Slow wave transmission line

Abstract

This slow wave transmission line comprises a signal conductor (2) and a ground conductor (3) that are disposed with an insulator (1) therebetween. The ground conductor (3) includes a plurality of slits (3a) that intersect the extension direction of the signal conductor (2). The distance of a contour line OL from one end to the other end in an intersecting direction intersecting the extension direction of the signal conductor (2) of the slits (3a) in the ground conductor (3) in which the slits (3a) are formed is longer than the distance of a straight line connecting one end and the other end in the intersecting direction.

Description

Slow Wave Transmission Line

[0001] The present disclosure relates to slow wave transmission lines.

[0002] A high-frequency transmission line capable of obtaining a high slow-wave effect is known from Patent Document 1. The high-frequency transmission line disclosed in Patent Document 1 includes a signal line conductor arranged on a first layer, a plurality of first ground conductors arranged on a second layer and extending in a direction different from the extension direction of the signal line conductor, and a plurality of second ground conductors arranged on a third layer and extending in a direction different from the extension direction of the signal line conductor and extending substantially parallel to the first ground conductor, and the plurality of first ground conductors and the plurality of second ground conductors are short-circuited by a plurality of columnar conductors such that short-circuit positions between the plurality of first ground conductors and the plurality of second ground conductors are alternately shifted.

[0003] JP 2012-209940 A

[0004] The high-frequency transmission line disclosed in Patent Document 1 has a configuration including a first ground conductor and a second ground conductor in a layer below a signal line conductor. There is a demand for a slow-wave transmission line with a layered structure that reduces the number of ground conductor layers arranged below the signal line conductor, making it easy to apply to, for example, a printed circuit board (PCB).

[0005] The present disclosure has been made in consideration of the above points, and aims to obtain a slow wave transmission line that is composed of a signal line conductor and a ground conductor, and in which the ground conductor is arranged in a single layer below the signal line conductor.

[0006] The slow wave transmission line according to the present disclosure includes a signal conductor and a ground conductor arranged with an insulator sandwiched between them, the ground conductor having a plurality of slits that intersect with the extension direction of the signal conductor, and the distance of the contour line from one end to the other end of the slits in the ground conductor that form the slits in the cross direction that intersects with the extension direction of the signal conductor is longer than the distance of a straight line connecting the one end and the other end in the cross direction.

[0007] According to the present disclosure, in a slow-wave transmission line that is configured with a signal line conductor and a ground conductor, and in which the ground conductor is placed in a single layer below the signal line conductor, delay of the slow-wave line is increased.

[0008] 10 is a schematic top view showing a see-through dielectric in the slow-wave transmission line according to the first embodiment. 11 is a schematic top view showing a ground conductor in the slow-wave transmission line according to the first embodiment. 12 is a cross-sectional view taken along line A-A in FIG. 1. 13 is an end view taken along line B-B in FIG. 1. 14 is an end view taken along line C-C in FIG. 1. 15 is an end view taken along line D-D in FIG. 1. 16 is a diagram showing a schematic view of a path of a current flowing through a ground conductor in the slow-wave transmission line according to the first embodiment. 17 is a diagram for explaining the length of the outline of a slit in the ground conductor in the slow-wave transmission line according to the first embodiment. 18 is a schematic top view showing a see-through dielectric in the slow-wave transmission line according to the second embodiment. 19 is a schematic top view showing a see-through dielectric in the slow-wave transmission line according to the third embodiment. 19 is an end view taken along line C-C in FIG. 10. 19 is an end view taken along line D-D in FIG. 10. 19 is a schematic top view showing a see-through dielectric in the slow-wave transmission line according to the fourth embodiment. 19 is a cross-sectional view taken along line A-A in FIG. 13. FIG. 10 is an end view showing a slow wave transmission line according to a fifth embodiment.

[0009] First Embodiment A slow-wave transmission line according to the first embodiment will be described with reference to Figures 1 to 8. The slow-wave transmission line according to the first embodiment is a high-frequency transmission line that slows the propagation speed of high-frequency signals, for example, in the millimeter wave band, by generating a slow-wave mode using a structure in which high-impedance sections and low-impedance sections are repeated at a very short period relative to the wavelength. The slow-wave transmission line according to the first embodiment constitutes a delay line mounted on a printed circuit board (PCB), which is a microstrip substrate.

