High-frequency circuit board

Abstract

Provided is a high-frequency circuit board which suppresses loss in a transmission mode conversion from a microstrip line to a coplanar line and can be manufactured through a simple process. A high-frequency circuit board according to the present disclosure comprises: a ground layer; a dielectric layer formed on the ground layer; a line including N layers of strip lines formed on the dielectric layer; and laminated ground conductors installed on the same plane as the strip lines of each of the second to N-th layers among the N layers of strip lines and on both sides, in the propagation direction of a high-frequency signal, of the strip lines of each of the second to N-th layers. In a cross section orthogonal to the propagation direction of the high-frequency signal, the intensity of an electric field generated in the ground layer from the lines and an electric field generated in the laminated ground conductors from the lines gradually change in N stages.

Description

High-frequency circuit board

[0001] The present disclosure relates to a high-frequency circuit board, and more particularly to a high-frequency circuit board for converting a transmission mode of a high-frequency signal in a semiconductor high-frequency module.

[0002] In a semiconductor high-frequency module, as a typical transmission line structure for propagating a signal at high speed on a transmission line substrate for high frequencies, a microstrip line, a coplanar line, a grounded coplanar line, etc. are used.

[0003] Among these, the coplanar line is often used when monolithically integrating a high-frequency circuit on a substrate. This is because the coplanar line has better compatibility with active elements such as transistors and diodes due to process constraints compared to the microstrip line, and because there is a ground portion for the signal only on one side of the surface, it is possible to perform measurements in a wafer state, etc.

[0004] However, it is not as easy for a coplanar line to convert the transmission characteristics to the coaxial mode of the measurement system as compared to a microstrip line. Therefore, a high-frequency circuit board that converts the mode of the coplanar line to the transmission mode of the microstrip line, which is easy to convert to the coaxial mode, that is, a high-frequency circuit board that converts the transmission mode from the coplanar line to the microstrip line (or from the microstrip line to the coplanar line) has been proposed (for example, see Patent Document 1).

[0005] FIG. 1 is a diagram showing a schematic structure of a high-frequency circuit board 100 that converts the transmission mode from a microstrip line to a coplanar line according to the prior art. (a) is a top view, (b) is a cross-sectional view taken along the Ib-Ib cross-section line, (c) is a cross-sectional view taken along the Ic-Ic cross-section line, and (d) is a cross-sectional view taken along the Id-Id cross-section line, respectively. Note that in FIG. 1, a form in the case of converting the transmission mode from a microstrip line to a coplanar line is illustrated.

[0006] As shown in Figure 1, the high-frequency circuit board 100 includes a ground surface 101, a dielectric substrate 102 formed on the ground surface 101, a conductor 103a formed on the dielectric substrate 102 and connected to the input terminal of the high-frequency circuit board 100, a conductor 103b connected to the output side of conductor 103a, a conductor 103c connected to the output side of conductor 103b and the output terminal of the high-frequency circuit board 100, open stubs 104a and 104b installed on the dielectric substrate 102 and on both sides in the width direction (y direction in Figure 1) of conductor 103b, and ground conductors 105a and 105b installed on the dielectric substrate 102 and on both sides in the width direction of conductor 103c. In the high-frequency circuit board 100, the longitudinal direction (x direction in Figure 1) corresponds to the signal propagation direction, and in this propagation direction, the region including conductor 103a corresponds to the microstrip line section 110, and the regions including conductors 103b and 103c correspond to the coplanar line section 120. Furthermore, the ground plane 101 is located only in the region corresponding to the microstrip line section 110 and is not located in the coplanar line section 120.

[0007] The high-frequency circuit board 100 has a typical circuit structure for virtual grounding, and the conversion of the transmission mode between the microstrip line section 110 and the coplanar line section 120 is achieved by making the connection point between the two virtual ground using open stubs 104a and 104b with a width of λ / 4 (where λ is the wavelength of the high-frequency signal).

[0008] Figure 2 shows a schematic structure of a high-frequency circuit board 200 that converts the transmission mode from a conventional microstrip line to a grounded coplanar line, where (a) is a top view, (b) is a cross-sectional view along the IIb-IIb cross-section, (c) is a cross-sectional view along the IIc-IIc cross-section, (d) is a cross-sectional view along the IId-IId cross-section, and (e) is a cross-sectional view along the IIe-IIe cross-section. Similar to Figure 1, Figure 2 illustrates an example of the configuration when converting the transmission mode from a microstrip line to a coplanar line.

