A low-loss microwave transmission line structure based on 3D printing and a microwave circuit

Abstract

This invention discloses a low-loss microwave transmission line structure and microwave circuit based on 3D printing. The invention includes a single-dielectric transmission layer and first and second shielding shells. The shielding shells are integrally formed by 3D printing, and both their inner and outer surfaces are metallized to form an electromagnetic shielding layer. The single-dielectric transmission layer is fixed as an independent physical layer between the first and second shielding shells. The inner surface of the first or second shielding shell has a de-resonance support structure along the routing direction of the radio frequency signal transmission line. This structure includes a recessed structure and a solid portion forming the recessed structure. The solid portion serves as a protrusion for positioning and support during assembly. When the three components are assembled, the protrusion passes through the single-dielectric transmission layer, and the recessed structure forms continuous air cavities on the upper and lower sides of the radio frequency signal transmission line, enabling the radio frequency signal transmission line to be in a self-encapsulated state. This invention provides a potentially applicable basic architecture for constructing complex microwave and millimeter-wave subsystems.

Description

Technical Field

[0001] This invention relates to the field of microwave integrated circuit technology, specifically to a low-loss microwave transmission line structure and microwave circuit based on 3D printing, wherein the microwaves cover conventional radio frequency bands, microwave bands and millimeter wave bands. Background Technology

[0002] With the rapid development of wireless communication technology, especially millimeter-wave communication and phased array radar systems, radio frequency microwave circuits and systems are facing increasingly higher requirements for low loss, low cost, lightweight, and high integration. As the fundamental and core components of microwave and millimeter-wave systems, the size, weight, and transmission performance (such as insertion loss, standing wave ratio, and radiation loss) of transmission lines and feed networks determine the performance of the entire antenna array or communication system.

[0003] In traditional microwave and millimeter-wave bands, common planar transmission lines (such as microstrip lines and coplanar waveguides) face severe dielectric loss and radiation leakage problems, and lack inherent self-encapsulation characteristics, which degrades the overall array gain. Although non-planar metallic waveguides have low loss, they suffer from drawbacks such as large size, heavy weight, high manufacturing cost, and difficulty in integrating with other planar circuits.

[0004] In recent years, Substrate Integrated Suspended Line (SISL) technology has been proposed and widely applied. SISL structures, utilizing air cavities and self-encapsulation, exhibit excellent low-loss performance in filters, couplers, and power dividers. However, traditional SISL technology faces bottlenecks in manufacturing processes: its structure typically relies on complex multilayer high-frequency printed circuit board (PCB) lamination processes, or requires expensive and cumbersome Computerized Numerical Control (CNC) metal machining techniques to construct its internal air cavity. These traditional manufacturing methods not only increase manufacturing costs and system weight but also lack design freedom when realizing complex internal three-dimensional geometries.

[0005] To effectively overcome the inherent limitations of traditional processing techniques in terms of structural complexity, manufacturing cost, and lightweight design, 3D printing technology exhibits significant advantages. It boasts high design freedom, low cost, and lightweight characteristics, enabling the efficient fabrication of complex structural components that are difficult to manufacture using traditional methods. Currently, in the radio frequency and microwave fields, the application of 3D printing technology mainly focuses on the fabrication of integrated microwave devices such as waveguide structures and horn antennas. For example, a Chinese invention patent (authorization announcement number CN107529274B) discloses a dielectric integrated suspension line circuit structure based on 3D printing. This scheme proposes to manufacture the cavity walls and circuit components using 3D printing technology, and to use several dielectric pillars printed from non-conductive materials as fixed parts to support the suspension circuit. Although this all-3D printing solution improves space utilization and reduces weight, existing 3D-printed suspension line solutions still have the following key problems in practical applications:

[0006] 1) Complex internal support structure, resulting in poor microwave circuit performance and mechanical stability: Existing pure 3D printing solutions typically require the design of numerous discrete internal dielectric pillars for suspension support. This support system not only increases the complexity of the structural design but also exhibits weak mechanical robustness, making it prone to deformation or damage during assembly or when subjected to external mechanical impacts. Furthermore, the microwave circuit portion of this solution relies entirely on 3D printing (such as conductive material coating or metal printing). Pure 3D printed circuits suffer from disadvantages in surface roughness, metal layer adhesion, and resolution of RF planar traces (especially fine gaps and edge linewidths), easily leading to a significant increase in high-frequency conductor losses and difficulty in controlling trace accuracy.

