A Microstrip Square Ring Resonator with Multi-Port Input and Its Design Method

Abstract

The present invention belongs to the technical field of insulation condition monitoring of power equipment, and relates to a microstrip square ring resonator with multi-terminal input and its design method. The microstrip square ring resonator includes a substrate, an input microstrip line attached to the surface of the substrate, and a square microstrip ring; the number of input microstrip lines is 3, and the number of input ports of the square microstrip ring is 3. This design method combines the advantages of multi-channel coupling and collaborative improvement. By increasing the number of input microstrip lines and optimizing the design of the microstrip line spacing and coupling gap, the best optimization parameters and energy transmission effect are obtained, thereby improving the overall test performance, enhancing the signal sensitivity of the resonator, and constructing a method for improving the coupling energy of the resonator and the detection sensitivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of insulation condition monitoring of power equipment, and particularly relates to a microstrip square ring resonator with multi-terminal input and its design method. Background Art

[0002] Oil-paper insulation is widely used in key equipment such as transformers. However, its insulation performance is significantly affected by moisture. Moisture can cause an increase in dielectric loss and a decrease in insulation strength, and may even lead to equipment failures or safety accidents in severe cases. Traditional insulation condition assessment methods, such as time-domain polarization / depolarization current method and frequency-domain dielectric spectroscopy technology, although they can effectively detect insulation aging and moisture content, their test cycles are long, the test process is complex and the equipment is expensive, making it difficult to meet the requirements of on-site rapid detection.

[0003] In recent years, new detection technologies based on microstrip resonance dielectric response have gradually emerged. In particular, microstrip ring resonators can efficiently characterize the dielectric properties of insulating materials in the GHz frequency band. Microstrip ring resonators have been widely studied and applied due to their small size, simple structure, and low manufacturing cost. As a typical planar resonator structure, microstrip ring resonators have good frequency selectivity and have become an important resonator structure in high-frequency applications.

[0004] In the existing methods for measuring moisture content using resonators, the following technical problems mainly exist:

[0005] (1) Low coupling efficiency: The current microstrip ring resonator structures mostly adopt single-point or simple coupling methods, with limited coupling energy. And for field enhancement or stronger coupling in a specific direction, the symmetry of the ring makes it not flexible enough. In the high-frequency band, the transmission efficiency of the existing coupling modes is insufficient, and part of the energy is lost at the coupling point, affecting the overall test performance.

[0006] (2) Insufficient sensitivity and resolution: In traditional resonator structures, the design of the coupling point is fixed, and the resonance frequency response range is relatively narrow, unable to capture the changes in the dielectric properties of the sample in multiple frequency bands. Especially in the case of high water content, the signal characteristics are significantly lost. The single-frequency resonance peak results in insufficient frequency resolution and inability to sensitively characterize local or trace water content changes in the sample, leading to insufficient signal sensitivity and detection accuracy of the resonator.

[0007] (3) Poor impedance matching: In a multi-path coupling system, it is difficult to achieve impedance matching between multiple microstrip lines. Especially at different frequencies, the impedance characteristics may change greatly. The reflection coefficient between the input port and the coupled resonator is relatively high, resulting in significant matching losses. Summary of the Invention

[0008] The purpose of the present invention is to provide a multi - terminal input microstrip square - loop resonator and its design method, which solves the problems of low coupling efficiency, insufficient sensitivity and resolution, and poor impedance matching of existing resonators.

[0009] The present invention is realized through the following technical solutions:

[0010] A design method of a multi - terminal input microstrip square - loop resonator includes the following steps:

[0011] S1. Construct an electromagnetic simulation model of the multi - terminal input microstrip square - loop resonator;

[0012] The multi - terminal input microstrip square - loop resonator includes a substrate, input microstrip lines attached to the surface of the substrate, and a square microstrip loop;

[0013] The number of input microstrip lines is 3, and the number of input ports of the square microstrip loop is 3;

[0014] S2. Based on the evaluation index of coupling efficiency, optimize the electromagnetic simulation model to obtain the interval, width of adjacent two input microstrip lines, substrate thickness, and the width of the coupling gap between the input microstrip line and the square microstrip loop;

[0015] The optimization design includes port impedance matching, multi - port excitation phase matching, and microstrip line interval optimization.

[0016] Furthermore, in S1, the construction of the electromagnetic simulation model of the multi - terminal input microstrip square - loop resonator is specifically as follows:

[0017] Draw a square microstrip loop and input microstrip lines to obtain a geometric model;

[0018] Set the dielectric constant and loss tangent for the substrate, create an air box around the geometric model, set the air radiation boundary; set the excitation port at the input end of the square microstrip loop, and set the frequency scanning range;

[0019] Set the solution region and mesh division method for the geometric model to obtain the electromagnetic simulation model of the microstrip square - loop resonator.

[0020] Furthermore, in S2, the interval between adjacent two input microstrip lines is 2.5 - 6 mm.

[0021] Furthermore, in S2, the width of the input microstrip line is 1.805 - 1.85 mm; the substrate thickness is 25 - 35 mil.

