Design and implementation method of electromagnetic hybrid coupled filter

Abstract

The application discloses a design and implementation method of an electromagnetic hybrid coupled filter. The method first determines a transmission zero target frequency according to an index, and synthesizes a coupling matrix containing non-resonant coupling; then, an electromagnetic hybrid coupling unit is designed, and a mapping model of physical parameters and coupling coefficients is established; next, the unit is used to realize the coupling topology of the filter, especially the direct coupling path of the source and the load; finally, the filter response is accurately realized through parameter extraction and iterative optimization. The core of the application lies in that transmission zeros can be accurately and flexibly generated at specified frequencies by actively designing and controlling electromagnetic hybrid coupling, especially source-load coupling, so that higher frequency selectivity can be realized with fewer resonant cavities, and the performance of the filter is significantly improved and the size of the filter is optimized.

Description

Technical Field

[0001] This invention belongs to the field of microwave filter design technology, specifically a design and implementation method for an electromagnetic hybrid coupling filter. Background Technology

[0002] Microwave filters are core components of wireless communication systems, used to filter signals in specific frequency bands and suppress interference signals. As communication systems rapidly develop towards higher frequencies, wider bandwidths, and smaller sizes, more stringent requirements are being placed on the out-of-band rejection capability, roll-off characteristics, and passband flatness of filters.

[0003] Existing filter designs mostly employ a single coupling mechanism of pure capacitive coupling (such as interdigital filters) or pure inductive coupling (such as hairpin filters), achieving signal filtering through conventional coupling between resonant cavities.

[0004] Traditional design schemes have obvious limitations: to meet the requirements of steep transition bands and high selectivity, the number of resonant cavities needs to be increased, which leads to increased filter size and increased insertion loss; at the same time, the process of controlling cross-coupling to generate transmission zeros is complex, and it is difficult to accurately and predictably place the transmission zeros at a specified frequency position, which cannot meet the high-performance development requirements of communication systems. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, the present invention aims to provide a design and implementation method for an electromagnetic hybrid coupling filter to solve the technical problems of increased size, increased insertion loss, and complex transmission zero generation and difficulty in accurately and predictably arranging the transmission zero at a specified frequency position, which are caused by the single coupling mechanism of existing filters. This achieves a synergistic optimization of high selectivity and miniaturization of the filter.

[0006] To achieve the above objectives, this invention discloses a method for designing and implementing an electromagnetic hybrid coupling filter, the method comprising the following steps: S1: Define the filter performance indicators, which include center frequency, bandwidth, return loss, and target frequency with at least one transmission zero. S2: Construct a comprehensive coupling matrix. Using filter synthesis theory, generate a coupling matrix for non-resonant nodes that include direct coupling between the source and the load. The coupling matrix defines the electrical and magnetic coupling coefficients between resonators, between the source and the resonator, and between the load and the resonator. S3: Perform electromagnetic hybrid coupling structure modeling, design electromagnetic hybrid coupling unit, the electromagnetic hybrid coupling unit is composed of capacitive coupling components and inductive coupling components in parallel or cascade, establish the analytical relationship model or electromagnetic simulation model of the physical structure parameters, coupling coefficient and external quality factor of the electromagnetic hybrid coupling unit. S4: Implement the filter topology by configuring the electromagnetic hybrid coupling unit in the coupling path between resonators and using an independent electromagnetic hybrid coupling unit to construct a direct coupling path between the source and the load without passing through any resonators, thereby generating a specified transmission zero at a preset target frequency.

[0007] S5: Conduct parameter extraction and iterative optimization, specifically including: S5.1: Simulate the initially designed filter model using electromagnetic simulation software to obtain the frequency response of the initially designed filter; S5.2: Using a parameter extraction algorithm, the actual coupling matrix is ​​derived from the frequency response; S5.3: Compare the actual coupling matrix with the target coupling matrix, and adjust the analytical relationship model or electromagnetic simulation model of the physical structure parameters, coupling coefficients and external quality factors of the electromagnetic hybrid coupling unit according to the difference between the actual coupling matrix and the target coupling matrix. S5.4: Repeat steps S5.1 to S5.3 until the simulation results meet the preset filter performance requirements.