[0007] 2) Inability to eliminate high-frequency parasitic resonances, disrupting transmission flatness: In the microwave and millimeter-wave bands, highly packaged cavities and complex internal support structures (such as dielectric pillars) inherently constitute a natural three-dimensional resonant cavity structure. This means that without specialized resonant suppression design, these structures cannot physically eliminate high-frequency parasitic resonant modes. This inherent resonant characteristic disrupts the transmission flatness of the transmission line over the wide bandwidth and may even lead to complete device failure.

[0008] 3) Limited accuracy and process compatibility of planar traces: Microwave RF traces that rely entirely on 3D printing technology to form fine traces often cannot achieve the accuracy of traditional mature single-layer printed circuit board (PCB) processes on planar RF traces, and it is difficult to achieve high-precision process compatibility with other mature planar passive / active devices.

[0009] Therefore, how to break through the process limitations of traditional multilayer PCB lamination or CNC metal machining, and develop a new type of microwave transmission line or feed network structure with low cost, lightweight, low loss characteristics, and effective overcoming of the poor mechanical stability of existing 3D printing solutions and effective suppression of high-frequency parasitic resonance, has become a key technical problem that urgently needs to be solved. Summary of the Invention

[0010] Purpose of the invention: The purpose of this invention is to provide a low-loss microwave transmission line structure and microwave circuit based on 3D printing, which solves the problems of existing dielectric integrated suspension line technology relying on complex multilayer board lamination process or expensive metal CNC machining, as well as the problems of existing pure 3D printing solutions having complex internal support structure, poor mechanical stability, low processing consistency and yield, and difficulty in suppressing parasitic resonance.

[0011] Technical solution: To achieve the above-mentioned objectives, in a first aspect, the present invention provides a low-loss microwave transmission line structure based on 3D printing, comprising:

[0012] A single-medium transmission layer is composed of a printed circuit board with at least one radio frequency signal transmission line printed on its surface.

[0013] The first shielding shell and the second shielding shell are both made of non-conductive materials and are integrally formed by 3D printing. Both the inner and outer surfaces are metallized to form an electromagnetic shielding layer.

[0014] The single-dielectric transmission layer, as an independent physical layer, is fixed between the first shielding shell and the second shielding shell. The inner surface of the first shielding shell or the second shielding shell is provided with a de-resonance support structure along the routing direction of the radio frequency signal transmission line. The de-resonance support structure includes a recessed structure and a solid portion forming the recessed structure. The solid portion serves as a protrusion for positioning and support during assembly. When the first shielding shell, the single-dielectric transmission layer, and the second shielding shell are fitted together, the protrusion passes through the single-dielectric transmission layer, and the recessed structure forms continuous air cavities on the upper and lower sides of the radio frequency signal transmission line, so that the radio frequency signal transmission line is in a self-encapsulated state.

[0015] Preferably, the single dielectric transmission layer has pre-formed hollow areas corresponding to the protrusions on both sides of the radio frequency signal transmission line. The hollow areas are fitted onto the protrusions to achieve the limiting and self-alignment of the single dielectric transmission layer with the first shielding shell or the second shielding shell.

[0016] Preferably, the physical dimensions of the de-resonance support structure are set according to the wavelength of the parasitic mode within the operating frequency band, in order to disrupt the boundary resonance conditions of the high-frequency parasitic mode within the cavity.

[0017] Preferably, the physical dimensions include the height and width of the solid portion, the distance between the solid portion and the edge of the radio frequency signal transmission line, and the distance between the solid portion and the sidewall of the shielding housing.

[0018] Furthermore, several metallized vias are provided at the transition area where the single-medium transmission layer connects to the external connector to enable mode switching at the interface and suppress energy leakage.

[0019] Preferably, the non-conductive materials used for the first and second shielding shells include 3D-printed photosensitive resin or thermoplastic polymer, and their metallization is performed using chemical plating or electroplating processes; the four edges of the single-medium transmission layer are clamped between the joint surfaces of the first and second shielding shells, and the three are detachably and securely connected.

[0020] Secondly, the present invention provides a low-loss microwave circuit based on 3D printing, comprising the low-loss microwave transmission structure based on 3D printing described in the first aspect.

