Millimeter wave microstrip conversion structure of double-ridge waveguide

Abstract

The invention relates to the technical field of millimeter wave conversion, and discloses a millimeter wave microstrip conversion structure of a double-ridge waveguide, and the structure comprises a double-ridge waveguide port which is used for transmitting a millimeter wave signal from a waveguide structure to a lambda / 4 single-section impedance transformer; the microstrip transmission line is used for receiving and transmitting the millimeter wave signal; the lambda / 4 single-section impedance transformer is used for transition from the impedance of the double-ridge waveguide port to the impedance of the microstrip transmission line; and the capacitance compensation structure is arranged between the lambda / 4 single-section impedance transformer and the microstrip transmission line so as to compensate step capacitance caused by electric field distribution difference of different transmission lines. By means of the lambda / 4 single-section impedance transformer, balance transition of impedance in space can be achieved by means of the phase characteristic of electromagnetic waves in a quarter-wavelength structure, the return effect of reflected waves is effectively weakened, it is ensured that impedance matching of signals in high-frequency transmission is more accurate by optimizing the impedance value and the length parameter, and the signal transmission efficiency is improved. The loss of transmission energy is reduced, and the signal stability is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of millimeter wave conversion, and in particular to a millimeter wave microstrip conversion structure of a double-ridge waveguide. Background Art

[0002] Millimeter-wave bands, with their high frequency and wide bandwidth, are widely used in high-speed wireless communications, radar detection, satellite transmission, and other fields. With the continuous development of millimeter-wave technology, systems have placed higher demands on signal transmission stability, loss control, and broadband performance. However, existing millimeter-wave waveguide-to-microstrip transition structures still face the following technical bottlenecks, which seriously restrict the system's transmission performance and application effectiveness.

[0003] Impedance matching is not accurate, and signal reflection problems are prominent

[0004] Impedance matching is a key factor influencing signal quality during millimeter-wave signal transmission. Traditional impedance converters often feature crude parameter design, failing to fully exploit the phase characteristics of electromagnetic waves within specific transmission structures. This leads to unbalanced impedance transitions and large reflected waves. Especially in the millimeter-wave frequency band, where the shorter signal wavelengths make reflections caused by impedance mismatch more pronounced, impacting signal transmission stability. Reflected waves not only reduce the effective transmission of signal energy but can also increase standing waves in the system, further degrading transmission quality.

[0005] The transmission loss is high and the signal energy is severely attenuated

[0006] Millimeter-wave signals have high frequency characteristics, which makes the skin effect particularly significant during transmission. According to the principle of the skin effect, current tends to concentrate on the surface area of the transmission line conductor. Once the surface has large roughness or irregular textures, the current distribution becomes uneven, resulting in increased signal scattering loss. Traditional microstrip transmission lines have difficulty achieving high levels of flatness in terms of machining accuracy and surface treatment, resulting in significant signal loss during transmission. In addition, the dimensional design of some transmission lines does not fully consider the optimal parameters of the millimeter-wave signal propagation path, further exacerbating the power attenuation of the signal during transmission.

[0007] At the interface between the waveguide and microstrip transmission line, significant differences in electric field distribution between the two easily lead to the formation of parasitic capacitance (step capacitance) at the connection interface. This capacitance effect can cause reflections during signal transmission, limiting transmission bandwidth, especially in applications with wider frequency bands. Some traditional compensation schemes have a single structure and fail to fully account for the gradual transition of electric field distribution, resulting in limited compensation effectiveness and further restricting system bandwidth and matching performance.

[0008] Millimeter-wave systems often operate in complex environments in practical applications, where external factors such as temperature fluctuations, mechanical vibration, and machining errors cannot be ignored in their signal transmission. Traditional impedance converters and compensation structures fail to adequately account for environmental variables in their parameter design. This leads to a rapid deterioration in system impedance matching and significant increase in signal reflections when the connection surface deviates or materials expand and contract due to thermal expansion, thus compromising the system's transmission stability and consistency. In high-frequency millimeter-wave systems, signal phase is particularly susceptible to environmental fluctuations, further exacerbating transmission instability. Summary of the Invention

[0009] In response to the shortcomings of the existing technology, the present invention provides a millimeter-wave microstrip conversion structure with a double-ridge waveguide, which solves the problems in the existing technology, such as inaccurate impedance matching and severe signal reflection, high transmission loss and obvious signal energy attenuation, insufficient compensation for capacitance effect and limited bandwidth expansion, as well as poor structural stability and insufficient environmental adaptability.

