Miniaturized wide-passband filter based on EMSIW and microstrip resonator

Abstract

The invention relates to the technical field of communication, in particular to a miniaturized wide-passband filter based on an EMSIW and a microstrip resonator. According to the miniaturized wide-passband filter, the two EMSIW cavities are adopted, the size of the filter can be effectively reduced, high-order modes TE120, TE210, TE220 and TE130 cannot be propagated in the EMSIW cavities, and therefore the filter has a wide stop band. Two microstrip resonators are embedded at a coupling window between two EMSIW cavities, and four-order quasi-elliptical filtering response is realized under the condition that no extra circuit area is occupied. Compared with other EMSIW filters, the filter has the advantages of being small in size, wide in passband, wide in stop band and good in selectivity, and has potential application value in a communication system.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and in particular to a miniaturized wideband filter based on EMSIW and a microstrip resonator. Background Technology

[0002] Substrate integrated waveguides (SIWs) have advantages such as low loss, high quality factor, low cost, and ease of integration, and are widely used in the design of various filters. However, compared with other types of filters, SIW filters still have a relatively large circuit size. At the same time, due to the dense distribution of higher-order modes in SIWs, the generated harmonics are often close to the passband.

[0003] To reduce the circuit size of SIW filters, some researchers have proposed cutting the complete SIW cavity along its equivalent magnetic wall to form 1 / n-mode SIW cavities (including half-mode substrate integrated waveguides (HMSIW), quarter-mode substrate integrated waveguides (QMSIW), and eighth-mode substrate integrated waveguides (EMSIW). Using EMSIW cavities for filter design can significantly reduce the filter size. Furthermore, the higher-order modes in an EMSIW cavity are far fewer than in a complete SIW cavity; therefore, filters designed using EMSIW cavities are also easier to achieve with wide stopbands.

[0004] In recent years, some research has emerged on filter design using EMSIW cavities. A balanced filter was proposed, utilizing a combination of EMSIW and QMSIW cavities. The filter's 20-dB stopband width can reach 2.56 f0, but the filter has a two-layer structure, making it difficult to manufacture, and its miniaturization is insufficient. A filter designed using EMSIW cavities and CPW resonators has a small size, but it only has one transmission zero on the right side of the passband, and its stopband width is narrow. Another small tunable filter uses two EMSIW cavities, introducing two transmission zeros on the right side of its passband, but because the transmission zeros are far from the passband, the filter's selectivity is poor. A wide stopband filter designed using two circular EMSIW cavities can achieve a 30-dB stopband width of 4.34 f0, but it also suffers from the problem of the transmission zeros being far from the passband and the filter's selectivity being poor. A filter designed using a combination of EMSIW and QMSIW cavities achieves a 20-dB stopband width of 2.1f0. However, the lack of a transmission zero on the left side of the passband results in poor selectivity and insufficient miniaturization. Another miniaturized filter utilizes a combination of an EMSIW cavity and a microstrip resonator. The microstrip resonator is located outside the EMSIW cavity, occupying additional circuit area and hindering miniaturization. A dual-passband filter designed by embedding a CPW resonator within the EMSIW cavity fails to achieve a single passband primarily due to the limited circuit area of ​​the EMSIW cavity, preventing the CPW resonator's resonant frequency from approaching the EMSIW cavity's resonant frequency.

[0005] The EMSIW filters proposed above suffer from problems such as insufficient stopband width, poor selectivity, or insufficient miniaturization. Summary of the Invention

[0006] This invention provides a miniaturized wide-passband filter based on EMSIW and a microstrip resonator. By combining microstrip and EMSIW technologies, the filter size is effectively reduced, the stopband width is extended, and a fourth-order filter response is achieved without increasing the additional circuit area. The filter also introduces cross-coupling, generating transmission zeros on both sides of the passband, achieving a quasi-elliptic filtering response, and improving the filter's selectivity, making it particularly suitable for high-performance communication systems.

[0007] This invention provides a miniaturized wideband filter based on EMSIW and a microstrip resonator, comprising:

[0008] dielectric substrate;

[0009] The first metal layer is fixedly disposed on one side of the dielectric substrate, and the dielectric substrate has the same shape as the first metal layer, which is an inverted planar diamond shape;

[0010] The second metal layer is fixedly disposed on the side of the dielectric substrate away from the first metal layer. The second metal layer is triangular, and the base of the triangle is connected to the base of the dielectric substrate. A coupling window is opened in the middle of the connection, and two microstrip resonators are embedded in the coupling window. A power supply port is fixedly connected to the middle position of the left and right sides of the second metal layer.

