Novel low-consumption semi-coaxial broadband transmission line easy to integrate

Abstract

The invention discloses an easy-to-integrate low-consumption semi-coaxial novel broadband transmission line, which comprises a dielectric substrate, a floor, a semi-coaxial inner conductor and a semi-coaxial outer conductor, and is characterized in that the dielectric substrate is fixed on the floor, the semi-coaxial outer conductor covers the dielectric substrate, a shielding cavity is formed by the inner wall of the semi-coaxial outer conductor and the upper surface of the dielectric substrate, and the semi-coaxial inner conductor covers the shielding cavity; the shielding cavity is filled with media, the lower surface of the semi-coaxial inner conductor is tightly attached to the upper surface of the dielectric substrate, the semi-coaxial inner conductor is located in the center of the shielding cavity formed by the semi-coaxial outer conductor and the dielectric substrate, and the distances between the semi-coaxial inner conductor and the inner walls of the left side and the right side of the semi-coaxial outer conductor are the same. Two ends of the semi-coaxial outer conductor are respectively provided with a first port and a second port, signals are transmitted between the two ports, and the radio frequency coaxial cable has very low insertion loss and return loss, has excellent transmission characteristics in a frequency range of 0-150G, and is especially suitable for application of low-frequency to high-frequency full-band signals in radio frequency circuits and packaging systems.

Description

Technical Field

[0001] This invention relates to a sub-millimeter-scale miniature low-loss transmission line, particularly a novel low-loss semi-coaxial broadband transmission line that is easy to integrate. It features low loss and low dispersion in the microwave to terahertz frequency bands, belongs to the field of radio frequency and microwave technology, and is particularly suitable for interconnection structures in various power supply networks and packaging systems. It is also easy to integrate with various reconfigurable and tunable devices and circuits. Background Technology

[0002] In radio frequency (RF) systems, various passive circuits and interconnect structures are all constructed using transmission lines as their basic unit. Common transmission lines include microstrip lines, substrate-integrated waveguides, air-filled waveguides, and dielectric suspension lines. However, microstrip lines and substrate-integrated waveguides, commonly used in low-frequency bands, often exhibit significant losses in high-frequency applications due to the loading of the dielectric substrate. While air-filled metal waveguides offer low-loss characteristics, they are bulky and difficult to integrate and package with PCB circuits. In general, traditional transmission lines often suffer from a trade-off between performance and size. Therefore, to meet the current demands for higher integration and performance in RF systems, there is an urgent need for a transmission line that covers frequencies from low to terahertz while possessing both small size and high performance. This fundamental change in the basic unit level would further satisfy the contemporary needs of passive networks and even RF packaged circuits.

[0003] A search revealed Chinese invention patent CN110416680A, which discloses a semi-coaxial microstrip combined radio frequency transmission line structure, belonging to the field of radio frequency and microwave technology. It includes a semi-coaxial cable and a matching microstrip. The semi-coaxial cable comprises an outer conductor, a semi-ring dielectric, and a semi-circular inner conductor, forming a unified mounting contact surface. The matching microstrip includes a substrate with a central conductor and a grounding metal layer mounted on it. In operation, the semi-coaxial cable presses against the upper surface of the matching microstrip, with their center lines aligned. Under the action of upper and lower pressure, the semi-circular inner conductor and the central conductor adhere, forming the central conductor. The outer conductor of the semi-coaxial cable serves as the upper grounding layer. Electromagnetic waves are transmitted in TEM mode within the carrier formed by the semi-ring dielectric and the substrate. This invention is applied to the transition of radio frequency connector structures from coaxial to microstrip lines (strip lines), and is particularly suitable for the design of horizontally press-fit radio frequency connectors.

[0004] The technical comparison between this application and the aforementioned patent is as follows: 1. The patent "A Semi-Coaxial Microstrip Combined RF Transmission Line Structure" is a designed transition structure that cannot be used for the construction of passive networks or systems; while this invention designs a novel transmission line that can be used for the design of various micro-miniature passive networks and the packaging and integration of RF systems. The two are completely different in type and application scenarios.

[0005] 2. The patent "A Semi-Coaxial Microstrip Combined RF Transmission Line Structure" proposes a solution for transitioning between striplines and dielectric-filled circular coaxial probes, serving as a bridge between the two types of transmission lines. It requires consideration of the electrical characteristics of both striplines and dielectric-filled circular coaxial probes, and its length is limited. This invention integrates the structure above the lower surface of the inner conductor in an air-filled submillimeter-scale rectangular micro-coaxial line with a dielectric substrate. Essentially, it still constitutes a transmission line, and its length is freely adjustable. The two differ significantly in structure, morphology, and electrical performance.

