Waveguide coaxial filter, design method thereof, and cryogenic receiver

Abstract

The present invention discloses a waveguide coaxial filter, a design method thereof, and a cryogenic receiver. The waveguide coaxial filter comprises: a waveguide input port for inputting electromagnetic wave signals; a waveguide filtering structure for transmitting electromagnetic wave signals in the form of a waveguide transmission line and filtering the spectrum signal of a set frequency in the electromagnetic wave signal; a waveguide coaxial conversion structure, provided in the output port cavity of the waveguide filtering structure, for realizing mode conversion and impedance matching between the waveguide transmission line and the coaxial transmission line, and then converting the waveguide transmission line mode signal into a coaxial transmission line mode signal; a coaxial output port, for connecting to the coaxial transmission line to output the coaxial transmission line mode signal. The present invention integrates the waveguide filtering structure and the waveguide coaxial conversion structure into an integrated design, which optimizes the insertion loss performance as a whole, greatly reduces the volume and weight of the device, is beneficial to the interconnection of the system and the stability of the system structure, and can be applied to cryogenic receivers in the aerospace field.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave power devices, and in particular to an integrated waveguide coaxial filter having both waveguide filtering and waveguide coaxial conversion functions, a design method thereof, and a cryogenic receiver containing the waveguide coaxial filter. Background Art

[0002] Microwave filter components are crucial in communication links, and their performance directly impacts transmission performance. Radio cryogenic receivers are used to receive weak electromagnetic signals from space and amplify them with low noise. Commercial amplifiers generally cannot perfectly match the receiver's receiving frequency, often exceeding the receiver's frequency range. To mitigate the interference of unwanted spectral signals with the desired signal due to amplification, microwave filters are widely used in communication systems.

[0003] Microwave filters are categorized by transmission line type into coaxial transmission lines, microstrip lines, metal waveguides, and substrate-integrated systems. Microstrip lines and substrate-integrated systems both rely on dielectric substrates, while metal waveguides rely on hollow metal tubes of fixed dimensions. Waveguide transmission lines offer advantages such as low insertion loss and high stability, making them widely used in high-frequency systems. Coaxial transmission lines are commonly used for low-frequency signal transmission.

[0004] As the name suggests, waveguide filters achieve filtering functions through waveguide transmission lines. Waveguide transmission lines are metal hollow tube structures. Compared with microstrip transmission lines and coaxial transmission lines, waveguide transmission lines have better environmental adaptability and structural stability. At the same time, waveguide transmission lines have better transmission performance for the transmission of electromagnetic wave signals.

[0005] There are generally two ways to implement waveguide filters:

[0006] (1) Using the cutoff characteristics of the waveguide transmission line itself to achieve filtering function, such as Figure 1 This is the simplest way to achieve filtering. The waveguide's cutoff characteristic refers to the fact that it can effectively transmit electromagnetic waves above a specific frequency, but cannot effectively propagate below this frequency. This specific frequency is called the cutoff frequency. When the frequency of electromagnetic waves falls below the cutoff frequency, the waveguide exhibits strong attenuation, which can be used to implement a high-pass filter.

[0007] (2) The cutoff characteristics are realized by introducing a transmission zero point by loading a resonant diaphragm, such as Figure 2 Introducing discontinuities in the waveguide, such as metal columns and diaphragms, creates a transmission zero point, thereby achieving cutoff characteristics.

[0008] Of the two implementations described above, the second implementation can achieve better out-of-band suppression and a smaller structural size than the first implementation, but the insertion loss is higher than the first implementation.

[0009] In the practical application of X-band cryogenic receiver systems, front-end passive components typically use low-loss waveguide transmission lines for signal transmission. When transmitting electromagnetic wave signals to a cryogenic low-noise amplifier (LNA), signals above 7.2 GHz must be filtered out. Since the LNA utilizes a coaxial transmission line, a separate waveguide-to-coaxial converter is required to connect the rectangular waveguide (TE10 mode) and the coaxial transmission line (TEM mode) to achieve mode conversion and impedance matching, thus enabling signal transmission to the downstream system.

[0010] There are two ways to implement a waveguide-to-coaxial converter:

[0011] (1) End-launch structure, that is, the waveguide input port and the coaxial output port are in the same direction. The end-launch structure is conducive to system interconnection. By feeding the coaxial probe into the back wall of the rectangular waveguide to generate excitation, the waveguide impedance value is adjusted by loading a multi-section stepped impedance in the waveguide cavity, eliminating the in-band adverse reflection, achieving matching between the waveguide transmission line and the coaxial transmission line, and obtaining excellent signal transmission performance.

[0012] Figure 3 It is a waveguide-coaxial converter with a contactless feeding end-launch structure. The waveguide input port 1 and the coaxial output port 2 are in the same direction, and the coaxial output port 2 does not contact the multi-section stepped impedance 3 in the waveguide cavity. Figure 3 As shown in A in the figure. This feeding form can achieve a wider working bandwidth and smaller insertion loss, but this structure requires higher processing precision.

