Bandpass filter, and laminated circuit board having the same

Abstract

To realize a bandpass filter capable of providing an excellent frequency selection characteristic for electromagnetic waves in a high frequency band from several hundreds GHz to terahertz band.SOLUTION: A bandpass filter 10 has a first metal pattern layer 12 formed on one surface of a resin substrate 11, and has a second metal pattern layer 13 formed on the other surface thereof. The first metal pattern layer and the second metal pattern layer are configured either in a mesh structure having a net shape or configured in a rectangular pattern structure in which a plurality of rectangle patterns are arranged in matrix. Longitudinal directions and lateral directions of the first metal pattern layer and the second metal pattern layer are mutually matched.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a bandpass filter that selectively transmits electromagnetic waves of a predetermined frequency, and a laminated circuit board that uses this bandpass filter, and in particular to a bandpass filter that has frequency selectivity for electromagnetic waves in a high frequency band of several hundred GHz or more, and a laminated circuit board in which circuit pattern layers are laminated on both sides of this bandpass filter. [Background technology]

[0002] In recent years, there has been increasing use of high-frequency electromagnetic waves, such as centimeter waves with a frequency band of several gigahertz (GHz), and even millimeter waves with a frequency band of 30 to 300 gigahertz, for mobile communications such as mobile phones, wireless LAN, and electronic toll collection systems (ETC).In addition, with the ever-evolving communications environment and the rise of IoT, there is a demand for the development of devices for Beyond 5G and 6G communications, and research into technologies that use radio waves with frequencies in the terahertz (THz, 1000 GHz and above) band is also progressing.

[0003] Thus, as the frequency of electromagnetic waves used increases, specific materials that are compatible with high-frequency electromagnetic waves are required for transmitting and receiving systems such as antenna circuits, testing equipment devices, and also for noise countermeasures for these devices, prevention of electromagnetic wave leakage, etc. In particular, in devices that handle electromagnetic waves in the terahertz band, location dependency cannot be ignored for all materials used, such as conductors within the circuit, circuit boards, and exterior materials, and strict adjustment and design of length, size, and thickness is required.

[0004] Conventionally, a bandpass filter has been proposed that selectively transmits electromagnetic waves of a predetermined frequency in the GHz band and blocks electromagnetic waves of other frequencies, and that is made by laminating a first component made of a mesh formed from a metal or conductive polymer and a second component made of a dielectric material (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. WO2018 / 047937 Summary of the Invention [Problem to be solved by the invention]

[0006] For example, when the bandpass filter described in Patent Document 1 is used as a radome that covers a millimeter-wave radar device, it is required that the material be transparent to electromagnetic waves in the frequency band used for the radar, be resistant to the external environment, have rigidity that allows it to maintain an appropriate distance from the antenna circuit, and have an appropriate thickness that matches the wavelength of the electromagnetic waves used for the radar. Furthermore, because the bandpass filter is placed in close proximity to the radar antenna circuit, if the impedance near the surface of the bandpass filter is not matched to the antenna circuit, reflection and attenuation of the electromagnetic waves will occur, resulting in a problem of reduced transmission efficiency of the electromagnetic waves by the antenna.

[0007] However, because the dielectric constant changes depending on the frequency of the electromagnetic waves being transmitted, even if the material and configuration are appropriate for millimeter-wave radar using frequencies of several tens of GHz, it has been difficult to achieve the electromagnetic wave transparency required for a radome of radar using electromagnetic waves of several hundred GHz or higher, particularly in the terahertz band, i.e., to reduce the reflection of electromagnetic waves of a specified frequency (low reflectivity) and allow more electromagnetic waves to pass through (high transmittance), while also achieving the desired surface impedance value.

[0008] Furthermore, when an antenna circuit for transmitting and receiving electromagnetic waves in a high frequency band, for example, on the order of several hundred GHz, is constructed as a laminated circuit board in which multiple circuit pattern layers are stacked, it is preferable to improve the impedance matching of the circuits formed on each of the stacked layers. However, it has been extremely difficult to ensure impedance matching between each layer while setting the impedance of the laminated circuit board to a desired value relative to the surrounding space.

[0009] The present disclosure is intended to solve the above-mentioned problems, and aims to realize a bandpass filter that can exhibit good frequency selection characteristics for electromagnetic waves in a high frequency band from several hundred GHz to the terahertz band, and further to realize a laminated circuit board in which multiple circuit boards are stacked, in which both the impedance between each layer and the impedance with respect to the surrounding space of the laminated circuit board are well matched. [Means for solving the problem]

[0010] In order to solve the above problems, the bandpass filter disclosed in the present application is a bandpass filter in which a first metal pattern layer is formed on one side of a resin substrate and a second metal pattern layer is formed on the other side, and the first metal pattern layer and the second metal pattern layer are either a mesh structure having a net shape or a rectangular pattern structure in which multiple rectangular patterns are arranged in a matrix, and the first metal pattern layer and the second metal pattern layer are characterized in that their vertical and horizontal directions are aligned with each other.

[0011] The laminated circuit board disclosed in the present application is characterized in that circuit pattern layers are laminated on both sides of the bandpass filter disclosed in the present application with a core material made of a dielectric material interposed therebetween. [Effects of the Invention]

[0012] The bandpass filter disclosed in the present application has metal pattern layers formed on both sides of a resin substrate, each having either a mesh structure or a rectangular pattern structure, which allows the metal pattern layers to absorb electromagnetic waves of specific frequencies incident on the bandpass filter, thereby achieving a frequency filter effect that selectively transmits electromagnetic waves of specific frequencies.