[0022] Furthermore, in S2, the width of the coupling gap between the input microstrip line and the square microstrip loop is 0.1 - 0.4 mm.

[0023] Further, in S2, the evaluation indexes of the coupling efficiency include the input power, the radiation efficiency, and the maximum gain.

[0024] Further, in S1, a serrated annular coupling structure is nested in the square microstrip loop;

[0025] The serrated annular coupling structure includes a serrated microstrip line and an internal square microstrip loop. The serrated microstrip line is connected to the inside of the internal square microstrip loop and is symmetrically arranged along the center of the internal square microstrip loop.

[0026] Further, there are several serrations on the same side of the serrated microstrip line, forming a plurality of coupling spacings.

[0027] The present invention also discloses a microstrip square loop resonator with multi-terminal input, which is characterized by including a substrate, an input microstrip line attached to the surface of the substrate, and a square microstrip loop;

[0028] The number of input microstrip lines is 3, and the number of input ports of the square microstrip loop is increased to 3.

[0029] Further, a serrated annular coupling structure is nested in the square microstrip loop;

[0030] The serrated annular coupling structure includes a serrated microstrip line and an internal square microstrip loop. The serrated microstrip line is connected to the inside of the internal square microstrip loop and is symmetrically arranged along the center of the internal square microstrip loop.

[0031] Compared with the prior art, the present invention has the following beneficial technical effects:

[0032] The present invention discloses a design method of a microstrip square loop resonator with multi-terminal input. The number of microstrip lines is increased to 3, and at the same time, the number of input ports of the square microstrip loop is increased to 3, which can form a higher electric field intensity in the coupling region, enhance the energy transfer efficiency, and the multi-path coupling design can minimize the energy loss when a single microstrip line is excited, realizing a higher power utilization rate; the combined action of 3 microstrip lines can generate a more concentrated electric field distribution in the coupling region, making the entire resonator more sensitive to the target region. More microstrip line inputs can generate a stronger signal response in the coupling region, thereby improving the detection ability of minute physical changes. In test applications, the multi-path design can more effectively detect the subtle differences in dielectric constant, moisture content, or material properties. This method combines the advantages of multi-path coupling and synergistic improvement. By increasing the number of input microstrip lines and optimizing the design of the microstrip line spacing and coupling gap, the optimal optimization parameters and energy transmission effects are obtained, thereby improving the overall test performance, enhancing the signal sensitivity of the resonator, and constructing a method for improving the coupling energy and detection sensitivity of the resonator.

[0033] The present invention also discloses a microstrip square ring resonator with multi - terminal input, increasing the number of coupled microstrip lines to 3, and at the same time increasing the input ports to 3, so as to enhance the electric field strength at the output port and the energy transmission ability. On the one hand, the three inputs are considered for the functional requirements of the resonator, that is, to enhance the coupled energy; on the other hand, it is considered for the electromagnetic field distribution, facilitating subsequent research on the interaction effects between microstrip lines, such as whether the influence of the middle microstrip line on the two side microstrip lines is the same.

[0034] Furthermore, the square ring structure is further optimized by nesting a serrated ring - shaped coupling structure in the square ring. This structure increases the coupling distance, introduces additional capacitance, concentrates the energy of the original square ring inward, and then enhances the electric field coupling at the output end, significantly improving the energy transmission efficiency of the resonator with the serrated ring - shaped coupling structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the optimization idea process of the present invention;

[0036] Figure 2 is the electromagnetic simulation model of the microstrip square ring resonator with single - terminal input constructed;

[0037] Figure 3 is the insertion loss characteristic curve of the resonator corresponding to different microstrip ring widths;

[0038] Figure 4 is the insertion loss characteristic curve of the resonator corresponding to different substrate thicknesses;

[0039] Figure 5 is the transmission loss situation of the middle microstrip line with different microstrip intervals;

[0040] Figure 6a is d = 2.5mm, P max = 72495 V / m, the planar distribution of the electric field strength of the resonator designed by the present invention;

[0041] Figure 6b is d = 3mm, P max = 94924 V / m, the planar distribution of the electric field strength of the resonator designed by the present invention;

[0042] Figure 6c is d = 3.5mm, P max = 71952 V / m, the planar distribution of the electric field strength of the resonator designed by the present invention;

[0043] Figure 6d is d= 4 mm, P max when = 85255 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention;

[0044] Figure 6e is d = 4.5 mm, P max when = 77113 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention;

[0045] Figure 6f is d = 5 mm, P max when = 68244 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention;

[0046] Figure 6g is d = 5.5 mm, P max when = 85737 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention;

[0047] Figure 6h is d = 6 mm, P max when = 71822 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention;

[0048] Figure 7 is the planar electric field distribution of the single-input-port resonator;

[0049] Figure 8 is the planar electric field distribution of the triple-input-port resonator;

[0050] Figure 9a is the schematic diagram of the simulation model of the serrated ring coupling structure;

[0051] Figure 9b is the structural schematic diagram of the serrated ring coupling structure;

[0052] 1. Inner square microstrip ring; 2. Serrated microstrip line; 3. Coupling spacing;

[0053] Figure 10 is the planar electric field distribution when 1 / 3 W input power is applied to three ports simultaneously;

[0054] Figure 11 is the schematic diagram of the simulation model of another serrated ring coupling structure. Detailed implementation manner

[0055] In order to make the objectives, technical solutions and advantages of the present invention clearer and more explicit, the following further detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only some embodiments of the present invention, rather than all embodiments.

