Suspended microstrip line directional coupler applied to magnetic resonance system

Abstract

The invention relates to the technical field of couplers, and discloses a suspended microstrip line directional coupler applied to a magnetic resonance system, the suspended microstrip line directional coupler comprises a top layer of a PCB, a first air cavity layer of the PCB, a signal transmission layer of the PCB, a second air cavity layer of the PCB and a bottom layer of the PCB which are connected in sequence, the second air cavity layer and the bottom layer are of a lower suspension structure. According to the suspension structure, the main signal line and the coupling line in the signal transmission layer are suspended in the air, the distance between the microstrip line and the top layer substrate and the distance between the microstrip line and the bottom layer substrate are increased, loss between a surface wave and a substrate medium is reduced, the influence of the medium effect on the transmission characteristic is reduced, the bandwidth of the directional coupler is expanded, the coupling consistency is improved, and the directional coupler has a wide application prospect. And relatively high directionality and power distribution precision are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of couplers, and in particular to a suspended microstrip line directional coupler applied to a magnetic resonance system. Background Art

[0002] A directional coupler is a widely used passive filtering device that can distribute signal power in a fixed ratio. Due to its directivity, a directional coupler can achieve the directional coupling of signals, and the magnitude of the output signal power at the output end is controllable. It can be used as a component of systems such as antenna feed networks, microwave distribution systems, amplifiers, and power detection systems.

[0003] In a magnetic resonance power amplifier, a directional coupler usually plays the roles of power monitoring, impedance matching, reflection signal detection, and protection. First, the directional coupler guides a part of the radio frequency signal from the output end of the power amplifier to the monitoring port, enabling the system to monitor the output power in real time and ensure that the output signal meets the set requirements. Second, it can detect the reflection signal returned from the load (such as a radio frequency coil). By monitoring the reflection coefficient, the directional coupler assists in adjusting the impedance matching of the radio frequency path, thereby ensuring maximum power transmission and reducing signal loss. If the reflection is too large (usually due to impedance mismatch or load failure), the directional coupler provides a feedback signal so that the system can make timely adjustments or protection to avoid damaging the power amplifier.

[0004] A directional coupler usually consists of two transmission lines. When the two transmission lines are at a certain distance, a part of the power can be coupled from the transmission line where the input end is located (main line) to the other transmission line (sub-line). According to different classification criteria, directional couplers can be divided into different types. For example, according to the different transmission lines used, they can be divided into waveguide directional couplers, coaxial line directional couplers, microstrip line directional couplers, and stripline directional couplers, etc. In the design of traditional microstrip line directional couplers, the microstrip line is usually directly placed on a uniform medium. Due to structural limitations, its directivity is poor, the conductor loss and dielectric loss are large, and the power capacity is also relatively limited. Therefore, in order to improve the directivity, reduce the loss, increase the power capacity, and better monitor the output power and reflection signal of a magnetic resonance radio frequency power amplifier, a new design scheme for a directional coupler is urgently needed. Summary of the Invention

[0005] Based on this, in view of the technical problem of the poor effect of the directional coupler in the prior art, a suspended microstrip line directional coupler applied to a magnetic resonance system is proposed, including: the top layer of the PCB, the first air cavity layer of the PCB, the signal transmission layer of the PCB, the second air cavity layer of the PCB, and the bottom layer of the PCB, which are connected in sequence, wherein the top layer and the first air cavity layer are in an upper suspended structure, and the second air cavity layer and the bottom layer are in a lower suspended structure;

[0006] The top layer is obtained by copper plating on the upper surface of the first PCB board material;

[0007] The first air cavity layer is obtained by hollowing out the middle of the second PCB board material;

[0008] The signal transmission layer is obtained by setting main signal lines and coupling lines on the upper surface of the third PCB board material;

[0009] The second air cavity layer is obtained by hollowing out the middle of the fourth PCB board material;

[0010] The bottom layer is obtained by copper plating on the upper surface of the fifth PCB board material;

[0011] Among them, the hollowed - out position of the first air cavity layer is above the main signal line and the coupling line, and the hollowed - out position of the second air cavity layer is below the main signal line and the coupling line.

