Multi-end input microstrip square ring resonator and design method thereof

Abstract

The invention belongs to the technical field of power equipment insulation state monitoring, and relates to a multi-end input microstrip square ring resonator and a design method thereof. The micro-strip square ring resonator comprises a substrate, an input micro-strip line attached to the surface of the substrate and a square micro-strip ring. The number of the input microstrip lines is three, and the number of the input ports of the square microstrip ring is three. According to the design method, the advantage of multi-path coupling cooperative improvement is combined, optimal parameters and an energy transmission effect are obtained by increasing the number of input end microstrip lines and optimally designing microstrip line intervals and coupling gaps, the overall test performance is further improved, the signal sensitivity of the resonator is enhanced, and the reliability of the resonator is improved. And a method for improving the coupling energy and the detection sensitivity of the resonator is constructed.

Description

Technical Field

[0001] The invention belongs to the technical field of insulation status monitoring of electric power equipment, and in particular relates to a multi-terminal input microstrip square ring resonator and a design method thereof. Background Art

[0002] Oil-paper insulation is widely used in key equipment such as transformers. However, its insulation performance is significantly affected by moisture, which can increase dielectric loss and reduce insulation strength. In severe cases, it may cause equipment failure or even safety accidents. Traditional insulation status assessment methods, such as time domain polarization / depolarization current method and frequency domain dielectric spectroscopy technology, can effectively detect insulation aging and moisture content, but their test cycle is long, the test process is complicated, and the equipment is expensive, making it difficult to meet the needs of rapid on-site detection.

[0003] In recent years, new detection technologies based on microstrip resonant dielectric response have gradually developed. In particular, microstrip ring resonators can efficiently characterize the dielectric properties of insulating materials in the GHz frequency band. Microstrip ring resonators are 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 resonant structure in high-frequency applications.

[0004] The existing resonator method for measuring moisture content mainly has the following technical problems: (1) Low coupling efficiency: The current microstrip ring resonator structure mostly adopts a single-point or simple coupling method, with limited coupling energy, and the symmetry of the ring makes it inflexible for field enhancement or stronger coupling in a specific direction. In the high frequency band, the transmission efficiency of the existing coupling mode is insufficient, and part of the energy is lost at the coupling point, affecting the overall test performance.

[0005] (2) Insufficient sensitivity and resolution: The coupling point design in the traditional resonator structure is fixed, and the resonant frequency response range is narrow, which cannot capture the changes in the dielectric properties of the sample in multiple frequency bands, especially in the case of high water content, where the signal characteristics are significantly lost. The single frequency resonance peak leads to insufficient frequency resolution, making it impossible to sensitively characterize local or trace water content changes in the sample, resulting in insufficient signal sensitivity and detection accuracy of the resonator.

[0006] (3) Poor impedance matching: In a multi-channel coupled system, impedance matching between multiple microstrip lines is difficult to achieve, especially at different frequencies, where the impedance characteristics may vary greatly. The reflection coefficient between the input port and the coupled resonator is high, resulting in significant matching loss. Summary of the invention

[0007] The object of the present invention is to provide a multi-port input microstrip square ring resonator and a design method thereof, which solves the problems of low coupling efficiency, insufficient sensitivity and resolution, and poor impedance matching of existing resonators.

[0008] The present invention is achieved through the following technical solutions: A design method for a multi-port input microstrip square ring resonator comprises the following steps: 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.

[0009] Further, 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.

[0010] Furthermore, in S2, the interval between two adjacent input microstrip lines is 2.5-6 mm.

[0011] Furthermore, in S2, the width of the input microstrip line is 1.805-1.85 mm; the thickness of the substrate is 25-35 mil.

[0012] Furthermore, in S2, the width of the coupling gap between the input microstrip line and the square microstrip ring is 0.1-0.4 mm.

[0013] Furthermore, in S2, the evaluation indicators of coupling efficiency include input power, radiation efficiency and maximum gain.

