connecting the above.

The first conductor layer 21 and the second conductor layer 22 are planar conductors arranged in parallel with the ZX plane, and face each other in the Y-axis direction. Examples of the material of the first conductor layer 21 and the second conductor layer 22 include silver and copper.

The dielectric 23 is a flat plate-like portion parallel to the ZX plane. Examples of the material of the dielectric 23 include glass such as silica glass, ceramics, a fluorine-based resin such as polytetrafluoroethylene, a liquid crystal polymer, and a cycloolefin polymer. As another embodiment, the dielectric 23 is not limited to a solid, but may be a gas such as air.

The conductor wall 24 is connected to the first conductor layer 21 on the upper side in the Y-axis direction and is connected to the second conductor layer 22 on the lower side in the Y-axis direction. In the form shown in FIG. 1, the conductor wall 24 is formed of a plurality of through holes.

Resonators R1 to R4 are waveguides having a waveguide formed by a pair of conductor layers 21 and 22 facing each other with the dielectric 23 interposed therebetween and a conductor wall 24 formed on the dielectric 23. Resonators R1 to R4 all resonate in TE101 mode. The TE101 mode represents a TE (Transverse Electric) mode in which an electric field distribution parallel to the Y axis perpendicular to the transmission direction and a magnetic field distribution parallel to the ZX plane parallel to the transmission direction occur. The first-stage resonator R1 and the second-stage resonator R2 are coupled via the iris 31, and the second-stage resonator R2 and the third-stage resonator R3 are coupled via the iris 32. The third-stage resonator R3 and the fourth-stage resonator R4 are coupled via the iris 33.

FIG. 2 is a plan view of the waveguide filter in the first configuration example. The filter 101 is provided with a slot 26 that intersects in a plan view with a conductor wall 25 that partitions between two adjacent resonators R1 and R4 among the plurality of resonators R1 to R4 without the intervention of an iris. The conductor wall 25 is a part of the conductor wall 24. The slot 26 is a groove formed only in one of the pair of conductor layers 21 and 22 (in this case, the first conductor layer 21).

FIG. 3 is a plan view schematically showing the waveguide filter in the first configuration example. The electromagnetic wave input from the input unit 11 propagates to the first-stage resonator R1, then propagates sequentially through the second to fourth-stage resonators R2 to R4, and is output from the output unit 12. On the other hand, when two adjacent resonators R1 and R4 are coupled via the slot 26 without the intervention of an iris, the first-stage resonator R2 and R3 do not propagate through the intermediate second and third-stage resonators R2 and R3. An electromagnetic wave propagating through the slot 26 is generated in the resonator R4 in the fourth stage from R1. Therefore, if the phase difference between the electromagnetic waves propagating sequentially through the resonators R1 to R4 and the electromagnetic waves propagating from the resonator R1 to the resonator R4 via the slot 26 without passing through the resonators R2 and R3 deviates by 180 °, both of them. Electromagnetic waves cancel each other out. As a result, the attenuation pole can be expressed on the low frequency side and the high frequency side of the pass band.

FIG. 4 is a diagram schematically showing the magnetic flow direction generated in each resonator in the pass band. FIG. 5 is a diagram schematically showing the magnetic flow direction generated in each resonator outside the pass band. As shown in FIG. 4, when the two resonators R1 and R4 are not coupled via the slot 26, the directions of the magnetic fields generated in each of the resonators R1 to R4 are the same, and the electromagnetic waves are the resonators R1 to R4. Propagate sequentially. On the other hand, as shown in FIG. 5, when the two resonators R1 and R4 are coupled via the slot 26, the direction of the magnetic field generated in the resonator R1 and the direction of the magnetic field generated in the resonator R4 are reversed. .. Therefore, the coupling coefficient of the coupling between the two resonators R1 and R4 via the slot 26 becomes negative, and the attenuation pole can be expressed on the low frequency side and the high frequency side of the pass band.