[0012] The suspended microstrip line directional coupler applied to the magnetic resonance system proposed by the present invention includes a top layer of the PCB, a first air cavity layer of the PCB, a signal transmission layer of the PCB, a second air cavity layer of the PCB, and a bottom layer of the PCB connected in sequence. Among them, the top layer and the first air cavity layer are upper - suspended structures, and the second air cavity layer and the bottom layer are lower - suspended structures; the top layer is obtained by copper plating on the upper surface of the first PCB board material; the signal transmission layer is obtained by setting main signal lines and coupling lines on the upper surface of the second PCB board material; the first air cavity layer is obtained by hollowing out the middle of the third PCB board material; the second air cavity layer is obtained by hollowing out the middle of the fourth PCB board material; the bottom layer is obtained by copper plating on the upper surface of the fifth PCB board material; among them, the hollowed - out position of the first air cavity layer is above the main signal line and the coupling line, and the hollowed - out position of the second air cavity layer is below the main signal line and the coupling line. The suspended structure of the present invention enables the main signal line and the coupling line in the signal transmission layer to be suspended in the air, increasing the distance between the microstrip line and the top and bottom substrates, reducing the loss between the surface wave and the substrate medium, and reducing the influence of the dielectric effect on the transmission characteristics, thereby expanding the bandwidth of the directional coupler and improving the coupling consistency, and achieving higher directivity and power distribution accuracy. Description of the Drawings

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0014] Among them:

[0015] Figure 1 It is the overall PCB structure diagram of a suspended microstrip line directional coupler in an embodiment;

[0016] Figure 2 It is the suspension structure diagram of a suspended microstrip line directional coupler in an embodiment;

[0017] Figure 3 It is the coupling circuit diagram of a suspended microstrip line directional coupler in an embodiment;

[0018] Figure 4 It is the schematic diagram of the function of a suspended microstrip line directional coupler in a magnetic resonance radio frequency power amplification system in an embodiment. Detailed implementation manners

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion. The terms "first", "second", etc. in the specification and claims of this application or the above drawings are used to distinguish different objects and are not used to describe a specific order.

[0020] Referring to "embodiment" herein means that a specific feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0022] Please refer to Figure 1 as shown in Figure 1A suspended microstrip line directional coupler applied to a magnetic resonance system provided by an embodiment of the present invention, the suspended microstrip line directional coupler comprising: a top layer of a PCB, a first air cavity layer of the PCB, a signal transmission layer of the PCB, a second air cavity layer of the PCB, and a bottom layer of the PCB connected in sequence, wherein the top layer and the first air cavity layer are an upper suspension structure, and the second air cavity layer and the bottom layer are a lower suspension structure;

[0023] The top layer is obtained by copper plating on the upper and lower surfaces of a first PCB board;

[0024] The first air cavity layer is obtained by hollowing out the middle of a second PCB board;

[0025] The signal transmission layer is obtained by arranging a main signal line and a coupling line on the upper surface of a third PCB board;

[0026] The second air cavity layer is obtained by hollowing out the middle of a fourth PCB board;

[0027] The bottom layer is obtained by copper plating on the upper and lower surfaces of a fifth PCB board;

[0028] Wherein, the hollowed-out position of the first air cavity layer is above the main signal line and the coupling line, and the hollowed-out position of the second air cavity layer is below the main signal line and the coupling line.

[0029] In one embodiment, the lower surface of the top layer is connected to the upper surface of the first air cavity layer, the lower surface of the first air cavity layer is connected to the upper surface of the signal transmission layer, the lower surface of the signal transmission layer is connected to the upper surface of the second air cavity layer, and the lower surface of the second air cavity layer is connected to the upper surface of the bottom layer.

[0030] In one embodiment, the signal transmission layer is provided with a main line, a first coupling line, and a second coupling line.

[0031] Reference Figure 1 , the suspended microstrip line directional coupler is a 5-layer PCB substrate structure, including the top layer 1 of the suspended microstrip line directional coupler, the first air cavity layer 2 of the suspended microstrip line directional coupler, the signal transmission layer 3 of the suspended microstrip line directional coupler, the second air cavity layer 4 of the suspended microstrip line directional coupler, and the bottom layer 5 of the suspended microstrip line directional coupler. Wherein the top layer 1 and the first air cavity layer 2 form an upper suspension structure, the second air cavity layer 4 and the bottom layer 5 form a lower suspension structure, the signal transmission path is located in the middle of the upper and lower suspension structures, and there is air above and below the signal transmission path.