[0014] Further, in S1, a sawtooth ring coupling structure is embedded in the square microstrip ring; The sawtooth annular coupling structure comprises a sawtooth microstrip line and an internal square microstrip ring. The sawtooth microstrip line is connected to the inside of the internal square microstrip ring and is symmetrically arranged along the center of the internal square microstrip ring.

[0015] Furthermore, there are a number of sawtooths on the same side of the sawtooth microstrip line, forming a plurality of coupling intervals.

[0016] The present invention also discloses a multi-port input microstrip square ring resonator, which is characterized by comprising 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 increased to 3.

[0017] Furthermore, a sawtooth ring coupling structure is nested in the square microstrip ring; The sawtooth annular coupling structure comprises a sawtooth microstrip line and an internal square microstrip ring. The sawtooth microstrip line is connected to the inside of the internal square microstrip ring and is symmetrically arranged along the center of the internal square microstrip ring.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention discloses a design method for a multi-port input microstrip square ring resonator. The number of microstrip lines is increased to 3, and the input ports of the square microstrip ring are increased to 3. A higher electric field strength can be formed in the coupling region, and the energy transfer efficiency can be enhanced. The multi-channel coupling design can minimize the energy loss when a single microstrip line is excited, and achieve a higher power utilization rate. The three microstrip lines work together to produce a more concentrated electric field distribution in the coupling region, making the entire resonator more sensitive to the response of the target region. More microstrip line inputs can produce a stronger signal response in the coupling region, thereby improving the detection capability of small physical changes. In test applications, the multi-channel design can more effectively detect subtle differences in dielectric constant, moisture content or material properties. This method combines the advantages of multi-channel coupling synergistic enhancement. By increasing the number of microstrip lines at the input end and optimizing the design of the microstrip line spacing and coupling gap, the optimal 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 and detection sensitivity of the resonator.

[0019] The present invention also discloses a multi-port input microstrip square ring resonator, which increases the number of coupled microstrip lines to 3 and the number of input ports to 3, thereby improving the electric field strength and energy transmission capacity of the output port. The three inputs are based on the functional requirements of the resonator, i.e., the coupling energy improvement, and on the electromagnetic field distribution, which facilitates the subsequent study of the interaction between microstrip lines, whether the middle microstrip line has the same effect on the microstrip lines on both sides, etc.

[0020] Furthermore, the square ring structure is further optimized by nesting a sawtooth ring coupling structure in the square ring. This structure increases the coupling spacing and introduces additional capacitance to concentrate the energy of the original square ring inward, thereby enhancing the electric field coupling at the output end, and significantly improving the energy transmission efficiency of the resonator with a sawtooth ring coupling structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the optimization thinking process of the present invention; Figure 2 The electromagnetic simulation model of the constructed single-ended input microstrip square ring resonator; Figure 3 The insertion loss characteristic curve of the resonator corresponding to different microstrip ring widths; Figure 4 The insertion loss characteristic curve of the resonator corresponding to different substrate thicknesses; Figure 5 The transmission loss of the middle microstrip line with different microstrip spacing; Figure 6a for d =2.5mm, P max =72495 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention; Figure 6b for d =3mm, P max =94924 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention; Figure 6c for d =3.5mm, P max =71952 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention; Figure 6d for d =4mm, P max =85255 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention; Figure 6e for d =4.5mm, P max =77113 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention; Figure 6f for d =5mm, P max=68244 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention; Figure 6g for d =5.5mm, P max =85737 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention; Figure 6h for d =6mm, P max =71822 V / m, the planar distribution of the electric field intensity of the resonator designed by the present invention; Figure 7 is the planar electric field distribution of a single input port resonator; Figure 8 is the planar electric field distribution of the three-input port resonator; Figure 9a It is a schematic diagram of the simulation model of the sawtooth ring coupling structure; Figure 9b It is a structural schematic diagram of a sawtooth ring coupling structure; 1. Internal square microstrip ring; 2. Sawtooth microstrip line; 3. Coupling spacing; Fig.10 The planar electric field distribution when 1 / 3W input power is applied to the three ports simultaneously; Fig.11 Schematic diagram of the simulation model of another zigzag ring coupling structure. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clear, the following is further described in detail with reference to 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 embodiments described are only part of the embodiments of the present invention, not all embodiments.