[0021] In some embodiments, the single-layer dielectric transmission layer integrates at least one active or passive device required for the microwave circuit using a surface mount process; the inner surface of the first or second shielding shell is locally conformally designed according to the three-dimensional geometric dimensions of the integrated components, so that the inner wall of the shielding shell undulates with the shape of the components, thereby controlling the total volume of the microwave cavity while reserving space for physical placement and heat dissipation.

[0022] In some embodiments, the radio frequency signal transmission lines printed on the single dielectric transmission layer constitute a topology network of one or more microwave passive devices. The topology network includes one or more of a power divider, coupler, filter, duplexer / multiplexer, and phase shifter. The de-resonance support structure of the first shielding shell or the second shielding shell is correspondingly arranged along the trace branch path of the topology network to form a continuous air cavity that encloses the entire topology network.

[0023] In some embodiments, the microwave passive device is a Wilkinson power divider, and the single dielectric transmission layer is printed with an input terminal, at least two transmission line branches, an isolation resistor connected between the branches, and an output terminal; the de-resonance support structure is bifurcated along the direction of the transmission line branches.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0025] 1) Combining high process compatibility with lightweight structure. Unlike pure 3D printing solutions that require complex internal dielectric pillars for support, this invention uses a single dielectric transmission layer composed of printed circuit boards as the carrier of RF signal transmission lines. Mature printed circuit board technology ensures high precision in planar RF wiring. At the same time, the first and second shielding shells are 3D printed in one piece, eliminating the need for multi-layer pressing and metal CNC machining of traditional dielectric integrated suspension lines, significantly reducing manufacturing costs and system weight. The three components can be connected by edge mechanical assembly, resulting in a simple structure and quick assembly. This achieves an optimal distribution of process capability and structural weight, improving the mechanical robustness and space utilization of the device.

[0026] 2) Overcoming substrate loss limitations to achieve low-cost, low-loss transmission. In this invention, the inner surface of the first or second shielding shell is provided with a de-resonance support structure, which includes a recessed structure and a solid portion forming the recess. When the three-layer structure is bonded and assembled, the recessed structure forms continuous air cavities on the upper and lower sides of the RF signal transmission line, putting the transmission line in a self-encapsulated state. This structure effectively confines electromagnetic energy within the air cavity formed by the 3D-printed structure, reducing the proportion of electromagnetic field distribution in the solid medium. Thanks to this, even using a low-cost, conventional thin FR4 substrate as a single dielectric transmission layer, excellent low insertion loss performance can still be achieved in the millimeter-wave band.

[0027] 3) Refined de-resonance system to ensure broadband electromagnetic compatibility. Addressing the issue of high-frequency parasitic resonance easily caused by microwave cavity packaging, this invention uses a de-resonance support structure as a core design element. By adjusting the position and physical dimensions of the support structure, the resonance conditions of parasitic modes can be disrupted, ensuring transmission flatness and high isolation within the designed broadband range. Furthermore, the de-resonance support structure designed in this invention achieves precise self-positioning and stable support while realizing de-resonance, improving the mechanical stability of the device.

[0028] 4) It possesses high integration advantages and supports co-packaging of heterogeneous components. The microwave transmission line structure or microwave circuit provided by this invention fully utilizes the PCB processing characteristics of a single dielectric transmission layer, allowing for the direct integration of various active and passive components such as chips, capacitors, and resistors within the cavity. Simultaneously, combined with the conformal design advantages of 3D printed housings, it effectively breaks through the integration bottlenecks of traditional structures, providing a potentially applicable basic architecture solution for constructing highly integrated, self-encapsulated complex microwave and millimeter-wave subsystems (such as RF front-end modules). Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute a limitation on the embodiments of the invention. In the drawings:

[0030] Figure 1This is a cross-sectional schematic diagram of the low-loss microwave transmission structure based on 3D printing provided in Embodiment 1 of the present invention.

[0031] Figure 2 This is a three-dimensional exploded view of the low-loss microwave transmission line structure based on 3D printing provided in Embodiment 1 of the present invention.

[0032] Figure 3 This is a planar layout diagram of the low-loss microwave transmission structure based on 3D printing provided in Embodiment 1 of the present invention on a single-layer dielectric transmission layer.

