High-roll-off rectangular micro coaxial line low-pass filter

Abstract

The invention belongs to the technical field of filters, and relates to a high-roll-off rectangular micro coaxial line low-pass filter which comprises a rectangular micro coaxial line. The two rectangular micro coaxial line-coplanar waveguide transition structures are located at the two ends of the rectangular micro coaxial line respectively to form an input port and an output port which are used for being connected with external elements. The loading structure based on the stepped impedance open-circuit branch knot and the defected ground loading structure are positioned in the middle of the rectangular micro coaxial line; the loading structure based on the stepped impedance open-circuit branches comprises a plurality of open-circuit branches which are uniformly distributed on the two sides of the rectangular micro coaxial line and are in a mirror image arrangement state by taking the center line of the rectangular micro coaxial line as a reference line, and the lengths of the open-circuit branches are gradually reduced from the middle to the two sides; the defected ground loading structure comprises a plurality of defected grounds, each defected ground is correspondingly arranged between two adjacent open circuit branches, and the lengths of the plurality of defected grounds are gradually reduced from the middle to the two sides. The low-loss and high-suppression band-pass filter has the advantages of being low in loss, high in roll-off, high in suppression degree, wide in stop band and good in transmission performance.

Description

Technical Field

[0001] The invention belongs to the technical field of filters, and in particular relates to a high roll-off rectangular micro-coaxial line low-pass filter. Background Art

[0002] In recent years, with the leap forward of wireless communication technology and breakthroughs in materials science, millimeter wave technology has ushered in an unprecedented opportunity for development. The millimeter wave band has its unique advantages: extremely short wavelength gives it extremely high spatial resolution, and its vast bandwidth resources support ultra-high-speed data transmission. In addition, its moderate penetration ability and low photon energy not only greatly promote the miniaturization and portability of communication equipment, but also millimeter wave technology is widely used in high-resolution radar imaging, the construction of 5G / 6G communication networks, precise remote sensing detection, high-speed data transmission links in aerospace, and cutting-edge biomedical imaging and non-invasive diagnostic technologies.

[0003] Because of the significant small size of devices and systems in the millimeter wave frequency band, unprecedented high standards are imposed on the fineness and accuracy of the processing technology. In recent years, in order to meet this challenge, a variety of innovative micro-processing technologies have emerged in the domestic and foreign scientific research and industrial circles, such as CNC processing technology, 3D printing technology, three-dimensional metal micro-processing technology, namely micro-coaxial process, etc. Although CNC processing can achieve high precision, it may face the challenge of precision limit when processing the extremely fine structures and complex shapes required for the millimeter wave frequency band. Assembly errors are difficult to avoid and are not conducive to large-scale production. 3D printing technology has advantages in the miniaturization and complex structures of devices and systems, but it may be difficult to achieve the same level of precision as traditional precision processing, and the processing speed is usually slow, which cannot be mass-produced on a large scale. Three-dimensional metal micro-processing technology, namely micro-coaxial process, combines multiple micro-processing technologies such as multi-layer electroplating, photolithography, and etching to construct air-filled rectangular coaxial transmission lines and waveguide structures on a microscale, and the conductor material is generally copper, so it has excellent thermal conductivity and ductility. The micro-coaxial line uses air as the medium and has no dielectric loss; it is fully copper-wrapped, has no radiation loss, and can efficiently transmit TEM waves. Therefore, it has excellent electrical properties such as low loss, high isolation, and low dispersion, which can improve the transmission efficiency and quality of signals. The transmission line has a quasi-planar structure, is easy to miniaturize and integrate, and can also be interconnected with other transmission lines. The rectangular micro-coaxial line (21) proposes a new solution for the design and development of high-performance millimeter-wave low-pass filters, which can not only reduce transmission losses but also simplify the complexity of communication system integration, thereby further realizing the large-scale, low-cost, high-performance, and miniaturized design of wireless communication equipment, providing strong support for the rapid development of modern communication systems.

