High-frequency multilayer substrate

Abstract

To provide a high-frequency multilayer substrate capable of having less reflection in a wide band, and having impedance matching.SOLUTION: A high-frequency multilayer substrate 100 comprises: a micro strip line 31 that includes a front layer signal line 31a arranged onto a front surface of a first dielectric layer 21, and is extended to a X direction; and a strip line 37 having a triplate structure. The high-frequency multilayer substrate 100 further comprises a conversion part 30 that connects the micro strip line 31 and the strip line 37. The conversion part 30 converts an electromagnetic field transmission mode of a high frequency signal transmitted to the strip line 37 from the micro strip line 31 into a transmission mode adopted to the strip line 37, and converts the electromagnetic field transmission mode of a high-frequency signal transmitted to the micro strip line 31 from the strip line 37 into the transmission mode adopted to the micro strip line 31.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a connection structure between a strip line and a microstrip line that has improved reflection characteristics over a wide band. [Background technology]

[0002] In order to achieve small size and high density in high-frequency boards, strip lines with a triplate structure are often used, in which the board is multi-layered and high-frequency wiring is passed through the board. The strip lines with a triplate structure in the inner layers of a multi-layered board can increase the degree of freedom in circuit connections by utilizing multi-layered wiring. Furthermore, the triplate structure strip line in the inner layer of the board also makes it possible to form a distributed constant circuit (such as a filter circuit) in the inner layer, enabling a significant reduction in size and density of high-frequency circuits to be achieved.

[0003] In a multi-layer high-frequency board, when mounting circuit components on the board surface or when connecting an external device to the multi-layer high-frequency board, it is necessary to expose the high-frequency wiring to the board surface layer. Microstrip lines are used for high-frequency wiring on the surface of the board. For this reason, a high-frequency multilayer board requires a connection portion for connecting the strip line and the microstrip line.

[0004] Regarding the connection, a method is known in which a strip line and a microstrip line are connected by an internally plated through-hole, in which an internally plated through-hole conductor penetrates vertically through a multilayer board to connect a signal line of a strip line in a triplate structure on an inner layer to a signal line of a microstrip line on a surface layer.

[0005] The above connection method using through holes with plated insides can have a problem that the electromagnetic field propagating through one transmission line cannot be smoothly transmitted to the other transmission line due to a sudden change in the transmission line shape (signal line) between the microstrip line in the surface layer and the strip line with a triplate structure in the inner layer, resulting in large signal reflection. Since it is not easy to analyze the electromagnetic field distribution at the connection part of the transmission lines, it has been conventionally considered by replacing it with a circuit model. In the circuit model, the transmission impedance of the two transmission lines, the triplate structure strip line in the inner layer and the microstrip line in the surface layer, is matched (for example, 50 Ω) to transmit smoothly. In the circuit model, the sudden change in the shape at the connection part of these two transmission lines is considered to be an impedance element added to the connection part, and this impedance mismatch has been considered to be the cause of large signal reflection.

[0006] A manufacturing process for a high frequency multilayer substrate for forming a high frequency transmission circuit will be described. The manufacturing process for high frequency multilayer boards includes an inner layer process and an outer layer process. First, in the inner layer process, the conductor layer of the inner substrate is etched to form wiring and ground patterns. After that, the pattern positions of each substrate are aligned, and the substrates are laminated with a prepreg material (insulating layer) sandwiched between them, and then press molded. Then, in the outer layer process, drilling, through-hole plating, pattern formation by etching the outer conductor layer, printing, outer shape processing, etc. are performed to complete the multilayer board.

[0007] In conventional methods (eg, Patent Document 1), the main cause of large signal reflection is said to be impedance mismatch, which is caused by a structure in which a conductive through-hole in a conversion section of a transmission line penetrates to a lower layer. In the high-frequency multilayer board of Patent Document 1, the part of the layer below the central conductor of the strip line of the through-hole of the connection part is not necessary for connecting the strip line and the microstrip line, and this unnecessary conductor part functions as a stub (stray capacitance is added to the connection part as an impedance element), which is thought to be the cause of the large signal reflection. Therefore, it is said that by providing an insulating hole that is connected to the through hole, has no conductor layer inside, and has a flat end, signal reflection is not large. The unnecessary conductor part that functions as a stub is considered to be an impedance element added to the connection part, and is physically removed. However, since a machining process for the through-hole conductor portion must be added in addition to the normal outer layer process, there is a problem that the number of steps and time required to manufacture a high-frequency multilayer board increases compared to the standard number of steps and time.

[0008] Also, another prior art (eg, Patent Document 2) shows a form of connection between a coaxial line that is vertically connected to a multilayer substrate and a strip line with a triplate structure. Patent Document 2 also claims that the reason for the large signal reflection in the above connection configuration is impedance mismatch, which is mainly caused by a structure in which the through-hole conductor of the conversion portion of the transmission line penetrates to the lower layer. To address this impedance mismatch, Patent Document 2 employs a structure that achieves impedance matching by adding a stub pattern (matching circuit) with a length of λ / 4 (λ: wavelength) to the bottom surface of the penetrating through-hole conductor. Therefore, it is possible to eliminate reflection at a specific frequency, which is a matching condition determined by the stub length. However, since the matching conditions are limited to a specific frequency, it is not possible to obtain matching over a wide band in the first place.