[0013] Furthermore, the laminated circuit board disclosed in the present application has a configuration in which circuit boards each having a circuit pattern layer are laminated on both sides of the bandpass filter disclosed in the present application. In this way, by disposing the bandpass filter that selectively transmits a predetermined frequency in the center of the laminated configuration of the laminated circuit board, in addition to the effect of the bandpass filter, it is possible to achieve impedance matching between the laminated circuits and impedance matching of the entire laminated circuit board with respect to the outside. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view illustrating a first configuration example of a bandpass filter according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view illustrating the mesh structure of a first metal pattern layer and a second metal pattern layer of the bandpass filter of the first configuration example. [Figure 3] FIG. 10 is a perspective view illustrating a second configuration example of the bandpass filter according to the present embodiment. [Figure 4] FIG. 10 is a plan view illustrating a rectangular pattern structure of a first metal pattern layer of the bandpass filter of the second configuration example. [Figure 5] FIG. 1 is an exploded perspective view illustrating a configuration of a multilayer circuit board according to an embodiment of the present invention. [Figure 6] FIG. 2 is a diagram showing the frequency characteristics of the laminated circuit board provided with the bandpass filter of the first configuration example with respect to electromagnetic waves. [Figure 7] FIG. 10 is a diagram showing the frequency characteristics of the laminated circuit board provided with the bandpass filter of the second configuration example with respect to electromagnetic waves. DETAILED DESCRIPTION OF THE INVENTION

[0015] The bandpass filter disclosed in the present application is a bandpass filter having a first metal pattern layer formed on one side of a resin substrate and a second metal pattern layer formed on the other side, wherein the first metal pattern layer and the second metal pattern layer are either a mesh structure having a net shape or a rectangular pattern structure in which a plurality of rectangular patterns are arranged in a matrix, and the vertical and horizontal directions of the first metal pattern layer and the second metal pattern layer are aligned with each other.

[0016] Here, the vertical and horizontal directions of the first metal pattern layer and the second metal pattern layer being aligned with each other means that in a mesh structure (the extension directions of the lattice that makes up the mesh are vertical and horizontal) and a rectangular pattern structure (the arrangement directions of the rectangular patterns are vertical and horizontal), both of which have clear vertical and horizontal directions as the pattern formation directions, the vertical and horizontal directions of the patterns of the metal pattern layers are aligned when the resin substrate is viewed from its thickness direction, i.e., one pattern is not rotated relative to the other pattern.

[0017] With this configuration, the bandpass filter disclosed in the present application can be configured as a bandpass filter having frequency selection characteristics that selectively transmit electromagnetic waves of a predetermined frequency in a high frequency band of several hundred GHz or more.

[0018] In the above-described bandpass filter, when one of the first metal pattern layer and the second metal pattern layer has a mesh structure and the other has a rectangular pattern structure, it is preferable that, when the bandpass filter is viewed in the thickness direction, the rectangular patterns forming the rectangular pattern structure do not straddle the lines forming the mesh structure. By doing so, it is possible to maximize the frequency selectivity of the electromagnetic waves passing through the bandpass filter by utilizing the electromagnetic wave absorption characteristics of the mesh-structured metal pattern layer and the rectangular pattern structure formed on both sides of the resin substrate.

[0019] Here, "the rectangular patterns forming the rectangular pattern structure are not arranged across the lines forming the mesh structure" means that one rectangular pattern overlaps with the lines forming the mesh structure and does not extend beyond either side of the lines forming the mesh structure. More specifically, this means that the meshes of the mesh structure and the lines forming the rectangles of the rectangular pattern overlap, or the rectangular pattern is formed so as to be inside the meshes of the mesh structure.

[0020] It is preferable that the surface resistance values ​​of the first metal pattern layer and the second metal pattern layer are both 60 Ω / □ or less.

[0021] It is also preferable that the mesh structure has an arrangement pitch of 0.1 mm or more and 1.5 mm or less.

[0022] Furthermore, it is preferable that the line width of the lines forming the mesh structure and the rectangular pattern structure is 15 μm or more and 100 μm or less.

[0023] The laminated circuit board disclosed in the present application has circuit pattern layers laminated on both sides of the bandpass filter disclosed in the present application with a core material made of a dielectric material interposed therebetween.

[0024] With this configuration, the laminated circuit board disclosed in the present application can achieve impedance matching between the layers stacked and impedance matching with the external space of the laminated circuit board, in addition to the function of a bandpass filter that selectively transmits electromagnetic waves of a predetermined frequency.

[0025] In the laminated circuit board, it is preferable that the number of the circuit pattern layers laminated on one surface of the bandpass filter is equal to the number of the circuit pattern layers laminated on the other surface of the bandpass filter, thereby improving the function of the bandpass filter included in the laminated circuit board to selectively transmit a predetermined frequency.

[0026] Hereinafter, a bandpass filter and a multilayer circuit board including the bandpass filter disclosed in the present application will be described with reference to the drawings.

[0027] In addition, in the drawings explaining the configuration of the bandpass filter and the laminated circuit board used in the following embodiments, the size of each component shown in the drawings, particularly the size in the thickness direction, is not necessarily shown based on reality in order to make the respective configurations easier to understand.

[0028] (Embodiment) [First example of a bandpass filter configuration] FIG. 1 is an enlarged perspective view of a main part showing a first configuration example of a bandpass filter according to this embodiment.

[0029] 1 is an enlarged view of a main part showing one mesh (lattice) portion of the mesh structure of the first metal pattern layer (and the second metal pattern layer) of the bandpass filter shown in this embodiment. In addition, in order to show the shape of the second metal pattern layer formed on the back surface (the lower surface in the figure) of the resin substrate, the second metal pattern layer is shown pulled out to the bottom in the figure.

[0030] In the first configuration example of the bandpass filter 10 described in this embodiment, the first metal pattern layer 12 and the second metal pattern layer 13 formed on both sides of the resin substrate 11 each have a mesh structure in the form of a mesh (lattice).