[0004] Low-pass filters are important devices in communication systems. They are used to extract low-frequency signals of interest and suppress or weaken high-frequency components that may introduce noise, interference, or exceed the system's processing capabilities. In the field of traditional technology, low-pass filters based on printed microstrip technology have become one of the most widely used filter types due to their low cost, flexible design, and easy integration. At present, there are a large number of low-pass filter products based on printed microstrip technology, but their frequency band coverage is mostly limited to lower frequency bands. The research and development and application of millimeter-wave-based low-pass filters are still in a blank stage that needs to be filled. Because as the frequency develops toward the millimeter-wave band, the radiation effect of the microstrip line gradually increases, the radiation loss increases, and there is the inherent dielectric loss of the dielectric substrate, which makes the low-pass filter based on printed microstrip technology have large in-band insertion loss, which cannot meet the stringent requirements of filter performance in emerging fields such as 5G and the Internet of Things. Summary of the invention

[0005] The present invention provides a high roll-off rectangular micro-coaxial line low-pass filter, which has the advantages of low loss, high roll-off, high suppression, wide stopband and good transmission performance, can realize board-level interconnection integration, and fills the gap of low-pass filters based on millimeter waves.

[0006] The technical solution of the present invention is:

[0007] A high roll-off rectangular micro-coaxial line low-pass filter, comprising:

[0008] Rectangular micro coaxial line;

[0009] Two rectangular micro-coaxial line-coplanar waveguide transition structures are respectively located at two ends of the rectangular micro-coaxial line, forming an input port and an output port for connecting to external components;

[0010] The loading structure based on the step impedance open-circuit branch and the defective ground loading structure are located in the middle of the rectangular micro-coaxial line and are used to load the rectangular micro-coaxial line; wherein the loading structure based on the step impedance open-circuit branch includes a plurality of open-circuit branches, the plurality of open-circuit branches are evenly distributed on both sides of the rectangular micro-coaxial line and are arranged in a mirror image with the center line of the rectangular micro-coaxial line as the reference line, and the lengths of the plurality of open-circuit branches decrease from the middle to both sides; the defective ground loading structure includes a plurality of defective grounds, each defective ground is correspondingly arranged between two adjacent open-circuit branches, and the lengths of the plurality of defective grounds decrease from the middle to both sides;

[0011] After the radio frequency signal is input through the input port of the filter, it is filtered by the low-pass filter, and the filtered signal is output from the output port.

[0012] Preferably, the rectangular micro-coaxial line includes a shell and a first conductor core, the first conductor core is wrapped in the shell, the axis of the first conductor core coincides with the axis of the shell, there is a gap between the inner wall of the shell and the first conductor core, and a cavity is formed between the two, and the cavity is filled with a medium for reducing transmission loss.

[0013] Preferably, the medium is air.

[0014] Preferably, the open-circuit branch includes a first impedance line and a second impedance line connected in sequence, the length of the first impedance line is equal to the length of the second impedance line, the impedance of the first impedance line is greater than the impedance of the second impedance line, the end of the first impedance line is loaded onto a rectangular micro-coaxial line, and the end of the second impedance line is separated from the shell to achieve an open circuit.

[0015] Preferably, the design length of the open branch is preliminarily determined by the following formula:

[0016] Z s1 tanθ s1 -Z s2 cotθ s2 =0

[0017]

[0018] Among them, Z s1 is the characteristic impedance of the first impedance line, Z s2 is the characteristic impedance of the second impedance line, θ s1 is the electrical length of the first impedance line, θ s2 is the electrical length of the second impedance line, l s1 is the actual physical length of the first impedance line, l s2 is the actual physical length of the second impedance line, f zs Represents the desired frequency point for generating a transmission zero point, v represents the propagation speed of the electromagnetic wave on the transmission line, and v is less than the speed of light c.

[0019] Preferably, the defective land includes a first groove body and two second groove bodies respectively arranged on both sides of the first groove body and connected to the first groove body, the two second groove bodies are symmetrically distributed with the center line of the rectangular micro-coaxial line as the reference line, and the width of the first groove body is smaller than that of the second groove body.

[0020] Preferably, the rectangular micro-coaxial line-coplanar waveguide transition structure includes a shell, a second conductor core and a boss support structure, wherein the boss support structure is located on the lower side of the second conductor core and is fixedly connected to the inner wall of the shell, one end of the second conductor core is fixedly connected to the first conductor core, and the other end of the second conductor core is provided with a boss, the upper end of the boss is located in a through opening opened on the shell and the upper end surface is flush with the shell surface, the boss and the through opening constitute a coplanar waveguide interconnected with external components, and the lower side of the second conductor core is also provided with a dielectric support strip for electromagnetic isolation and supporting the second conductor core, and the dielectric support strip is provided on the boss support structure.