[0009] In the above-mentioned conventional technique (Patent Document 1), it is a common method to make the transmission impedance of the strip line and the microstrip line match (for example, 50Ω).

[0010] In this case, when comparing the signal line width of each transmission line, the transmission line width of the inner layer triplate structure strip line is narrower than the transmission line width of the surface layer microstrip line, as shown in Fig. 1 of Patent Document 1. Although it depends on the dielectric constant of the substrate, the strip line width is narrowed to about 1 / 4 to 1 / 2. There is a limit to etching precision, and when the line width is narrower than the limit, problems arise due to manufacturing variations. When forming a distributed constant circuit (for example, a filter circuit) using a strip line with an inner layer triplate structure, variations in pattern dimensions (line width and distance) due to insufficient etching precision lead to variations in the impedance of the circuit components, which in turn leads to variations in the circuit characteristics (center frequency, transmission characteristics, etc. in a filter circuit). It is also important to make the line width of the strip line as wide as that of a microstrip line so that it is not affected by etching precision. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 4585587 [Patent Document 2] Patent No. 6305066 Summary of the Invention [Problem to be solved by the invention]

[0012] The present disclosure aims to provide a high-frequency multilayer board that is easy to manufacture without additional processing, suppresses characteristic variations in distributed constant circuits of inner layer strip lines, and has low reflection over a wide band and impedance matching. [Means for solving the problem]

[0013] The high frequency multilayer substrate according to the present disclosure comprises: A plurality of stacked ground conductors; a dielectric region sandwiched between ground conductors at both ends in a lamination direction; a microstrip line having a surface signal line on a surface of the dielectric region and extending in a direction perpendicular to the lamination direction; a strip line having an inner layer signal line inside the dielectric region and extending in the perpendicular direction; a conversion unit that converts a transmission mode of an electromagnetic field of a high-frequency signal output from the microstrip line into a transmission mode that is compatible with the strip line; Equipped with The strip line has an appropriate distance between the upper and lower ground planes sandwiching the inner layer signal line, i.e., a dielectric thickness, which is ensured by using a plurality of layers of a multilayer board. The conversion unit is a first conversion line that extends from the microstrip line in the extending direction of the microstrip line and gradually increases a first width direction component of an electric field of a high frequency signal output from the microstrip line along a width direction of the surface signal line as it moves away from the extending direction of the microstrip line; a vertical coaxial line connected to the first conversion line and extending in the lamination direction from the surface of the dielectric region to the inside of the dielectric region; a second conversion line that extends from the strip line toward the vertical coaxial line in the direction in which the strip line extends within the dielectric region and is connected to the vertical coaxial line, and that gradually reduces a second width direction component of the electric field of the high frequency signal output from the vertical coaxial line along the width direction of the inner layer signal line as it moves away from the vertical coaxial line toward the strip line; Equipped with. Effect of the Invention

[0014] The high frequency multilayer board of the present disclosure has a conversion section, and the electromagnetic field is smoothly transmitted and converted by the conversion section. This makes it possible to provide a high frequency multilayer board with low reflection over a wide band and impedance matching. In addition, the high frequency multilayer board of the present disclosure has the same width of the surface layer signal line and the inner layer signal line. For a strip line signal line whose width is smaller than that of a microstrip line, the high frequency multilayer board of the present disclosure can ensure a wide strip line signal line width by appropriately ensuring the dielectric thickness of the strip line. This makes it possible to suppress the characteristic variation of the distributed constant circuit of the inner layer strip line. [Brief description of the drawings]

[0015] [Figure 1] 1 is a perspective view of a high-frequency multilayer substrate 100 according to a first embodiment, with a portion thereof in cross section. [Diagram 2] 1A and 1B are a top view and a cross-sectional view of a high-frequency multilayer substrate 100 according to a first embodiment. [Diagram 3] FIG. 2 is a plan view of each ground conductor in the first embodiment. [Figure 4] FIG. 2 is a perspective view of each line in the first embodiment. [Diagram 5] FIG. 2 is a diagram of the first embodiment, showing an image of an electric field at a cross section of each line. [Figure 6] FIG. 11 is a diagram of the first embodiment, showing a curved shape that can be substituted for a tapered shape. [Figure 7] FIG. 1 is a perspective view of a high-frequency multilayer substrate 100-1 according to a first modified example of the first embodiment, with a part in section. [Figure 8] 1A and 1B are a top view and a cross-sectional view of a high-frequency multilayer substrate 100-1 according to a first modified example of the first embodiment. [Figure 9] FIG. 1 is a diagram of the first embodiment, showing the vicinity of a penetrating through hole 34a in each ground conductor of a high-frequency multilayer board 100-1 which is a first modified example. [Figure 10] FIG. 1 is a perspective view, partly in section, showing a high-frequency multilayer substrate 100-2 according to a second modified example of the first embodiment. [Figure 11]FIG. 11 is a perspective view, partly in section, showing a high-frequency multilayer substrate 100-3 according to the first embodiment, which is a third modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In the description of the embodiments and the drawings, the same elements and corresponding elements are denoted by the same reference numerals. Descriptions of elements denoted by the same reference numerals will be omitted or simplified as appropriate.

