A coplanar waveguide and microstrip transmission transition structure

Abstract

The application relates to a transition structure of a coplanar waveguide and a microstrip transmission, which comprises a grounding layer, a dielectric base layer and a top metal layer. The transition structure is divided into a microstrip transmission area, a coplanar waveguide area and a transition area. A top signal line and a pair of grounding electrodes distributed on both sides of the top signal line are formed on the top metal layer. The top signal line forms a coplanar waveguide guide band in the coplanar waveguide area, forms a microstrip line in the microstrip transmission area and forms a trapezoidal guide band in the transition area. The grounding electrodes cover the transition area and the coplanar waveguide area. A rectangular slot and a trapezoidal slot are arranged on the grounding layer in connection. A plurality of metal bridges connecting the two sides of the rectangular slot are arranged on the rectangular slot in intervals. The rectangular slot is arranged directly below the coplanar waveguide guide band, and the trapezoidal slot is arranged directly below the trapezoidal guide band. Through the above structure, the application has the performances of wide band and low insertion loss, and has the characteristics of small size, dense wiring and easy bending.

Description

Technical Field

[0001] This invention relates to the field of microwave technology, and more particularly to a broadband transition structure from a coplanar waveguide transmission line to a microstrip. Background Technology

[0002] With the development of microwave and millimeter-wave technologies and the high-frequency, miniaturized design of semiconductor devices, thin-film probe card testing systems are evolving towards wider bandwidth and lower loss. Microstrip lines and coplanar waveguide transmission lines are widely used as the main transmission line types in thin-film probe cards. To achieve signal transmission from one transmission line to another, the microwave transition structure between transmission lines is a key technology. Therefore, achieving a small-size, low-loss, wide-bandwidth transition structure that adapts to the bending operation of thin films aligns with the development trend of thin-film probe card testing systems; however, the design of such a transition structure remains a significant challenge.

[0003] In existing designs, the transition structure from coplanar waveguide to microstrip line can be roughly divided into two types: one is the transition from traditional coplanar waveguide (CPW) to microstrip, which is prone to generating slot modes at discontinuities, affecting transmission; the other is the transition from grounded coplanar waveguide (GCPW) to microstrip, which has the disadvantages of large insertion loss and difficulty in bending when used in high-frequency applications. Summary of the Invention

[0004] The purpose of this invention is to propose a transition structure from a coplanar waveguide transmission line with a loaded metal bridge to a microstrip transmission line, which combines the advantages of wide bandwidth, low loss, easy bending, and suitability for dense cabling.

[0005] To achieve the above objectives, the solution adopted in this application is: a transition structure for coplanar waveguide and microstrip transmission, comprising a ground layer, a dielectric substrate, and a top metal layer stacked sequentially. The transition structure is divided into a microstrip line transmission region, a coplanar waveguide region, and a transition region between the microstrip line transmission region and the coplanar waveguide region. A top signal line and a pair of ground electrodes distributed on both sides of the top signal line are formed on the top metal layer. The top signal line forms a coplanar waveguide guide band with a first width W1 in the coplanar waveguide region. A microstrip line with a second width W2 is formed in the microstrip transmission region, and a trapezoidal guide strip is formed in the transition region. The bottom edge width of the trapezoidal guide strip is W1, and the top edge width is W2. The ground electrode covers the transition region and the coplanar waveguide region. A connected rectangular slot and a trapezoidal slot are formed on the ground layer. Several metal bridges connecting the two sides of the rectangular slot are spaced apart on the rectangular slot. The rectangular slot is formed directly below the coplanar waveguide guide strip, and the trapezoidal slot is formed directly below the trapezoidal guide strip.

[0006] In some embodiments, the grounding electrode includes a pair of trapezoidal electrodes located in the transition region, wherein the lower base of the trapezoidal electrodes is connected to the coplanar waveguide region and the upper base is connected to the microstrip line transmission region.

[0007] In some embodiments, the lower base of the trapezoidal electrode is collinear with the lower base of the trapezoidal conductor, and the upper base of the trapezoidal electrode is collinear with the upper base of the trapezoidal conductor.

[0008] In some embodiments, the lower base angle of the trapezoidal electrode near the trapezoidal conductor is 85°-100°.

[0009] In some embodiments, the shortest distance from the bottom edge to the top edge of the trapezoidal guide belt is H, where H = 0.1-0.2 mm.

[0010] In some embodiments, the first width W1 = 0.08-0.15 mm, and the second width W2 = 0.04-0.045 mm.