[0010] To achieve the above objectives, the present invention is implemented through the following technical solutions: a millimeter-wave microstrip conversion structure of a double-ridge waveguide, comprising:

[0011] A double-ridge waveguide port for transmitting millimeter-wave signals from the waveguide structure to a λ / 4 single-section impedance converter;

[0012] Microstrip transmission lines, used to receive and transmit millimeter-wave signals;

[0013] a λ / 4 single-section impedance converter, one end of which is connected to the double-ridged waveguide port and the other end of which is connected to the microstrip transmission line, for transitioning from the impedance of the double-ridged waveguide port to the impedance of the microstrip transmission line;

[0014] The capacitance compensation structure is arranged between the λ / 4 single-section impedance transformer and the microstrip transmission line to compensate for the step capacitance caused by the difference in electric field distribution of different transmission lines.

[0015] Preferably, a trapezoidal transition groove with a depth of 0.1-0.2λg is provided at the end of the double-ridge waveguide, and the angle of the transition groove is 55°±2°.

[0016] Preferably, the line width of the microstrip transmission line is 40-60 μm, and the edge roughness is <Ra0.8μm。

[0017] Preferably, the microstrip transmission line adopts Rogers-RT / duroid-5880 dielectric plate with a thickness of 0.2-0.3 mm.

[0018] Preferably, the impedance value of the λ / 4 single-section impedance converter is 180-200Ω, and the length is 2-4mm, and is used to match the impedance of a 50Ω microstrip transmission line to a 190Ω double-ridge waveguide.

[0019] Preferably, the length of the λ / 4 single-section impedance transformer corresponds to a phase shift of 15 degrees.

[0020] Preferably, the capacitance compensation structure includes a high-resistance compensation component, and the high-resistance compensation component compresses the width of the microstrip transmission line guide strip.

[0021] Preferably, the width of the capacitance compensation structure is compressed to 75-85% of the original width.

[0022] Preferably, the capacitance compensation structure adopts a stepped high-resistance compensation structure, and obtains three-level compensation parameters through particle swarm optimization to improve signal matching and expand bandwidth.

[0023] Preferably, when the lateral misalignment of the connection surface using the stepped high-resistance compensation structure is ≤8% of the guide wavelength, the S11 degradation is <0.5dB.

[0024] The present invention provides a millimeter-wave microstrip conversion structure with a double-ridge waveguide. It has the following beneficial effects:

[0025] 1. The present invention utilizes the phase characteristics of electromagnetic waves in a quarter-wavelength structure through a λ / 4 single-section impedance transformer to achieve a balanced impedance transition in space, effectively weakening the return effect of the reflected wave. By optimizing the impedance value and length parameters, the impedance matching of the signal in high-frequency transmission is ensured to be more accurate, which significantly reduces the loss of transmission energy and improves the stability of the signal.

[0026] 2. The present invention precisely controls key parameters of the microstrip transmission line, such as line width and edge roughness. According to the skin effect principle, high-frequency signal current is more likely to concentrate on the surface of the conductor. If the surface roughness is large, the current distribution will become uneven, resulting in scattering and loss of signal energy. To this end, the present invention reduces current distortion at the microscopic level and reduces the resistance loss on the surface of the conductive strip by optimizing the surface flatness of the transmission line. At the same time, by adjusting the size of the transmission line, the propagation path of the signal's electromagnetic wave in the conductive strip is ensured to be the shortest, further reducing the power attenuation during transmission, thereby improving the transmission efficiency of the system.

[0027] 3. This invention incorporates a capacitance compensation structure between the impedance converter and the microstrip transmission line. This structure gradually adjusts the width of the transmission line's conduction strip to create a progressive electric field distribution, reducing the capacitive effect caused by sudden changes in the electric field. Based on the principle of electric field coupling, the smooth electric field transition effectively suppresses signal reflections caused by parasitic capacitance. By optimizing the compensation structure, signal reflection loss is significantly reduced and the bandwidth is effectively expanded, meeting the requirements of wideband applications.

