CONNECTION STRUCTURE BETWEEN DIELECTRIC WAVEGUIDE LINE AND WAVEGUIDE

TECHNICAL FIELD

The present disclosure relates to a connection structure between a dielectric waveguide line and a waveguide.

BACKGROUND ART

Recently, communication traffic has increased rapidly due to the expansion of large-capacity communication applications such as streaming video in addition to the increase in the number of terminals because of the spread of mobile terminal devices such as smartphones. Under such circumstances, it is expected to achieve large-capacity communication using the sub-terahertz band having a wide frequency band. The sub-terahertz band here generally refers to a frequency band of 100 GHz or more.

In a high frequency band module such as a millimeter wave band according to related art, LTCC (Low Temperature Co-fired Ceramics), which is easy to be multilayered and has a high degree of freedom in design, is widely used. Resin substrates are often used, because the loss of the material is inherently low and transmission loss of the resin substrate is also low because of a low dielectric constant (reduction of wavelength shortening effect). The resin substrate is PTFE (PolyTetraFluoroEthylene), LCP (Liquid Crystal Polymer), or the like.

Since the wavelength is very small in the sub-terahertz band, higher processing accuracy is required for a transmission line or the like of a high-frequency signal. Further, there is no room in gain performance of a semiconductor element such as an amplifier, and thus it is important to transmit a high frequency signal more efficiently. Thus, it is desirable that the loss of materials used for the package be low. Since the dimensional accuracy of LTCC, which is commonly used in the millimeter wave band, is not very high and the loss thereof is relatively large, it is difficult to employ LTCC in the sub-terahertz band. On the other hand, although the loss of the resin substrate is low, the resin substrate has low rigidity, the methods of mounting the resin substrate are limited, and its dimensional accuracy is not very high, which makes it difficult to employ the resin substrate in the sub-terahertz band, like the LTCC.

Quartz is known as a substrate material having high rigidity, easy to achieve high dimensional accuracy, low loss, and low dielectric constant. However, since the formation of via holes is difficult, the use of the via holes has been limited, and thus the via holes have not been widely used. Recently, the progress of the technique for forming via holes has enabled fine via holes to be formed with high accuracy, which results in an increase in the use of quartz for millimeter-wave band packages.

When a high antenna gain is required for long-distance transmission in wireless communication, an antenna having a waveguide interface such as a cassegrain antenna or a lens antenna is commonly used. In this case, it is important to efficiently transmit the high-frequency signal from the package to the waveguide.

Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2000-196301) describes a structure for connecting a dielectric waveguide line to a rectangular waveguide using a dielectric waveguide line having low loss as compared with a transmission line having a planar structure such as a microstrip line or a coplanar line as a transmission line on a package. The dielectric waveguide line structure is formed by connecting conductor surfaces formed on both top and bottom surfaces of a dielectric substrate by two via hole arrays. Each via hole array is composed of via holes formed at spacings of ½ or less of the guide wavelength, and functions equivalently as a waveguide sidewall surface. Here, the guide wavelength λ_g is λ/√(1−(λ/λ_c){circumflex over ( )}2). Here, λ is 1/√(ε_r) of a vacuum wavelength of an operating frequency signal, ε_r is a dielectric constant of a dielectric substrate, and λ_c is a cutoff wavelength (which is two times the width of the dielectric waveguide line in TE_10 mode) of the dielectric waveguide line.

An opening for coupling is provided in one of the top and bottom conductor surfaces of one end of the dielectric waveguide line, and a rectangular waveguide is connected to the opening in the vertical direction. The transmission of electromagnetic waves between the dielectric waveguide line and the rectangular waveguide is achieved by electric field coupling through the opening for coupling. Since the thickness of the dielectric substrate of the dielectric waveguide line is set to ¼ of the guide wavelength, the electric field intensity reaches its maximum at the opening for coupling. Thus, efficient transmission of electromagnetic waves between the dielectric waveguide line and the rectangular waveguide is achieved.