[0011] In some embodiments, the top-level signal line is located at the center of the top-level metal layer, and the microstrip line, trapezoidal guide strip, and coplanar waveguide guide strip are located on the central axis of the top-level signal line.

[0012] In some embodiments, the distance between two adjacent metal bridges is 0.4-0.5 mm.

[0013] The grounding layer, dielectric base layer, and top metal layer are respectively provided with a number of metal through holes, and the grounding layer, dielectric base layer, and top metal layer are electrically connected through the number of metal through holes.

[0014] The spacing between two adjacent metal through holes is 0.2-0.3 mm.

[0015] The shape and size of the trapezoidal groove are the same as those of the trapezoidal guide belt.

[0016] The aforementioned trapezoidal conductor and trapezoidal electrode can rapidly increase the low impedance of the top-layer signal line to 50Ω of the microstrip line, achieving broadband impedance matching. Simultaneously, the resulting tapered double-conductor structure effectively enables quasi-TEM mode transmission, allowing the transition structure of this application to achieve transitions at any position within the metal bridge cycle. The trapezoidal slot reduces the capacitive coupling between the trapezoidal conductor and the underlying metal layer, further improving the broadband impedance matching capability of the transition structure, reducing the overall size of the transition structure, and lowering conductor losses.

[0017] Through the above technical solution, this application constructs a tapered structure of trapezoidal conductors and trapezoidal slots in the transition region between the coplanar waveguide transmission line and the microstrip line. The periodically distributed metal bridges effectively suppress slot modes generated at impedance discontinuities, ensuring high-frequency performance in the transition region and achieving broadband, low-loss passband effects within a small size. The broadband matching of this invention primarily relies on tapered trapezoidal conductors, trapezoidal electrodes, and metal vias for control, supplemented by trapezoidal slots. Simultaneously, rectangular slots, trapezoidal slots, and the top-layer signal line work together to achieve low insertion loss performance. Attached Figure Description

[0018] Figure 1 A three-dimensional structural diagram of a coplanar waveguide transmission line with a loaded metal bridge;

[0019] Figure 2 This is a three-dimensional structural diagram of one embodiment of the transition structure of this application;

[0020] Figure 3 This is a plan view of the transition structure of this application;

[0021] Figure 4 This is the frequency response diagram of the transition structure in this application.

[0022] Among them: 1. Top metal layer; 11. Top signal line; 2. Dielectric base layer; 3. Metallized via; 4. Ground layer; 41. Metal bridge; 42. Rectangular slot; 5. Coplanar waveguide strip; 51. Ground electrode; 510. Trapezoidal electrode; 52. Trapezoidal strip; 6. Microstrip line; 7. Trapezoidal slot. Specific Implementation

[0023] To illustrate the technical content, structural features, achieved objectives, and effects of the invention in detail, the technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. In the following description, for illustrative purposes, numerous specific details are set forth to provide a detailed description of various exemplary embodiments or implementations of the invention. However, various exemplary embodiments may also be implemented without these specific details or in one or more equivalent arrangements. Furthermore, the various exemplary embodiments may differ, but are not necessarily exclusive. For example, the specific shape, construction, and characteristics of the exemplary embodiments may be used or implemented in another exemplary embodiment without departing from the inventive concept.

[0024] Furthermore, in this application, spatial relative terms such as “below,” “under,” “below,” “down,” “above,” “above,” “higher,” and “side” (e.g., as in a “sidewall”) are used to describe the relationship between one element and another (other) element as shown in the accompanying drawings. Spatial relative terms are intended to include different orientations of the device in use, operation, and / or manufacture other than those depicted in the drawings. For example, if the device in the drawings is flipped, an element described as “below” or “under” another element or feature would then be positioned “above” said other element or feature. Thus, the exemplary term “below” can include both above and below orientations. Furthermore, the device may be otherwise positioned (e.g., rotated 90 degrees or in other orientations), thus interpreting the spatial relative descriptive terms used herein accordingly.

[0025] It should be noted that when an element is considered "connected to" or "attached to" another element, it can be directly connected to the other element or may have an intervening element present. When an element is said to be "disposed on" or "located on" another element, it can be directly on the other element or may have an intervening element present. In this specification, "a plurality of" refers to two or more, and "several" refers to one or more. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] This application provides a transition structure between a coplanar waveguide and a microstrip transmission, particularly a broadband transition structure from a coplanar waveguide transmission line with a loaded metal bridge to a microstrip line transmission.

