Coaxial filter

Abstract

To obtain a coaxial filter capable of realizing a capacitance component required for a filter circuit without complex processing of a central conductor.SOLUTION: A coaxial filter 1 includes: a cylindrical dielectric unit 12 having a central hole penetrating in an extension direction in a region including the central axis; a central conductor 11 filled in the central hole of the dielectric unit 12; and a cylindrical external conductor 13 provided so as to cover a side surface along the central axis of the dielectric unit 12. The dielectric unit 12 has: a cylindrical dielectric 122 having a conductor pattern 142 in contact with the central conductor 11 arranged on one bottom surface; and a cylindrical dielectric 123 having a conductor pattern 143 in contact with the external conductor 13 arranged on one bottom surface, and has a structure in which the dielectric 122 and the dielectric 123 are laminated in the extension direction of the central axis such that the conductor patterns 142 and 143 do not come into contact with each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a coaxial filter that suppresses leakage of harmonics generated within a module. [Background technology]

[0002] Generally, RF (Radio Frequency) amplifiers and switching diodes mounted in high-frequency transmission and reception modules are nonlinear devices that generate harmonics. In many cases, a harmonic filter is implemented in the module to prevent harmonics from leaking outside the module. Harmonic filters are generally formed on transmission line substrates such as microstrip lines and strip lines. There are various types of filter circuits, such as band-rejection filters (BRFs) using short stubs and low-pass filters (LPFs) that alternate between high impedance and low impedance. To ensure the desired amount of harmonic suppression, an appropriate filter is selected taking into consideration the surrounding circuits and board area.

[0003] However, due to the recent demand for miniaturization and broadband of modules, the space available on the board for adding functions is becoming limited.In addition, filters formed by microstrip lines on the board are not effective against harmonics that propagate through space, so it is necessary to take other measures, such as raising the cutoff frequency of the module.

[0004] Patent Document 1 discloses a technology for a coaxial filter that provides a coaxial connector with a filter function for suppressing harmonics, which solves the problems of the circuit area constraints in such a module and the measures against harmonics propagating through space.Patent Document 1 discloses a coaxial filter having a function of a low-pass filter, which has an outer conductor formed of a metal cylinder, a central conductor in which high impedance sections formed of metal cylinders inserted into the outer conductor and arranged so as to be continuous along the central axis of the outer conductor, and disk-shaped low impedance sections radially extending from the high impedance section as the center are alternately formed in succession, and at least one low impedance section has a bent section in which a tip region is bent so as to be parallel to the high impedance section.

[0005] Patent Document 2 discloses a coaxial cable with a filtering function, which includes a central conductor extending from the input side to the output side, a dielectric covering the periphery of the central conductor, an outer conductor covering the outer periphery of the dielectric, and fringe conductors extending along the outer periphery of the central conductor in the dielectric between the central conductor and the outer conductor. The filtering effect provided by the coaxial cable can be changed by changing the number of fringe conductors included in one coaxial cable, as well as the diameter, position and thickness of each fringe conductor. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4913217 [Patent Document 2] JP 2022-91193 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, according to the above-mentioned conventional technology, in order to realize the high impedance part and the low impedance part, i.e., the inductance component and the capacitance component, required for the filter circuit, the central conductor of the coaxial filter or the coaxial cable having the filtering function is processed in a complex manner. Therefore, when trying to realize a filter in the microwave band with a high frequency, there is a problem that the size of the connector itself is reduced, so fine processing accuracy is required. In addition, in order to support the central conductor and reduce the size by using the wavelength shortening effect of the dielectric, a dielectric may be loaded in the coaxial filter or the coaxial cable having the filtering function, but there is also a problem that it is difficult to mount the dielectric on the complexly processed central conductor.

