A millimeter wave microstrip waveguide converter

Abstract

The application belongs to the technical field of microstrip waveguide converters, and discloses a millimeter wave microstrip waveguide converter, wherein the waveguide is a stepped structure, the first waveguide part has a first height, the second waveguide part has a second height, the first height is greater than the second height, a waveguide cavity is formed in the first waveguide part, and a waveguide opening is arranged at the junction of the first waveguide part and the second waveguide part; the first end of the first PCB board extends into the waveguide cavity, the second end of the first PCB board is arranged on the surface of the second waveguide part, a microstrip line and a grounding plate are arranged on the first PCB board, a probe is located in the waveguide cavity, a transmission line is located on the upper side of the second waveguide part, at least a part of an impedance conversion section is located in the waveguide opening, the grounding plate is arranged on the part of the first PCB board located on the surface of the second waveguide part, and a matching conversion structure is arranged on the lower side of the part of the first PCB board located in the waveguide cavity, so that the application has the advantages of simple structure, small size, simple processing and wide working bandwidth.

Description

Technical Field

[0001] This invention relates to microstrip waveguide converters, and more particularly to a millimeter-wave microstrip waveguide converter. Background Technology

[0002] With the rapid development of millimeter-wave technology, various high-performance millimeter-wave integrated circuits have been widely used in medical diagnostics, security imaging, industrial flaw detection, broadband communication, radar detection, and other fields. Microstrip lines, due to their ease of fabrication, excellent transmission characteristics, and ease of interconnection with microwave integrated circuits, have become the most commonly used microwave guiding structure in microwave integrated circuits. Waveguides, on the other hand, are widely used in both microwave and millimeter-wave frequency bands due to their low-loss characteristics. Therefore, microstrip waveguide conversion has become the most common conversion method in microwave systems.

[0003] Currently, the main structures for microstrip-to-waveguide conversion include probe transitions, ridge waveguide transitions, and ridge fin transitions. In common E-plane and H-plane probe structures, the probe is perpendicular to the waveguide aperture normal and requires a short-circuit structure of 1 / 4 wavelength, resulting in a large overall conversion unit size. Ridge fin transitions typically have a length of about one wavelength and are structurally complex, requiring the waveguide to be split in half and the probe sandwiched between them. The ridge portion of the ridge waveguide transition structure is difficult to fabricate, has a narrow bandwidth, and is prone to poor contact between the ridge transition structure and the microstrip line in millimeter-wave applications, affecting practical reliability. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention discloses a millimeter-wave microstrip waveguide converter, which has the advantages of simple structure, small size, simple processing, and wide operating bandwidth.

[0005] The specific technical solution of the present invention is as follows: A millimeter-wave microstrip waveguide converter, comprising: The waveguide has a stepped structure and includes a first waveguide portion and a second waveguide portion. The first waveguide portion has a first height, and the second waveguide portion has a second height. The first height is greater than the second height. A waveguide cavity is formed within the first waveguide portion, and a waveguide opening is provided at the junction of the first waveguide portion and the second waveguide portion. A first PCB board has a first end extending into a waveguide cavity and a second end disposed on the surface of a second waveguide portion. The first PCB board is provided with a microstrip line and a ground plane. The microstrip line includes a probe, an impedance conversion section, and a transmission line. The probe is located inside the waveguide cavity, and the transmission line is located on the upper side of the second waveguide portion. At least a portion of the impedance conversion section is located at the waveguide opening for connecting the probe and the transmission line. The ground plane is disposed on the portion of the first PCB board located on the surface of the second waveguide portion. A matching conversion structure is disposed on the lower side of at least the portion of the first PCB board located within the waveguide cavity.

[0006] This application extends the first PCB board directly into the waveguide cavity using a stepped waveguide, which allows for a reasonable layout of the microstrip line and effectively avoids the limitation of reserving a 1 / 4 wavelength short path in the traditional E-plane / H-plane probe structure, thereby reducing the overall size of the microstrip waveguide converter. The microstrip line of this application adopts a three-segment structure, which, together with the ground plane on the surface of the second waveguide section and the matching conversion structure on the underside of the first PCB board, can achieve low-loss matching conversion over a wide bandwidth. This structure is simple and easy to manufacture. Therefore, this application has the advantages of simple structure, compact size, easy processing and assembly, and wide operating bandwidth.