[0027] Figure 1 This is a three-dimensional structural diagram of a coplanar waveguide transmission line with a loaded metal bridge. Figure 1 As can be seen, the coplanar waveguide transmission line with the loaded metal bridge includes a ground layer 4, a dielectric substrate, and a top metal layer 1 stacked sequentially from bottom to top. Several metallized vias 3 are respectively opened at corresponding positions on the ground layer 4, the dielectric substrate, and the top metal layer 1.

[0028] A rectangular slot 42 is formed on the central axis of the grounding layer 4, and the two sides of the rectangular slot 42 are connected by several equally spaced metal bridges 41. A top-level signal line 11 is located on the center line of the top-level metal layer 1, and a pair of grounding electrodes 51 are symmetrically distributed on both sides of the top-level signal line 11. The rectangular slot 42 is located directly below the top-level signal line 11, dividing the grounding layer 4 into two equal parts, left and right. The metal bridges 41 are arranged periodically in the rectangular slot 42, connecting the left and right parts of the grounding layer 4.

[0029] Coplanar waveguide transmission lines with loaded metal bridges are constructed by loading periodically occurring metal bridges onto the grounding layer of a grounded coplanar waveguide. They possess the advantages of low radiation loss and weak dispersion typical of coplanar waveguide transmission lines. The periodic metal bridge structure also provides excellent flexibility, while the wider signal conduction band results in lower conductor loss, making them an important solution for reducing losses in thin-film probe card testing systems. Meanwhile, microstrip lines, due to their simple structure and small wiring area, are often used to address dense wiring problems.

[0030] Please refer to Figure 2-3 As shown, the transition structure between the coplanar waveguide and microstrip transmission in this application includes: a ground layer 4, a dielectric substrate 2, and a top metal layer 1 stacked sequentially. Both the ground layer 4 and the top metal layer 1 are metallic conductors, typically copper or gold. The material of the dielectric substrate 2 can be determined based on the dielectric constant, the thickness of the dielectric material, the operating frequency, and loss simulation, and is not specifically limited; it can be designed according to actual needs.

[0031] The transition structure is divided into the microstrip line transmission region, the coplanar waveguide region, and the transition region between the microstrip line transmission region and the coplanar waveguide region. In the coplanar waveguide region, the transmission line structure is similar to... Figure 1 The coplanar waveguide transmission line shown is consistent with the loaded metal bridge. In the microstrip line transmission region, the structure of the transmission line is consistent with the traditional microstrip line structure. In the transition region, the connection and impedance matching of the coplanar waveguide transmission line to the microstrip line are achieved by setting a tapered trapezoidal conductor, trapezoidal electrode and trapezoidal slot.

[0032] Please continue to refer to Figure 2 As shown, a top-layer signal line 11 and a pair of ground electrodes 51 symmetrically distributed on both sides of the top-layer signal line 11 are formed on the top-layer metal layer 1. The ground electrodes 51 only cover a part of the dielectric substrate 2, namely the transition region and the coplanar waveguide region, while the microstrip line transmission region has no top-layer metal.

[0033] The top-layer signal line 11 forms a coplanar waveguide guide band 5 in the coplanar waveguide region, a microstrip line 6 in the microstrip line transmission region, and a trapezoidal guide band 52 in the transition region. The top-layer signal line 11 is located in the center of the top-layer metal layer 1, and the microstrip line 6, the trapezoidal guide band 52, and the coplanar waveguide guide band 5 are located on the central axis of the top-layer signal line 11 to ensure that the overall transition structure can be positioned at any position within the repetition period of the metal bridge 41, thereby achieving broadband impedance matching.

[0034] See Figure 3As shown, the coplanar waveguide strip 5 has a first width W1, and the microstrip line 6 has a second width W2. The lower bottom edge of the trapezoidal strip 52 is connected to the coplanar waveguide strip 5, and its width is W1. The upper bottom edge of the trapezoidal strip 52 is connected to the microstrip line 6, and its width is W2, where W1 > W2. Typically, the first width W1 = 0.115 mm, and the second width W2 = 0.04 mm. There is a gap between the coplanar waveguide strip 5 and a pair of ground electrodes 51. Typically, the width of this gap is 0.022 mm. This value ensures that both the coplanar waveguide and the microstrip line can maintain their own 50-ohm impedance. The wider bandwidth W1 of the coplanar waveguide reduces conductor loss, thereby reducing overall trace loss. The narrower microstrip line W2 facilitates wiring, connecting signal lines to chip pins.