[0031] The resin substrate 11 constituting the bandpass filter 10 is a so-called printed circuit board (PCB) excluding flexible substrates, but preferably excludes metal substrates such as aluminum substrates, and substrates made of inorganic materials such as glass and ceramic substrates. When a substrate made of an inorganic material is used for the substrate 11, the disadvantage is that in many cases, these inorganic materials exhibit a high dielectric constant, resulting in large transmission loss. However, on the other hand, because it can be expected to have extremely high strength, it can also be used in applications where strength is particularly important, such as when used as the outermost layer of a laminated circuit board.

[0032] Resin substrates include those in which glass fiber is partially contained in the resin material to improve strength. For example, glass composite substrates (CEM-3) containing glass fiber material, glass epoxy substrates (FR-4), and glass polyimide substrates are included in the resin substrates referred to in this specification.

[0033] While the type of resin for the resin substrate is not limited, resins such as epoxy, polyamide, polyamideimide, polyethylene, polyester, polypropylene, and phenolic resins containing glass fibers are expected to improve strength and are therefore suitable for use as substrates. Among these, polyamideimide, polypropylene, polyethylene, polypropylene, and epoxy resins with a dielectric constant of less than 4.0 are particularly desirable in the present invention. Resins with high dielectric constants result in significant electromagnetic wave loss, making them undesirable when high transmittance is required.

[0034] There is no particular limitation on the thickness of the resin substrate 11, but a thickness of about 50 μm to 3 mm, which is a commonly used thickness, can be suitably used.

[0035] The first metal pattern layer 12 formed on the upper surface of the resin substrate 11 in Figure 1 and the second metal pattern layer 13 formed on the lower surface of the resin substrate 11 in Figure 1 can both be formed using a metal plating film such as an electroless plating film or an electrolytic plating film, or a metal paste.

[0036] In the bandpass filter shown in this embodiment, the vertical and horizontal directions of the first metal pattern layer 12 and the second metal pattern layer 13 are aligned with each other. Here, the vertical and horizontal directions of the two metal pattern layers being aligned means that, when the first metal pattern layer 12 and the second metal pattern layer 13 both have a mesh structure as shown in Fig. 1, the extension directions of the vertical and horizontal lines forming the mesh are the same on both sides of the resin substrate 11.

[0037] A conventionally known method for forming printed wiring on a resin substrate can be used to form the predetermined patterns of the first metal pattern layer 12 and the second metal pattern layer 13. More specifically, a method for transferring a predetermined pattern that has been printed in advance on a transfer sheet or the like by heat pressing or a method for directly forming a pattern on a resin substrate by screen printing or inkjet printing can be suitably used.

[0038] Other methods that can be used include printing a metal paste onto the resin substrate 11 using various printing methods such as inkjet printing or screen printing, applying the above-mentioned metal material to the entire surface of the resin substrate 11 that serves as the base material, masking the area where the metal pattern layer is to be formed, and then removing the conductive material from the area not covered by the mask using acid or the like, or irradiating laser light onto areas other than the metal pattern layer to remove the conductive material.

[0039] In addition, a wide variety of conventional pattern formation methods can be adopted that are suited to the characteristics of the metal material being used, such as a photolithography method using a photocurable resin and a mask pattern, or a method in which a deactivator that inhibits the function of an electroless plating catalyst is applied to the entire surface of the substrate, and then the deactivator is removed from the area where the metal pattern layer is to be formed using light or heat, and then the electroless plating catalyst solution and the electroless plating solution are contacted sequentially to form an electroless plating film in the area where the metal pattern layer is to be formed, and then an electrolytic plating film on top of that.

[0040] It is preferable to form the first metal pattern layer 12 and the second metal pattern layer 13 using a printing method such as inkjet printing or screen printing in order to achieve the desired shape, i.e., the desired pitch and line width, and further to achieve the desired surface resistance value by adjusting the thickness of the first metal pattern layer 12 and the second metal pattern layer 13. Furthermore, it is preferable that the first metal pattern layer 12 and the second metal pattern layer 13 have a lower resistance value, so it is more preferable to use copper (Au) as the material rather than silver (Ag), for example.

[0041] As shown in Figure 1, the bandpass filter 10 shown in this embodiment is configured so that, when viewed from the thickness direction, the formation positions of the grid patterns of the first metal pattern layer 12 and the second metal pattern layer 13 overlap, i.e., the line widths and grid pitches of the first metal pattern layer 12 and the second metal pattern layer 13 are the same, and further, the pattern formation positions are also the same.

[0042] FIG. 2 is a plan view illustrating the mesh structure of the first metal pattern layer and the second metal pattern layer of the bandpass filter of this embodiment.

[0043] The pitch a of the meshes forming the mesh structure, i.e., the distance between the center lines of adjacent meshes, is determined depending on the frequency of the electromagnetic waves to be transmitted by the bandpass filter 10 and the dielectric constant of the substrate material. The inventors' investigations have confirmed that when the dielectric constant of the substrate material is, for example, 2.5 to 3.5, it is preferable to set the pitch a of the mesh structure to approximately the same size as the wavelength of the electromagnetic waves to be transmitted through the bandpass filter. In the bandpass filter 10 according to this embodiment shown in FIG. 1, the frequency of the electromagnetic waves to be absorbed is 300 GHz (wavelength λ≈1 mm), so the pitch a of the mesh structure is approximately 1 mm, and is preferably set to a value between 0.1 mm and 1.5 mm.

[0044] The width b of the lines forming the mesh of the mesh structure is desirably narrower in order to minimize the amount of transmission attenuation of electromagnetic waves occurring in the mesh area, and it is preferable to set the width to 15 μm or more and 100 μm or less, which allows the mesh pitch a and line width b to be formed with precision.

[0045] The manufacturing error range of the mesh structure is approximately ±5% for the entire pattern, and errors in the mesh pitch a, line width b, and the amount of misalignment between the first metal pattern layer 12 and the second metal pattern layer 13 are also within the acceptable range of approximately ±5%.