[0010] The slow wave transmission line according to the first embodiment includes a signal conductor 2 and a ground conductor 3, which are arranged with an insulator 1 sandwiched between them. When the slow wave transmission line according to the first embodiment is mounted on a printed circuit board, the insulator 1 is the dielectric of the printed circuit board. The insulator 1 is made of a material commonly used for printed circuit boards, such as ceramic. As shown in FIGS. 3 to 5 , the signal conductor 2 is formed on the surface of the insulator 1, and is made of, for example, a conductive foil, in a manner similar to a commonly known method for forming a conductive foil on a dielectric that constitutes a board.

[0011] As shown in Figures 3 to 6, the ground conductor 3 is, for example, a conductor foil formed continuously with the ground conductor of the printed circuit board formed on the back surface of the insulator 1, and is formed in the same manner as a commonly known method for forming a conductor foil on a dielectric that constitutes a substrate. The signal conductor 2, the ground conductor 3, and the insulator 1 form a microstrip line. The ground conductor 3 has multiple slits 3a that intersect with the extension direction of the signal conductor 2. The slits 3a are areas where no ground conductor exists.

[0012] The signal conductor 2 is arranged so as to pass through the central portions of the plurality of slits 3 a in the crossing direction. Although five slits 3 a are shown in Fig. 1, this number is shown for the purpose of explanation and is not limited to five.

[0013] In the slow wave transmission line according to the first embodiment, the region where the slits 3 a are present in the ground conductor 3 is a region where the characteristic impedance is high, i.e., a high-impedance section, and the region where the slits 3 a are not present in the ground conductor 3 is a region where the characteristic impedance is low, i.e., a low-impedance section. Because the ground conductor 3 has a plurality of slits 3 a arranged along the extension direction of the signal conductor 2, the slow wave transmission line according to the first embodiment is a transmission line in which high-impedance sections and low-impedance sections alternate at a minute period relative to the wavelength of the high-frequency signal transmitted through the signal conductor 2, and the propagation speed of the high-frequency signal transmitted through the signal conductor 2 is slowed down.

[0014] In the ground conductor 3, as shown in FIG. 8, the distance L of the contour line OL from one end P1, P4 to the other end P2, P3 of the slit 3a in the cross direction intersecting with the extending direction of the signal conductor 2 in the ground conductor 3 where the slit 3a is formed is equal to the distance L of the straight lines P1-P2 and P4-P3 connecting the one end P1, P4 and the other end P2, P3 in the cross direction. ０ Although Figure 8 shows only one slit 3a, all other slits have the same configuration.

[0015] The slit 3a has a rectangular shape with the longer side in the intersecting direction, and if the four corners are labeled p2, p3, and p4 clockwise from P1, the contour line OL located on a pair of opposing long sides P1-P2 and P4-P3 is zigzag. Because the contour line OL from one end P1 to the other end P2 is zigzag, it is longer than the distance of the straight line P1-P2 connecting the one end P1 and the other end P2. Because the contour line OL from one end P4 to the other end P3 is zigzag, it is longer than the distance of the straight line P4-P3 connecting the one end P4 and the other end P3.

[0016] As shown in Figures 1 and 2, the ground conductor 3 has a frame portion 30 having a pair of parallel direction portions 31, 32 that are parallel to the extension direction of the signal conductors 2 and face each other, and a pair of cross direction portions 33, 34 that are parallel to the cross direction that intersects the extension direction of the signal conductors 2 and face each other, and a plurality of cross direction connecting portions 35 that are located between the pair of cross direction portions 33, 34 in the frame portion 30 and are located between adjacent slits 3a in the plurality of slits 3a to separate the adjacent slits 3a.

[0017] The contour line OL from one end P1 to the other end P2 of the slit 3a is also the contour line OL from one end P1 to the other end P2 of the cross-directional connecting portion 35, and the contour line OL from one end P4 to the other end P3 of the slit 3a is also the contour line OL from one end P4 to the other end P3 of the cross-directional connecting portion 35. Therefore, the contour line OL is the contour shape of the boundary between the low-impedance portion and the high-impedance portion.