[0011] The metal vias sequentially penetrate the first metal layer, the dielectric substrate, and the second metal layer, and multiple metal vias are provided.

[0012] According to the miniaturized wide passband filter based on EMSIW and microstrip resonator provided by the present invention, a plurality of metal vias are arranged in an inverted T-shape and the plurality of metal vias are formed at the top of the coupling window.

[0013] The miniaturized wide passband filter based on EMSIW and microstrip resonators provided by the present invention uses ZYF300CA-P as the dielectric substrate material, which has a relative permittivity of 3, a loss tangent of 0.0018, and a thickness of 0.762 mm.

[0014] According to the miniaturized wide passband filter based on EMSIW and microstrip resonators provided by the present invention, the short-circuit terminals of the two microstrip resonators are close to each other, and the feed port, including the input port and the output port, both adopt 50-ohm microstrip lines. The 50-ohm microstrip lines are connected to the second metal layer in a trapezoidal transition manner.

[0015] According to the miniaturized wide passband filter based on EMSIW and microstrip resonators provided by the present invention, the second metal layer is an equilateral triangle with a side length of 16.55 nm, the center distance between adjacent circular holes of the metal via is 1.2 nm, and the spacing between the two microstrip resonators is 0.45 nm.

[0016] The miniaturized wide passband filter based on EMSIW and microstrip resonators provided by the present invention has an insertion loss of 0.9 dB, a relative bandwidth of 30.25%, and a stopband of >10.41 GHz.

[0017] This invention provides a hybrid structure filter that embeds a microstrip resonator into an EMSIW cavity, which can overcome the problems mentioned in the background art to a certain extent. Firstly, using an EMSIW cavity can effectively reduce the size of the filter, and the higher-order mode TE... 120 TE 210 TE 220 and TE 130The inability to propagate within the EMSIW cavity effectively increases the stopband width of the filter. Secondly, by embedding two microstrip resonators at the coupling window between the two EMSIW cavities, a transmission zero is generated on each side of the passband. The fourth-order quasi-elliptic filter response is achieved using only the circuit area of ​​the two EMSIW cavities. Finally, the filter designed in this invention has a single-layer structure, is simple to manufacture, and is easy to integrate into a communication system.

[0018] The beneficial effects of this invention are:

[0019] This invention combines microstrip and EMSIW technologies to propose a miniaturized wide-passband filter with a quasi-elliptic filtering response and a wide stopband. The use of an EMSIW resonant cavity effectively reduces the filter's size, preventing some higher-order modes from propagating within the cavity, thus extending the filter's stopband width. By embedding two microstrip resonators into the EMSIW cavity, a fourth-order filter response is achieved without increasing the circuit area. The filter also introduces cross-coupling, generating transmission zeros on both sides of the passband, achieving a quasi-elliptic filtering response and improving the filter's selectivity. The filter's wide passband, low insertion loss, and small size make it ideal for applications in high-performance communication systems.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a three-dimensional structural diagram of a miniaturized wideband filter based on EMSIW and a microstrip resonator;

[0023] Figure 2 This is a dimension diagram of the second metal layer in the filter;

[0024] Figure 3 It is TE 110 Pattern and TE 110 / 8 mode;

[0025] Figure 4 This is a schematic diagram of the filter's coupling topology;

[0026] Figure 5 This is a graph showing the variation of the main coupling coefficients of different simulation models with W3 or g;

[0027] Figure 6 It represents the electric field intensity distribution of some modes in SIW and EMSIW cavities;

[0028] Figure 7 It is the electric field intensity distribution of the filter's principal mode and first higher-order mode;

[0029] Figure 8 This is a physical diagram of a miniaturized wideband filter based on EMSIW and a microstrip resonator;

[0030] Figure 9 This is a graph of the S-parameters of the filter obtained through synthesis, measurement, and simulation.