[0046] Furthermore, in the bandpass filter 10 disclosed in the present application, the vertical and horizontal directions of the first metal pattern layer 12 and the second metal pattern layer 13 are aligned with each other, but if the two metal pattern layers are misaligned in the rotational direction, the tolerance is that the error in the misalignment between the patterns in the part farthest from the center of rotation, where the misalignment amount is greatest, is within ±10%.

[0047] 1 illustrates an example in which the first metal pattern layer 12 and the second metal pattern layer 13 have mesh structures with the same pitch a and line width b, and are arranged in the same positions, but the relationship between the first metal pattern layer 12 and the second metal pattern layer 13 of the bandpass filter 10 disclosed in the present application is not limited to that shown in Fig. 1. A configuration in which metal pattern layers (12, 13) with different pitches (a, a') are formed on both sides of the resin substrate 11 can be adopted, as long as the pitch a of the mesh structure of one (first metal pattern layer 12) is an integer multiple of the pitch a' of the mesh structure of the other (second metal pattern layer 13) and they do not cross each other's lines.

[0048] Furthermore, the line width b of one mesh structure (first metal pattern layer 12) and the line width b' of the other (second metal pattern layer 13) may be different. As mentioned above, the line width b (b') is preferably as narrow as possible because it reduces transmission loss, while the resistance value is preferably lower as the line width b (b') is wider. This is a trade-off relationship. For this reason, it is preferable to use the narrowest line width possible so that the resistance value is smaller than a predetermined value. A specific resistance value of 60 Ω / □ or less is desirable, more preferably 20 Ω / □ or less, and even more preferably 1 Ω / □ or less. The metal materials forming the metal pattern layers 12 and 13 may be different.

[0049] [Second example of a bandpass filter configuration] FIG. 3 is an enlarged perspective view of a main part showing a second configuration example of the bandpass filter according to this embodiment.

[0050] 3 is an enlarged view of a main part, similar to Fig. 1, showing an enlarged view of one mesh (lattice) portion of the mesh structure of the second metal pattern layer provided in the bandpass filter shown in this embodiment. In addition, to explain the relationship between the mesh structure of the second metal pattern layer formed on the back surface (the lower surface in the figure) of the resin substrate and the position of the rectangular pattern of the first metal pattern layer relative to the second metal pattern layer, the second metal pattern layer is shown pulled out downward in the figure, and the first metal pattern layer is shown by a dashed line.

[0051] In the bandpass filter 20 of the second configuration example described in this embodiment, the first metal layer 22 formed on the upper surface of the resin substrate 21 in the drawing has a rectangular pattern structure in which a plurality of rectangular patterns are arranged in a matrix in the vertical and horizontal directions. Also, the second metal pattern layer 23 formed on the lower surface of the resin substrate 21 in the drawing has a mesh structure.

[0052] The resin substrate 21 of the second bandpass filter 20 shown in Figure 3 is a printed circuit board (PCB) containing a resin material, similar to the resin substrate 11 of the bandpass filter 10 of the first configuration example shown in Figure 1, and from the standpoint of the strength (rigidity) and dielectric constant of the substrate itself, a glass epoxy substrate (FR-4) can be suitably used.

[0053] The thickness of the resin substrate 21 is preferably about 50 μm to 3 mm, which is a commonly used thickness, similar to the resin substrate 11 of the bandpass filter 10 of the first configuration example.

[0054] The first metal pattern layer 22 formed on the upper surface of the resin substrate 21 in Figure 3 and the second metal pattern layer 23 formed on the lower surface can also be formed by a conventionally known method of forming printed wiring using a metal plating film such as an electroless plating film or an electrolytic plating film, or a metal paste, similar to the first metal pattern layer 12 and the second metal pattern layer 13 of the bandpass filter 10 of the first configuration example.

[0055] As shown in Figure 3, in the bandpass filter 20 of the second configuration example, the rectangular patterns that make up the rectangular pattern structure of the first metal pattern layer 22 are formed so that a total of 16, four vertically and four horizontally, are located within one opening of the mesh pattern that forms the mesh structure of the second metal pattern layer 23.

[0056] In the case of the bandpass filter 20 of the second configuration example shown in FIG. 3 , when viewed in the thickness direction of the bandpass filter 20, the rectangular pattern of the first metal pattern layer 22 is formed so as not to straddle the lines of the mesh structure of the second metal pattern layer 23 formed on the opposite surface of the resin substrate 21. More specifically, the center lines of the lines forming the mesh structure are formed so as to be positioned in the gaps between the individual rectangular patterns forming the rectangular pattern structure. Note that if the lines forming the mesh structure are wide, it is possible that the lines of the mesh structure and the rectangular pattern may partially overlap when viewed in the thickness direction of the bandpass filter 20. However, in this case, there is no problem because the rectangular pattern does not straddle the lines of the mesh structure, in other words, does not extend to the left or right of the lines of the mesh structure. However, from the viewpoint of minimizing transmission loss, it is preferable that the lines forming the rectangular pattern structure and the lines forming the mesh structure do not overlap when viewed in the thickness direction of the bandpass filter 20.

[0057] FIG. 4 shows the shape of the rectangular pattern structure which is the first metal pattern layer of the bandpass filter of this embodiment.

[0058] 4, the first metal pattern layer 22 of the second configuration example 20 of the bandpass filter shown in this embodiment has hollow rectangular patterns arranged in a matrix in both the vertical and horizontal directions. The rectangular pattern structure is determined according to the frequency of the electromagnetic waves that are selectively transmitted by the bandpass filter 20.