[0009] As shown in Figure 2, the high-frequency circuit board 200 includes a ground plane 201, dielectric substrates 202a and 202b formed on the ground plane 201, a conductor 203a formed on the dielectric substrate 202a, a conductor 203b formed on the dielectric substrate 202b, ground conductors 204a and 204b installed on the dielectric substrate 202b and on both sides of the width direction (y direction in Figure 2) of the conductor 203b, via holes 205a and 205b connecting the ground conductors 204a and 204b to the ground plane 201, and a conductor ribbon 206 connecting the conductor 203a and the conductor 203b. In the high-frequency circuit board 200, as in Figure 1, the longitudinal direction (x direction in Figure 2) corresponds to the propagation direction of the high-frequency signal, and in this propagation direction, the region including the conductor 203a corresponds to the microstrip line section 210, and the region including the conductor 203b corresponds to the grounded coplanar line section 220.

[0010] In the high-frequency circuit board 200, the ground conductors 204a and 204b and the ground plane 201 are connected by via holes 205a and 205b in the grounded coplanar line section 220, thereby enabling conversion of the transmission mode between the microstrip line section 210 and the grounded coplanar line section 220.

[0011] However, conventional high-frequency circuit boards 100 and 200 have the problem of increased losses because the transmission mode conversion from the microstrip line section 110 to the coplanar line section 120 and from the microstrip line section 210 to the grounded coplanar line section 220 occurs abruptly.

[0012] In addition, in the high-frequency circuit board 200, the formation of via holes 205a and 205b is necessary to obtain good transmission characteristics in the high-frequency band, but there are process constraints, such as the need for difficult processing to form such via holes 205a and 205b.

[0013] Japanese Patent Application Publication No. 01-005102

[0014] This disclosure has been made in view of the above-mentioned problems, and its purpose is to provide a high-frequency circuit board that suppresses losses in the conversion of the transmission mode from a microstrip line to a coplanar line (or from a coplanar line to a microstrip line) and can be manufactured using a simple process.

[0015] To address the above-mentioned problems, this disclosure provides a high-frequency circuit board for converting the transmission mode of a high-frequency signal, comprising: a ground layer; a dielectric layer formed on the ground layer; and a transmission line formed on the dielectric layer, having a structure in which N layers (where N is an integer of 2 or more) of strip lines are stacked in the thickness direction; and a laminated ground conductor installed on the same plane as each of the 2nd to Nth layers of the N-layer strip lines, and on both sides in the propagation direction of the high-frequency signal with respect to each of the 2nd to Nth layers of the strip lines, having a structure in which N-1 pairs of ground conductors are stacked, and the input and output end faces of the N-1 pairs of ground conductors are from the 2nd to Nth layer A high-frequency circuit board is provided, comprising a laminated ground conductor located in the same plane as the input and output end faces of each strip line, wherein the length of each of the N-1 pairs of ground conductors in the direction perpendicular to the propagation direction increases in steps with increasing number of layers, wherein in a cross section perpendicular to the propagation direction of the high-frequency signal, the electric field generated from the line to the ground layer gradually decreases in N steps, and the electric field generated from the line to the laminated ground conductor gradually increases in N steps, or the electric field generated from the line to the ground layer gradually increases in N steps, and the electric field generated from the line to the laminated ground conductor gradually decreases in N steps.