SUMMARY OF INVENTION
Technical Problem

Patent Literature 1 describes an example of manufacturing a dielectric waveguide line using a multilayer ceramic technology. The thickness of the dielectric waveguide line is adjusted by the number of layers of the green sheet to be laminated. Further, a green sheet may be laminated on a surface of a substrate on which the dielectric waveguide line is formed, which is the surface opposite to the surface in which the opening for coupling is formed. If this dielectric waveguide line is applied to the sub-terahertz band, even when the thickness of the dielectric waveguide line is very small, the thickness of the entire substrate can be increased, which enables the strength of the entire substrate to be sufficient. However, it is difficult to use this dielectric waveguide line in terms of transmission loss.

On the other hand, when a dielectric waveguide line is formed using quartz, which is expected to be used in a sub-terahertz band, for example, in a dielectric waveguide line having a cross-sectional shape with a lateral width of 0.75 mm, ¼ of the guide wavelength at 160 GHz becomes 0.31 mm, which is very small. Since quartz is rigid and easily cracked, the optimum thickness of a quartz substrate, which is difficult to be multilayered, becomes very small, and thus ensuring the strength of the substrate has been a problem.

An object of the present disclosure is to provide a connection structure that solves any of the foregoing problems.

Solution to Problem

According to the present disclosure, a connection structure between a dielectric waveguide line and a waveguide is provided. The dielectric waveguide line includes: a first dielectric substrate including a first substrate surface and a second substrate surface opposite to the first substrate surface; a first conductor layer disposed on the first substrate surface; a second conductor layer disposed on the second substrate surface; and two arrays of through conductor groups composed of a plurality of through conductors formed in a transmission direction of the dielectric waveguide line at spacings of ½ or less of a dielectric guide wavelength as a guide wavelength of a high-frequency signal in the dielectric waveguide line, the two arrays of through conductor groups electrically connecting the first conductor layer to the second conductor layer and being formed apart from each other in a direction orthogonal to the transmission direction, and a transmission region, in which the high-frequency signal propagates, being formed surrounded by the first conductor layer, the second conductor layer, and the two arrays of through conductor groups. A coupling window is formed in the second conductor layer.

The waveguide is disposed in such a way that an open end surface of the waveguide faces the coupling window, and that the transmission direction of the dielectric waveguide line becomes orthogonal to the transmission direction of the waveguide. A plurality of recesses are formed in the first substrate surface in the vicinity of the coupling window. A recessed conductor layer electrically connected to the first conductor layer is formed on inner wall surfaces of the plurality of recesses.

Advantageous Effects of Invention

According to the present disclosure, in the connection structure between the dielectric waveguide line and the waveguide, by forming a local recess in the dielectric substrate without thinning the entire dielectric substrate, satisfactory transmission characteristics can be achieved while ensuring mechanical strength of the dielectric substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of a connection structure according to a first example embodiment;

FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1;

FIG. 3 is a cross-sectional view taken along the line of FIG. 1;

FIG. 4 is a plan view of a connection structure according to a second example embodiment;

FIG. 5 is a plan view of a connection structure according to a third example embodiment;

FIG. 6 is a plan view of a connection structure according to a fourth example embodiment;

FIG. 7 is a plan view of a connection structure according to a fifth example embodiment;

FIG. 8 is a cross-sectional view of a connection structure according to a sixth example embodiment;

FIG. 9 is a plan view of a connection structure according to a seventh example embodiment;

FIG. 10 is a graph showing an improvement in transmission characteristics because of the connection structure; and

FIG. 11 is a cross-sectional view of a connection structure according to an eighth example embodiment.

DESCRIPTION OF EMBODIMENTS
First Example Embodiment

Hereinafter, a first example embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is a plan view of a connection structure according to the first example embodiment. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1. FIG. 3 is a cross-sectional view taken along the line of FIG. 1.

FIGS. 1 to 3 show a connection structure 3 between a dielectric waveguide line 1 and a rectangular waveguide 2. As shown in FIG. 2, the connection structure 3 includes a dielectric waveguide line 1 and a rectangular waveguide 2. The dielectric waveguide line 1 and the rectangular waveguide 2 are connected to each other in such a way that a transmission direction 1A of an operating frequency signal in the dielectric waveguide line 1 becomes orthogonal to a transmission direction 2A of a operating frequency signal in the rectangular waveguide 2. The operating frequency signal is a specific example of a high frequency signal.