[0008] The present disclosure has been made in consideration of the above, and has an object to provide a coaxial filter that can achieve the capacitance component required for a filter circuit without complex processing of the central conductor. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, a coaxial filter according to the present disclosure includes a cylindrical dielectric section having a central hole penetrating in an extension direction to a region including a central axis, a central conductor filled in the central hole of the dielectric section, and a cylindrical outer conductor provided so as to cover a side surface along the central axis of the dielectric section. The dielectric section has a cylindrical first dielectric having a first conductor pattern in contact with the central conductor arranged on one bottom surface, and a cylindrical second dielectric having a second conductor pattern in contact with the outer conductor arranged on one bottom surface, and has a structure in which the first dielectric and the second dielectric are layered in the extension direction of the central axis so that the first conductor pattern and the second conductor pattern do not come into contact with each other. Effect of the Invention

[0010] According to the present disclosure, it is possible to achieve an effect of realizing a capacitance component required for a filter circuit without complex processing of the central conductor. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating a schematic example of a configuration of a coaxial filter according to a first embodiment. [Diagram 2] FIG. 1 is an exploded perspective view showing a schematic example of a configuration of a dielectric portion that constitutes the coaxial filter according to the first embodiment; [Diagram 3] A diagram showing the equivalent circuit of a typical low-pass filter [Figure 4] FIG. 1 is a diagram for explaining parameters used when calculating capacitance in a coaxial filter according to a first embodiment; [Diagram 5] FIG. 1 is a diagram showing an example of inductance and capacitance in a coaxial filter according to a first embodiment; [Figure 6] FIG. 1 is a diagram showing an example of an equivalent circuit of a coaxial filter according to a first embodiment when parasitic capacitance is ignored; [Figure 7] FIG. 1 is a cross-sectional view illustrating a schematic example of a configuration of a coaxial filter according to a first embodiment. [Figure 8] FIG. 1 is an exploded perspective view showing a schematic example of a configuration of a dielectric section in a coaxial filter according to a first embodiment; [Figure 9] FIG. 9 is a diagram showing an example of a calculation result of the frequency characteristics of the coaxial filter shown in FIGS. 7 and 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Coaxial filters according to embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0013] Embodiment 1 FIG. 1 is a cross-sectional view showing a schematic example of a configuration of a coaxial filter according to the first embodiment. FIG. 2 is an exploded perspective view showing a schematic example of a configuration of a dielectric part constituting the coaxial filter according to the first embodiment. The coaxial filter 1 is a coaxial cable having a filter function for a predetermined frequency component. Connectors (not shown) are connected to both ends of the coaxial filter 1. The coaxial filter 1 includes a central conductor 11, a dielectric part 12, and an outer conductor 13. Note that the central conductor 11 and the outer conductor 13 of the coaxial filter 1 in FIG. 1 are not shown in FIG. 2.

[0014] The dielectric part 12 is a cylindrical member made of a dielectric material having a central hole 12a penetrating in an extension direction in a region including the central axis. The central hole 12a is provided along the central axis connecting the centers of the two bottom surfaces of the cylindrical dielectric part 12. The shape of the central hole 12a is cylindrical in one example. The central conductor 11 is inserted into the central hole 12a so as to contact the inner side surface 12c, which is the side surface that forms the central hole 12a. The diameter of the central hole 12a is the same as the outer diameter of the central conductor 11.

[0015] The dielectric portion 12 has three types of cylindrical dielectrics 121, 122, and 123 that are shorter in the extending direction than the dielectric portion 12. The three types of dielectrics 121, 122, and 123 differ in whether or not a conductor pattern 14 is arranged and in the manner in which it is arranged.

[0016] The dielectrics 121, 122, 123 have an outer side surface 12b which is a cylindrical side surface that is parallel to the extension direction of the central conductor 11 and forms the outer shape of the dielectrics 121, 122, 123, an inner side surface 12c which is a cylindrical side surface that is parallel to the extension direction of the central conductor 11 and forms the central hole 12a, and a pair of bottom surfaces 12d, 12e which are perpendicular to the extension direction of the central conductor 11. Here, the boundary between the outer side surface 12b and the bottom surfaces 12d, 12e is referred to as an outer edge portion, and the boundary between the inner side surface 12c and the bottom surfaces 12d, 12e is referred to as an inner edge portion.