[0016] The first diagram shows the schematic structure of a high-frequency circuit board 100 that converts the transmission mode from a conventional microstrip line to a coplanar line, where (a) is a top view, (b) is a cross-sectional view along the Ib-Ib cross-section, (c) is a cross-sectional view along the Ic-Ic cross-section, and (d) is a cross-sectional view along the Id-Id cross-section. The second diagram shows the schematic structure of a high-frequency circuit board 200 that converts the transmission mode from a conventional microstrip line to a grounded coplanar line, where (a) is a top view, (b) is a cross-sectional view along the IIb-IIb cross-section, (c) is a cross-sectional view along the IIc-IIc cross-section, (d) is a cross-sectional view along the IId-IId cross-section, and (e) is a cross-sectional view along the IIe-IIe cross-section. This figure shows the schematic structure of a high-frequency circuit board 300 that converts the transmission mode from a microstrip line to a grounded coplanar line according to the first embodiment of the present disclosure, where (a) is a top view, (b) is a cross-sectional view along the IIIb-IIIb cross-sectional line, (c) is a cross-sectional view along the IIIc-IIIc cross-sectional line, (d) is a cross-sectional view along the IIId-IIId cross-sectional line, (e) is a cross-sectional view along the IIIe-IIIe cross-sectional line, and (f) is a cross-sectional view along the IIIf-IIIf cross-sectional line. This figure schematically shows the electric field distribution in a cross section perpendicular to the propagation direction of the high-frequency signal of the high-frequency circuit board 300 according to the first embodiment of the present disclosure, where (a) shows the electric field distribution in the cross section along the IIIc-IIIc cross section line in Figure 3, (b) shows the electric field distribution in the cross section along the IIId-IIId cross section line in Figure 3, (c) shows the electric field distribution in the cross section along the IIIe-IIIe cross section line in Figure 3, and (d) shows the electric field distribution in the cross section along the IIIf-IIIf cross section line in Figure 3. This figure shows a schematic structure of a high-frequency circuit board 500 that converts the transmission mode from a microstrip line to a grounded coplanar line according to a second embodiment of the present disclosure, where (a) is a top view, (b) is a cross-sectional view along the Vb-Vb cross-section, (c) is a cross-sectional view along the Vc-Vc cross-section, (d) is a cross-sectional view along the Vd-Vd cross-section, (e) is a cross-sectional view along the Ve-Ve cross-section, and (f) is a cross-sectional view along the Vf-Vf cross-section.

[0017] Various embodiments of this disclosure are described below in detail with reference to the drawings. Identical or similar reference numerals indicate identical or similar elements, and redundant descriptions may be omitted. Materials and numerical values ​​are illustrative and are not intended to limit the technical scope of this disclosure. The following description is illustrative and some configurations may be omitted or modified, or implemented with additional configurations, without departing from the gist of one embodiment of this disclosure.

[0018] Furthermore, in the following description, the high-frequency circuit board according to this disclosure will be described as having a configuration in which a microstrip line is arranged on the input side and a granted coplanar line is arranged on the output side. However, this is intended as an example, and the high-frequency circuit board according to this disclosure may, for example, have a granted coplanar line on the input side and a microstrip line on the output side. Moreover, the high-frequency circuit board according to this disclosure may have a coplanar line on the input side and a microstrip line on the output side, or a microstrip line on the input side and a coplanar line on the output side.

[0019] The high-frequency circuit board according to this disclosure is configured such that, in a cross-section perpendicular to the propagation direction of the high-frequency signal, the electric field distribution changes in N steps with respect to the propagation direction. Furthermore, as the electric field distribution moves from the input terminal to the output terminal, the electric field strength generated from the transmission line (corresponding to the "conductor" in the prior art) to the ground layer (corresponding to the "ground surface" in the prior art) gradually decreases in N steps, while the electric field strength generated from the transmission line to the laminated ground conductor (corresponding to the "ground conductor" in the prior art) gradually increases in N steps.

[0020] However, as stated above, this applies to the case where a microstrip line is arranged on the input side and a grounded coplanar line is arranged on the output side. When the high-frequency circuit board according to this disclosure is arranged in the configuration where a grounded coplanar line is arranged on the input side and a microstrip line is arranged on the output side, in the electric field distribution described above, if the strength of the electric field generated from the line to the ground layer gradually increases in N steps, the strength of the electric field generated from the line to the laminated ground conductor is configured to gradually decrease in N steps.

[0021] (First Embodiment) Figure 3 shows a schematic structure of a high-frequency circuit board 300 that converts the transmission mode from a microstrip line to a grounded coplanar line according to the first embodiment of the present disclosure, where (a) is a top view, (b) is a cross-sectional view along the IIIb-IIIb cross-section, (c) is a cross-sectional view along the IIIc-IIIc cross-section, (d) is a cross-sectional view along the IIId-IIId cross-section, (e) is a cross-sectional view along the IIIe-IIIe cross-section, and (f) is a cross-sectional view along the IIIf-IIIf cross-section. As with Figures 1 and 2, Figure 3 illustrates an example of a configuration in which the transmission mode is converted from a microstrip line to a coplanar line.