[0059] Specifically, the arrangement pitch c of the rectangular patterns shown in FIG. 4 is set to 1 / constant of the wavelength λ, which is the reciprocal of the frequency f of the electromagnetic wave selectively transmitted by the bandpass filter 20. In the bandpass filter 20 of the second configuration example shown in FIG. 3, if the frequency of the electromagnetic wave selectively transmitted is 300 GHz, the pitch (a shown in FIG. 2) of the second metal pattern layer 23 of the mesh structure is approximately 1 mm, as described above. In this case, by setting the arrangement pitch c of the rectangular pattern structure to 1 / 4 of that, or 0.25 mm, a configuration in which 16 rectangular patterns are arranged in a 4×4 array within one mesh structure opening shown in FIG. 3 is obtained. In this case, if the arrangement pitch c of the rectangular patterns is set to 1 / 2 the pitch a of the mesh structure, then c = 0.5 mm. If the arrangement pitch c of the rectangular patterns is set to 1 / 5 the pitch a of the mesh structure, then c = 0.2 mm.

[0060] The value of d in Figure 4, which represents the size of each rectangular pattern, can be set within a range smaller than the arrangement pitch c of the rectangular patterns. However, particularly when the constant 1 / λ of the wavelength λ of the electromagnetic wave to be transmitted increases and the arrangement pitch c of the rectangular patterns decreases, the value of the opening width e of each rectangular pattern becomes small, resulting in a shape with no openings. As mentioned above regarding the line width b of the mesh structure, if the line width f is too narrow, sufficient resistance cannot be obtained, making it difficult to generate effective radio wave interference. Therefore, it is preferable to set the line width so that a resistance value of 20 Ω / □ or less can be ensured. The relationship between line width and resistance varies depending on the type of metal used, so it is difficult to generalize. For example, for silver paste, a line width of approximately 30 μm or more is preferable to achieve a resistance value of 1 Ω / □, which is the most desirable value. Therefore, to ensure effective openings with this line width, the pitch c should be approximately 5 times that width, or 0.15 mm or more. In this way, after the rectangular pattern is set to values ​​corresponding to the frequency of the electromagnetic waves, the size d of each rectangular pattern, the size e of the opening, and the line width f must be determined to be optimal sizes according to the physical properties of the material used.

[0061] The second metal pattern layer 23 of the bandpass filter 20 of the second configuration example shown in Figure 3 has a mesh structure similar to the first metal pattern layer 12 and the second metal pattern layer 13 of the bandpass filter 10 of the first configuration example.

[0062] The specific shape of the second metal pattern layer 23 is the same as that of the mesh structure shown in Fig. 2. Since the frequency of the electromagnetic waves that are the absorption target is 300 GHz (wavelength λ ≈ 1 mm) and the dielectric constant of the substrate material used is 3.35, the pitch a of the mesh structure is approximately 1 mm, and is preferably 0.1 mm to 1.5 mm. Furthermore, the width b of the lines that form the mesh of the mesh structure is also preferably 15 µm to 100 µm, as in Fig. 2.

[0063] The manufacturing error range for both the rectangular pattern structure of the first metal pattern layer 22 and the mesh structure of the second metal pattern layer 23 is approximately ±10% for the entire pattern, and the pitch c of the rectangular pattern structure, the size d and e of each rectangular pattern, its line width f, the pitch a and line width b of the mesh of the second metal pattern layer 23, and even the amount of misalignment between the first metal pattern layer 22 and the second metal pattern layer 23 are all within the acceptable range of approximately ±10%.

[0064] In Figure 3, 16 rectangular patterns of the first metal pattern layer 22 are shown arranged in one mesh of the mesh of the second metal pattern layer 23. However, as described above, the pitch c of the rectangular patterns formed in the first metal pattern layer 22 is 1 / constant of the pitch a of the mesh structure of the second metal pattern layer 23. Therefore, the number of rectangular patterns included in one mesh of the mesh structure is not limited to 16, and various configurations can be realized in which the same number of rectangular patterns are included in both the vertical and horizontal directions, such as 4 patterns (2 x 2) or 9 patterns (3 x 3).

[0065] [Laminated circuit board] FIG. 5 is an enlarged exploded perspective view of a main part showing the configuration of the multilayer circuit board according to this embodiment.

[0066] The laminated circuit board 100 shown in this embodiment in Figure 5 is composed of the bandpass filter 10 of the first configuration example described in Figure 1, a first laminated circuit layer 30 laminated on the first metal pattern layer 12 side of the bandpass filter 10, and a second laminated circuit layer 40 laminated on the second metal pattern layer 13 side.

[0067] The first laminated circuit layer 30 is made up of three laminated circuit boards, each made up of a circuit pattern layer formed on a core material made of a dielectric, and these are laminated in the following order from the top surface, i.e., from the side farthest from the bandpass filter 10: first circuit pattern layer 31, core material 32, second circuit pattern layer 33, core material 34, third circuit pattern layer 35, and core material 36. Similarly to the first laminated circuit layer 30, the second laminated circuit layer 40 is made up of three laminated circuit boards, each made up of a circuit pattern layer formed on a core material made of a dielectric, and these are laminated in the following order from the bottom surface, i.e., from the side farthest from the bandpass filter 10: first circuit pattern layer 41, core material 42, second circuit pattern layer 43, core material 44, third circuit pattern layer 45, and core material 46.

[0068] The circuit board in which a circuit pattern layer is formed on a core material laminated in the first laminated circuit layer 30 and the second laminated circuit layer 40 is what is called a printed circuit board (PCB) that performs various functions that have been conventionally used, and is configured by using a material similar to the resin substrate used in the bandpass filters 10 and 20 described in this embodiment as the core material, and mounting various circuit components such as integrated circuits, resistors, coils, and capacitors on a wiring pattern formed on the surface of the core material using a conductive material such as copper foil.

[0069] For example, an antenna circuit requires an antenna pattern made of a conductive material such as copper foil to be formed on a resin substrate, which inevitably results in a large board area if all circuit components are to be arranged on a single resin substrate. Therefore, in order to meet the demand for miniaturization of antenna circuit boards and to solve the problem of the tendency of long wiring patterns to pick up external noise, it is preferable to configure the circuit board as a laminated circuit board in which components are distributed across multiple circuit boards and then stacked.