[0018] 2, the distance between the peaks of the slits 3a (valleys for the cross-directional connecting portion 35) is d1, and the distance between the valleys of the slits 3a (peaks for the cross-directional connecting portion 35) is d2. The cross-directional connecting portion 35 has a rectangular shape with a series of isosceles triangular peaks with a height of (d1-d2) / 2 formed on the long side.

[0019] 7, when a high-frequency signal is transmitted to the signal conductor 2, current concentrates in the ground conductor 3 at the intersecting coupling portion 35 located directly below the signal conductor 2, and currents IA and IB flow concentrating at the boundary between the intersecting coupling portion 35 and the slit 3a. That is, in the intersecting coupling portion 35 located between adjacent slits 3a, current IA flows in a current path from the left-side contour line OL to the center to the right-side contour line OL in the upper part of FIG. 7, and current IB flows in a current path from the left-side contour line OL to the center to the right-side contour line OL in the lower part of FIG.

[0020] In order to explain the current path in the ground conductor 3, Figure 7 shows a part of the ground conductor 3 at the cross-directional connecting portion 35 located between adjacent slits 3a, but the current path is similar for all other cross-directional connecting portions 35.

[0021] The current path through which current IA flows and the current path through which current IB flows are zigzag current paths along contour line OL, and are longer than the current paths along lines P1-P2 and P4-P3. Therefore, the inductance component per unit length in the current path through which current IA flows and the current path through which current IB flows is greater than the inductance component per unit length in the current paths along lines P1-P2 and P4-P3. As a result, the high-frequency signal transmitted through signal conductor 2 can be slowed down, and the delay in the slow wave transmission line is increased.

[0022] Next, we will explain the operation of the slow wave transmission line according to embodiment 1. When a high-frequency signal in the millimeter wave band is transmitted to the signal conductor 2, the propagation speed of the high-frequency signal transmitted through the signal conductor 2 slows down because regions in the ground conductor 3 where the slits 3 a are present, i.e., high-impedance sections, and regions in the ground conductor 3 where the slits 3 a are not present, i.e., low-impedance sections, alternate at a period that is very small relative to the wavelength of the high-frequency signal transmitted through the signal conductor 2.

[0023] Moreover, in the slow wave transmission line according to the first embodiment, the boundary between the low impedance portion and the high impedance portion is formed by a contour line OL that is longer than the distance between the straight lines P1-P2 and P4-P3, that is, a zigzag contour line OL. Therefore, the current paths of the currents IA and IB flowing through the cross-directional coupling portion 35 in the ground conductor 3 become longer, and the delay in the slow wave transmission line increases.

[0024] The slow wave transmission line according to the first embodiment includes a signal conductor 2 and a ground conductor 3 arranged with an insulator 1 sandwiched therebetween. A plurality of slits are formed in the ground conductor, and low impedance portions and high impedance portions are alternately repeated at a period that is minute with respect to the wavelength of a high frequency signal transmitted through the signal conductor 2, thereby generating a slow wave mode. In addition, the distance L of a contour line OL from one end P1, P4 of the slit 3a in the ground conductor 3 to the other end P2, P3 in the cross direction that intersects with the extension direction of the signal conductor 2 is smaller than the distance L of the straight lines P1-P2 and P4-P3 connecting the one end P1, P4 and the other end P2, P3 in the cross direction. ０ The longer length also increases the delay in the slow wave transmission line.

[0025] The slow wave transmission line according to the first embodiment has a three-layer structure including a signal conductor 2 and a ground conductor 3 sandwiched between an insulator 1, which makes it possible to obtain a slow wave transmission line with increased delay. Therefore, the insulator 1 serves as the dielectric of the printed circuit board, the signal conductor 2 is formed by a conductor foil formed on the surface of the dielectric, and the ground conductor is formed by a ground conductor formed on the back surface of the dielectric, and therefore the slow wave transmission line can be easily mounted on a printed circuit board.

[0026] Furthermore, in the slow wave transmission line according to the first embodiment, the amount of delay can be set by the shape of the contour line OL, for example, the number and height of the mountain shapes forming the zigzag shape, and therefore the design of the slow wave transmission line is simple and easy.