[0007] Preferably, the waveguide cavity has an inverted tuning step near the waveguide opening, and the impedance conversion section is located below the tuning step.

[0008] In this application, an inverted tuning step is provided. This structure can convert the electric field polarization direction of electromagnetic waves. Specifically, after the tuning step is introduced, the tuning step causes the electric field polarization direction of the electromagnetic waves generated by the probe to be twisted by 90 degrees, so that it can be smoothly coupled into the waveguide cavity and transmitted along the waveguide, thereby achieving efficient conversion while effectively realizing a compact structure.

[0009] Preferably, the ground plane has two sets, which are symmetrically arranged on the first PCB board with the axis of the transmission line as the line of symmetry.

[0010] This structure enhances the electromagnetic field confinement capability of the transmission line in the region outside the waveguide port, effectively suppressing potential losses. At the same time, the symmetrical layout ensures the purity of mode conversion, thereby improving the transmission stability of the microstrip waveguide converter.

[0011] Preferably, the matching transformation structure includes: A matching conversion cavity is disposed within the waveguide cavity, and the matching conversion cavity is located on the lower side of the first PCB board.

[0012] The matching conversion cavity can adjust the region of strongest electromagnetic field distribution within the waveguide cavity. In other words, the matching conversion cavity enables the probe to couple in the region of highest electric field energy, thereby enhancing the probe's excitation efficiency and receiving sensitivity, and effectively reducing coupling loss in a small-sized structure.

[0013] Preferably, the matching conversion cavity is provided with a ridge transition structure, and the first PCB board is disposed on the ridge transition structure.

[0014] The ridge transition structure provided in this application can enhance the concentration of electromagnetic field in the matching conversion cavity. Specifically, the ridge transition structure can achieve the convergence of electromagnetic field, thereby improving the coupling strength of the probe and effectively reducing the space required for the matching conversion cavity to achieve good matching, thereby reducing the size of the matching conversion cavity. This also greatly reduces the size of the microstrip waveguide converter, and better achieves a compact and miniaturized structure.

[0015] Preferably, a microstrip copper foil is present between the ridge transition structure and the first PCB board.

[0016] This structure can effectively eliminate any gaps that may exist between the ridge transition structure and the first PCB board, thereby improving the reliability of the transition.

[0017] Preferably, a second PCB board is disposed inside the matching conversion cavity, and the surface of the second PCB board has a second microstrip copper strip, and the first PCB board is connected to the second microstrip copper strip; The second PCB board and the microstrip copper foil are provided with at least one concentric first metal via.

[0018] This application uses a second PCB board and a microstrip copper foil to replace the ridge transition structure, which can greatly reduce the processing difficulty and cost; while the concentric first metal via forms a shielding via, which can effectively suppress electromagnetic energy leakage and cavity resonance in the matching conversion cavity, thereby ensuring in-band flatness.

[0019] Preferably, the matching transformation structure includes: A third PCB board extends from inside the waveguide cavity to the surface of the second waveguide portion, and an adhesive layer is present between the third PCB board and the first PCB board. The third PCB board has a microstrip copper strip on at least one side, and the third PCB board and the microstrip copper strip are provided with at least one concentric second metal via.

[0020] This structure can replace the matching conversion cavity and ridge transition structure, which is beneficial to the simplification of the structure and can be easily integrated with the subsequent circuit module design. In addition, this structure can maintain the field concentration and broadband matching characteristics comparable to the matching conversion cavity and ridge transition structure, thereby ensuring the application effect of the microstrip waveguide converter.

[0021] Preferably, the first PCB board has a microstrip copper foil four on the side away from the microstrip line, and the first PCB board, the third PCB board, and the microstrip copper foil four are provided with at least one concentric third metal via.

[0022] This structure can avoid the radiation loss of millimeter-wave signals into the external space and avoid the large requirements for assembly tolerances of microstrip waveguide converters, thereby ensuring product consistency.

[0023] Preferably, the third PCB board has a microstrip copper strip on the side away from the adhesive layer, and the second metal via and the third metal via extend to the microstrip copper strip.

