A rectangular waveguide to microstrip probe transition structure for heat conduction through a quasi-coaxial cavity

Abstract

The present application relates to the field of microwave technology, in particular to a rectangular waveguide to microstrip probe transition structure through coaxial cavity heat conduction, which takes into account the heat conduction characteristics of the transition structure and the low insertion loss transmission characteristics of the microwave signal. The present application comprises: an input waveguide, a dielectric substrate, a probe, a coaxial cavity and a microstrip. By utilizing the extremely high thermal conductivity characteristics of metal materials, a metal cylindrical inner conductor is added between the microstrip and the probe area and the rectangular waveguide metal shell to construct a coaxial cavity, which is integrated into the ground return circuit of the probe and an efficient heat conduction channel. While effectively improving the heat conduction of the transition structure, good impedance matching and transmission performance are maintained, the structure is simplified, the cost is controllable, and significant economic advantages are achieved. At the same time, the present application realizes a new design of the heat conduction type rectangular waveguide to microstrip probe transition structure, enriches and expands the existing technical route, and has a very broad engineering practice prospect.

Description

Technical Field

[0001] This invention relates to the field of microwave (electromagnetic waves with wavelengths of 0.1 mm to 1 m) technology, and specifically to a rectangular waveguide-to-microstrip probe transition structure with heat conduction via a coaxial cavity. Background Technology

[0002] The rectangular waveguide-to-microstrip transition structure is one of the key passive circuits in microwave circuit systems, widely used in microwave RF front-end modules such as phased array radar, satellite communication, and 5G / 6G base stations to achieve efficient signal transmission between three-dimensional waveguide transmission lines and planar microstrip circuits. Rectangular waveguides are characterized by low loss, high power capacity, and good shielding, while microstrip lines have the advantages of small size, light weight, and easy integration with active circuits. The characteristic impedances and transmission modes of the two differ significantly; therefore, the core design goal of the transition structure is to achieve broadband impedance matching and ensure low insertion loss during mode switching.

[0003] In existing technologies, such transition structures typically employ probes or coupling rings inserted into the waveguide to achieve signal mode conversion and transmission via electromagnetic coupling. Simultaneously, appropriate grounding and microstrip matching structures are incorporated on the dielectric substrate to meet the circuit grounding and impedance matching requirements of microwave components. However, with the increasing output power of current microwave RF systems, the power handling capability of microstrip lines has become a critical bottleneck, necessitating a simultaneous upgrade in power capacity for the accompanying waveguide-to-microstrip transition structures.

[0004] However, in existing transition structures, the microwave heat loss generated by the probe or coupling loop and matching microstrip region is typically conducted slowly to the ground plane or waveguide outer wall through the dielectric substrate with low thermal conductivity. Due to the lack of a low thermal resistance heat conduction path, and the increased heat dissipation caused by the high-frequency skin effect, the heat generated in this region is difficult to dissipate effectively, easily leading to localized heat accumulation. This results in a significant increase in the local temperature of the dielectric substrate, affecting the circuit's operational stability and lifespan. Although some circuits use substrates with high thermal conductivity, such as ceramics, their high processing cost and long lead time make them inconvenient for engineering use.

[0005] In existing rectangular waveguide-to-microstrip transition structures, the microstrip extension direction is perpendicular to the longitudinal propagation direction of the rectangular waveguide, and the microstrip is inserted into the waveguide through the wide side of the rectangular waveguide (Zhang Shengchun et al., A Dielectric-Sealed Miniaturized Broadband Microstrip Waveguide Converter, Chinese Invention Patent, Application No. CN201610153471.5). This design achieves hermetic protection of the microwave component and overall structural miniaturization by introducing a dielectric-sealed structure in the probe and transition region, and also achieves good impedance matching over a wide frequency band. However, this structure does not employ any auxiliary heat dissipation methods, inevitably resulting in poor heat dissipation. Therefore, the key to improving the long-term operational stability and lifespan of power microwave systems lies in solving the bottleneck of heat accumulation in rectangular waveguide-to-microstrip transition structures during high-power operation under low thermal conductivity substrate conditions. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a rectangular waveguide to microstrip probe transition structure with heat conduction through a coaxial cavity. Under the premise of ensuring that the transmission characteristics of the transition from the rectangular waveguide to the microstrip are not affected, the traditional waveguide short-circuit cavity is improved into a coaxial cavity, that is, a metal cylindrical inner conductor is added for heat conduction to suppress local overheating of the microstrip. At the same time, this structure has the advantages of simple processing and compact design.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A rectangular waveguide-to-microstrip probe transition structure with heat conduction via a coaxial cavity includes an input waveguide, a dielectric substrate, a probe, a coaxial cavity, and a microstrip. The input waveguide, dielectric substrate, probe, and coaxial cavity are stacked and connected sequentially from bottom to top. One end face of the microstrip, whose normal is parallel to the longitudinal direction of the input waveguide, is connected to the wide side of the waveguide, and the other end face serves as the output end.