[0035] The ground electrode 51 includes a rectangular electrode located in the coplanar waveguide region and a pair of trapezoidal electrodes 510 located in the transition region. The lower base of the trapezoidal electrode 510 is connected to the rectangular electrode in the coplanar waveguide region, and the upper base is connected to the microstrip line transmission region. Furthermore, the lower base of the trapezoidal electrode 510 is collinear with the lower base of the trapezoidal conductor 52, and the upper base of the trapezoidal electrode 510 is collinear with the upper base of the trapezoidal conductor 52. This collinear arrangement allows the trapezoidal transition region to form a gradually changing impedance, ultimately achieving impedance matching.

[0036] In one embodiment, a pair of trapezoidal electrodes 510 can be right trapezoids, with the hypotenuse of the trapezoidal electrode 510 close to the trapezoidal conductor 52. Furthermore, from the coplanar waveguide region to the microstrip line transmission region, the distance between the hypotenuse of the trapezoidal electrode 510 and the trapezoidal conductor 52 gradually increases, and one of the lower base angles of the trapezoidal electrode 510 close to the trapezoidal conductor 52 is 95°.

[0037] In one embodiment, the shortest distance from the bottom edge to the top edge of the trapezoidal conductor 52 is H, where H = 0.1-0.2 mm. Achieving structural transition and impedance matching within a shorter distance saves space.

[0038] A plurality of equally spaced metal through holes 3 are formed on a pair of grounding electrodes 51 of the top metal layer 1. These metal through holes 3 penetrate downward through the dielectric substrate 2 and the grounding layer 4. By depositing metal in the metal through holes 3, the grounding electrodes 51 are electrically connected to the grounding layer 4. In one embodiment of this application, the spacing between two adjacent metal through holes 3 is 0.24 mm.

[0039] A rectangular slot 42 and a trapezoidal slot 7 are connected on the central axis of the grounding layer 4. The rectangular slot 42 is located directly below the coplanar waveguide strip 5, and the trapezoidal slot 7 is located directly below the trapezoidal strip 52. This can reduce the capacitive coupling between the trapezoidal strip 52 and the grounding layer 4, further improve the broadband impedance matching capability of the transition structure, reduce the overall size of the transition structure, and reduce conductor loss.

[0040] The rectangular slot 42 has a third width W3, which is greater than the width W1 of the coplanar waveguide strip 5. The trapezoidal slot 7 also has a lower base and an upper base, and its dimensions are the same as those of the trapezoidal strip 52: the lower base length is W1, the upper base length is W2, and the height is H. The lower base of the trapezoidal slot 7 is connected to the lower base of the rectangular slot 42, creating a gradual impedance transition when the rectangular slot transitions to the microstrip transmission region, thus avoiding abrupt impedance changes.

[0041] This invention constructs trapezoidal electrodes and trapezoidal conductors in the transition region and creates trapezoidal slots at corresponding positions in the ground layer, achieving a transition from a coplanar waveguide transmission line with a loaded metal bridge to a microstrip. This results in broadband performance and low insertion loss, while also being small in size, suitable for dense wiring, and easily bendable. The electromagnetic field gradually transforms from the quasi-transverse electromagnetic wave mode (TEM) of the coplanar waveguide to the quasi-TEM mode of the microstrip line through the trapezoidal gradient structure.

[0042] A number of metal bridges 41 connecting the two sides of the rectangular slot 42 are arranged at intervals on the rectangular slot 42. The distance between two adjacent metal bridges 41 is 0.45mm, which can make the coplanar waveguide maintain an impedance of 50 ohms. If they are too dense, the impedance will decrease and it will not be easy to bend. If they are too loose, the impedance will increase.

[0043] In one embodiment of this application, flexible polyimide substrate with a dielectric constant of 3.71, a loss angle of 0.02, and a thickness of 50 μm was selected to fabricate a transition structure with physical dimensions of 3 mm × 0.85 mm. Frequency response testing was performed on this transition structure, and the results are as follows: Figure 4 As shown, the horizontal axis represents frequency variation, and the vertical axis represents impedance amplitude. S11 represents the frequency-amplitude curve of the transition structure of this application, and S21 represents the loss of the transition structure (length 3mm). It can be seen that within the passband of 0-40GHz, the impedance matching of S11 is better than -24dB, and the insertion loss is better than 0.65dB.

