Side-fed coaxial-to-microstrip ultra-wideband impedance matching structure and microwave circuit

Abstract

The application provides a side-fed coaxial-to-microstrip ultra-wideband impedance matching structure and microwave circuit, and relates to the technical field of microwave and radio frequency communication. The structure comprises a structure carrier, a coaxial connector and a microstrip circuit. The coaxial connector is provided with an elastic probe, and the extending end of the elastic probe is provided with a flat contact end face. The end side of the microstrip substrate is provided with a downward extending cladding type microstrip matching plane, the elastic probe is in lateral elastic surface contact with the matching plane, and the orthographic projection contour of the two has a size difference to form an assembly tolerance area. The structure carrier is recessed with an impedance matching cavity directly below the substrate. The application converts two-dimensional rigid welding into three-dimensional elastic surface contact, completely eliminates the hidden danger of thermal mechanical stress, significantly reduces the eccentricity sensitivity of high frequency device assembly by using the size difference, and realizes extremely low standing wave ratio and excellent impedance continuity in the super wide band of DC to 110GHz by relying on the double variable collaborative de-embedding mechanism of the impedance matching cavity and the matching plane.

Description

Technical Field

[0001] This invention relates to the field of microwave and radio frequency communication technology, and more specifically, to a side-fed coaxial-to-microstrip ultrawideband impedance matching structure and microwave circuit. Background Technology

[0002] With the rapid development of modern wireless communication, aerospace electronics, radar systems, and ultra-high frequency test and measurement instruments, the operating frequency bands of microwave RF systems are constantly extending into millimeter-wave and even submillimeter-wave bands, and the demand for system bandwidth is also increasing. In these high-frequency electronic systems, coaxial lines and microstrip lines are two of the most basic and widely used transmission line types. Coaxial lines have excellent electromagnetic shielding performance and primarily support transverse electromagnetic wave (TEM mode) transmission, often used for signal input / output between modules; while microstrip lines are easily integrated with various active or passive surface-mount devices, primarily supporting quasi-transverse electromagnetic wave (quasi-TEM mode) transmission, and are often used for signal routing within circuit boards. Therefore, in almost all microwave RF systems, it is inevitable to use a "coaxial-to-microstrip" conversion structure to interconnect signals between different transmission media.

[0003] In current engineering practice, the most common coaxial-to-microstrip connection method in existing technology is "parallel press-fit welding connection". Specifically, this traditional structure usually fixes the coaxial connector horizontally to the side of the metal housing, so that its center probe extends directly out and overlaps the microstrip signal line on the top surface of the microstrip circuit board. Finally, solder is applied to the contact point between the center probe and the microstrip line by manual means or equipment to achieve electrical connection.

[0004] However, as the system's operating frequency continues to increase, the aforementioned traditional welded transition structure has gradually revealed the following serious inherent limitations and technical defects: In terms of electrical performance, traditional structures face severe impedance mismatch and signal reflection problems at extremely high frequencies. Due to the fundamental differences in electromagnetic field distribution characteristics between the TEM mode of a coaxial line and the quasi-TEM mode of a microstrip line, the signal inevitably undergoes drastic reconstruction of the electromagnetic field boundary conditions at the conversion interface. In traditional soldering structures, due to abrupt changes in the geometry of the center probe, uncontrollable three-dimensional morphology of the solder paste, and the introduction of steps in the structural carrier, significant parasitic parallel capacitance and series inductance inevitably form at the connection point between the probe and the microstrip line. This drastic change in physical structure leads to severe discontinuities in the local impedance of the transition region. Under ultra-high frequency and ultra-wideband (e.g., 110 GHz) conditions, this impedance mismatch is amplified dramatically, triggering strong electromagnetic wave reflections, causing a sharp deterioration in the port voltage standing wave ratio (VSWR) and a sharp increase in insertion loss, thus severely limiting the operating bandwidth and signal transmission quality of high-frequency microwave circuits.

[0005] In terms of mechanical reliability and environmental adaptability, traditional solder joints are highly susceptible to fatigue failure. In real-world applications, equipment often experiences drastic temperature fluctuations. Due to the significant differences in the coefficients of thermal expansion between the metal materials, solder materials, and microstrip substrate materials of the coaxial connector, temperature cycling generates continuous thermal stress at the solder joint. Furthermore, when used as a test fixture or pluggable module, frequent plugging and unplugging of external coaxial cables and mechanical vibrations generate mechanical stress transmitted along the coaxial probe axis. Traditional point-contact rigid solder joints cannot effectively release these stresses, making them prone to micro-cracks, metal fatigue, and even contact fracture under long-term service, leading to complete system failure.

[0006] In terms of assembly processes and manufacturing yield, traditional structures are extremely sensitive to eccentricity tolerance. In the millimeter-wave band, the wavelength is extremely short, and any tiny mechanical assembly deviation can significantly degrade RF performance. Traditional probes are directly attached to extremely narrow microstrip lines, requiring extremely high center alignment accuracy during assembly. Even a tiny radial eccentricity can easily lead to poor contact or drastic impedance deviation, posing a severe challenge to the assembly yield of large-scale industrial production.

[0007] In summary, the industry urgently needs a new transition circuit structure that can achieve a smooth transition and low-loss impedance matching from coaxial TEM mode to microstrip quasi-TEM mode in ultra-high frequency and ultra-wide bandwidth, while eliminating traditional welding stress from the physical structure and providing a high-tolerance and high-reliability mechanical connection. Summary of the Invention

[0008] The present invention aims to solve at least one of the aforementioned technical problems existing in the prior art.