[0006] 3. The patent "A Semi-Coaxial Microstrip Combined RF Transmission Line Structure" is a large-size structure and cannot be applied to high-frequency scenarios due to its high loss. The transmission line of this invention has the characteristics of low loss and low dispersion in the ultra-wideband range, making it very suitable for high-frequency and even terahertz frequency bands.

[0007] A search revealed that US Patent Publication No. US06653915B1 discloses a method for forming a coaxial transmission line on a high-density PCB. A metal layer (102) on the PCB (104) forms the bottom of a shield and is covered by a first dielectric (112). Two parallel trenches (122) are formed in the first dielectric to expose portions (123) of a metal strip. A signal conductor (132) is then formed on the first dielectric. A second dielectric (142) covers the signal conductor and the first dielectric. A second set of two parallel trenches (172) is formed in the second dielectric immediately above the first two trenches. A metal deposit (182) is electroplated in the parallel trenches to contact the metal strip and also covers a portion of the second dielectric located between the trenches to form a shield. The resulting coaxial transmission line has a center conductor insulated from the shield by the dielectric.

[0008] The technical comparison between this application and the aforementioned patent is as follows: 1. This patent is for an irregular cross-section multi-substrate all-dielectric transmission line, while this invention is for a regular cross-section single-substrate air transmission line.

[0009] 2. The patented structure is entirely dielectric-filled, resulting in limited bandwidth and significant dispersion, making it difficult to meet wideband transmission requirements. In contrast, the transmission in this invention is primarily concentrated in an air-shielded cavity, achieving a bandwidth of 0-150GHz, suitable for full-band signal transmission.

[0010] 3. The dielectric loss in this patented material is relatively high, increasing with higher frequencies. In the structure proposed in this invention, electromagnetic waves primarily propagate through the air, effectively avoiding dielectric loss. The dielectric constant of the dielectric material in patent US6653915B1 limits the signal transmission speed. In the structure proposed in this invention, electromagnetic waves propagate much faster. Summary of the Invention

[0011] This invention proposes a novel low-power semi-coaxial broadband transmission line that is easy to integrate, has very low insertion loss and return loss, and exhibits excellent transmission characteristics in the 0-150G frequency range. It is particularly suitable for the application of low-frequency to high-frequency full-band signals in radio frequency circuits and packaging systems.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A novel low-power semi-coaxial broadband transmission line that is easy to integrate includes a dielectric substrate, a ground plane, a semi-coaxial inner conductor, and a semi-coaxial outer conductor. The dielectric substrate is fixed to the ground plane, and the semi-coaxial outer conductor is placed on the dielectric substrate. The inner wall of the semi-coaxial outer conductor and the upper surface of the dielectric substrate form a shielded cavity, which is filled with dielectric. The lower surface of the semi-coaxial inner conductor is in close contact with the upper surface of the dielectric substrate, and the semi-coaxial inner conductor is located at the center of the shielded cavity formed by the semi-coaxial outer conductor and the dielectric substrate. The two ends of the semi-coaxial outer conductor are respectively provided with a first port and a second port, and the signal is transmitted between the two ports.

[0013] As a preferred technical solution of the present invention: the semi-coaxial outer conductor includes a first side plate, a second side plate and a top plate. The first side plate and the second side plate are respectively vertically fixed on both sides of the same end face of the top plate, and the first side plate and the second side plate are symmetrically arranged about the center point of the top plate.

[0014] As a preferred technical solution of the present invention, the thickness of the first side plate, the second side plate and the top plate can be selected to be the same or different values.

[0015] As a preferred technical solution of the present invention: a first mounting groove and a second mounting groove are provided on the dielectric substrate along its width direction, a mounting platform is formed between the first mounting groove and the second mounting groove, the semi-coaxial inner conductor is mounted on the mounting platform, the first side plate and the second side plate are respectively located in the first mounting groove and the second mounting groove, and the end faces of the first side plate and the second side plate are fixed to the floor.

[0016] As a preferred embodiment of the present invention, the height of the first side plate and the second side plate is greater than the total thickness of the dielectric substrate and the semi-coaxial inner conductor.