[0070] However, in general, antenna circuits using multilayer circuit boards must take into consideration radio wave interference in the wiring formed on each layer of the laminate, and measures are taken to minimize electromagnetic wave radiation by optimizing the layer configuration and prevent the circuit from being interfered with by external noise. In particular, in antenna circuits that transmit and receive high-frequency electromagnetic waves, the reflectivity increases depending on the frequency of the electromagnetic waves, for example, when the input impedance value of the circuit board located on the top surface of the multilayer circuit board is shifted from the air impedance of 377 Ω, and it becomes necessary to take measures to ensure consistency between the incident electromagnetic waves and the circuit by sacrificing some of the incident electromagnetic waves.

[0071] In contrast, in the laminated circuit board 100 described in this embodiment, the above-mentioned bandpass filter 10 (or 20) is disposed in the center in the stacking direction of the laminated circuit board 100 that constitutes the antenna circuit, and therefore the impedance of the surrounding space can be controlled simultaneously by the filter function of the bandpass filter 10 (20), thereby achieving matching between the antenna circuits formed on each layer of the laminated circuit board 100. As a result, in the laminated circuit board 100 provided with the bandpass filter 10 (20) described in this embodiment, the filter and the antenna circuit are designed as an integrated unit, which makes it easy to optimize the reflection characteristics and transmission characteristics, and eliminates the need to sacrifice antenna input / output for impedance matching, thereby realizing an antenna circuit with high antenna input / output efficiency.

[0072] [Frequency characteristics] The results of a study on the frequency characteristics of electromagnetic waves in the multilayer circuit board according to this embodiment will be described below.

[0073] In the following studies, simulations were performed using full-wave 3D electromagnetic field software "Ansys HFSS (product name: manufactured by ANSYS, Inc.)" that uses the finite element method.

[0074] FIG. 6 is a diagram showing frequency characteristics of incident attenuation and return loss of a laminated circuit board including the bandpass filter of the first configuration shown in FIG.

[0075] 6, the frequency characteristics of the transmission attenuation, which is the attenuation of the electromagnetic waves that are incident on the laminated circuit board and that are transmitted through the back surface of the laminated circuit board, are shown by a thin solid line denoted by reference numeral 61, and the frequency characteristics of the return attenuation, which is the attenuation of the energy of the incident electromagnetic waves that are reflected on the surface of the laminated circuit board, are shown by a thick solid line denoted by reference numeral 62. Both the transmission attenuation and the return attenuation are shown in units of dB.

[0076] The bandpass filter of the first configuration example included in the laminated circuit board whose electromagnetic wave frequency characteristics are shown in Figure 6 has a mesh structure pitch a of 0.76 mm, a mesh line width b of 70 μm, and thicknesses of the metal pattern layer 12 and the second metal pattern layer 13 of 35 μm, and a surface resistance value of the first metal pattern layer 12 and the second metal pattern layer 13 of 0.8 Ω / □.

[0077] The resin substrate 11 of the bandpass filter 10 has a dielectric constant of 3.35 and a thickness of 0.1 mm (100 μm), and since no specific circuit patterns can be assumed for the first laminated circuit layer 30 and the second laminated circuit layer 40, calculations were made assuming that a 13 μm thick space is formed on a 40 μm thick core material (32, 34, 36, 42, 44, 46) with a dielectric constant of 3.35. The thicknesses of the first laminated circuit layer 30 and the second laminated circuit layer 40 are both 159 μm.

[0078] The design values ​​of the mesh structure of the first metal pattern layer 12 and the second metal pattern layer 13 described above were optimized by taking into account the overall impedance of the first laminated circuit layer 30 and the second laminated circuit layer 40 stacked on the bandpass filter 10, and setting the target frequency of the electromagnetic waves selectively transmitted by the bandpass filter 10 to 280 GHz.

[0079] From the frequency characteristics of the transmission attenuation indicated by the reference symbol 61 in FIG. 6, in the laminated circuit board 100 using the bandpass filter 10 of the first configuration example, the transmission attenuation for frequencies in an extremely wide band from about 90 GHz to about 330 GHz, including 280 GHz, which is set as the frequency to be transmitted, is suppressed to −5 dB or less, forming a good transmission region, and in the frequency bands on both sides of this, there are formed blocking regions, which are regions where electromagnetic waves with a transmission attenuation of −10 dB or more are absorbed and transmission is suppressed.

[0080] 6, the frequency characteristic of the return loss indicated by reference numeral 62 shows that in the multilayer circuit board 100 using the bandpass filter 10 of the first configuration example, the return loss is suppressed to -5 dB or less for an extremely wide frequency band from about 100 GHz to about 330 GHz, including 280 GHz, which is set as the frequency to be transmitted. This shows that the multilayer circuit board 100 suppresses reflection on the surface of the multilayer circuit board 100 of electromagnetic waves in a wide band from about 90 GHz to about 330 GHz, including 280 GHz, which is the frequency to be selectively transmitted, and efficiently transmits electromagnetic waves in the frequency band including 280 GHz, which is the set target frequency.

[0081] As shown in Figure 5, the first metal pattern layer 12 and the second metal pattern layer 13 of the bandpass filter 10 included in the laminated circuit board 100 have the same mesh structure, so the frequency characteristics of the return loss shown as symbol 62 in Figure 6 are the same regardless of the incident direction of the electromagnetic wave.

[0082] As described above, it has been confirmed that the laminated circuit board 100 shown in this embodiment functions as a bandpass filter that selectively transmits electromagnetic waves in a wide frequency band including the target frequency of 280 GHz with high transmittance.