[0009] Furthermore, the dielectric substrate is fixed to the upper part of the input waveguide, and partially extends into the waveguide wall of the input waveguide to the other side of the microstrip for fixation. The thermal conductivity of this dielectric substrate is less than 10 W / (m·K), resulting in poor thermal conductivity.

[0010] Furthermore, the metal probes attached to the dielectric substrate are connected to the metal conduction bands of the microstrip.

[0011] Furthermore, the coaxial cavity is formed by short-circuiting one end of the coaxial line, and the inner conductor at the other end is connected to the probe for heat conduction.

[0012] Furthermore, the microstrip includes a main microstrip and a matching microstrip as the output end, and a shielding cavity is provided on the upper part of the microstrip. One end of the shielding cavity is closely connected to the outer side of a wide surface of the circumferential surface of the coaxial cavity.

[0013] Furthermore, the cross-sectional area of ​​the inner conductor of the coaxial cavity is greater than 0.02 square millimeters, which facilitates processing and makes it easy to conduct the heat generated by the probe and microstrip to the short-circuit surface of the coaxial cavity.

[0014] The working principle of the rectangular waveguide-to-microstrip probe transition structure with heat conduction via a coaxial cavity according to the present invention is as follows:

[0015] On the one hand, its probe functions as a transition probe between ordinary rectangular waveguides and microstrip probes, that is, to transmit TE signals propagating within a rectangular waveguide. 10 The mode electric field is concentrated and confined in a local region between the probe and the wide side of the opposite waveguide, feeding the electromagnetic energy in the rectangular waveguide into the microstrip, thus achieving a smooth conversion and energy transition between waveguide modes and microstrip modes.

[0016] On the other hand, the electrical length of the coaxial cavity is set to approximately one-quarter of the operating frequency. According to transmission line theory, the input impedance of the coaxial cavity, viewed from the probe location, tends to infinity, approximately equivalent to a high-frequency open-circuit state. When the electromagnetic wave reaches the short-circuit surface of the coaxial cavity, total reflection occurs. The reflected wave and the incident wave coherently superimpose in the probe region, forming a standing wave, causing the electric field strength at that location to reach its peak, thereby enhancing the coupling effect of the probe. Simultaneously, this coaxial cavity serves the dual purpose of grounding and efficient heat conduction. The inner conductor, made of metal, is grounded, forming a low thermal resistance conduction path between the microstrip and probe regions and the rectangular waveguide metal shell. Heat generated by transmission losses is rapidly dissipated through this path, effectively reducing local heat accumulation and temperature rise on the low thermal conductivity substrate, thereby improving the thermal reliability and long-term operational stability of this transition structure in high-power applications.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] 1. This invention utilizes the extremely high thermal conductivity of metallic materials to construct a coaxial cavity by adding a cylindrical metal inner conductor between the microstrip and probe regions and the rectangular waveguide metal shell, integrating it as both the probe's grounding loop and a highly efficient heat conduction channel. The shape and cross-sectional area of ​​this inner conductor are controllable, allowing for a much larger cross-sectional area than the metal conductor on the substrate, resulting in a much lower thermal resistance than the grounding conductor or gold wire on the substrate.

[0019] 2. This invention introduces a coaxial cavity conductor heat conduction path, which effectively improves the heat dissipation of the transition structure while maintaining good impedance matching and transmission performance.

[0020] 3. This invention, through a coaxial cavity structure, not only provides a stable grounding channel for the probe, solving the problem of poor grounding in traditional transition structures, but also has the advantages of easy processing and low cost, resulting in significant economic advantages.

[0021] 4. This invention features a simplified structure and controllable cost, achieving a novel design for the transition structure from a thermally conductive rectangular waveguide to a microstrip probe, enriching and expanding existing technical approaches. By enhancing the system's adaptability to high-temperature environments, this structure effectively improves the long-term operational stability and durability of the equipment, demonstrating extremely broad prospects for engineering practice. Attached Figure Description

[0022] Figure 1 This is a three-dimensional schematic diagram of a rectangular waveguide-to-microstrip probe transition structure with heat conduction via a coaxial cavity, according to Embodiment 1 of the present invention.

[0023] Figure 2 This is a top view schematic diagram of a rectangular waveguide-to-microstrip probe transition structure with heat conduction via a coaxial cavity, according to Embodiment 1 of the present invention.

