A filter-type waveguide coaxial conversion structure based on hairpin loop resonator

Abstract

The application provides a filter type waveguide coaxial conversion structure based on hairpin loop resonator, comprising: a coaxial connector for inputting or outputting TEM mode signal; a waveguide for transmitting TE mode signal; a filter probe structure connected between the coaxial connector and the waveguide; the filter probe structure comprises a dielectric substrate, a microstrip filter circuit arranged on the dielectric substrate and a metal probe; the microstrip filter circuit comprises a filter circuit composed of a hairpin loop resonator, which is used for filtering signals; one end of the microstrip filter circuit is connected with an inner conductor of the coaxial connector, and the other end of the microstrip filter circuit is connected with one end of the metal probe; the other end of the metal probe extends and is inserted into a cavity of the waveguide. The application aims to provide an innovative design scheme with small size, low loss, high selectivity and strong out-of-band suppression capability for high-frequency application scenarios such as millimeter waves.

Description

Technical Field

[0001] This invention relates to the field of microstrip line technology, and more particularly to a filter-type waveguide coaxial converter structure based on a hairpin ring resonator. Background Technology

[0002] With the continuous iterative evolution of microwave and millimeter-wave technologies, the demand for efficient energy transfer between different types of transmission lines is becoming increasingly urgent. Among them, microstrip lines, with their core advantages of planar layout and ease of integration with other circuits, have become the core carrier driving the miniaturization and integration of microwave circuits.

[0003] Currently, common techniques for waveguide-to-planar circuit conversion include ridge waveguide transitions, fin wire transitions, and probe-coupled transitions. These structures introduce discontinuities such as steps, fin wires, or metal probes into the waveguide to perturb the electromagnetic field distribution within the waveguide, thereby exciting the transmission modes required by the planar circuit. These traditional solutions are relatively mature and can achieve basic impedance matching and mode conversion functions within specific frequency bands.

[0004] However, as operating frequencies rise to the millimeter-wave band and system performance requirements become increasingly stringent, the aforementioned existing technologies have revealed several significant shortcomings: First, it is difficult to simultaneously achieve broadband transmission characteristics and high out-of-band rejection performance. Traditional structures are mostly designed for narrow-band scenarios, and when extended to broadband applications, not only is in-band ripple distortion prone to occur, but out-of-band rejection performance also significantly degrades. Second, the insertion loss problem is particularly prominent. In the millimeter-wave band, the influence of parasitic parameters is amplified dramatically. After being superimposed with the inherent energy loss of the mode conversion stage, the overall insertion loss is generally high, making it difficult to meet the low-loss transmission requirements of high-frequency systems. Third, there is a prominent contradiction between structural compactness and fabrication feasibility. The resonant units or transition structures added to improve transmission performance can easily lead to structural volume redundancy. On the other hand, if the structural size is excessively compressed in pursuit of miniaturization, it will exceed the conventional processing accuracy threshold, resulting in a significant decrease in yield. Fourth, the frequency selection characteristics are poor. The existing structures have a small number of transmission zeros and low position control accuracy, resulting in weak suppression of adjacent interference bands and failing to meet the requirements for precise signal selection in complex electromagnetic environments. Therefore, there is an urgent need for a compact waveguide coaxial converter structure that integrates efficient filtering functions to solve the above problems. Summary of the Invention

[0005] To address the aforementioned technical challenges in integrating broadband, high-efficiency conversion with high-selectivity filtering in existing technologies, and the inherent contradictions between size, loss, and suppression performance, this invention provides a filter-type waveguide coaxial converter structure based on a hairpin ring resonator. This invention primarily utilizes a filter probe structure integrating at least two stages of hairpin ring resonators and a metal probe, connected to the waveguide via impedance matching steps to form an integrated structure. This achieves broadband filtering and mode conversion functions with low insertion loss, strong out-of-band suppression, and high frequency selectivity.

[0006] The technical means employed in this invention are as follows:

[0007] A filter-type waveguide-coaxial converter structure based on a hairpin ring resonator includes: Coaxial connectors are used for inputting or outputting TEM mode signals; Waveguides are used to transmit TE-mode signals; A filter probe structure is connected between a coaxial connector and a waveguide; the filter probe structure includes a dielectric substrate, a microstrip filter circuit disposed on the dielectric substrate, and a metal probe. The microstrip filter circuit includes a filter circuit composed of two coupled hairpin ring resonators for filtering signals; one end of the microstrip filter circuit is connected to the inner conductor of a coaxial connector, and the other end of the microstrip filter circuit is connected to one end of a metal probe; the other end of the metal probe extends and is inserted into the cavity of the waveguide.