[0027] In the first embodiment, the contour line OL, which is the contour shape of the boundary between the low impedance portion and the high impedance portion, is zigzag. However, the point is that the distance L from one end P1, P4 to the other end P2, P3 in the crossing direction is the distance L between the straight lines P1-P2 and P4-P3 connecting the one end P1, P4 and the other end P2, P3 in the crossing direction. ０ Since the longer the length is, the contour line OL between one end P1 and the other end P2 and the contour line OL between one end P4 and the other end P3 may each be a curve such as a sine curve.

[0028] In the first embodiment, the signal conductor 2 is a straight line, but it may be a curved line or a meander wiring. Even when the signal conductor 2 is a meander line, the ground conductor 3 may have a structure having a plurality of slits 3a that intersect with the extension direction of the signal conductor 2, which is a meander line, and the signal conductor 2 passes through the center of the plurality of slits 3a in the intersecting direction.

[0029] Second Embodiment A slow wave transmission line according to a second embodiment will be described with reference to FIG. 9. The slow wave transmission line according to the second embodiment differs from the slow wave transmission line according to the first embodiment in that the slit 3a is replaced with a slit 3b, but the other points are the same. Therefore, the following description will focus on the slit 3b, which is different from the slow wave transmission line according to the first embodiment. In FIG. 9, the same reference numerals as those in FIGS. 1 to 8 indicate the same or corresponding parts.

[0030] The slow-wave transmission line according to the second embodiment includes a signal conductor 2 and a ground conductor 3 arranged with an insulator 1 sandwiched between them. When the slow-wave transmission line according to the second embodiment is mounted on a printed circuit board, which is a microstrip board, the signal conductor 2, the ground conductor 3, and the insulator 1 form a microstrip line.

[0031] The ground conductor 3 has a plurality of slits 3b that intersect with the extending direction of the signal conductor 2. In the ground conductor 3, as in the first embodiment, the distance L of the contour line OL from one end P1, P4 to the other end P2, P3 is equal to the distance L of the straight lines P1-P2 and P4-P3 connecting the one end P1, P4 and the other end P2, P3. ０ Longer.

[0032] In the ground conductor 3, the distance L2 of the contour line OL2 from one end P1, P2 to the other end P4, P3 in the parallel direction parallel to the extension direction of the signal conductor 2 of the slit 3b in the ground conductor 3 is the distance L ０２ In Figure 9, P1 to P4 and OL2 are shown for one slit 3b, but the same is true for all other slits.

[0033] In the slit 3b, the contour line OL2 from one end P1 to the other end P4 has a zigzag shape, and therefore is longer than the distance of the straight line P1-P4 connecting the one end P1 and the other end P4. The contour line OL2 from one end P2 to the other end P3 also has a zigzag shape, and therefore is longer than the distance of the straight line P2-P3 connecting the one end P2 and the other end P3.

[0034] The distance between the peaks (valleys for the parallel direction portions 31, 32 in the frame portion 30 of the ground conductor 3) located in the crossing direction in the slits 3b is defined as d3, and the distance between the valleys (peaks for the parallel direction portions 31, 32 in the frame portion 30 of the ground conductor 3) in the slits 3b is defined as d4. Each of the parallel direction portions 31 and 32 has a rectangular shape with a continuous isosceles triangular peak shape with a height of (d3-d4) / 2 formed on the long side.

[0035] 9, contour line OL2 is the boundary between the slit 3b and the parallel direction portion 31, and in the lower part of FIG. 9, contour line OL2 is the boundary between the slit 3b and the parallel direction portion 32. When a high-frequency signal is transmitted through the signal conductor 2, the boundary between the parallel direction portion 31 and the slit 3b and the boundary between the parallel direction portion 32 and the slit 3b also become current paths through which current flows. Therefore, because contour line OL2 has a zigzag shape, the current paths at these boundaries are also longer than the current paths along the lines P1-P4 and P2-P3. As a result, the high-frequency signal transmitted through the signal conductor 2 can be further slowed, increasing the delay in the slow wave transmission line.