In this way, by providing the slot 26 that intersects the conductor wall 25 that partitions between the two resonators R1 and R4 in which the order of the number of stages is not continuous in a plan view, the blocking characteristics on both sides of the pass band are improved. Further, since the resonators R1 to R4 that resonate in the TE101 mode can be smaller in size than the resonator in the higher-order mode of the TE102 mode or higher, the conventional waveguide that requires the resonator in the higher-order mode of the TE102 mode or higher is required. The filter 101 can be made smaller than the filter. That is, it is possible to realize a waveguide filter capable of improving the cutoff characteristics on both sides of the pass band and reducing the size.

Further, since the slots 26 need not be formed in both of the pair of conductor layers 21 and 22 but only in one conductor layer, the filter manufacturing process can be simplified and the filter manufacturing cost can be suppressed.

Further, when there is a metal object in the vicinity of the place where the filter is installed, when the slot approaches the metal object, the degree of coupling in the slot changes, which may affect the blocking characteristics of the filter. However, in the filter according to the present disclosure, since the slot is formed in only one conductor layer, the slot is easily separated (avoided) from the metal object as compared with the form in which the slot is formed in both conductor layers. And the degree of freedom in filter placement is high.

Next, the configuration of the filter 101 will be described in more detail.

In FIG. 2, slot 26 is a linear line segment slot having a first slot portion 27, a second slot portion 28, and a third slot portion 29. The first slot portion 27 is a groove portion that overlaps the resonator R1 in a plan view, and its stretching direction has an X-axis direction component and a Z-axis direction component. The second slot portion 28 is a groove portion that overlaps the resonator R4 in a plan view, and its stretching direction has an X-axis direction component and a Z-axis direction component. The third slot portion 29 is a groove portion that connects the first slot portion 27 and the second slot portion 28, and its stretching direction has an X-axis direction component and a Z-axis direction component.

The X-axis direction component is an example of a first direction component along the conductor wall 25, and the Z-axis direction component is an example of a second direction component perpendicular to the first direction component in a plan view.

In terms of improving the blocking characteristics on both sides of the pass band of the filter 101, the stretching directions of the first slot portion 27 and the second slot portion 28 are the X-axis direction component and the Z-axis direction component in a plan view. It is preferable to have both directional components.

Further, the third slot portion 29 preferably passes through the center of the conductor wall 25 in order to improve the blocking characteristics on both sides of the pass band of the filter 101. In this example, the third slot portion 29 passes between adjacent through holes in a plan view.

Further, among a plurality of resonators connected in multiple stages, the number of intermediate resonators connected via an iris between two adjacent resonators without the intervention of an iris is even-numbered. It is preferable in that it improves the cutoff characteristics on both sides of the pass band of the filter as compared with the case of an odd number. In the case of the filter 101, among the resonators R1 to R4, the number of intermediate resonators R2 and R3 connected via the iris between two adjacent resonators R1 and R4 without the intervention of the iris is an even number. It is 2.

The slot 26 intersects the conductor wall 25 in plan view of the filter 101. The intersection angle θ (acute angle) between the slot 26 and the conductor wall 25 in a plan view is preferably 10 ° to 80 °, more preferably 20 ° to 70 °, in terms of improving the blocking characteristics on both sides of the pass band of the filter. Preferably, 40 ° to 50 ° is particularly preferable, and 45 ° is most preferable.

FIG. 6 is a plan view of the waveguide filter in the second configuration example. FIG. 7 is an enlarged view of the slots of the waveguide filter in the second configuration example. The description of the same configuration and effect as the above-mentioned configuration example will be omitted or simplified by referring to the above-mentioned description. The filter 102 in the second configuration example differs from the filter 101 in the first configuration example in the shape of the slot intersecting the conductor wall 25 in a plan view.

The slot 46 is a groove that intersects the conductor wall 25 in a plan view, and is formed only in one of the pair of conductor layers 21 and 22 (in this case, the first conductor layer 21).