[0032] Reference Figure 2, the suspension structure formed by the suspended microstrip line directional coupler includes a signal directional coupling microstrip line 9; an air cavity 6 above the microstrip line 9; an air cavity 7 below the microstrip line 9; and a microstrip line PCB dielectric substrate 8.

[0033] Reference Figure 3 , the signal transmission layer is provided with a main line, a first coupling line, and a second coupling line. The main line 16 includes an input end 10 of the suspended microstrip line directional coupler and an output end 11 of the suspended microstrip line directional coupler. The first coupling line 17 includes a coupling end 12 of the suspended microstrip line directional coupler and an isolation end 13 of the suspended microstrip line directional coupler. The second coupling line 18 includes a coupling end 14 of the suspended microstrip line directional coupler and an isolation end 15 of the suspended microstrip line directional coupler. Among them, the input end 10, the output end 11, the coupling end 12, and the isolation end 13 form a directional coupler 1 for monitoring forward and reflected signals inside the RF power amplifier; the input end 10, the output end 11, the coupling end 14, and the isolation end 15 form a directional coupler 2 for monitoring external forward and reflected signals.

[0034] Reference Figure 4 , the RF signal obtained from the power splitter passes through the input detection circuit and the ADC sampling to verify the signal correctness and control the RF switch. After passing through the RF switch, the signal is linearly corrected and then enters the RFPA (RF power amplifier) to amplify the power of the RF signal. After passing through the RFPA, it enters the suspended microstrip line directional coupler of the present invention. The signal is coupled through the microstrip line, and two forward detection signals and a reflection monitoring signal are output at the two coupling ends and the isolation end respectively. The reflection monitoring circuit reads the isolation end 13 and then performs ADC sampling. The result acts on the RF switch to control the on and off of the power amplifier. The forward monitoring circuit reads the coupling end 12 and then performs ADC sampling. The result is used as the input for linear correction to continuously adjust the input signal of the RF power amplifier to form a closed-loop control. The external reflection monitoring circuit reads the isolation end 15 and then can be connected to connectors such as BNC, and directly uses a measuring instrument to read the reflection monitoring signal, and information such as the voltage standing wave ratio (VSWR) can be obtained. The external forward monitoring circuit reads the coupling end 14 and then can also be connected to connectors such as BNC, and uses a measuring instrument to read the forward monitoring signal, and information such as the output power of the RF power amplifier can be obtained.

[0035] The working process of the present invention is as follows: when a radio frequency signal is input from the input end 10 of the suspended microstrip line directional coupler into the main line 16, energy coupling is generated between the main line 16 and the coupling lines 17 and 18 through the spatial electromagnetic field to form a coupled output. The remaining power continues to propagate along the main transmission line and is transmitted out from its output end. At the isolation ends 13 and 15 of the coupler, through structural design and characteristic impedance matching, the uncoupled redundant signals are minimized, thereby achieving a high isolation degree between the input end 10 and the isolation ends 13 and 15. The suspended structure enables the microstrip lines 16, 17, and 18 to be suspended in the air, increasing the distance between the microstrip lines and the top (ground plane) and bottom (ground plane) substrates, reducing the loss between the surface wave and the substrate medium, reducing the influence of the dielectric effect on the transmission characteristics, expanding the bandwidth of the directional coupler and improving the coupling consistency, and achieving a high directivity and power distribution accuracy.

[0036] The present invention is directed to a suspended structure for a microstrip line directional coupler applied to a magnetic resonance power amplification system. The core design principle of the suspended microstrip line directional coupler is similar to that of the traditional microstrip line directional coupler used in a magnetic resonance power amplification system, both of which achieve signal distribution or sampling through the coupling between two microstrip lines. The difference is that the suspended microstrip line directional coupler utilizes the electromagnetic characteristics of the suspended signal line to optimize the coupling efficiency and performance. In the suspended microstrip line structure, the signal transmission line (usually a microstrip line) is no longer directly located on a substrate with a high dielectric constant, but is suspended in a region with a low dielectric constant. The method is to suspend the microstrip line on the substrate through a support structure (such as an air gap or a support material with a low dielectric constant), which has lower transmission losses compared with the traditional microstrip line. Since the dielectric constant of air is close to 1, the propagation loss of electromagnetic waves is small, reducing the energy loss in signal transmission, which is very important for radio frequency signal transmission.

