Design method of waveguide-microstrip hybrid integrated low-cost low-insertion-loss differential transmission line

Abstract

The invention discloses a design method of a waveguide-microstrip hybrid integrated low-cost low-insertion-loss differential transmission line, and belongs to the technical field of low-insertion-loss board-level signal transmission. The waveguide-microstrip hybrid integrated low-cost low-insertion-loss differential transmission line comprises a dielectric substrate, a transmission assembly is arranged on the dielectric substrate, coplanar metal grounds are arranged on the two sides of the transmission assembly, first metal through holes are formed in the coplanar metal grounds, and a second metal through hole is formed in the coplanar metal grounds; the transmission assembly is provided with a second metal through hole. By adopting the design method of the waveguide-microstrip hybrid integrated low-cost low-insertion-loss differential transmission line, the transmission loss is remarkably reduced, natural impedance matching is realized in a wide frequency band, and the common-mode rejection ratio is improved; the PCB is completely compatible with a traditional PCB in process, a low-cost substrate is adopted, and the material cost is reduced; an electromagnetic field is restrained through the metal through hole array, radiation loss is reduced, the crosstalk rejection ratio is improved, meanwhile, heat dissipation and breakdown characteristics are optimized through the air through holes, the power capacity is improved, and a low-loss, low-cost and high-reliability transmission solution is provided for scenes such as high-frequency communication and high-speed interconnection.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-insertion-loss board-level signal transmission, and in particular relates to a design method for a low-cost, low-insertion-loss differential transmission line of a waveguide-microstrip hybrid integration. Background Art

[0002] In modern communication systems, transmission line performance impacts system efficiency and signal quality. With advances in microwave communication technology and integrated circuits, transmission line loss has become increasingly important. Traditional transmission line structures, such as microstrip and coplanar waveguides, perform well in many applications, but they still suffer from significant dielectric and reflection losses when transmitting high-frequency signals. In particular, as frequency increases, the loss of traditional transmission line structures increases dramatically, leading to signal attenuation and low transmission efficiency, impacting signal quality and system reliability.

[0003] In order to solve these problems, researchers have proposed a variety of methods to reduce transmission line losses. For example, the loss can be reduced by introducing low-loss substrate materials (such as Rogers series plates), optimizing line width / spacing design, or adding shielding structures (such as through-hole arrays). Patent CN114759331A reduces edge loss through a planar slow-wave structure, but does not improve the dielectric loss of the substrate itself; Patent CN115882183A uses multi-layer metal through-holes and air slots to reduce loss, but relies on a metal jumper shielding structure, resulting in increased processing complexity and increased costs. Similarly, Patent CN119627387A reduces loss through a substrate-integrated transmission line formed by air holes, periodic non-uniform line widths, and metal holes, but the structure is sensitive to parameters, has high processing complexity, and is poorly compatible with traditional PCB manufacturing processes.

[0004] Therefore, it is particularly urgent to develop a transmission line structure with low insertion loss, low cost, compatibility with standard PCB processes, easy production, and wide operating bandwidth. Summary of the Invention

[0005] The purpose of the present invention is to provide a low-cost, low-insertion-loss differential transmission line design method for waveguide-microstrip hybrid integration. This method significantly reduces transmission loss, achieves natural impedance matching within a wide frequency band, and improves the common-mode rejection ratio. The process is fully compatible with traditional PCBs, and a low-cost substrate is used to reduce material costs. The electromagnetic field is constrained by a metal through-hole array, reducing radiation loss and improving the crosstalk rejection ratio. At the same time, air vias optimize heat dissipation and breakdown characteristics, thereby increasing power capacity, providing a low-loss, low-cost, and highly reliable transmission solution for scenarios such as high-frequency communications and high-speed interconnection.

[0006] To achieve the above objectives, the present invention provides a low-cost, low-insertion-loss differential transmission line design method for waveguide-microstrip hybrid integration, comprising a dielectric substrate, a transmission component disposed on the dielectric substrate, coplanar metal grounds disposed on both sides of the transmission component, a first metal through-hole disposed on the coplanar metal ground, and a second metal through-hole disposed on the transmission component.