[0008] Furthermore, the hairpin ring resonator is of two orders, and the two hairpin ring resonators are symmetrically arranged; a metal patch is provided on the upper part of the internal transverse branch of the hairpin ring resonator.

[0009] Furthermore, the microstrip filter circuit also includes an input feed line and an output feed line; the input feed line connects the coaxial connector to the first-order hairpin ring resonator, and the output feed line connects the second-order hairpin ring resonator to the metal probe.

[0010] Furthermore, the coupling coefficient M can be tuned by adjusting the coupling spacing g1 between the two hairpin ring resonators and by using coupling matrix theory. 12 The formula is as follows:

[0011] Where FBW is the fractional bandwidth, and g0 and g1 are the coefficients of the normalized filter prototype.

[0012] Furthermore, the external quality factor Q is tuned by adjusting the lengths of the input and / or output feed lines and their spacing g2 with the corresponding hairpin ring resonator. e The formula is as follows:

[0013] Where FBW is the fractional bandwidth, and g0 and g1 are the coefficients of the normalized filter prototype.

[0014] Furthermore, the waveguide is a WR-28 standard rectangular waveguide.

[0015] Furthermore, the metal probe is inserted vertically into the center of the wide wall of the waveguide.

[0016] Furthermore, a metal impedance matching step is provided at the connection between the filter probe structure and the waveguide structure.

[0017] Furthermore, the metal impedance matching step includes a first step, a second step, and a third step that are sequentially attached from the side away from the waveguide end to the side near the waveguide end. The first step, the second step, and the third step are cuboid structures, with the width direction from the side away from the waveguide end to the side near the waveguide end as the width direction of the cuboid, the length direction from the side away from the filter probe structure to the side near the filter probe structure as the length direction of the cuboid, and the vertical line direction as the height direction of the cuboid. The first step, the second step, and the third step have the same height, the width of the first step, the second step, and the third step increase sequentially, the length of the first step, the second step, and the third step decrease sequentially, the sides of the first step, the second step, and the third step that are away from the filter probe structure are flush, the upper surfaces of the first step, the second step, and the third step are flush, the lower surfaces of the first step, the second step, and the third step are flush, and the sides of the first step, the second step, and the third step that are near the filter probe structure are stepped.

[0018] Furthermore, the coaxial connector is a 2.4mm standard coaxial connector with a characteristic impedance of 50Ω; the dielectric substrate is made of Alumina high-frequency board with a dielectric constant of 9.9 and a thickness of 0.127mm.

[0019] Compared with the prior art, the present invention has the following advantages: This invention directly embeds the filtering function into the mode conversion structure, forming a functionally integrated device. This design effectively avoids the additional insertion loss and connection mismatch that are inevitably introduced when using discrete mode conversion and filtering components. At the same time, by utilizing the low-loss characteristics of the waveguide itself and the optimized resonator coupling design, extremely low signal attenuation in the passband is achieved while ensuring excellent filtering performance.

[0020] This invention, through its unique resonator structure and coupling design, enables efficient conversion of wideband signals while generating transmission zeros at the passband edge, thus achieving a steep filter roll-off characteristic. This characteristic gives the device not only excellent broadband matching but also strong out-of-band clutter suppression capability, solving the problem of performance degradation when traditional conversion structures extend bandwidth.

[0021] The integrated structure employed in this invention eliminates the need for external filtering and matching circuits, significantly reducing the overall physical size. Its core filtering unit, through a special structural design, achieves the required resonant mode and coupling strength within a limited space, reducing reliance on ultra-high precision machining. While achieving miniaturization, it also improves the manufacturability and reliability of the device.

[0022] The integrated structure employed in this invention produces a sharp frequency response, with a rapid transition between the passband and stopband and good frequency selectivity. Furthermore, its core frequency response parameters for filtering and conversion can be effectively controlled by adjusting the structural parameters of its internal resonant units, thereby adapting to the specific needs of different millimeter-wave application scenarios and offering high design flexibility. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a front view of the device structure of the present invention; Figure 2 This is a diagram of the filter probe structure and waveguide structure of the present invention.