[0023] The components described and shown in the drawings and embodiments of the present invention may be arranged and designed in various 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 claimed invention, but merely represents a selected embodiment of the present invention. Based on the drawings and embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0024] It should be noted that the terms "comprises", "includes" or any other variations are intended to cover non-exclusive inclusion, so that a process, element, method, article or equipment that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to the process, element, method, article or equipment.

[0025] First, the relevant technical terms are explained as follows: Microstrip line: A common planar transmission line consisting of a conductive layer (usually copper), a dielectric layer and a ground layer. It is used to transmit high-frequency signals and its characteristics are determined by line width, dielectric constant and thickness.

[0026] Coupling: The process by which a signal or energy is transferred from one microstrip line to another microstrip line or resonator.

[0027] Resonant frequency: The resonance point of a resonator at a specific frequency, at which the resonator transfers energy most efficiently.

[0028] Transmission coefficient: It indicates the ratio of the input signal transmitted from one port to another port and is used to evaluate the transmission efficiency of the system.

[0029] Microstrip ring resonator: It is a planar resonant structure based on microstrip lines, usually designed as a closed ring. The standing wave of electromagnetic waves in the ring forms a resonance phenomenon, which is used for testing and transmitting signals. It is often used to evaluate material properties (such as dielectric constant, loss tangent) or design filters and antennas.

[0030] Resonance peak: The maximum amplitude at a specific frequency (called resonant frequency) in the frequency response curve. At this time, the response of the system or circuit reaches its highest point, and the energy is concentrated near this frequency, showing resonance.

[0031] Resonance side peaks: Secondary peaks that appear at frequencies near the resonant main peak, usually on either side 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 the main peak, and their frequencies deviate from the resonant main frequency.

[0032] The present invention proposes a multi-terminal input microstrip square ring resonator for coupling energy enhancement and oil-paper insulation moisture content detection sensitivity improvement. This method combines the advantages of multi-channel coupling synergy enhancement, increases the number of microstrip lines at the input end, and optimizes the design of microstrip line spacing and coupling gap to obtain the best optimization parameters and energy transmission effect, thereby improving the overall test performance and enhancing the signal sensitivity of the resonator.

[0033] Mainly based on the electromagnetic simulation model, the coupling efficiency of single input and single output is used as a benchmark to quantify whether the coupling efficiency of multiple inputs is improved. The influence of the synergy between the input ends on the output energy is studied, the input phase and power distribution are adjusted, and finally the output energy is optimized.

[0034] The present invention first considers the design of a multi-port input resonator, such as Figure 1 As shown, Figure 1 The single-port input microstrip ring resonator shown in Figure a is first designed as Figure 1 The multi-port input microstrip ring resonator shown in Figure b improves the energy transmission effect and enhances the signal sensitivity of the resonator.

[0035] After optimizing again, Figure 1 The multi-port input microstrip circular ring resonator shown in Figure b is further improved to a square ring structure to achieve accurate regulation of the gap between the microstrip line and the microstrip ring. Figure 1 In the microstrip square ring resonator shown in Figure c, the distances from multiple microstrip lines to the square ring are the same. The gap between the ring lines is controlled to achieve impedance matching.

[0036] Then optimize again, such as Figure 1 As shown in Figure d, the spacing of the microstrip lines is controlled and varied to achieve the synergistic effect of the microstrip lines. Combining the advantages of multi-path coupling, the influence of the synergistic effect between the input ends on the output energy is studied.

[0037] Afterwards, phase control is used to optimize the phase and power distribution at the input end and improve the overall test performance.

[0038] Afterwards, based on the calculation of transmission energy and transmission efficiency, taking the single-input single-output coupling efficiency as a benchmark, it is quantified whether multi-channel input improves the coupling efficiency, and finally the output energy is optimized.