The slot 46 is a crank-shaped slot having a first slot portion 47, a second slot portion 48, and a third slot portion 49. The first slot portion 47 is a groove portion that overlaps the resonator R1 in a plan view, and its stretching direction has an X-axis direction component without a Z-axis direction component. The second slot portion 48 is a groove portion that overlaps the resonator R4 in a plan view, and its stretching direction has an X-axis direction component without a Z-axis direction component. The third slot portion 49 is a groove portion connecting the first slot portion 47 and the second slot portion 48, and the extending direction thereof has a Z-axis direction component without having an X-axis direction component.

In terms of improving the blocking characteristics on both sides of the pass band of the filter 102, it is preferable that each of the stretching directions of the first slot portion 47 and the second slot portion 48 has an X-axis direction component in a plan view. Further, the third slot portion 49 preferably passes through the center of the conductor wall 25 in order to improve the blocking characteristics on both sides of the pass band of the filter 102.

FIG. 8 is a plan view of the waveguide filter in the third configuration example. FIG. 9 is an enlarged view of the slots of the waveguide filter in the third configuration example. The description of the same configuration and effect as the above-mentioned configuration example will be omitted or simplified by referring to the above-mentioned description. The filter 103 in the third configuration example differs from the filter 102 in the second configuration example in the shape of the slot intersecting the conductor wall 25 in a plan view.

The slot 56 is a groove that intersects the conductor wall 25 in a plan view, and is formed only in one of the pair of conductor layers 21 and 22 (in this case, the first conductor layer 21).

The slot 56 is a crank-shaped slot having a first slot portion 57, a second slot portion 58, and a third slot portion 59. The first slot portion 57 is a groove portion that overlaps the resonator R1 in a plan view, and its stretching direction has an X-axis direction component and a Z-axis direction component. The second slot portion 58 is a groove portion that overlaps the resonator R4 in a plan view, and its stretching direction has an X-axis direction component and a Z-axis direction component. The third slot portion 59 is a groove portion that connects the first slot portion 57 and the second slot portion 58, and its stretching direction has a Z-axis direction component without having an X-axis direction component.

The first slot portion 57 has a groove 57a of an X-axis direction component and a groove 57b of a Z-axis direction component. One end of the groove 57a is connected to one end of the third slot portion 59, and the other end is connected to one end of the groove 57b. The second slot portion 58 has a groove 58a having an X-axis direction component and a groove 58b having a Z-axis direction component. One end of the groove 58a is connected to the other end of the third slot portion 59, and the other end is connected to one end of the groove 58b.

In terms of improving the blocking characteristics on both sides of the pass band of the filter 103, the stretching directions of the first slot portion 57 and the second slot portion 58 are the X-axis direction component and the Z-axis direction component in a plan view. It is preferable to have both directional components. Further, the third slot portion 59 preferably passes through the center of the conductor wall 25 in order to improve the blocking characteristics on both sides of the pass band of the filter 103.

FIG. 10 is a perspective view of the waveguide filter in the fourth configuration example. The description of the same configuration and effect as the above-mentioned configuration example will be omitted or simplified by referring to the above-mentioned description. The filter 201 in the fourth configuration example differs from the filter 101 in the first configuration example in the number of resonators connected in multiple stages.

The filter 201 includes a plurality of resonators R1 to R6 connected in multiple stages via irises 31 to 35, an input unit 11 connected to the input side of the first first stage resonator R1, and the final six stages. It includes an output unit 12 connected to the output side of the resonator R6 of the eye. The resonators R1 to R6, the input unit 11 and the output unit 12 are formed in a plane and integrally along the ZX plane. The input unit 11 and the resonator R1 are connected via the iris 36, and the output unit 12 and the resonator R6 are connected via the iris 37.

Resonators R1 to R6 are waveguides having a waveguide formed by a pair of conductor layers 21 and 22 facing each other with the dielectric 23 interposed therebetween and a conductor wall 24 formed on the dielectric 23. Resonators R1 to R6 all resonate in the TE101 mode. The first-stage resonator R1 and the second-stage resonator R2 are coupled via the iris 31, and the second-stage resonator R2 and the third-stage resonator R3 are coupled via the iris 32. The third-stage resonator R3 and the fourth-stage resonator R4 are coupled via the iris 33. The fourth-stage resonator R4 and the fifth-stage resonator R5 are coupled via the iris 34, and the fifth-stage resonator R5 and the sixth-stage resonator R6 are coupled via the iris 35. ..