[0056] The components described and illustrated in the accompanying drawings and embodiments of the present invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present invention provided in the following drawings is not intended to limit the scope of the present invention claimed, but merely represents a selected embodiment of the present invention. Based on the accompanying drawings and embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention.

[0057] It should be noted that the term "comprising", "including" or any other variant is intended to cover non-exclusive inclusion, so that a process, element, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to the process, element, method, article or device.

[0058] First, the following explanations are made for relevant technical terms:

[0059] Microstrip line: A common planar transmission line composed of a conductive layer (usually copper), a dielectric layer and a ground layer, used to transmit high-frequency signals, and its characteristics are determined by the line width, dielectric constant and thickness.

[0060] Coupling: The process by which a signal or energy is transferred from one microstrip line to another microstrip line or resonator.

[0061] Resonant frequency: The resonance point of a resonator at a specific frequency, at which the resonator has the highest energy transfer efficiency.

[0062] Transmission coefficient: Represents the ratio of the input signal transmitted from one port to another port, and is used to evaluate the transmission efficiency of the system.

[0063] Microstrip ring resonator: A planar resonant structure based on microstrip lines, usually designed as a closed ring. Resonance phenomena are formed by the standing waves of electromagnetic waves in the ring, and are used to test and transmit signals. Commonly used to evaluate material properties (such as dielectric constant, loss tangent) or design filters and antennas.

[0064] Resonant main peak: In the frequency response curve, the maximum amplitude that appears at a specific frequency (referred to as the resonant frequency). At this time, the response of the system or circuit reaches the highest, and the energy is concentrated near this frequency, showing a resonance phenomenon.

[0065] Resonant side peaks: Secondary peaks that appear at frequencies near the main resonant peak, usually located on both sides of the main peak. These side peaks generally reflect the non-ideality of the system. The amplitude of the side peaks is usually lower than that of the main peak, and their frequencies deviate from the main resonant frequency.

[0066] The present invention proposes a multi-port input microstrip square ring resonator for coupling energy enhancement and improving the detection sensitivity of the water content in oil-paper insulation. This method combines the advantages of multi-path coupling and synergy improvement. By increasing the number of input microstrip lines and optimizing the design of the microstrip line spacing and coupling gap, the best optimization parameters and energy transmission effect are obtained, thereby improving the overall test performance and enhancing the signal sensitivity of the resonator.

[0067] Mainly based on the electromagnetic simulation model, taking the coupling efficiency of single input and single output as a benchmark, quantifying whether the multi-path input improves the coupling efficiency. Studying the influence of the synergy between the input ends on the output energy, adjusting the input phase and power distribution, and finally realizing the optimization of the output energy.

[0068] The present invention first considers the design of the multi-port input resonator, such as Figure 1 shown, the microstrip circular ring resonator with single-port input shown in Figure a of Figure 1 is first designed as the multi-port input microstrip circular ring resonator shown in Figure b of Figure 1 to improve the energy transmission effect and enhance the signal sensitivity of the resonator.

[0069] After that, it is optimized again. The multi-port input microstrip circular ring resonator shown in Figure b of Figure 1 is further improved to a square ring structure to accurately control the gap between the microstrip line and the microstrip ring. The microstrip square ring resonator shown in Figure c of Figure 1 is designed, and the distances from multiple microstrip lines to the square ring are the same. Controlling the loop gap to achieve impedance matching.

[0070] After that, it is optimized again. As shown in Figure d of Figure 1 , controlling the spacing of the microstrip lines, variable spacing, to achieve the synergy of the microstrip lines. Combining the advantages of multi-path coupling, studying the influence of the synergy between the input ends on the output energy.

[0071] After that, through phase control, optimizing the phase and power distribution of the input ends to improve the overall test performance.

[0072] After that, based on the calculation of the transmitted energy and transmission efficiency, taking the single input and single output coupling efficiency as a benchmark, quantifying whether the multi-path input improves the coupling efficiency, and finally realizing the optimization of the output energy.

[0073] The present invention proposes a method for exploring based on a microstrip square ring resonator. The specific technical solution includes four main steps: model establishment, obtaining the reference coupling efficiency, multi-channel coupling optimization design, and analysis of coupling energy and sensitivity improvement. Each step will be detailed below one by one.