[0009] To this end, the first aspect of the present invention provides a side-fed coaxial microstrip ultrawideband impedance matching structure.

[0010] A second aspect of the present invention provides a microwave circuit.

[0011] This invention provides a side-fed coaxial-to-microstrip ultrawideband impedance matching structure, comprising: Structural carrier; A coaxial connector is horizontally disposed on the side wall of the structural carrier, and an elastic probe is coaxially disposed inside the coaxial connector, with one end of the elastic probe extending out in the horizontal direction; A microstrip circuit is disposed on the structural carrier and opposite to the coaxial connector. The microstrip circuit includes a microstrip substrate and a microstrip signal line disposed on the top surface of the microstrip substrate. Wherein, the end of the microstrip signal line extends toward the end side of the microstrip substrate toward the coaxial connector, forming an overlay microstrip mating plane that covers the end side downward; the protruding end of the elastic probe of the coaxial connector elastically abuts against the overlay microstrip mating plane to form a surface contact; The structural carrier is located below the microstrip substrate, and an impedance matching cavity is recessed downward from the upper surface of the structural carrier. The impedance matching cavity extends from the abutment transition area between the overlay microstrip matching plane and the coaxial connector to the inner side of the bottom surface of the microstrip substrate, and the top opening of the impedance matching cavity is covered by the bottom surface of the microstrip substrate.

[0012] The side-fed coaxial-to-microstrip ultrawideband impedance matching structure according to the above-described technical solution of the present invention may also have the following additional technical features: In the above technical solution, the encapsulated microstrip matching plane is a cross-sectional semi-hole metal layer structure; the cross-sectional semi-hole metal layer structure is formed by processing metallized through holes on the microstrip substrate and laser cutting along the central axis of the metallized through holes, thereby making the microstrip signal line smoothly transition to the end side of the microstrip substrate.

[0013] In the above technical solution, the protruding end of the elastic probe has a flat contact end face; The orthographic projection profiles of the contact end face and the matching plane of the overlay microstrip have a dimensional difference in at least one radial direction, such that the orthographic projection profile of at least one has an extension margin that exceeds that of the other, thereby forming an assembly tolerance area around the abutment. When a radial assembly offset occurs between the elastic probe and the microstrip circuit, the assembly tolerance region is used to compensate for the offset, so that the actual surface contact state between the two remains unchanged.

[0014] In the above technical solution, the impedance matching cavity is a milled groove or blind hole structure opened on the structural carrier; The edge of the impedance matching cavity near the coaxial connector is aligned with the vertical reference plane where the end side of the microstrip substrate is located.

[0015] In the above technical solution, the microstrip circuit further includes a ground metal layer disposed on the bottom surface of the microstrip substrate; In the region above the impedance matching cavity, the ground metal layer on the bottom surface of the microstrip substrate is partially or completely removed, so that the air medium in the impedance matching cavity directly contacts the insulating medium bottom surface of the microstrip substrate, thereby reducing parasitic capacitance by adjusting the local equivalent dielectric constant.

[0016] In the above technical solution, the size and depth of the impedance matching cavity and the aspect ratio of the encapsulated microstrip matching plane form a dual-variable impedance matching synergistic adjustment structure. The numerical configuration of the impedance matching cavity's dimensions, depth, and aspect ratio is used to collaboratively compensate for the impedance mismatch generated in the contact transition region during the conversion of the electromagnetic wave from a coaxial TEM mode to a microstrip quasi-TEM mode.

[0017] In the above technical solution, the elastic probe includes a probe housing and a compression spring built into the probe housing; The protruding end is slidably disposed along the axial direction of the probe housing and is elastically protruded outward by the deformation restoring force of the compression spring, so as to dynamically maintain the adhesion force with the mating plane of the encapsulated microstrip when the temperature changes or mechanical vibration occurs. In the above technical solution, the structural carrier includes a substrate support platform for horizontally supporting the microstrip circuit, and a vertical side plate for mounting the coaxial connector. A non-contact anti-collision gap is left between the end face of the microstrip substrate and the vertical side plate. The elastic probe passes through the vertical side plate in the horizontal direction, crosses the anti-collision gap, and then makes suspended contact with the matching plane of the encapsulated microstrip.

[0018] The present invention provides a microwave circuit comprising a side-fed coaxial-to-microstrip ultrawideband impedance matching structure as described in any of the above technical solutions.

[0019] In the above technical solution, the microwave circuit is a radio frequency transceiver module or an ultra-high frequency test fixture. The coaxial connector is configured to receive or output ultra-wideband microwave signals with a frequency range covering DC to 110 GHz. Through the cooperative impedance compensation mechanism of the enclosed microstrip matching plane and the impedance matching cavity, the microwave signal is transmitted to the microstrip circuit, and the port standing wave ratio in the working frequency band is less than a preset threshold.