[0036] The slow-wave transmission line according to the second embodiment has the same effect as the slow-wave transmission line according to the first embodiment, and in addition, in the ground conductor 3 forming the slit 3b, the distance L2 of the contour line OL2 from one end P1, P2 of the slit 3b to the other end P4, P3 in the parallel direction parallel to the extending direction of the signal conductor 2 is the same as the distance L1 of the straight lines P1-P4 and P2-P3 connecting the one end P1, P2 and the other end P4, P3 in the parallel direction. ０２ The longer length increases the delay in the slow wave transmission line.

[0037] In the second embodiment, the contour line OL2, which is the contour shape of the boundary between the parallel direction portion 31 and the slit 3b, and the contour line OL2, which is the contour shape of the boundary between the parallel direction portion 32 and the slit 3b, are zigzag. However, the point is that the distance L2 from one end P1, P2 to the other end P4, P3 in the parallel direction is the distance L1 between the straight lines P1-P4 and P2-P3 connecting the one end P1, P2 and the other end P4, P3 in the parallel direction. ０２ Since the longer the length is, the contour line OL2 between the one end P1 and the other end P4 and the contour line OL2 between the one end P2 and the other end P3 may each be a curve such as a sine curve.

[0038] Also, in the slow wave transmission line according to the second embodiment, as in the first embodiment, the contour line OL between one end P1 and the other end P2 and the contour line OL between one end P4 and the other end P3 may each be a curve, such as a sine curve. Furthermore, although the signal conductor 2 is a straight line in the second embodiment, it may also be a curved line or a meander wiring. Even when the signal conductor 2 is a meander line, the ground conductor 3 may have a structure including a plurality of slits 3 b that intersect with the extension direction of the signal conductor 2, which is a meander line, and the signal conductor 2 passes through the center of the plurality of slits 3 b in the intersecting direction.

[0039] Third Embodiment A slow-wave transmission line according to a third embodiment will be described with reference to Figures 10 to 12. The slow-wave transmission line according to the third embodiment is the same as the slow-wave transmission line according to the first embodiment in that the ground conductor 3A has a plurality of slits 3a, but the planar outer shape of the ground conductor 3A is different from that of the ground conductor 3, and the other points are the same. Therefore, the following description will focus on the ground conductor 3A, which is different from the slow-wave transmission line according to the first embodiment. Note that in Figures 10 to 12, the same reference numerals as those in Figures 1 to 8 indicate the same or corresponding parts.

[0040] The slow-wave transmission line according to the third embodiment includes a signal conductor 2 and a ground conductor 3A arranged with an insulator 1 sandwiched therebetween. When the slow-wave transmission line according to the third embodiment is mounted on a printed circuit board, which is a microstrip board, the signal conductor 2, the ground conductor 3A, and the insulator 1 form a microstrip line.

[0041] The ground conductor 3 has a plurality of slits 3a that intersect with the extension direction of the signal conductor 2. The planar outer shape of each of the plurality of slits 3a is the same as the planar outer shape of each of the plurality of slits 3a of the ground conductor 3 in the slow wave transmission line according to the first embodiment.

[0042] The ground conductor 3A has a plurality of enclosures 36 surrounding each of the plurality of slits 3a, and a plurality of parallel connecting portions 37 facing the signal conductor 2 and connecting adjacent ones of the plurality of enclosures 36. Each of the parallel connecting portions 37 is located directly below the signal conductor 2 and is wider than the line width of the signal conductor 2.

[0043] The parallel connecting portions 37 are connected to each other at the center in the crossing direction of adjacent enclosure portions 36. Between adjacent enclosure portions 36, there is a region 36a where no ground conductor exists other than the parallel connecting portions 37. That is, the ground conductor 3A is provided with regions 36a where no ground conductor exists above and below the signal conductor 2 as shown in FIG. 10 in the crossing connecting portion 35 of the ground conductor 3 in the slow wave transmission line according to the first embodiment.