[0074] Step 1: Model establishment

[0075] The microstrip ring resonator is composed of a substrate and microstrip lines and microstrip rings attached to the surface of the substrate. Usually, a circular ring is used as the structure of the microstrip ring. The circular ring has rotational symmetry and uniform electromagnetic field distribution. However, for field enhancement or stronger coupling in a specific direction, the symmetry of the circular ring makes it less flexible. Compared with the circular ring, the square ring is more flexible in the distribution design of multiple microstrip lines. The coupling distance between the microstrip lines and different sides can be adjusted, and the coupling points can be arranged more flexibly. Different design requirements can be easily achieved by adjusting the coupling gap. In this structure, the phase velocity of electromagnetic waves cannot achieve transverse electromagnetic mode (TEM) matching at the interface of discontinuous media, and the transmission mode of electromagnetic waves is a hybrid mode of transverse electric mode - transverse magnetic mode (TE - TM).

[0076] The model diagram of the microstrip square ring resonator is as Figure 2 shown, including a substrate and microstrip lines and microstrip rings attached to the surface of the substrate. There is an insulating cardboard above the microstrip lines and microstrip rings. Among them, h1 is the substrate thickness; h2 is the total thickness after stacking the upper layer of dielectric; w is the width of the microstrip lines and microstrip rings, and the widths of the microstrip lines and microstrip rings are the same; g is the width of the coupling gap between the microstrip lines and the microstrip rings. The microstrip square ring resonator reflects the change of the dielectric characteristics of the material to be measured through the shift of the resonance peak. By superimposing the change of the resonance frequency and the insertion loss value at the resonance frequency before and after the material to be measured, the dielectric characteristics of the material to be measured are deduced.

[0077] The upper layer of dielectric is an insulating cardboard, and the purpose is to verify the ability of the resonator to detect the dielectric characteristics of materials: when a dielectric material (insulating cardboard) is stacked above the resonator, the resonance characteristics represented by the insertion loss will change, specifically manifested as the shift of the resonance frequency, the change of the numerical value and sharpness of the insertion loss resonance peak.

[0078] The process of establishing the electromagnetic simulation model of the microstrip square ring resonator includes:

[0079] Create a rectangular plane, define the size of the substrate, set the substrate thickness, and ensure compliance with the actual microstrip process. Draw geometric structures such as a square microstrip ring and input / output microstrip lines.

[0080] Set the dielectric constant and loss tangent for the substrate, create an air box around the model, and set the air radiation boundary. Set excitation ports at both ends of the square microstrip loop and set the frequency scan range.

[0081] Set the solution region and the mesh division method to obtain the electromagnetic simulation model of the microstrip square loop resonator.

[0082] After that, simulate and solve the scattering parameters. Specifically, optimize the scattering parameter curve through the Ansys HFSS (Ansys High Frequency Structure Simulator) simulation software. The optimization directions are: the main resonance peak is sharper, the number of side peaks is less or there are no side peaks, and the curve outside the resonance peak is as smooth as possible without burrs and distortions.

[0083] Among them, the scattering parameter is an important parameter in microwave transmission. The scattering parameters include the reflection coefficient S 11 of the antenna port and the forward transmission coefficient S 21 . The forward transmission coefficient S 21 is used to characterize the insertion loss characteristic (Insertion Loss, IL ) of the resonator. IL = 20lg(| S 21 |). The sharper the S 21 curve, the smaller the insertion loss.

[0084] Step 2: Obtain the reference coupling efficiency

[0085] The single input-output port is the reference for the analysis of multi-port resonators and is used to evaluate whether the multi-port design brings performance improvement. The input port provides the excitation signal to test the reflection characteristics of the system, and the output port is used to receive the signal that arrives after transmission or radiation to analyze the transmission characteristics. Figure 2 The resonator shown is a single input-output port resonator, which is used to test the insertion loss and reflection loss of the transmission line and perform performance analysis.

[0086] The resonance frequency f can be expressed as:

[0087]

[0088] Among them, L is the equivalent inductance of the resonator, and C is the equivalent capacitance of the resonator.

[0089] The reflection and transmission performance of the single input-output port model serves as a reference value for the multi-port system; the total gain and radiation efficiency in the case of single input are used as benchmarks to evaluate the improvement of multi-input synergy; based on the electromagnetic field strength in the input and coupling regions of the single input port, it is analyzed whether there is synergy or energy loss between multiple input ends.

[0090] The evaluation indicators of coupling efficiency include incident power, radiation efficiency, gain, etc., and the specific definitions are as follows:

[0091] (1) Incident power

[0092] In the HFSS simulation software, the incident power refers to the defined port excitation power, and the default value is 1W. It is set that the single-port incident power is equal to the total power of the multi-port input ports.

[0093] (2) Radiation efficiency

[0094] Radiation efficiency is the ratio of the radiation power P rad and the net input power P acc .

[0095] The radiation power refers to the electromagnetic energy radiated into free space via the antenna. The radiation power of the antenna can be calculated by the surface integral of the Poynting vector, that is:

[0096]

[0097] In the formula, P rad is the radiation power; H * is the conjugate of the magnetic field strength H ; n is the unit normal vector of the outer normal of the closed surface S ; E represents the electric field strength.