[0017] The dielectric portion 12 includes a dielectric 121 on which no conductor pattern 14 is arranged, a dielectric 122 on which a conductor pattern 142 is arranged so as to be in contact with the inner edge portion but not with the outer edge portion, and a dielectric 123 on which a conductor pattern 143 is arranged so as not to be in contact with the inner edge portion but to be in contact with the outer edge portion. The outer diameters of all the dielectrics 121, 122, and 123 are the same. The diameters of the central holes 12a of all the dielectrics 121, 122, and 123 are also the same. The dielectric 122 corresponds to the first dielectric, the dielectric 123 corresponds to the second dielectric, and the dielectric 121 corresponds to the third dielectric. The conductor pattern 142 corresponds to the first conductor pattern, and the conductor pattern 143 corresponds to the second conductor pattern.

[0018] The conductor pattern 14 is not disposed on the dielectric material 121 .

[0019] The conductor pattern 142 is disposed on the dielectric 122 over a range from the inner edge on the bottom surface 12d to the outer edge. As described above, the conductor pattern 142 is in contact with the inner edge but not with the outer edge. In other words, the dielectric 122 has the annular conductor pattern 142 disposed so as to be in contact with the inner edge, i.e., the central conductor 11.

[0020] The dielectric 123 has a conductor pattern 143 arranged on the bottom surface 12d over a range from the outer edge to the inner edge. As described above, the conductor pattern 143 is in contact with the outer edge but not with the inner edge. In other words, the dielectric 123 has an annular conductor pattern 143 arranged to be in contact with the outer edge, i.e., the external conductor 13. The conductor patterns 142 and 143 are not arranged on the bottom surfaces 12e of the dielectrics 122 and 123. Hereinafter, the conductor patterns 142 and 143 will be referred to as conductor patterns 14 when they are not distinguished from one another.

[0021] In the dielectrics 122, 123 on which the conductor pattern 14 is arranged, when a coaxial filter 1 is constructed as shown in Figures 1 and 2, the conductor patterns 142, 143 are arranged on one of a pair of opposing bottom surfaces 12d, 12e, namely, the bottom surface 12d, which is not the outer surface 12b or the inner surface 12c parallel to the central conductor 11 of the cylindrical dielectrics 122, 123, and the conductor patterns 142, 143 are not arranged on the other bottom surface 12e.

[0022] The dielectric material constituting the dielectric portion 12 may be a Teflon (registered trademark)-based material such as polytetrafluoroethylene (PTFE), which has been widely used in conventional coaxial connectors, a low-dielectric-constant glass cloth resin or glass epoxy-based material, or an alumina-based material with a high dielectric constant. The dielectric material may be selected from a variety of materials that have a proven track record in laminated substrates, and is not limited to a specific material.

[0023] The central conductor 11 is a member made of a conductive material that fills the central hole 12a of the dielectric part 12. In the example shown in Figures 1 and 2, the central conductor 11 is made of a solid cylindrical conductive material. The outer surface of the central conductor 11 is in contact with the inner surface 12c of the dielectric part 12.

[0024] The outer conductor 13 is a cylindrical member made of a conductive material and provided so as to be in contact with the outer surface 12b, which is the side surface of the dielectric portion 12 along the central axis of the dielectric portion 12. Examples of materials for the central conductor 11 and the outer conductor 13 are copper and aluminum.