[0083] Next, the frequency characteristics of the laminated circuit board 100 provided with the bandpass filter 20 of the second configuration example shown in FIG. 3 with respect to electromagnetic waves were confirmed.

[0084] FIG. 7 is a diagram showing frequency characteristics of transmission loss and return loss of a multilayer circuit board provided with a bandpass filter of the second configuration example.

[0085] The laminated circuit board 100 shown in FIG. 7 employs the bandpass filter 20 of the second configuration example shown in FIG. 3 as the bandpass filter arranged in the center portion in the thickness direction of the laminated circuit board 100 shown in FIG. 5.

[0086] In a second configuration example of a bandpass filter 20, the rectangular patterns of the first metal pattern layer 22 formed on both sides of the resin substrate 21 have an arrangement pitch c of 0.25 mm, an outer diameter d of each rectangular pattern of 0.18 mm, an inner diameter e of 0.11 mm, and a line width f of 35 μm, as shown in FIG. 4. The mesh structure of the second metal pattern layer 23 has a pitch a of 1.00 mm and a mesh line width b of 70 μm, as shown in FIG. 2. As shown in FIG. 3, 16 rectangular patterns are arranged in a 4×4 pattern within one frame of the mesh structure. The thickness of each of the metal pattern layers 22 and 23 is 13 μm, and the surface resistance of the metal pattern layers 22 and 23 is 0.8 Ω / □.

[0087] The resin substrate 21 of the bandpass filter 20 has a dielectric constant of 3.35 and a thickness of 0.1 mm (100 μm), and the first laminated circuit layer 30 and the second laminated circuit layer 40 each have a thickness of 40 μm, as in the case of the laminated circuit board 100 using the bandpass filter 10 of the first configuration example described above, with a space of 13 μm in thickness formed on the base material (32, 34, 36, 42, 44, 46) having a dielectric constant of 3.35. The thickness of each of the laminated circuit layers 30 and 40 is 159 μm.

[0088] As in the case of using the bandpass filter 10 of the first configuration example described above, the design values ​​of the rectangular pattern structure of the first metal pattern layer 22 and the mesh structure of the second metal pattern layer 23 were optimized by taking into account the overall impedance of the first laminated circuit layer 30 and the second laminated circuit layer 40 stacked on the bandpass filter 20, and setting the target frequency of the electromagnetic waves selectively transmitted by the bandpass filter 20 to 280 GHz.

[0089] The frequency characteristics of the laminated circuit board 100 equipped with the band-pass filter 20 of the second configuration example, shown in FIG. 7 by the thin solid line denoted by the symbol 71, form a favorable transmission region in which the transmission attenuation for frequencies in the band from approximately 255 GHz to approximately 285 GHz, including 280 GHz, which is set as the frequency to be transmitted, is suppressed to −5 dB or less, and in the frequency bands on both sides of this band, there are formed stop regions in which electromagnetic waves with a transmission attenuation of −8 dB or more are absorbed and transmission is suppressed.

[0090] As shown in Figure 3, in the bandpass filter 20 of the second configuration example, the first metal pattern layer 22 and the second metal pattern layer 23 have different structures, so the frequency characteristics of the return loss, which indicates the attenuation, in dB, of the electromagnetic waves incident on the laminated circuit board 100 that are reflected on the surface of the laminated circuit board 100, differ depending on the side on which the electromagnetic waves are incident.

[0091] The frequency characteristics indicated by the dashed line 72 in Fig. 7 represent the frequency characteristics of the return loss of the electromagnetic wave incident from the first metal pattern layer 22 side having a rectangular pattern structure. Also, the frequency characteristics indicated by the thick solid line 73 in Fig. 7 represent the frequency characteristics of the return loss of the electromagnetic wave incident from the second metal pattern layer 23 side having a mesh structure.

[0092] As shown in Figure 7, the frequency characteristics of the return loss of electromagnetic waves incident from the first metal pattern layer 22 side (symbol 82) and the frequency characteristics of the return loss of electromagnetic waves incident from the second metal pattern layer 23 side (symbol 83) both have return loss suppressed to -5 dB or less for frequencies in the band from approximately 260 GHz to approximately 290 GHz, including the target frequency of 280 GHz.This shows that the laminated circuit board 100 suppresses reflection on the surface of the laminated circuit board 100 of electromagnetic waves having frequencies near the 280 GHz frequency band, which is the frequency band to be selectively transmitted, and can efficiently transmit electromagnetic waves in the selected frequency band.

[0093] As explained above, it has been confirmed that a laminated circuit board including the bandpass filter disclosed in the present application in its central portion in the thickness direction functions as a bandpass filter that selectively transmits electromagnetic waves in a wide frequency band including the target frequency of 280 GHz with high transmittance. In addition to this, it has the effect of facilitating impedance matching of each wiring pattern layer when constructing the above-mentioned laminated circuit board, and further has the effect of being able to adjust the impedance around the laminated circuit board, making it particularly suitable for use as an antenna circuit for transmitting and receiving high-frequency electromagnetic waves.

[0094] In the above study, the frequency characteristics were shown when the first metal pattern layer and second metal pattern layer of the bandpass filter were designed with a target frequency of 280 GHz electromagnetic waves, which is the so-called 300 GHz band. However, for electromagnetic waves of frequencies in the terahertz band, which is a higher frequency band, it is possible to realize a laminated circuit board with a bandpass filter function that has similarly good frequency selective transmission characteristics by designing the shapes of the mesh structure and rectangular pattern structure of the first metal pattern layer and second metal pattern layer, i.e., the mesh pitch and the arrangement pitch and size of the rectangular pattern, to match the frequency of the electromagnetic waves to be transmitted.

[0095] Furthermore, the laminated circuit board disclosed in the present application can be used particularly well as a laminated circuit board that constitutes the above-mentioned antenna circuit, taking advantage of its frequency-selective transparency for high-frequency electromagnetic waves and its ability to facilitate impedance matching in the laminated circuit. Furthermore, if it is applied to a lens antenna in which a lens is provided in front of the antenna, it becomes possible to design it in such a way that the matching between the lens and the antenna is improved and reflection loss is reduced.