FIG. 11 is a plan view of the waveguide filter in the fourth configuration example. The filter 201 is provided with a slot 26 that intersects in a plan view with a conductor wall 25 that partitions two resonators R1 and R6 that are adjacent to each other without the intervention of an iris among the plurality of resonators R1 to R6. The slot 26 is a pair of conductor layers 21 and 22 so as to intersect in a plan view with a conductor wall 25 partitioning between two adjacent resonators R2 and R5 among the plurality of resonators R1 to R6 without the intervention of an iris. It may be formed only on one of the conductor layers (in this case, the first conductor layer 21). There may be two or more slots 26 formed.

In the case of the filter 201, among the resonators R1 to R6, the number of intermediate resonators R2 to R5 connected via the iris between two adjacent resonators R1 and R6 without the intervention of the iris is an even number. It is 4. Therefore, the cutoff characteristics on both sides of the pass band of the filter are improved.

FIG. 12 is a plan view of the waveguide filter in the fifth configuration example. FIG. 13 is a plan view of the waveguide filter in the sixth configuration example. The description of the same configuration and effect as the above-mentioned configuration example will be omitted or simplified by referring to the above-mentioned description. The filter 202 in the fifth configuration example differs from the filter 102 in the second configuration example in that the number of resonators connected in multiple stages is six. The filter 203 in the sixth configuration example is different from the filter 103 in the third configuration example in that the number of resonators connected in multiple stages is six.

FIG. 14 is a diagram showing a modified example of the slot. The slot 66 shown in FIG. 14 is a modified example of a slot that intersects the conductor wall 25 in a plan view.

The slot 56 is an S-shaped slot having a first slot portion 67, a second slot portion 68, and a third slot portion 69. The first slot portion 67 is a groove portion that overlaps the resonator R1 in a plan view, and its stretching direction has an X-axis direction component and a Z-axis direction component. The second slot portion 68 is a groove portion that overlaps the resonator R4 in a plan view, and its stretching direction has an X-axis direction component and a Z-axis direction component. The third slot portion 69 is a groove portion connecting the first slot portion 67 and the second slot portion 68, and the extending direction thereof has a Z-axis direction component without having an X-axis direction component.

The first slot portion 67 has a groove 67a of an X-axis direction component and a groove 67b of a Z-axis direction component. One end of the groove 67a is connected to one end of the third slot portion 69, and the other end is connected to one end of the groove 67b. The second slot portion 68 has a groove 68a having an X-axis direction component and a groove 68b having a Z-axis direction component. One end of the groove 68a is connected to the other end of the third slot portion 69, and the other end is connected to one end of the groove 68b.

In terms of improving the blocking characteristics on both sides of the pass band of the filter, the stretching directions of the first slot portion 67 and the second slot portion 68 are both the X-axis direction component and the Z-axis direction component in a plan view. It is preferable to have a directional component of. Further, the third slot portion 69 preferably passes through the center of the conductor wall 25 in order to improve the blocking characteristics on both sides of the pass band of the filter.

FIG. 15 is a diagram showing an example of simulation results of filter characteristics of filters 100 to 103 in four forms in which four resonators R1 to R4 are connected in multiple stages. The vertical axis shows the passage characteristic S21, which is one of the S parameters. The filter 100 is a comparative example in which the slot 26 is deleted from the filter 101 (FIG. 2). As shown in FIG. 15, since the slots 101 to 103 have attenuation poles on the low frequency side and the high frequency side of the pass band, they have attenuation poles on both sides of the pass band as compared with the filter 100 without slots. Excellent blocking characteristics.

In the simulation of FIG. 15, the dimensions of each part are as follows, assuming that the unit is mm.