[0020] In summary, due to the adoption of the above-mentioned technical features, the beneficial effects of the present invention are: This invention overcomes the technical bottleneck of traditional structures that struggle to simultaneously compensate for parasitic capacitance and inductance. By precisely introducing an "impedance matching cavity" beneath the microstrip substrate in the transition region between the coaxial and microstrip interfaces, the local ceramic dielectric in the high-frequency electric field distribution area is replaced with air, significantly reducing the local distributed capacitance at the transition interface. Simultaneously, combined with the optimized aspect ratio of the "encased microstrip matching plane," a three-dimensionally tunable bivariate compensation model is formed. This electromagnetic field "de-embedding compensation" mechanism perfectly smooths the boundary abrupt change when the electromagnetic wave converts from the coaxial TEM mode to the microstrip quasi-TEM mode, achieving ultra-low insertion loss and excellent impedance matching across an extremely wide frequency band from DC to 110 GHz, with the port voltage standing wave ratio stably controlled below 1.25 across the entire frequency band.

[0021] To address the inherent fatigue fracture problem of traditional probe-top surface spot welding structures, this invention creatively transforms the two-dimensional "point / line" welding contact into a three-dimensional sidewall elastic surface contact. Utilizing an elastic probe with a built-in spring, it directly presses against the metallized semi-hole profile on the sidewall of the microstrip substrate. This not only completely eliminates welding thermal stress caused by differences in thermal expansion coefficients between different materials (copper alloy, solder, ceramic substrate), but also effectively absorbs mechanical vibrations from high-frequency testing or frequent insertion / removal through the dynamic expansion and contraction of the spring. This structure significantly improves the fatigue strength, mechanical stability, and insertion / removal lifespan of the microwave connection port.

[0022] This invention ingeniously utilizes the dimensional difference between the probe contact surface and the matching plane of the encapsulated microstrip in the orthographic projection profile, ensuring that at least one side has an extension margin exceeding the other, thereby creating a tolerance region at the physical intersection. This structure breaks the traditional limitation that the probe must be perfectly centered and aligned with the ultra-narrow microstrip line; in actual industrial assembly, when radial misalignment occurs between the elastic probe and the microstrip circuit, this extension margin can perfectly absorb assembly tolerances, ensuring that the actual effective surface contact state for electromagnetic wave transmission remains unchanged. This structural design, which is insensitive to concentricity errors, greatly reduces the precision assembly difficulty of ultra-high frequency microwave modules and plays a decisive role in improving mass production yield.

[0023] The overlay microstrip matching plane of this invention is formed in one step through a combination of through-hole metallization and laser profile cutting, creating a cross-sectional semi-hole structure. This avoids the inefficiency and precision errors of traditional sidewall etching processes, ensuring a smooth transition of the microscopic plane and RF consistency in batch processing. Simultaneously, the non-contact anti-collision gap reserved between the structural carrier side plate and the microstrip substrate end face effectively prevents edge chipping and breakage of the rigid substrate during assembly and extrusion, further improving the product's process reliability.

[0024] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention. Attached Figure Description

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a cross-sectional schematic diagram of a traditional probe-welded coaxial microstrip connection structure in the prior art. Figure 2 for Figure 1 The diagram shows a partially enlarged schematic of a traditional probe-welded coaxial microstrip connection structure. Figure 3 This is a schematic cross-sectional view of the side-fed coaxial microstrip ultrawideband impedance matching structure provided in an embodiment of the present invention. Figure 4 for Figure 3 A partially enlarged schematic diagram of the side-fed coaxial microstrip ultrawideband impedance matching structure shown. Figure 5 A simulation diagram of the vector electric field distribution at the transition interface of the impedance matching structure provided in an embodiment of the present invention; Figure 6 Simulation curves of port voltage standing wave ratio (VSWR) of the impedance matching structure provided in the embodiments of the present invention in the DC to 110 GHz frequency band; Figure 7 A three-dimensional perspective view of the core area of ​​the connector impedance matching structure provided in an embodiment of the present invention.

[0026] in, Figures 1 to 7 The correspondence between the reference numerals and component names in the attached drawings is as follows: 10. Structural carrier; 11. Impedance matching cavity; 12. Air cavity; 13. Vertical side plate; 14. Substrate support platform; 20. Coaxial connector; 21. Elastic probe; 22. Spring; 23. Contact end face; 24. Coaxial outer conductor; 25. Coaxial center needle.

[0027] 30. Microstrip circuits; 31. Microstrip substrate; 32. Microstrip signal line; 33. Encased microstrip matching plane; 34. Grounding metal layer. Detailed Implementation

[0028] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0030] The following reference Figures 1 to 7 This describes a side-fed coaxial-to-microstrip ultrawideband impedance matching structure and microwave circuit provided according to some embodiments of the present invention.

[0031] Some embodiments of this application provide a side-fed coaxial to microstrip ultrawideband impedance matching structure.

[0032] Before detailing the innovative structure of this invention, let's first consider the current... Figure 1 and Figure 2 This paper provides a brief description of the traditional probe-welded coaxial microstrip connection structure in the prior art.

[0033] like Figure 1 and Figure 2 As shown, in a conventional connection structure, the structural carrier 10 carries the microstrip circuit 30 and the horizontally mounted coaxial connector 20, and an air cavity 12 is provided above the microstrip substrate 31. The rigid center pin of the coaxial connector 20 (i.e., the coaxial center pin 25 in the figure) extends out and directly overlaps the microstrip signal line 32 on the top surface of the microstrip substrate 31, and electrical connection is achieved by top manual spot soldering or solder paste reflow soldering.