[0028] 4. This invention improves the system's environmental adaptability by optimizing the dimensional parameters of the impedance converter and compensation structure. In particular, the optimized width of the compensation structure and the conduction band spacing provide enhanced anti-drift capability, maintaining low signal reflections even when small lateral misalignments occur on the connection surface. Furthermore, precise phase shift control is designed to minimize the impact of temperature fluctuations on signal phase, ensuring excellent signal stability and consistency in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the present invention;

[0030] Figure 2 Schematic diagram of input return loss of the present invention;

[0031] Figure 3 Schematic diagram of insertion loss simulation results of the present invention;

[0032] Figure 4 Schematic diagram of the input return loss simulation results of the present invention. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the specification of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] In order to better understand the present invention, the above contents are described in detail below in conjunction with specific embodiments.

[0035] Please see the attached Figure 1-Figure 4 The embodiment of the present invention provides a millimeter-wave microstrip conversion structure of a double-ridge waveguide, comprising:

[0036] A double-ridge waveguide port for transmitting millimeter-wave signals from the waveguide structure to a λ / 4 single-section impedance converter;

[0037] In this embodiment, the double-ridge waveguide port is used to transmit the millimeter wave signal from the waveguide structure to the λ / 4 single-section impedance converter. To ensure a smooth transition of the signal, especially for the effective transmission of high-frequency millimeter wave signals, a transition structure with good impedance matching performance is required.

[0038] Specifically, the double-ridge waveguide is a waveguide structure commonly used in the millimeter-wave frequency band. It has high transmission capacity and is particularly suitable for transmitting high-frequency signals. However, when connecting the double-ridge waveguide to a microstrip transmission line, signal reflection and reduced transmission efficiency are easily caused due to differences in impedance and electric field distribution.

[0039] The design of the double-ridge waveguide port enables impedance matching and signal transition through appropriate structure. Specifically, the end of the double-ridge waveguide is provided with a trapezoidal transition groove with a depth of 0.1-0.2λg, such as 0.12λg. The trapezoidal transition groove design provides a smooth impedance transition at the connection between the waveguide and the microstrip transmission line, reducing signal reflections and losses.

[0040] Specifically, the angle of the transition slot is 55°±2°, chosen based on the characteristics of millimeter-wave signals to ensure low reflection and high transmission efficiency over a wide frequency range. The transition slot depth is 0.1-0.2λg, where λg is the length of the guided wave. The specific depth is adjusted based on actual application requirements. With this design, the transition slot provides a smooth transition region when the signal is transmitted from the waveguide to the impedance converter, minimizing reflections and signal attenuation caused by the step impedance.

[0041] In one embodiment, to further optimize signal transition and impedance matching, the depth of the trapezoidal transition groove can be adjusted based on the operating frequency. For example, for higher-frequency applications, the groove depth may need to be slightly reduced, while for lower-frequency applications, the depth can be appropriately increased to ensure good signal transmission performance across different frequency ranges.

[0042] For the angle of the transition slot, the value is kept within the range of 55°±2°, which can ensure that the reflection loss during the impedance transition process is controlled to a minimum, thereby ensuring stable signal transmission.

[0043] Therefore, the double-ridged waveguide port structure provided in this embodiment, through its trapezoidal transition groove and precise angle design, effectively transmits millimeter-wave signals from the waveguide structure to the λ / 4 single-section impedance transformer, achieving low reflection loss and high transmission efficiency. Through reasonable design and optimization, this structure can achieve excellent performance in high-frequency millimeter-wave systems, meeting the requirements of modern communications and radar technology.

[0044] Microstrip transmission lines, used to receive and transmit millimeter-wave signals;

[0045] In this embodiment, a microstrip transmission line is used to receive and transmit millimeter-wave signals. As a key component in signal transmission, the microstrip transmission line carries the signal after transitioning from the double-ridged waveguide port and transmits it backward. To achieve efficient millimeter-wave signal transmission, the design of the microstrip transmission line must consider multiple factors, including signal frequency, impedance matching, and transmission loss.

[0046] Microstrip transmission lines are a common method for signal transmission in the microwave and millimeter wave frequency bands, offering a simple structure and ease of integration. To ensure effective transmission of millimeter wave signals, the microstrip transmission lines designed in this paper have specific geometric shapes and material properties to optimize their performance and ensure stable and efficient signal transmission.

[0047] Specifically, the microstrip transmission line width is designed to be 40-60μm. This range effectively ensures signal transmission without excessive attenuation or distortion. Depending on the operating frequency and dielectric material properties, the line width of the microstrip transmission line affects its characteristic impedance, which in turn affects signal reflection and transmission efficiency. By precisely controlling the line width, impedance matching between the microstrip transmission line and the double-ridge waveguide port is ensured, reducing signal reflections.

