TRANSITION STRUCTURE BETWEEN TRANSMISSION LINE OF MULTILAYER PCB AND WAVEGUIDE

Abstract

A transition structure between a transmission line of a multilayer PCB and a waveguide is proposed. The transition structure includes the waveguide comprising an interior space on one side thereof and having an inlet for accommodating a part of a stripline, the transmission line comprising a first ground layer of the multilayer PCB composed of at least two or more dielectric layers, the stripline extending from the transmission line and protruding into the waveguide through the inlet of the waveguide, and a single via hole or a plurality of via holes formed between the first ground layer and a bottommost ground layer, wherein each via hole is positioned at the inlet of the waveguide.

Claims

1. A transition structure between a transmission line of a multilayer PCB and a waveguide, the transition structure comprising: the waveguide comprising an interior space on one side thereof and having an inlet for accommodating a part of a stripline; the transmission line comprising the stripline and at least two ground layers below the stripline of the multilayer PCB composed of at least two or more dielectric layers; the stripline extending from the transmission line and protruding into the waveguide through the inlet of the waveguide; and a single via hole or a plurality of via holes formed between the at least two ground layers, wherein each via hole is positioned at the inlet of the waveguide.

2. The transmission line of claim 1, wherein a dielectric layer comprising the stripline is connected from a dielectric layer of the transmission line.

3. The transition structure of claim 1, wherein the stripline is spaced apart from a backshort of the waveguide by a predetermined distance.

4. The transition structure of claim 1, wherein each via hole is arranged at a last end of the inlet of the waveguide.

5. The transition structure of claim 1, wherein each via hole is installed as a single via hole array or a plurality of via hole arrays

6. The transition structure of claim 1, wherein each via hole is installed by arranging in a zigzag vertically or horizontally.

7. The transition structure of claim 1, wherein a spacing between each via hole is arranged in a range of 10 to 500 μm.

8. The transition structure of claim 1, wherein a via pillar is used instead of each via hole.

9. The transition structure of claim 1, wherein the dielectric layers constituting the multilayer PCB are composed of at least one or more different dielectrics.

10. The transition structure of claim 1, wherein a dielectric dissipation factor of a topmost dielectric layer constituting the multilayer PCB is lower than dielectric dissipation factors of other dielectric layers other than the topmost dielectric layer.

Description

DESCRIPTION OF DRAWINGS

[0042] FIGS. 1(a) and 1(b) are respectively a cross-sectional view and a plan view illustrating an example of applying a multilayer PCB to a transition structure between a transmission line of a PCB and a waveguide according to a conventional disclosure.

[0043] FIGS. 2(a) and 2(b) are respectively a cross-sectional view and a plan view illustrating a transition structure between a transmission line of the multilayer PCB and a waveguide according to an exemplary embodiment of the present disclosure, and FIG. 2(c) is a plan view illustrating a first ground layer b-b′ in the transition structure between the transmission line of the multilayer PCB and the waveguide according to the exemplary embodiment of the present disclosure.

[0044] FIGS. 3(a) and 3(b) are respectively a cross-sectional and a plan view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to another exemplary embodiment of the present disclosure, and FIG. 3(c) is a plan view in the first ground layer b-b′ in the transition structure between the transmission line of the multilayer PCB and the waveguide according to the exemplary embodiment of the present disclosure.

[0045] FIG. 4 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to yet another exemplary embodiment of the present disclosure.

[0046] FIG. 5 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to still another exemplary embodiment of the present disclosure.

[0047] FIG. 6 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to still another exemplary embodiment of the present disclosure.

[0048] FIG. 7 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to still another exemplary embodiment of the present disclosure.

[0049] FIG. 8 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to still another exemplary embodiment of the present disclosure.

[0050] FIG. 9 is a set of signal transmission characteristic graphs respectively obtained by the transition structures between the transmission lines of the multilayer PCBs and the waveguides according to the present disclosure.