As shown in FIGS. 1 and 2, the dielectric waveguide line 1 includes a first dielectric substrate 5, a first conductor layer 6, a second conductor layer 7, and two arrays of via hole groups 8.

The first dielectric substrate 5 is, for example, quartz. As shown in FIG. 2, the first dielectric substrate 5 includes a first substrate surface 5a facing upward and a second substrate surface 5b facing downward on a surface opposite to the first substrate surface 5a. A thickness 5T of the first dielectric substrate 5 is, for example, 0.35 millimeters.

The first conductor layer 6 is a conductor layer disposed on the first substrate surface 5a of the first dielectric substrate 5. The second conductor layer 7 is a conductor layer disposed on the second substrate surface 5b of the first dielectric substrate 5. The first conductor layer 6 and the second conductor layer 7 are made of, for example, copper. The thickness of the first conductor layer 6 and the second conductor layer 7 is, for example, 20 micrometers.

The two arrays of via hole groups 8 are specific examples of the two arrays of conductor through-hole groups. As shown in FIG. 1, the two arrays of via hole groups 8 include a first via hole group 9 and a second via hole group 10.

The first via hole group 9 includes a plurality of via holes 9a. The plurality of via holes 9a are arranged at predetermined spacings along the transmission direction 1A of the dielectric waveguide line 1. The plurality of via holes 9a electrically connect the first conductor layer 6 to the second conductor layer 7. The above predetermined spacing is ½ or less of a dielectric guide wavelength as a guide wavelength of the operating frequency signal in the dielectric waveguide line 1. Note that the guide wavelength λ_g is calculated by λ/√(1−(λ/λ_c){circumflex over ( )}2). Here, λ is 1/√(ε_r) of a vacuum wavelength of an operating frequency signal, ε_r is a dielectric constant of a dielectric substrate, and λ_c is a cutoff wavelength (which is two times the width of the dielectric waveguide line in TE_10 mode) of the dielectric waveguide line.

The second via hole group 10 includes a plurality of via holes 10a. The plurality of via holes 10a are arranged at the above predetermined spacings along the transmission direction 1A of the dielectric waveguide line 1. The plurality of via holes 10a electrically connect the first conductor layer 6 to the second conductor layer 7.

The first via hole group 9 and the second via hole group 10 are formed to extend along the transmission direction 1A of the dielectric waveguide line 1.

The first via hole group 9 and the second via hole group 10 are formed to be parallel to each other. The first via hole group 9 and the second via hole group 10 are formed apart from each other in a direction orthogonal to the transmission direction 1A of the dielectric waveguide line 1 in a plan view shown in FIG. 1.

The first via hole group 9 and the second via hole group 10 function equivalently as a waveguide sidewall. Thus, a transmission region Q surrounded by the first conductor layer 6, the second conductor layer 7, and two arrays of the via hole groups 8 is defined. The operating frequency signal is transmitted in the transmission region Q.

As shown in FIG. 1, the dielectric waveguide line 1 includes a third via hole group 11. The third via hole group 11 includes a plurality of via holes 11a. The plurality of via holes 11a are arranged at the above predetermined spacings along the direction orthogonal to the transmission direction 1A of the dielectric waveguide line 1 in the plan view shown in FIG. 1. The plurality of via holes 11a electrically connect the first conductor layer 6 to the second conductor layer 7. Thus, the third via hole group 11 functions as a short-circuit termination of the transmission region Q.