[0098] The net input power refers to the input power actually flowing into the antenna port. If P acc and P inc are used to represent the net input power and the input power respectively, for a single-port antenna with only one transmission mode, then there is

[0099] P acc = P inc (1 - | S 11 | 2 )

[0100] In the formula, S 11 is the reflection coefficient of the antenna port.

[0101] (3)Peak Gain

[0102] The peak gain refers to the ratio of the radiation power density of the antenna in the maximum radiation direction to the radiation power density of an isotropic antenna in the same direction under the same net input power and the same distance.

[0103] Antenna gain G can be calculated by the following formula:

[0104] G = 4π U / P acc

[0105] G = η A D

[0106] where, U represents the radiation intensity; D represents the directivity coefficient, D = 4π U / P rad . The directivity coefficient refers to the ratio of the radiation power density of the antenna in the maximum radiation direction to the radiation power density of an isotropic antenna in the same direction under the same radiation power and the same distance. η A represents the radiation efficiency, which is the ratio of the radiation power P rad and the net input power P acc .

[0107] The input power is generally user-defined, and the radiation efficiency and peak gain are calculation results. The present invention mainly considers the radiation efficiency.

[0108] Step 3: Multiplex coupling optimization design

[0109] In the multiplex coupling system of the microstrip ring resonator, to achieve higher energy transfer efficiency and coupling performance, the key points of the optimization design include port impedance matching and multi-port parameter optimization design (multi-port excitation phase matching, microstrip line interval optimization). The change of the coupled energy can be quantitatively analyzed through parameters such as the radiation efficiency, and the influence can be reflected by the change of the electromagnetic field distribution.

[0110] (1)Port impedance matching

[0111] The impedance matching degree between the resonator interface and the test cable interface plays a crucial role in signal transmission. The characteristic impedance of the microstrip line is determined by the values of the microstrip line width and the substrate thickness. The characteristic impedance of the test cable is generally 50Ω. Therefore, the characteristic impedance of the microstrip line part of the microstrip ring resonator needs to be as close to 50Ω as possible. As the microstrip line width increases, the characteristic impedance of the microstrip ring decreases; as the substrate thickness increases, the characteristic impedance of the microstrip ring increases. Both the microstrip line width and the substrate thickness affect the magnitude of the characteristic impedance. In order to obtain more accurate microstrip line width and substrate thickness parameters that meet the actual working requirements of the resonator, first, the HFSS software is used to optimize the microstrip line width to obtain the optimal insertion loss ( S 21 ) curve. Then, the microstrip square ring resonator is optimized and designed.

[0112] The characteristic impedance of the microstrip line part can be calculated using the printed circuit board impedance calculation and simulation software. First, use the Polar Si9000 software to calculate the characteristic impedance of the microstrip line part of the microstrip ring resonator with a substrate thickness of 30 mil (≈ 0.762 mm), a substrate material dielectric constant of 3.2, and a copper foil thickness of 0.5 oz (≈ 18 μm), and optimize the characteristic impedance to 50Ω by adjusting the line width. The calculation interface and optimization results of the Polar Si9000 software are as Figure 3 shown. It can be seen that when the microstrip line width is 1.805 mm, the calculated result of the characteristic impedance of the microstrip line part is 50Ω.

[0113] The Polar Si9000 software is the Polar Si9000 advanced transmission line field solver. It is a professional software widely used in the field of printed circuit board (PCB) design, mainly used to accurately calculate parameters such as the characteristic impedance of transmission lines on the PCB. With the help of various transmission line models built into the software, such as microstrip lines and striplines, combined with information such as the material properties and line dimensions of the PCB, the field solution algorithm is used to simulate and calculate the electrical performance of the transmission line, assisting engineers in PCB design and optimization to ensure reliable signal transmission.

[0114] Then, in order to obtain more accurate microstrip ring width and substrate thickness that meet the actual working requirements of the resonator, the Ansys HFSS (Ansys High Frequency Structure Simulator) simulation software is used to optimize the microstrip line width of the microstrip ring resonator in an interval near 1.805 mm to obtain the optimal insertion loss curve. For the microstrip line width wNear the software optimization value of 1.805 mm, values of 1.70 mm, 1.75 mm, 1.80 mm, 1.805 mm, 1.85 mm, and 1.90 mm were taken respectively to calculate the scattering parameters of the resonator, as shown in Figure 3 Figures (a) - (f) therein. When w = 1.85 mm, as shown in Figure 3 Figure (e) therein, the resonant main peak of the resonator insertion loss curve is significant, the curve outside the resonant peak is smooth, only one resonant side peak appears, and the peak - valley difference ratio is only 6.27%. Therefore, w the insertion loss curve measured for the resonator corresponding to = 1.85 mm can more accurately reflect the resonant information, and the resonant characteristics are relatively good. When w = 1.70 mm, 1.75 mm, 1.80 mm, 1.90 mm, three resonant side peaks appear in the insertion curve of the resonator, and the peak - valley difference ratios of two resonant side peaks are about 50%, which is relatively serious. Preferably, the width of the input microstrip line is 1.805 - 1.85 mm.