MODE FOR INVENTION

[0051] Hereinafter, the objectives, other objectives, features and advantages of the present disclosure will be readily understood through the following preferred exemplary embodiments in conjunction with the accompanying drawings. However, the present disclosure is not limited to the exemplary embodiments described herein and may be embodied in other forms.

[0052] Rather, the exemplary embodiments introduced herein are provided so that the disclosed subject matter may be thorough and complete, and that the spirit of the present disclosure may be sufficiently conveyed to those skilled in the art.

[0053] The exemplary embodiments described and illustrated herein also include complementary exemplary embodiments thereof.

[0054] In this specification, the singular form also includes the plural form unless otherwise specified in the phrase. As used herein, “comprises” and/or “comprising” does not exclude the presence or addition of one or more other components in addition to the mentioned components.

[0055] Hereinafter, the present disclosure will be described in detail with reference to the drawings. In describing the specific exemplary embodiments below, various characteristic contents have been prepared to more specifically explain the disclosure and help understanding. However, a reader having enough knowledge in this field to understand the present disclosure may recognize that the present disclosure may be used without these various specific details. In some cases, it is mentioned in advance that in describing the present disclosure, parts that are commonly known and not largely related to the present disclosure are not described in order to avoid confusion in explaining the present disclosure.

[0056] FIG. 1 is a view illustrating a multilayer PCB applied to a transition structure between a transmission line and a waveguide according to a conventional disclosure. The transmission line of the PCB is connected from an integrated circuit (not shown) to transmit input/output signals, and transmit the signals in a form of CPWGs, microstrips, etc.

[0057] Such a transmission line 200 is composed of a dielectric layer 210, a metal layer 220 for signal transmission on an upper surface of the dielectric layers 210, and a metal layer 221 as a ground layer on a lower surface of the dielectric layer 210 corresponding to the metal layer 220. At a last end of the transmission line, a stripline 300 having no ground layer on a bottom of the dielectric layer protrudes and is positioned inside a waveguide 100, so as to be coupled thereto. Meanwhile, a metal layer 222 for a ground layer of the entire PCB is also formed on a lowermost bottom surface of the entire dielectric layers 210 and 211 constituting the multilayer PCB, that is, a bottom surface of the lowermost dielectric layer 211.

[0058] For impedance matching to reduce loss, each of these transmission lines such as CPWGs and microstrips has a different width of a metal layer that transmits signals, and accordingly the stripline protruding into the waveguide should also be planned with a design and a size, which reduce the loss.

[0059] FIG. 2 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to the exemplary embodiment of the present disclosure. FIG. 2(a) is a cross-sectional view according to the exemplary embodiment of the present disclosure, and FIG. 2(b) is a plan view illustrating a structure in a state in which an upper cover a-a′ of the waveguide on the view is removed for description. FIG. 2(c) is a plan view illustrating a first ground layer b-b′ to indicate a structure of via holes according to the exemplary embodiment of the present disclosure.

[0060] The transition structure between the transmission line of the multilayer PCB and the waveguide according to the exemplary embodiment of the present disclosure is configured to include: a waveguide 100 including an interior space 110 on one side thereof and having an inlet 120 configured to accommodate a part of a stripline 300; a transmission line 200 including a first ground layer 221 of the multilayer PCB composed of at least two or more dielectric layers 210 and 211; the stripline 300 extending from the transmission line 200 and protruding into the waveguide 100 through the inlet 120 of the waveguide 100; and a single via hole or a plurality of via holes 400 formed between the first ground layer 221 and a lowermost ground layer 222, wherein each via hole 400 is positioned at the inlet 120 of the waveguide 100.

[0061] More specifically, the transmission line 200 of the PCB is connected from an integrated circuit (not shown) to transmit input/output signals, and transmit the signals in a form of CPWG, microstrip, or the like. Such CPWG or microstrip is described as a general form of the configuration, but is not limited thereto.