[0013] Figure 4 A waveguide-coaxial converter with contact-feed end-launch structure is proposed. The waveguide input port 1 and the coaxial output port 2 are in the same direction, and the coaxial output port 2 is in contact with the multi-section stepped impedance 3 in the waveguide cavity. Figure 4 As shown in B in the figure, this type of feeding method can bring a 3:1 bandwidth. At the same time, the contact method makes the structure relatively stable, but the insertion loss is relatively large.

[0014] (2) 90° angle structure, that is, the waveguide input port and the coaxial output port are in a 90° cross structure. This type of waveguide-coaxial converter has a compact structure and low insertion loss, but the input and output ports are not in the same direction, which is not conducive to system cascading and the stability of the system structure.

[0015] Figure 5A waveguide-to-coaxial converter with a 90° angle is proposed. A coaxial probe 4 is inserted into the wide wall of a rectangular waveguide. The outer conductor 5 of the coaxial transmission line is connected to the wide wall of the rectangular waveguide. The waveguide input port 1 is at a 90° angle to the coaxial probe 4. The coaxial probe 4 inserted into the waveguide forms a radiating antenna, exciting electromagnetic waves in the TE10 mode. By adjusting the position and insertion depth of the coaxial probe 4, conversion between a waveguide transmission line and a coaxial transmission line can be achieved.

[0016] Current cryogenic receiver systems use two discrete components, a waveguide filter and a waveguide-to-coaxial converter, to achieve signal filtering and transmission line conversion. The two components are connected via screw holes on the flange. This approach has the following problems:

[0017] (1) High insertion loss. The performance of the two devices can only be designed separately, and the final insertion loss is the sum of the insertion losses of the two devices. In addition, the unevenness of the connecting surface of the two devices and the deviation during connection will cause additional insertion loss, affecting the performance of the system.

[0018] (2) Large size. The discrete device connections are large, occupying limited system space and weight, and are not conducive to the overall mechanical design of the system. Summary of the Invention

[0019] The embodiments of the present application provide a waveguide coaxial filter that integrates a waveguide filtering structure and a waveguide coaxial conversion structure, thereby solving the problems of large insertion loss and large volume caused by the cascade connection of two discrete components, a waveguide filter and a waveguide coaxial converter, in the prior art.

[0020] In order to solve the above technical problems, in a first aspect, an embodiment of the present application provides a waveguide coaxial filter, comprising:

[0021] A waveguide input port, used for inputting electromagnetic wave signals;

[0022] A waveguide filter structure is used to transmit the electromagnetic wave signal in the form of a waveguide transmission line and filter the spectrum signal of a set frequency in the electromagnetic wave signal;

[0023] A waveguide-coaxial conversion structure is provided in the output port cavity of the waveguide filter structure, and is used to realize mode conversion and impedance matching between the waveguide transmission line and the coaxial transmission line, thereby converting the waveguide transmission line mode signal output by the waveguide filter structure into a coaxial transmission line mode signal;

[0024] The coaxial output port is used to connect to the coaxial transmission line to output the coaxial transmission line mode signal.

[0025] Preferably, the waveguide input port, the waveguide filtering structure and the waveguide coaxial conversion structure are formed by an integrated all-metal tube.

[0026] Preferably, the waveguide filtering structure includes:

[0027] The first waveguide transition section and the second waveguide transition section are used to achieve filtering effect;

[0028] Waveguide transmission section, used to achieve out-of-band signal suppression;

[0029] The output port cavity is used as the output port of the filtered signal and also serves as a waveguide cavity for realizing waveguide-to-coaxial conversion;

[0030] The first waveguide transition section, the waveguide transmission section, the second waveguide transition section and the output port cavity are sequentially connected and formed as an integrated whole.

[0031] More preferably, the waveguide transmission section is a curved waveguide structure.

[0032] Preferably, the waveguide-to-coaxial conversion structure includes a T-shaped impedance matching column, the T-shaped impedance matching column is provided on the bottom wide wall of the output port cavity, and the coaxial output port is provided on the output end face of the output port cavity;

[0033] The height of the coaxial output port is greater than the height of the T-shaped impedance matching column, so as to meet the following requirements: after the coaxial probe of the coaxial transmission line is inserted into the coaxial output port, the coaxial probe is suspended above the T-shaped impedance matching column, and the coaxial probe does not contact the T-shaped impedance matching column.

[0034] Furthermore, the T-shaped impedance matching column includes a first column and a second column, both of which are rectangular columns, and the length and width of the first column are smaller than those of the second column, and the wide side of the first column is connected to the middle of the wide side of the second column and is integrally formed.

[0035] Furthermore, the gap between the coaxial probe and the T-shaped impedance matching column is capacitive, and the coaxial probe, the T-shaped impedance matching column and the bottom wide wall of the output port cavity form a magnetic coupling ring, which completes the conversion of the signal between the waveguide transmission line mode and the coaxial transmission line mode through magnetic coupling.