[0007] Preferably, the transmission component includes a differential transmission line, which is symmetrically arranged on the dielectric substrate, and the differential transmission line and the coplanar metal ground are in the same plane.

[0008] Preferably, the first metal through-hole vertically penetrates the dielectric substrate and is connected to the bottom floor, and the coplanar metal ground is connected to the bottom floor through the first metal through-hole.

[0009] Preferably, the second metal through hole vertically penetrates the dielectric substrate, and a gap is provided between the second metal through hole and the bottom floor.

[0010] Preferably, a second air via is provided in the dielectric substrate between the differential transmission lines, and the second air via vertically penetrates the dielectric substrate.

[0011] Preferably, a first air via is provided in the dielectric substrate between the coplanar metal ground and the differential transmission line, and the first air via vertically penetrates the dielectric substrate.

[0012] Preferably, the first metal vias, the second metal vias, the first air vias and the second air vias are designed in multiple rows according to the width and spacing of the differential transmission lines, and the first metal vias, the second metal vias, the first air vias and the second air vias are staggered.

[0013] Therefore, the present invention adopts the above-mentioned waveguide-microstrip hybrid integrated low-cost and low-insertion-loss differential transmission line design method. Compared with the prior art, the present invention has the following significant beneficial effects:

[0014] (1) The design of the present invention can maintain stable impedance matching within a wide bandwidth, eliminating the need for additional impedance conversion structures and simplifying system complexity.

[0015] (2) The design of the present invention can maintain the overall architecture of the traditional differential transmission line unchanged, is fully compatible with the traditional PCB process, does not require new process steps or special materials, and does not increase process costs. It is compatible with conventional substrate materials such as FR4 and has a high cost-effectiveness.

[0016] (3) The design of the present invention constrains the electromagnetic field distribution through the metal through-hole array, reduces conductor loss and improves power capacity, and the air vias are equivalent to reducing the loss tangent of the dielectric material, significantly reducing the dielectric loss, and achieving comprehensive optimization of the overall transmission loss.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the overall structure of the design method of the waveguide-microstrip hybrid integrated low-cost and low-insertion-loss differential transmission line of the present invention;

[0019] Figure 2 A top view of the overall structure of the design method for a low-cost, low-insertion-loss differential transmission line with hybrid integration of waveguide and microstrip according to the present invention;

[0020] Figure 3 A bottom view of the overall structure of the design method for a low-cost, low-insertion-loss differential transmission line with hybrid waveguide-microstrip integration according to the present invention;

[0021] Figure 4 A comparison diagram of S(1, 1) of an embodiment of the present invention and a conventional differential line of the same size;

[0022] Figure 5 1 is a comparison diagram of S(2, 1) of the embodiment of the present invention and the traditional differential line of the same size.

[0023] Reference numerals

[0024] 1. Coplanar metal ground; 2. Differential transmission line; 3. Dielectric substrate; 4. First metal through hole; 5. First air via; 6. Second metal through hole; 7. Second air via; 8. Gap. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used in the present invention should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs.

[0026] Example 1

[0027] like Figure 1-Figure 3As shown, the low-cost, low-insertion-loss differential transmission line design method for waveguide-microstrip hybrid integration of the present invention includes a dielectric substrate 3. The dielectric substrate 3 serves as the physical support for the entire structure. The main body adopts an epoxy glass fiber cloth substrate (FR4), which has the advantages of low cost and mature processing technology. At the same time, it can also be flexibly replaced with materials such as quartz, glass, microwave dielectric plates, etc. that can be printed with metal on the surface according to actual application requirements. For example, in scenarios where high-frequency performance is required, microwave dielectric plates can be selected to utilize their low loss and high stability characteristics to further improve the overall performance of the transmission line. Differential transmission lines 2 are symmetrically arranged on the upper end surface of the dielectric substrate 3, and the differential transmission lines 2 are arranged in parallel. The differential transmission lines 2 are used to transmit differential electromagnetic wave signals, and the two key parameters of line width and spacing jointly determine the characteristic impedance. In actual design, by precisely adjusting the line width and spacing, good impedance matching with different circuit systems can be achieved to ensure efficient signal transmission. A coplanar metal ground 1 is provided on both sides of the differential transmission line 2. Coplanar metal ground 1 and differential transmission line 2 are coplanar (the upper surface of the dielectric substrate 3) and separated by air, forming a coplanar waveguide structure. This coplanar metal ground 1 provides a return path for the signal, effectively reducing electromagnetic interference during signal transmission and ensuring stable signal transmission.