[0024] Figure 3 This is a simulation result of the S-parameter curve of a rectangular waveguide-to-microstrip probe transition structure with heat conduction through a coaxial cavity, according to Embodiment 1 of the present invention.

[0025] Figure 4 This is a thermal simulation result diagram of a rectangular waveguide-to-microstrip probe transition structure with heat conduction through a coaxial cavity, according to Embodiment 1 of the present invention.

[0026] Figure 5 This is a thermal simulation result of the transition structure from a traditional rectangular waveguide to a microstrip probe in the W-band.

[0027] The markings in the figure are as follows: 1-Input waveguide, 2-Dielectric substrate, 3-Probe, 4-Coaxial cavity, 41-Perimeter surface, 5-Microstrip, 51-Main microstrip, 52-Matching microstrip, 53-Shielding cavity. Detailed Implementation

[0028] To make the objectives, technical problems solved, and technical solutions of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the invention.

[0029] Example 1:

[0030] Figure 1 This is a three-dimensional schematic diagram of a specific embodiment of the present invention. Figure 2This is a top-view schematic diagram, including an input waveguide 1, a dielectric substrate 2, a probe 3, a coaxial cavity 4, and a microstrip 5. The input waveguide 1 and the coaxial cavity 4 are chamfered with a radius of 0.5 mm according to processing requirements. In a specific embodiment of the invention oriented towards the W-band, the input waveguide 1 uses a standard rectangular waveguide BJ900 with a cross-sectional dimension of 2.54 mm × 1.27 mm, and the main mode operating frequency covers 75 GHz ~ 110 GHz. The coaxial cavity 4 has the same cross-section as the input waveguide 1 and is aligned with it, with its end short-circuited, and a cavity height of 0.81 mm. The dielectric substrate 2 uses Rogers RT / duroid 5880 material, with a relative permittivity of 2.2, a thermal conductivity of approximately 0.2 W / (m·K), and a thickness of 0.127 mm. The dielectric substrate 2 is located above the input waveguide 1. Its plane of symmetry overlaps with that of the input waveguide 1 and the coaxial cavity 4. One end of the substrate is chamfered with a radius of 0.5 mm and extends 0.53 mm into the wide wall of the input waveguide 1. The suspended dimension inside the input waveguide 1 is 1.27 mm × 1 mm. The planes of symmetry of the microstrip 5, the dielectric substrate 2, and the probe 3 overlap. The microstrip 5 uses the same substrate as the dielectric substrate 2. Its conductor is connected to the probe 3. Both are made of copper with a thickness of 0.017 mm and are chamfered with a radius of 0.03 mm at right angles. The probe 3 has a width of 0.2 mm. One end of the probe is connected to the inner conductor of the coaxial cavity 4 by conductive adhesive or low-temperature soldering. The inner conductor has a radius of 0.25 mm, and its axis is 0.539 mm away from the wide surface of the microstrip 5. The matching microstrip 52 has a conductor length of 0.398 mm and a width of 0.18 mm. The probe 3 is connected to the main microstrip 51 after impedance matching via the matching microstrip 52. The main microstrip 51 has a conductor width of 0.38 mm, corresponding to 50 Ω. The shielding cavity 53 located above the microstrip 5 has a cross-sectional width and height of 1 mm and 0.517 mm, respectively, and a length of 0.778 mm.

[0031] Figure 3 This is a simulation result of the S-parameter curve in the W-band of a specific embodiment of the present invention. Within the entire W-band frequency range of 75 GHz to 110 GHz, the return loss is better than 20 dB, demonstrating excellent impedance matching characteristics, significantly reducing reflection loss and enhancing coupling efficiency. Simultaneously, the insertion loss remains below 0.055 dB throughout the entire W-band frequency band, providing excellent and efficient transmission for the system.

[0032] Figure 4This is a thermal simulation result diagram of a specific embodiment of the present invention. The peripheral surface 41 of the input waveguide 1 and the coaxial cavity 4, as well as the thickness of the short-circuit surface, are all equal to the length of the shielding cavity 53 above the microstrip 5, i.e., 0.778 mm. Under ambient temperature of 25 ℃ and input power of 5 W, the results show that the highest temperature in this embodiment is approximately 33.2 ℃, concentrated on the main microstrip 51. The temperature gradually decreases along the matching microstrip 52, probe 3, and the inner conductor of the coaxial cavity 4, with the lowest temperature being approximately 31.7 ℃. This indicates that heat is efficiently conducted to the short-circuit surface of the coaxial cavity 4 through the inner conductor. The highest temperature on probe 3 is approximately 32.6 ℃, with a uniform temperature distribution and no obvious local heat accumulation.