[0044] In summary, this application achieves a wideband, low-loss passband response within a relatively small size. The periodically distributed metal bridge effectively suppresses slot modes generated at impedance discontinuities, ensuring the high-frequency performance of the transition structure. The trapezoidal conductor and trapezoidal ground electrode rapidly increase the low impedance of the top-layer signal line to 50Ω of the microstrip line, achieving wideband impedance matching. Simultaneously, their graded-dip double-conductor structure effectively enables quasi-TEM mode transmission, allowing the overall transition structure to transition at any position within the metal bridge period. Furthermore, the trapezoidal slot structure reduces the capacitive coupling between the trapezoidal conductor and the ground layer, further improving the wideband impedance matching capability of the transition structure, reducing the overall size of the transition structure, and lowering conductor losses.

[0045] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope. The scope of protection of the present invention is defined by the appended claims, specification, and their equivalents.

Claims

1. A transition structure between a coplanar waveguide and microstrip transmission, characterized in that: The structure includes a ground layer (4), a dielectric substrate (2), and a top metal layer (1) stacked sequentially. The transition structure is divided into a microstrip line transmission region, a coplanar waveguide region, and a transition region between the microstrip line transmission region and the coplanar waveguide region. A top signal line (11) and a pair of ground electrodes (51) distributed on both sides of the top signal line (11) are formed on the top metal layer (1). The top signal line (11) forms a coplanar waveguide band (5) with a first width W1 in the coplanar waveguide region and a microstrip line (6) with a second width W2 in the microstrip line transmission region. A trapezoidal guide strip (52) is formed in the transition region. The bottom edge of the trapezoidal guide strip (52) has a width of W1 and the top edge has a width of W2. The grounding electrode (51) covers the transition region and the coplanar waveguide region. A rectangular groove (42) and a trapezoidal groove (7) are connected on the grounding layer (4). A number of equally spaced metal bridges (41) are arranged on the rectangular groove (42) to connect the two sides of the rectangular groove (42). The rectangular groove (42) is located directly below the coplanar waveguide guide strip (5), and the trapezoidal groove (7) is located directly below the trapezoidal guide strip (52).

2. The transition structure between a coplanar waveguide and microstrip transmission according to claim 1, characterized in that: The grounding electrode (51) includes a pair of trapezoidal electrodes (510) located in the transition region, wherein the lower bottom edge of the trapezoidal electrode (510) is connected to the coplanar waveguide region and the upper bottom edge is connected to the microstrip line transmission region.

3. The transition structure between a coplanar waveguide and microstrip transmission according to claim 2, characterized in that: The lower base of the trapezoidal electrode (510) is collinear with the lower base of the trapezoidal conductor (52), and the upper base of the trapezoidal electrode (510) is collinear with the upper base of the trapezoidal conductor (52).

4. The transition structure between a coplanar waveguide and microstrip transmission according to claim 3, characterized in that: The trapezoidal electrode (510) has a bottom angle of 85°-100° near the trapezoidal conductor (52).

5. The transition structure between a coplanar waveguide and microstrip transmission according to claim 1, characterized in that: The shortest distance from the bottom edge to the top edge of the trapezoidal guide strip (52) is H, where H = 0.1-0.2 mm.

6. The transition structure between a coplanar waveguide and microstrip transmission according to claim 1, characterized in that: The first width W1 is 0.08-0.15mm, and the second width W2 is 0.04-0.045mm.

7. The transition structure between a coplanar waveguide and microstrip transmission according to claim 1, characterized in that: The top-level signal line (11) is located in the center of the top-level metal layer (1), and the microstrip line (6), trapezoidal guide strip (52) and coplanar waveguide guide strip (5) are located on the central axis of the top-level signal line (11).

8. The transition structure between a coplanar waveguide and microstrip transmission according to claim 1, characterized in that: The distance between two adjacent metal bridges (41) is 0.4-0.5 mm.

9. The transition structure between a coplanar waveguide and microstrip transmission according to claim 1, characterized in that: The grounding layer (4), dielectric base layer (2) and top metal layer (1) are respectively provided with a number of metal through holes (3), and the grounding layer (4), dielectric base layer (2) and top metal layer (1) are electrically connected through the number of metal through holes (3).

10. The transition structure between a coplanar waveguide and microstrip transmission according to claim 1, characterized in that: The shape and size of the trapezoidal groove (7) are the same as those of the trapezoidal guide belt (52).

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