[0025] Figure 3 This is a structural diagram of the filter probe of the present invention.

[0026] Figure 4 This is a diagram of the original hairpin ring resonator structure.

[0027] Figure 5 The graph shows the S11 and S21 parameters of the conversion structure of the present invention.

[0028] Figure 6 This is a graph showing the S11 parameter curve of the conversion structure of the present invention.

[0029] Figure 7 This is the S21 parameter curve of the conversion structure of the present invention.

[0030] Figure 8This is a schematic diagram of the integrated structure of the filter probe and standard waveguide of the present invention.

[0031] In the figure: 1. Coaxial connector; 2. Integrated structure of filter probe and standard waveguide; 3. Waveguide flange; 4. First input port; 5. First input port feed line; 6. First HRR resonator; 7. First metal patch; 8. Second input port feed line; 9. Metal probe structure; 10. Filter probe structure; 11. Waveguide; 12. Metal impedance matching step; 13. Second input port; 14. Second HRR resonator; 15. Second metal patch. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0036] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0037] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0038] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0039] like Figure 1-3 and Figure 8 As shown, this invention provides a filter-type waveguide coaxial converter structure based on a hairpin ring resonator, comprising: Coaxial connector 1 is used for inputting or outputting TEM mode signals; Waveguide 11 is used to transmit TE mode signals; A filter probe structure 10 is connected between a coaxial connector and a waveguide; the filter probe structure includes a dielectric substrate, a microstrip filter circuit disposed on the dielectric substrate, and a metal probe. The microstrip filter circuit includes a filter circuit composed of two coupled hairpin ring resonators for filtering signals; one end of the microstrip filter circuit is connected to the inner conductor of a coaxial connector, and the other end of the microstrip filter circuit is connected to one end of a metal probe; the other end of the metal probe extends and is inserted into the cavity of the waveguide.

[0040] In addition to the advantages of microstrip probe transitions, this invention significantly reduces the size of the transition structure compared to traditional transition circuits. The structure mainly consists of three parts: a filter probe structure, a waveguide, and a coaxial connector. The microstrip filter circuit of the filter probe structure comprises a second-order hairpin ring resonator (HRR). Utilizing the independent controllable odd and even modes of the hairpin ring resonator, it provides the physical basis for broadband coverage. By leveraging the transmission poles of the structure itself, the bandwidth is extended without increasing the physical size. Furthermore, by optimizing the geometry of the hairpin ring resonator, the resonator size can be reduced while ensuring multi-mode operation, significantly decreasing the space occupied by individual devices.

[0041] The structural characteristics of waveguides and coaxial connectors differ significantly. If the waveguide end face is directly connected to the inner conductor of the coaxial connector, efficient transmission of electromagnetic waves from the waveguide to the coaxial line is difficult, and significant energy reflection easily occurs at the connection point, directly leading to degradation of the device's broadband transmission performance. To achieve efficient conversion between the TE mode within the waveguide and the TEM mode of the coaxial connector, this invention adds a filter probe structure between the waveguide and the coaxial connector. The TEM mode signal transmitted in the microstrip filter circuit of the filter probe structure achieves energy coupling and mode conversion via an extended metal probe. This probe is vertically inserted into the region near the center of the wide wall of the WR-28 standard waveguide (this region is the waveguide TE mode). 10 At the point where the dominant mode electric field is strongest, the TEM mode energy of the microstrip line is converted into TE mode energy within the waveguide through direct coupling between the probe and the electric field inside the waveguide. 10The output impedance can be adjusted by changing the probe length, insertion depth, and the shape and size of the probe. Simultaneously, controlling the probe size and fabrication precision reduces radiation and conductor losses caused by parasitic parameters, ultimately achieving efficient signal transmission from the microstrip line to the waveguide. This structure guides electromagnetic waves to achieve a smooth transition from the waveguide's TE mode to the coaxial connector's TEM mode. By progressively optimizing mode matching efficiency, it effectively suppresses energy reflection at the connection point, ultimately significantly improving the device's broadband transmission performance. For high out-of-band suppression, the inherent transmission zeros of the hairpin ring resonator can be utilized. The hairpin ring resonator generates band-edge zeros due to its dual signal paths, thus improving suppression performance. Regarding insertion loss, a cascaded resonator approach with metal probes used to transition the waveguide offers advantages such as simple design and low insertion loss, making it suitable for broadband applications sensitive to insertion loss. For structural compactness, optimizing the hairpin ring resonator structure and introducing internal loading patches enables independent excitation of multiple modes while achieving miniaturization. Regarding frequency selectivity, cascaded topologies are designed, and the relationship between coupling strength and bandwidth expansion is quantified using coupling matrix theory, clarifying the transmission zero introduction mechanism to improve frequency selectivity.