[0044] When a high-frequency signal is transmitted through the signal conductor 2, there are regions 36a where no ground conductor is present above and below the parallel-direction connecting portions 37 between adjacent enclosures 36 as shown in Figure 10, sandwiching the parallel-direction connecting portions 37. Therefore, the current path is limited to the boundary between the enclosure 36 and the slit 3a. As a result, the high-frequency signal transmitted through the signal conductor 2 can be further slowed, increasing the delay in the slow-wave transmission line. In addition, the zigzag shape of the enclosure 36 provides a delay effect for low-frequency currents that are less likely to localize at the boundary between the enclosure 36 and the slit 3a.

[0045] The slow-wave transmission line according to the third embodiment has the same effects as the slow-wave transmission line according to the first embodiment. In addition, the ground conductor 3A has a plurality of enclosures 36 that surround each of the plurality of slits 3a, and a plurality of parallel connecting portions 37 that face the signal conductor 2 and each connect adjacent ones of the plurality of enclosures 36. As a result, there are regions 36a where no ground conductor is present on both sides of the parallel connecting portions 37 between adjacent enclosures 36, and only the boundaries between the enclosures 36 and the slits 3a form current paths, further increasing the delay in the slow-wave transmission line.

[0046] Also in the slow-wave transmission line according to the third embodiment, the contour line OL between one end P1 and the other end P2 and the contour line OL between one end P4 and the other end P3 may each be a curve such as a sine curve, as described in the first embodiment. Furthermore, also in the slow-wave transmission line according to the third embodiment, the contour shape of the boundary between the portion of the enclosure 36 parallel to the signal conductor 2 and the slit 3a may be a zigzag contour line or a curve such as a sine curve, as described in the second embodiment.

[0047] Furthermore, in the third embodiment, the signal conductor 2 is a straight line, but it may be a curved line or a meander wiring. Even when the signal conductor 2 is a meander line, the ground conductor 3A may have a structure having a plurality of slits 3a that intersect with the extension direction of the signal conductor 2, which is a meander line, and the signal conductor 2 passes through the center of the plurality of slits 3a in the intersecting direction.

[0048] Fourth Embodiment A slow wave transmission line according to a fourth embodiment will be described with reference to FIGS. 13 and 14. The slow wave transmission line according to the fourth embodiment differs from the slow wave transmission line according to the first embodiment in that the slit 3a is replaced with a slit 3c, but the other points are the same. Therefore, the following description will focus on the slit 3c, which is the difference from the slow wave transmission line according to the first embodiment. In FIGS. 13 and 14, the same reference numerals as those in FIGS. 1 to 8 indicate the same or corresponding parts.

[0049] The slow-wave transmission line according to the fourth embodiment includes a signal conductor 2 and a ground conductor 3B arranged with an insulator 1 sandwiched therebetween. When the slow-wave transmission line according to the fourth embodiment is mounted on a printed circuit board, which is a microstrip board, the signal conductor 2, the ground conductor 3B, and the insulator 1 form a microstrip line.

[0050] The ground conductor 3B has a plurality of slits 3c that intersect with the extending direction of the signal conductor 2. Each of the plurality of slits 3c has a contour line OL3 that is meandering as a whole from one end P1, P4 to the other end P2, P3 in the intersecting direction that intersects with the extending direction of the signal conductor 2.

[0051] Each of the plurality of slits 3c has a shape in which the entire slit is bent greatly alternately in the extending direction of the signal conductor 2, that is, in the left-right direction in Fig. 13. In this way, the entire slit 3c has a meandering shape in which the entire slit 3c is bent greatly alternately forward and backward in the extending direction of the signal conductor 2. Therefore, the distance L3 of the contour line OL3 from one end P1, P4 to the other end P2, P3 in the cross direction intersecting the extending direction of the signal conductor 2 of the slit 3c is equal to the distance L1-P2, P2-P3 of the straight lines P1-P2, P4-P3 connecting the one end P1, P4 and the other end P2, P3 in the cross direction. ０３ Longer.

[0052] The ground conductor 3B has a frame portion 30 having a pair of parallel direction portions 31, 32 that are parallel to the extension direction of the signal conductor 2 and face each other, and a pair of cross direction portions 33, 34 that are parallel to the cross direction that intersects the extension direction of the signal conductor 2 and face each other, and a plurality of cross direction connecting portions 35 that are located between the pair of cross direction portions 33, 34 in the frame portion 30 and are located between adjacent slits 3c in the plurality of slits 3c to separate the adjacent slits 3c, connecting the pair of parallel direction portions 31, 32 in the frame portion 30.