[0033] For comparison, the traditional rectangular waveguide-to-microstrip probe transition structure in the W-band was optimized. The resulting probe width was exactly the same as the conduction band width of the matching microstrip, both being 0.228 mm. The probe length was 0.584 mm, the conduction band length of the matching microstrip was 0.354 mm, and the short-circuit cavity height was 0.787 mm. Other dimensions remained consistent with Specific Embodiment 1. This transition structure exhibited a return loss better than 22 dB across the entire W-band frequency range.

[0034] Figure 5 This is a thermal simulation result of a traditional rectangular waveguide-to-microstrip probe transition structure in the W-band. Under ambient temperature of 25°C and input power of 5 W, the results show that the highest temperature of this traditional transition structure is approximately 41.2°C, concentrated near the probe, while the lowest temperature occurs at the main microstrip, at approximately 40.6°C. This traditional transition structure does not create an efficient heat conduction channel, resulting in the inability to effectively dissipate the accumulated heat in this area. In contrast, the transition structure in Specific Embodiment 1, which uses a coaxial cavity 4 for heat conduction, reduces the highest temperature by approximately 8°C, and the highest temperature on probe 3 by approximately 8.6°C; the temperature of the main microstrip 51 also decreases by approximately 7.4°C. This indicates that the structure not only reduces the temperature of the transition itself but also the temperature of the main microstrip 51. These results demonstrate that the inner conductor of the coaxial cavity 4 creates an efficient heat conduction channel, effectively suppressing local heat accumulation and thus significantly improving the long-term operational stability of the system.

[0035] Example 2:

[0036] In this embodiment, the inner conductor of the coaxial cavity 4 can be replaced with other cross-sectional shapes, such as square or triangular, and the longitudinal direction can also be non-uniform. The outer conductor, i.e., the peripheral surface 41, can also be other shapes, and the short surface can also be non-planar. The whole is still equivalent to the coaxial cavity 4. By adjusting the probe 3, matching the size of the microstrip 52, the size and position of the inner conductor of the coaxial cavity 4, and completing the impedance matching, the function of the present invention can also be realized.

[0037] Example 3:

[0038] In this embodiment, the input waveguide 1 is changed from the standard rectangular waveguide BJ900 to a standard waveguide covering other microwave frequency bands (such as the Ka-band standard waveguide BJ320) or other non-standard waveguides such as height-reduced waveguides. By adjusting the dimensions of the dielectric substrate 2, probe 3, and microstrip 5, as well as the dimensions and position of the inner conductor of the coaxial cavity 4, the operating frequency can be changed, and the present invention can be used in other microwave frequency bands, thus achieving the function of the present invention.

[0039] Example 4:

[0040] In this embodiment, the dielectric substrate 2 is replaced with other high-frequency materials, the thickness of which depends on the actual operating frequency and assembly requirements. The structure of other parts is the same as that of Embodiment 1, and the function of the present invention can also be achieved.

[0041] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the scope of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A rectangular waveguide-to-microstrip probe transition structure with heat conduction via a coaxial cavity, comprising an input waveguide (1), a dielectric substrate (2), a probe (3), a coaxial cavity (4), and a microstrip (5), characterized in that: The input waveguide (1), dielectric substrate (2), probe (3), and coaxial cavity (4) are stacked and connected sequentially from bottom to top. One end face of the microstrip (5), whose normal is parallel to the longitudinal direction of the input waveguide (1), is connected to the wide side of the waveguide, and the other end face serves as the output end. The thermal conductivity of the dielectric substrate (2) is less than 10. W / (m·K), fixed to the upper part of the input waveguide (1), and partially extending into the waveguide wall of the input waveguide (1) to the other side of the microstrip (5) for fixation; the metal probe (3) attached to the dielectric substrate (2) is connected to the metal conductor of the microstrip (5); the coaxial cavity (4) is formed by short-circuiting one end of the coaxial line, and the inner conductor of its other end is connected to the probe (3) for heat conduction; the microstrip (5) includes a main microstrip (51) and a matching microstrip (52) as the output end, and a shielding cavity (53) is provided on the upper part of the microstrip (5), one end of which is closely connected to the outer side of a wide surface of the peripheral surface (41) of the coaxial cavity (4).

2. The rectangular waveguide-to-microstrip probe transition structure with heat conduction via a coaxial cavity as described in claim 1, characterized in that: The inner conductor cross-sectional area of ​​the coaxial cavity (4) is greater than 0.02 square millimeters, which is convenient for processing and facilitates the conduction of heat generated by the probe (3) and microstrip (5) to the short-circuit surface of the coaxial cavity (4).

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