[0115] To determine whether the resonator substrate thickness h 1 = 30 mil (equivalent to 0.762 mm) is the optimal parameter, while keeping the width of the resonator microstrip line w at 1.85 mm, the substrate material, and other parameters unchanged, the substrate thickness h 1 was taken at 10 mil, 15 mil, 20 mil, 25 mil, 30 mil, 35 mil respectively near the common thickness of 30 mil to calculate the scattering parameters of the resonator, as shown in Figure 4 Figures (a) - (f) therein. 30 mil is the common thickness of the microstrip antenna substrate. When h 1 = 30 mil, only side peaks appear near the resonant main peak 4 in the insertion loss curve, and the peak - valley difference ratio is only 6.27%, which has basically no impact on the resonant main peak. Therefore, the insertion loss characteristics of the resonator are the best. When h 1 = 10 mil, four resonant side peaks appear in the insertion loss curve, and the peak - valley difference ratio of the third side peak reaches 40.58%. The curve distortion between the second resonant peak and the fifth resonant peak is relatively serious; when h 1 = 15 mil, 20 mil, a certain degree of distortion appears in the insertion loss curve, resonant side peaks appear near the resonant main peak, and the heights of some resonant side peaks are comparable to those of the corresponding resonant main peaks. Preferably, the resonator substrate thickness is 25 - 35 mil.

[0116] (2) Multi - port parameter optimization design

[0117] Although increasing the number of microstrip lines can provide multiple input channels and disperse the impact of interference on a single microstrip line, it may lead to increased structural complexity and manufacturing difficulty. Also, it is necessary to consider that multiple microstrip lines may introduce mutual interference and affect the coupling efficiency. Therefore, subsequent research needs to use the Ansys HFSS simulation tool to optimize the layout, gap, and input conditions of each microstrip line, adjust the phase difference and distance between microstrip lines, and ensure a uniform field distribution within the coupling region.

[0118] First, the number of input microstrip lines is increased to 3, and the number of input ports is increased to 3. The electromagnetic simulation model is shown in Figure 6. The width of the coupling gap between the microstrip line and the square microstrip loop is designed to be 0.1 - 0.4 mm. To explore the improvement effect of multi-channel coupling, multi-channel coupling is compared with single-port input while controlling the same coupling gap, and the optimal design scheme for the multi-port excitation phase and microstrip line spacing is studied. Through simulation and experiments, it is proved that when the coupling gap is 0.1 - 0.4 mm, the design requirements can be met, and among them, 0.4 mm is the optimal design parameter. By setting the excitation magnitude of the three input ports in the simulation to be 1 / 3 of that of a single port, the influence of different excitation port phases on the resonant performance is studied, and finally the optimal phase matching result is obtained, realizing the improvement of coupling energy without cancellation due to phase mismatch.

[0119] On the one hand, three input microstrip lines are considered for the functional requirements of the resonator, that is, the improvement of coupling energy; on the other hand, it is considered for the electromagnetic field distribution to facilitate subsequent research on the interaction effects between microstrip lines, whether the influence of the middle microstrip line on the two side microstrip lines is the same.

[0120] Furthermore, the spacing distance between two adjacent microstrip lines is simulated. Denote the microstrip spacing as d , and the insertion loss curve is obtained as shown in Figure 5 . The curves in the figure respectively represent the losses from the middle input port to the output port when d is 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm. It can be obtained that the influence of different microstrip spacings on the loss from the middle input port to the output port is mainly reflected in the loss amplitude and the side peaks of the resonant point, reflecting the rationality of parameter design. The optimization direction is that the main resonant peak is sharper, the number of side peaks is less or there are no side peaks, and the curve outside the resonant peak is as smooth as possible without burrs and distortions.

[0121] Figures 6a - 6h shows the planar distribution of the electric field intensity under different microstrip spacings d , as well as the maximum value of the field strength P max . Among them, Figure 6a in d = 2.5 mm, P max= 72495 V / m; Figure 6b in d = 3 mm, P max = 94924 V / m; Figure 6c in d = 3.5 mm, P max = 71952 V / m; Figure 6d in d = 4 mm, P max = 85255 V / m; Figure 6e in d = 4.5 mm, P max = 77113 V / m; Figure 6f in d = 5 mm, P max = 68244 V / m; Figure 6g in d = 5.5 mm, P max = 85737 V / m; Figure 6h in d = 6 mm, P max = 71822 V / m. It can be seen from Figure 6 that the field strength is mainly concentrated at the loop coupling of the input end, and the electric field distributions are similar. By comparison, d when it is 3 mm, the field strength is the largest. Considering the resonance peak and the field strength comprehensively, the interval between adjacent input microstrip lines is 2.5 - 6 mm, and preferably the interval between adjacent input microstrip lines is 3 mm.