[0033] Figure 4 This is a three-dimensional schematic diagram of the metallized via structure provided in Embodiment 1 of the present invention;

[0034] Figure 5 This is a schematic diagram showing the physical dimensions of the protruding portion in the 3D-printed low-loss microwave transmission structure provided in Embodiment 1 of the present invention, as well as the specific dimensions of the spatial distance between the protruding portion and the edge of the central transmission line and the side shielding wall.

[0035] Figure 6 The full-wave simulation S-parameter diagrams of the low-loss microwave transmission structure based on 3D printing provided in Embodiment 1 of the present invention with and without the resonant support structure are shown.

[0036] Figure 7 This is a three-dimensional exploded view of Comparative Example 1 of the present invention;

[0037] Figure 8 This is a three-dimensional exploded view of a design example of a low-loss microwave circuit based on 3D printing provided in Embodiment 2 of the present invention.

[0038] Figure 9 This is a planar layout diagram of the broadband Wilkinson power divider on a single-layer medium transmission layer in Embodiment 2 of the present invention;

[0039] Figure 10 The full-wave simulation S-parameter diagrams of the broadband Wilkinson power divider in Embodiment 2 of the present invention are shown with and without the resonant support structure.

[0040] Figure 11 This is a three-dimensional exploded view of Comparative Example 2 of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are for illustrative purposes only and are not intended to limit the invention.

[0042] This invention discloses a low-loss microwave transmission line structure based on 3D printing, comprising a single-dielectric transmission layer, a first shielding shell, and a second shielding shell. The single-dielectric transmission layer is composed of a printed circuit board with at least one radio frequency (RF) signal transmission line printed on its surface. The first and second shielding shells are used to encapsulate the suspended line circuit. Both are made of non-conductive materials through 3D printing, and their inner and outer surfaces are metallized to form an electromagnetic shielding layer. The single-dielectric transmission layer, as an independent physical layer, is fixed between the first and second shielding shells. The inner surface of the first or second shielding shell is provided with a de-resonance support structure along the routing direction of the RF signal transmission line. The de-resonance support structure includes a recessed structure and a solid portion forming the recessed structure. The solid portion serves as a protrusion for positioning and support during assembly. When the first shielding shell, the single-dielectric transmission layer, and the second shielding shell are fitted together, the protrusion passes through the single-dielectric transmission layer, and the recessed structure forms continuous air cavities on the upper and lower sides of the RF signal transmission line, so that the RF signal transmission line is in a self-encapsulated state.

[0043] The low-loss microwave transmission line structure based on 3D printing provided in this embodiment combines the advantages of high design freedom, low cost, and lightweight of 3D printed structures with the high precision and robustness of PCB printed circuits. It can achieve low-loss transmission of high-frequency microwave radio frequency signals, and at the same time, it can achieve high integration and self-encapsulation of electronic components by combining the common design advantages of 3D printed shells.

[0044] As an optional implementation, the single dielectric transmission layer has pre-formed hollow areas corresponding to the protrusions on both sides of the radio frequency signal transmission line. The hollow areas are fitted onto the protrusions to achieve precise positioning and self-alignment of the single dielectric transmission layer with the first shielding shell or the second shielding shell.

[0045] In practical applications, the physical dimensions of the de-resonance support structure are set according to the wavelength of the parasitic modes within the operating frequency band, in order to disrupt the boundary resonance conditions of the high-frequency parasitic modes within the cavity.

[0046] Preferably, the physical dimensions include the height and width of the solid portion, the spacing between the solid portion and the edge of the RF signal transmission line, and the spacing between the solid portion and the sidewall of the shielding housing, all set according to the wavelength of the parasitic modes within the operating frequency band. The physical spacing and support structure dimensions are adjusted based on simulation or measurement results of the specific design frequency band to disrupt the boundary resonance conditions of the high-frequency parasitic modes within the cavity without interfering with the electromagnetic field distribution of the main mode of the transmission line. Furthermore, to suppress electromagnetic energy leakage at the interface, several metallized vias are provided at the transition area where the single-dielectric transmission layer connects to the external connector.

[0047] Preferably, the non-conductive materials used for the first and second shielding shells include 3D-printed photosensitive resin or thermoplastic polymer; their metallization can be achieved using chemical plating or electroplating processes; the dielectric substrate of the single-dielectric transmission layer is preferably made of FR4 epoxy resin board or Rogers series high-frequency special board, etc., which are suitable for high-frequency microwave radio frequency scenarios. The four edges of the single-dielectric transmission layer are clamped between the joint surfaces of the first and second shielding shells, and the three are detachably and securely connected.