[0017] Embodiment 1 ***Configuration Description*** Hereinafter, a high frequency multilayer substrate 100 according to the first embodiment will be described with reference to FIGS. FIG. 1 is a perspective view of a high-frequency multilayer substrate 100, with a portion thereof in cross section. FIG. 2 is a top view and a cross-sectional view of the high frequency multilayer substrate 100. The cross-sectional view corresponds to pqrs in Figure 1. FIG. 3 shows a plan view of each ground conductor in the high-frequency multilayer substrate 100, in which each ground conductor is viewed in the -Z direction. FIG. 4 shows a perspective view of each line. FIG. 5 shows an image of the electric field at the cross section of each line.

[0018] The cross section aa in FIG. 2 corresponds to FIG. 4(a) and FIG. 5(a). The b1-b1 and b2-b2 cross sections in FIG. 2 correspond to FIG. 4(b) and FIG. 5(b). The c1-c1 and c2-c2 cross sections in FIG. 2 correspond to FIG. 4(c) and FIG. 5(c), The cross section dd in FIG. 2 corresponds to FIG. 4(d) and FIG. 5(d).

[0019] 1 is cut at the center of the surface layer signal line 31a and the inner layer signal line 37a of the microstrip line 31 and the strip line 37 that are connected on the left and right sides of the high-frequency multilayer substrate 100. The high-frequency multilayer substrate 100 has five conductor layers of the ground conductor and four dielectric regions. Note that the high-frequency multilayer substrate 100 is assumed to be a commonly used glass epoxy multilayer substrate.

[0020] (Direction definition) FIG. 1 shows XYZ coordinates. The +X or -X direction is the horizontal direction. The +Z or -Z direction is the vertical direction. The vertical direction is also the up-down direction. The +Z direction is the upward direction, and the Z direction is the downward direction. The left side of FIG. 1 shows a microstrip line 31 on the upper surface layer. The right side of FIG. 1 shows a strip line 37 on an inner layer.

[0021] (Configuration of high frequency multilayer substrate 100) The high-frequency multilayer substrate 100 includes five stacked ground conductors, a dielectric region, a microstrip line 31, a strip line 37 having a triplate structure, and a conversion section 30. The dielectric region is the entire first dielectric layer 21 to the fourth dielectric layer 24. The number of ground conductors is just an example and is not limited to five. The conversion unit 30 converts the transmission mode of the high-frequency electromagnetic field transmitted from the microstrip line 31 to the strip line 37 into a transmission mode that is compatible with the strip line 37, and also converts the transmission mode of the high-frequency electromagnetic field transmitted from the strip line 37 to the microstrip line 31 into a transmission mode that is compatible with the microstrip line 31. As shown in FIG. 2, the conversion section 30 includes a first tapered section 32, a half coaxial line 33, a vertical coaxial line , a horizontal coaxial line 35, and a second tapered section .

[0022] (Conversion unit 30) The high frequency multilayer substrate 100 is characterized by a transition section 30 between a microstrip line 31 and a strip line 37 of a triplate structure. On the microstrip line 31 side of the transition section 30, the configuration of the microstrip line 31 is gradually converted into a half-split coaxial line 33 by a first taper section 32 toward the vertical coaxial line 34. The line width W31a of the surface signal line 31 of the microstrip line 31 is the same from the microstrip line 31 to the vertical coaxial line 34. Similarly, on the stripline 37 side of the transition portion 30, the configuration of the stripline 37 is gradually converted into a horizontal coaxial line 35 by the second tapered portion 36 as it approaches the vertical coaxial line 34. The line width W37a of the inner layer signal line 37a of the stripline 37 having the triplate structure is the same from the stripline 37 to the vertical coaxial line 34.

[0023] (Connection Relationship of Each Transmission Line in the Converter 30) The microstrip line 31 on the upper surface layer and the strip line 37 on the inner layer are connected via a conversion section 30. To connect the surface layer and the inner layer, it is essential to connect the signal lines (surface layer signal line 31a and inner layer signal line 37a) with a vertical penetrating through hole 34a. The through-hole 34a is connected to the surrounding ground through-hole 51 and the vertical coaxial line 34 Therefore, the conversion unit 30 becomes a transmission line conversion circuit of "microstrip line 31-coaxial line (including half-split coaxial line)-strip line 37". If the portion that changes the transmission direction from horizontal to vertical at a right angle is connected in a coaxial line configuration, the change in transmission direction is a change in the same electromagnetic field mode, and the electromagnetic field can be transmitted. Therefore, the conversion unit 30 has a converter configuration of five portions, namely, the half-split coaxial line 33, the vertical coaxial line 34, and the horizontal coaxial line 35, and the first taper section 3 and the second taper section 36 on both sides, so that the electromagnetic field is transmitted smoothly.

[0024] (Microstrip line 31) The microstrip line 31 will be described with reference to Figures 4(a) and 4(b). Figure 4(a) shows the microstrip line 31 of the high-frequency multilayer substrate 100. The microstrip line 31 is composed of a surface signal line 31a, a first dielectric layer 21, and a second ground conductor 12. Figure 5(a) shows an image of the electric field generated in the microstrip line 31 with arrows. The arrows in the other figures also show the electric field.