[0096] In an antenna circuit formed using a laminated circuit board, electromagnetic waves are received by circuits located on upper layers of the circuit board, frequency-modulated in a direction that successively lowers the frequency, and input to a receiver by a circuit on the bottom layer. However, in the laminated circuit board shown in this embodiment, a band-pass filter performs a filtering function before the waves reach the lower layers, thereby enabling noise removal. Furthermore, the laminated circuit board includes a robust band-pass filter in which metal pattern layers are formed on both sides of a resin substrate, thereby increasing the strength of the laminated circuit board. Therefore, the radome formed to protect the antenna circuit board does not need to be strong enough to protect the antenna circuit board, and it only needs to function as a surface protection material. This makes it possible to select a resin material with as small a dielectric tangent as possible, thereby reducing the effect of the radome on the impedance of the antenna circuit surface, and as a result, improving the efficiency and S / N ratio of the antenna circuit.

[0097] In the above embodiment, the first metal pattern layer and the second metal pattern layer are both described as having a mesh structure, and as a combination of a rectangular pattern structure and a mesh structure. However, both metal pattern layers can have a rectangular pattern structure. Since the input / output impedance of the bandpass filter changes depending on the pattern arrangement of the first metal pattern layer and the second metal pattern layer, the pattern combination is optimized to achieve impedance matching with the antenna circuit.

[0098] In addition, when both the first metal pattern layer and the second metal pattern layer have rectangular pattern structures, the rectangular pattern structures of the first metal pattern layer and the second metal pattern layer must be arranged at a pitch c equal to a constant multiple of the wavelength of the electromagnetic waves to be absorbed by the bandpass filter, as described above. Here, the relationship between the two rectangular patterns, similar to the relationship with the mesh structure described above, can be any combination as long as the pitch c of one is a constant multiple of the pitch c' of the other and they do not cross the lines forming each other's rectangular patterns. For example, if one rectangular pattern has a large rectangular pattern with a side d and the other has a small rectangular pattern with a side d' that can be arranged inside it, the arrangement pitch c of the small rectangular pattern must also be isotropically continuous. Therefore, either all of the rectangular patterns constituting the small-pitch rectangular pattern are arranged within the openings of the rectangular patterns constituting the large-pitch rectangular pattern, or the rectangular patterns constituting the small-pitch rectangular pattern are arranged at a predetermined pitch within the openings of the rectangular patterns constituting the large-pitch rectangular pattern and in the arrangement intervals of the rectangular patterns constituting the large-pitch rectangular pattern.

[0099] Furthermore, in the above-described embodiment, the laminated circuit board disclosed herein has been exemplified in which the first circuit pattern layer and the second circuit pattern layer disposed on both sides of the bandpass filter each have a three-layer laminated structure. However, the circuit pattern layers disposed on both sides of the bandpass filter of the laminated circuit board disclosed herein are not limited to a three-layer laminated structure. Circuit pattern layers may be formed by laminating one or more layers selected according to the area of ​​the board and the circuit components to be disposed. The overall dielectric constant of the circuit pattern layers laminated on both sides of the bandpass filter is preferably close to λ / 4√ε, where λ (=1 / f) is the reciprocal of the target frequency of the electromagnetic waves selectively transmitted by the bandpass filter. Within this range, the total number of circuit pattern layers disposed on both sides of the bandpass filter may be different. However, in order to achieve impedance matching of the circuit pattern layers in the laminated circuit board, it is more preferable that the number of layers of the first circuit pattern layer and the second circuit pattern layer be the same. [Industrial Applicability]

[0100] The bandpass filter and the laminated circuit board including the bandpass filter disclosed in the present application are useful as a bandpass filter and a laminated circuit board having good frequency selective transmission performance for electromagnetic waves in the hundreds of GHz band or higher high frequency band. [Explanation of symbols]

[0101] 10 Bandpass Filter 11 Resin substrate 12 First metal pattern layer 13 Second metal pattern layer 30 First laminated circuit 40 Second laminated circuit 100 Multilayer Circuit Board

Claims

1. A bandpass filter having a resin substrate on one surface of which a first metal pattern layer is formed and on the other surface of which a second metal pattern layer is formed, The first metal pattern layer and the second metal pattern layer have either a mesh structure or a rectangular pattern structure in which a plurality of rectangular patterns are arranged in a matrix, A bandpass filter, wherein the first metal pattern layer and the second metal pattern layer are aligned in a vertical direction and a horizontal direction.

2. When one of the first metal pattern layer and the second metal pattern layer has a mesh structure and the other has a rectangular pattern structure, 2. The bandpass filter according to claim 1, wherein, when the bandpass filter is viewed in the thickness direction, the rectangular patterns forming the rectangular pattern structure are not arranged across the lines forming the mesh structure.

3. 2. The bandpass filter according to claim 1, wherein the surface resistance values ​​of the first metal pattern layer and the second metal pattern layer are both 60 Ω / □ or less.

4. 2. The bandpass filter according to claim 1, wherein the mesh structure has an arrangement pitch of 0.1 mm or more and 1.5 mm or less.

5. 2. The bandpass filter according to claim 1, wherein the mesh structure and the rectangular pattern structure each have a line width of 15 μm or more and 100 μm or less.

6. 6. A laminated circuit board, comprising: the bandpass filter according to claim 1; and a circuit pattern layer laminated on each of both sides of the bandpass filter via a core material made of a dielectric material.

7. 7. The laminated circuit board according to claim 6, wherein the number of the circuit pattern layers laminated on one surface of the bandpass filter is equal to the number of the circuit pattern layers laminated on the other surface of the bandpass filter.

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