[0024] This structure can better maintain low insertion loss and high port isolation.

[0025] Compared with existing technologies, the microstrip waveguide converter of the present invention is small in size and simple in structure, and the depth of the matching conversion cavity can be reduced to 1 / 15 of the wavelength; the microstrip line of the present invention does not need to be connected to the metal structure, thereby effectively increasing the redundancy of processing and assembly and facilitating production; since the microstrip conversion structure of the present invention is parallel to the normal direction of the waveguide port, it can better improve the integration and thus expand the application range. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of Embodiment 1 of the present invention; Figure 2 for Figure 1 Top view; Figure 3 This is a schematic diagram of the matching conversion cavity in Embodiment 1 of the present invention; Figure 4 for Figure 1 A sectional view; Figure 5 This is a schematic diagram of the return loss simulation results for Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the insertion loss simulation results for Embodiment 1 of the present invention; Figure 7 This is a schematic diagram of Example 2; Figure 8 This is a schematic diagram of Embodiment 3 of the present invention; Figure 9 This is a schematic diagram of the return loss simulation results for Embodiment 3 of the present invention; Figure 10 This is a schematic diagram of the insertion loss simulation results for Embodiment 3 of the present invention.

[0027] In the diagram: 1-waveguide; 2-first PCB board; 3-first waveguide section; 4-second waveguide section; 5-waveguide cavity; 6-microstrip line; 7-ground plane; 8-probe; 9-impedance conversion section; 10-transmission line; 11-waveguide port; 12-tuning step; 13-matching conversion cavity; 14-ridge transition structure; 15-microstrip copper foil one; 16-microstrip copper foil two; 17-first metal via; 18-third PCB board; 19-adhesive layer; 20-microstrip copper foil three; 21-second metal via; 22-microstrip copper foil four; 23-third metal via. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0029] Example 1 like Figures 1-4 As shown, a millimeter-wave microstrip waveguide converter includes a waveguide 1, a first PCB board 2, and a matching conversion structure. The waveguide 1 has a stepped structure, including a first waveguide portion 3 and a second waveguide portion 4. The first waveguide portion 3 has a first height, and the second waveguide portion 4 has a second height, wherein the first height is greater than the second height. A waveguide cavity 5 is formed within the first waveguide portion 3, and a waveguide opening 11 is provided at the junction of the first waveguide portion 3 and the second waveguide portion 4. A first end of the first PCB board 2 extends into the waveguide cavity 5, and a second end of the first PCB board 2 is provided with... A microstrip line 6 and a ground plane 7 are disposed on the surface of the second waveguide portion 4. The microstrip line 6 includes a probe 8, an impedance conversion section 9, and a transmission line 10. The probe 8 is located inside the waveguide cavity 5, and the transmission line 10 is located on the upper side of the second waveguide portion 4. At least a portion of the impedance conversion section 9 is located at the waveguide port 11 for connecting the probe 8 and the transmission line 10. The ground plane 7 is disposed on the portion of the first PCB board 2 located on the surface of the second waveguide portion 4. The matching conversion structure is disposed on the lower side of the portion of the first PCB board 2 located at least inside the waveguide cavity 5. Furthermore, the ground plane 7 has two sets, symmetrically arranged on the first PCB board 2 with the axis of the transmission line 10 as the line of symmetry.

[0030] In this embodiment, the stepped structure of the waveguide 1 is a single-step structure, wherein the upper step of the stepped structure is the upper surface of the first waveguide portion 3, and the lower step of the stepped structure is the upper surface of the second waveguide portion 4. The upper and lower steps are parallel, and there is a step connecting surface between the upper and lower steps that is perpendicular to the upper / lower steps. Therefore, the first waveguide portion 3 has a relatively large first height, and the second waveguide portion 4 has a relatively small second height. A waveguide cavity 5 is formed inside the first waveguide portion 3 for transmitting millimeter-wave signals.