[0036] Preferably, the first waveguide transition section and the second waveguide transition section are centrally symmetrical structures.

[0037] Preferably, the T-shaped impedance matching column is located in the center of the bottom wall width of the output port cavity; the coaxial output port is located in the center of the output end face width of the output port cavity, and the coaxial output port and the waveguide input port are in the same direction.

[0038] In a second aspect, an embodiment of the present application further provides a method for designing a waveguide coaxial filter, comprising the following steps:

[0039] Electromagnetic simulation software was used to simulate and optimize the waveguide filter structure. During the first simulation, a straight waveguide was used for the waveguide transmission section to determine the dimensions of the first waveguide transition section, the second waveguide transition section, and the straight waveguide. After the simulation optimization was completed, the straight waveguide was replaced with a curved waveguide with the same waveguide dimensions. The effects of different bending radii on performance were simulated to determine the optimal bending radius for the curved waveguide.

[0040] After completing the simulation design of the waveguide filter structure, the simulation design of the waveguide-to-coaxial conversion structure was added. The dimensions of the T-shaped impedance matching column and the height and depth of the coaxial probe were simulated and optimized using electromagnetic simulation software to ultimately determine the specific dimensions of the waveguide-to-coaxial conversion structure.

[0041] The dimensions of the waveguide input port and the coaxial output port are based on the standard waveguide dimensions of the adapted mode.

[0042] In a third aspect, an embodiment of the present application further provides a cryogenic receiver, comprising:

[0043] Antenna, used to collect electromagnetic wave signals in space;

[0044] The waveguide coaxial filter is used to filter the spectrum signal of the set frequency in the electromagnetic wave signal, transmit the electromagnetic wave signal in the form of a waveguide transmission line, and then convert the waveguide transmission line mode signal into a coaxial transmission line mode signal;

[0045] a low-temperature low-noise amplifier, configured to receive the coaxial transmission line mode signal and perform low-noise amplification;

[0046] The waveguide input port of the waveguide coaxial filter is connected to the antenna, and the coaxial output port of the waveguide coaxial filter is connected to the low-temperature low-noise amplifier; the antenna has a waveguide output port, and the low-temperature low-noise amplifier has a coaxial input port, the waveguide input port of the waveguide coaxial filter is connected to the waveguide output port of the antenna, and the coaxial output port of the waveguide coaxial filter is connected to the coaxial input port of the low-temperature low-noise amplifier.

[0047] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0048] 1. The integrated design of the waveguide filter structure and the waveguide coaxial conversion structure optimizes the insertion loss performance as a whole. The insertion loss performance is equivalent to the contribution of only one traditional device, and the additional insertion loss contribution caused by the cascade of two devices is avoided.

[0049] 2. The waveguide filter structure and the waveguide-to-coaxial converter structure are integrated into a single design. The design of the waveguide-to-coaxial converter structure is completed by utilizing the rear space of the waveguide filter structure. This significantly reduces the size and weight of the device, conserving limited system space and avoiding the additional space and weight requirements of cascading two devices. While meeting performance requirements, it also offers the advantages of miniaturization and lightweighting.

[0050] 3. The waveguide filter structure of the waveguide coaxial filter provided by the present invention combines the advantages of both conventional waveguide filter implementations, namely, the waveguide cutoff characteristic and the resonant diaphragm loading. This invention utilizes the inherent cutoff characteristics of the waveguide transmission line to achieve filtering, offering advantages such as simple structure, high mechanical strength, and low insertion loss. Furthermore, the innovative incorporation of curved waveguides further reduces size, achieving even greater device miniaturization.

[0051] 4. The waveguide-to-coaxial conversion structure of the waveguide-to-coaxial filter provided by the present invention integrates the advantages of both the traditional end-launch structure and the 90° angle structure of the waveguide-to-coaxial converter. The present invention utilizes the final waveguide cavity of the waveguide filter structure to achieve the waveguide-to-coaxial conversion function. It innovatively combines a non-contact T-shaped impedance matching column, coaxial probe excitation, and the wide wall of the waveguide bottom surface to form a magnetic coupling loop. This magnetic coupling method achieves mode conversion and impedance matching between the waveguide transmission line and the coaxial transmission line. The waveguide input port and the coaxial output port are aligned in the same direction, which facilitates system interconnection and structural stability. Furthermore, the structure is compact and insertion loss is low.