[0034] This traditional structure has significant technical drawbacks in the high-frequency microwave band: First, the abrupt physical step change formed by the rigid center pin directly overlapping the top surface of the substrate introduces a large amount of parasitic parallel capacitance and series inductance at the contact point, resulting in severe high-frequency impedance mismatch and strong signal reflection; Second, since the thermal expansion coefficients of the structural carrier 10, coaxial center pin 25, solder, and ceramic microstrip substrate 31 are very different, the thermomechanical stress generated when the ambient temperature changes will be concentrated on the fragile rigid solder joint, which is very easy to cause fatigue cracking of the solder joint or breakage of the center pin; Finally, the traditional top overlap is a "point / line" contact, which requires extremely high axial and radial concentricity during assembly, and even the slightest assembly misalignment will lead to deterioration of the RF link.

[0035] In order to overcome the inherent limitations of the prior art, the present invention provides a novel side-fed coaxial microstrip ultrawideband impedance matching structure.

[0036] Please refer to the following: Figure 3 , Figure 4 as well as Figure 7 The diagrams show a cross-sectional view, a partially enlarged view, and a three-dimensional perspective view of the core area of ​​the impedance matching structure provided in the embodiments of the present invention.

[0037] This invention provides a side-fed coaxial-to-microstrip ultrawideband impedance matching structure, which mainly includes a structural carrier 10, a coaxial connector 20, and a microstrip circuit 30.

[0038] Specifically, the coaxial connector 20 is horizontally disposed on the side wall of the structural carrier 10 (e.g., Figure 4 The vertical side plate 13 shown is provided. An elastic probe 21 is coaxially disposed inside the coaxial connector 20, and one end of the elastic probe 21 extends horizontally from the coaxial outer conductor 24 into the interior of the structural carrier 10.

[0039] The microstrip circuit 30 is horizontally disposed on the structural carrier 10 (e.g., flat against the substrate support 14) and is disposed opposite to the coaxial connector 20. The microstrip circuit 30 includes an insulated microstrip substrate 31 and microstrip signal lines 32 laid on the top surface of the microstrip substrate 31. Figure 4 (Middle red line).

[0040] In the core architecture of this invention, the end of the microstrip signal line 32 does not remain only on the top surface of the substrate as in conventional structures, but extends further towards the side of the microstrip substrate 31 facing the coaxial connector 20, thereby forming a wrap-around microstrip mating plane 33 that covers the side of the substrate downwards. Simultaneously, the horizontally extending end of the elastic probe 21 of the coaxial connector 20 elastically abuts against this wrap-around microstrip mating plane 33, thus directly transforming the traditional two-dimensional top point / line overlap into a three-dimensional horizontal lateral surface contact.

[0041] Furthermore, to compensate for the abrupt change in electromagnetic field boundary at the aforementioned transition interface, an impedance matching cavity 11 is recessed downwards from the upper surface of the structural carrier 10, located below the microstrip substrate 31. In terms of spatial geometry, the impedance matching cavity 11 extends horizontally towards the inner side of the bottom surface of the microstrip substrate 31, starting from the abutment transition area between the encapsulated microstrip matching plane 33 and the coaxial connector 20. In terms of assembly, the top of the impedance matching cavity 11 is open, and when the microstrip substrate 31 is mounted flat on the structural carrier 10, it is completely covered by the bottom surface of the microstrip substrate 31, thereby forming a closed low-dielectric-constant air region directly below the microstrip signal line 32.

[0042] Through the above structural arrangement, the present invention utilizes the surface contact between the elastic probe 21 and the lateral encapsulated microstrip matching plane 33 to effectively release axial thermomechanical stress and provide excellent electrical contact rigidity. Simultaneously, the impedance matching cavity 11 extending inward from the bottom introduces air dielectric to reduce the local distributed capacitance in the interface transition region, perfectly offsetting the parasitic capacitance abrupt change at the structural junction, thereby achieving excellent impedance continuity over an ultra-wideband frequency range. In some embodiments, this structure can easily support millimeter-wave ultra-wideband low-loss transmission up to 110 GHz.

[0043] In some embodiments, please refer to Figure 4 and Figure 7 The encapsulated microstrip matching plane 33 can be constructed as a planar rectangular conductive layer vertically laid along the end side of the microstrip substrate 31, which has a regular rectangular orthographic projection outline to provide a basic lateral overlap plane.

[0044] In some other preferred embodiments, the encapsulated microstrip matching plane 33 is constructed as a special cross-sectional semi-perforated metal layer structure. From a microscopic geometric perspective, this cross-sectional semi-perforated metal layer structure extends vertically downward from the end of the microstrip signal line 32 along the end side of the microstrip substrate 31, appearing as a columnar conductive groove extending vertically on the sidewall of the substrate.

[0045] It should be understood that the cross-sectional profile of the columnar conductive groove is not limited to a semi-circle; in some specific embodiments, based on different substrate grooving processes (e.g., mechanical drilling, laser micro / nano etching, or green ceramic tape stamping), the cross-section of the columnar conductive groove can also be constructed as a rectangle, U-shape, V-shape, or other polygonal profile (e.g., in...). Figure 4 In the axial sectional view shown, the cross-sectional projection left on the two-dimensional cut plane appears as a regular rectangular outline.