[0017] As a preferred technical solution of the present invention: the heights of the first side plate and the second side plate can be selected to be different values. When the heights of the first side plate and the second side plate are the same, the shielding cavity is a rectangular shielding cavity. When the heights of the first side plate and the second side plate are different, the shielding cavity is a trapezoidal shielding cavity.

[0018] As a preferred embodiment of the present invention: the portions of the first side plate and the second side plate that are embedded in the first mounting groove and the second mounting groove and the portions located outside the first mounting groove and the second mounting groove are processed independently.

[0019] As a preferred technical solution of the present invention, the medium filling the space between the semi-coaxial inner conductor and the semi-coaxial outer conductor is preferably air.

[0020] As a preferred embodiment of the present invention, both the semi-coaxial inner conductor and the semi-coaxial outer conductor are metallic materials with conductive properties.

[0021] This invention proposes a novel low-loss semi-coaxial broadband transmission line integrating a microcoaxial cable with a dielectric substrate. Its main structure involves placing half of the outer conductor of the microcoaxial cable (i.e., half of the semi-coaxial cable) onto the dielectric substrate. However, the transmission is still concentrated within the shielded cavity formed by the upper part of the dielectric substrate and the outer conductor of the semi-coaxial cable. Therefore, its loss characteristics, dispersion characteristics, and bandwidth are similar to those of a microcoaxial cable. Consequently, the transmission line proposed in this invention exhibits very low insertion loss and return loss, and excellent transmission characteristics in the 0-150 GHz frequency range, making it particularly suitable for applications of low-frequency to high-frequency full-band signals in RF circuits and packaging systems.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention enables the application of ultra-wideband transmission lines that combine small size and high performance in passive networks and RF packaging systems. Compared to traditional transmission lines, it features submillimeter-wave dimensions and exhibits low insertion loss and low dispersion characteristics across the 0-150 GHz frequency band, with a maximum insertion loss of 0.12 dB across the entire band. The integrated dielectric substrate facilitates integration of this transmission line structure with PCB circuits and reconfigurable, adjustable components. Furthermore, the transmission line can be fabricated using traditional PCB processes and electroplating, eliminating the need for costly microfabrication techniques. Its small size, low loss, and low cost offer new possibilities for next-generation packaging integration.

[0023] The transmission line of this invention has a maximum insertion loss of 0.12dB in the 0-150G frequency band, and the reflection loss is kept below -15dB. The reflected signal is extremely small, resulting in good transmission performance. The thickness of the first and second side plates and the top plate on both sides of the transmission line, as well as the height of the first and second side plates, can be different. By adjusting the values ​​of various parameters, smooth transmission can be ensured. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0025] Figure 2 This is a cross-sectional view of the present invention.

[0026] Figure 3 It is an S-parameter characteristic curve.

[0027] Figure 4 It is a phase velocity characteristic curve.

[0028] List of reference numerals in the attached diagram: 1. Dielectric substrate; 2. Ground plane; 3. Semi-coaxial inner conductor; 4. Semi-coaxial outer conductor; 41. First side plate; 42. Second side plate; 43. Top plate; 5. First port; 6. Second port; 7. Shielding cavity; 8. Mounting platform. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] like Figure 1-2 As shown, the present invention proposes a novel low-power semi-coaxial broadband transmission line that is easy to integrate, comprising a dielectric substrate 1, a ground plane 2, a semi-coaxial inner conductor 3, and a semi-coaxial outer conductor 4. The dielectric substrate 1 is fixed on the ground plane 2, and the semi-coaxial outer conductor 4 is disposed on the dielectric substrate 1. The inner wall of the semi-coaxial outer conductor 4 and the upper surface of the dielectric substrate 1 form a shielding cavity 7, which is filled with dielectric. The lower surface of the semi-coaxial inner conductor 3 is in close contact with the upper surface of the dielectric substrate 1, and the semi-coaxial inner conductor 3 is located at the center of the shielding cavity 7 formed by the semi-coaxial outer conductor 4 and the dielectric substrate 1, that is, the distance between the semi-coaxial inner conductor 3 and the inner walls on both sides of the semi-coaxial outer conductor 4 is the same. The two ends of the semi-coaxial outer conductor 4 are respectively provided with a first port 5 and a second port 6, and the signal is transmitted between the two ports.