[0025] (First tapered portion 32) As shown in Fig. 2, the shape of the microstrip line 31 changes to a half-coaxial line 33 via a first tapered portion 32. In the first ground conductor 11 of Fig. 3, a tapered shape is formed at "p1-p2" and "p3-p4". The half-coaxial line 33 is also called a grounded coplanar structure. The connection portion of the microstrip line 31 and the first taper portion 32 has the configuration shown in FIG. 4(a), and the first ground conductors 11 on both sides of the surface signal line 31a are sufficiently separated from the surface signal line 31a. Here, in the first taper portion 32, the gap between the first ground conductors 11 on both sides and the surface signal line 31a narrows in a tapered shape toward the half-coaxial line 33, approaching the shape of the half-coaxial line 33 (grounded coplanar structure). The first taper portion 32 has a grounded coplanar structure at the connection portion with the half-coaxial line 33. FIG. 5(b) shows an image of an electric field generated in the half-coaxial line 33 (grounded coplanar structure) with arrows. By changing the shape from the microstrip line 31 to the half-coaxial line 33 (grounded coplanar structure), the electromagnetic field distribution changes from Fig. 5(a) through Fig. 5(b) to Fig. 5(e). Fig. 5(e) is a diagram showing the electromagnetic field distribution in the half-coaxial line 33 as a half-coaxial line. That is, the electromagnetic field distribution starts from a state in which it is concentrated in the dielectric part directly below the surface signal line 31a of the microstrip line 31 (Fig. 5(a)), and gradually spreads in the left and right directions as it moves away from the microstrip line 31. Finally, the electromagnetic field distribution changes to a distribution that exists below the surface signal line 31a of the half-coaxial line 33 and in the dielectric parts on the left and right.

[0026] (Half-split coaxial line 33) The shape of the half-split coaxial line 33 (grounded coplanar structure) is shown in Fig. 4(b). As shown in Fig. 4(b), the grounded coplanar structure is formed of a first ground conductor 11, a first dielectric layer 21, and a second ground conductor 12 on both sides of the surface signal line 31a with a gap therebetween. The first ground conductor 11 and the second ground conductor 12 are connected by a plurality of ground through holes 51. As described in the explanation of the first tapered portion 32, in the grounded coplanar structure, since there are ground conductors below and on the left and right of the surface signal line 31a, the electromagnetic field exists in the dielectric parts below and on the left and right.

[0027] (Vertical coaxial line 34) The configuration of the vertical coaxial line 34 will be described. The vertical coaxial line 34 is composed of a through hole 34a and the first ground conductor 11 to the fifth ground conductor 15 surrounding the through hole 34a. The through hole 34a penetrates from the first ground conductor 11 in the top layer to the fifth ground conductor 15 in the bottom layer. The through hole 34a is a signal line. The five ground conductors, the first ground conductor 11 to the fifth ground conductor 15 surrounding the through hole 34a, are electrically connected to each other by a large number of ground through holes 51. FIG. 5(f) is a schematic diagram showing the distribution of the electromagnetic field in the vertical coaxial line 34 as a coaxial line. The electromagnetic field distribution of the vertical coaxial line 34 is a shape that is uniformly distributed in the circumferential direction in the dielectric layer between the central conductor and the outer conductor (axially symmetric distribution). Penetrating through hole 34a, which is a signal line, is connected to surface signal line 31a of half-split coaxial line 33 on the top layer, and is connected to inner-layer signal line 37a of horizontal coaxial line 35 on the third inner conductor layer (layer of third ground conductor 13). In Fig. 1, surface signal line 31a extends in the -X direction and inner-layer signal line 37a extends in the +X direction, in straight lines of 180 degrees, with penetrating through hole 34a at the center, but because the electromagnetic field distribution of vertical coaxial line 34 is axially symmetric, inner-layer signal line 37a can be selected at any angle on the XY plane.

[0028] (Land 41, 42, 43) Lands 41, 42, and 43 are formed on three conductor layers, the top surface, the bottom surface, and the triplate signal surface (the surface on which the inner layer signal line 37a exists) of the penetrating through hole 34a. The other conductor layers are landless. The land diameter of the top and bottom surfaces of the penetrating through hole 34a is equivalent to the line width W31a of the surface layer signal line 31a which is the signal line of the microstrip line 31. The land diameter of the triplate signal surface of the penetrating through hole 34a is equivalent to the line width W37a of the inner layer signal line 37a which is the signal line of the strip line 37.

[0029] (Horizontal coaxial line 35) FIG. 4(c) shows a horizontal coaxial line 35. The horizontal coaxial line 35 has a structure in which an inner-layer signal line 37a and first to fifth ground conductor surfaces are present in a dielectric layer between the upper first ground conductor 11 and the lower fifth ground conductor 15, surrounding the dielectric layer. FIG. 5(c) shows the distribution of the electromagnetic field in the horizontal coaxial line 35. The electromagnetic field is present in the inner-layer signal line 37a and in the dielectric layer between the upper ground conductor surface and the lower ground conductor surface, and is particularly concentrated directly above and below the inner-layer signal line 37a.