[0025] The central conductor 11 is inserted into the central hole 12a of the laminated multiple types of dielectrics 121, 122, and 123, and the laminated multiple types of dielectrics 121, 122, and 123 are inserted into the external conductor 13, thereby obtaining a coaxial filter 1 having the structure shown in Fig. 1. This results in a structure in which the conductor pattern 142 of the dielectric 122 is conductive with the central conductor 11 but not conductive with the external conductor 13, and the conductor pattern 143 of the dielectric 123 is conductive with the external conductor 13 but not conductive with the central conductor 11.

[0026] Thus, the dielectric portion 12 has the dielectric 122 and the dielectric 123, and has a structure in which the dielectric 122 and the dielectric 123 are laminated in the extension direction of the central axis so that the conductor pattern 142 and the conductor pattern 143 do not contact each other. The dielectric portion 12 further has a dielectric 121, and has a structure in which the dielectric 122 and the dielectric 123 are laminated between the two dielectrics 121 in the extension direction of the central axis.

[0027] Next, an outline of a method for manufacturing the coaxial filter 1 having such a structure will be described. In one example, the conductor patterns 142, 143 arranged on the dielectrics 122, 123 are printed by a printing method. In one example, the conductor patterns 142, 143 are formed on the bottom surfaces 12d of the dielectrics 122, 123, respectively. The central holes 12a of the dielectrics 121, 122, 123 may be provided as cavities when stacking, or may be formed collectively in the plurality of dielectrics 121, 122, 123 by drilling after stacking the plurality of dielectrics 121, 122, 123, and the method is not limited.

[0028] With the dielectrics 121, 122, and 123 having a central hole 12a stacked, the central conductor 11 is filled into the central hole 12a. In one example, the processing of the central conductor 11 may be a method of passing a core wire through the central hole 12a and soldering it, or a method of filling the central hole with a conductive material, and the method is not limited. In this way, the central conductor 11 corresponding to the size and shape of the central hole 12a is formed in the central hole 12a of the stacked dielectrics 121, 122, and 123.

[0029] The processing of the external conductor 13 may be performed by thermocompression bonding a conductive tube to the laminated dielectrics 121, 122, and 123, physically compressing the dielectrics, or by wrapping a conductive film or sheet-like material around the dielectrics. There is no limitation on the method. In this way, the external conductor 13 is formed in contact with the outer surface 12b of the laminated dielectrics 121, 122, and 123. In this way, the coaxial filter 1 is manufactured.

[0030] In the lamination process for laminating the plurality of dielectrics 121, 122, and 123, a mask is provided on one dielectric sheet, and after lamination, dicing is performed according to the mask, making it possible to accommodate mass production.

[0031] Next, the operation of the coaxial filter 1 according to the first embodiment will be described by taking the case where the filter is a low-pass filter as an example. FIG. 3 is a diagram showing an equivalent circuit of a general low-pass filter. The characteristics of a low-pass filter are determined by a series inductance L and a parallel capacitance C, and the attenuation characteristics of the filter change depending on the number of stages. In one example, the attenuation in the low-pass filter increases as the number of stages increases. In high-frequency circuits such as those in the microwave band, the above-mentioned inductance L and capacitance C are generally realized by distributed constants, and the inductance L operates as a high impedance, and the capacitance C operates as a low impedance. In the conventional technology, the low impedance section corresponding to the above-mentioned capacitance component is realized by a disk section with a large diameter of the central conductor.

[0032] On the other hand, in the coaxial filter 1 according to the first embodiment, a high impedance section corresponding to the above-mentioned inductance component is realized by the dielectric 121, the central conductor 11, and the outer conductor 13. Also, a low impedance section corresponding to the above-mentioned capacitance component is realized by the dielectric 122, the dielectric 123, the central conductor 11, and the outer conductor 13.