[0031] Innovative integrated applications of microcoaxial cable and dielectric substrate 1: This invention effectively integrates the microcoaxial structure with the dielectric substrate 1 structure, while maintaining the broadband, low-power, and low-dispersion stability characteristics of the microcoaxial structure in the microwave to millimeter-wave frequency band, exhibiting performance far superior to traditional structures. Furthermore, the loading of the dielectric substrate 1 facilitates integration with traditional circuit structures, expanding the application scope and scenarios of classic microcoaxial technology. Key design features include the precise adjustment of the relationship between the dimensions and performance of the semi-coaxial inner conductor 3 and the semi-coaxial outer conductor 4, as well as the design and matching adjustment of the transition structure when transitioning the proposed scheme to other transmission lines such as coplanar waveguides and microstrip lines during subsequent testing.

[0032] The concentrated transmission characteristics of semi-coaxial cables in air: In this invention, when a micro-coaxial cable is integrated with a dielectric substrate 1 to form a novel semi-coaxial broadband transmission line, the vast majority of signals are still confined to the shielded cavity 7 for transmission. Therefore, the dielectric loss caused by the dielectric substrate 1 is minimal, and the overall transmission line maintains low-loss and low-dispersion characteristics over the broadband range. A key design feature of this application is controlling the distance between the top plate 43 of the semi-coaxial outer conductor 4 and the dielectric substrate 1 to maintain good transmission characteristics.

[0033] In this embodiment of the invention, the semi-coaxial outer conductor 4 includes a first side plate 41, a second side plate 42, and a top plate 43. The first side plate 41 and the second side plate 42 are respectively vertically fixed on both sides of the same end face of the top plate 43. The first side plate 41 and the second side plate 42 are symmetrically arranged about the center point of the top plate 43.

[0034] In this embodiment of the invention, the thicknesses of the first side plate 41, the second side plate 42, and the top plate 43 can be selected to be the same or different values.

[0035] In this embodiment of the invention, a first mounting groove and a second mounting groove are provided on the dielectric substrate 1 along its width direction, and a mounting platform 8 is formed between the first mounting groove and the second mounting groove. The semi-coaxial inner conductor 3 is mounted on the mounting platform 8. The first side plate 41 and the second side plate 42 are respectively located in the first mounting groove and the second mounting groove, and the end faces of the first side plate 41 and the second side plate 42 are fixed on the floor 2.

[0036] In this embodiment of the invention, the height of the first side plate 41 and the second side plate 42 is greater than the total thickness of the dielectric substrate 1 and the semi-coaxial inner conductor 3.

[0037] In this embodiment of the invention, when the heights of the first side plate 41 and the second side plate 42 are the same, the shielding cavity 7 is a rectangular shielding cavity; when the heights of the first side plate 41 and the second side plate 42 are different, the shielding cavity 7 is a trapezoidal shielding cavity.

[0038] The portions of the first side plate 41 and the second side plate 42 that are embedded in the first mounting groove and the second mounting groove, and the portions located outside the first mounting groove and the second mounting groove, are processed independently.

[0039] The first side plate 41 and the second side plate 42 of the novel semi-coaxial broadband transmission line proposed in this invention can be divided into a part in the air and a part embedded in the first mounting groove and the second mounting groove on the dielectric substrate 1. The two parts can be processed separately and independently, which can effectively reduce the processing cost. The processing method can adopt low-cost processing technologies such as PCB process and electroplating.

[0040] The size of the dielectric substrate 1 extending outside the semi-coaxial outer conductor 4 is unlimited. Therefore, the thickness of the dielectric substrate 1 can be adjusted. At the same time, the size of other structures must also be adjusted accordingly to ensure good transmission characteristics.

[0041] The invention will be further illustrated below with specific examples.

[0042] In this embodiment of the invention, the floor 2, the semi-coaxial inner conductor 3, and the semi-coaxial outer conductor 4 are all made of metal materials with conductive properties. In this embodiment of the invention, copper is used, but other metal materials with good conductivity can also be used. The dielectric substrate 1 can be made of materials with different relative permittivity. In this embodiment of the invention, Rogers 5880 board with a thickness of 0.2 mm is used.

[0043] In this embodiment of the invention, the medium filling the space between the semi-coaxial inner conductor 3 and the semi-coaxial outer conductor 4 is preferably air, the size of which is adjustable, but the cross-sectional dimensions of the restricted shielding space are still within the sub-millimeter range.

[0044] In this embodiment of the invention, for example, the height of the semi-coaxial inner conductor 3 is set to 0.1 mm and the width is set to 0.25 mm.

[0045] In this embodiment of the invention, for example, the thickness of the semi-coaxial outer conductor 4 is set to 0.1 mm, the distance between the first side plate 41 and the second side plate 42 is 0.7 mm, and the distance between the lower surface of the top plate 43 and the dielectric substrate 1 is 0.2 mm.