[0062] Such a transmission line 200 is configured in a way that a partial area 300 extending and protruding toward the inside of the waveguide 100 is coupled to the waveguide 100, and as such, signals are transmitted to the inside of the waveguide 100 by means of the coupling of the stripline 300 that is the last end of the transmission line protruding into the waveguide 100. The strip line is formed to be spaced apart from an inner surface of an upper cover a-a′ of the waveguide, that is, a backshort 130 of the waveguide, by a predetermined space. Such a separation space becomes an important design factor of a transition structure in order to reduce transition loss.

[0063] In addition, since the transmission line and the stripline extending and protruding therefrom may be manufactured at the same time when the same PCB, that is, the same dielectric substrate layer is used, the transmission line and the stripline may be easily manufactured while reducing the cost.

[0064] For impedance matching to reduce loss, each of these transmission lines such as CPWG and microstrip has a different width of a metal layer 220 transmitting signals, and accordingly, the stripline 300 protruding into the waveguide 100 should also be planned with a design and a size, which reduce the loss.

[0065] In this case, in an area adjacent to the stripline 300 protruding from the transmission line 200 of the multilayer PCB, via holes 400 are formed between the ground layers of the transmission line of the multilayer PCB, that is, a first ground layer 221 from the top of the multilayer PCB and a bottommost ground layer 222 formed on the bottom surface of the multilayer PCB, so as to serve as a via fence, thereby reducing signal loss due to the second dielectric layer and effectively propagating signals toward an output unit of the waveguide 100.

[0066] Here, the via hole refers to a structure that electrically connects metal layers in multilayer wiring to each other by means of a hole formed to have a circular cross-section and provided with a metal layer coated on a side surface thereof in a vertical direction therein for electrical connections between the metal layers in the multilayer wiring in a common PCB process. In this way, only the side surface of the interior of the via hole is composed of the metal layer to electrically connect upper and lower metal layers to each other, but when necessary, the via hole may also be used by filling the inside thereof with metal. Such via holes are manufactured using in the common PCB manufacturing process, and is formed in a circular shape having a size of a diameter of several tens to hundreds of micrometers in the manufacturing process. Naturally, the via holes may also be manufacturable for use in a size greater than or equal to the said size, or smaller than or equal to the said size according to the manufacturing process. In addition, it is noted that as for the shape of the via holes, various shapes easy to be manufactured, the shapes having not only a circular cross section and the like, but also a rectangular cross section may also be usable.

[0067] These via holes 400 may be arranged in a line as shown in FIG. 2(c) in order to enhance the effect of reducing loss in a transition structure.

[0068] Here, it is noted that the arrangement means that the plurality of via holes 400 is aligned in one direction.

[0069] A spacing between via holes 400 may also be a spacing of several tens to hundreds of pm depending on the manufacturing process. In particular, when the spacing of the via holes becomes 10 to 500 μm corresponding to a frequency domain of the ultra-high frequencies used and transmitted in such ultra-high frequency circuits, the effect caused by the spacing of the via holes may be increased.

[0070] FIGS. 3(a) and 3(b) are respectively a cross-sectional view and a plan view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to another exemplary embodiment of the present disclosure. FIG. 3(c) is a plan view in a first ground layer b-b′ in the transition structure between the transmission line of the multilayer PCB and the waveguide according to the exemplary embodiment of the present disclosure.

[0071] The configuration of the transition structure of the transmission line of the multilayer PCB and the waveguide is the same as shown in FIG. 2, and shown in FIG. 3(c), this view illustrates a form in which via holes 400 formed between the ground layer 221 of the transmission line and a ground layer 222 of a bottom surface of the PCB, that is, a first ground layer 221 and a bottommost ground layer 222 of the multilayer PCB, are arranged in two rows. By arranging the via holes 400 in two rows in this way, it is possible to increase the effect of reducing signal loss. As described above, the spacing between the first and second rows of the via holes may be tens to hundreds of μm depending on the manufacturing process.