[0039] This paper proposes a research method based on microstrip square ring resonator. The specific technical solution includes four main steps: model establishment, obtaining benchmark coupling efficiency, multi-path coupling optimization design, and coupling energy and sensitivity improvement analysis. Each step will be described in detail below.

[0040] Step 1: Model building The microstrip ring resonator consists of a substrate and a microstrip line and a microstrip ring attached to the surface of the substrate. A circular ring is usually used as the structure of the microstrip ring. The circular ring has rotational symmetry and uniform electromagnetic field distribution. However, the symmetry of the circular ring makes it inflexible for field enhancement or stronger coupling in a specific direction. 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 line and different edges can be adjusted. The coupling point arrangement is more flexible, and different design requirements can be easily achieved by adjusting the coupling gap. In this structure, the phase velocity of the electromagnetic wave cannot achieve transverse electromagnetic mode (TEM) matching at the interface where the medium is discontinuous, and the transmission mode of the electromagnetic wave is a hybrid mode of transverse electric mode and transverse magnetic mode (TE-TM).

[0041] The microstrip square ring resonator model is shown in the figure Figure 2 As shown, it includes a substrate and a microstrip line and a microstrip ring attached to the surface of the substrate, and an insulating paperboard is provided above the microstrip line and the microstrip ring. Among them, h1 is the thickness of the substrate; h2 is the total thickness after the upper dielectric is superimposed; w is the width of the microstrip line and the microstrip ring, and the width of the microstrip line and the microstrip ring are the same; g is the width of the coupling gap between the microstrip line and the microstrip ring. The microstrip square ring resonator reflects the change in the dielectric properties of the material to be tested through the shift of the resonance peak. The dielectric properties of the medium to be tested are derived by superimposing the change in the resonant frequency before and after the medium to be tested and the insertion loss value at the resonant frequency.

[0042] The upper medium is insulating cardboard, the purpose of which is to verify the resonator's ability to detect the dielectric properties of the material: when the dielectric material (insulating cardboard) is superimposed on the resonator, the resonance characteristics represented by the insertion loss will change, which is specifically manifested in the shift of the resonant frequency, the value of the insertion loss resonance peak, and the change in sharpness.

[0043] The process of establishing the electromagnetic simulation model of the microstrip square ring resonator includes: Create a rectangular plane, define the size of the substrate, set the substrate thickness to ensure that it is consistent with the actual microstrip process. Draw a square microstrip ring and input and output microstrip lines and other geometric structures.

[0044] Set the dielectric constant and loss tangent for the substrate, create an air box around the model, set the air radiation boundary, set the excitation ports at both ends of the square microstrip ring, and set the frequency sweep range.

[0045] Set the solution area and mesh generation method to obtain the electromagnetic simulation model of the microstrip square ring resonator.

[0046] Then, the scattering parameters are simulated and solved. Specifically, the scattering parameter curve is optimized through the Ansys HFSS (Ansys High Frequency Structure Simulator) simulation software. The optimization direction is: the main resonance peak is sharper, the number of side peaks is smaller or there are no side peaks, and the curve outside the resonance peak is as smooth as possible without burrs and distortion.

[0047] Among them, the scattering parameter is an important parameter in microwave transmission. The scattering parameter includes the reflection coefficient S of the antenna port 11 and the forward transmission coefficient S 21 , forward transmission coefficient S 21 Used to characterize the insertion loss characteristics of the resonator (InsertionLoss, IL ), IL =20lg(| S 21 |), S 21 The sharper the curve, the lower the insertion loss.

[0048] Step 2: Obtain the benchmark coupling efficiency The single input and output port is a reference for multi-port resonator analysis and is used to evaluate whether the multi-port design brings performance improvements. The input port provides an 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 and output port resonator, which is used to test the insertion loss and reflection loss of the transmission line and perform performance analysis.

[0049] The resonant frequency f can be expressed as:

[0050] in, L is the equivalent inductance of the resonator, C is the equivalent capacitance of the resonator.

[0051] The reflection and transmission performance of the single-input and output port model are used as reference values ​​for the multi-port system. The total gain and radiation efficiency at 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 areas of the single-input port, it is analyzed whether there is synergy or energy loss between the multiple input ports.