[0008] Furthermore, the coupling matrix is ​​a 4th-order matrix formed using Chebyshev functions or generalized Chebyshev functions.

[0009] Furthermore, the coupling matrix includes cross-coupling terms between resonators; these cross-coupling terms, in conjunction with the direct coupling terms between the source and the load, enable transmission zero-point location.

[0010] Furthermore, the resonator is a square microstrip patch resonator; the square microstrip patch resonator is attached to the surface of the substrate.

[0011] Furthermore, the capacitive coupling component is selected from interdigital capacitors, gap coupling, or parallel plate capacitors, and the inductive coupling component is selected from inductive windows, coupling lines, or toroidal inductors.

[0012] Furthermore, the net coupling coefficient generated by the electromagnetic hybrid coupling unit The following relationship must be satisfied:

[0013] in, Indicates the strength of magnetic hybrid coupling; The value represents the electrical coupling strength, and K is a constant related to the structure of the coupling unit.

[0014] Furthermore, the number of transmission zeros is two, which are respectively arranged in the upper and lower sidebands of the filter passband.

[0015] Furthermore, the electromagnetic simulation software is HFSS or CST three-dimensional electromagnetic simulation software; the electromagnetic simulation software is used to model the mapping relationship between the physical structure parameters, coupling coefficient and external quality factor of the electromagnetic hybrid coupling unit, as well as the initial model construction and frequency response simulation of the overall filter topology, to simulate the electromagnetic hybrid coupling effect, the coupling characteristics between resonators and the electromagnetic behavior of the source-load direct coupling path, and to output complete frequency response data including return loss and insertion loss.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention can accurately generate one or more transmission zeros at a specified frequency through electromagnetic hybrid coupling, especially the source-load coupling path, which greatly improves the out-of-band rejection capability and roll-off characteristics of the filter.

[0017] (2) By adjusting the strength of the electric coupling and the magnetic coupling respectively, the present invention can independently control the magnitude and nature (positive and negative) of the coupling coefficient, thereby flexibly arranging the transmission zero point on any side or both sides of the passband.

[0018] (3) The method of the present invention can achieve excellent frequency selectivity with fewer resonant cavities, which helps to reduce the size and insertion loss of the filter and overcomes the contradiction of increasing the number of cavities in order to improve performance in traditional methods.

[0019] (4) This invention combines filter synthesis theory with precise electromagnetic simulation and parameter extraction technology to form a closed-loop design process, which reduces the trial and error cost in traditional design and improves design efficiency and success rate. Attached Figure Description

[0020] Figure 1 This is a flowchart of the steps of the method of the present invention.

[0021] Figure 2 This is a schematic diagram of the topology of the electromagnetic hybrid coupling unit in the method of the present invention.

[0022] Figure 3 A schematic diagram of the coupling topology of a four-cavity filter designed for the method of this invention.

[0023] Figure 4 This is a simulation curve of the frequency response of the four-cavity filter in the method of the present invention.

[0024] Figure 5 This is a schematic diagram showing the relationship between the electromagnetic hybrid coupling strength and the transmission zero-point frequency in the method of the present invention. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Please see Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 This application provides a detailed description of the technical solutions provided in each embodiment.

[0027] This application provides a design and implementation method for an electromagnetic hybrid coupling filter, with specific steps including: S1: Define the filter performance indicators, which include center frequency, bandwidth, return loss, and target frequency with at least one transmission zero. S2: Construct a comprehensive coupling matrix. Using filter synthesis theory, generate a coupling matrix for non-resonant nodes that include direct coupling between the source and the load. The coupling matrix defines the electrical and magnetic coupling coefficients between resonators, between the source and the resonator, and between the load and the resonator. S3: Perform electromagnetic hybrid coupling structure modeling, design electromagnetic hybrid coupling unit, the electromagnetic hybrid coupling unit is composed of capacitive coupling components and inductive coupling components in parallel or cascade, establish the analytical relationship model or electromagnetic simulation model of the physical structure parameters, coupling coefficient and external quality factor of the electromagnetic hybrid coupling unit. S4: Implement the filter topology by configuring the electromagnetic hybrid coupling unit in the coupling path between resonators and using an independent electromagnetic hybrid coupling unit to construct a direct coupling path between the source and the load without passing through any resonators, thereby generating a specified transmission zero at a preset target frequency.