[0042] The proposed filter-type waveguide coaxial converter structure based on a hairpin ring resonator in this invention achieves low loss, strong out-of-band rejection, and high selectivity in the millimeter-wave band by integrating signal transmission and filtering. This is achieved through the independently adjustable modes of the hairpin ring resonator and the inherent closed cavity structure of the WR-28 standard waveguide, reducing electromagnetic leakage and external interference. The main details are as follows: Waveguide section: A WR-28 (7.12mm×3.556mm) standard waveguide is selected, with an operating frequency band covering 26.5-40GHz, precisely adapted to the target 35-40GHz solar observation frequency band. The waveguide is copper-plated, utilizing its inherent closed cavity structure to reduce electromagnetic leakage and external interference, laying the foundation for low loss and strong anti-interference. The waveguide end face is reserved with a mounting interface matching the filter probe structure.

[0043] The filter probe structure consists of a microstrip filter circuit composed of two cascaded hairpin ring resonators. The substrate is made of Alumina (99.5%) high-frequency board with a dielectric constant of 9.9 and a thickness of 0.127 mm. The hairpin ring resonator design follows the principle of independent control of odd and even modes. By optimizing the linewidth (0.01-0.03 mm), coupling gap (0.02-0.15 mm), and the length of each segment, the odd mode (…) is controlled independently. f o ) and even mode ( f eThe resonant frequencies are respectively adapted to both ends of the passband to achieve 5GHz broadband coverage; small metal patches are loaded inside the hairpin ring resonator to achieve impedance matching, and additional energy loss is avoided through coupling structure optimization.

[0044] The filter probe structure includes 50 Ω First input port 4 ( Y 1. w 1) Second output port 13 ( Y 11 , w 11 ), First input port feeder 5 ( Y 2. w 2) Second output port feeder 8 ( Y 21 , w 21 ),First HRR Resonator 6 ( a 1. a 2. b 1. b 2. w ,),second HRR Resonator 14, First metal patch 7 ( c , d ), second metal patch 15, metal probe structure 9 ( Y 11 , e , h , f The signal is composed of two components. The signal is transmitted from the first input port 4 to the directly connected first input port feeder 5, through the coupling gap. x 2. The first input port feed line 5 is coupled to the first HRR resonator 6; by adopting axisymmetry on the structure described above, the second HRR resonator 14, the second metal patch 15, the second input port feed line 8, and the second output port 13 are obtained. The two resonators are connected by a coupling gap. x 1. Coupled for signal transmission; the second output port 13 is directly connected to the metal probe structure 9 for smooth signal transition.

[0045] Coaxial connector section: It adopts a 50Ω 2.4mm standard coaxial connector with a beryllium copper gold-plated inner conductor, a PTFE dielectric material, and a stainless steel passivated shell and coupling nut. The operating frequency covers DC-50GHz and is fully compatible with the 35-40GHz target frequency band. One end of the coaxial connector is connected to the filter probe structure through a 2.4mm-SMA adapter, and the other end is directly adapted to the millimeter-wave receiver interface. It utilizes the low loss characteristics (≤0.15dB / m) of the 2.4mm coaxial cable in the 26.5-40GHz frequency band to improve transmission efficiency.

[0046] Metal probe: A metal probe is added between the waveguide and the microstrip filter circuit of the filter probe structure. The probe is made of metal and its length matches the field distribution characteristics of the TE10 mode of the WR-28 waveguide. One end is connected to the output end of the second-order hairpin ring resonator, and the other end extends to the central region of the waveguide cavity to achieve a smooth transition from the TE mode to the TEM mode.