[0052] The evaluation indicators of coupling efficiency include incident power, radiation efficiency, maximum gain, etc., which are specifically defined as: (1) Input power In HFSS simulation software, input power refers to the defined port excitation power, and the default value is 1 W. Set the single-port input power to be equal to the total power of the multi-port input port.

[0053] (2) Radiation efficiency Radiant efficiency is the radiated power P rad and net input power P acc ratio.

[0054] Radiated power refers to the electromagnetic energy radiated into free space by an antenna. The radiated power of an antenna can be calculated using the surface integral of the Poynting vector, that is:

[0055] In the formula, P rad is the radiated power; H * is the magnetic field strength H of common conjugation; n Is a closed surface S The external normal unit vector; E Represents the electric field strength.

[0056] Net input power refers to the actual input power flowing into the antenna port. P acc and P inc represents the net input power and the input power. For a single-port antenna with only one transmission mode, we have P acc = P inc (1-| S 11 | 2 ) In the formula, S 11 is the reflection coefficient of the antenna port.

[0057] (3) Peak Gain Maximum gain refers to the ratio of the radiated power density of the antenna in the direction of maximum radiation to the radiated power density of the omnidirectional antenna in that direction under the same net input power and the same distance.

[0058] Antenna gain G It can be calculated by the following formula: G=4π U / P acc G= ηA D in, U Indicates radiation intensity; D indicates directivity coefficient, D=4π U / P rad The directivity coefficient refers to the ratio of the radiation power density of the antenna in the direction of maximum radiation to the radiation power density of the non-directional antenna in that direction under the conditions of the same radiation power and the same distance. η A represents the radiation efficiency, which is the radiation power P rad and net input power P acc ratio.

[0059] The input power is usually customized, and the radiation efficiency and maximum gain are calculated results. The present invention mainly considers the radiation efficiency.

[0060] Step 3: Multi-channel coupling optimization design In the multi-channel coupling system of microstrip ring resonators, in order to achieve higher energy transmission efficiency and coupling performance, the optimization design focuses on port impedance matching and multi-port parameter optimization design (multi-port excitation phase matching, microstrip line spacing optimization). The change of coupling energy can be quantitatively analyzed through parameters such as radiation efficiency, and the impact can be reflected through changes in electromagnetic field distribution.

[0061] (1) Port impedance matching The impedance matching degree between the resonator interface and the test cable interface plays a key role in signal transmission. The values ​​of the microstrip line width and the substrate thickness determine the characteristic impedance of the microstrip line. The characteristic impedance of the test cable is generally 50Ω, so the characteristic impedance of the microstrip line part of the microstrip ring resonator needs to be as close to 50Ω as possible. As the width of the microstrip line increases, the characteristic impedance of the microstrip ring decreases; as the thickness of the substrate increases, the characteristic impedance of the microstrip ring increases. Both the microstrip line width and the substrate thickness will affect the size 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, the microstrip line width is first optimized using HFSS software to obtain the optimal insertion loss ( S 21 ) curve. Afterwards, the microstrip square ring resonator is optimized and designed.

[0062] The characteristic impedance of the microstrip line can be calculated using the printed circuit board impedance calculation and simulation software. First, the Polar Si9000 software is used to calculate the characteristic impedance of the microstrip line of the microstrip ring resonator with a substrate thickness of 30mil (≈ 0.762mm), a substrate material dielectric constant of 3.2, and a copper foil thickness of 0.5oz (≈ 18μm). The characteristic impedance is optimized to 50Ω by adjusting the line width. The Polar Si9000 software calculation interface and optimization results are shown in the figure. Figure 3 As shown, it can be seen that when the width of the microstrip line is 1.805mm, the calculated characteristic impedance of the microstrip line part is 50Ω.