[0030] (Second tapered portion 36) 4(c) and 4(d) also show the shape of the second tapered portion 36. In the second ground conductor 12, the third ground conductor 13, and the fourth ground conductor 14 in FIG. 3, the tapered shapes are formed by "q1-q2" and "q3-q4". As shown in FIG. 2, the horizontal coaxial line 35 changes in shape to a strip line 37 via the second tapered portion 36. The connection portion of the second tapered portion 36 and the horizontal coaxial line 35 has the shape of the horizontal coaxial line 35 (FIG. 4(c)), and the connection portion of the second tapered portion 36 and the strip line 37 has the shape of the strip line 37 (FIG. 4(d)). The shape of the strip line 37 will be described. As shown in FIG. 4(d), the strip line 37 is composed of an inner-layer signal line 37a, a first ground conductor 11 and a fifth ground conductor 15 sandwiching the inner-layer signal line 37a, and a dielectric layer sandwiched between the first ground conductor 11 and the fifth ground conductor 15. The first ground conductor 11 on the upper surface and the fifth ground conductor 15 on the lower surface are also connected by a large number of ground through holes 51. In the strip line 37, the ground conductors 12-14 on both sides of the inner-layer signal line 37a are sufficiently separated. In contrast, in the second tapered portion 36, the gap (distance) between the inner-layer signal line 37a and the ground conductors 12-15 narrows in a tapered shape toward the horizontal coaxial line 35, so that the connection point with the horizontal coaxial line 35 has the shape of the horizontal coaxial line 35. When this shape change is viewed from the horizontal coaxial line 35 toward the strip line 37, the electromagnetic field distribution changes from Fig. 5(c) to Fig. 5(d). That is, the distribution (Fig. 5(cd)) that exists above and below the inner layer signal line 37a of the horizontal coaxial line 35 and in the dielectric parts on the left and right gradually changes to a distribution (Fig. 5(d)) that exists above and below the inner layer signal line 37a.

[0031] (Stripline 37) The configuration of the strip line 37 and the distribution of the electromagnetic field are as described in the description of the second tapered section . In the first conversion path and the second conversion path, the transmission mode of the electromagnetic field of the high frequency signal is gradually converted by using the tapered shape of each ground conductor. To gradually convert the transmission mode, the shape of each ground conductor may be "smoothly changed", not limited to the tapered shape. FIG. 6 is a diagram for explaining "smooth change". In the high frequency multilayer substrate 100 shown in FIGS. 1 to 5, the transmission mode of the electromagnetic field of the high frequency signal is gradually converted by the tapered shapes of the first ground conductor 11, the second ground conductor 12, the third ground conductor 13, and the fourth ground conductor 14. In FIG. 6, a curved shape is shown as a shape that "changes smoothly". In the first ground conductor 11 in FIG. 6, the width W2 in the microstrip line 31 becomes the width W1 in the half-split coaxial line 33 due to the curved shape. The same applies to the second ground conductor 12 to the fourth ground conductor 14. In the case of the curved shape, the transmission mode of the electromagnetic field of the high frequency signal is gradually converted, as in the case of the tapered shape.

[0032] ***Effects of 100 high frequency multilayer boards*** Since the high-frequency multilayer substrate 100 has the conversion section 30, it is possible to transmit high-frequency signals from the microstrip line 31 to the strip line 37 with reduced reflection, and also possible to transmit high-frequency signals from the strip line 37 to the microstrip line 31 with reduced reflection.

[0033] <Variation 1> 7 to 9 are diagrams showing a high frequency multilayer board 100-1 which is a modified example of the high frequency multilayer board 100. The high frequency multilayer board 100-1 has six ground conductors and is made up of five dielectric layers. FIG. 7 is a perspective view showing a part of the high frequency multilayer substrate 100-1 in cross section. FIG. 8 is a top view and a cross-sectional view of the high frequency multilayer substrate 100-1. FIG. 9 is a diagram showing the vicinity of the penetrating through-holes 34a in each ground conductor of the high-frequency multilayer substrate 100-1.

[0034] (Dielectric Thickness) By adjusting the thicknesses H1 and H2 of the dielectric material described later with reference to FIG. 8, the line width W31a of the surface layer signal line 31a and the line width W37a of the inner layer signal line 37a can be made equal to each other. 7, the line width W31a of the surface layer signal line 31a and the line width W37a of the inner layer signal line 37a are equal to each other. For example, the value obtained by dividing the line width W37a by the line width W31a is greater than 2 / 3 and equal to or less than 1.1. That is, 2 / 3<[W37a / W31a]≦1.1.

[0035] A specific description is given below. The wiring pattern is designed so that the transmission impedance of the microstrip line 31 on the upper surface layer and the strip line 37 of the triplate structure on the inner layer are the same (for example, 50 Ω). The line width is calculated from the thickness and dielectric constant of the dielectric layer. By removing the conductor layer in the inner layer, the dielectric of the triplate-structure stripline 37 is thickened. With this structure, the line width W37a of the inner-layer signal line 37a of the triplate-structure stripline 37 can be made the same as or equivalent to the line width W31a of the surface-layer signal line 31a of the microstrip line 31 in the upper surface layer. The thickness of the dielectric layer can only be changed in integer increments, such as 1, 2, ..., which is the number of substrates. However, when the asymmetry between the top and bottom is taken into account, the thickness can be adjusted in half-integer increments, such as 1, 1.5, 2, 2.5, 3, ... In Fig. 8, the dielectric thickness above the stripline 2 (inner layer) of the triplate structure is three layers (first to third dielectric layers), and the dielectric thickness below the stripline 2 is two layers (fourth and fifth dielectric layers). In this case, the dielectric thicknesses above and below are asymmetric, but are equivalent to the 2.5 layer thickness when the top and bottom are symmetric.