[0028] S5: Conduct parameter extraction and iterative optimization, specifically including: S5.1: Simulate the initially designed filter model using electromagnetic simulation software to obtain the frequency response of the initially designed filter; S5.2: Using a parameter extraction algorithm, the actual coupling matrix is ​​derived from the frequency response; S5.3: Compare the actual coupling matrix with the target coupling matrix, and adjust the analytical relationship model or electromagnetic simulation model of the physical structure parameters, coupling coefficients and external quality factors of the electromagnetic hybrid coupling unit according to the difference between the actual coupling matrix and the target coupling matrix. S5.4: Repeat steps S5.1 to S5.3 until the simulation results meet the preset filter performance requirements.

[0029] This embodiment aims to design a bandpass filter suitable for high-frequency wireless communication systems. The filter's performance specifications are defined as follows: Center frequency =3.5GHz, operating bandwidth BW=100MHz, passband return loss S11 greater than 20dB, out-of-band transmission zero upper sideband =3.35GHz, lower sideband =3.65GHz, the filter topology adopts a four-cavity structure because fewer resonant cavities achieve high selectivity, and the structure adopts a microstrip line integrated structure, which is more suitable for miniaturization requirements.

[0030] Based on the signal filtering requirements of wireless communication systems, the performance indicators of the above filters are defined. The design of the transmission null position is intended to specifically suppress interference signals near 3.35GHz and 3.65GHz, ensuring the pure transmission of the 3.5GHz main passband signal.

[0031] Based on the metrics from step S1, the generalized Chebyshev function is used to synthesize the coupling matrix, generating a fourth-order non-resonant node coupling matrix [M] containing source-load direct coupling terms. The matrix form is shown in Table 1. Table 1. Examples of Coupling Matrix [M]

[0032] In Table 1, the 0.1 in row 2, column 7 and row 7, column 2 represents the direct coupling term between the source and load, which is the core non-resonant coupling path that generates the transmission zero. The 0.15 in row 3, column 6 and row 6, column 3 represents the cross-coupling term between resonator 1 and resonator 4, which works in conjunction with the direct coupling between the source and load to achieve precise positioning of the two transmission zeros. Other non-zero terms outside the main line are the main line coupling coefficients between the resonators, ensuring the normal transmission of the passband signal. Constructing the comprehensive coupling matrix nodes provides mathematical model support for the subsequent topology implementation.

[0033] Design a parallel electromagnetic hybrid coupling unit (capacitive and inductive components in parallel), such as... Figure 2 As shown, Figure 2 The meanings of the symbols in the text are as follows: The capacitive coupling component employs a microstrip interdigitated wire structure, consisting of two pairs of parallel-extending microstrip metal fingers. The electrical coupling strength is controlled by adjusting the length and spacing of the interdigitated wires. ; The inductive coupling component employs a thin metal pillar structure, perpendicularly connected between two microstrip transmission lines, and is equivalent to a lumped-parameter inductor. The magnetic coupling strength is controlled by adjusting the diameter of the metal pillar. ; Single-layer substrate, using Rogers 5880 dielectric substrate, dielectric constant =2.2, loss tangent =0.0009, with a thickness of 1mm, ensuring low loss characteristics at high frequencies.

[0034] Based on the 3D electromagnetic simulation software HFSS, a parametric scan of the coupled unit was performed. Scan variables included the length and spacing of the interdigitated lines and the diameter of the metal pillars, to obtain the coupling coefficient under different physical parameters. and external quality factors Establish a mapping relationship database. Among them, The net coupling coefficient satisfies the formula:

[0035] in, Indicates the strength of magnetic hybrid coupling; This represents the electrical coupling strength, and K is a constant related to the structure of the coupling unit. Positive and negative switching and magnitude adjustment can be achieved by independently adjusting and .