[0052] 5. The waveguide coaxial filter provided by the present invention integrates the waveguide filtering structure and the waveguide coaxial conversion structure into an integrated design, and adopts an integrally formed all-metal tube, which meets the requirements of low insertion loss, strong structural stability, miniaturization and lightweight in aerospace environment applications, and can be used in cryogenic receivers in the aerospace field. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0054] Figure 1 This is a schematic diagram of the structure for achieving filtering by utilizing the cutoff characteristics of the waveguide transmission line itself;

[0055] Figure 2 Schematic diagram of the structure for loading the resonant diaphragm to achieve filtering;

[0056] Figure 3 Schematic diagram of the waveguide-coaxial converter with contactless feeding end-launch structure;

[0057] Figure 4 Schematic diagram of the waveguide-to-coaxial converter with contact-feed end-launch structure;

[0058] Figure 5 This is a schematic diagram of the structure of a waveguide-to-coaxial converter with a 90° angle structure;

[0059] Figure 6 This is a schematic diagram of the overall structure of the waveguide coaxial filter provided in an embodiment of the present application;

[0060] Figure 7 An exploded view of the waveguide coaxial filter provided in an embodiment of the present application;

[0061] Figure 8 Schematic diagram of the main structure of the waveguide coaxial filter provided in an embodiment of the present application;

[0062] Figure 9 Schematic diagram of the upper cover structure of the waveguide coaxial filter provided in an embodiment of the present application;

[0063] Figure 10 A schematic diagram of a waveguide coaxial filter provided in an embodiment of the present application;

[0064] Figure 11 This is a schematic structural diagram of a T-shaped impedance matching column in an embodiment of the present application;

[0065] Figure 12 Schematic diagram of the positional relationship between the T-shaped impedance matching column and the coaxial probe in an embodiment of the present application;

[0066] Figure 13 This is a schematic diagram of the size design of the waveguide input port in an embodiment of the present application;

[0067] Figure 14 Schematic diagram of the replacement of straight waveguide and curved waveguide in the embodiment of the present application;

[0068] Figure 15 Schematic diagram of the waveguide coaxial conversion structure design in the embodiment of the present application; (a) front view, (b) top view;

[0069] Figure 16 The simulation and measured results of the reflection coefficient and out-of-band suppression of the waveguide input port of the waveguide coaxial filter in the embodiment of the present application are as follows;

[0070] Figure 17 The simulation and measured results of the reflection coefficient and out-of-band suppression of the coaxial output port of the waveguide coaxial filter in the embodiment of the present application are as follows;

[0071] Figure 18These are the simulation and measured results of the insertion loss between the waveguide input port and the coaxial output port of the waveguide-coaxial filter in the embodiment of the present application.

[0072] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0073] The embodiments of the present application provide a waveguide coaxial filter that integrates a waveguide filtering structure and a waveguide coaxial conversion structure, thereby solving the problems of large insertion loss and large volume caused by the cascade connection of two discrete components, a waveguide filter and a waveguide coaxial converter, in the prior art.

[0074] To better understand the above technical solutions, exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numbers in different drawings represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of devices consistent with certain aspects of the present application, as detailed in the appended claims.

[0075] Figures 6-10 This is a schematic diagram of the structure and principle of the waveguide coaxial filter provided in an embodiment of the present application. The waveguide coaxial filter includes:

[0076] Waveguide input port 1, used for inputting electromagnetic wave signals;

[0077] A waveguide filter structure is used to transmit the electromagnetic wave signal input from the waveguide input port 1 in the form of a waveguide transmission line and filter the spectrum signal of a set frequency in the electromagnetic wave signal;

[0078] A waveguide-to-coaxial conversion structure is provided in the output port cavity of the last section of the waveguide filter structure, and is used to achieve mode conversion and impedance matching between the waveguide transmission line and the coaxial transmission line, thereby converting the waveguide transmission line mode signal output by the waveguide filter structure into a coaxial transmission line mode signal;

[0079] The coaxial output port 2 is used to output the coaxial transmission line mode signal.

[0080] Among them, the waveguide input port 1, the waveguide filtering structure and the waveguide coaxial conversion structure adopt an integrated all-metal tube.

[0081] The waveguide filter structure utilizes the inherent cutoff characteristics of the waveguide transmission line to achieve filtering. Specifically, the waveguide transmission line has a specific cutoff frequency. When the signal frequency is lower than this cutoff frequency, the waveguide cannot effectively transmit the signal, thereby suppressing out-of-band signals. This embodiment utilizes this characteristic to design a filter structure to achieve out-of-band signal suppression.

[0082] In a preferred embodiment, the waveguide filter structure includes a first waveguide transition section 6, a waveguide transmission section 7, a second waveguide transition section 8, and an output port cavity 9, which are sequentially connected. The first waveguide transition section 6 and the second waveguide transition section 8 are centrally symmetrical and function as filters. The waveguide transmission section 7 is used to suppress out-of-band signals. The output port cavity 9 serves as the output port for the filtered signal and also serves as a waveguide cavity for waveguide-to-coaxial conversion.

[0083] The length of the waveguide transmission section 7 determines the out-of-band suppression; a longer length improves the out-of-band suppression. To ensure both high out-of-band suppression and device miniaturization, this section of the waveguide used for out-of-band suppression is designed as a curved waveguide structure, connecting the first waveguide transition section 6 and the second waveguide transition section 8.