[0036] (thickness of dielectric layer) As shown in FIG. 8, the thickness of the dielectric layer in the upward direction from the inner layer signal line 37a toward the surface layer signal line 31a is taken as H1. The thickness of the dielectric layer from the inner-layer signal line 37a in the downward direction, which is the opposite direction to the upward direction, is defined as H2. In this case, H1 and H2 are asymmetric in the up-down direction with respect to the inner-layer signal line 37a, as shown in Fig. 8. The high-frequency multilayer substrate 100-1 has been described above.

[0037] <Variation 2> FIG. 10 shows the configuration of a high-frequency multilayer board 100-2 of the second modification. The high-frequency multilayer board 100-2 shows a connection structure between a strip line 2 and a microstrip line 3 in a four-layer board. The appropriate line width of the signal line and the number of laminated boards change depending on the dielectric constant of the board material. When the dielectric constant of the board material is small compared to that of a glass epoxy board, the surface signal line 31a of the microstrip line 31 becomes thicker and is less susceptible to the influence of etching accuracy. In addition, when the dielectric constant of the board material is small, the ratio of the line width of the inner layer signal line 37a of the inner layer triplate structure strip line 37 to the line width of the surface layer signal line 31a of the surface layer is small. In other words, the line width of the inner layer signal line 37a does not become very thin. For this reason, when the dielectric constant is small, it is possible to form an inner layer triplate structure strip line that is not affected by etching accuracy even if the dielectric thickness is not made too thick. This leads to the reduction in the number of laminated boards in the multilayer board. Reducing the number of layers in a board directly translates into reduced board costs, making it possible to use multilayer boards with four conductor layers (four-layer boards), which are the lowest cost.

[0038] <Variation 3> 11 shows a high-frequency multilayer board 100-3 of Modification 3. The high-frequency multilayer board 100-3 has a multilayer board configuration in which a signal wiring section of another signal wiring layer and a power wiring section of a power supply layer are stacked under a multilayer board for high-frequency transmission. The high-frequency multilayer board 100-3 has at least one of a signal wiring section and a power wiring section. In addition to circuits based on board patterns such as transmission lines and distributed constant circuits, high-frequency multilayer boards often have high-frequency components and other electronic components (signal processing and power supplies) surface-mounted to make the device smaller and lighter. When electronic components are surface mounted, power supply wiring for these various electronic components and other signal wiring that is not high-frequency transmission are required. In that case, high-frequency transmission circuit blocks and other circuit blocks are placed on the board, and the blocks are separated using many ground through holes 51. A multilayer board is then used in which other signal wiring layers and layers for power supply are stacked under the multilayer board for high-frequency transmission. 11 is a multilayer board in which a signal wiring section, which is a signal wiring layer, and a power wiring section, which is a power supply layer, are laminated under a high-frequency transmission section. In the high-frequency multilayer board 100-3, the ground through-hole 51 of the vertical coaxial line 34 is left penetrating through to the eighth ground conductor 18 in the lowest layer. The high frequency multilayer substrate 100-3 has been described above.

[0039] The high-frequency multilayer substrate 100 and each of the modified examples described above have the following features with respect to the triplate-structure strip line 37 in the inner layer and the microstrip line 31 and transition section 30 in the upper surface layer. (1) The wiring pattern is designed to match the transmission impedance (for example, 50 Ω) of the microstrip line 31 on the upper surface layer and the triplate structure strip line 37. The wiring (signal line) width is determined by the thickness and dielectric constant of the dielectric layer. The triplate-structure stripline 37 in the inner layer has a thicker dielectric by removing the conductor layer between the upper and lower dielectric layers by etching. This allows the line width W37a of the inner layer signal line 37a of the triplate-structure stripline 37 to be equal to the line width W31a of the surface layer signal line 31a of the microstrip line 31 in the upper surface layer when the transmission impedance of the microstrip line 31 and the triplate-structure stripline 37 is made the same. When the dielectrics on the top and bottom of the triplate-structure stripline 37 are made thicker, the thicknesses may be asymmetric between the top and bottom. (2) The conversion unit 30 is composed of five parts: three types of coaxial transmission lines, namely, a half-split coaxial line 33, a vertical coaxial line 34, and a horizontal coaxial line 35, and a first taper section 32 and a second taper section 36 on both sides of the three types of coaxial transmission lines. The surface signal line 31a of the microstrip line 31 has the same line width W31a whether it is the first taper section 32 or the half-split coaxial line 33 of the conversion unit 30. The inner layer signal line 37a of the strip line 37 with the triplate structure has the same line width W37a whether it is the second taper section 36 or the horizontal coaxial line 35. (3) The triplate-structure stripline in the inner layer forms a tapered horizontal coaxial line (multiple ground conductors are arranged to surround the signal line of the triplate-structure stripline) near the vertical coaxial line, which is the connection point. (4) The vertical coaxial line, which is the connection part, is a vertical coaxial structure consisting of a signal line through hole and a number of ground conductors surrounding the signal line through hole. The signal line through hole is left penetrating to the lowest conductor layer. The signal line through hole is not scraped off, and a stub circuit or the like is not added to the lowest layer surface. Lands 41, 42, and 43 are provided on the conductor layers of the top surface, bottom surface, and triplate signal surface of the penetrating through hole 34a, respectively. However, on other conductor layers, the penetrating through hole 34a is landless. (5) The diameter of the lands 41, 43 on the top and bottom surfaces of the penetrating through hole 34a is set to the same length as the line width W31a of the microstrip surface layer signal line 31a. The diameter of the land 42 on the conductor layer of the triplate signal surface is also set to the same length as the line width W31a.