[0021] Preferably, the boss support structure comprises a square boss, one end of the square boss is fixedly connected to the inner wall of the shell, and the other end of the square boss is in contact with the medium support strip.

[0022] Preferably, a plurality of dielectric support strips are arranged between the first conductor core and the shell to support the first conductor core to achieve positioning. The plurality of dielectric support strips are periodically arranged at a predetermined interval. The dielectric support strips are passed through the first conductor core, and both ends are embedded in the shell. A pair of side surfaces of the dielectric support strips are respectively fixed to a pair of inner walls of the shell to improve the stability of the dielectric support strips.

[0023] Preferably, the rectangular micro-coaxial line has periodically arranged release holes.

[0024] Compared with the prior art, the present invention provides a high roll-off rectangular micro-coaxial line low-pass filter, which utilizes step impedance open-circuit branch loading and defect ground loading to achieve device miniaturization and high suppression and wide stopband. At the same time, the first conductor inner core is transformed from a horizontal plane to a vertical plane through a second conductor inner core and a boss in sequence, and the boss and the through opening on the shell form a coplanar waveguide interconnected with an external component to form a micro-coaxial line-coplanar waveguide transition structure. This structure greatly reduces the size of the micro-coaxial line-coplanar waveguide transition structure, is conducive to board-level interconnection and integration of the low-pass filter with other devices, and broadens the application range of the low-pass filter. It has the advantages of low loss, high roll-off, high suppression, wide stopband and good transmission performance, fills the gap in low-pass filters based on millimeter waves, has strong practicality, and is worthy of promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a three-dimensional diagram of the structure of the present invention.

[0026] Figure 2 It is a perspective view of the structure of the present invention in a top-down state.

[0027] Figure 3 It is a three-dimensional perspective view of the structure of the present invention.

[0028] Figure 4 It is a top view of the structure of the present invention after removing the upper cover.

[0029] Figure 5 It is a top view of the structure of the present invention.

[0030] Figure 6 A cross-sectional view of the structure of the present invention Figure 1 .

[0031] Figure 7 A cross-sectional view of the structure of the present invention Figure 2 .

[0032] Figure 8 A cross-sectional view of the structure of the present invention Figure 3 .

[0033] Fig. 9 A cross-sectional view of the structure of the present invention Figure 4 .

[0034] Fig.10 It is a schematic structural diagram of the conductor inner core of the present invention.

[0035] Fig.11 It is a schematic diagram of the structure of the output port 2 of the present invention.

[0036] Fig.12 It is a cross-sectional view of the output port 2 of the present invention.

[0037] Fig.13 It is a schematic diagram of the structure of the input port 1 of the present invention.

[0038] Fig.14 This is a diagram of the S parameter simulation results of the filter provided by the present invention. DETAILED DESCRIPTION

[0039] The technical solution in the present application will be described clearly and in detail below in conjunction with the accompanying drawings. Among them, in the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B: "and / or" in the text is only a description of the association relationship of associated objects, indicating that there can be three relationships, such as A and / or B, which can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, "multiple" refers to two or more than two. The following terms "first" and "second" are used for descriptive purposes only and cannot be understood as implying or suggesting relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0040] The present invention provides a high roll-off rectangular micro-coaxial line low-pass filter, which is combined with Figures 1 to 13 The present invention is described with reference to the structural schematic diagram of FIG.

[0041] Example 1

[0042] The present invention provides a high roll-off rectangular micro-coaxial line low-pass filter, which is based on a rectangular micro-coaxial line 21 low-pass filter, such as Figures 1 to 4 As shown, its structure includes a rectangular micro-coaxial line 21, two rectangular micro-coaxial line-coplanar waveguide transition structures 25, a loading structure 22 based on a stepped impedance open-circuit branch, and a defective ground loading structure 11, wherein the loading structure 22 based on a stepped impedance open-circuit branch and the defective ground loading structure 11 are arranged in the middle section of the rectangular micro-coaxial line 21 to realize the loading of the rectangular micro-coaxial line 21, and the two rectangular micro-coaxial line-coplanar waveguide transition structures 25 are respectively located at both ends of the rectangular micro-coaxial line 21, forming the input port 1 and the output port 2 of the filter.