[0053] When a high-frequency signal is transmitted through the signal conductor 2, current in the ground conductor 3B is concentrated at the cross-directional coupling portion 35 located directly below the signal conductor 2, and the current flows in a concentrated manner at the boundary between the cross-directional coupling portion 35 and the slit 3c. The current path through the cross-directional coupling portion 35 is a meandering current path along the contour line OL3, and is longer than the current paths along the lines P1-P2 and P4-P3. As a result, the high-frequency signal transmitted through the signal conductor 2 can be slowed down, and the delay in the slow wave transmission line increases.

[0054] The slow wave transmission line according to the fourth embodiment has the same effect as the slow wave transmission line according to the first embodiment. In the fourth embodiment, the slit 3c is bent linearly, but it may be bent in a curved, serpentine shape.

[0055] Fifth Embodiment A slow-wave transmission line according to a fifth embodiment will be described with reference to FIG. 15 . The slow-wave transmission line according to the fifth embodiment differs from the slow-wave transmission line according to the first embodiment in that it further includes a second ground conductor 5, but is otherwise the same. Therefore, the following description will focus on the second ground conductor 5, which is the difference from the slow-wave transmission line according to the first embodiment. Note that in FIG. 15 , the same reference numerals as those in FIGS. 1 to 8 indicate the same or corresponding parts.

[0056] The slow-wave transmission line according to the fifth embodiment includes a signal conductor 2 and a first ground conductor 3 arranged with an insulator 1 sandwiched between them, and further includes a second ground conductor 5 sandwiching a second insulator 4 between the signal conductor 2 and the second insulator 4. The second insulator 4 is an insulating layer that is a dielectric layer. When the slow-wave transmission line according to the fifth embodiment is mounted on a printed circuit board that is a microstrip board, the signal conductor 2, the first ground conductor 3, and the insulator 1 form a microstrip line, and the signal conductor 2, the second ground conductor 5, and the second insulator 4 also form a microstrip line.

[0057] The signal conductor 2, first ground conductor 3, and insulator 1 that constitute the microstrip line are the same as the signal conductor 2, ground conductor 3, and insulator 1 that constitute the microstrip line in the slow wave transmission line according to embodiment 1, and therefore a description thereof will be omitted. The second ground conductor 5 is formed on the opposite side of the signal conductor 2 from the first ground conductor 3, via a dielectric layer 4. In other words, the second ground conductor 5 is a conductive layer that is formed on the surface of the signal conductor 2 via the dielectric layer 4 and is at ground potential.

[0058] The second ground conductor 5 has the same planar shape as the first ground conductor 3. That is, it has a plurality of second slits 5a that intersect with the extension direction of the signal conductors 2. The second ground conductor 5 is arranged so that the signal conductors 2 pass through the centers of the plurality of second slits 5a in the intersecting direction.

[0059] The planar outer shape of each of the plurality of second slits 5a is the same as the planar outer shape of each of the plurality of slits 3a in the first ground conductor 3. That is, the distance of the outline from one end to the other end of each second slit 5a in the intersecting direction that intersects with the extension direction of the signal conductor 2 in the second ground conductor 5 forming the second slit 5a is longer than the distance of the straight line connecting the one end and the other end in the intersecting direction.

[0060] Similar to the first ground conductor 3, the second ground conductor 5 has a frame portion 50 having a pair of parallel portions (51, 52, not shown) and a pair of intersecting portions 53, 54, and a plurality of intersecting connecting portions 55. The second ground conductor 5 is disposed opposite the first ground conductor 3 so that their planar shapes coincide with each other.

[0061] When a high-frequency signal is transmitted through the signal conductor 2, as in the slow-wave transmission line according to the first embodiment, in the first ground conductor 3, a current flows through a current path formed at the boundary between the first ground conductor 3 and the slit 3a in the cross-directional coupling 35. At the same time, in the second ground conductor 5, a current flows through a current path formed at the boundary between the first ground conductor 3 and the second slit 5a in the cross-directional coupling 55. Because the contour line OL is zigzag, the current path in the first ground conductor 3 is a zigzag current path along the contour line OL. Because the contour line OL3 is also zigzag, the current path in the second ground conductor 5 is also a zigzag current path along the contour line OL3. As a result, the high-frequency signal transmitted through the signal conductor 2 can be slowed down, and the delay in the slow-wave transmission line increases.