[0040] The conductor extends from the layer of the inner layer signal line 37a of the strip line 37 with a triplate structure to the bottom conductor layer through which it penetrates, and at frequencies higher than the frequency band where this conductor length (stub length) is about λ / 4 (λ is the wavelength), the effect of reflection appears. However, at frequencies lower than that, the effect of reflection can be ignored in the wide high frequency bands that are commonly used, as mentioned above.

[0041] The high frequency multilayer substrate including the modified examples described above is as follows. In the high frequency multilayer substrate 100, the connection from the microstrip line to the strip line via the vertical coaxial line is a connection of the grounded coplanar structure, the vertical coaxial line, and the horizontal coaxial structure of the inner layer. The grounded coplanar structure can be regarded as a half-coaxial structure. In addition, the signal line width of the microstrip line and the strip line are the same. Also, due to the characteristics of the connection structure via a vertical coaxial structure consisting of a through hole with a land whose diameter is the line width of these signal lines, electromagnetic waves can be transmitted smoothly. In other words, there is an effect of obtaining a conversion method with little reflection over a wide band. It should be noted that the structure in which through-holes, which are signal lines of vertical coaxial lines, penetrate to the lower layers as in the normal manufacturing process for multilayer boards, remains intact. The effect of reflection from this through hole is limited to the vicinity of the frequency band (millimeter wave band) where the length of the through hole (stub length) is λ / 4 (λ is the wavelength). Therefore, the effect in the wide range of commonly used high frequency bands (microwave, ultrashort wave, short wave, and medium wave bands) can be ignored. Therefore, the through hole should be left as a lower layer through hole and there is no need to cut it off. Since a connection method with little reflection over a wide bandwidth is obtained, there is no need to add a stub circuit or the like to the lower layer for matching. By appropriately thickening the dielectric layer, the strip line width becomes the same as or wider than the microstrip line width, and the etching precision becomes insensitive. This has the effect of suppressing the characteristic variation of the distributed constant circuit using the inner layer triplate structure strip line. In the prior art, the dielectric thicknesses above and below the triplate-structure stripline are symmetrical (same thickness). In contrast, the high-frequency multilayer substrate 100 also incorporates asymmetry above and below to increase the design options for the thickness of the dielectric layer. This increases the options for the number of layers in the high-frequency multilayer substrate, and the options for the width of the triplate-structure stripline. Reducing the number of constituent layers of a multilayer board directly translates into reduced board costs, and ensuring a wide stripline width in the triplate structure directly translates into reduced characteristic variation, so increasing the number of options is an advantage in each case.

[0042] When the width of the signal line of the inner layer triplate structure strip line is made narrower than that of the microstrip line of the surface layer in order to match the transmission impedance (for example, 50 Ω), the following problems arise. Even if a circuit with good characteristics (low variation) can be formed within the etching accuracy using microstrip lines on the surface layer of a multilayer board, the line width will be thinner in the inner layer triplate structure strip lines that have a matched transmission impedance (for example, 50 Ω). The etching precision is insufficient for the required precision of the line width of the thin strip line. Manufacturing variations in the line width of the strip line due to etching precision cause variations in the transfer impedance. In the high-frequency multilayer substrate 100 including the modified example, the line width of the surface layer signal line 31a of the microstrip line 31 is equal to that of the inner layer signal line 37a of the strip line 70. Therefore, impedance matching can be achieved when connecting the microstrip line 31 to the strip line 70.

[0043] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) A plurality of stacked ground conductors; a dielectric region sandwiched between ground conductors at both ends in a lamination direction; a microstrip line having a surface signal line on a surface of the dielectric region and extending in a direction perpendicular to the lamination direction; a strip line having an inner layer signal line inside the dielectric region and extending in the perpendicular direction; a conversion unit that converts a transmission mode of an electromagnetic field of a high-frequency signal output from the microstrip line into a transmission mode that is compatible with the strip line; Equipped with The conversion unit is a first conversion line that extends from the microstrip line in the extending direction of the microstrip line and gradually increases a first width direction component of an electric field of a high frequency signal output from the microstrip line along a line width direction of the surface signal line as it moves away from the extending direction of the microstrip line; a vertical coaxial line connected to the first conversion line and extending in the lamination direction from the surface of the dielectric region to the inside of the dielectric region; a second conversion line that extends from the stripline toward the vertical coaxial line in the direction in which the stripline extends within the dielectric region and is connected to the vertical coaxial line, and that gradually reduces a second width direction component of an electric field of a high frequency signal output from the vertical coaxial line along a line width direction of the inner layer signal line as it moves away from the vertical coaxial line toward the stripline; A high frequency multilayer board comprising: (Appendix 2) The conversion unit is It functions as a conversion line that converts the transmission mode of the electromagnetic field of the high frequency signal output from the strip line into a transmission mode that is compatible with the microstrip line, The second conversion line includes: the second width direction component of the electric field of the high frequency signal output from the strip line is gradually increased toward the vertical coaxial line as it moves away from the strip line; The first conversion line includes: 2. The high frequency multilayer board according to claim 1, wherein the first width direction component of the electric field of the high frequency signal output from the vertical coaxial line is gradually reduced toward the microstrip line as it moves away from the vertical coaxial line. (Appendix 3) The surface signal line is extending to and connected to the vertical coaxial line, The first conversion line includes: a first portion of a first ground conductor among the plurality of ground conductors is disposed on one of both sides of the surface signal line, a second portion of the first ground conductor is disposed on the other side, and distances from the surface signal line to the first portion and the second portion in a line width direction of the surface signal line are gradually shortened toward the vertical coaxial line, The inner layer signal line is extending to and connected to the vertical coaxial line, The second conversion line includes: 3. The high-frequency multilayer board according to claim 1, wherein, in a cross section normal to the direction in which the inner layer signal wire extends, the inner layer signal wire is surrounded by the plurality of ground conductors, a triplate structure is formed at a connection point with the strip line, and a coaxial line structure is formed at a connection point with the vertical coaxial line. (Appendix 4) The dielectric region is a first thickness from the inner layer signal line toward one of the ground conductors at both ends in the stacking direction along the stacking direction; a second thickness from the inner layer signal line toward the other of the ground conductors at both ends in the stacking direction along the stacking direction; 4. The high-frequency multilayer board according to claim 1, which is asymmetric. (Appendix 5) 5. The high-frequency multilayer board according to claim 4, wherein a value obtained by dividing the line width of the inner layer signal line by the line width of the surface layer signal line is greater than 2 / 3 and is not greater than 1.1.