As shown in FIGS. 1 to 3, a coupling window 12 is formed in the second conductor layer 7. The coupling window 12 is an opening in the second conductor layer 7. As shown in FIG. 1, the coupling window 12 is formed in a rectangular shape which is narrow in the transmission direction 1A of the dielectric waveguide line 1 and wide in the direction orthogonal to the transmission direction 1A of the dielectric waveguide line 1. The coupling window 12 is formed in the vicinity of the third via hole group 11. The coupling window 12 is formed on the upstream side of the transmission direction 1A of the dielectric waveguide line 1 as viewed from the third via hole group 11. As shown in FIGS. 2 and 3, the rectangular waveguide 2 is disposed in such a way that an open end surface 13 of the rectangular waveguide 2 faces the coupling window 12. The rectangular waveguide 2 is disposed in such a way that at least a part of the open end surface 13 of the rectangular waveguide 2 faces the coupling window 12. The rectangular waveguide 2 is disposed in such a way that the coupling window 12 is inside the open end surface 13. The operating frequency signal is transmitted between the dielectric waveguide line 1 and the rectangular waveguide 2 through the coupling window 12.

Returning to FIG. 1, a plurality of recesses 15 are formed in the first substrate surface 5a of the first dielectric substrate 5 in the vicinity of the coupling window 12. The plurality of recesses 15 include a plurality of transmission-direction translational recesses 15a (stretching recess) and a plurality of transmission-direction orthogonal recesses 15b (stretching recess).

The plurality of transmission-direction translational recesses 15a extend along the transmission direction 1A of the dielectric waveguide line 1. The plurality of transmission-direction orthogonal recesses 15b extend along the direction in which the two arrays of the via hole groups 8 of face each other. The plurality of transmission-direction translational recesses 15a and the plurality of transmission-direction orthogonal recesses 15b are formed in a lattice shape.

Specifically, the plurality of transmission-direction translational recesses 15a are formed at the above predetermined spacings in the direction in which the two arrays of via hole groups 8 face each other. The plurality of transmission-direction translational recesses 15a are formed parallel to each other. The plurality of transmission-direction translational recesses 15a are formed apart from each other.

Similarly, the plurality of transmission-direction orthogonal recesses 15b are formed at the above predetermined spacings in the transmission direction 1A of the dielectric waveguide line 1. The plurality of transmission-direction orthogonal recesses 15b are formed parallel to each other. The plurality of transmission-direction orthogonal recesses 15b are formed apart from each other. The transmission-direction orthogonal recess 15b on the most downstream side in the transmission direction 1A among the plurality of transmission-direction orthogonal recesses 15b of the dielectric waveguide line 1 is formed so as to overlap with the third via hole group 11.

As shown in FIGS. 2 and 3, a recessed conductor layer 16 electrically connected to the first conductor layer 6 is formed on inner wall surfaces of the plurality of recesses 15. The recessed conductor layer 16 is formed, for example, by plating.

As described above, by forming the plurality of transmission-direction translational recesses 15a at the above predetermined spacings, the plurality of transmission-direction translational recesses 15a function equivalently as an upper surface of the waveguide for the operating frequency signal. The same applies to the plurality of transmission-direction orthogonal recesses 15b. It is desirable that the above predetermined spacings be ¼ or less of the dielectric guide wavelength in order to make the bottom surfaces of the plurality of recesses 15 function as substantially uniform conductor surfaces equivalently.

By forming the plurality of recesses 15 in this manner, it is possible to make the thickness of the first dielectric substrate 5 in the vicinity of the coupling window 12 approximately ¼ of the dielectric guide wavelength, which is equivalently optimum, without reducing the thickness of the entire first dielectric substrate 5 in the vicinity of the coupling window 12. In this example embodiment, as shown in FIG. 2, a distance 5S between bottom surfaces of the plurality of recesses 15 and the second substrate surface 5b is set to ¼ of the dielectric guide wavelength. In particular, the thickness of the first dielectric substrate 5 in the vicinity of the coupling window 12 dominantly contributes to the transmission characteristics of the connection structure between the dielectric waveguide line 1 and the rectangular waveguide 2.

Further, since the plurality of recesses 15 are formed in the lattice shape, the mechanical strength of the first dielectric substrate 5 can be ensured as compared with the case where the first dielectric substrate 5 is made uniformly thin in the vicinity of the coupling window 12.

Here, for example, an example of a method of forming a plurality of recesses 15 when the first dielectric substrate 5 is made of quartz will be described. In order to form each of the recesses 15, a via hole not penetrating the first dielectric substrate 5 may be formed a plurality of times at a pitch of a radius of the via hole.

Next, an example of a method of forming the via hole will be described.