[0022] As shown in Figure 3, the high-frequency circuit board 300 comprises a ground layer 301, a dielectric substrate 302 formed on the ground layer 301, a first strip line 303a formed on the dielectric substrate 302 and having a length from the input end to the output end, a second strip line 303b formed on the first strip line 303a, having a length shorter than the first strip line 303a in the high-frequency signal propagation direction (x direction in Figure 3), and arranged to be in contact with the output end, and the second strip line A third strip line 303c is formed on the trip line 303b, has a length shorter than the second strip line 303b in the direction of high-frequency signal propagation, and is positioned to be in contact with the output terminal; a fourth strip line 303d is formed on the third strip line 303c, has a length shorter than the third strip line 303c in the direction of high-frequency signal propagation, and is positioned to be in contact with the output terminal; and the second strip line 303b is on the same plane as the second strip line 303b and in the direction of high-frequency signal propagation The first ground conductors 304a and 304b are installed on both sides opposite to the first ground conductors 304a and 304b, and their length in the direction of propagation of the high-frequency signal is the same as the length of the second strip line 303b in the direction of propagation of the high-frequency signal. The first ground conductors 304a and 304b are installed on the same plane as the third strip line 303c, and on both sides opposite to the direction of propagation of the high-frequency signal, and their length in the direction of propagation of the high-frequency signal is the same as the length of the third strip line 303c in the direction of propagation of the high-frequency signal, and their length in the width direction (y direction in Figure 3) is the first ground conductors 304a and 304b are installed on both sides opposite to the first ground conductors 304a and 304b, and their length in the direction of propagation of the high-frequency signal is the same as the length of the third strip line 303c in the direction of propagation of the high-frequency signal. It includes second ground conductors 304c and d, which are longer than the widthwise length of the ground conductors 304a and b, and third ground conductors 304e and f, which are installed on the same plane as the fourth strip line 303d and on both sides with respect to the propagation direction of the high-frequency signal, and whose length in the propagation direction of the high-frequency signal is the same as the length of the fourth strip line 303d in the propagation direction of the high-frequency signal, and whose length in the widthwise is longer than the widthwise length of the second ground conductors 304c and d.

[0023] In the high-frequency circuit board 300, the first to fourth strip lines 303a-d are stacked in the thickness direction to form a single line. Here, the input end face of the first strip line 303a (more generally, the first layer of strip lines) is in contact with the input terminal of the high-frequency circuit board 300, and the input end faces of the second to fourth strip lines 303b-d (more generally, the second to Nth layers of strip lines) are shifted stepwise toward the output terminal side of the high-frequency circuit board 300 as the number of layers increases.

[0024] Similarly, in the high-frequency circuit board 300, the first to third ground conductors 304a, c, e and the first to third ground conductors 304b, d, g are stacked in pairs in the thickness direction to form a pair of stacked ground conductors. Here, the input and output end faces of the first to third ground conductors 304a-b, c-d, e-f (more generally, ground conductors from the 1st to the N-1th layer) are arranged to be in the same plane as the input and output end faces of the corresponding second to fourth strip lines 303b-d (more generally, strip lines from the 2nd to the Nth layer). In addition, the widthwise length of each of the first to third ground conductors 304a-b, c-d, e-f (more generally, ground conductors from the 1st to the N-1th layer) increases with the number of layers.

[0025] Furthermore, in the high-frequency circuit board 300, in the direction of high-frequency signal propagation, the region from the input end to the input-side end face of the second strip line 303b corresponds to the microstrip line section 310. On the other hand, in the direction of signal propagation, the region from the input-side end face of the second strip line 303b to the output end corresponds to the grounded coplanar line section 320.

[0026] As shown in Figure 3, if the distance between the second strip line 303b and the first ground conductors 304a and 304b is g1, the distance between the third strip line 303c and the second ground conductors 304c and 304d is g2, and the distance between the fourth strip line 303d and the third ground conductors 304e and 304f is g3, then the high-frequency circuit board 300 is configured such that g1 > g2 > g3.

[0027] Furthermore, it is preferable that the distance (g1) between the second strip line 303b and the first ground conductors 304a and 304b is the same as the distance (h1) between the first strip line 303a and the ground layer 301. Moreover, it is preferable that the distance (g2) between the third strip line 303c and the second ground conductors 304c and 304d is shorter than the distance (h1) between the first strip line 303a and the ground layer 301. This is due to achieving the electric field distribution described later.

[0028] In the high-frequency circuit board 300 having this configuration, the abrupt conversion of the transmission mode that occurred in the conventional high-frequency circuit boards 100 and 200 is suppressed. As a result, the high-frequency circuit board 300 can perform the conversion of the transmission mode from a microstrip line to a coplanar line with low loss. The mechanism that achieves this effect is described in detail below.