[0047] Figure 8 This is a three-dimensional structural diagram of a filter-type waveguide coaxial converter structure based on a hairpin ring resonator provided in an embodiment of the present invention. The structure includes: a standard 2.4mm coaxial connector 1, an integrated structure 2 of a filter probe and a standard waveguide, and a waveguide flange 3. The physical dimensions of the waveguide flange are M=19.1mm, Q=5mm, and N=19.1mm. The structure is connected to the 50Ω input port of the filter probe structure via a standard 2.4mm coaxial connector, and the metal probe part of the filter probe structure is connected via a standard waveguide.

[0048] The WR-28 waveguide features low radiation loss, while the optimized hairpin ring resonator coupling structure and the low-loss characteristics of the 2.4mm standard coaxial connector provide triple protection to keep the total insertion loss in the passband below -0.02dB. The waveguide cavity blocks external clutter, and the hairpin ring resonator generates a transmission zero through dual paths, achieving suppression below -36dB.

[0049] Figure 2 Structure 2 is an integrated structure of a filter probe and a standard waveguide, which contains... Figure 3 The filter probe structure and standard waveguide are described. The standard waveguide has dimensions of k1=7.12mm and k2=3.56mm. The waveguide is internally housed as an air cavity, and the outer surface of the air cavity is plated with a 0.02mm thick copper layer.

[0050] The waveguide port of the conversion structure of this invention adopts a standard WR-28 waveguide, and with the waveguide feeding method, it can not only significantly reduce insertion loss, but also effectively improve power capacity, fully adapting to the high power and low loss transmission requirements of the millimeter wave band.

[0051] Figure 4 This is the original hairpin ring resonator structure, corresponding to Figure 3 The original structure of the first HRR resonator 6 and the second HRR resonator 14. The structure includes: stubs. L 1. L 2. L 3. L It consists of 4 components, and the width of the microstrip line is... W The structural feature is that the resonant modes of the hairpin ring resonator include odd-mode resonance and even-mode resonance, and the odd-mode frequency is calculated according to the following formula:

[0052] in, f o1 Indicates the odd modulus frequency. L 1 indicates the length of the card-opening path. L 4 represents the length of the first connecting line. Indicates the effective dielectric constant. c Represents the speed of light; The even-mode frequency is calculated according to the following formula:

[0053] in, f e1 Indicates even-mode frequency, L 2 represents the length of the loop connector. L 3 indicates the length of the second connecting line.

[0054] The odd and even mode resonant frequencies of a hairpin ring resonator can be controlled by adjusting the physical dimensions of the resonator stubs; the physical dimensions of the hairpin ring resonator for the required operating frequency band can be designed and calculated using the above formulas.

[0055] The filter probe structure comprises: a 50Ω input / output port, a port feed line, a hairpin ring resonator, a metal patch, and a metal probe. The distance between the feed line and the resonator is g2. A second hairpin ring resonator, obtained through axisymmetry, is used, along with the metal patch and the 50Ω output microstrip feed line. The coupling distance between the two resonators is [missing information]. g 1. The physical dimensions of the filter probe are L1=0.2mm, L2=0.62mm, w1=0.12mm, w2=0.02mm, a1=0.81mm, a2=0.87mm, b1=0.53mm, b2=0.45mm, c=0.245mm, d=0.743mm, e=0.5mm, h=0.24mm, f=0.9mm, and g=0.02mm.

[0056] The hairpin ring resonator can control the odd and even mode resonant frequencies by adjusting the physical dimensions of the resonator stubs; the two resonators improve the traditional hairpin ring resonator structure by adding metal patches to the resonators, which not only achieves good impedance matching, but also achieves miniaturization without increasing the overall size of the resonator.

[0057] The coupling coefficient is a key parameter measuring the intensity of electromagnetic energy exchange between two resonators. Its core function is to determine the correlation between energy transfer efficiency and frequency response between the resonators. By adjusting the coupling strength (coupling coefficient) of the two resonators, their resonant frequencies can overlap and broaden, forming a continuous wide passband suitable for millimeter-wave broadband transmission requirements. Furthermore, it can reduce energy reflection between resonators, lowering insertion loss. Simultaneously, it avoids in-band ripple distortion caused by over-coupling or insufficient bandwidth caused by under-coupling, ensuring the coordinated achievement of low-loss and broadband characteristics of the filter. The filter probe structure calculates and controls the coupling strength by changing the spacing g1 between the two resonators and using coupling matrix theory. The coupling coefficient M... 12 The calculation formula is as described above.