[0084] The waveguide filter structure combines the advantages of traditional waveguide filter implementations: the waveguide cutoff characteristic and the resonant diaphragm loading. By utilizing the waveguide transmission line's inherent cutoff characteristics to achieve filtering, it offers advantages such as simple structure, high mechanical strength, and low insertion loss. Furthermore, the innovative addition of curved waveguides further reduces size, achieving even greater device miniaturization.

[0085] The waveguide input port 1 is integrally connected to the first waveguide transition section 6. The size of the output port surface of the output port surface cavity 9 is consistent with that of the waveguide input port 1, so as to achieve impedance matching.

[0086] In a preferred embodiment, the waveguide input port 1 is a BJ84 standard waveguide input port, using the TE10 mode. The size of the waveguide aperture of the output aperture cavity 9 is consistent with that of the waveguide input port 1, also being a standard BJ84 waveguide size.

[0087] In a preferred embodiment, the coaxial output port 2 is an SMA standard coaxial connector and adopts a TEM mode.

[0088] The waveguide input port 1 and the coaxial output port 2 are in the same direction.

[0089] The waveguide-to-coaxial conversion structure includes a T-shaped impedance matching column 10, which is fixed on the bottom wide wall of the output port cavity 9, preferably located in the center of the width of the bottom wide wall; the coaxial output port 2 is horizontally arranged on the output end face of the output port cavity 9, preferably located in the center of the width of the output end face and in the same direction as the waveguide input port 1.

[0090] The coaxial output port 2 is arranged parallel to the bottom wide wall of the output port cavity 9, and the height of the coaxial output port 2 is greater than the height of the T-shaped impedance matching post 5. This ensures that after the coaxial probe 4 of the coaxial transmission line is inserted into the coaxial output port 2, the coaxial probe 4 and the T-shaped impedance matching post 10 do not contact each other, and the gap between them is capacitive. The coaxial probe 4, the T-shaped impedance matching post 10, and the bottom wide wall of the output port cavity 9 form a magnetic coupling loop, which converts the signal between the TEM mode of the coaxial line and the TE10 mode of the rectangular waveguide through magnetic coupling.

[0091] Combine Figure 11 The T-shaped impedance matching column 10 includes a first column 11 and a second column 12. Both the first column 11 and the second column 12 are rectangular columns. The length and width of the first column 11 are smaller than those of the second column 12. The wide side of the first column 11 is connected to the middle of the wide side of the second column 12. The first column 11 and the second column 12 are integrally formed. The impedance matching column thus constructed has an overall T-shaped structure. The T-shaped impedance matching column can achieve impedance matching through two-stage matching dimensions.

[0092] In a preferred embodiment, a first curved skirt 13 is formed at the bottom of the first column 11, and a second curved skirt 14 is formed at the bottom of the second column 12. The curved skirt is connected and fixed to the bottom wide wall of the output port cavity 9, which can enhance the firmness and stability of the connection.

[0093] Combine Figure 12 The T-shaped impedance matching post 10 is mounted on the bottom wide wall of the output port cavity 9, with the first post 11 located on the inside and the second post 12 on the outside. Specifically, the second post 12 is located on the side closest to the coaxial output port 2. After the coaxial probe 4 is inserted into the coaxial output port 2, the tip of the coaxial probe 4 is suspended above the T-shaped impedance matching post 10, without contacting the post. The T-shaped impedance matching post 10 and the coaxial probe 4 are positioned symmetrically about the center of the bottom wide wall of the output port cavity 9.

[0094] In this embodiment, the T-shaped impedance matching post 10 employs a two-stage matching approach. By adjusting the dimensions of the two stages and the gap between the post and the coaxial probe, impedance matching is achieved over a wide bandwidth. Furthermore, a non-contact approach is employed to achieve both impedance matching and mode conversion. This approach effectively mitigates the issues of high electromagnetic wave emission and slow conversion at the connection point caused by the structural differences between the coaxial line and the waveguide, thereby increasing the conversion bandwidth.

[0095] The invention utilizes a T-shaped impedance matching post, a coaxial probe, and a wide waveguide bottom wall to achieve impedance matching between the waveguide and coaxial converters. This structure combines the advantages of both traditional end-launch and 90° angle waveguide-to-coaxial converters. The waveguide input and coaxial output ports are aligned, facilitating system interconnection and ensuring a stable structure. Furthermore, the structure is compact and minimizes insertion loss.

[0096] In a preferred embodiment, the waveguide input port 1, waveguide filtering structure, and waveguide coaxial conversion structure are integrated into a main body 100, which is formed as an integrally formed all-metal tube. Specifically, the main body 100 comprises the waveguide input port 1, the first waveguide transition section 6, the waveguide transmission section 7, the second waveguide transition section 8, the output port cavity 9, and the T-shaped impedance matching post 10. This is achieved through an integrated molding process to ensure that the device's performance meets the requirements of aerospace applications.