[0048] In high-frequency transmission, the surface roughness of microstrip transmission lines significantly impacts signal transmission performance. To reduce signal loss and distortion caused by surface roughness, this embodiment rigorously controls the edge roughness of the microstrip transmission lines, ensuring a roughness of less than Ra0.8μm. This design effectively reduces scattering losses caused by surface roughness, ensuring efficient transmission of millimeter-wave signals.

[0049] In some embodiments, the microstrip transmission lines utilize Rogers-RT / duroid-5880 dielectric sheet material. This material has excellent electrical properties and is particularly well-suited for high-frequency and millimeter-wave applications. Its low loss characteristics ensure minimal signal attenuation and distortion during transmission, thereby improving signal transmission quality. Specifically, RT / duroid-5880's relatively stable dielectric constant makes it suitable for high-frequency microwave circuit and antenna design, and its low dissipation factor effectively suppresses signal attenuation.

[0050] Microstrip transmission lines have a sheet thickness of 0.2-0.3mm, which provides good impedance control and maintains performance stability at higher frequencies. Thinner sheet thickness reduces signal transmission delay and helps reduce device size, meeting the demands of modern communications equipment for miniaturization and high performance.

[0051] Due to the significant impedance difference between microstrip transmission lines and double-ridge waveguides, precise adjustment of the microstrip transmission line width and dielectric material ensures a smooth impedance transition from the double-ridge waveguide port to the microstrip transmission line, avoiding reflections caused by impedance mismatch. By controlling the size, material, and surface roughness of the microstrip transmission line, signal reflections and transmission losses can be minimized.

[0052] Generally speaking, in practical applications, the design of microstrip transmission lines is adjusted based on the operating frequency band, signal bandwidth, and specific device requirements. For example, in higher-frequency applications, the line width of the microstrip transmission line may need to be appropriately reduced or the material properties adjusted to meet more stringent signal transmission requirements. In addition, the integration of microstrip transmission lines with other high-frequency components (such as antennas and filters) also requires consideration of impedance matching and signal transmission efficiency.

[0053] In one possible implementation, adding an appropriate capacitance compensation structure to a microstrip transmission line can further improve transmission stability, reduce reflection loss, and expand bandwidth. The specific design of the capacitance compensation structure can be optimized using a particle swarm algorithm, tailored to different frequency bands and application scenarios, to achieve optimal signal matching.

[0054] Therefore, the microstrip transmission line design in this embodiment combines multiple factors, including line width, material selection, and edge roughness control, to ensure efficient transmission of millimeter-wave signals within the microstrip transmission line. By using Rogers-RT / duroid-5880 dielectric sheet material and strictly controlling the structural characteristics of the transmission line, signal loss and distortion can be significantly reduced, ensuring the stability and efficiency of high-frequency millimeter-wave systems.

[0055] A λ / 4 single-section impedance converter, one end of which is connected to a double-ridge waveguide port and the other end is connected to a microstrip transmission line, for transitioning from the impedance of the double-ridge waveguide port to the impedance of the microstrip transmission line;

[0056] In this embodiment, the λ / 4 single-section impedance transformer performs impedance matching between the double-ridge waveguide port and the microstrip transmission line, ensuring a smooth transition of the signal and reducing signal reflection and loss caused by impedance mismatch.

[0057] In millimeter-wave signal transmission, the impedance difference between a double-ridge waveguide and a microstrip transmission line is typically significant, leading to signal reflection loss. To effectively address this issue, the present invention designs a λ / 4 single-section impedance converter. This converter serves as an impedance matching device, located between the double-ridge waveguide port and the microstrip transmission line, providing a crucial transition. Leveraging its unique structure and impedance characteristics, the λ / 4 single-section impedance converter smoothly transitions the impedance of the double-ridge waveguide to that of the microstrip transmission line, thereby avoiding reflection loss and improving signal transmission efficiency and stability.

[0058] Specifically, the design parameters for the λ / 4 single-section impedance transformer are an impedance value of 180-200Ω. This impedance range effectively matches the impedance of a 50Ω microstrip transmission line with a 190Ω double-ridge waveguide. The impedance transformer length is designed to be 2-4mm, optimized based on standard λ / 4 transformer design principles and the waveguide's operating frequency. Specifically, the length of the λ / 4 impedance transformer is closely related to the operating frequency and waveguide characteristics, and the selected length ensures effective impedance matching of the signal within the transformer.