[0033] Here, the low impedance portion will be described in more detail. As shown in FIG. 1 and FIG. 2, the conductor pattern 142 printed on the dielectric 122 and the conductor pattern 143 printed on the dielectric 123 are arranged parallel to each other in a direction perpendicular to the central axis of the coaxial filter 1 through the thickness of the dielectric 122. The central axis of the coaxial filter 1 corresponds to the central axis of the central conductor 11. FIG. 4 is a diagram for explaining parameters used when calculating the capacitance in the coaxial filter according to the first embodiment. As shown in FIG. 4, if the relative dielectric constant of the dielectric portion 12 is εr, the thickness of the dielectric 122 is d, and the overlapping area between the conductor pattern 142 of the dielectric 122 and the conductor pattern 143 of the dielectric 123 is S, the capacitance C can be calculated by the following formula (1). The thickness d of the dielectric 122 is also the distance between the conductor pattern 142 and the conductor pattern 143.

[0034] C = εr × S / d (1)

[0035] In other words, by stacking a dielectric 122 having a conductor pattern 142 electrically connected to the central conductor 11 and a dielectric 123 having a conductor pattern 143 electrically connected to the outer conductor 13, it is possible to realize a capacitance component without processing the central conductor 11.

[0036] FIG. 5 is a diagram showing an example of inductance and capacitance in the coaxial filter according to the first embodiment. Strictly speaking, as shown in FIG. 5, the conductor pattern 142 printed on the dielectric 122 has a parasitic capacitance Cs2 between it and the outer conductor 13. In addition, the conductor pattern 143 printed on the dielectric 123 has a parasitic capacitance Cs3 between it and the central conductor 11. However, since these parasitic capacitances Cs2 and Cs3 are small, these parasitic capacitances Cs2 and Cs3 are ignored here. FIG. 6 is a diagram showing an example of an equivalent circuit of the coaxial filter according to the first embodiment when the parasitic capacitance is ignored. When the parasitic capacitance component is ignored, the equivalent circuit of the coaxial filter 1 in FIG. 1 is as shown in FIG. 6, and it can be seen that the filter functions as a three-stage low-pass filter having a high impedance section with two inductance components and a low impedance section with one capacitance component.

[0037] Furthermore, in the coaxial filter 1 according to the first embodiment, the use of a laminated structure also makes it easy to adjust the capacitance C. For example, from equation (1), lamination with dielectric 122 having a large thickness d can reduce the capacitance C. Also, from equation (1), lamination with dielectric 122 having a small thickness d can increase the capacitance C. Similarly, it is clear from equation (1) that the capacitance C can be adjusted by the relative dielectric constant εr of the dielectric portion 12 or by the overlapping area S between the printed conductor patterns 142 and 143.

[0038] 1 and 2, the dielectrics 123 and 122 are laminated so that the bottom surface 12d of the dielectric 123 on which the conductor pattern 143 is disposed faces the bottom surface 12e of the dielectric 122, and therefore the thickness d of the dielectric 122 is changed to change the capacitance C, but the capacitance C may be changed by other methods. In one example, when changing the capacitance C of the coaxial filter 1 in which the dielectrics 122 and 123 are laminated so that the bottom surface 12d of the dielectric 122 on which the conductor pattern 142 is disposed faces the bottom surface 12e of the dielectric 123, the thickness d of the dielectric 123 may be changed. In other words, the capacitance C of the coaxial filter 1 can be changed by changing the distance along the central conductor 11 between the conductor patterns 142 and 143, i.e., the thickness d of the dielectric 122 or the dielectric 123 present between the conductor patterns 142 and 143.

[0039] As described above, the capacitance C of the coaxial filter 1 can be adjusted by changing at least one of the thickness d of the dielectric 122 or dielectric 123 sandwiched between the conductor patterns 142 and 143 in the direction along the central axis, the area S of the overlap between the conductor patterns 142 and 143 in a plane perpendicular to the central axis, and the relative dielectric constant of the dielectric portion 12.

[0040] Moreover, by changing the size of the central hole 12a of the dielectric portion 12, the diameter of the central conductor 11 can be changed, and therefore the inductance L can be adjusted.