[0046] In this embodiment of the invention, for example, the width of the dielectric substrate 1 is set to 3 mm.

[0047] In this embodiment of the invention, for example, the distance between the first port 5 and the second port 6 is set to 3mm. This distance represents the physical length of the transmission line and can be freely adjusted.

[0048] Based on the above exemplary settings, such as Figure 3 As shown, the S-parameter characteristic curves of the present invention are given. The maximum insertion loss in the entire 0-150G frequency band is 0.12dB, and the return loss is below -15dB, which shows the characteristics of ultra-wideband low power consumption.

[0049] Based on the above exemplary settings, such as Figure 4 As shown, the phase velocity characteristic curve of the present invention is given. The phase velocity is stable at 0.12dB in the entire frequency band of 0-150G, and the return loss is about 0.84, which has ultra-wideband low dispersion characteristics.

[0050] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A novel low-power semi-coaxial broadband transmission line that is easy to integrate, characterized in that: The device includes a dielectric substrate (1), a ground plane (2), a semi-coaxial inner conductor (3), and a semi-coaxial outer conductor (4). The dielectric substrate (1) is fixed on the ground plane (2). The semi-coaxial outer conductor (4) is placed on the dielectric substrate (1). The inner wall of the semi-coaxial outer conductor (4) and the upper surface of the dielectric substrate (1) form a shielding cavity (7). The shielding cavity (7) is filled with dielectric. The lower surface of the semi-coaxial inner conductor (3) is in close contact with the upper surface of the dielectric substrate (1). The semi-coaxial inner conductor (3) is located at the center of the shielding cavity (7) formed by the semi-coaxial outer conductor (4) and the dielectric substrate (1). The two ends of the semi-coaxial outer conductor (4) are respectively provided with a first port (5) and a second port (6), and the signal is transmitted between the two ports.

2. The novel low-power semi-coaxial broadband transmission line with easy integration according to claim 1, characterized in that: The semi-coaxial outer conductor (4) includes a first side plate (41), a second side plate (42), and a top plate (43). The first side plate (41) and the second side plate (42) are respectively vertically fixed on both sides of the same end face of the top plate (43). The first side plate (41) and the second side plate (42) are symmetrically arranged about the center point of the top plate (43).

3. The novel low-power semi-coaxial broadband transmission line with easy integration according to claim 2, characterized in that: The thicknesses of the first side plate (41), the second side plate (42), and the top plate (43) can be selected to be the same or different values.

4. The novel low-power semi-coaxial broadband transmission line with easy integration according to claim 2, characterized in that: A first mounting groove and a second mounting groove are provided on the dielectric substrate (1) along its width direction. A mounting platform (8) is formed between the first mounting groove and the second mounting groove. The semi-coaxial inner conductor (3) is mounted on the mounting platform (8). The first side plate (41) and the second side plate (42) are located in the first mounting groove and the second mounting groove, respectively. The end faces of the first side plate (41) and the second side plate (42) are fixed on the floor (2).

5. A novel low-power semi-coaxial broadband transmission line with easy integration according to claim 4, characterized in that: The height of the first side plate (41) and the second side plate (42) is greater than the total thickness of the dielectric substrate (1) and the semi-coaxial inner conductor (3).

6. The novel low-power semi-coaxial broadband transmission line with easy integration according to claim 5, characterized in that: The heights of the first side plate (41) and the second side plate (42) can be selected to be different values. When the heights of the first side plate (41) and the second side plate (42) are the same, the shielding cavity (7) is a rectangular shielding cavity. When the heights of the first side plate (41) and the second side plate (42) are different, the shielding cavity (7) is a trapezoidal shielding cavity.

7. A novel low-power semi-coaxial broadband transmission line with easy integration according to claim 4, characterized in that: The portions of the first side plate (41) and the second side plate (42) that are embedded in the first mounting groove and the second mounting groove, and the portions located outside the first mounting groove and the second mounting groove, are processed independently.

8. The novel low-power semi-coaxial broadband transmission line with easy integration according to claim 1, characterized in that: The medium filling the space between the semi-coaxial inner conductor (3) and the semi-coaxial outer conductor (4) is preferably air.

9. A novel low-power semi-coaxial broadband transmission line with easy integration according to claim 1, characterized in that: Both the semi-coaxial inner conductor (3) and the semi-coaxial outer conductor (4) are metallic materials with electrical conductivity.

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