[0059] In some embodiments, the impedance of the λ / 4 single-section impedance transformer is 180Ω to 200Ω, a range that effectively matches the characteristics of the double-ridge waveguide, enabling efficient signal transmission. The transformer's length is set between 2 and 4 mm, adjusted based on the operating frequency band and application requirements. This effectively balances the impedance difference between the microstrip transmission line and the double-ridge waveguide, minimizing signal reflections and transmission losses.

[0060] Specifically, in a λ / 4 single-section impedance converter, the length design is closely related to the phase shift. In this embodiment, the length of the λ / 4 single-section impedance converter corresponds to a 15-degree phase shift. While ensuring impedance matching, the phase change of the signal during transmission is also taken into account. Phase shift control is a very important factor in microwave and millimeter wave signal transmission. By using an appropriate phase shift, signal interference and loss caused by phase mismatch can be avoided. Specifically, a 15-degree phase shift can effectively control the phase of the signal, ensuring that the signal is not distorted during transmission and helping the system operate stably in the high-frequency band.

[0061] In one possible implementation, a single-section λ / 4 impedance transformer is designed using a microstrip transmission line structure. Through optimization simulation and experimental verification, a design with an impedance of 180-200Ω and a length of 2-4mm was determined. This design ensures a low reflection coefficient during the transition between the 50Ω microstrip transmission line and the 190Ω double-ridge waveguide, significantly reducing signal attenuation during transmission.

[0062] In order to further optimize the signal transmission quality, optimization techniques such as particle swarm optimization can also be used to adjust the size, material and layout of the impedance converter to obtain the best impedance matching effect and improve bandwidth and signal transmission efficiency.

[0063] Generally speaking, as signal frequencies increase, the impedance matching requirements of millimeter-wave systems become more stringent. Therefore, when designing a single-section λ / 4 impedance transformer, it is necessary to account for frequency variations to ensure good signal transmission performance across different frequency bands. Alternatively, precise adjustment of the transformer length and impedance can be used to adapt to varying operating frequencies, enabling the structure to operate stably across a wide frequency band.

[0064] The coordination between the capacitive compensation structure of the λ / 4 single-section impedance converter and the microstrip transmission line is also crucial. By further optimizing the matching between the capacitive compensation structure and the impedance converter, the system bandwidth can be expanded and transmission loss and reflections can be further reduced.

[0065] Therefore, in summary, the precise design of the λ / 4 single-section impedance transformer in this embodiment ensures a smooth impedance transition from the double-ridge waveguide to the microstrip transmission line. By properly setting the impedance value (180-200Ω) and transformer length (2-4mm), and controlling the phase shift to 15 degrees, signal reflections and losses can be significantly reduced, optimizing signal transmission. This technical solution can be widely applied to high-frequency millimeter-wave systems and meet the efficient transmission requirements of modern communications, radar, and other millimeter-wave applications.

[0066] The capacitance compensation structure is arranged between the λ / 4 single-section impedance transformer and the microstrip transmission line to compensate for the step capacitance caused by the difference in electric field distribution of different transmission lines.

[0067] In this embodiment, a capacitance compensation structure is used to reduce signal reflections and improve signal transmission stability. This capacitance compensation structure, placed between the λ / 4 single-section impedance transformer and the microstrip transmission line, primarily compensates for step capacitance issues caused by differences in electric field distribution across the transmission lines, thereby improving signal matching. By designing an appropriate capacitance compensation structure, the performance of millimeter-wave systems can be effectively improved, reducing signal loss caused by impedance mismatch.

[0068] In millimeter-wave systems, the presence of step capacitance, often caused by differences in electric field distribution between microstrip transmission lines and other circuit components, can cause signal reflections and reduce system transmission efficiency. To address this issue, the present invention provides a capacitance compensation structure that, through a specific design, compensates for these capacitance effects, reducing signal reflections and improving system transmission stability and efficiency.

[0069] Specifically, the capacitance compensation structure includes a high-impedance compensation component designed to compensate for the step capacitance by compressing the conduction width of the microstrip transmission line. Specifically, the width of the capacitance compensation structure is compressed to between 75% and 85% of its original width. This design effectively alters the electric field distribution along the transmission line, reducing reflections caused by electric field discontinuities.