[0058] The external quality factor is a key parameter for measuring the coupling strength between a resonator and external circuitry (input / output ports). Its core function is to regulate the energy exchange efficiency between the resonator and the ports, balancing passband matching, bandwidth, and insertion loss. Differentiated design of the Q-factor of two resonators... e This design enhances the synergy between energy confinement and release at the passband edge, and, in conjunction with internal coupling, introduces transmission zeros, resulting in a steeper transition between the passband and stopband, thus improving the suppression of out-of-band interference. The external quality factor Q is calculated and controlled by varying the length of the microstrip feedline and the spacing g2 between the feedline and the resonator. e The calculation formula is as described above.

[0059] The filter probe structure is the core functional unit of this invention, and it adopts an integrated design of "hairpin ring resonator + metal probe". The hairpin ring resonator is the core of the filtering function. Through its inherent resonance characteristics, it achieves selective transmission and clutter suppression of the target frequency band signal, solving the defects of weak out-of-band suppression and poor frequency selectivity of traditional structures. The metal probe is the key carrier for energy coupling and mode conversion. Its size and layout are precisely matched to ensure efficient adaptation with the hairpin ring resonator and the waveguide internal field distribution, while reducing energy loss during the coupling process.

[0060] The waveguide, labeled as WR-28, has clearly defined physical dimensions: wide wall length k1 = 7.12 mm and narrow wall length k2 = 3.56 mm. These dimensions are standard industrial specifications for the WR-28 waveguide, suitable for millimeter-wave frequency signal transmission. As a signal transmission carrier, the WR-28 waveguide's inner wall is made of metal, which can confine the electromagnetic field to form a stable guided wave mode, providing physical space for efficient energy transmission. The physical dimensions of the metal impedance matching steps are s = 1.75 mm, z1 = 0.9 mm, z2 = 0.95 mm, z3 = 2.7 mm, p1 = 0.55 mm, p2 = 1.7 mm, and p3 = 1.78 mm.

[0061] The third-order metallic impedance matching step 12, made of highly conductive copper, is typically positioned at the transition interface between the filter probe structure and the standard waveguide. The physical dimensions of the metallic step are all s=1.75mm in height. The physical dimensions of the first step are z1=0.9mm, p1=1.78mm; the second step is z2=0.95mm, p2=1.7mm; and the third step is z3=2.7mm, p3=0.55mm. The core function of the metallic step is to achieve impedance gradient matching between the filter probe and the waveguide. Because the characteristic impedance of the filter probe structure (including the HRR resonator and the metallic probe) differs from that of the WR-28 waveguide (hundreds of Ω), the solid copper step, through precisely designed height and length dimensions, constructs a gradually changing impedance transition region, effectively suppressing signal reflection and laying the foundation for efficient energy coupling.

[0062] The overall signal transmission path follows an integrated process of "frequency selection-coupling-matching-conversion-transmission," specifically: 1. The input signal (coaxial form) enters the filter probe structure, first passing through a hairpin ring resonator. The target frequency band signal is selectively transmitted, while non-target clutter signals are suppressed by the resonator; 2. The filtered target signal excites the metal probe to generate an induced electromagnetic field; 3. The metal probe initially injects TEM mode energy into the WR-28 waveguide through electric field coupling. Simultaneously, the metal impedance matching step suppresses signal reflection through impedance gradient, optimizing energy transmission efficiency in the transition region; 4. The matched energy is efficiently converted into the TE10 master mode within the waveguide. This mode signal is stably transmitted along the axial direction within the WR-28 waveguide, and the waveguide's inner metal wall constrains the electromagnetic field to prevent energy radiation loss; 5. Finally, the TE10 mode signal is output from the waveguide, completing the entire "filtering-coupling-matching-conversion-transmission" process. This path, through the synergistic design of the metal impedance matching step and the hairpin ring resonator, further improves energy transmission efficiency while eliminating the need for independent filtering and matching modules in traditional systems, achieving structural integration.

[0063] Figures 5-7 The figures show the S11 (return loss) and S21 (insertion loss) parameter curves for the proposed conversion structure. The results demonstrate that within the 35–40 GHz design bandwidth, the return loss is ≤-13 dB, the insertion loss is ≤-0.02 dB, the upper stopband suppression level reaches below -36 dB, and precise deep suppression is achieved at specific out-of-band interference frequencies in the millimeter-wave band, fully meeting the stringent requirements of high electromagnetic compatibility systems.