[0029] (Electric field distribution in a high-frequency circuit board according to the present disclosure) Figure 4 is a schematic representation of the electric field distribution in a cross section perpendicular to the propagation direction of the high-frequency signal of a high-frequency circuit board 300 according to the first embodiment of the present disclosure, where (a) shows the electric field distribution in the cross section along the IIIc-IIIc cross section in Figure 3, (b) shows the electric field distribution in the cross section along the IIId-IIId cross section in Figure 3, (c) shows the electric field distribution in the cross section along the IIIe-IIIe cross section in Figure 3, and (d) shows the electric field distribution in the cross section along the IIIf-IIIf cross section in Figure 3. In Figure 4, the electric field is schematically depicted by a dashed arrow.

[0030] The electric field distribution shown in Figure 4(a) is the electric field distribution in the microstrip line section 310, and corresponds to the electric field distribution near the input terminal of the high-frequency circuit board 300. In this region, the electric field is generated around the line (i.e., the first strip line 303a) and (approximately perpendicular to) the ground layer 301.

[0031] On the other hand, the electric field distribution shown in Figure 4(d) corresponds to the electric field distribution near the output terminal of the high-frequency circuit board 300. In this region, the electric field is generated around the transmission line (i.e., the first to fourth strip transmission lines 303a-d) and between the transmission line and the laminated ground conductor, along approximately the width direction, but not with respect to the ground layer 301.

[0032] The high-frequency circuit board 300 according to this disclosure is characterized in that regions that generate an intermediate electric field distribution are provided between regions having such electric field distributions. By generating such an intermediate electric field distribution, an intermediate signal transmission mode can be easily formed, making it possible to suppress the abrupt conversion of the transmission mode, which is a problem in the prior art.

[0033] The electric field distribution shown in Figure 4(b) is the electric field distribution in a cross-section perpendicular to the propagation direction of the high-frequency signal in the region from the input end face of the second strip line 303b to the input end face of the third strip line 303c. The electric field distribution in this region differs from the electric field distribution in the microstrip line section 310 shown in Figure 4(a), as an electric field is also generated between the line and the ground conductors 304a and 304b. In order to realize such an electric field distribution, it is preferable that the distance (g1) between the second strip line 303b and the first ground conductors 304a and 304b is the same as the distance (h1) between the first strip line 303a and the ground layer 301.

[0034] The electric field distribution shown in Figure 4(c) is the electric field distribution in a cross-section perpendicular to the propagation direction of the high-frequency signal in the region from the input end face of the third strip line 303c to the input end face of the fourth strip line 303d. Compared to the electric field distribution shown in Figure 4(b), the electric field strength with respect to the ground layer 301 is weaker in this region, while conversely, the electric field generated between the line and the laminated ground conductor is stronger. In order to generate such an electric field distribution, it is preferable that the distance (g2) between the third strip line 303c and the second ground conductors 304c and d is shorter than the distance (h1) between the first strip line 303a and the ground layer 301.

[0035] Thus, the high-frequency circuit board 300 according to this disclosure is configured such that, in a cross-section perpendicular to the propagation direction of the high-frequency signal, the electric field generated from the transmission line to the ground layer gradually weakens as it moves from the input terminal to the output terminal. Conversely, the electric field generated from the transmission line to the laminated ground conductor gradually strengthens as it moves from the input terminal to the output terminal. As a result, the abrupt conversion of the transmission mode that occurred in the prior art is suppressed, and low-loss conversion of the transmission mode can be achieved.

[0036] Furthermore, as described above, the high-frequency circuit board 300 has a structure that can be manufactured solely by stacking two-dimensional structures. Therefore, the high-frequency circuit board 300 does not require difficult processing for the formation of via holes and can be manufactured using a simple manufacturing process. This effect can contribute to reducing manufacturing costs and manufacturing lead times.

[0037] (Second Embodiment) A second embodiment of the present disclosure will be described in detail below with reference to the drawings. The high-frequency circuit board according to the second embodiment of the present disclosure has a configuration in which the distance between the line and the ground layer (corresponding to h1 in Figure 3) also changes in steps with respect to the propagation direction of the high-frequency signal, in order to suppress changes in the characteristic impedance with respect to the propagation direction of the high-frequency signal compared to the high-frequency circuit board 300 described above.