[0043] The input port 1 and the output port 2 are used to connect with external components and are connected through two rectangular micro-coaxial line-coplanar waveguide transition structures 25 and two ends of the rectangular micro-coaxial line 21 to form a signal path.

[0044] Among them, more specifically, Figure 2 As shown, the rectangular micro-coaxial line 21 includes a housing 10 and a first conductor core 20, the first conductor core 20 is wrapped in the housing 10, the first conductor core 20 coincides with the axis of the housing 10, there is a gap between the inner wall of the housing 10 and the first conductor core 20, and a cavity is formed between the two, the cavity is filled with a medium for greatly reducing transmission loss, preferably, the medium is air. The housing 10, the first conductor core 20 and the two rectangular micro-coaxial line-coplanar waveguide transition structures 25 are all axisymmetric structures.

[0045] As a further illustration of this embodiment, the rectangular micro-coaxial line 21 and the loading structure 22 based on the stepped impedance open-circuit branch in the structure of the high roll-off rectangular micro-coaxial line low-pass filter provided by the present invention are both designed based on the rectangular micro-coaxial line 21 .

[0046] More specifically, the rectangular micro coaxial line 21 has a thickness of 100 um, a width of 75 um, and a length of 5939 um.

[0047] Specifically, Fig.10 As shown, the loading structure 22 based on the step impedance open-circuit branch includes a plurality of open-circuit branches, the input ends of the plurality of open-circuit branches are respectively connected to the rectangular micro-coaxial line 21, and the output ends are respectively kept at a preset distance from the shell 10 to achieve open circuit, and the plurality of open-circuit branches are evenly distributed on both sides of the rectangular micro-coaxial line 21 and are arranged in a mirror image with the center line of the rectangular micro-coaxial line 21 as the reference line, and the lengths of the plurality of open-circuit branches decrease from the middle to both sides.

[0048] The loading structure 22 based on the stepped impedance open-circuit branch can generate different characteristic impedances by changing the thickness and width of the first conductor core 20 of the rectangular micro-coaxial line 21. The open-circuit branch includes a first impedance line and a second impedance line connected in sequence, wherein the impedance of the first impedance line is greater than the impedance of the second impedance line, the first impedance line is a high impedance line, the second impedance line is a low impedance line, the high impedance line and the low impedance line are equal in length, the end of the high impedance line is loaded onto the rectangular micro-coaxial line 21, and the end of the low impedance line is separated from the shell 10 to achieve an open circuit.

[0049] More specifically, the thickness of the low-impedance line is 200um, and the thickness of the high-impedance line is 100um, which is only half of the thickness of the low-impedance line. The width of the high-impedance line is 60um, and the width of the low-impedance line is 300um. The narrower the width of the first conductor core 20, the higher the characteristic impedance, and the smaller the thickness of the first conductor core 20, the higher the characteristic impedance.

[0050] In this embodiment, the impedance ratio of the step impedance is changed mainly by changing the width of the first conductor inner core 20 , and the length of the high impedance line is the same as the length of the low impedance line.

[0051] The loading structure 22 based on the step impedance open-circuit branch will generate a transmission zero in the stopband, which can form a high roll-off and improve the stopband suppression. Multiple open-circuit branches will generate multiple transmission zeros and the reasonable distribution of zero positions can effectively suppress harmonics in a larger frequency range and expand the stopband width.

[0052] In this example, Fig.10 As shown, the twelve open branches form a stepped impedance and are symmetrically distributed about the center axis of the filter. The longest open branch is closer to the center line of the filter. The length of the open branches decreases from the middle to both sides, and the branch lengths are 930um*2, 905um*2, and 609um*2 respectively. The length of the open branches is not limited to the above values ​​and can be adjusted according to the design goals and requirements of different frequency bands. The design length of the open branches can be preliminarily determined by the following formula:

[0053] Z s1 tanθ s1 -Z s2 cotθ s2 =0

[0054]

[0055] Among them, Z s1 is the characteristic impedance of the first impedance line, Z s2 is the characteristic impedance of the second impedance line, θ s1 is the electrical length of the first impedance line, θ s2 is the electrical length of the second impedance line, l s1is the actual physical length of the first impedance line, l s2 is the actual physical length of the second impedance line, f zs Represents the desired frequency point for generating a transmission zero point, v represents the propagation speed of the electromagnetic wave on the transmission line, and v is less than the speed of light c.