[0031] Reference numerals: 1. Dielectric substrate; 2. First metal layer; 3. Second metal layer; 301. Coupling window; 302. Microstrip resonator; 303. Feed port; 4. Metal via. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] In the description of the embodiments of the present invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the mechanism or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0035] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0036] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0037] This invention provides a miniaturized wideband filter based on EMSIW and microstrip resonator 302, the three-dimensional structure of which is as follows: Figure 1 As shown, it specifically includes a first metal layer 2, a second metal layer 3, and a dielectric substrate. The dielectric substrate is made of ZYF300CA-P, with a relative permittivity of 3, a loss tangent of 0.0018, and a thickness of 0.762 mm.

[0038] The first metal layer 2 is fixedly disposed on one side of the dielectric substrate 1. The dielectric substrate 1 and the first metal layer 2 have the same shape, which is an inverted planar diamond shape. The second metal layer 3 is fixedly disposed on the side of the dielectric substrate 1 away from the first metal layer 2. The second metal layer 3 is triangular, and the base of the triangle is connected to the base of the dielectric substrate 1. A coupling window 301 is opened in the middle of the connection. Two microstrip resonators 302 are embedded in the coupling window 301. A power supply port 303 is fixedly connected to the middle of the left and right sides of the second metal layer 3. Multiple metal vias 4 penetrate the first metal layer 2, the dielectric substrate 1 and the second metal layer 3 in sequence.

[0039] Multiple metal vias 4 are arranged in an inverted T-shape and are located at the top of the coupling window 301.

[0040] Figure 2 This is a dimensional diagram of the upper metal layer of the filter. The filter is generally composed of two EMSIW cavities and operates at TE.110 / 8 mode.

[0041] Figure 2 The specific physical dimensions are (mm): W=16.55, W 50 =1.88, L1=2, W1=1, P=1.2, d=0.8, W2=8, W3=3, g=0.45, a=6, S1=0.1, S2=0.15 and S3=0.22.

[0042] Figure 3 This demonstrates the complete TE in the SIW cavity. 110 TE mode in EMSIW cavity 110 In the / 8 mode, a coupling window 301 is set at the common side of the two resonant cavities, and two microstrip resonators 302 are embedded in the coupling window 301. The microstrip resonator 302 can be equivalent to a quarter-wavelength short-circuit resonator.

[0043] A pair of metal vias 4 are provided above the microstrip resonator 302. The coupling between the 1 / 8 mode substrate integrated waveguide (EMSIW) cavity and the microstrip resonator 302 can be adjusted by adjusting the size W3. The coupling between the two microstrip resonators 302 can be adjusted by their spacing g.

[0044] Both the input and output ports use 50-ohm microstrip lines, and the 50-ohm microstrip lines are connected to the EMSIW using a trapezoidal transition method.

[0045] Based on the filter's structure, its coupling topology is as follows: Figure 4 As shown, the coupling between the EMSIW cavity and the microstrip resonator is magnetic coupling. The short-circuited ends of the two microstrip resonators 302 are close to each other, making them magnetically coupled as well.

[0046] A relatively weak electrical coupling exists between the two EMSIW cavities because part of the electric field can be coupled through the opening edge of the coupling window 301. This electrical coupling between the EMSIW cavities achieves cross-coupling, thus generating transmission zeros on both sides of the filter's passband, forming a quasi-elliptic filter response, and improving the filter's selectivity.

[0047] Example 2

[0048] This embodiment provides the design and principle analysis of a miniaturized wideband filter based on EMSIW and microstrip resonators, as described in Embodiment 1.

[0049] 1. Determination of EMSIW cavity size and microstrip resonator size.

[0050] The size of the EMSIW cavity is 1 / 8 that of a complete SIW cavity. The resonant frequency of the master mode TE110 / 8 of the EMSIW cavity is determined by the TE of the SIW cavity.110 The mode determines the TE of the SIW cavity. 110 The resonant frequency of the mode is calculated using the following formula.

[0051] ;

[0052] Where c0 is the speed of light in a vacuum, ε r W is the relative permittivity of the dielectric substrate. eff-SIW and L eff-SIW The equivalent width and length of the SIW cavity are defined as follows: ;

[0053] Among them, W SIW and L SIW Let represent the width and length of the SIW cavity, d be the diameter of the metal via, and P be the center distance between adjacent metal vias. This filter uses a square SIW cavity, and... .