[0072] FIG. 4 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to yet another exemplary embodiment of the present disclosure. As previously described in FIG. 3, two rows of via holes 400 formed between a corresponding ground layer of the transmission line and a ground layer of a bottom surface of the PCB, that is, a first ground layer 221 and a bottommost ground layer 222 of the multilayer PCB may be arranged in a zigzag on a horizontal side surface, so as to increase the effect thereof.

[0073] FIG. 5 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to still another exemplary embodiment of the present disclosure. This view illustrates a case where via holes 400 formed between a corresponding ground layer of the transmission line and a ground layer of a bottom surface of the PCB, that is, a first ground layer 221 and a bottommost ground layer 222 of the multilayer PCB is arranged in a first entrance area further away from a last end of an inlet area, rather than the last end of the waveguide inlet area formed for the transmission line 200 to enter the inside of the waveguide 100. In this case as well, by means of such via holes 400, an effect of increasing the signal transfer efficiency may be achieved by reducing signal loss. However, the effect may be lower than that in the case of designing the via holes according to FIGS. 2 to 4 described above (i.e., the case where a via hole or via holes in arrangement are positioned at the last end of the inlet area), so the adjustment of the frequency band for transmitting the signals may be required.

[0074] FIG. 6 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to still another exemplary embodiment of the present disclosure. A via hole 400 formed between a ground layer of the transmission line and a ground layer of a bottom surface of the PCB, that is, a first ground layer 221 and a bottommost ground layer 222 of the multilayer PCB, is formed as a single via pillar, rather than formed in a form of an array. In this case as well, as in the case of using the via holes arranged in one or two rows, the via hole serves as a via fence and may effectively transfer signals by reducing transition loss.

[0075] Here, it should be noted that the via pillar means a structure having a predetermined area, not the shape of a via hole 400.

[0076] FIG. 7 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to still another exemplary embodiment of the present disclosure. This view illustrates a case of using a PCB having three dielectric layers 210, 211, and 212, other than a multilayer PCB having two dielectric layers.

[0077] Via holes 400 are similarly applied between a corresponding ground layer of the transmission line and a ground layer of a bottom surface, that is, a first ground layer 221 and a third bottommost ground layer 222 of the multilayer PCB, so as to reduce transition loss due to PCB substrate layers, thereby effectively transmit signals.

[0078] As described above, these dielectric layers 210, 211, and 212 may all use the same dielectric material or, when necessary, may use heterogeneous dielectric materials by bonding heterogeneous materials. In particular, it is preferable to apply a dielectric layer, made of a material such as Teflon having low dielectric loss, to a first layer at the top, the first layer playing an important signal transmission role. In the case of the multilayer PCB in which heterogeneous dielectric materials are bonded in this way, some layers have particularly low dielectric loss (i.e., loss tangent), and a low-cost layer with good mechanical properties may be applied to a lower layer.

[0079] In addition, the dielectric layers constituting the multilayer PCB presented in the present disclosure may be composed of at least one or more different dielectrics, but it is preferable to make a dielectric dissipation factor of the top dielectric layer constituting the multilayer PCB to be low compared to dielectric dissipation factors of other dielectric layers other than the topmost dielectric layer.

[0080] In addition, although the multilayer PCB having three dielectric layers 210, 211, and 212 has been illustrated and described in FIG. 7, the same transition structure may be applied to a transition structure of a multilayer PCB having three or more layers. Via holes 400 are similarly applied between a corresponding ground layer of a transmission line and a ground layer of a bottom surface of the PCB, that is, a first ground layer 221 and a bottommost ground layer 222 of the multilayer PCB, so as to reduce transition loss due to the substrate layers of the PCB, thereby effectively transmitting signals.