[0031] In this embodiment, the first end of the first PCB board 2 extends into the waveguide cavity 5 along the waveguide opening 11, and the second end of the first PCB board 2 is laid flat and fixed on the upper surface of the second waveguide portion 4. In this embodiment, the microstrip line 6 has a three-segment structure and is arranged on the upper surface of the first PCB board 2. The microstrip line 6, along the signal transmission direction, consists of a probe 8 located in the waveguide cavity 5, an impedance conversion segment 9 passing through the waveguide opening 11, and a transmission line 10 located on the upper surface of the second waveguide portion 4. Alternatively, it can be understood that the microstrip line 6 extends from the second waveguide portion 4 into the waveguide cavity 5 through an air cavity.

[0032] In this embodiment, the first PCB board 2 is a commonly used millimeter-wave board material, specifically Rogers RO5880, with a dielectric constant of 2.2 and a thickness of 0.127mm; the transmission line 10 has a specification of 50 ohms and a width of 0.3mm, the impedance conversion section 9 has a width of 0.2mm, and the probe 8 has a size of 0.9mm × 1.2mm; the waveguide port 11 is a standard W-band waveguide 1 with a size of 1.27mm × 2.54mm.

[0033] In this embodiment, an inverted tuning step 12 is provided near the waveguide opening 11 in the waveguide cavity 5, and the impedance conversion section 9 is located below the tuning step 12. The tuning step 12 is a stepped structure protruding from the first waveguide portion 3 into the waveguide cavity 5. Its inverted shape reduces the size of the waveguide cavity 5 at the waveguide opening 11, and this structure is used to change the transmission direction of the electromagnetic wave, twisting the electric field polarization direction of the electromagnetic wave induced by the probe 8 by 90 degrees, so that the transmission of the electromagnetic wave is in the same direction as the extension of the waveguide cavity 5, thereby better realizing the conversion of the microstrip waveguide 1.

[0034] To address the matching and miniaturization issues in millimeter-wave conversion, in this embodiment, the matching conversion structure includes a matching conversion cavity 13 disposed within the waveguide cavity 5, located on the lower side of the first PCB board 2. This achieves the purpose of actively adjusting the location of the strongest electromagnetic field distribution within the waveguide cavity 5, thereby drawing the electric field peak to the probe 8. Thus, without relying on a traditional quarter-wavelength short-pathway, efficient coupling can be achieved with a cavity depth of only about 1 / 15 of the wavelength.

[0035] To better concentrate the electromagnetic field and effectively reduce the size of the matching conversion cavity 13, a ridge transition structure 14 is provided inside the matching conversion cavity 13, and the first PCB board 2 is disposed on the ridge transition structure 14. Furthermore, a microstrip copper foil 15 is provided between the ridge transition structure 14 and the first PCB board 2. It can be understood that the microstrip waveguide 1 conversion essentially utilizes the probe 8 to connect the quasi-TEM mode transmitted by the transmission line 10 with the TE mode transmitted by the waveguide 1. 10 The modes are switched between each other, and the signal is propagated continuously with the lowest possible loss.

[0036] Therefore, based on the technical solution of Embodiment 1, when the millimeter-wave signal propagates along the transmission line 10 on the upper surface of the first PCB board 2 in quasi-TEM mode, the electric field is mainly distributed between the microstrip line 6 and the ground reference surface of the second waveguide section 4; as the signal enters the impedance conversion section 9 and finally reaches the probe 8 located in the waveguide cavity 5, a local electromagnetic excitation source is formed at the probe 8. This excitation source excites an electromagnetic field in the waveguide cavity 5 that matches the size of the waveguide cavity 5; at this time, in the electromagnetic field generated by the excitation, the electric field polarization direction of the electromagnetic wave is mainly perpendicular to the plane where the first PCB board 2 is located, while the TE in the waveguide 1 10 The electric field polarization direction of the electromagnetic wave generated by the mode needs to be parallel to the extension direction of the probe 8. Therefore, in this embodiment, the tuning step 12 is used to twist the electric field polarization direction of the electromagnetic wave generated by the excitation by 90 degrees, thereby better meeting the coupling requirements of the two. Furthermore, the matching conversion cavity 13 can change the size of the waveguide 1, thereby enabling TE 10 The peak electric field of the mode is pulled and concentrated towards the position of probe 8, thereby adjusting the position with the greatest electromagnetic field strength, thus better shortening the coupling length and reducing losses.