[0054] Since a microstrip resonator can be equivalent to a quarter-wavelength short-circuit resonator, its input admittance can be expressed as Y. in =-jY0cotθ0, when Y in When the resonant frequency is zero, the formula for calculating its resonant frequency can be expressed as: ;

[0055] Where, ε e Let l be the equivalent dielectric constant of the microstrip resonator. R Let i be the length of the resonator, i = 0, 1, 2, ... When i = 0, it represents the main resonant mode; when i > 0, it represents the higher-order resonant mode.

[0056] Once the center frequency of the filter is determined, the dimensions of the EMSIW cavity and the microstrip resonator can be preliminarily determined using the formulas described above.

[0057] 2. Specifications and Design Curves

[0058] As an example, the proposed filter has a fourth-order quasi-elliptic response centered at 4.15 GHz, a return loss of 13 dB, and a relative bandwidth of 27.5%. The coupling matrix parameters can be synthesized according to the process outlined in "Wide Stopband SubstrateIntegrated Waveguide Filter Implemented by Orthogonal Ports' Offset (P. Chu, L. Guo, L. Zhang, F. Xu, W. Hong and K. Wu, IEEE Transactions on Microwave Theory and Techniques, vol. 68, no. 3, pp. 964-970, March 2020)". The filter's coupling coefficients and external quality factor are:

[0059] K 12 = K 34 = 0.2, K 23 = 0.19, K 14 = −0.038, Qe = 4.96;

[0060] K ij For resonator R i and R j The coupling coefficient between them, Qe is the external quality factor. According to the expected target specifications, Figure 5 The main coupling coefficients, i.e., K, can be extracted when the external coupling is weak. 12 and K 34 K 23 The corresponding simulation model is as follows Figure 5 As shown in the illustration.

[0061] from Figure 5 (a) It can be seen that as W3 increases, K 12 and K 34 The decrease is because as W3 increases, the electromagnetic signal is more easily short-circuited to the ground.

[0062] from Figure 5 (b) It can be seen that K 23 When the gap g increases from 0.35 mm to 0.45 mm, it changes from 0.22 to 0.18, showing a decreasing trend.

[0063] The cross-coupling coefficient K extracted through intrinsic imitation 14 like Figure 5 As shown in (c), K 14 Primarily controlled by the dimension g, it can be seen that K 14The absolute value of first increases and then decreases as g increases.

[0064] This may be due to K 14 The absolute value is influenced by both the electric field strength at the open boundary and the distance between the two open boundaries. Although these extracted curves deviate somewhat from the comprehensive parameters, they provide guidance for filter design.

[0065] 3. Suppression of higher-order modes

[0066] When the SIW cavity is cut along the plane of symmetry, the open side can be regarded as an ideal magnetic wall. The electric field distribution of the dominant mode in the EMSIW cavity is 1 / 8 of that in the SIW cavity. For the higher-order modes of the EMSIW cavity, they can only propagate in the EMSIW cavity if they are equivalent to a magnetic wall at the plane of symmetry.

[0067] Figure 6 (a) shows the first 5 resonant modes of the SIW cavity. Figure 6 (b) shows the first two resonant modes of the EMSIW cavity. It can be seen that, utilizing only the structural characteristics of the EMSIW, it is possible to achieve high-order mode TE. 120 TE 210 TE 220 and TE 130 The inhibition.

[0068] Figure 7 The dominant mode TE in the filter is shown. 110 Electric field distribution diagrams for the 8th mode and the higher-order mode closest to the passband. It can be seen that the dominant mode TE... 110 The / 8 mode can propagate normally in the filter, and the highest-order mode closest to the passband is TE. 310 / 8, it will generate a small amount of output in the filter, forming a parasitic passband. No higher-order modes (TE) with the SIW cavity were observed in the filter. 120 TE 210 TE 220 and TE 130 The parasitic passbands generated by the corresponding patterns prove the correctness of the above inference.

[0069] Example 3

[0070] This embodiment fabricates a miniaturized wideband filter based on EMSIW and a microstrip resonator, as described in Embodiment 1, and verifies the experimental results.

[0071] To verify the performance of the proposed filter, it was fabricated using PCB technology. A schematic diagram of the filter is shown below. Figure 8 As shown, its physical dimensions are (16.55 × 16.55) / 2 mm. 2 (Excluding input and output ports).