[0063] Polar Si9000 software is Polar Si9000 advanced transmission line field solver, which is a professional software widely used in the field of printed circuit board (PCB) design, mainly used to accurately calculate the characteristic impedance and other parameters of the transmission line on the PCB. With the help of multiple transmission line models built into the software, such as microstrip line, stripline, etc., combined with PCB material properties, line size and other information, the field solving algorithm is used to simulate and calculate the electrical performance of the transmission line, assisting engineers in PCB design and optimization, and ensuring reliable signal transmission.

[0064] Afterwards, in order to obtain a more accurate microstrip ring width and substrate thickness that meets the actual working requirements of the resonator, the microstrip line width of the microstrip ring resonator was optimized in a range around 1.805mm using Ansys HFSS (Ansys High Frequency Structure Simulator) software to obtain the optimal insertion loss curve. w In the vicinity of the software optimized value 1.805mm, we take 1.70mm, 1.75mm, 1.80mm, 1.805mm, 1.85mm, and 1.90mm respectively to calculate the resonator scattering parameters, such as Figure 3 As shown in Figures (a) to (f). w =1.85mm, such as Figure 3 As shown in Figure (e), the resonant insertion loss curve has a significant resonant main peak and the curve outside the resonant peak is smooth. Only one resonant side peak appears and the peak-to-valley difference ratio is only 6.27%. w =1.85mm corresponding to the resonator measured insertion loss curve can more accurately reflect the resonance information, the resonance characteristics are relatively good. When w=1.70mm, 1.75mm, 1.80mm, 1.90mm, the insertion curve of the resonator has three resonance side peaks, each with two resonance side peaks with a peak-to-valley difference ratio of about 50%, which is relatively serious. Preferably, the width of the input microstrip line is 1.805-1.85mm.

[0065] To determine the thickness of the resonator substrate h Is 1=30mil (equivalent to 0.762mm) the optimal parameter to maintain the width of the resonator microstrip line? w The substrate thickness is 1.85 mm, the substrate material and other parameters remain unchanged. h 1. Take 10mil, 15mil, 20mil, 25mil, 30mil, and 35mil respectively near the commonly used thickness of 30mil to calculate the resonator scattering parameters, such as Figure 4 As shown in Figures (a) to (f) in the figure. 30mil is the commonly used thickness of the microstrip antenna substrate. h When 1=30mil, the insertion loss curve only has a side peak near the main resonance peak 4, and the peak-to-valley difference ratio is only 6.27%, which has little effect on the main resonance peak. Therefore, the insertion loss characteristics of the resonator are the best. h When 1=10mil, the insertion loss curve has four resonant side peaks, and the peak-to-valley difference ratio of the third side peak reaches 40.58%. The curve distortion between the second resonant peak to the fifth resonant peak is more serious. h When 1=15mil and 20mil, the insertion loss curve is distorted to a certain extent, and resonance side peaks appear near the resonance main peak, and some resonance side peaks are of the same height as the corresponding resonance main peak. Preferably, the thickness of the resonator substrate is 25-35mil.

[0066] (2) Multi-port parameter optimization design 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 increased manufacturing difficulty. It is also necessary to consider that multiple microstrip lines may introduce mutual interference and affect the coupling efficiency. For this reason, 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 uniform field distribution in the coupling area.

[0067] 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 ring is designed to be 0.1-0.4mm. In order to explore the effect of multi-channel coupling enhancement, the multi-channel coupling is compared with the single-port input, and the coupling gap is controlled to be the same, and the optimal design scheme of the multi-port excitation phase and microstrip line spacing is studied. Through simulation and experiments, it is proved that the coupling gap of 0.1-0.4mm can meet the design requirements, among which 0.4mm is the optimal design parameter. Through simulation, the excitation size of the three input ports is set to 1 / 3 of that of the single port, and the influence of different excitation port phases on the resonance performance is studied. Finally, the best phase matching result is obtained, and the coupling energy is improved without cancellation due to phase mismatch.

[0068] On the one hand, the three inputs take into account the functional requirements of the resonator, that is, the enhancement of coupling energy; on the other hand, they take into account the distribution of the electromagnetic field, which is convenient for subsequent research on the interaction between microstrip lines and whether the middle microstrip line has the same effect on the microstrip lines on both sides.