[0036] Based on the comprehensive coupling matrix [M], a four-cavity filter topology is implemented using a microstrip line structure, as shown below. Figure 3 As shown, Figure 3 The labels and topological relationships are as follows: There are 4 resonators, all of which are square microstrip patch resonators. The size calculation formula of the microstrip resonator is derived based on the center frequency of 3.5GHz. They are arranged in the main line along the horizontal direction: resonator 1 → resonator 2 → resonator 3 → resonator 4. The main coupling paths between resonators 1 and 2, 2 and 3, and 3 and 4 are respectively configured with electromagnetic hybrid coupling units designed in step S3. By calling the mapping relationship database, the unit parameters are set to match the coupling coefficients respectively. ; Cross-coupling is achieved between resonators 1 and 4 through an independent electromagnetic hybrid coupling unit that spans resonators 2 and 3, with matched coupling coefficients. =0.15, providing an auxiliary coupling path for the transmission zero point; The source and load are directly coupled, with an independent electromagnetic hybrid coupling unit between the source (S) and the load (L), without any resonator, and the coupling coefficient is matched. =0.1, this path is the key non-resonant coupling path that generates the transmission zero; The source / load is fed using a microstrip line edge-coupled feeding method.

[0037] By implementing the filter topology, the mathematical model is transformed into a physical structure, and the multi-path coupling design lays the hardware foundation for transmission zero generation.

[0038] A complete 3D model of the filter was built in HFSS, and the simulation frequency range was set to 3.2~3.8GHz. Full-wave electromagnetic simulation was performed to obtain the S-parameters: S21: insertion loss, S11: return loss. The initial simulation results are as follows: Figure 4 As shown: The passband return loss S11 = -18dB, and the actual transmission zero point Actual coupling matrix , .

[0039] Import the S-parameters from the initial simulation into the coupling matrix extraction tool to deduce the actual coupling matrix. By comparing the matrix with the target matrix [M], the adjustment direction is determined: Increasing the length of the interdigitated wires in the source-load coupling unit enhances the electrical coupling strength. Reducing the diameter of the metal pillar in this unit weakens the magnetic coupling strength. ,make Approaching 0.1; Increasing the interdigital spacing of the coupling elements between resonators 1 and 4 weakens the electrical coupling strength. Keep the diameter of the metal column constant, so that Approaching 0.15; Fine-tune the side lengths of resonators 2 and 3 to optimize passband flatness.

[0040] The process of repeated simulation, extraction, comparison, and adjustment was followed, and after three iterations, the actual coupling matrix was determined. The error between the target matrix [M] and the target matrix is ​​less than 5%, and the simulation results are completely consistent. Figure 4 As shown: S21 curve: Passband (3.45~3.55 GHz) insertion loss less than or equal to 1.5dB, stopband (3.2~3.4 GHz, 3.6~3.8 GHz) rejection greater than 40dB, transmission zeros =3.35GHz, lower sideband Attenuation reaches 60dB at 3.65GHz, achieving steep roll-off characteristics; S11 curve: Return loss within the passband is less than or equal to -25dB (meets the requirement of >20dB), and the transition at the edge of the passband is smooth; The overall size of the filter is 25mm×12mm×1mm, achieving a balance between miniaturization and high performance.

[0041] Figure 5 This diagram illustrates the relationship between electromagnetic hybrid coupling strength and transmission zero frequency, visually reflecting the net coupling coefficient. The control rules for the transmission zero point position: The current sideband needs to set the transmission zero point. At 3.35 GHz, adjust the source-load coupling unit. ,make At this point, the phase cancellation between the coupled path signal and the main line signal occurs below the passband; When the upper band needs to set the transmission zero point At 3.65 GHz, adjust the coupling unit between resonators 1 and 4. ,make At this point, the phase cancellation between the coupled path signal and the main line signal occurs above the passband; Figure 5 The two curves in the middle correspond to the control trajectories with zero points on the upper and lower sides, respectively. As the absolute value increases, the distance between the transmission zero and the center frequency also increases, verifying that independent adjustment... Its core advantage lies in its ability to flexibly control the zero point position.