[0046] In one specific embodiment, taking a semi-circular cross-section semi-hole metal layer structure as an example, it is integrally formed using a precision machining process of "through-hole metallization combined with laser profile cutting". In the specific manufacturing process: First, on the copper-clad microstrip substrate 31, a through-hole is machined at the predetermined module outline boundary; then, the hole wall of the micro-hole is metallized, depositing a dense and uniform conductive metal layer on the inner surface of the hole wall; finally, using high-precision laser cutting equipment, the outline is precisely cut along the vertical central axis of the metallized through-hole, dividing the metallized through-hole in two. After cutting, a half-circular hole metal wall remains in situ on the remaining end face of the microstrip substrate 31, thus precisely shaping it into the aforementioned semi-circular metal layer structure.

[0047] This columnar groove structure breaks the rigid physical boundary created by traditional right-angle bending of copper foil. The continuous geometric profile of the groove's inner wall allows the high-frequency current transmitted from the horizontal microstrip signal line 32 to transition with an extremely smooth curvature to the vertical end face. At ultra-high frequencies up to 110 GHz, this structure effectively suppresses excessive accumulation of high-frequency surface waves at structural corners and tip radiation loss, avoiding impedance mismatch caused by sudden changes in local electric field. This provides exceptionally superior RF consistency for the mass production of ultra-wideband microwave circuits.

[0048] In some embodiments, please refer to Figure 4 and Figure 7 To address the industry challenge of extreme sensitivity to eccentricity tolerance during the assembly of ultra-high frequency microwave modules, this invention employs a special optimized design in the topological geometry of the contact surface. Specifically, the protruding end of the elastic probe 21 does not adopt the traditional pointed cone or arc shape, but instead has a contact end surface 23 that has been ground or machined into a flat shape.

[0049] More importantly, the orthographic projection profile of the contact end face 23 and the orthographic projection profile of the covering microstrip matching plane 33 are intentionally designed to have a dimensional difference in at least one radial direction. This dimensional difference ensures that the contact intersection is not a perfect 1:1 overlap, but rather that at least one of the orthographic projection profiles has an extension margin exceeding that of the other. For example, in... Figure 4 In the partially enlarged embodiment shown, the cylindrical diameter of the elastic probe 21 is significantly larger than the thickness of the microstrip substrate 31 and the width of its covering metal layer. In this case, the larger contact end face 23 of the probe extends beyond the smaller covering microstrip matching plane 33. The extra physical space around the contact point naturally forms a sufficient assembly tolerance area.

[0050] Due to the existence of this assembly tolerance region, when assembling high-frequency devices on an industrial production line, even if an unavoidable radial assembly offset (i.e., assembly eccentricity) occurs between the central axis of the elastic probe 21 and the microstrip circuit 30, the assembly tolerance region can completely absorb and compensate for the offset as long as the contour of the smaller area (e.g., the side surface of the substrate) does not slip out of the boundary of the larger area (e.g., the probe end face). This means that the actual effective surface contact state and conductive area of ​​the two can always remain unchanged. This alignment-dependent design, which allows for movement in a relatively intermediate position, greatly reduces the assembly accuracy threshold and significantly improves the yield of finished products in mass production.

[0051] In one specific embodiment, please continue to refer to the key text. Figure 4 The cross-sectional structure and Figure 7The present invention provides a three-dimensional perspective structure, which precisely defines the spatial shaping and geometric position of the impedance matching cavity 11 used for electromagnetic tuning.

[0052] In terms of processing and forming, the impedance matching cavity 11 is preferably a milled groove or blind hole structure opened on the structural carrier 10 (such as a base). Since it is a downwardly recessed blind hole or groove, it not only preserves the high-frequency electromagnetic shielding integrity of the sidewalls and bottom metal of the structural carrier 10 and prevents energy radiation leakage, but also allows for extremely precise control of the cutting depth through high-precision CNC milling, thereby accurately quantifying the volume of the air medium in the cavity.

[0053] In terms of spatial geometric alignment, the edge of the impedance matching cavity 11 near the coaxial connector 20 (i.e. Figure 4 and Figure 7 The rightmost edge of the cavity is aligned with the end face of the coaxial outer conductor 24 of the coaxial connector 20, thereby forming the closure of the impedance matching cavity 11 by means of the end face of the coaxial outer conductor 24.

[0054] In some embodiments, please refer to Figure 3 and Figure 4 The microstrip circuit 30 is typically a microstrip line structure or a grounded coplanar waveguide (GCPW) structure, which includes not only the microstrip signal line 32 laid on the top surface of the microstrip substrate 31, but also a grounded metal layer 34 laid on the bottom surface of the microstrip substrate 31. To effectively couple the high-frequency electromagnetic field of the microstrip signal line 32 into the space below, and to avoid a complete electromagnetic shielding effect from the bottom metal layer, this invention employs a specific windowing and de-embedding design for the grounded metal layer 34 at the bottom of the microstrip substrate 31.

[0055] In one specific embodiment, the grounding metal layer 34 is partially removed (or has an opening) in the region directly above the impedance matching cavity 11, allowing the air dielectric within the impedance matching cavity 11 to be directly exposed below the electromagnetic transmission path. This partial removal of the bottom copper opens a physical channel for the downward propagation of the electromagnetic field. When the high-frequency microwave signal passes through the transition region, its downward electromagnetic field can penetrate the unshielded ceramic insulation region, directly enter the impedance matching cavity 11, and ultimately couple and terminate on the cavity bottom metal surface of the structural carrier 10. Since the dielectric constant of air is much lower than that of the ceramic substrate, the direct participation of this air dielectric significantly reduces the overall equivalent dielectric constant of the interface transition region, providing a real physical channel for the adjustment of the distributed capacitance of the high-frequency signal.