[0028] First metal vias 4 are provided on the coplanar metal ground 1. These first metal vias 4 vertically penetrate the dielectric substrate 3 and connect to the subfloor (ground). A large number of these first metal vias 4 are arranged in an orderly fashion, forming an electromagnetic shielding boundary. During high-frequency signal transmission, this boundary effectively constrains the lateral diffusion of the electromagnetic field, significantly reducing radiation losses. The coplanar metal ground 1 is connected to the subfloor via these first metal vias 4.

[0029] A second metal through-hole 6 is provided on the differential transmission line 2. The second metal through-hole 6 vertically passes through the dielectric substrate 3, but the bottom is discontinuous with the floor (suspended) to avoid short-circuiting the differential signal. The second metal through-hole 6 is used to enhance the magnetic field coupling of the differential signal and improve the anti-interference capability. A gap 8 is provided between the second metal through-hole 6 and the bottom floor. The gap 8 blocks the ground connection of the second metal through-hole 6 so that the through-hole 6 is not in direct contact with the floor. If the second metal through-hole 6 is directly grounded, part of the signal current will be shunted to the ground plane, destroying the balance characteristics of the differential pair and increasing common-mode noise. The gap 8 ensures that the second metal through-hole 6 only participates in the electromagnetic field regulation without affecting the current path of the differential signal, and forms a "magnetic wall" for the ungrounded second metal through-hole 6, thereby reducing radiation loss. The gap 8 can be achieved by controlling the patterning of the PCB copper layer without the need for additional process steps, and is fully compatible with traditional PCB processes.

[0030] A first air via 5 is provided in the dielectric substrate 3 between the coplanar metal ground 1 and the differential transmission line 2. The first air via 5 extends vertically through the dielectric substrate 3. This first air via 5 optimizes the electromagnetic field distribution, reduces radiation loss caused by edge effects, and makes the electromagnetic field distribution around the transmission line more reasonable and uniform. For example, in electronic devices with high electromagnetic compatibility requirements, the first air via 5 can effectively reduce electromagnetic interference from the transmission line to surrounding circuits, thereby improving the performance and stability of the entire device.

[0031] A second air via 7 is provided in the dielectric substrate 3 between the two differential transmission lines 2. This second air via 7 vertically penetrates the dielectric substrate 3, reducing dielectric loss between the differential pairs. This dielectric loss reduction is particularly effective during high-frequency signal transmission, significantly reducing the overall transmission loss of the transmission line. For example, in millimeter-wave frequency band communication systems, this second air via 7 can effectively reduce signal attenuation, ensuring long-distance, high-quality signal transmission.

[0032] The first metal vias 4, second metal vias 6, first air vias 5, and second air vias 7 can be designed in a single row or multiple rows, depending on the width and spacing of the differential transmission lines 2. When arranged in multiple rows, the first metal vias 4, second metal vias 6, first air vias 5, and second air vias 7 are typically arranged alternately or symmetrically to enhance electromagnetic field confinement. The spacing between the coplanar metal ground 1 and the differential transmission lines 2 can be adjusted based on impedance matching requirements and is typically in the micron range (e.g., d = 0.1-1 mm). A smaller spacing provides greater electromagnetic field confinement.

[0033] In order to further intuitively verify the low loss characteristics of the transmission line structure of the present invention, the following Figure 4 (Reflection coefficient curve) and Figure 5 (Transmission loss curve) Both figures compare the characteristics of a conventional differential transmission line structure and the structure of an embodiment of the present invention under the conditions of equal length transmission lines, the same material, and the same dielectric thickness.