[0037] Compared with the conventional microstrip line directional coupler, the microstrip line is suspended in the air or above a material with high conductivity, reducing the contact between the signal and the substrate material with a high dielectric constant, thereby significantly reducing the dielectric loss; the suspended structure reduces the dispersion effect when electromagnetic waves propagate in the medium, and at the same time reduces the influence of parasitic capacitance and parasitic inductance, enabling the directional coupler to operate in a wider frequency range; it reduces the coupling effect between the substrate surface wave and the parasitic mode, making the electromagnetic field distribution more concentrated, with higher directivity and better isolation performance; air or a low-loss medium provides a higher signal propagation speed (close to the speed of light in a vacuum), while reducing the power loss, and can transmit signals more efficiently, being suitable for a low-loss magnetic resonance radio frequency power amplification system.

[0038] Compared with traditional microstrip line directional couplers, the suspended microstrip line directional coupler used in a magnetic resonance radio frequency power amplification system has lower loss, wider bandwidth, and higher isolation. The suspended microstrip line structure reduces transmission loss by suspending or fixing the signal line on the lower part of the dielectric (usually air or low-loss material). In contrast, the signal line of a traditional microstrip line coupler is usually on a dielectric with a high dielectric constant, which introduces more electromagnetic wave loss. Therefore, the insertion loss of the suspended microstrip line directional coupler is usually low, and it can transmit radio frequency signals more efficiently. In an MRI system, the bandwidth requirement for radio frequency signals is relatively high, especially in terms of high-power transmission and frequency response. The structural design of the suspended microstrip line coupler can better control the propagation characteristics of signals, thereby increasing its operating bandwidth. The suspended microstrip line coupler can reduce interference between adjacent channels by optimizing the distribution of the electric field through design, thereby providing higher isolation, which helps reduce signal interference in the system and thus improve the overall performance and reliability of the system. Using a suspended microstrip line directional coupler has significant advantages in a magnetic resonance radio frequency power amplification system compared with a traditional microstrip line directional coupler, especially in terms of reducing loss, increasing bandwidth, and enhancing isolation. These characteristics make the suspended microstrip line directional coupler a more ideal choice in high-performance radio frequency applications, especially in MRI systems.

[0039] The above-described embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A suspended microstrip line directional coupler applied to a magnetic resonance system, characterized in that, The suspended microstrip directional coupler includes: the top layer of the PCB, the first air cavity layer of the PCB, the signal transmission layer of the PCB, the second air cavity layer of the PCB, and the bottom layer of the PCB, which are connected in sequence. Among them, the top layer and the first air cavity layer are upper suspension structures, and the second air cavity layer and the bottom layer are lower suspension structures; The top layer is obtained by copper plating on the upper surface of the first PCB board; The first air cavity layer is obtained by hollowing out the middle of the second PCB board; The signal transmission layer is obtained by setting a main signal line and a coupling line on the upper surface of the third PCB board; The second air cavity layer is obtained by hollowing out the middle of the fourth PCB board; The bottom layer is obtained by copper plating on the upper surface of the fifth PCB board; Among them, the hollowed position of the first air cavity layer is above the main signal line and the coupling line, and the hollowed position of the second air cavity layer is below the main signal line and the coupling line.

2. The suspended microstrip line directional coupler applied to a magnetic resonance system according to claim 1, characterized in that The lower surface of the top layer is connected to the upper surface of the first air cavity layer, the lower surface of the first air cavity layer is connected to the upper surface of the signal transmission layer, the lower surface of the signal transmission layer is connected to the upper surface of the second air cavity layer, and the lower surface of the second air cavity layer is connected to the upper surface of the bottom layer.

3. The suspended microstrip line directional coupler applied to a magnetic resonance system according to claim 1, wherein The signal transmission layer is provided with a main line, a first coupling line, and a second coupling line.

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