[0097] The coaxial output port 2 is located on the rear cover 300, which mates with the output end face of the main body 100. Screws and locating pins secure the rear cover 300 and main body 100 to ensure precise assembly. The upper cover 200 sits above the rear cover 300 and main body 100, securing the upper cover 200 to the rear cover 300 and main body 100 with screws. The screws are arranged according to the waveguide's orientation to ensure zero electromagnetic leakage after assembly.

[0098] In a preferred embodiment, the main body 100, upper cover 200, and rear cover 300 are all made of aluminum alloy. The main body 100, upper cover 200, and rear cover 300 enclose a waveguide filter and waveguide coaxial conversion cavity. The main body 100 and upper cover 200 are separated at the extreme edge of the E-plane where electromagnetic wave energy is relatively low.

[0099] The waveguide coaxial filter provided in this embodiment integrates the waveguide filtering structure and the waveguide coaxial conversion structure into an integrated design, thereby optimizing the insertion loss performance as a whole. The insertion loss performance is equivalent to the contribution of only one traditional device, and the additional insertion loss contribution caused by the cascade of two devices is avoided.

[0100] At the same time, the design of the waveguide-to-coaxial conversion structure is completed by utilizing the rear space of the waveguide filter structure, which greatly reduces the size and weight of the device, saves limited system space, and avoids the additional space and weight required by cascading two devices. While meeting performance requirements, it has the advantages of miniaturization and lightweight.

[0101] In addition, the present invention adopts an integrally formed all-metal tube, which meets the requirements of low insertion loss, strong structural stability, miniaturization and lightweight in aerospace environment applications, and can be applied to aerospace systems.

[0102] The design method and application effect of the present invention are described below with a specific embodiment.

[0103] China's space industry has flourished in recent years. The fourth phase of my country's lunar exploration program proposes deploying lunar-orbit VLBI equipment on the Queqiao-2 relay satellite, establishing a lunar-orbit VLBI station to conduct joint observations with ground-based VLBI stations, and conducting the first Earth-Moon ultra-long baseline (VLBI) scientific experiment. Based on this, the development of China's first satellite-borne ultra-high-sensitivity X-band cryogenic receiver was proposed.

[0104] The waveguide coaxial filter provided in this embodiment is designed to serve X-band cryogenic receivers. Installed inside the X-band cryogenic receiver's dewar, it is cooled to 100K along with the cryogenic components within the dewar, operating at a frequency of 8 GHz to 9 GHz. The waveguide input port of the waveguide coaxial filter is connected to the waveguide output port of the antenna, and the coaxial output port of the waveguide coaxial filter is connected to the coaxial input port of a cryogenic low-noise amplifier.

[0105] The antenna collects weak electromagnetic wave signals in space, and then filters out signals before 7.2 GHz through the waveguide coaxial filter provided in this embodiment. The signals are then transmitted through the waveguide and converted into coaxial transmission line mode signals and transmitted to a low-temperature low-noise amplifier for low-noise amplification.

[0106] During design, first determine the size of the X-band BJ84 standard waveguide, and then determine the size of the waveguide input port 1, such as Figure 13 As shown, the waveguide input port 1 is a rectangular cavity, the wide side length c of the waveguide input port 1 is 28.5 mm, and the narrow side length d of the waveguide input port 1 is 12.62 mm. The shape and size of the output port cavity 9 are consistent with those of the waveguide input port 1.

[0107] Then, the electromagnetic simulation software is used to simulate and optimize the waveguide filter structure. Figure 14As shown, during the initial simulation, the waveguide transmission section 7 was replaced with a rectangular straight waveguide 7' instead of a curved waveguide structure. The lengths and dimensions of the first waveguide transition section 6, the second waveguide transition section 8, and the replaced straight waveguide were determined. After the simulation optimization was completed, the straight waveguide was replaced with a curved waveguide with the same waveguide dimensions and length, and the effects of different bending radii R on performance were simulated.

[0108] The contribution of passive components to the system's noise temperature comes from their insertion loss, which is equal to their noise figure. The conversion formula for noise figure and noise temperature is NF = T / T0 + 1, where NF is the noise figure, T is the noise temperature, and T0 is the ambient temperature (typically 290K). Therefore, at room temperature, an insertion loss of 0.1dB will result in a noise temperature contribution of 6.7K, which is the normal noise temperature contribution of a straight waveguide due to conductor losses and other factors. Simulations of selecting the bending radius for curved waveguides revealed that a bend radius that is too small would not effectively achieve device miniaturization, while a bend radius that is too large would result in insertion loss exceeding 0.1dB and deteriorate out-of-band suppression. The experimental balance was determined to be the maximum bend radius at which the insertion loss of the curved waveguide does not exceed 0.1dB. The final bend radius was determined to be R = 14.8mm.

[0109] After completing the simulation design of the waveguide filter structure, the design of the waveguide coaxial conversion structure is added, and the size of the T-shaped impedance matching column 10 and the height and depth of the coaxial probe 4 are simulated and optimized through electromagnetic simulation software. Figure 15 As shown, the specific dimensions of the waveguide coaxial conversion structure are finally determined as shown in Table 1 below.