[0034] Figure 4 In the graph, the horizontal axis is the frequency (unit: GHz), and the vertical axis is the reflection coefficient S (1, 1) (unit: dB). Compared with the traditional differential line transmission line (dashed line), the transmission line technology of the present invention (solid line) has a lower reflection coefficient curve than the transmission line of the present invention in the wide operating frequency band of 12.5-30.0 GHz. This means that within this frequency band, the signal reflection degree of the transmission line structure of the present invention is smaller, and the energy loss caused by reflection during signal transmission is less, thereby being able to better maintain the integrity of the signal. At the same time, it can be seen that the transmission line structure of the present invention maintains a matching of less than -20 dB within the wide operating frequency band, indicating that it has good impedance matching characteristics within the wide frequency band, effectively reducing signal reflection and ensuring efficient signal transmission.

[0035] Figure 5 In the figure, the horizontal axis is frequency (unit: GHz), and the vertical axis is transmission loss S(2, 1) (unit: dB). At 25 GHz, the loss of the traditional differential transmission line structure is 2.17 dB / inch, while the loss of the structure of the embodiment of the present invention is only 1.61 dB / inch. It can be clearly seen that the transmission line structure of the present invention has lower loss at the same frequency. From the overall trend of the curve, in the frequency band of 12.5-30.0 GHz, the transmission loss curve of the transmission line structure of the present invention is always lower than that of the traditional differential transmission line structure, which fully demonstrates that the structure of the present invention can effectively reduce the transmission loss of the differential transmission line, which can make the energy decay of the signal slower during transmission, and is more conducive to long-distance and high-quality transmission of the signal.

[0036] Therefore, the present invention adopts the above-mentioned waveguide-microstrip hybrid integrated low-cost and low-insertion-loss differential transmission line design method, which significantly reduces transmission loss, realizes natural impedance matching within a wide bandwidth, and improves the common-mode rejection ratio; the process is fully compatible with traditional PCBs, adopts a low-cost substrate, and reduces material costs; the electromagnetic field is constrained by a metal through-hole array, reducing radiation loss and improving the crosstalk rejection ratio; at the same time, the air via optimizes the heat dissipation and breakdown characteristics, and improves the power capacity, providing a low-loss, low-cost, and high-reliability transmission solution for scenarios such as high-frequency communication and high-speed interconnection.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A low-cost, low-insertion-loss differential transmission line design method for waveguide-microstrip hybrid integration, characterized in that: The invention comprises a dielectric substrate, a transmission component is arranged on the dielectric substrate, a coplanar metal ground is arranged on both sides of the transmission component, a first metal through hole is arranged on the coplanar metal ground, and a second metal through hole is arranged on the transmission component.

2. The design method of a low-cost, low-insertion-loss differential transmission line for hybrid waveguide-microstrip integration according to claim 1, characterized in that: The transmission component includes a differential transmission line, which is symmetrically arranged on the dielectric substrate. The differential transmission line and the coplanar metal ground are in the same plane.

3. The design method of a low-cost, low-insertion-loss differential transmission line for hybrid waveguide-microstrip integration according to claim 2, characterized in that: The first metal through-hole vertically penetrates the dielectric substrate and is connected to the bottom floor. The coplanar metal ground is connected to the bottom floor through the first metal through-hole.

4. The design method of a low-cost, low-insertion-loss differential transmission line for waveguide-microstrip hybrid integration according to claim 3, characterized in that: The second metal through hole vertically penetrates the dielectric substrate, and a gap is set between the second metal through hole and the bottom floor.

5. The design method of a low-cost, low-insertion-loss differential transmission line for hybrid waveguide-microstrip integration according to claim 4, characterized in that: A second air via is provided in the dielectric substrate between the two differential transmission lines, and the second air via vertically penetrates the dielectric substrate.

6. The design method of a low-cost, low-insertion-loss differential transmission line for hybrid waveguide-microstrip integration according to claim 5, characterized in that: A first air via is provided in the dielectric substrate between the coplanar metal ground and the differential transmission line, and the first air via vertically penetrates the dielectric substrate.

7. The design method of a low-cost, low-insertion-loss differential transmission line for hybrid waveguide-microstrip integration according to claim 6, characterized in that: The first metal vias, the second metal vias, the first air vias and the second air vias are designed in multiple rows according to the width and spacing of the differential transmission lines, and the first metal vias, the second metal vias, the first air vias and the second air vias are staggered.

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