[0042] The core working mechanism of this embodiment is based on the phase complementarity of electromagnetic coupling: the electrically coupled signal lags behind by 90°, while the magnetically coupled signal leads by 90°. At the transmission zero-point frequency, the signal through the electromagnetic hybrid coupling path has the same amplitude but opposite phase to the signal through the main coupling path, resulting in complete destructive interference and thus forming an extremely deep transmission zero. This is achieved through precise control of the electromagnetic hybrid coupling unit. It can precisely control the frequency of destructive interference and achieve the designated location of transmission zero; at the same time, the 4-cavity structure combined with multi-path coupling can achieve high selectivity without increasing the number of resonant cavities, effectively reducing the size and insertion loss of the filter.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A design and implementation method for an electromagnetic hybrid coupling filter, characterized in that, The method steps include: S1: Define the filter performance indicators, which include center frequency, bandwidth, return loss, and target frequency with at least one transmission zero. S2: Construct a comprehensive coupling matrix. Using filter synthesis theory, generate a coupling matrix for non-resonant nodes that include direct coupling between the source and the load. The coupling matrix defines the electrical and magnetic coupling coefficients between resonators, between the source and the resonator, and between the load and the resonator. S3: Perform electromagnetic hybrid coupling structure modeling, design electromagnetic hybrid coupling unit, the electromagnetic hybrid coupling unit is composed of capacitive coupling components and inductive coupling components in parallel or cascade, establish the analytical relationship model or electromagnetic simulation model of the physical structure parameters, coupling coefficient and external quality factor of the electromagnetic hybrid coupling unit. S4: Implement the filter topology by configuring the electromagnetic hybrid coupling unit in the coupling path between resonators and using an independent electromagnetic hybrid coupling unit to construct a direct coupling path between the source and the load without passing through any resonators, thereby generating a specified transmission zero at a preset target frequency. S5: Conduct parameter extraction and iterative optimization, specifically including: S5.1: Simulate the initially designed filter model using electromagnetic simulation software to obtain the frequency response of the initially designed filter; S5.2: Using a parameter extraction algorithm, the actual coupling matrix is ​​derived from the frequency response; S5.3: Compare the actual coupling matrix with the target coupling matrix, and adjust the analytical relationship model or electromagnetic simulation model of the physical structure parameters, coupling coefficients and external quality factors of the electromagnetic hybrid coupling unit according to the difference between the actual coupling matrix and the target coupling matrix. S5.4: Repeat steps S5.1 to S5.3 until the simulation results meet the preset filter performance requirements.

2. The design and implementation method of an electromagnetic hybrid coupling filter according to claim 1, characterized in that, The coupling matrix is ​​a 4th-order matrix formed using Chebyshev functions or generalized Chebyshev functions.

3. The design and implementation method of an electromagnetic hybrid coupling filter according to claim 2, characterized in that, The coupling matrix includes cross-coupling terms between resonators; these cross-coupling terms, in conjunction with the direct coupling terms between the source and the load, enable transmission zero-point location.

4. The design and implementation method of an electromagnetic hybrid coupling filter according to claim 1, characterized in that, The resonator is a square microstrip patch resonator; the square microstrip patch resonator is attached to the surface of the substrate.

5. The design and implementation method of an electromagnetic hybrid coupling filter according to claim 1, characterized in that, The capacitive coupling component is selected from interdigital capacitors, gap coupling, or parallel plate capacitors, and the inductive coupling component is selected from inductive windows, coupling lines, or toroidal inductors.

6. The design and implementation method of an electromagnetic hybrid coupling filter according to claim 1, characterized in that, The net coupling coefficient generated by the electromagnetic hybrid coupling unit The following relationship must be satisfied: in, Indicates the strength of magnetic hybrid coupling; The value represents the electrical coupling strength, and K is a constant related to the structure of the coupling unit.

7. The design and implementation method of an electromagnetic hybrid coupling filter according to claim 1, characterized in that, The number of transmission zeros is two, which are respectively arranged in the upper sideband and lower sideband of the filter passband.

8. The design and implementation method of an electromagnetic hybrid coupling filter according to claim 1, characterized in that, The electromagnetic simulation software is HFSS or CST three-dimensional electromagnetic simulation software; the electromagnetic simulation software is used to model the mapping relationship between the physical structure parameters, coupling coefficient and external quality factor of the electromagnetic hybrid coupling unit, as well as the initial model construction and frequency response simulation of the overall filter topology, to simulate the electromagnetic hybrid coupling effect, the coupling characteristics between resonators and the electromagnetic behavior of the source-load direct coupling path, and to output complete frequency response data including return loss and insertion loss.

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