[0037] The microstrip waveguide converter of Example 1 was simulated using electromagnetic full-wave analysis software. The simulation results are as follows: Figure 5 and Figure 6 As shown, the simulation results show that the return loss is less than -10dB and the insertion loss is no more than 0.55dB in the frequency range from 70GHz to 100GHz, which meets the conversion requirements of W-band microstrip waveguide 1.

[0038] Example 2 like Figure 7 As shown, this embodiment can replace the ridge transition structure 14. Specifically, a second PCB board is provided in the matching conversion cavity 13. The surface of the second PCB board has a microstrip copper strip 16. The first PCB board 2 is connected to the microstrip copper strip 16. The second PCB board and the microstrip copper strip 16 are provided with at least one concentric first metal via 17.

[0039] In Example 1, the ridge transition structure 14 can effectively concentrate the electromagnetic field, so that the electric field energy is highly concentrated below the probe 8. In this example, the microstrip copper foil 16 and the first metal via 17 can also achieve this purpose well.

[0040] Example 3 like Figure 8As shown, this embodiment can effectively replace the matching conversion cavity 13 and the ridge transition structure 14. Specifically, the matching conversion structure includes a third PCB board 18, which extends from the waveguide cavity 5 to the surface of the second waveguide portion 4. An adhesive layer 19 is present between the third PCB board 18 and the first PCB board 2. At least one side of the third PCB board 18 has a microstrip copper foil 20, and the third PCB board 18 and the microstrip copper foil 20 are provided with at least one concentric second metal via 21. To better utilize this embodiment, the side of the first PCB board 2 away from the microstrip line 6 has a microstrip copper foil 22, and the first PCB board 2, the third PCB board 18, and the microstrip copper foil 22 are provided with at least one concentric third metal via 23. Specifically, the side of the third PCB board 18 away from the adhesive layer 19 has the microstrip copper foil 20, and the second metal via 21 and the third metal via 23 extend to the microstrip copper foil 20.

[0041] In this embodiment, a microstrip line 6 is disposed on the upper side of the first PCB board 2, and a microstrip copper foil 22 is disposed on the lower side of the first PCB board 2 in the region from the surface of the second waveguide portion 4 to the waveguide port 11. A microstrip copper foil 20 is disposed on the upper surface of the third PCB board 18, and the microstrip copper foil 20 on this side is located at the position corresponding to the waveguide cavity 5. A microstrip copper foil 20 is also disposed on the lower surface of the third PCB board 18, and the microstrip copper foil 20 on this side extends from the upper side of the second waveguide portion 4 into the waveguide cavity 5. Based on the above structure, the portion of the third PCB board 18 located in the waveguide cavity 5 and the microstrip copper foil 20 on both sides are provided with concentric second metal vias 21. The first PCB board 2, the third PCB board 18, the microstrip copper foil 22, and the microstrip copper foil 20 on the lower side of the third PCB board 18 are provided with concentric third metal vias 23. Therefore, in this embodiment, the ridge transition structure 14 is simulated by using the microstrip copper foil 20 and the second metal via 21 on both sides of the third PCB board 18, and the replacement matching conversion cavity 13 of the third PCB board 18 is used in this way. Based on this structure, the first PCB board 2 and the third PCB board 18 are bonded together by the adhesive layer 19 to form a multilayer PCB structure. This results in a simple overall structure and facilitates the PCB design of subsequent modules.

[0042] The microstrip waveguide converter of Example 3 was simulated using electromagnetic full-wave analysis software. The simulation results are as follows: Figure 9 and Figure 10 As shown, the simulation results show that the return loss is less than -10dB and the insertion loss is no more than 0.75dB in the frequency range from 75GHz to 90GHz, which meets the conversion requirements of W-band microstrip waveguide 1.