[0070] Compressing the width of a microstrip transmission line's conductive strip can, to a certain extent, alter the characteristic impedance of the transmission line, thereby adjusting the distribution of the electric field. In this way, the capacitance compensation structure effectively reduces signal reflections caused by discontinuities between the transmission line and the impedance transformer. Compressing the width to 75%-85% of the original width improves signal transmission stability while meeting impedance matching requirements.

[0071] Specifically, in this embodiment, the capacitance compensation structure adopts a stepped high-impedance compensation structure. This structure gradually changes the conduction band width of the transmission line to form a trapezoidal transition region, thereby optimizing the electric field distribution and further improving impedance matching. The key to this stepped design is its ability to smoothly transition the electric field distribution between different parts, avoiding the generation of step capacitance.

[0072] To ensure optimal matching across a wide frequency band, the present invention employs a particle swarm optimization algorithm to optimize the compensation structure's parameters. This algorithm can find the optimal configuration among multiple design parameters, improving signal matching and expanding the system's bandwidth. This optimization method effectively addresses the inaccurate parameter adjustments inherent in traditional design methods, further enhancing overall system performance.

[0073] Specifically, when using a stepped high-impedance compensation structure, the lateral misalignment of the connection surface is ≤8% of the guide wavelength. In this case, the S11 degradation is less than 0.5dB. This design effectively reduces reflection loss while ensuring signal matching. The S11 parameter is a key indicator of reflection loss. A smaller S11 value indicates lower reflection loss. Good impedance matching can significantly improve the system's signal quality and transmission efficiency.

[0074] Therefore, in some embodiments, the design of the capacitance compensation structure not only optimizes the transmission quality of the signal, but also expands the bandwidth of the system, making the structure adaptable to a wider range of application scenarios. Especially in high-frequency millimeter-wave systems, a good capacitance compensation design is crucial to improving the overall performance of the system. Specifically, in high-frequency applications such as microwave communications, radar systems, and satellite communications, the capacitance compensation structure can significantly improve signal transmission stability and signal quality.

[0075] The capacitance compensation structure in this embodiment utilizes high-resistance compensation components and a stepped design to effectively compensate for the step capacitance caused by differences in the electric field distribution of the transmission line, reducing signal reflections and improving signal transmission stability. Furthermore, a particle swarm algorithm is used to optimize the compensation structure's parameters, further enhancing the system's matching and bandwidth performance. By compressing the width of the microstrip transmission line and precisely designing it, this capacitance compensation structure can achieve excellent signal transmission performance in a variety of high-frequency applications.

[0076] In summary:

[0077] 1. Transmission line electric field distribution and impedance analysis

[0078] The microstrip transmission line plane is used as the center plane of the double-ridge waveguide. The center plane is regarded as an equipotential surface. The electric fields on and below the equipotential surface are symmetrically distributed, which is similar to the electric field distribution on the end face of the TEM mode of the microstrip transmission line. Therefore, the two transmission lines are directly connected during design.

[0079] The characteristic impedance of a ridged waveguide can be defined in various ways, such as the ratio of voltage squared to power or voltage to current, resulting in different calculation results. This paper uses HFSS simulation results to calculate the characteristic impedance of the double-ridged waveguide and the λ / 4 single-section impedance transformation segment. Based on the calculated microstrip transmission line dimensions, a Rogers-RT / duroid-5880 dielectric sheet with a thickness of 0.254mm was selected. A 50Ω microstrip transmission line impedance corresponds to a 0.78mm width. This sheet offers high dielectric constant stability and excellent corner loss characteristics in the millimeter-wave frequency band, enhancing the accuracy of the design and simulation of the entire millimeter-wave microstrip transformation structure. HFSS simulations show that the double-ridged waveguide port impedance at the center frequency of 26.5-40GHz corresponds to a microstrip transmission line characteristic impedance of 50Ω. Directly connecting the two transmission lines would result in strong reflections, necessitating an impedance transformation design.

[0080] 2. Impedance transformation design

[0081] Considering the project's bandwidth requirements, the most commonly used λ / 4 single-section impedance transformer was used to achieve minimal reflection matching from a 50Ω microstrip transmission line to a 190Ω double-ridge waveguide. Since the impedance transformer is a lossless device, microwave attenuation is solely due to reflection, so only the reflection attenuation, L, needs to be calculated. From the equivalent circuit of a three-stage simple two-port network, the frequency response characteristic of the impedance transformer, reflection attenuation, is deduced as:

[0082]

[0083] Among them, Z 01 and Z 02is the impedance of the microstrip line and double-ridge waveguide that need to be matched; Z0 is the impedance of the λ / 4 single-section impedance transformer; (cosθ) 2 is the phase shift of microwave transmission in the conversion section.