(1) First, a locus part of a focal point of a quartz substrate is modified by irradiating a center position of the via hole with a femtosecond laser and scanning the focal point.

(2) Next, the quartz substrate is treated with hydrofluoric acid. Then, the modified part of the quartz substrate is selectively and preferentially etched, and then etched isotropically and gently. By doing so, non-penetrating via holes are formed in the quartz substrate.

(3) When the via hole is formed a plurality of times at the pitch of about the radius of the via holes, the adjacent via holes are connected to each other in an isotropic etching process to thereby form the recesses 15 extending in a predetermined direction.

(4) When the locus of the focal point is formed so as to penetrate through the quartz substrate, a through via hole can be formed in a manner similar to the above.

As described above, the connection structure 3 between the dielectric waveguide line 1 and the rectangular waveguide 2 (waveguide) includes the dielectric waveguide line 1 and the rectangular waveguide 2. The dielectric waveguide line 1 includes the first dielectric substrate 5 having the first substrate surface 5a and the second substrate surface 5b opposite to the first substrate surface 5a. The dielectric waveguide line 1 includes the first conductor layer 6 disposed on the first substrate surface 5a and the second conductor layer 7 disposed on the second substrate surface 5b. The dielectric waveguide line 1 includes the two arrays of via hole groups 8 (through conductor group). The two arrays of via hole groups 8 are formed by forming a plurality of via holes 9a and via holes 10a (through conductors) in the transmission direction 1A of the dielectric waveguide line 1 at spacings of ½ or less of the dielectric guide wavelength as the guide wavelength of the high-frequency signal in the dielectric waveguide line 1. The two arrays of via hole groups 8 electrically connect the first conductor layer 6 to the second conductor layer 7. The two arrays of via hole groups 8 are formed apart from each other in the direction orthogonal to the transmission direction 1A. The dielectric waveguide line 1 transmits the high frequency signal in the transmission region Q surrounded by the first conductor layer 6, the second conductor layer 7, and the two arrays of via hole groups 8 (through conductor group). The coupling window 12 is formed in the second conductor layer 7. The rectangular waveguide 2 is disposed in such a way that the open end surface 13 of the rectangular waveguide 2 faces the coupling window 12 and the transmission direction 1A of the dielectric waveguide line 1 becomes orthogonal to the transmission direction 2A of the rectangular waveguide 2. The plurality of recesses 15 are formed in the first substrate surface 5a in the vicinity of the coupling window 12. The recessed conductor layer 16 electrically connected to the first conductor layer 6 is formed on the inner wall surfaces of the plurality of recesses 15.

According to the above-described configuration, the local recesses 15 are formed in the first dielectric substrate 5 without reducing the thickness of the entire first dielectric substrate 5, thereby achieving satisfactory transmission characteristics while ensuring the mechanical strength of the first dielectric substrate 5.

Second Example Embodiment

Next, a second example embodiment will be described with reference to FIG. 4. Hereinafter, a difference between this example embodiment and the first example embodiment will be mainly described, and the repeated description will be omitted.

As shown in FIG. 4, in this example embodiment, the plurality of recesses 15 do not include the plurality of transmission-direction translational recesses 15a, and instead include only the plurality of transmission-direction orthogonal recesses 15b. The plurality of transmission-direction orthogonal recesses 15b are formed in the vicinity of the coupling window 12. Thus, the area where the plurality of recesses 15 are formed is smaller as compared with the first example embodiment, and thus the uniformity of the function as the upper surface of the waveguide is deteriorated, but productivity and mechanical strength can be improved.

Third Example Embodiment

Next, a third example embodiment will be described with reference to FIG. 5. Hereinafter, a difference between this example embodiment and the first example embodiment will be mainly described, and the repeated description will be omitted.

As shown in FIG. 5, in this example embodiment, the plurality of recesses 15 do not include the plurality of transmission-direction orthogonal recesses 15b, and instead include only the plurality of transmission-direction translational recesses 15a. The plurality of transmission-direction translational recesses 15a are formed in the vicinity of the coupling window 12. Thus, the area where the plurality of recesses 15 are formed is smaller as compared with the first example embodiment, and thus the uniformity of the function as the upper surface of the waveguide is deteriorated, but productivity and mechanical strength can be improved.