[0043] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A millimeter-wave microstrip waveguide converter, characterized in that, include: The waveguide has a stepped structure and includes a first waveguide portion and a second waveguide portion. The first waveguide portion has a first height, and the second waveguide portion has a second height. The first height is greater than the second height. A waveguide cavity is formed within the first waveguide portion, and a waveguide opening is provided at the junction of the first waveguide portion and the second waveguide portion. A first PCB board has a first end extending into a waveguide cavity and a second end disposed on the surface of a second waveguide portion. The first PCB board is provided with a microstrip line and a ground plane. The microstrip line includes a probe, an impedance conversion section, and a transmission line. The probe is located inside the waveguide cavity, and the transmission line is located on the upper side of the second waveguide portion. At least a portion of the impedance conversion section is located at the waveguide opening for connecting the probe and the transmission line. The ground plane is disposed on the portion of the first PCB board located on the surface of the second waveguide portion. A matching conversion structure is disposed on the lower side of at least the portion of the first PCB board located within the waveguide cavity; The matching transformation structure includes: A matching conversion cavity is disposed within the waveguide cavity, the matching conversion cavity being located on the lower side of the first PCB board; The matching conversion cavity is provided with a ridge transition structure, the first PCB board is disposed on the ridge transition structure, and the microstrip line and the ridge transition structure are separated by the first PCB board; or The matching conversion cavity is provided with a second PCB board, the surface of which has a microstrip copper strip, and the first PCB board is connected to the microstrip copper strip. The second PCB board and the microstrip copper strip are provided with at least one concentric first metal via.

2. The millimeter-wave microstrip waveguide converter as described in claim 1, characterized in that, When a ridge transition structure is provided in the matching conversion cavity, and the first PCB board is disposed on the ridge transition structure, there is a microstrip copper foil between the ridge transition structure and the first PCB board.

3. A millimeter-wave microstrip waveguide converter as described in claim 1 or 2, characterized in that, The waveguide cavity has an inverted tuning step near the waveguide opening, and the impedance conversion section is located below the tuning step.

4. A millimeter-wave microstrip waveguide converter as described in claim 1 or 2, characterized in that, The ground plane has two sets, which are symmetrically arranged on the first PCB board with the axis of the transmission line as the line of symmetry.

5. A millimeter-wave microstrip waveguide converter, characterized in that, include: The waveguide has a stepped structure and includes a first waveguide portion and a second waveguide portion. The first waveguide portion has a first height, and the second waveguide portion has a second height. The first height is greater than the second height. A waveguide cavity is formed within the first waveguide portion, and a waveguide opening is provided at the junction of the first waveguide portion and the second waveguide portion. A first PCB board has a first end extending into a waveguide cavity and a second end disposed on the surface of a second waveguide portion. The first PCB board is provided with a microstrip line and a ground plane. The microstrip line includes a probe, an impedance conversion section, and a transmission line. The probe is located inside the waveguide cavity, and the transmission line is located on the upper side of the second waveguide portion. At least a portion of the impedance conversion section is located at the waveguide opening for connecting the probe and the transmission line. The ground plane is disposed on the portion of the first PCB board located on the surface of the second waveguide portion. A matching conversion structure is disposed on the lower side of at least the portion of the first PCB board located within the waveguide cavity; The matching transformation structure includes: A third PCB board extends from inside the waveguide cavity to the surface of the second waveguide portion, and an adhesive layer is present between the third PCB board and the first PCB board. The third PCB board has a microstrip copper strip on at least one side, and the third PCB board and the microstrip copper strip are provided with at least one concentric second metal via.

6. A millimeter-wave microstrip waveguide converter as described in claim 5, characterized in that, The first PCB board has a microstrip copper foil four on the side away from the microstrip line, and the first PCB board, the third PCB board, and the microstrip copper foil four are provided with at least one concentric third metal via.

7. A millimeter-wave microstrip waveguide converter as described in claim 6, characterized in that, The third PCB board has a microstrip copper strip on the side away from the adhesive layer, and the second metal via and the third metal via extend to the microstrip copper strip.

8. A millimeter-wave microstrip waveguide converter as described in any one of claims 5 to 7, characterized in that, The waveguide cavity has an inverted tuning step near the waveguide opening, and the impedance conversion section is located below the tuning step.

9. A millimeter-wave microstrip waveguide converter as described in any one of claims 5 to 7, characterized in that, The ground plane has two sets, which are symmetrically arranged on the first PCB board with the axis of the transmission line as the line of symmetry.

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