[0048] Based on the microwave transmission line structure described above, this embodiment of the invention further provides a low-loss microwave circuit based on 3D printing, wherein the microwave circuit includes the microwave transmission line structure.

[0049] Thanks to the mature printed circuit board technology employed in the single-layer dielectric transmission layer, its surface can be directly surface-mount (SMT) integrated into various components required for microwave circuits, including but not limited to passive components such as capacitors, inductors, and resistors, as well as active components such as RF chips, control circuits, and amplifiers. Correspondingly, the inner surface of the first or second shielding shell can be locally conformally designed according to the three-dimensional geometry of the integrated components. That is, leveraging the advantages of 3D printing, the inner wall of the shielding shell can conform to the shape of the components. This provides space for the physical placement and heat dissipation of the chip while strictly controlling the shape and volume of the microwave cavity, preventing the generation of electromagnetic parasitic resonances.

[0050] As some optional implementations, the radio frequency signal transmission lines printed on the single-dielectric transmission layer can constitute a topology network of one or more microwave passive devices. Exemplarily, the topology network includes, but is not limited to, power dividers, couplers, filters, duplexers / multiplexers, phase shifters, etc. In this case, the de-resonance support structure of the first or second shielding shell is correspondingly arranged along the trace branch path of the topology network, forming a continuous air cavity capable of enclosing the entire topology network, thereby constructing a high-performance microwave / millimeter-wave functional module with low loss and self-encapsulation characteristics.

[0051] Example 1

[0052] like Figures 1 to 3 As shown, this embodiment provides a low-loss microwave transmission line structure based on 3D printing. Figure 1 This is a cross-sectional schematic diagram of this embodiment. Figure 2 Here is a three-dimensional decomposition diagram. Figure 3This is a planar layout diagram of a single-layer dielectric transmission layer. As can be seen from the three-dimensional exploded schematic diagram, the circuit structure is mainly composed of three independent physical layers stacked and assembled sequentially from top to bottom: the first shielding shell 11 (upper cavity wall), the single-dielectric transmission layer 12 (middle circuit part), and the second shielding shell 13 (lower cavity wall).

[0053] In this embodiment, both the first shielding shell 11 and the second shielding shell 13 are made of non-conductive photosensitive resin or thermoplastic polymer and are integrally molded using 3D printing technology. In order to form effective electromagnetic shielding, the inner and outer surfaces of the first shielding shell 11 and the second shielding shell 13 are metallized (e.g., copper plating).

[0054] The single-dielectric transport layer 12 is sandwiched as an independent physical layer between the first shielding shell 11 and the second shielding shell 13. It is composed of an FR4 substrate 121 (relative permittivity ε). r = 4.4, loss tangent tanδ = 0.02) constitutes a structure with RF signal transmission lines 122 printed on the surface. Figure 1 In the diagram, h1 = 1mm, h2 = 0.74mm, h3 = 0.254mm, h4 = 0.5mm, and h5 = 1mm. Here, h1 represents the thickness of the solid outer shell at the top of the first shielding shell 11, which is primarily used to ensure the mechanical strength and electromagnetic shielding integrity of the upper shielding structure; h2 represents the height of the upper air cavity 15, i.e., the vertical distance from the inner top wall of the first shielding shell 11 to the upper surface of the single dielectric transmission layer 12; h3 represents the dielectric thickness of the single dielectric transmission layer 12, i.e., the substrate material of the printed circuit board itself; h4 represents the height of the lower air cavity 16, i.e., the vertical distance from the lower surface of the single dielectric transmission layer 12 to the inner bottom wall of the second shielding shell 13; and h5 represents the thickness of the solid outer shell at the bottom of the second shielding shell 13, primarily used to ensure the structural support and mechanical stability of the entire base.

[0055] In terms of structural design and assembly, this embodiment adopts a unique asymmetric shielding housing configuration: the first shielding housing 11 serves only as the upper electromagnetic encapsulation cover, and its interior does not contain any specific structure along the transmission line; the second shielding housing 13 has an internal design with a de-resonance support structure 131 along the direction of the central radio frequency signal transmission line. Optionally, the de-resonance support structure can also be placed inside the first shielding housing 11, and the second shielding housing 13 can serve only as the lower electromagnetic encapsulation cover.