[0110] Table 1 Waveguide-to-coaxial conversion structure size design

[0111] parameter Dimensions (mm) parameter Dimensions (mm) a 28.5 b 12.62 a1 4.83 b1 5.22 a2 5.34 b2 6.11 a3 7.4 b3 1 a4 5.1 b4 2.1 a5 0.51 a6 2.57

[0112] In Table 1, a represents the length of the wide side of the output port cavity 9, a1 is the distance from the T-shaped impedance matching column 10 to the back wall of the output port cavity 9 (i.e., the wall opposite to the output port end face, hereinafter referred to as the waveguide back wall), a2 is the distance from the inner side of the second column 12 (i.e., the side away from the waveguide back wall) to the waveguide back wall, a3 is the distance from the inner side of the first column 11 to the waveguide back wall, a4 is the insertion distance of the coaxial probe, a5 is the length of the second column 12, and a6 is the length of the T-shaped matching column 10; b represents the length of the narrow side of the output port cavity 9, b1 is the height of the T-shaped matching column 5, b2 is the distance from the center of the coaxial probe to the bottom of the waveguide, b3 is the width of the second column 12, and b4 is the width of the first column 11.

[0113] In this embodiment, the mechanical design of the waveguide coaxial filter is made of all-aluminum alloy (2A12-H112) and is processed into three parts: the main body 100, the upper cover 200, and the back cover 300, which are then fastened together using screws. The main body 100 includes a waveguide input port 1, a first waveguide transition section 6, a waveguide transmission section 7, a second waveguide transition section 8, an output port cavity 9, and a T-shaped impedance matching column 10. It adopts an integrated molding process, and the processing accuracy is controlled to ±0.02mm to ensure device performance. The distribution of screws is based on the waveguide direction to ensure that there is no electromagnetic leakage after assembly. The back cover 300 is the mounting surface of the coaxial connector, and the coaxial output port 2 is provided on the back cover 300. The assembly of the back cover 300 and the main body 100 is fastened and positioned by screws and positioning pins to ensure assembly accuracy. The separation position of the main body 100 and the upper cover 200 is selected from the edge of the E surface where the electromagnetic wave energy is smaller.

[0114] The total length of the waveguide coaxial filter is 120mm. Compared to conventional technologies, the length of a discrete commercial X-band waveguide filter @Qualwave is 300mm, and the length of a commercial X-band post-fed waveguide coaxial converter @Qualwave is 73.35mm. The total length of the two cascaded devices is 373.35mm. This shows that the size of the waveguide coaxial filter provided by this embodiment is much smaller than the sum of the dimensions of the two conventional cascaded devices. The integrated design effectively achieves device miniaturization.

[0115] Figure 16 The simulation and measured results of the reflection coefficient and out-of-band suppression of the waveguide input port 1 of the waveguide coaxial filter designed and processed in this embodiment are given. Figure 17 The simulation and measured results of the reflection coefficient and out-of-band suppression of the coaxial output port 2 of the waveguide coaxial filter designed and processed in this embodiment are given. Figure 18 The simulation and measured results of the insertion loss between the waveguide input port 1 and the coaxial output port 2 of the waveguide coaxial filter designed and processed in this embodiment are given. Figures 16 to 18 It can be seen that the waveguide coaxial filter designed and processed in this embodiment has an out-of-band suppression of better than 27dB at 7.2GHz, an insertion loss of better than 0.22dB in the operating frequency band of 8-9GHz, and a reflection coefficient of better than 15dB. In traditional technology, a discretely designed waveguide coaxial converter usually results in an insertion loss of 0.1dB, and a waveguide filter usually results in an insertion loss of 0.4dB, for a total insertion loss of 0.5dB. The insertion loss of the waveguide coaxial filter designed and processed in this embodiment is much smaller than the insertion loss caused by the traditional cascade of two devices. At an operating temperature of 100K, the system noise temperature can be reduced by 6K, greatly improving the system receiving sensitivity.

[0116] The waveguide coaxial filter provided in this embodiment does not use any processes or materials that are prohibited or restricted for use in aerospace, and at the same time has good mechanical properties, meeting the requirements of aerospace application environments for low insertion loss, strong structural stability, miniaturization, and lightweight. It can be directly used in the aerospace field and installed on systems or devices in the aerospace field to realize the transmission, filtering, and coaxial conversion functions of electromagnetic wave signals.

[0117] It should be understood that although the terms "first," "second," and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element without departing from the scope of the exemplary embodiments.

[0118] The directional terms such as up, down, left, right, front, back, front, back, top, and bottom mentioned or possibly mentioned in this specification are defined relative to the structure shown in the drawings. They are relative concepts and may vary depending on the location and usage of the device. Therefore, these or other directional terms should not be interpreted as restrictive.