[0038] In general, in parallel plate capacitors where the distance between the plates is extremely small compared to the length of one side of the plates, the electric field between the plates can be considered uniform, and the parallel capacitance in this case is known to be proportional to the plate area and inversely proportional to the distance between the plates, as shown in equation (1).

[0039]

[0040] Here, C is the parallel capacitance, h is the plate spacing, ε is the dielectric constant, and S is the plate area. As can be seen from equation (1), the parallel capacitance C increases as the plate spacing h decreases.

[0041] On the other hand, it is generally known that the characteristic impedance of the plates is given by equation (2).

[0042]

[0043] Here, \(Z_0\) is the characteristic impedance, \(R\) is the series resistance per unit length, \(L\) is the series inductance, \(G\) is the shunt conductance, \(C\) is the shunt capacitance, \(j\) represents the imaginary unit, and \(\omega\) represents the angular frequency, respectively.

[0044] In the high-frequency circuit board 300 described above, the distance (\(h_1\)) between the first strip line 303a and the ground layer 301 is configured to be always constant with respect to the propagation direction of the high-frequency signal. In such a configuration, as can be understood from equations (1) and (2), the characteristic impedance decreases as it goes towards the output side.

[0045] The high-frequency circuit board according to the second embodiment takes such an event into consideration and has a configuration in which the change in the characteristic impedance with respect to the propagation direction of the high-frequency signal is suppressed as compared with the high-frequency circuit board 300.

[0046] FIG. 5 is a diagram showing a schematic structure of a high-frequency circuit board 500 that converts the transmission mode from a microstrip line to a grounded coplanar line according to the second embodiment of the present disclosure. (a) is a top view, (b) is a cross-sectional view taken along the Vb - Vb cross-section line, (c) is a cross-sectional view taken along the Vc - Vc cross-section line, (d) is a cross-sectional view taken along the Vd - Vd cross-section line, (e) is a cross-sectional view taken along the Ve - Ve cross-section line, and (f) is a cross-sectional view taken along the Vf - Vf cross-section line, respectively. Note that, similar to FIGS. 1 - 3, in FIG. 5, a form in the case of converting the transmission mode from a microstrip line to a coplanar line is exemplified.

[0047] As shown in FIG. 5, the high-frequency circuit board 500 includes a ground layer 501, a dielectric substrate 502 formed on the ground layer 501, a first strip line 503a disposed on the dielectric substrate 502 and contacting the input end, a second strip line 503b formed on the first strip line 503a, a third strip line 503c formed on the second strip line 503b, a fourth strip line 503d formed on the third strip line 503c, first ground conductors 504a and 504b that are on the same plane as the second strip line 503b and are installed on both sides in the width direction (y direction in FIG. 5) of the second strip line 503b and have the same length in the signal propagation direction (x direction in FIG. 5) as the propagation direction length of the second strip line 503b, second ground conductors 504c and 504d that are on the same plane as the third strip line 503c and are installed on both sides in the width direction (y direction in FIG. 5) of the third strip line 503c, have the same length in the signal propagation direction (x direction in FIG. 5) as the propagation direction length of the third strip line 503c, and have a longer length in the width direction (y direction in FIG. 5) than the first ground conductors 504a and 504b, and third ground conductors 504e and 504f that are on the same plane as the fourth strip line 503d and are installed on both sides in the width direction (y direction in FIG. 3) of the fourth strip line 503d, have the same length in the signal propagation direction (x direction in FIG. 3) as the propagation direction length of the fourth strip line 503d, and have a longer length in the width direction (y direction in FIG. 3) than the second ground conductors 504c and 504d.

[0048] In the high-frequency circuit board 500, unlike the high-frequency circuit board 300 according to the first embodiment, the output end face of the first strip line 503a is configured to be at a position corresponding to the input end face of the third strip line 503c, rather than the output terminal of the high-frequency circuit board 500. Similarly, the output end face of the second strip line 503b is configured to be at a position corresponding to the input end face of the fourth strip line 503d, rather than the output terminal of the high-frequency circuit board 500. With this configuration, in the high-frequency circuit board 500, the distance between the ground layer 501 and the lines increases in a stepwise manner with respect to the propagation direction of the high-frequency signal, corresponding to the stepwise change in the electric field distribution shown in Figure 4. Therefore, from equations (1) and (2), the change in characteristic impedance with respect to the signal propagation direction is suppressed in the high-frequency circuit board 500 compared to the high-frequency circuit board 300.