[0072] When testing the filter, SMA-KHD coaxial connectors need to be soldered to the input and output ports of the filter and connected to a vector network analyzer (Agilent E8363C) for measurement.

[0073] Figure 9 The synthesized, measured, and simulated S-parameters were depicted in the frequency range of 2–11 GHz, and good agreement was observed. The measured center frequency was 4.13 GHz, slightly lower than the simulated value of 4.15 GHz. The measured 3-dB fractional relative bandwidth (FBW) was 30.25%, and the minimum insertion loss, including the loss of the ultra-small version a (SMA) connector, was 0.9 dB.

[0074] Meanwhile, the stopband is greater than 10.41 GHz, the suppression level is greater than 20 dB, and as expected, two transmission zeros were observed on both sides of the passband. The measured insertion loss is 0.5 dB higher than the simulated value, and the return loss is better than 11 dB, which is 2 dB lower than the simulated value.

[0075] The difference between the measured results and the simulation results is mainly attributed to processing errors, medium loss, and conversion structure loss.

[0076] Table 1 Filter Data

[0077] λ0: Wavelength in free space;

[0078] The performance of the proposed filter is shown in Table 1. Compared with other EMSIW filters, it exhibits a wider passband, lower insertion loss, wider stopband, and smaller size.

[0079] Furthermore, this filter has only a single-layer structure, making it simple to manufacture and easier to integrate into communication systems.

[0080] Combining microstrip and EMSIW technologies, this invention proposes a miniaturized wide-passband filter with a quasi-elliptic filtering response and a wide stopband. The use of an EMSIW resonant cavity effectively reduces the filter's size, preventing some higher-order modes from propagating within the cavity, thus extending the filter's stopband width. By embedding two microstrip resonators into the EMSIW cavity, a fourth-order filter response is achieved without increasing the circuit area. The filter also introduces cross-coupling, generating transmission zeros (TZ) on both sides of the passband, achieving a quasi-elliptic filtering response and improving the filter's selectivity. The filter's wide passband, low insertion loss, and small size make it ideal for applications in high-performance communication systems.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A miniaturized wideband filter based on EMSIW and a microstrip resonator, characterized in that, include: dielectric substrate (1); The first metal layer (2) is fixedly disposed on one side of the dielectric substrate (1). The dielectric substrate (1) and the first metal layer (2) have the same shape, which is an inverted planar diamond shape. The second metal layer (3) is fixedly disposed on the side of the dielectric substrate (1) away from the first metal layer (2). The second metal layer (3) is triangular, and the base of the triangle is connected to the base of the dielectric substrate (1). A coupling window (301) is opened in the middle of the connection. Two microstrip resonators (302) are embedded in the coupling window (301). A power supply port (303) is fixedly connected to the middle of the left and right sides of the second metal layer (3). The metal vias (4) penetrate the first metal layer (2), the dielectric substrate (1), and the second metal layer (3) in sequence, and there are multiple metal vias (4).

2. The miniaturized wideband filter based on EMSIW and microstrip resonator (302) according to claim 1, characterized in that, The plurality of metal vias (4) are arranged in an inverted T-shape and are located at the top of the coupling window (301).

3. The miniaturized wideband filter based on EMSIW and microstrip resonator (302) according to claim 1, characterized in that, The dielectric substrate (1) is made of ZYF300CA-P, with a relative permittivity of 3, a loss tangent of 0.0018, and a thickness of 0.762 mm.

4. The miniaturized wideband filter based on EMSIW and microstrip resonator (302) according to claim 1, characterized in that, The short-circuit ends of the two microstrip resonators (302) are close to each other. The power supply port (303) includes an input port and an output port, both of which use 50-ohm microstrip lines. The 50-ohm microstrip lines are connected to the second metal layer (3) in a trapezoidal transition manner.

5. The miniaturized wideband filter based on EMSIW and microstrip resonator (302) according to claim 1, characterized in that, The second metal layer (3) is an equilateral triangle with a side length of 16.55 nm. The center distance between adjacent circular holes of the metal via (4) is 1.2 nm, and the spacing between the two microstrip resonators (302) is 0.45 nm.

6. The miniaturized wideband filter based on EMSIW and microstrip resonator according to claim 1, characterized in that, The miniaturized wide passband filter has an insertion loss of 0.9 dB, a relative bandwidth of 30.25%, and a stopband of >10.41 GHz.

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