[0122] Step Four: Coupling Energy and Sensitivity Enhancement

[0123] The main purpose of the research on the enhancement of multi-path coupling energy is to increase the received energy of the output microstrip line, so that when multiple input ports work simultaneously, the energy received at the output end is higher than that in the case of a single input port, and to study whether multi-path input will trigger a coupling synergy effect to enhance the output energy.

[0124] To intuitively compare the coupling energy changes between single input and multi-input, evaluate whether the excitation of different input ports can evenly or effectively transfer energy to the output end, and the coupling efficiency changes of multi-path input excitation at different frequencies, with the help of simulation tools, the electromagnetic field distribution is compared.

[0125] When the input power of single-port excitation is 1 W, the electromagnetic field distribution in its plane area is as Figure 7As shown. The mark m1 represents the position where the output microstrip line receives energy, with an electric field strength of 3311 V / m. The mark m2 represents the position where the input microstrip line transmits energy, with an electric field strength of 70560 V / m, and the transmission efficiency is 4.69%.

[0126] When all three ports are excited simultaneously, the power of each input port is set to be equal. Figure 8 It is the planar electric field distribution when a 1 / 3 W input power is applied to all three ports simultaneously. The mark m1 represents the position where the output microstrip line receives energy, with an electric field strength of 4896 V / m; the mark m2 represents the position where the middle input microstrip line transmits energy, with an electric field strength of 40150 V / m; the marks m3 and m4 respectively represent the positions where the upper and lower input microstrip lines transmit energy, with electric field strengths of 32840 V / m and 31930 V / m respectively, and the transmission efficiency is 4.67%. From the comparison of transmission efficiency, the ratio of the transmitted electric field between the multi-port and the single-port is similar, indicating that the power concentration is higher when there is a single input port, while there may be power dispersion or loss in the multi-input port. However, at the same time, the electric field strength at the output end of the multi-port is significantly higher than that of the single-port, indicating that the energy transmission ability of the multi-input end is stronger.

[0127] Furthermore, evaluate the coupling uniformity and effectiveness of the excitations of different input ports. From Figure 8 It can be obtained that when the input powers of different excitation ports are the same, the energy coupled to the gap by the three microstrip lines is the strongest at the middle gap, and the difference between the upper and lower ends is not significant, indicating that the coupled energy has a tendency to concentrate inward, which is also closely related to the electric field distribution in the figure. Compared with Figure 7 it can be obtained that the multi-path coupling enhances the electric field and more energy flows to the output end.

[0128] The microstrip ring resonator is essentially a microstrip antenna. The radiation efficiency in the calculation results of its antenna parameters can quantify the input-output coupling energy efficiency. The net input power, radiation power, maximum gain, and radiation efficiency of the single-port and multi-port are shown in Tables 1 and 2. Table 1 shows the calculation results of radiation efficiency and other parameters for the single-port case, and Table 2 shows the calculation results of radiation efficiency and other parameters for the multi-port case. The comparison verifies the effect of multi-path coupling on energy improvement.

[0129] Table 1

[0130]

[0131] Table 2

[0132]

[0133] The multi-channel coupling system can significantly improve the test sensitivity by optimizing the input energy distribution and output coupling efficiency. The final design is that the input power of each input port is equal, and the phase at the input end is 0 degrees. When the excitation signals of multiple input ports are optimized, the energy forms a coherent superposition in the coupling region, effectively enhancing the output signal intensity. A higher output signal intensity can increase the signal-to-noise ratio, reduce system errors, and thus enhance the test sensitivity. When testing weak physical properties, namely low water content or small dielectric changes in oil-paper insulation, the energy boost helps to accurately capture the response of the test object even at low signal intensities.

[0134] Based on the microstrip square loop resonator with multi-terminal input, aiming at Figure 8 the problem that the internal electric field of the square loop is not concentrated, it is further optimized, and a serrated annular coupling structure inside the square loop is designed, as Figure 9a shown. By adding the serrated annular coupling structure, additional capacitance is introduced to concentrate the energy of the external square microstrip loop shown in Figure 7 inward, thereby enhancing the electric field coupling at the output end and improving the energy transmission efficiency.

[0135] Specifically, as Figure 9b shown, the serrated annular coupling structure is composed of serrated microstrip lines 2 and an internal square microstrip loop 1. The serrated microstrip lines 2 are connected to the inside of the internal square microstrip loop 1 and are symmetrically arranged along the center of the internal square microstrip loop 1; there are 4 serrations on the same side of the serrated microstrip lines 2, forming 3 coupling spacings 3.

[0136] The surface of the microstrip line of the serrated annular coupling structure resembles a sawtooth and is embedded in the external square microstrip loop, forming a channel from left to right inside the loop, increasing multiple coupling spacings 3.