[0049] (Modifications) In the high-frequency circuit boards 300 and 500 according to the present disclosure described above, the dielectric substrates 302 and 502 may be, for example, resin materials such as benzocyclolobutene (BCB), polyphenylene ether resin (PPE), bismalade triazine (BT-resin), polyimide resin, epoxy resin, cyanide resin, phenolic resin, or inorganic materials such as ceramics. Also, the ground layers 301 and 501 and the first to fourth strip lines 303a-d and 503a-d may be made of Au. However, these are examples and are not intended to limit the materials used for each. The dielectric substrates 302 and 502 may be made of any dielectric material depending on the design, and the ground layers 301 and 501 and the first to fourth strip lines 303a-d and 503a-d may be made of any conductor depending on the design.

[0050] Furthermore, in Figures 3 and 5, the lengths in the width direction (y-direction in Figures 3 and 5) and the lengths in the thickness direction (z-direction in Figures 3 and 5) of the first to fourth strip lines 303a-d and 503a-d are depicted as being the same. However, these are intended as examples, and the width and thickness of the first to fourth strip lines 303a-d and 503a-d can be arbitrarily set according to the design (more specifically, to satisfy the electric field distribution described above). In addition, in the high-frequency circuit boards 300 and 500, the characteristic impedances of the input and output sides may be set to be the same or different.

[0051] Furthermore, in Figures 3 and 5, the transmission line is depicted as having a structure in which four layers of strip lines are stacked in the thickness direction. Similarly, the laminated ground conductor is depicted as having a structure in which three pairs of ground conductors are stacked in the thickness direction. However, the number of strip line layers in the high-frequency circuit board according to this disclosure may be multiple, and the number of layers of ground conductor pairs may be one less than the number of strip lines (excluding the 1 corresponding to the region closest to the input terminal). In other words, in the high-frequency circuit board according to this disclosure, the transmission line may consist of N (where N is an integer of 2 or more) layers of strip lines, and the laminated ground conductor may have a structure in which N-1 layers of ground conductors are stacked.

[0052] As described above, the high-frequency circuit board according to this disclosure can suppress the abrupt transmission mode conversion from microstrip lines to coplanar lines (or from coplanar lines to microstrip lines) compared to the prior art. As such a high-frequency circuit board capable of low-loss transmission mode conversion, it is expected to be applied to semiconductor high-frequency modules and the like.

Claims

1. A high-frequency circuit board for converting the transmission mode of a high-frequency signal, comprising: a ground layer; a dielectric layer formed on the ground layer; a line formed on the dielectric layer, having a structure in which N layers (where N is an integer of 2 or more) of strip lines are stacked in the thickness direction; and a laminated ground conductor installed on the same plane as each of the 2nd to Nth layers of the N-layer strip lines, and on both sides in the propagation direction of the high-frequency signal with respect to each of the 2nd to Nth layers of the strip lines, having a structure in which N-1 pairs of ground conductors are stacked, the input and output end faces of the N-1 pairs of ground conductors are located in the same plane as the input and output end faces of each of the 2nd to Nth layers of the strip lines, and the length of each of the N-1 pairs of ground conductors in the direction perpendicular to the propagation direction increases in stages with increasing number of layers.

2. The high-frequency circuit board according to claim 1, wherein, as the number of layers increases, the length of each of the N layers of strip lines in the propagation direction gradually decreases in N steps, the input end face of the first layer of strip lines is in contact with the input terminal of the high-frequency circuit board, and the output end face is in contact with the output terminal of the high-frequency circuit board, and the output end faces of the second to the Nth layer of strip lines are in contact with the output terminal of the high-frequency circuit board.

3. The high-frequency circuit board according to claim 2, configured such that the distance between the second layer strip line and the first layer ground conductor corresponding to the second layer strip line is the same as the distance between the first layer strip line and the ground layer, and the distance between the third layer strip line and the second layer ground conductor corresponding to the third layer strip line is shorter than the distance between the first layer strip line and the ground layer.

4. The high-frequency circuit board according to claim 1, wherein, as the number of layers increases, the position of the input end face of each of the N layers of strip lines in the propagation direction is gradually shifted toward the output side, the input end face of the first layer of strip lines is in contact with the input terminal of the high-frequency circuit board, the output end face of the Nth layer of strip lines is in contact with the output terminal of the high-frequency circuit board, and the distance between the line and the ground layer is gradually increased as the number of layers increases.

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