[0069] Furthermore, the spacing between two adjacent microstrip lines is simulated, and the microstrip spacing is denoted as d , the insertion loss curve is as follows Figure 5 As shown, the curves in the figure represent d The loss from the intermediate input port to the output port when the microstrip spacing is 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, and 6mm. It can be obtained that the influence of different microstrip spacing on the loss from the intermediate input port to the output port is mainly reflected in the loss amplitude and the side peaks of the resonance point, reflecting the rationality of the parameter design. The optimization direction is to make the main resonance peak sharper, the number of side peaks less or no side peaks appear, and the curve outside the resonance peak is as smooth as possible without burrs and distortion.

[0070] Figure 6a-6h Different microstrip spacing is shown in d Planar distribution of electric field strength and maximum field strength P max .in, Figure 6a middle d =2.5mm, P max =72495 V / m; Figure 6b middle d =3mm, P max =94924 V / m; Figure 6c middle d =3.5mm, P max =71952 V / m; Figure 6d middle d=4mm, P max =85255 V / m; Figure 6e middle d =4.5mm, P max =77113 V / m; Figure 6f middle d =5mm, P max =68244 V / m; Figure 6g middle d =5.5mm, P max =85737 V / m; Figure 6h middle d =6mm, P max =71822 V / m. As shown in Figure 6, the field strength is mainly concentrated at the input end loop coupling, and the electric field distribution is similar. By comparison, d When the distance is 3 mm, the field strength is the maximum. Taking into account the resonance peak and the field strength, the interval between two adjacent input microstrip lines is 2.5-6 mm, and preferably the interval between two adjacent input microstrip lines is 3 mm.

[0071] Step 4: Coupling Energy and Sensitivity Improvement The main purpose of the multi-channel coupling energy enhancement study is to improve the receiving energy of the output microstrip line so that when multiple input ports work simultaneously, the energy received by the output port is higher than that of a single input port, and to study whether multiple inputs will induce coupling synergy effects and enhance the output energy.

[0072] In order to intuitively compare the changes in coupling energy between single input and multiple inputs, evaluate whether the excitation of different input ports can transfer energy to the output end evenly or effectively, and the changes in coupling efficiency of multiple input excitations at different frequencies, the electromagnetic field distribution is compared with the help of simulation tools.

[0073] When the single-port excitation input power is 1W, the electromagnetic field distribution in the plane area is as follows: Figure 7 Mark m1 represents the location where the output microstrip line receives energy, with a field strength of 3311 V / m, and mark m2 represents the location where the input microstrip line transmits energy, with a field strength of 70560 V / m and a transmission efficiency of 4.69%.

[0074] When the three ports are excited simultaneously, the power of each input port is set equal. Figure 8The planar electric field distribution when 1 / 3W input power is applied to the three ports at the same time. Mark m1 represents the location where the output microstrip line receives energy, and the field strength is 4896V / m; mark m2 represents the location where the middle input microstrip line transmits energy, and the field strength is 40150V / m; marks m3 and m4 represent the locations where the upper and lower input microstrip lines transmit energy, and the field strengths are 32840V / m and 31930V / m respectively, and the transmission efficiency is 4.67%. In terms of transmission efficiency, the ratio of the electric field transmitted by multi-ports is similar to that of single-ports, indicating that the power concentration is higher when the single input port is used, while there may be power dispersion or loss in multi-input ports. But at the same time, the electric field strength at the output of the multi-port is significantly higher than that of the single port, indicating that the energy transmission capability of the multi-input port is stronger.

[0075] Furthermore, the coupling uniformity and effectiveness of the excitation at different input ports are evaluated. Figure 8 It can be seen that when the input power of different excitation ports is the same, the energy coupled to the gap by the three microstrip lines is strongest in the middle gap, and the difference between the upper and lower ends is not much, indicating that the coupled energy tends to concentrate inward, which is also closely related to the electric field distribution in the figure. Figure 7 By comparison, it can be seen that multi-path coupling enhances the electric field and more energy flows to the output end.