[0056] In some embodiments, please refer to Figure 5 Simulation diagram of vector electric field distribution and Figure 6The port voltage standing wave ratio (VSWR) simulation curve is shown in the figure. Based on the above physical structure, this invention constructs a precise three-dimensional bivariate cooperative electromagnetic matching mechanism.

[0057] from Figure 5 As can be seen from the microscopic electromagnetic field vector cross-section, when a high-frequency microwave signal is transmitted from the coaxial connector 20 to the microstrip circuit 30, the electromagnetic wave mode needs to undergo spatial reconstruction from the standard transverse electromagnetic wave (TEM mode) inside the coaxial line to the quasi-transverse electromagnetic wave (quasi-TEM mode) on the microstrip line. In the traditional rigid overlap structure, due to the presence of physical right-angle steps, the electric field lines are prone to severe distortion, edge radiation, and energy accumulation at the corner intersection. However, in the configuration of this invention, thanks to the precise de-embedding of the impedance matching cavity 11 below the microstrip substrate 31, the dielectric directly below the transition interface is partially replaced by air with a low dielectric constant from the high dielectric constant solid ceramic. This dielectric space replacement effectively disperses the dense electric field lines drilling downwards and significantly weakens the parasitic parallel capacitance at the interface. At the same time, the lateral enveloping microstrip matching plane 33 provides a continuous and smooth three-dimensional guiding surface for the crossing of high-frequency surface currents, effectively compensating for the parasitic series inductance excited by the bending of the spatial path. Figure 5 The smooth, convergent electric field vector distribution traces without obvious local energy divergence directly and fully demonstrate that the structural design of this invention successfully smooths out the spatial abrupt changes in the electromagnetic field boundary.

[0058] Figure 6 The graph shows the simulation results of the port voltage standing wave ratio (VSWR) of the impedance matching structure provided in this embodiment of the invention over an ultra-wide bandwidth. This graph is obtained based on the ANSYS high-frequency three-dimensional electromagnetic field simulation tool.

[0059] like Figure 6 As shown, the horizontal axis of the graph represents the frequency (Freq) of the high-frequency microwave signal, in GHz, with a scale range covering 0.00 GHz to 120.00 GHz; the vertical axis represents the absolute value of the voltage standing wave ratio (Y1). To ensure mesh generation and solution accuracy over an extremely wide frequency band, this simulation employs a segmented frequency sweep solution strategy (i.e., Setup1, Setup2, and Setup3 in the figure, corresponding to the red, dark blue, and light blue curve segments smoothly spliced ​​together in different frequency bands, respectively).

[0060] from Figure 6 The curve trend can be objectively observed: after excluding the initial fluctuations at the extremely low frequency (near DC) end, the VSWR curve exhibits extremely excellent flatness throughout the entire ultra-wide operating frequency band up to about 110 GHz, closely approaching the ideal value of 1.00 for absolute matching, without any towering peaks caused by parasitic resonance.

[0061] Further observation of the data markers in the graph reveals that the structure exhibits extremely high impedance stability across the entire test frequency band. Two relatively distinct peak locations are highlighted in the graph: the first marker is located at a frequency of 40.63 GHz, with a corresponding VSWR value of only 1.22; the second marker is located at a frequency of 72.54 GHz, with its corresponding VSWR value also well suppressed to 1.22. At the high-frequency end of 110 GHz, the curve even converges further and falls below the aforementioned peaks.

[0062] The simulation data above conclusively demonstrates that, thanks to the unique three-dimensional elastic surface contact mechanism, semi-hole transition structure, and impedance matching cavity de-embedding compensation of this invention, the transition interface successfully eliminates the parasitic capacitance and inductance mismatch caused by abrupt changes in the physical step. Within an extremely wide frequency band of 0 to 110 GHz, its maximum peak standing wave ratio is only 1.22 (far lower than the preset threshold of 1.25 required by conventional engineering), achieving near-lossless, extremely low-reflection ultra-wideband microwave signal interconnection and transmission.

[0063] In one specific embodiment, the dimensional parameters of the impedance matching cavity 11 (including its downward recess depth and horizontal span extending inwards towards the substrate, i.e., determining the air volume involved in adjusting the equivalent dielectric constant) serve as the first tuning variable; simultaneously, the geometric dimensions of the encapsulated microstrip matching plane 33 (including its length and width extending vertically along its end face, i.e. determining the lateral contact area and distributed inductance) serve as the second tuning variable. In actual high-frequency module design, these two tuning variables are jointly optimized and coordinated based on high-frequency three-dimensional electromagnetic field simulation of the target operating frequency band.

[0064] Through this bivariate synergistic regulation, when the high-frequency electric field distribution passes through the complex three-dimensional bending of the "probe-sidewall-microstrip line," the anomalous parasitic parallel capacitance introduced by the abrupt change at the coaxial probe end face is precisely canceled by the low dielectric constant air introduced by the impedance matching cavity 11; while the parasitic series inductance introduced by the abrupt change in structural steps is smoothed by the surface high-frequency current return path optimized by the encapsulated microstrip matching plane 33. Thus, the impedance matching structure of this invention perfectly smooths the boundary reconstruction process when the electromagnetic wave is converted from a coaxial transverse electromagnetic wave (TEM mode) to a microstrip quasi-transverse electromagnetic wave (quasi-TEM mode). Figure 6 The simulation results show that the bivariate cooperative matching mechanism successfully achieves excellent impedance continuity and ultra-low insertion loss in an extremely wide bandwidth from DC to 110 GHz. The port voltage standing wave ratio (VSWR) in the operating frequency band can be stably controlled within 1.25, which excellently meets the stringent requirements of current millimeter wave and submillimeter wave systems for ultra-wideband RF interconnects.