Fourth Example Embodiment

Next, a fourth example embodiment will be described with reference to FIG. 6. Hereinafter, a difference between this example embodiment and the first example embodiment will be mainly described, and the repeated description will be omitted.

In the first example embodiment, the plurality of recesses 15 include the plurality of transmission-direction translational recesses 15a and the plurality of transmission-direction orthogonal recesses 15b.

On the other hand, in this example embodiment, the plurality of recesses 15 include a plurality of transmission-direction oblique recesses 15c (stretching recess) extending obliquely with respect to the transmission direction 1A of the dielectric waveguide line 1 in a plan view shown in FIG. 6. The plurality of transmission-direction oblique recesses 15c are formed in the vicinity of the coupling window 12. The plurality of transmission-direction oblique recesses 15c are formed in a lattice shape.

Some of the transmission-direction oblique recesses 15c among the plurality of transmission-direction oblique recesses 15c are formed parallel to each other and at the above predetermined spacings.

Further, the recesses 15 further include two transmission-direction translational recesses 15a and two transmission-direction orthogonal recesses 15b so as to surround the plurality of transmission-direction oblique recesses 15c formed in the lattice shape. The two transmission-direction translational recesses 15a and the two transmission-direction orthogonal recesses 15b are formed in a rectangular shape so as to surround the plurality of transmission-direction oblique recesses 15c.

Fifth Example Embodiment

Next, a fifth example embodiment will be described with reference to FIG. 7. Hereinafter, a difference between this example embodiment and the first example embodiment will be mainly described, and the repeated description will be omitted.

On the other hand, in this example embodiment, the plurality of recesses 15 include a plurality of cylindrical recesses 15d extending in shapes of cylinders from the first conductor layer 6 toward the second conductor layer 7. The plurality of cylindrical recesses 15d are formed in the vicinity of the coupling window 12. The plurality of cylindrical recesses 15d are formed in a matrix shape. The plurality of cylindrical recesses 15d are non-penetrating via holes. Thus, the area where the plurality of recesses 15 are formed is smaller as compared with the first example embodiment, and thus the uniformity of the function as the upper surface of the waveguide is deteriorated, but productivity and mechanical strength can be improved.

Sixth Example Embodiment

Next, a sixth example embodiment will be described with reference to FIG. 8. Hereinafter, a difference between this example embodiment and the first example embodiment will be mainly described, and the repeated description will be omitted.

In this example embodiment, a depth D of each of the plurality of recesses 15 is gradually increased toward the transmission direction 1A of the dielectric waveguide line 1. In this configuration, the thickness of the first dielectric substrate 5 is equivalently and gradually reduced toward the transmission direction 1A of the dielectric waveguide line 1. According to the above configuration, an electric field vector in the longitudinal direction in the dielectric waveguide line 1 can be smoothly converted into an electric field vector in the lateral direction in the rectangular waveguide 2. Thus, more efficient transmission can be performed.

The configuration in which the depth D of each the plurality of recesses 15 is gradually increased as described above can be applied to the above-described first to fifth example embodiments. In particular, when the plurality of recesses 15 include the plurality of cylindrical recesses 15d, the depth D of each the plurality of cylindrical recesses 15d is gradually changed. It is desirable that depth D of each of the plurality of cylindrical recesses 15d be increased stepwise, in order to prevent the thickness of the first dielectric substrate 5 from changing suddenly toward the transmission direction 1A of the dielectric waveguide line 1. By doing so, it is expected that stress can be reduced in the first dielectric substrate 5, more specifically, the mechanical strength can be improved in the first dielectric substrate 5.

Seventh Example Embodiment

Next, a seventh example embodiment will be described with reference to FIG. 9. Hereinafter, a difference between this example embodiment and the first example embodiment will be mainly described, and the repeated description will be omitted.

In this example embodiment, the distance between the first via hole group 9 and the second via hole group 10 is locally increased in the vicinity of the coupling window 12. That is, the lateral dimension of the transmission region Q is locally increased in the vicinity of the coupling window 12. With such a configuration, a resonator is formed in the vicinity of the coupling window 12, thereby making it possible to increase the bandwidth of the transmission characteristic.