[0119] The above description is only a preferred embodiment of the present application and does not limit the present application in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present application, and these improvements and supplements should also be considered as the scope of protection of the present application. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present application by using the technical content disclosed above are all equivalent embodiments of the present application; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present application are still within the scope of the technical solution of the present application.

Claims

1. A waveguide coaxial filter, characterized in that: include: A waveguide input port, used for inputting electromagnetic wave signals; A waveguide filter structure is used to transmit the electromagnetic wave signal in the form of a waveguide transmission line and filter the spectrum signal of a set frequency in the electromagnetic wave signal; A waveguide-coaxial conversion structure is provided in the output port cavity of the waveguide filter structure, and is used to realize mode conversion and impedance matching between the waveguide transmission line and the coaxial transmission line, thereby converting the waveguide transmission line mode signal output by the waveguide filter structure into a coaxial transmission line mode signal; A coaxial output port, configured to be connected to a coaxial transmission line to output the coaxial transmission line mode signal; The waveguide input port, waveguide filter structure and waveguide coaxial conversion structure adopt an integrated all-metal tube; The waveguide-to-coaxial conversion structure includes a T-shaped impedance matching column, which is arranged on the bottom wide wall of the output port cavity, and the coaxial output port is arranged on the output end surface of the output port cavity; The height of the coaxial output port is greater than the height of the T-shaped impedance matching column, so as to meet the following requirements: after the coaxial probe of the coaxial transmission line is inserted into the coaxial output port, the coaxial probe is suspended above the T-shaped impedance matching column, and the coaxial probe does not contact the T-shaped impedance matching column.

2. The waveguide coaxial filter according to claim 1, wherein The waveguide filtering structure comprises: The first waveguide transition section and the second waveguide transition section are used to achieve filtering effect; Waveguide transmission section, used to achieve out-of-band signal suppression; The output port cavity is used as the output port of the filtered signal and also serves as a waveguide cavity for realizing waveguide-to-coaxial conversion; The first waveguide transition section, the waveguide transmission section, the second waveguide transition section and the output port cavity are sequentially connected and formed as an integrated whole.

3. The waveguide coaxial filter according to claim 2, wherein: The waveguide transmission section is a curved waveguide structure.

4. The waveguide coaxial filter according to claim 1, wherein The T-shaped impedance matching column includes a first column and a second column. The first column and the second column are both rectangular columns, and the length and width of the first column are smaller than those of the second column. The wide side of the first column is connected to the middle of the wide side of the second column and are integrally formed.

5. The waveguide coaxial filter according to claim 2, wherein: The gap between the coaxial probe and the T-shaped impedance matching column is capacitive. The coaxial probe, the T-shaped impedance matching column and the bottom wide wall of the output port cavity form a magnetic coupling ring, which completes the conversion of the signal between the waveguide transmission line mode and the coaxial transmission line mode through magnetic coupling.

6. The waveguide coaxial filter according to claim 5, wherein: The first waveguide transition section and the second waveguide transition section are centrally symmetrical structures; and / or The T-shaped impedance matching column is located in the center of the bottom wall width of the output port cavity; the coaxial output port is located in the center of the output end face width of the output port cavity and is in the same direction as the waveguide input port.

7. A method for designing a waveguide coaxial filter according to any one of claims 1 to 6, characterized in that: The steps include: Electromagnetic simulation software was used to simulate and optimize the waveguide filter structure. During the first simulation, a straight waveguide was used for the waveguide transmission section to determine the dimensions of the first waveguide transition section, the second waveguide transition section, and the straight waveguide. After the simulation optimization was completed, the straight waveguide was replaced with a curved waveguide with the same waveguide dimensions. The effects of different bending radii on performance were simulated to determine the optimal bending radius for the curved waveguide. After completing the simulation design of the waveguide filter structure, the simulation design of the waveguide-to-coaxial conversion structure was added. The dimensions of the T-shaped impedance matching column and the height and depth of the coaxial probe were simulated and optimized using electromagnetic simulation software to ultimately determine the specific dimensions of the waveguide-to-coaxial conversion structure. The dimensions of the waveguide input port and the coaxial output port are based on the standard waveguide dimensions of the adapted mode.

8. A cryogenic receiver, characterized in that: include: Antenna, used to collect electromagnetic wave signals in space; The waveguide coaxial filter according to any one of claims 1 to 6, configured to filter a spectrum signal of a set frequency in the electromagnetic wave signal, transmit the electromagnetic wave signal in the form of a waveguide transmission line, and then convert the waveguide transmission line mode signal into a coaxial transmission line mode signal; a low-temperature low-noise amplifier, configured to receive the coaxial transmission line mode signal and perform low-noise amplification; The antenna has a waveguide output port, the low-temperature low-noise amplifier has a coaxial input port, the waveguide input port of the waveguide coaxial filter is connected to the waveguide output port of the antenna, and the coaxial output port of the waveguide coaxial filter is connected to the coaxial input port of the low-temperature low-noise amplifier.

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