[0064] In summary, this invention, through the innovative design of a filter-type waveguide coaxial converter structure based on a hairpin ring resonator, successfully achieves excellent performance in the millimeter-wave band, including low loss, strong out-of-band suppression, and high selectivity, providing a reliable solution for efficient transmission of high-frequency signals.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A filter-type waveguide coaxial converter structure based on a hairpin ring resonator, characterized in that, include: Coaxial connectors are used for inputting or outputting TEM mode signals; Waveguides are used to transmit TE-mode signals; A filter probe structure is connected between the coaxial connector and the waveguide; The filter probe structure includes a dielectric substrate, a microstrip filter circuit disposed on the dielectric substrate, and a metal probe. The microstrip filter circuit includes a filter circuit composed of two coupled hairpin ring resonators, used to filter the signal; One end of the microstrip filter circuit is connected to the inner conductor of the coaxial connector, and the other end of the microstrip filter circuit is connected to one end of the metal probe; the other end of the metal probe extends and is inserted into the cavity of the waveguide.

2. The filter-type waveguide coaxial converter structure based on a hairpin ring resonator according to claim 1, characterized in that, The hairpin ring resonator is of two order and the two order hairpin ring resonators are symmetrically arranged; a metal patch is provided on the upper part of the internal transverse branch of the hairpin ring resonator.

3. The filter-type waveguide coaxial converter structure based on a hairpin ring resonator according to claim 2, characterized in that, The microstrip filter circuit also includes an input feed line and an output feed line; the input feed line connects the coaxial connector to the first-order hairpin ring resonator, and the output feed line connects the second-order hairpin ring resonator to the metal probe.

4. The filter-type waveguide coaxial converter structure based on a hairpin ring resonator according to claim 1, characterized in that, The coupling coefficient M is controlled by adjusting the coupling spacing g1 between the two-order hairpin ring resonators and by applying coupling matrix theory. 12 The formula is as follows: Where FBW is the fractional bandwidth, and g0 and g1 are the coefficients of the normalized filter prototype.

5. The filter-type waveguide coaxial converter structure based on a hairpin ring resonator according to claim 1, characterized in that, The external quality factor Q is controlled by adjusting the length of the input and / or output feed lines and their spacing g2 from the corresponding hairpin ring resonator. e The formula is as follows: Where FBW is the fractional bandwidth, and g0 and g1 are the coefficients of the normalized filter prototype.

6. The filter-type waveguide coaxial converter structure based on a hairpin ring resonator according to claim 1, characterized in that, The waveguide is a WR-28 standard rectangular waveguide.

7. The filter-type waveguide coaxial converter structure based on a hairpin ring resonator according to claim 1, characterized in that, The metal probe is inserted vertically into the center of the wide wall of the waveguide.

8. The filter-type waveguide coaxial converter structure based on a hairpin ring resonator according to claim 1, characterized in that, A metal impedance matching step is provided at the connection between the filter probe structure and the waveguide.

9. The filter-type waveguide coaxial converter structure based on a hairpin ring resonator according to claim 8, characterized in that, The metallic impedance matching steps include a first step, a second step, and a third step that are sequentially attached from the waveguide end to the waveguide end. The first step, the second step, and the third step are cuboid structures, with the width direction from the waveguide end to the waveguide end as the width direction, the length direction from the filter probe structure to the filter probe structure as the length direction, and the vertical direction as the height direction. The first step, the second step, and the third step have the same height. The width of the first step, the second step, and the third step increase sequentially, and the length of the first step, the second step, and the third step decrease sequentially. The sides of the first step, the second step, and the third step that are away from the filter probe structure are flush. The upper surfaces of the first step, the second step, and the third step are flush. The lower surfaces of the first step, the second step, and the third step are flush. The sides of the first step, the second step, and the third step that are close to the filter probe structure are stepped.

10. The filter-type waveguide coaxial converter structure based on a hairpin ring resonator according to claim 1, characterized in that, The coaxial connector is a 2.4mm standard coaxial connector with a characteristic impedance of 50Ω; the dielectric substrate is made of Alumina high-frequency board with a dielectric constant of 9.9 and a thickness of 0.127mm.

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