(Effectiveness Demonstration Test Report)

Next, a result of a test conducted to verify the improvement effect of the transmission characteristics by the connection structure 3 is shown below. FIG. 10 is a graph showing the improvement effect of the transmission characteristics by the connection structure 3. In this graph, a result of an electromagnetic field analysis of the transmission characteristics when the plurality of recesses 15 are formed in the lattice shape (with a lattice groove structure) in an optimized structure are compared with that of an electromagnetic field analysis of the transmission characteristics when the plurality of recesses 15 are not formed (without groove structure) in an optimized structure.

In FIG. 1, the thickness 5T of the first dielectric substrate 5 was 0.35 mm, which was sufficiently strong in an actual trial production. The diameter of a number of via holes constituting the two arrays of via hole groups 8 was 0.1 mm, the pitch of the via holes was 0.2 mm, and the clearance distance between the two arrays of via hole groups 8 was 0.75 mm. The depth D of each of the plurality of optimized recesses 15 was 0.075 mm, the spacing between the plurality of transmission-direction translational recesses 15a was 0.2 mm, and the spacing between the plurality of transmission-direction orthogonal recesses 15b was 0.3 mm. In addition, the resonator structure shown in the seventh example embodiment was optimized and employed in both cases where the plurality of recesses 15 are provided in the first dielectric substrate 5 and where the plurality of recesses 15 are not provided in the first dielectric substrate 5. According to FIG. 10, by providing the plurality of recesses 15 in the first dielectric substrate 5, it was confirmed that a wider band and satisfactory transmission characteristics were obtained. Note that the distance 5S between the bottom surfaces of the plurality of optimized recesses 15 and the second substrate surface 5b is affected by the size of the resonator structure, the uniformity of the function of the bottom surfaces of the recesses 15 as the upper surface of the waveguide, the coupling window 12, and so on. Therefore, the distance 5S in the optimized structure does not have to be exactly ¼ of the guide wavelength.

Eighth Example Embodiment

Next, an eighth example embodiment will be described with reference to FIG. 11. Hereinafter, a difference between this example embodiment and the first example embodiment will be mainly described, and the repeated description will be omitted.

As shown in FIG. 11, a plurality of recesses 15 are formed in the first dielectric substrate 5 in the vicinity of the coupling window 12. In other words, the first dielectric substrate 5 includes a part where the plurality of recesses 15 are not formed in the vicinity of the coupling window 12. Another substrate may be laminated on this part. Thus, in this example embodiment, a second dielectric substrate 20 is laminated on the first dielectric substrate 5, regardless of whether or not it is in the vicinity of the coupling window 12. To be more specific, the second dielectric substrate 20 is laminated on the first conductor layer 6, regardless of whether or not it is in the vicinity of the coupling window 12. A third conductor layer 21 is formed on the upper surface 20a of the second dielectric substrate 20 opposite to the first dielectric substrate 5. The dielectric waveguide line 1 and the second dielectric substrate 20 are electrically and completely separated by the first conductor layer 6. Therefore, the third conductor layer 21 can be used to form a microstrip line or a coplanar line. When the third conductor layer 21 is used to constitute a microstrip line, the first conductor layer 6, the second dielectric substrate 20, and the third conductor layer 21 are used. When the third conductor layer 21 is used to constitute a coplanar line, the second dielectric substrate 20 and the third conductor layer 21 are used. An IC or the like may be mounted using the third conductor layer 21.

The second dielectric substrate 20 may be quartz. However, since quartz is highly rigid and easily cracked, the lamination of quartz is difficult. For this reason, it is desirable that a sheet made of a resin material having low rigidity and having a small load on the first dielectric substrate 5 such as polyimide be attached to the first conductor layer 6 to constitute the second dielectric substrate 20. In this example embodiment, the second dielectric substrate 20 can be supported on the first dielectric substrate 5 periodically in the coupling window 12, so that even if the second dielectric substrate 20 has low rigidity, the second dielectric substrate 20 is hard to bend and the flatness of the second dielectric substrate 20 can be ensured.