[0041] Furthermore, it is possible to adjust the number of filter stages by the number of layers. Although a three-stage low-pass filter is exemplified in FIG. 2 and FIG. 6, the number of layers may be increased to increase the number of filter stages. FIG. 7 is a cross-sectional view showing an example of the configuration of a coaxial filter according to the first embodiment, and FIG. 8 is an exploded perspective view showing an example of the configuration of a dielectric part in the coaxial filter according to the first embodiment. In FIG. 8, the central conductor 11 and the outer conductor 13 in the coaxial filter 1A of FIG. 7 are omitted. In these figures, the same components as those in FIG. 1 and FIG. 2 are given the same reference numerals, and their description is omitted. In the coaxial filter 1A shown in these figures, the combination of the dielectric 122 and the dielectric 123 is repeated twice via the dielectric 121, and the dielectric 121 is disposed at both ends. With such a configuration, a five-stage low-pass filter is realized. That is, the laminated structure of the dielectric 122 and the dielectric 123 may be repeated multiple times with the dielectric 121 sandwiched therebetween.

[0042] Fig. 9 is a diagram showing an example of the calculation results of the frequency characteristics of the coaxial filter shown in Fig. 7 and Fig. 8. In this diagram, the horizontal axis indicates frequency (GHz) and the vertical axis indicates insertion loss (dB). As shown in this diagram, there is almost no insertion loss for radio waves with frequencies below 10 GHz, but the insertion loss increases for frequencies above 10 GHz. In other words, it can be seen that a low-pass filter is formed that passes frequencies below 10 GHz and attenuates frequencies above 10 GHz.

[0043] The coaxial filter 1 according to the first embodiment includes a cylindrical dielectric portion 12 having a central hole 12a penetrating an area including the central axis in an extending direction, a central conductor 11 filled in the central hole 12a of the dielectric portion 12, and a cylindrical external conductor 13 provided so as to cover a side surface along the central axis of the dielectric portion 12, the dielectric portion 12 having a cylindrical dielectric 122 on one bottom surface 12d of which a conductor pattern 142 in contact with the central conductor 11 is disposed, and a cylindrical dielectric 123 on one bottom surface 12d of which a conductor pattern 143 in contact with the external conductor 13 is disposed, and the dielectric 122 and the dielectric 123 are laminated in the extending direction of the central axis so that the conductor patterns 142 and 143 do not come into contact with each other. With this structure, it is possible to realize a low impedance portion, which is a capacitance component required for a distributed constant type filter circuit, only by the laminated conductor patterns 142 and 143, without complex processing of the central conductor 11. In particular, when attempting to realize a filter in the high-frequency microwave band, the size of the connector itself attached to the coaxial filter 1 is reduced, but even in such a case, there is no need to process the central conductor 11 with a process that requires fine processing accuracy. In other words, there is an effect that a coaxial filter 1 that can realize a capacitance component required for a filter circuit can be obtained without complex processing of the central conductor 11.

[0044] Furthermore, with regard to the dielectric material that determines the filter characteristics of the coaxial filter 1, not only Teflon-based dielectric materials such as PTFE that are widely used in conventional coaxial connectors, but also a variety of materials that have a proven track record in use in laminated substrates, such as low-dielectric-constant glass cloth resin, glass epoxy-based materials, and alumina-based materials with a high dielectric constant, can be used. As a result, there is also the effect that improvements in filter performance and design freedom can be expected.

[0045] Furthermore, the capacitance of the coaxial filter 1 can be adjusted by changing at least one of the thickness d of the dielectric 122 or 123 sandwiched between the conductor patterns 142 and 143 in the direction along the central axis, the area S of the conductor patterns 142 and 143 overlapping in a plane perpendicular to the central axis, and the relative dielectric constant of the dielectric part 12. The inductance of the coaxial filter 1 can be adjusted by changing the diameter of the central conductor 11. Furthermore, the number of layers of the filter can be adjusted by adjusting the number of layers so that the layered structure of the dielectric 122 and the dielectric 123 is repeated multiple times with the dielectric 121 sandwiched therebetween. This also has the effect of realizing the coaxial filter 1, 1A having the desired filter characteristics.