[0056] Specifically, the de-resonance support structure 131 integrates mechanical positioning, cavity construction, and electromagnetic de-resonance function: In this embodiment, the structure is recessed below the radio frequency signal transmission line 122, forming the bottom air-dominant cavity; simultaneously, the solid portion extending upwards from the edge of the structure directly serves as a protrusion for assembly auxiliary positioning. During assembly, simply aligning the pre-cut hollow area 123 on the single dielectric transmission layer 12 precisely with and fitting it onto the upward protrusion of the de-resonance support structure 131 on the second shielding shell 13 achieves precise positioning and self-alignment between the single dielectric transmission layer 12 and the second shielding shell 13 in the horizontal plane. Subsequently, the first shielding shell 11 is closed, and the three components are secured together using edge mechanical assembly. Once the three components are fitted together, the upper and lower air-dominant cavities together enclose the central transmission line.

[0057] This assembly architecture not only eliminates the complex multi-layer lamination process in traditional integrated dielectric suspension lines (SISLs) and avoids expensive and cumbersome computer numerical control (CNC) metal machining, but also ensures high precision in the relative position between the core electromagnetic structure and the RF transmission line at the physical assembly level through the direct nesting of the dielectric layer and the de-resonance support structure, reducing random deviations caused by manual assembly.

[0058] In practical millimeter-wave engineering applications, highly packaged microwave cavities naturally act as resonators, easily introducing high-frequency parasitic resonances and disrupting transmission flatness. Therefore, this embodiment utilizes the aforementioned unique asymmetric assembly architecture to systematically construct a resonance suppression system, specifically including:

[0059] Interface transition zone mode conversion: Several through-holes 124 are provided in the transition zone where the single dielectric transport layer 12 connects to the external SMA connector 14, such as... Figure 4 As shown, it is used to implement mode switching at the interface and suppress energy leakage.

[0060] Internal resonance disruption within the cavity: Based on the completion of dielectric layer support and air cavity construction, the aforementioned core de-resonance support structure 131 optimizes and adjusts the physical dimensions of its protruding portion and the spatial spacing between it and the edge of the central transmission line and the side shielding walls according to the design frequency band. This disrupts the conditions for high-frequency parasitic resonance generation, suppresses unwanted high-order electromagnetic modes within the cavity, and thus ensures impedance matching and transmission flatness over a wide bandwidth. For example, Figure 5 Examples of the physical dimensions of the protruding portion and the specific dimensions of the spatial spacing between it and the edge of the central transmission line and the side shielding wall are given. The width of the protruding portion is 3.3 mm, the height is 1.1 mm, the horizontal spacing between the protruding portion and the edge of the central transmission line is 1.2 mm, and the horizontal spacing between the protruding portion and the side shielding wall is 3.6 mm.

[0061] Working principle and low-loss mechanism: During transmission, electromagnetic energy is effectively confined within an air-dominated cavity, significantly reducing the proportion of the electromagnetic field distributed in the solid lossy medium. Thanks to this, even using a low-cost, conventional high-loss FR4 substrate as the single-dielectric transmission layer, this structure still exhibits low insertion loss in the millimeter-wave band.

[0062] like Figure 6 As shown, to preliminarily verify the low-loss characteristics of the 3D printed structure described in this invention, a full-wave simulation evaluation was performed on a basic transmission line with a length of 60 mm (i.e., two center wavelengths at a center frequency of 10 GHz). Specifically, at a center frequency of 10 GHz, the insertion loss of the transmission line using an FR4 substrate was 0.24 dB. Furthermore, its return loss was better than 25 dB across the ultra-wide bandwidth of 0-20 GHz. This demonstrates the effective confinement of electromagnetic energy by the air-dominated cavity.

[0063] Comparative Example 1

[0064] To further highlight the crucial role of the de-resonance support structure in millimeter-wave broadband transmission, this embodiment includes a comparative example. This comparative structure also includes a first shielding shell 21, a single-dielectric transmission layer 22, and a second shielding shell 23. For example... Figure 7 As shown, the three-dimensional decomposition diagram of the comparative structure is... Figure 2 Compared with Embodiment 1, the materials, dimensions and assembly methods of the first shielding shell 11, the single dielectric transmission layer 12 and the second shielding shell 13 are completely the same. The only difference is that the de-resonance support structure 131 on the second shielding shell 13 is removed.