[0084] According to the reflection attenuation formula, when When L=1, microwaves pass through without reflection.

[0085] Substituting the impedance value of this design into the calculation, it is found that the impedance of the transformation section should be designed to be 190Ω. The simulation shows that the length corresponding to a 15-degree phase shift is approximately 3mm.

[0086] 3. Capacitor compensation design

[0087] The calculations for impedance transformation described above only consider impedance values and don't account for the sudden changes in the connections between different transmission lines. In reality, when connecting transmission lines with different end faces, step capacitance exists at the connection due to differences in electric field distribution. To achieve an ideal match, capacitance compensation should be designed at the connection to reduce reflections caused by step capacitance.

[0088] The presence of cascaded capacitors often reduces the impedance at the connection. To reduce or eliminate reflections caused by the step capacitors, the impedance at the connection must be increased to compensate for high impedance. In this design, high impedance compensation can be achieved by compressing the width of the microstrip conductor at the connection.

[0089] 4. Structural sensitivity analysis

[0090] To evaluate the robustness of the compensation structure, a three-dimensional electromagnetic model was established for parametric study:

[0091] (1) Transverse offset tolerance: When the transverse misalignment of the connection surface is ≤8% of the guide wavelength, the S11 degradation is <0.5dB

[0092] (2) Dielectric thickness deviation: A substrate thickness variation of ±10% causes an impedance shift of <1.5Ω.

[0093] (3) Temperature stability: within the temperature range of -55 to +85°C, the phase linearity deviation is <3° / GHz

[0094] (4) Multi-level compensation topology optimization

[0095] In response to the needs of wide-band applications, a stepped impedance compensation structure is proposed, and its impedance transformation function is:

[0096]

[0097] Among them, Z(ω) is the total impedance of the system, an impedance function that varies with the angular frequency ω; Z0 is the reference characteristic impedance, usually used for normalization or representing the reference impedance of the system; N is the total number of stages, representing the number of compensation structures or components in the system; n is the index variable in the quadrature operation, ranging from 1 to N; j is the imaginary unit, satisfying j 2 = -1; ω is the angular frequency, with the unit of radians per second (rad / s), defined as ω = 2πf, where f is the signal frequency (unit Hz); C n is the capacitance value of the nth-stage compensation structure, with the unit of farad (F); Z n is the impedance value of the nth-stage compensation structure, with the unit of ohm (Ω).

[0098] 5. Test Verification and Comparison

[0099] A test platform was built in the Ka band. The measured data shows that the backscatter suppression is effective. The compensation structure expands the S11 < -20 dB bandwidth to 23.6% (9.4% without compensation); the power capacity is effectively improved, and the power tolerance of the compensation structure is increased to 2.1 W / mm 2 , meeting the usage requirements of the application scenario.

[0100] The performance comparison with the existing technology is shown in Table 1:

[0101] Technical Solution bandwidth(%) Insertion loss (dB / cm) <![CDATA[Dimension (λg 2 )]]> Traditional gradient line 15.8 0.45 2.3 Literature Resonance Compensation 21.2 0.62 1.8 This plan (three-level compensation) 28.7 0.33 1.2

[0102] Based on the above calculation results, with 26.5 - 40 GHz as the center frequency, a model of the double-ridge waveguide and microstrip line converter was established in the HFSS software, making the microstrip line conductor strip and the microstrip line ground plane connect to the upper and lower ridges of the double-ridge waveguide respectively. The model is as follows:

[0103] A. The product uses the manufacturing process of the microstrip line - double-ridge waveguide transition structure, selects the Rogers - RT / duroid - 5880 substrate (εr = 2.2 ± 0.02), and realizes the positioning reference holes with a diameter of 0.15 mm through laser drilling, with a positioning accuracy of ±5 μm;

[0104] B. The 50 - μm line-width microstrip line is fabricated using the ultraviolet lithography process, and the edge roughness is controlled to be < Ra 0.8 μm (meeting the surface skin depth requirement of 40 GHz).

[0105] C. A trapezoidal transition groove with a depth of 0.12λg is machined at the end of the double-ridge waveguide (angle 55° ± 2°), and the surface finish of V6 is ensured by numerical control electrical discharge machining.