[0056] It should be noted that the design length of the open-circuit branch obtained by theoretical calculation is inaccurate, and there are a lot of parasitic effects in the 3D electromagnetic software simulation. Therefore, the final length of the open-circuit branch needs to be obtained through parameter optimization of the 3D simulation software.

[0057] Specifically, Figures 2 to 9 As shown, the defective ground loading structure 11 includes a plurality of defective grounds arranged on the housing 10, the defective grounds are in the form of dumbbell-shaped grooves, and the dumbbell-shaped grooves are symmetrically structured with the center line of the rectangular micro-coaxial line 21 as the reference line, and the dumbbell-shaped grooves have a certain depth and do not damage the integrity of the lower surface of the housing 10. Each defective ground is arranged between two adjacent open-circuit branches, and the lengths of the plurality of defective grounds decrease from the middle to both sides.

[0058] More specifically, if Figure 2 and Figure 3 As shown, the defective ground includes a first slot body and a second slot body disposed on both sides of the first slot body and connected to the first slot body, and the width of the first slot body is smaller than the width of the second slot body. Specifically, in this embodiment, the width of the second slot body is 260um, the width of the first slot body is 90um, the length of the first slot body is 265um, and the slot height is 700um.

[0059] Changing the length and width of the second slot body and the first slot body can change the loading effect of the defect loading structure 11 on the filter. In this embodiment, there are five defective grounds, the longest defective ground is located at the center of the filter, and the remaining four defective grounds are symmetrically distributed on both sides of the longest defective ground and the length decreases from the middle to both sides. The lengths are 1850um+265um+1850um, 1650um+265um+1650um, and 450um+265um+450um, respectively. Due to the symmetrical setting, three defective grounds of different sizes are formed, which can improve the stopband suppression effect without increasing the size. The size of the defective ground is not limited to the above values ​​and can be adjusted according to different design goals and requirements.

[0060] The basic structure of this embodiment is a rectangular micro-coaxial line 21, which can be processed by electrochemical additive technology. The manufacturing process of the rectangular micro-coaxial line 21 based on this study has 10 layers, and the thickness of each layer is 50-100 um.

[0061] It should be noted that although the circular coaxial line has lower loss than the rectangular coaxial line, the air-filled circular coaxial line is not easy to process, and the rectangular coaxial line is more suitable for this layer-by-layer sequential processing manufacturing process.

[0062] The height of the rectangular micro-coaxial line 21 is only 800 um, and can be regarded as a quasi-planar structure. The transmitted electromagnetic wave is a TEM wave with extremely low loss.

[0063] The rectangular micro-coaxial line 21 needs to add periodically arranged release holes 12 during the electrochemical additive processing. Multiple release holes 12 are periodically arranged on the housing 10 to release the photoresist used in the manufacturing process. In addition, the defective ground can also serve as a large release hole to better release the photoresist. In the actual design, the number of release holes 12 should not be too many or too few. Too many will cause electromagnetic leakage, and too few will lead to incomplete removal of the photoresist, resulting in residue, affecting the quality and transmission performance of the rectangular micro-coaxial line 21. The characteristic impedance of the rectangular micro-coaxial line 21 is determined by the thickness and width of the first conductor core 20.

[0064] During manufacturing, in order to ensure the relative position between the first conductor core 20 and the inner wall of the housing 10, a plurality of dielectric support strips 30 are provided between the first conductor core 20 and the housing 10 to support the first conductor core 20 to achieve positioning, such as Figures 5 to 9 As shown, multiple dielectric support strips 30 are periodically arranged at a predetermined spacing. Too dense arrangement will result in excessive electromagnetic loss, and too sparse arrangement will result in insufficient support for the first conductor core 20, affecting the device structure and strength. Multiple dielectric support strips 30 are all inserted into the first conductor core 20, and both ends are embedded in the housing 10. One pair of side surfaces of the dielectric support strip 30 are respectively fixed to a pair of inner walls of the housing 10 to improve the stability of the dielectric support strip 30.