[0065] In some embodiments, see Figure 4In order to completely solve the problem of thermomechanical stress failure of traditional rigid welded structures under complex environmental conditions, the present invention constructs a special elastic dynamic compensation mechanism inside the coaxial connector 20.

[0066] In one specific embodiment, the elastic probe 21 structurally includes a fixed probe housing and a compression spring 22 built into the cavity of the probe housing. The probe housing is placed inside the coaxial outer conductor 24, and the protruding end of the elastic probe 21 (i.e., the portion with the flat contact end face 23) is slidably disposed along the axial direction of the probe housing. When actually assembled and in working condition, this protruding end is driven by the deformation restoring force of the compression spring 22, and always maintains an elastic upward pressing tendency (i.e., towards the side of the microstrip substrate).

[0067] When the microwave RF module experiences drastic temperature fluctuations, components made of different materials (such as copper alloy probes and alumina ceramic microstrip substrates 31) will inevitably undergo microscopic expansion and contraction along the axial direction due to the significant difference in their coefficients of thermal expansion (CTE). Alternatively, when the module is used as a test fixture and frequently plugs and unplugs external coaxial cables, mechanical stress and high-frequency vibrations will be generated and transmitted along the probe axis. In these situations, the compression spring 22 can perfectly absorb and buffer these microscopic displacements and mechanical vibrations through its own dynamic expansion and contraction, thereby dynamically maintaining a stable contact force between the contact end face 23 and the encapsulated microstrip matching plane 33. This purely mechanical elastic pressure surface contact fundamentally eliminates the physical hazards of stress tearing and fatigue fracture in traditional solder joints, significantly improving the mechanical stability and long-term service life of the ultra-high frequency microwave port.

[0068] In some embodiments, the present invention also cleverly incorporates a stress-free anti-collision design into the spatial assembly layout of the structural carrier 10.

[0069] In one specific embodiment, the structural carrier 10 mainly includes a substrate support 14 for horizontally supporting the microstrip circuit 30, and a vertical side plate 13 located on the side of the microstrip substrate 31. The coaxial connector 20 is installed and penetrates the vertical side plate 13 by means of threading or flange fitting.

[0070] It is particularly noteworthy that the end face of the microstrip substrate 31 facing the coaxial connector 20 does not rest tightly against the inner wall of the vertical side plate 13, but rather a non-contact anti-collision gap is intentionally reserved between it and the vertical side plate 13. During the assembly process of pushing the hard and brittle ceramic microstrip substrate 31 into the structural carrier 10 and overcoming the elasticity of the compression spring 22 to assemble with the coaxial connector 20, this anti-collision gap provides an absolutely safe physical buffer. This structural arrangement effectively avoids the rigid microstrip substrate edge directly impacting the metal vertical side plate 13, thereby eliminating the risk of chipping and breakage caused by mechanical stress concentration at the substrate edge. It also protects the fragile encapsulated microstrip mating plane 33 on the end face from mechanical damage caused by the external metal shell's pressure and scratches, further improving the reliability of the product's manufacturing process.

[0071] In some embodiments, please refer to Figure 3 and Figure 4 The side-fed coaxial microstrip ultrawideband impedance matching structure also includes a metal cover plate mounted on the top of the structural carrier 10. The metal cover plate, together with the substrate support platform 14 and the vertical side plate 13 of the structural carrier 10, together form a closed shielded cavity (i.e., an air cavity 12). The microstrip circuit 30 is housed in this shielded cavity, and the air cavity 12 is defined directly above the microstrip substrate 31.

[0072] In one specific embodiment, the vertical height and horizontal span of the air cavity 12 are designed based on waveguide cutoff frequency theory. In ultra-high frequency operating environments from DC to 110 GHz, high-frequency electromagnetic waves on the surface of the microstrip signal line 32 are easily converted into spatial radiation waves or excited into higher-order modes within the cavity, resulting in severe energy dispersion and radiation loss. By setting the metal cover and strictly limiting the geometry of the air cavity 12, it can effectively cut off harmful higher-order modes within the operating frequency band, strictly confining electromagnetic energy around the transmission path of the quasi-TEM mode of the microstrip signal line 32. This design not only provides excellent shielding protection against external electromagnetic interference (EMI) for the entire microstrip circuit 30, but also significantly suppresses high-frequency radiation leakage in the interface transition region, further reducing the insertion loss of ultra-wideband signals.

[0073] In other embodiments, the present invention also provides a microwave circuit comprising a side-fed coaxial-to-microstrip ultrawideband impedance matching structure as described in any of the foregoing embodiments.

[0074] In one specific embodiment, the microwave circuit is a radio frequency transceiver module or an ultra-high frequency test fixture. In practical applications, the coaxial connector 20 is configured to receive or output ultra-wideband microwave signals covering a frequency range from DC to 110 GHz. Through the cooperative impedance compensation mechanism of the enclosed microstrip matching plane 33 and the impedance matching cavity 11, the microwave signal is smoothly and with low loss transmitted to the microstrip circuit 30, and the port VSWR of the microwave circuit in the operating frequency band is stably less than a preset threshold (for example, the preset threshold is 1.25).