A separate conductor layer may be formed on a lower surface of the second dielectric substrate 20, which faces the plurality of recesses 15. In this case, even if the transmission line formed in the third conductor layer 21 is formed across the recesses 15, continuity as a transmission line can be ensured.

Although to preferred example embodiments of the present disclosure have been described above, the above example embodiments can be modified as follows.

That is, the pitch of the plurality of transmission-direction translational recesses 15a, the pitch of the plurality of transmission-direction orthogonal recesses 15b, the pitch of the plurality of transmission-direction oblique recesses 15c, and the pitch of the plurality of cylindrical recesses 15d can be appropriately changed. The length and width of the transmission-direction translational recess 15a, the transmission-direction orthogonal recess 15b, and the transmission-direction oblique recess 15c can also be appropriately changed. As shown in FIGS. 1 and 4, in the vicinity of the coupling window 12, the transmission-direction orthogonal recesses 15b are formed so as to connect the via hole 9a to the via hole 10a, but the transmission-direction orthogonal recess 15b may not be connected to the via hole 9a or the via hole 10a.

The two arrays of via hole groups 8 are not necessarily formed in a straight line. Outer peripheral ends of the plurality of lattice-shaped recesses 15 need not be rectangular. At least one of the recesses 15 may protrude outside the two arrays of via hole groups 8. The coupling window 12 may be rectangular, circular, or other polygonal.

In each of the above example embodiments, a plurality of recesses 12 are formed only in the vicinity of the coupling window 15. Alternatively, the plurality of recesses 12 may be formed in a part away from the coupling window 15. In this case, when the operating frequency signal transmitted through the dielectric waveguide line 1 approaches the vicinity of the coupling window 12, a rapid change in the electromagnetic field distribution can be lessened.

The rectangular waveguide 2 employed in each of the above example embodiments may be replaced with a circular waveguide depending on the purpose. In this case, however, the operating band of the rectangular waveguide is narrower than that of a standard waveguide having a cross-sectional aspect ratio of 1:2.

In each of the above example embodiments, the first dielectric substrate 5 is made of quartz. However, instead of quartz, a dielectric substrate such as a ceramic substrate or a resin substrate may be used.

In each of the above example embodiments, the plurality of recesses 15 may be formed by, for example, router processing.

Although the present disclosure has been described above with reference to the example embodiments, the present disclosure is not limited by the above. Various changes in the structure and details of the present invention can be understood by a person skilled in the art within the scope of the invention.

This application is based upon and claims the benefit of priority from Japanese patent application No. 2018-106896, filed on Jun. 4, 2018, the disclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

1 DIELECTRIC WAVEGUIDE LINE

1A TRANSMISSION DIRECTION

2 RECTANGULAR WAVEGUIDE

2A TRANSMISSION DIRECTION

3 CONNECTION STRUCTURE

5 FIRST DIELECTRIC SUBSTRATE

5
a FIRST SUBSTRATE SURFACE

5
b SECOND SUBSTRATE SURFACE

6 FIRST CONDUCTIVE LAYER

7 SECOND CONDUCTIVE LAYER

8 VIA HOLE GROUP

9 FIRST VIA HOLE GROUP

9
a VIA HOLE

10 SECOND VIA HOLE GROUP

10
a VIA HOLE

11 THIRD VIA HOLE GROUP

11
a VIA HOLE

12 COUPLING WINDOW

13 OPEN END SURFACE

15 RECESS

15
a TRANSMISSION-DIRECTION TRANSLATIONAL RECESS

15
b TRANSMISSION-DIRECTION ORTHOGONAL RECESS

15
c TRANSMISSION-DIRECTION OBLIQUE RECESS

15
d CYLINDRICAL RECESS

16 RECESS CONDUCTOR LAYER

20 SECOND DIELECTRIC SUBSTRATE

20
a UPPER SURFACE

21 THIRD CONDUCTIVE LAYER

CONNECTION STRUCTURE BETWEEN DIELECTRIC WAVEGUIDE LINE AND WAVEGUIDE

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