[0081] FIG. 8 is a view illustrating a transition structure between a transmission line of a multilayer PCB and a waveguide according to still another exemplary embodiment of the present disclosure. In a multilayer PCB having three dielectric layers 210, 211, and 212, via holes 400 are arranged and applied, in a zigzag in a vertical direction, between a corresponding ground layer of the transmission line and a ground layer of a bottom surface of the PCB, that is, a first ground layer 221 and a third bottommost ground layer 222 of the multilayer PCB, so as to reduce transition loss due to the substrate layers of the PCB, thereby effectively transmit signals.

[0082] In addition, although the multilayer PCB having the three dielectric layers 210, 211, and 212 has been illustrated and described in FIG. 8, the same transition structure may be applied to a transition structure of a multilayer PCB having three or more layers. Via holes 400 are similarly applied, in a zigzag in the vertical direction, between a corresponding ground layer of the transmission line and a ground layer of a bottom surface of the PCB, that is, a first ground layer 221 of the multilayer PCB and a bottommost ground layer 222 of the multilayer PCB, so as to reduce transition loss due to the substrate layers of the PCB, thereby effectively transmit signals.

[0083] FIG. 9 is a set of signal transmission characteristic graphs respectively obtained by the transition structures between the transmission lines of the multilayer PCBs and the waveguides according to the present disclosure. These graphs illustrate design structures for transmitting frequencies of around 28 GHz band, and the waveguide is also applied with WR28 specifications having a cross section of 3.556 mm×7.112 mm that transmits the frequencies of the frequency band.

[0084] In a case of FIG. 9(a), this view illustrates a graph that simulates signal transmission characteristics for a transition structure in which a multilayer PCB is applied to a configuration of the conventional disclosure of FIG. 1 described above. In the 28 GHz band, a return loss S11 characteristic is significantly bad, and an insertion loss S21 characteristic is also high at −4 dB or less.

[0085] In the case of FIG. 9(b), this view illustrates a signal transmission characteristic graph to which the first exemplary embodiment of FIG. 2 is applied by using the same multilayer PCB structure. In the 28 GHz band, the return loss S11 is about −24 dB, and the insertion loss S21 is −1 dB or less, so the loss is significantly small compared to the loss of the case of FIG. 9(a), whereby signals are effectively transferred in a target frequency band.

[0086] In the case of FIG. 9(c), this view illustrates a signal transfer characteristic graph according to the exemplary embodiment of FIG. 3. The return loss and the insertion loss are improved compared to the case of FIG. 9(b). Even in this case, the loss is significantly small compared to the loss in the conventional case, whereby signals are transferred very effectively in the target frequency band.

[0087] In the case of FIG. 9(d), this view illustrates a signal transfer characteristic graph according to the exemplary embodiment of FIG. 4. The insertion loss S21 is −1 dB or less, so the loss is significantly small compared to the case of FIG. 9(a), whereby signals are effectively transferred in the target frequency band.

[0088] In the case of FIG. 9(e), this view illustrates a signal transfer characteristic graph according to the exemplary embodiment of FIG. 5. The return loss S11 is about −14 dB, so a pass frequency band is also shifted. Although the transmission characteristics are improved compared to that of FIG. 9(a), the transmission characteristics are not good compared to the previous exemplary embodiments, and the frequency band is also shifted. Among the transition structures, it may be confirmed that the previous exemplary embodiments in which the via holes are applied close to the inlet area where the last end of the stripline of the transmission line of the multilayer PCB protrudes into the waveguide are more effective. Naturally, even in the case of the exemplary embodiment of FIG. 5, the signal transmission frequency band may be redesigned and applied to a transition structure of a transmission line of a multilayer PCB and a waveguide.

[0089]

[0090] The exemplary embodiments described in the present specification and the configurations shown in the drawings are only the most preferred exemplary embodiments of the present disclosure, and do not represent all the technical ideas of the present disclosure, and accordingly, it should be appreciated that there may be equivalents and modifications at the time when the present application is filed.