[0065] like Figure 6 The figure shows the full-wave simulation S-parameter results for the comparative structure (i.e., the case without the de-resonant support structure). Comparing the cases with and without the de-resonant support structure reveals that, in the absence of mode suppression by the de-resonant support structure, high-frequency parasitic modes are easily excited inside the microwave cavity. This parasitic effect leads to strong resonance spikes in the comparative structure within the band, a drastic deterioration in the transmission coefficient (S21), and a rebound in return loss (S11), disrupting the transmission flatness and impedance matching over a wide bandwidth. This comparative result demonstrates that the de-resonant support structure introduced in this invention plays a significant role in ensuring broadband electromagnetic compatibility and suppressing parasitic resonances.

[0066] Example 2

[0067] Building upon the basic transmission line architecture of Example 1, this example further utilizes the surface metallization 3D printing platform to design a highly integrated broadband Wilkinson power divider, serving as a specific design example of a high-performance, low-loss microwave and millimeter-wave RF circuit, thereby demonstrating the ability to integrate electronic components such as resistors and its self-packaging characteristics.

[0068] like Figure 8 and Figure 9 As shown, a low-loss microwave circuit based on 3D printing includes a first shielding shell 31, a single-dielectric transmission layer 32, and a second shielding shell 33. A low-loss broadband Wilkinson power divider is printed on the single-dielectric transmission layer 32, which is made of an FR4 (ε) plate. r = 4.4, tanδ = 0.02) constitutes this, at this time Figure 1 In the diagram, h1 = 1mm, h2 = 0.74mm, h3 = 0.254mm, h4 = 0.5mm, and h5 = 1mm. Its circuit topology includes an input terminal 321, two power distribution transmission line branches 322 for splitting the power, an isolation resistor 323 bridging the branches (used to absorb reflected energy and ensure isolation between output ports), two output terminals 324, a cutout area 325 similar to Example 1, and a metallized via 326.

[0069] Furthermore, in terms of assembly structure, the second shielding housing 33 is internally designed with a de-resonance support structure 331 that matches the shape of the branch transmission lines of the power divider, forming a continuous air cavity that completely encloses the entire power divider network. Thanks to the air-dominated cavity structure and de-resonance suppression system described in Embodiment 1, the electromagnetic signal, after passing through the input end, can have its energy smoothly distributed along the branch transmission lines printed on a single-layer medium in a low-loss air cavity environment.

[0070] like Figure 10 The figure shows the full-wave simulation S-parameter results of this broadband Wilkinson power divider. The results demonstrate that even with a low-cost FR4 substrate exhibiting inherently higher losses, this structure still demonstrates good RF performance: at a center frequency of 10 GHz, its transmission coefficient (S21) is only 3.19 dB. Simultaneously, the power divider exhibits excellent impedance matching characteristics over a wide frequency range, with return loss (S11) at the input ports less than -10 dB in the 2-20 GHz band (relative bandwidth up to 163.6%). Furthermore, in the 4.9-17.4 GHz band (relative bandwidth up to 112.1%), the isolation between the output ports (S23) remains consistently below -15 dB. This design provides a low-cost, low-loss, and lightweight high-performance feed network solution for millimeter-wave phased array antenna systems.

[0071] Comparative Example 2

[0072] To further verify the crucial role of the de-resonance support structure in complex microwave passive devices (such as power dividers), a comparative example is also provided in this embodiment. This comparative structure includes a first shielding shell 41, a single-dielectric transmission layer 42, and a second shielding shell 43. For example... Figure 11 As shown, the three-dimensional decomposition diagram of the comparative structure is... Figure 7 In comparison, the overall dielectric, shell size and topology routing are exactly the same, except that the de-resonance support structure 331 on the second shield shell 33 is removed.

[0073] like Figure 10 The figure shows the full-wave simulation S-parameters of the comparative structure (i.e., the case without the de-resonant support structure). Comparing the cases with and without the de-resonant support structure reveals that, in the absence of the de-resonant support structure, the complex internal cavity of the power divider easily excites high-frequency parasitic resonant modes. This parasitic effect not only disrupts the original odd-even mode impedance matching, leading to jitter and deterioration in transmission loss (S21) over the broadband range, but also causes multiple resonant spikes in return loss (S11); the coupling of cavity parasitic modes causes the isolation resistors between branches to fail, resulting in bounces in the isolation between output ports (S23) at multiple frequency points. This comparison demonstrates that when using 3D printing to construct RF devices with complex cavity packages, the de-resonant suppression system proposed in this invention plays a significant role in ensuring the operating bandwidth and electromagnetic performance of the device.