[0062] The slow-wave transmission line according to the fifth embodiment has the same effect as the slow-wave transmission line according to the first embodiment. If the first ground conductor 3 is the ground conductor 3 shown in the second embodiment, the second ground conductor 5 may also have the same planar shape as the ground conductor 3 shown in the second embodiment. If the first ground conductor 3 is the ground conductor 3A shown in the third embodiment, the second ground conductor 5 may also have the same planar shape as the ground conductor 3A shown in the third embodiment. If the first ground conductor 3 is the ground conductor 3B shown in the fourth embodiment, the second ground conductor 5 may also have the same planar shape as the ground conductor 3B shown in the second embodiment.

[0063] It should be noted that the embodiments may be freely combined, any of the components of the embodiments may be modified, or any of the components of the embodiments may be omitted.

[0064] The slow wave transmission line according to the present disclosure is applied as a high frequency transmission line used in the field of wireless communication using the millimeter wave band, and is particularly suitable as a slow wave transmission line mounted on a printed circuit board.

[0065] 1 insulator, 2 signal conductor, 3, 3A, 3B ground conductor, 3a, 3b, 3c slit, 30 frame portion, 31, 32 parallel direction portion, 33, 34 cross direction portion, 35 cross direction connecting portion, 36 enclosure portion, 37 parallel direction connecting portion.

Claims

1. A slow wave transmission line comprising a signal conductor and a ground conductor arranged with an insulator between them, wherein the ground conductor has a plurality of slits that intersect with the extension direction of the signal conductor, and wherein the distance of the contour line from one end to the other end of the slits in the cross direction that intersects with the extension direction of the signal conductor in the ground conductor that forms the slits is longer than the distance of a straight line connecting the one end and the other end in the cross direction.

2. The slow wave transmission line according to claim 1, wherein the contour line of the ground conductor forming the slit from one end to the other end in a direction intersecting the extension direction of the signal conductor is zigzag.

3. The slow wave transmission line according to claim 1, wherein the contour line of the slit in the ground conductor forming the slit from one end to the other in a direction intersecting the extension direction of the signal conductor is meandering.

4. A slow wave transmission line according to any one of claims 1 to 3, wherein the distance of a contour line from one end to the other end of the slit in the ground conductor in a parallel direction parallel to the extension direction of the signal conductor is longer than the distance of a straight line connecting the one end and the other end in the parallel direction.

5. The slow wave transmission line according to claim 4, wherein the contour line of the slit in the ground conductor from one end to the other end in a direction parallel to the extension direction of the signal conductor is zigzag.

6. A slow wave transmission line according to any one of claims 1 to 5, wherein the ground conductor has a frame portion having a pair of parallel direction portions that are parallel to the extension direction and opposed to each other, and a pair of intersecting direction portions that are parallel to the intersecting direction and opposed to each other, and a plurality of intersecting direction connecting portions that are located between the pair of intersecting direction portions in the frame portion and are located between adjacent slits in the plurality of slits to separate the adjacent slits.

7. A slow wave transmission line according to any one of claims 1 to 5, wherein the ground conductor has a plurality of enclosures surrounding each of the plurality of slits, and a plurality of parallel connecting portions facing the signal conductor, each connecting adjacent ones of the plurality of enclosures.

8. A slow wave transmission line according to any one of claims 1 to 7, wherein the signal conductor is a meander line.

9. The slow wave transmission line according to any one of claims 1 to 8, further comprising a second ground conductor on the opposite side of the signal conductor from the ground conductor, with a dielectric layer interposed therebetween, the second ground conductor having a plurality of second slits that intersect with the extension direction of the signal conductor, and the distance of a contour line from one end to the other end of the second slits in a cross direction that intersects with the extension direction of the signal conductor in the second ground conductor forming the second slits is longer than the distance of a straight line connecting the one end and the other end in the cross direction.

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