[0076] The microstrip ring resonator is essentially a microstrip antenna. The radiation efficiency in the calculation results of its antenna parameters can quantify the input and output coupling energy efficiency. The net input power, radiation power, maximum gain, and radiation efficiency of 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.

[0077] Table 1

[0078] Table 2

[0079] 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 input phase is 0 degrees. When the excitation signals of multiple input ports are optimized, the energy forms a coherent superposition in the coupling area, which effectively improves the output signal strength. Higher output signal strength can improve the signal-to-noise ratio, reduce system errors, and thus enhance test sensitivity. When testing weak physical properties, such as low moisture content of oil-paper insulation or small dielectric changes, energy boost helps to accurately capture the response of the test object at low signal strength.

[0080] Based on the multi-port input microstrip square ring resonator, Figure 8 The problem of non-concentration of electric field inside the square ring was further optimized by designing a sawtooth ring coupling structure inside the square ring, such as Figure 9a By adding a sawtooth ring coupling structure and introducing additional capacitance, Figure 7 The energy of the outer square microstrip ring shown is concentrated inward, thereby enhancing the electric field coupling at the output end and improving the energy transfer efficiency.

[0081] Specifically, Figure 9b As shown, the sawtooth annular coupling structure is composed of a sawtooth microstrip line 2 and an internal square microstrip ring 1. The sawtooth microstrip line 2 is connected to the inside of the internal square microstrip ring 1 and is symmetrically arranged along the center of the internal square microstrip ring 1. There are 4 sawtooths on the same side of the sawtooth microstrip line 2, forming 3 coupling spacings 3.

[0082] The microstrip line surface of the sawtooth ring coupling structure is shaped like a sawtooth and is embedded in the outer square microstrip ring to form a channel from left to right in the ring, increasing multiple coupling spacings by 3.

[0083] Fig.10 The planar electric field distribution when 1 / 3W input power is applied to the three ports at the same time. Mark m1 represents the position where the output microstrip line receives energy, and the field strength is 15450V / m; mark m2 represents the position where the middle input microstrip line transmits energy, and the field strength is 44080V / m; mark m3 represents the position where the upper input microstrip line transmits energy, and the field strength is 48950V / m, and mark m4 represents the position where the lower input microstrip line transmits energy, and the field strength is 45400V / m; the transmission efficiency is 11.16%. In terms of transmission efficiency, the electric field transmission efficiency of the zigzag ring coupling structure has been greatly improved, which is 2~3 times that of the single port and the three ports without the zigzag ring coupling structure, indicating that the optimized design structure makes the electric field concentration higher, thereby achieving an improvement in coupling efficiency. At the same time, the electric field strength at the output end of the zigzag ring coupling structure is significantly higher than that of the single port and the three ports, indicating that the zigzag ring coupling structure has a stronger energy transmission capability.

[0084] like Fig.11As shown in the figure, there are 5 sawtooths on the same side of the sawtooth microstrip line 2, forming 4 coupling spacings 3. Mark m1 represents the position where the output microstrip line receives energy, with a field strength of 14420V / m; mark m2 represents the position where the middle input microstrip line transmits energy, with a field strength of 67930V / m; mark m3 represents the position where the upper input microstrip line transmits energy, with a field strength of 48420V / m, and mark m4 represents the position where the lower input microstrip line transmits energy, with a field strength of 53190V / m; the transmission efficiency is 8.51%. In terms of transmission efficiency, the electric field transmission efficiency of the sawtooth ring coupling structure has been greatly improved, indicating that the optimized design structure makes the electric field more concentrated, thereby achieving an improvement in coupling efficiency.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection 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.

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 design method for a multi-port input microstrip square ring resonator according to any one of claims 1 to 6, characterized in that: 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).

8. The design method of a multi-port input microstrip square ring resonator according to any one of claim 7, characterized in that: There are a plurality of saw teeth on the same side of the sawtooth microstrip line (2), forming a plurality of coupling intervals (3).

9. 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.

10. The multi-port input microstrip square ring resonator according to claim 9, characterized in that: 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).

Images