[0065] Specifically, Figure 11 to Figure 13 As shown, each rectangular micro-coaxial line-coplanar waveguide transition structure 25 includes a housing 10, a second conductor core, a dielectric support strip 30 and a boss support structure 18. One end of the second conductor core is fixedly connected to the first conductor core 20, and the other end of the second conductor core is provided with a boss. The boss is used to transition the second conductor core from horizontal placement to vertical placement. The upper end of the boss is located in the through opening opened on the housing 10 and the upper end surface is flush with the surface of the housing 10. The boss and the through opening constitute a coplanar waveguide interconnected with an external component. A dielectric support strip 30 is provided on the lower side of the boss. The dielectric support strip 30 is located between the second conductor core and the boss support structure 18, and is used for electromagnetic isolation and supporting the second conductor core. The boss support structure 18 is located on the inner wall of the housing 10 and is fixedly connected to the inner wall of the housing 10 to enhance the support of the dielectric support strip 30 to the second conductor core.

[0066] Specifically, the boss support structure 18 includes a square boss, one end of which is fixedly connected to the inner wall of the housing 10 , and the other end of which is in contact with the medium support strip 30 .

[0067] Specifically, the second conductor inner core is a 50Ω coaxial line, and the width direction of the second conductor inner core is a gradual structure, and its width gradually decreases from the first end to the second end, and its first end is connected to the first conductor inner core 20.

[0068] Specifically, the boss is a stepped transition structure, including a first rectangular block and a second rectangular block fixedly connected to the first rectangular block, the cross-sectional area of ​​the first rectangular block is larger than the cross-sectional area of ​​the second rectangular block, the first rectangular block is fixedly connected to the second conductor core, the upper end of the second rectangular block is located in a through opening opened on the shell 10 and the upper end surface is flush with the surface of the shell 10.

[0069] It should be noted that the distance between the center point of the second rectangular block and the two sides of the through-hole must meet the GSG200 probe test requirements.

[0070] When the high roll-off rectangular micro-coaxial line low-pass filter provided by the present invention is used, after the radio frequency signal is input through the input port 1 of the filter, the low-pass filter selectively passes the radio frequency signal for filtering, and the filtered signal is output from the output port 2. The designed rectangular micro-coaxial line-coplanar waveguide transition structure 25 makes the coplanar waveguide interface located on the upper surface of the overall device and a square boss is added under the dielectric support bar. While ensuring that the electrical performance is not significantly deteriorated, the supporting strength of the dielectric support bar to the second conductor core is improved, the test and other device board-level interconnection capabilities are improved, and the application scope of the filter is broadened.

[0071] The characteristics of the DC-21GHz rectangular micro-coaxial line 21 low-pass filter with a coplanar waveguide transition structure of the present invention are simulated, and the simulation results are as follows: Fig.14 As shown, where S 11 The return loss of the filter is S21, and the insertion loss of the filter is S21. The simulation results show that the return loss of the filter structure is better than 18dB in the DC-21GHz range, and the maximum insertion loss in the passband is 0.7dB, which is currently impossible for microstrip low-pass filters in the millimeter wave band. The transition band between the passband and the stopband is narrow, with a high roll-off characteristic. The stopband suppression is better than 40dB in the range of 26-58.6GHz, and better than 60dB in the range of 26-56GHz. Fig.14 It can be seen from the simulation results that the low-pass filter of the present invention has the advantages of low insertion loss, high roll-off, and a wider stop band, and provides a solution for high-performance millimeter-wave low-pass filters.

[0072] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A high roll-off rectangular micro-coaxial line low-pass filter, characterized in that: include: Rectangular micro coaxial line (21); Two rectangular micro-coaxial line-coplanar waveguide transition structures (25) are respectively located at two ends of the rectangular micro-coaxial line (21) and constitute an input port (1) and an output port (2) for connecting to external components; The loading structure (22) based on the step impedance open-circuit branch and the defective ground loading structure (11) are located in the middle of the rectangular micro-coaxial line (21) and are used to load the rectangular micro-coaxial line (21); wherein the loading structure (22) based on the step impedance open-circuit branch comprises a plurality of open-circuit branches, the plurality of open-circuit branches are evenly distributed on both sides of the rectangular micro-coaxial line (21) and are arranged in a mirror image with the center line of the rectangular micro-coaxial line (21) as the reference line, and the lengths of the plurality of open-circuit branches decrease from the middle to both sides; the defective ground loading structure (11) comprises a plurality of defective grounds, each defective ground is correspondingly arranged between two adjacent open-circuit branches, and the lengths of the plurality of defective grounds decrease from the middle to both sides; After the radio frequency signal is input through the input port (1) of the filter, it is filtered by the low-pass filter, and the filtered signal is output from the output port (2).