[0106] D. Use Au 80 Sn 20 solder to weld the waveguide - substrate interface in a vacuum environment at 280°C ± 3°C, and the solder layer thickness is controlled within 8 - 12 μm.

[0107] E. Use 15 MPa pressure and 150°C for 120 seconds to achieve molecular-level bonding between the dielectric substrate and the waveguide wall. Apply a 5 μm thick BCB dielectric layer (εr = 2.65) at the connection and form an airtight package after curing at 350°C.

[0108] For key dimensions such as the length of the λ / 4 single-section impedance transformation segment and the ridge height, a small range is set according to the above calculation results to perform parameter sweeps and device simulations.

[0109] The simulation results of gain and loss are shown in the attached Figure 2 、 Figure 3 and Figure 4 As shown;

[0110] It can be seen that the transmission loss in the full frequency band of Ka is less than 0.13dB, the input return loss is better than 14dB, and the standing wave is better than 1.4:1. All indicators meet the design goals. Compared with the traditional ones, the key parameters are compared as follows:

[0111] Comparison Item Traditional transition structure This technical solution Improvement Insertion loss @40GHz 0.82dB 0.53dB 35.4％↓ Return loss (>20dB bandwidth) 12.6％ 28.7％ 127.8％↑ Voltage Standing Wave Ratio (VSWR) 1.48 1.19 19.6％↓ Power handling (continuous wave) <![CDATA[1.2W / mm 2 ]]> <![CDATA[2.8W / mm 2 ]]> 133.3％↑ Temperature stability (-55~85℃) ±0.15dB / dB ±0.06dB / dB 60％↑

[0112] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A millimeter-wave microstrip conversion structure of a double-ridge waveguide, characterized in that: include: A double-ridge waveguide port for transmitting millimeter-wave signals from the waveguide structure to a λ / 4 single-section impedance converter; Microstrip transmission lines, used to receive and transmit millimeter-wave signals; a λ / 4 single-section impedance converter, one end of which is connected to the double-ridged waveguide port and the other end of which is connected to the microstrip transmission line, for transitioning from the impedance of the double-ridged waveguide port to the impedance of the microstrip transmission line; The capacitance compensation structure is arranged between the λ / 4 single-section impedance transformer and the microstrip transmission line to compensate for the step capacitance caused by the difference in electric field distribution of different transmission lines.

2. The millimeter-wave microstrip conversion structure of a double-ridge waveguide according to claim 1, characterized in that: The end of the double-ridge waveguide is provided with a trapezoidal transition groove with a depth of 0.1-0.2λg, and the angle of the transition groove is 55°±2°.

3. The millimeter-wave microstrip conversion structure of a double-ridge waveguide according to claim 1, characterized in that: The line width of the microstrip transmission line is 40-60 μm and the edge roughness is <Ra0.8μm。 4. The millimeter-wave microstrip conversion structure of a double-ridge waveguide according to claim 1, characterized in that: The microstrip transmission line adopts Rogers-RT / duroid-5880 dielectric plate with a thickness of 0.2-0.3 mm.

5. The millimeter-wave microstrip conversion structure of a double-ridge waveguide according to claim 1, characterized in that: The λ / 4 single-section impedance converter has an impedance value of 180-200Ω and a length of 2-4mm, and is used to match the impedance of a 50Ω microstrip transmission line to a 190Ω double-ridge waveguide.

6. The millimeter-wave microstrip conversion structure of a double-ridge waveguide according to claim 5, characterized in that: The length of the λ / 4 single-section impedance transformer corresponds to a phase shift of 15 degrees.

7. The millimeter-wave microstrip conversion structure of a double-ridge waveguide according to claim 1, characterized in that: The capacitance compensation structure includes a high-resistance compensation component, and the high-resistance compensation component compresses the width of the microstrip transmission line.

8. The millimeter-wave microstrip conversion structure of a double-ridge waveguide according to claim 7, characterized in that: The width of the capacitance compensation structure is compressed to 75-85% of the original width.

9. The millimeter-wave microstrip conversion structure of a double-ridge waveguide according to claim 8, characterized in that: The capacitance compensation structure adopts a stepped high-resistance compensation structure and obtains three-level compensation parameters through particle swarm optimization to improve signal matching and expand bandwidth.

10. The millimeter-wave microstrip conversion structure of a double-ridge waveguide according to claim 9, characterized in that: When the lateral misalignment of the connection surface using the stepped high-resistance compensation structure is ≤8% of the guide wavelength, the S11 degradation is <0.5dB.

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