[0137] Figure 10 This is the planar electric field distribution when an input power of 1 / 3 W is applied to three ports simultaneously. The mark m1 represents the position where the output-end microstrip line receives energy, and the field strength is 15450 V / m; the mark m2 represents the position where the middle input-end microstrip line transmits energy, and the field strength is 44080 V / m; the mark m3 represents the position where the upper input-end microstrip line transmits energy, and the field strength is 48950 V / m, and the mark m4 represents the position where the lower input-end microstrip line transmits energy, and the field strength is 45400 V / m; the transmission efficiency is 11.16%. Comparing from the transmission efficiency, the electric field transmission efficiency of the serrated annular coupling structure has been greatly improved, which is 2 to 3 times that of the single-port and the three-port without the serrated annular coupling structure, indicating that the optimized structure makes the electric field concentration higher, thus realizing the improvement of the coupling efficiency. At the same time, the electric field intensity at the output end of the serrated annular coupling structure is significantly higher than that of the single-port and the three-port, indicating that the serrated annular coupling structure has a stronger energy transmission ability.

[0138] AsFigure 11 As shown, there are a total of 5 sawteeth on the same side of the serrated microstrip line 2, forming 4 coupling spacings 3. The mark m1 represents the position where the output-end microstrip line receives energy, and the field strength is 14420 V / m; the mark m2 represents the position where the middle input-end microstrip line transmits energy, and the field strength is 67930 V / m; the mark m3 represents the position where the upper input-end microstrip line transmits energy, and the field strength is 48420 V / m, and the mark m4 represents the position where the lower input-end microstrip line transmits energy, and the field strength is 53190 V / m; the transmission efficiency is 8.51%. From the comparison of the transmission efficiency, the electric field transmission efficiency of the serrated ring coupling structure has been greatly improved, indicating that the optimized design structure makes the electric field concentration higher, thus realizing the improvement of the coupling efficiency.

[0139] Finally, it should be noted that the above 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 above embodiments, those of ordinary skill in the art should understand that: still modifications or equivalent replacements can be made to the specific embodiments of the present invention, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A design method for a multi-port input microstrip square ring resonator, characterized in that: The following steps are involved: S1. Construct an electromagnetic simulation model of a multi-port input microstrip square ring resonator; The multi-port input microstrip square ring resonator comprises a substrate, an input microstrip line attached to the surface of the substrate, and a square microstrip ring; The number of input microstrip lines is 3, and the number of input ports of the square microstrip ring is 3; S2. Optimize the design of the electromagnetic simulation model based on the evaluation index of coupling efficiency to obtain the interval, width, substrate thickness of two adjacent input microstrip lines, and the width of the coupling gap between the input microstrip line and the square microstrip ring; The optimization design includes port impedance matching, multi-port excitation phase matching and microstrip line spacing optimization; In S1, a sawtooth ring coupling structure is embedded in the square microstrip ring; The sawtooth annular coupling structure comprises a sawtooth microstrip line (2) and an internal square microstrip ring (1); the sawtooth microstrip line (2) is connected to the interior of the internal square microstrip ring (1) and is symmetrically arranged along the center of the internal square microstrip ring (1); There are a plurality of saw teeth on the same side of the sawtooth microstrip line (2), forming a plurality of coupling intervals (3).

2. The design method of a multi-port input microstrip square ring resonator according to claim 1, characterized in that: In S1, the electromagnetic simulation model of the multi-port input microstrip square ring resonator is constructed as follows: Draw a square microstrip ring and input microstrip line to obtain the geometric model; Set the dielectric constant and loss tangent for the substrate, create an air box around the geometric model, and set the air radiation boundary; set the excitation port at the input end of the square microstrip ring and set the frequency sweep range; The solution region and mesh division method are set according to the geometric model to obtain the electromagnetic simulation model of the microstrip square ring resonator.

3. The design method of a multi-port input microstrip square ring resonator according to claim 1, characterized in that: In S2, the interval between two adjacent input microstrip lines is 2.5-6 mm.

4. The design method of a multi-port input microstrip square ring resonator according to claim 1, characterized in that: In S2, the width of the input microstrip line is 1.805-1.85 mm; the substrate thickness is 25-35 mil.

5. The design method of a multi-port input microstrip square ring resonator according to claim 1, characterized in that: In S2, the width of the coupling gap between the input microstrip line and the square microstrip ring is 0.1-0.4 mm.

6. The design method of a multi-port input microstrip square ring resonator according to claim 1, characterized in that: In S2, the evaluation indicators of coupling efficiency include input power, radiation efficiency and maximum gain.

7. A multi-port input microstrip square ring resonator, characterized in that: It includes a substrate, an input microstrip line and a square microstrip ring attached to the surface of the substrate; The number of input microstrip lines is 3, and the number of input ports of the square microstrip ring is increased to 3; A zigzag ring coupling structure is nested in the square microstrip ring; The sawtooth annular coupling structure comprises a sawtooth microstrip line (2) and an internal square microstrip ring (1); the sawtooth microstrip line (2) is connected to the interior of the internal square microstrip ring (1) and is symmetrically arranged along the center of the internal square microstrip ring (1); There are a plurality of saw teeth on the same side of the sawtooth microstrip line (2), forming a plurality of coupling intervals (3).

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