2. A high roll-off rectangular micro-coaxial line low-pass filter according to claim 1, characterized in that: The rectangular micro-coaxial line (21) comprises a shell (10) and a first conductor core (20), wherein the first conductor core (20) is wrapped in the shell (10), the axis of the first conductor core (20) coincides with the axis of the shell (10), there is a gap between the inner wall of the shell (10) and the first conductor core (20), and a cavity is formed between the two, and the cavity is filled with a medium for reducing transmission loss.

3. A high roll-off rectangular micro-coaxial line low-pass filter according to claim 2, characterized in that: The medium is air.

4. A high roll-off rectangular micro-coaxial line low-pass filter according to claim 2, characterized in that: The open-circuit branch comprises a first impedance line and a second impedance line connected in sequence, the length of the first impedance line is equal to the length of the second impedance line, the impedance of the first impedance line is greater than the impedance of the second impedance line, the end of the first impedance line is loaded on a rectangular micro-coaxial line (21), and the end of the second impedance line is separated from the housing (10) to achieve an open circuit.

5. A high roll-off rectangular micro-coaxial line low-pass filter according to claim 4, characterized in that: The design length of the open branch is preliminarily determined by the following formula: WITH s1 tanθ s1 -WITH s2 cotθ s2 =0 Among them, Z s1 is the characteristic impedance of the first impedance line, Z s2 is the characteristic impedance of the second impedance line, θ s1 is the electrical length of the first impedance line, θ s2 is the electrical length of the second impedance line, l s1 is the actual physical length of the first impedance line, l s2 is the actual physical length of the second impedance line, f zs Represents the desired frequency point for generating a transmission zero point, v represents the propagation speed of the electromagnetic wave on the transmission line, and v is less than the speed of light c.

6. A high roll-off rectangular micro-coaxial line low-pass filter according to claim 1, characterized in that: The defective land comprises a first groove body and two second groove bodies respectively arranged on both sides of the first groove body and connected to the first groove body, the two second groove bodies are symmetrically distributed with the center line of the rectangular micro-coaxial line (21) as the reference line, and the width of the first groove body is smaller than that of the second groove body.

7. A high roll-off rectangular micro-coaxial line low-pass filter according to claim 2, characterized in that: The rectangular micro-coaxial line-coplanar waveguide transition structure (25) comprises a shell (10), a second conductor core and a boss support structure (18), wherein the boss support structure (18) is located at the lower side of the second conductor core and is fixedly connected to the inner wall of the shell (10), one end of the second conductor core is fixedly connected to the first conductor core (20), and the other end of the second conductor core is provided with a boss, the upper end of the boss is located in a through opening opened on the shell (10) and the upper end surface is flush with the surface of the shell (10), the boss and the through opening constitute a coplanar waveguide interconnected with an external component, and the lower side of the second conductor core is also provided with a dielectric support strip (30) for electromagnetic isolation and supporting the second conductor core, and the dielectric support strip (30) is provided on the boss support structure (18).

8. The high roll-off rectangular micro-coaxial line low-pass filter according to claim 2, characterized in that: The boss support structure (18) comprises a square boss, one end of which is fixedly connected to the inner wall of the shell (10), and the other end of which is in contact with the medium support strip (30).

9. The high roll-off rectangular micro-coaxial line low-pass filter according to claim 2, characterized in that: A plurality of dielectric support strips (30) are arranged between the first conductor core (20) and the shell (10) to support the first conductor core (20) to achieve positioning. The plurality of dielectric support strips (30) are periodically arranged at a predetermined interval. The dielectric support strips (30) are inserted into the first conductor core (20) and have both ends embedded in the shell (10). A pair of side surfaces of the dielectric support strips (30) are respectively fixed to a pair of inner walls of the shell (10) to improve the stability of the dielectric support strips (30).

10. The high roll-off rectangular micro-coaxial line low-pass filter according to claim 1, characterized in that: The rectangular micro-coaxial line (21) has periodically arranged release holes (12).

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