<Filter 101 (Fig. 2)>
L1: 7.33
L2: 3.4
L3: 3.7
L4: 1.85
L5: 0.21
L6: 2.4
L7: 2.96
L8: 2.41
L9: 0.03
Crossing angle θ: 45 °

<Filter 102 (Figs. 6 and 7)>
L11: 1.14
L12: 1.14
L13: 0.39
L14: 0.45

<Filter 103 (FIGS. 8 and 9)>
L21: 2.34
L22: 0.45
L23: 0.39
L24: 0.22

Further, in the simulation of FIG. 15, a finite element method (FEM) is used, and silica glass (relative permittivity εr = 3.85, dielectric loss tangent tan δ = 0.0005) is used as the material of the dielectric 23. Was assumed.

FIG. 16 is a diagram showing an example of simulation results of filter characteristics of filters 200 to 204 of four forms in which six resonators R1 to R6 are connected in multiple stages. The vertical axis shows the passage characteristic S21, which is one of the S parameters. The filter 200 is a comparative example in which the slot 26 is deleted from the filter 201 (FIG. 11). As shown in FIG. 16, since the filters 201 to 203 in which the slots are formed have attenuation poles on the low frequency side and the high frequency side of the pass band, the filters 200 on both sides of the pass band are compared with the filter 200 without slots. Excellent blocking characteristics.

In the simulation of FIG. 16, the dimensions of each part are as follows, assuming that the unit is mm.

<Filter 201 (FIG. 11)>
L31: 7.33
L32: 3.5
L33: 3.4
L34: 3.7
L35: 1.85
L36: 1.7
L37: 2.01
L38: 2.01
L39: 0.21
L40: 2.96
L41: 2.4
L42: 2.13
L43: 0.03
Crossing angle θ: 45 °

<Filter 202 (Figs. 7 and 12)>
L11: 1.11
L12: 1.11
L13: 0.39
L14: 0.45

<Filter 203 (Figs. 9 and 13)>
L21: 2.34
L22: 0.45
L23: 0.39
L24: 0.22

Further, the finite element method (FEM) is used for the simulation of FIG. 16, and silica glass (relative permittivity εr = 3.85, dielectric loss tangent tan δ = 0.0005) is used as the material of the dielectric 23. Was assumed.

Although the waveguide filter has been described above according to the embodiment, the present invention is not limited to the above embodiment. Various modifications and improvements, such as combinations and substitutions with some or all of the other embodiments, are possible within the scope of the present invention.

11 Input section 12 Output section 21 First conductor layer 22 Second conductor layer 23 Dielectric 24,25 Conductor wall 26,46,56,66 Slots 27,47,57,67 First slot sections 28,48, 58,68 Second slot section 29,49,59,69 Third slot section 31-35 Iris 100-103, 200-203 Filter R1-R4 Resonator

Claims (5)

It is equipped with multiple resonators that are connected in multiple stages via an iris and resonate in TE101 mode.
The plurality of resonators have a pair of conductor layers facing each other with a dielectric interposed therebetween.
A slot that intersects in a plan view with a conductor wall that separates two adjacent resonators among the plurality of resonators without the intervention of an iris is provided.
The slot is a waveguide filter formed in only one of the pair of conductor layers. The slot has a first slot portion that overlaps with one of the two resonators in a plan view, and a second slot portion that overlaps with the other resonator of the two resonators in a plan view. It has a third slot portion that connects the first slot portion and the second slot portion.
The waveguide filter according to claim 1, wherein the stretching directions of the first slot portion and the second slot portion each have a first directional component along the conductor wall in a plan view. The waveguide according to claim 2, wherein each of the stretching directions of the first slot portion and the second slot portion further has a second directional component perpendicular to the first directional component in a plan view. Tube filter. The waveguide filter according to claim 2 or 3, wherein the third slot portion passes through the center of the conductor wall in a plan view. The waveguide according to any one of claims 1 to 4, wherein the number of intermediate resonators connected between the two resonators via an iris is an even number among the plurality of resonators. Tube filter.

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