[0075] In this specification, the illustrative expressions of the terms used do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0076] Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention shall be included within the scope of protection of this invention.

Claims

1. A side-fed coaxial-to-microstrip ultrawideband impedance matching structure, characterized in that, include: Structural carrier; A coaxial connector is horizontally disposed on the side wall of the structural carrier, and an elastic probe is coaxially disposed inside the coaxial connector, with one end of the elastic probe extending horizontally. A microstrip circuit is disposed on the structural carrier and opposite to the coaxial connector. The microstrip circuit includes a microstrip substrate and a microstrip signal line disposed on the top surface of the microstrip substrate. Wherein, the end of the microstrip signal line extends toward the end side of the microstrip substrate toward the coaxial connector, forming an overlay microstrip mating plane that covers the end side downward; the protruding end of the elastic probe of the coaxial connector elastically abuts against the overlay microstrip mating plane to form a surface contact; The structural carrier is located below the microstrip substrate, and an impedance matching cavity is recessed downward from the upper surface of the structural carrier. The impedance matching cavity extends from the abutment transition area between the overlay microstrip matching plane and the coaxial connector to the inner side of the bottom surface of the microstrip substrate, and the top opening of the impedance matching cavity is covered by the bottom surface of the microstrip substrate.

2. The side-fed coaxial microstrip ultrawideband impedance matching structure according to claim 1, characterized in that, The encapsulated microstrip matching plane is a cross-sectional semi-hole metal layer structure; the cross-sectional semi-hole metal layer structure is formed by processing metallized through holes on the microstrip substrate and laser cutting along the central axis of the metallized through holes, thereby allowing the microstrip signal line to smoothly transition to the end side of the microstrip substrate.

3. The side-fed coaxial-to-microstrip ultrawideband impedance matching structure according to claim 1, characterized in that, The protruding end of the elastic probe has a flat contact end face; The orthographic projection profiles of the contact end face and the matching plane of the overlay microstrip have a dimensional difference in at least one radial direction, such that the orthographic projection profile of at least one has an extension margin that exceeds that of the other, thereby forming an assembly tolerance area around the abutment. When a radial assembly offset occurs between the elastic probe and the microstrip circuit, the assembly tolerance region is used to compensate for the offset, so that the actual surface contact state between the two remains unchanged.

4. The side-fed coaxial-to-microstrip ultrawideband impedance matching structure according to claim 1, characterized in that, The impedance matching cavity is a milled groove or blind hole structure opened on the structural carrier. The edge of the impedance matching cavity near the coaxial connector is aligned with the vertical reference plane where the end side of the microstrip substrate is located.

5. The side-fed coaxial microstrip ultrawideband impedance matching structure according to claim 1, characterized in that, The microstrip circuit also includes a ground metal layer disposed on the bottom surface of the microstrip substrate; In the region above the impedance matching cavity, the ground metal layer on the bottom surface of the microstrip substrate is partially or completely removed, so that the air medium in the impedance matching cavity directly contacts the insulating medium bottom surface of the microstrip substrate, thereby reducing parasitic capacitance by adjusting the local equivalent dielectric constant.

6. The side-fed coaxial-to-microstrip ultrawideband impedance matching structure according to claim 1, characterized in that, The dimensions and depth of the impedance matching cavity, together with the aspect ratio of the encapsulated microstrip matching plane, form a dual-variable impedance matching synergistic adjustment structure. The numerical configuration of the impedance matching cavity's dimensions, depth, and aspect ratio is used to collaboratively compensate for the impedance mismatch generated in the contact transition region during the conversion of the electromagnetic wave from a coaxial TEM mode to a microstrip quasi-TEM mode.

7. The side-fed coaxial-to-microstrip ultrawideband impedance matching structure according to claim 1, characterized in that, The elastic probe includes a probe housing and a compression spring built into the probe housing; The protruding end is slidably disposed along the axial direction of the probe housing and is driven to elastically protrude outward by the deformation restoring force of the compression spring, so as to dynamically maintain the adhesion force between the probe end and the matching plane of the encapsulated microstrip when the temperature changes or mechanical vibration occurs.

8. The side-fed coaxial-to-microstrip ultrawideband impedance matching structure according to claim 1, characterized in that, The structural carrier includes a substrate support platform for horizontally supporting the microstrip circuit, and a vertical side plate for mounting the coaxial connector. A non-contact anti-collision gap is left between the end face of the microstrip substrate and the vertical side plate. The elastic probe passes through the vertical side plate in the horizontal direction, crosses the anti-collision gap, and then makes suspended contact with the matching plane of the encapsulated microstrip.

9. A microwave circuit, characterized in that, Includes the side-fed coaxial microstrip ultrawideband impedance matching structure as described in any one of claims 1 to 8.

10. The microwave circuit according to claim 9, characterized in that, The microwave circuit is a radio frequency transceiver module or an ultra-high frequency test fixture. The coaxial connector is configured to receive or output ultra-wideband microwave signals covering a frequency range from DC to 110 GHz. The microwave signal is transmitted to the microstrip circuit through the cooperative impedance compensation mechanism of the encapsulated microstrip matching plane and the impedance matching cavity, and the port standing wave ratio within the operating frequency band is less than a preset threshold.

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