[0074] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It is understood that the descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-loss microwave transmission line structure based on 3D printing, characterized in that, include: A single-medium transmission layer is composed of a printed circuit board with at least one radio frequency signal transmission line printed on its surface. The first shielding shell and the second shielding shell are both made of non-conductive materials and are integrally formed by 3D printing. Both the inner and outer surfaces are metallized to form an electromagnetic shielding layer. The single-dielectric transmission layer is fixed between the first shielding shell and the second shielding shell as an independent physical layer; the inner surface of the first shielding shell or the second shielding shell is provided with a de-resonance support structure along the routing direction of the radio frequency signal transmission line, the de-resonance support structure includes a recessed structure and a solid part forming the recessed structure, the solid part serving as a protrusion for positioning and support during assembly; When the first shielding shell, the single dielectric transmission layer, and the second shielding shell are fitted together, the protrusion passes through the single dielectric transmission layer, and the recessed structure forms a continuous air cavity on the upper and lower sides of the radio frequency signal transmission line, so that the radio frequency signal transmission line is in a self-encapsulated state.

2. The low-loss microwave transmission line structure based on 3D printing according to claim 1, characterized in that, The single-dielectric transmission layer has pre-formed hollow areas corresponding to the protrusions on both sides of the radio frequency signal transmission line. The hollow areas are fitted onto the protrusions to achieve the limiting and self-alignment of the single-dielectric transmission layer with the first shielding shell or the second shielding shell.

3. The low-loss microwave transmission line structure based on 3D printing according to claim 1, characterized in that, The physical dimensions of the de-resonance support structure are set according to the wavelength of the parasitic modes within the operating frequency band, and are used to disrupt the boundary resonance conditions of the high-frequency parasitic modes within the cavity.

4. The low-loss microwave transmission line structure based on 3D printing according to claim 3, characterized in that, The physical dimensions include the height and width of the solid portion, the distance between the solid portion and the edge of the radio frequency signal transmission line, and the distance between the solid portion and the sidewall of the shielding housing.

5. The low-loss microwave transmission line structure based on 3D printing according to claim 1, characterized in that, Several metallized vias are provided at the transition area where the single-medium transmission layer connects to the external connector to enable mode switching at the interface and suppress energy leakage.

6. The low-loss microwave transmission line structure based on 3D printing according to claim 1, characterized in that, The first and second shielding shells are made of non-conductive materials including 3D-printed photosensitive resin or thermoplastic polymer, and their metallization is performed by chemical plating or electroplating processes; the four edges of the single-medium transmission layer are clamped between the joint surfaces of the first and second shielding shells, and the three are detachably and fastened together.

7. A low-loss microwave circuit based on 3D printing, characterized in that, It includes a 3D-printed low-loss microwave transmission structure according to any one of claims 1 to 6.

8. The low-loss microwave circuit based on 3D printing according to claim 7, characterized in that, The single-layer dielectric transmission layer integrates at least one active or passive device required for the microwave circuit using surface mount technology; the inner surface of the first or second shielding shell is locally conformally designed according to the three-dimensional geometric dimensions of the integrated components, so that the inner wall of the shielding shell undulates with the shape of the components, thereby controlling the total volume of the microwave cavity while reserving space for physical placement and heat dissipation.

9. The low-loss microwave circuit based on 3D printing according to claim 7, characterized in that, The radio frequency signal transmission lines printed on the single dielectric transmission layer constitute a topology network of one or more microwave passive devices. The topology network includes one or more of the following: power divider, coupler, filter, duplexer / multiplexer, and phase shifter. The de-resonance support structure of the first shielding shell or the second shielding shell is correspondingly arranged along the trace branch path of the topology network to form a continuous air cavity that encloses the entire topology network.

10. The low-loss microwave circuit based on 3D printing according to claim 9, characterized in that, The microwave passive device is a Wilkinson power divider. The single dielectric transmission layer has an input terminal, at least two transmission line branches, an isolation resistor connected between the branches, and an output terminal printed on it. The de-resonance support structure is bifurcated along the direction of the transmission line branches.

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