[0044] The above describes the embodiments and modifications of the present disclosure. Some of these embodiments and modifications may be combined and implemented. Also, one or some of them may be partially implemented. Note that the present disclosure is not limited to the above embodiments and modifications, and various modifications are possible as necessary. [Explanation of symbols]

[0045] W31a, W37a line width, 11 first ground conductor, 12 second ground conductor, 13 third ground conductor, 14 fourth ground conductor, 15 fifth ground conductor, 16 sixth ground conductor, 21 first dielectric layer, 22 second dielectric layer, 23 third dielectric layer, 24 fourth dielectric layer, 25 fifth dielectric layer, 30 conversion portion, 31 microstrip line, 31a surface signal line, 32 first tapered portion, 33 half-split coaxial line, 34 vertical coaxial line, 34a through hole, 35 horizontal coaxial line, 36 second tapered portion, 37 strip line, 37a inner signal line, 41, 42, 43 lands, 51 ground through hole, 100 high frequency multilayer board.

Claims

1. A plurality of stacked ground conductors; a dielectric region sandwiched between ground conductors at both ends in a lamination direction; a microstrip line having a surface signal line on a surface of the dielectric region and extending in a direction perpendicular to the lamination direction; a strip line having an inner layer signal line inside the dielectric region and extending in the perpendicular direction; a conversion unit that converts a transmission mode of an electromagnetic field of a high-frequency signal output from the microstrip line into a transmission mode that is compatible with the strip line; Equipped with The conversion unit is a first conversion line extending from the microstrip line in the extending direction of the microstrip line, and gradually increasing a first width direction component of an electric field of a high frequency signal output from the microstrip line along a line width direction of the surface signal line as the first conversion line moves away from the extending direction of the microstrip line; a vertical coaxial line connected to the first conversion line and extending in the lamination direction from the surface of the dielectric region to the inside of the dielectric region; a second conversion line that extends from the stripline toward the vertical coaxial line in the direction in which the stripline extends within the dielectric region and is connected to the vertical coaxial line, and that gradually reduces a second width direction component of an electric field of a high frequency signal output from the vertical coaxial line along a line width direction of the inner layer signal line as it moves away from the vertical coaxial line toward the stripline; A high frequency multilayer board comprising:

2. The conversion unit is It functions as a conversion line that converts the transmission mode of the electromagnetic field of the high frequency signal output from the strip line into a transmission mode that is compatible with the microstrip line, The second conversion line includes: the second width direction component of the electric field of the high frequency signal output from the strip line is gradually increased toward the vertical coaxial line as it moves away from the strip line; The first conversion line includes:

2. The high frequency multilayer board according to claim 1, wherein the first width direction component of the electric field of the high frequency signal output from the vertical coaxial line is gradually reduced toward the microstrip line as it moves away from the vertical coaxial line.

3. The surface signal line is extending to and connected to the vertical coaxial line, The first conversion line includes: a first portion of a first ground conductor among the plurality of ground conductors is disposed on one of both sides of the surface signal line, a second portion of the first ground conductor is disposed on the other side, and distances from the surface signal line to the first portion and the second portion in a line width direction of the surface signal line are gradually shortened toward the vertical coaxial line, The inner layer signal line is extending to and connected to the vertical coaxial line, The second conversion line includes:

3. The high-frequency multilayer board according to claim 1, wherein in a cross section normal to the direction in which the inner layer signal line extends, the inner layer signal line is surrounded by the plurality of ground conductors, a triplate structure is formed at a connection point with the strip line, and a coaxial line structure is formed at a connection point with the vertical coaxial line.

4. The dielectric region is a first thickness from the inner layer signal line toward one of the ground conductors at both ends in the stacking direction along the stacking direction; a second thickness from the inner layer signal line toward the other of the ground conductors at both ends in the stacking direction along the stacking direction; 3. The high frequency multilayer board according to claim 1, which is asymmetric.

5. 5. The high frequency multilayer board according to claim 4, wherein a value obtained by dividing the line width of the inner layer signal line by the line width of the surface layer signal line is greater than 2 / 3 and is equal to or smaller than 1.1.

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