[0046] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies. Parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0047] Various aspects of the present disclosure are summarized below as appendices.

[0048] [Appendix 1] a cylindrical dielectric portion having a central hole penetrating in an extension direction in a region including a central axis; a central conductor filled in the central hole of the dielectric portion; a cylindrical outer conductor provided so as to cover a side surface of the dielectric portion along the central axis; Equipped with a first dielectric having a cylindrical shape and a first conductor pattern in contact with the central conductor disposed on one bottom surface thereof, and a second dielectric having a cylindrical shape and a second conductor pattern in contact with the external conductor disposed on one bottom surface thereof, the first dielectric and the second dielectric being laminated in the direction of extension of the central axis so that the first conductor pattern and the second conductor pattern do not come into contact with each other. [Appendix 2] The coaxial filter described in Appendix 1, characterized in that the dielectric portion further has a cylindrical third dielectric having no conductor pattern on its bottom surface, and has a structure in which the first dielectric and the second dielectric are stacked between two of the third dielectrics in the extension direction of the central axis. [Appendix 3] 3. The coaxial filter according to claim 2, wherein the laminated structure of the first dielectric and the second dielectric is repeated multiple times with the third dielectric sandwiched therebetween. [Appendix 4] 4. The coaxial filter according to claim 1, wherein a capacitance of the coaxial filter is adjusted by changing at least one of a thickness of the first dielectric or the second dielectric sandwiched between the first conductor pattern and the second conductor pattern in a direction along the central axis, an area where the first conductor pattern and the second conductor pattern overlap in a plane perpendicular to the central axis, and a relative dielectric constant of the dielectric portion. [Appendix 5] 5. The coaxial filter according to claim 1, wherein the inductance of the coaxial filter is adjusted by changing the diameter of the central conductor. [Explanation of symbols]

[0049] 1,1A coaxial filter, 11 central conductor, 12 dielectric part, 12a central hole, 12b outer surface, 12c inner surface, 12d,12e bottom surface, 13 outer conductor, 14,142,143 conductor pattern, 121,122,123 dielectric.

Claims

1. a cylindrical dielectric portion having a central hole penetrating in an extension direction in a region including a central axis; a central conductor filled in the central hole of the dielectric portion; a cylindrical outer conductor provided so as to cover a side surface of the dielectric portion along the central axis; Equipped with a first dielectric having a cylindrical shape and a first conductor pattern in contact with the central conductor disposed on one bottom surface thereof, and a second dielectric having a cylindrical shape and a second conductor pattern in contact with the external conductor disposed on one bottom surface thereof, the first dielectric and the second dielectric being laminated in the direction of extension of the central axis so that the first conductor pattern and the second conductor pattern do not come into contact with each other.

2. The coaxial filter according to claim 1, characterized in that the dielectric portion further has a cylindrical third dielectric having no conductor pattern disposed on its bottom surface, and has a structure in which the first dielectric and the second dielectric are stacked between two of the third dielectrics in the direction of extension of the central axis.

3. 3. The coaxial filter according to claim 2, wherein the laminated structure of the first dielectric and the second dielectric is repeated a plurality of times with the third dielectric interposed therebetween.

4. 2. The coaxial filter according to claim 1, wherein a capacitance of the coaxial filter is adjusted by changing at least one of a thickness of the first dielectric or the second dielectric sandwiched between the first conductor pattern and the second conductor pattern in a direction along the central axis, an area where the first conductor pattern and the second conductor pattern overlap in a plane perpendicular to the central axis, and a relative dielectric constant of the dielectric portion.

5. 2. The coaxial filter according to claim 1, wherein the inductance of the coaxial filter is adjusted by changing the diameter of the central conductor.

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