A wideband FSIW-like dual-band filter

Abstract

The application discloses a wide-band FSIW-like dual-band filter, which comprises a top metal layer, a middle metal layer, a bottom metal layer, a dielectric layer, a first array of metallized through holes, a second array of metallized through holes, a third array of metallized through holes and an input / output port. The first and second modes of the FSIW-like rectangular cavity are used to construct the first and second passbands of the filter respectively. The width of the rectangular gap at the folding position of the FSIW-like rectangular cavity is changed, so that the resonant frequency of the second mode can be adjusted, and the resonant frequencies of the first and third modes are not changed, thereby effectively improving the stopband bandwidth of the dual-band filter while the frequency of the second passband is independently adjustable.

Description

Technical Field

[0001] This invention belongs to the field of microwave technology and relates to a dual-band filter, particularly a wide-stopband FSIW-like dual-band filter. Background Technology

[0002] Modern wireless communication systems require filters to have characteristics such as small size, low insertion loss, high frequency selectivity, and multifunctionality. Substrate integrated waveguides (SIWs) have been widely used in filter design due to their advantages such as low loss, low cost, ease of fabrication, and ease of integration. However, compared with microstrip or coplanar waveguide (CPW) filters, SIW filters are relatively large. Therefore, folded substrate integrated waveguide (FSIW) filters have emerged, which can achieve a size reduction of nearly half.

[0003] As a crucial component for miniaturizing and enhancing the functionality of wireless communication systems, dual-band bandpass filters have been a hot research topic in both academia and industry. Researchers have proposed various integrated design methods for dual-band filters to address diverse wireless communication applications, which can be broadly categorized into the following four types:

[0004] First, there's the passband parallel technique. This technique uses impedance matching networks or common input / output ports to connect two separately designed single-band filters in parallel, thereby achieving spectrum superposition. The advantage of this technique is that the frequencies and performance of both passbands can be independently designed and adjusted; the disadvantage is the relatively large circuit size.

[0005] Second, there is the band splitting technique. This technique splits a wide passband into two sub-passbands by introducing transmission zeros or inserting band-stop filter responses in the middle of the wideband. There are three main methods for implementation: First, using direct optimization algorithms or frequency transformation methods to synthesize the dual-frequency filter function or corresponding coupling matrix, and then using practical technical solutions and circuit structure mapping to achieve the desired dual-frequency response; second, cascading or integrating a band-stop filter onto a wideband filter to achieve a relatively flexible split-frequency response; third, using transverse signal interference technology to superimpose two forward signals of different amplitudes and phases to generate transmission zeros at suitable locations, and then cascading the units to achieve the required order of dual-frequency response. Because the number of resonators required by method one is the sum of the orders of the two passbands, and method two requires cascading or integrating band-pass and band-stop filters, the filter circuit designed using the band splitting technique is also relatively large.

[0006] Third, the single multimode resonator technique. This technique separates degenerate modes by introducing perturbations into ring resonators or patch resonators, or by adding resonators with stubs to increase the number of resonant modes. It divides the resonant modes of a single multimode resonator into two groups according to frequency, and combines this with appropriate input-output coupling to achieve the desired dual-frequency response. Dual-band filters designed using this method have advantages such as simple implementation and compact circuit structure. However, the resonant modes of the multimode resonator used are often interdependent and difficult to adjust independently, sometimes failing to obtain the desired useful frequency position and passband performance.

[0007] Fourth, dual-mode resonator coupling technology. This technology utilizes the coupling of the first two modes of dual-mode resonators, such as half-wavelength or quarter-wavelength step impedance resonators, stubular or capacitively loaded microstrip line resonators, lumped or composite left-handed or right-handed resonators, to construct the two passbands of a dual-band filter. Because filters designed and implemented using this technology have simple structures and compact sizes, it is currently the most classic and popular design method for dual-band bandpass filters. However, since this method greatly reduces design freedom, controlling the dual-mode frequencies and coupling has always been a major challenge in the design.

[0008] Currently, a SIW dual-band filter based on the fourth technology has also been proposed. However, due to the large number of high-order modes in the SIW cavity, the filter's stopband bandwidth is limited, and the center frequencies of the two passbands are mutually constrained, making it difficult to achieve independent adjustment. Summary of the Invention

[0009] The purpose of this invention is to address the problems of difficult dual-mode frequency control and narrow stopband bandwidth of existing SIW dual-band filters. It proposes a wide-stopband FSIW-like dual-band filter, which utilizes the first and second modes of the FSIW-like rectangular cavity to construct the first and second passbands of the filter, respectively. By changing the width of the rectangular notch (2a) at the fold of the FSIW-like filter, the second passband frequency of the dual-mode filter can be independently controlled without affecting the position of the first passband and the parasitic passband, thereby achieving a wider stopband.

[0010] The present invention adopts the following technical solution:

[0011] A folded dual-band filter with high harmonic suppression ratio, comprising:

[0012] Dielectric layer (4);

[0013] The top metal layer (1) is located on the upper surface of the dielectric layer (4);

[0014] The bottom metal layer (3) is located on the lower surface of the dielectric layer (4);

[0015] An intermediate metal layer (2) is located within the dielectric layer (4);

[0016] A first metallized via array (5) connecting the top metal layer (1), the middle metal layer (2), and the bottom metal layer (3);

[0017] A second metallized via array (6) connecting the intermediate metal layer (2) and the bottom metal layer (3);

[0018] A third metallized via array (7) connecting the top metal layer (1) and the middle metal layer (2);

[0019] in:

[0020] The first metallized via array (5) encloses two connected rectangles; the two connected rectangles share a common sidewall, and the common sidewall has a coupling window; the outer sidewalls of the two connected rectangles each have a first window and a second window; the coupling window has no metallized vias, the first window has a second metallized via array (6), and the second window has a third metallized via array (7).

[0021] The top metal layer (1) includes a microstrip line (1a) and a rectangular metal patch (1c); one end of the microstrip line (1a) is connected to one side of the rectangular metal patch (1c), and the other end serves as the input and output ports of the filter; a slot line (1b) is opened on each side of the microstrip line (1a) of the rectangular metal patch (1c); the microstrip line (1a) and the two slot lines (1b) all fall within the first window;

[0022] The bottom metal layer (3) and the top metal layer (1) have the same shape and the same size; with the geometric center of the dielectric layer (4) as the origin, the top metal layer (1) and the bottom metal layer (3) are centrally symmetrical;

[0023] The top metal layer (1), bottom metal layer (3), middle metal layer (2), dielectric layer (4) and first metallized via array (5) together construct two FSIW-like rectangular cavities, which are connected by a coupling window on a common sidewall.

[0024] The intermediate metal layer (2) is a metal patch with two rectangular notches (2a); the two rectangular notches (2a) are located at the folds of the two FSIW-like rectangular cavities respectively;

[0025] Preferably, the two FSIW-like rectangular cavities have the same size, and are coupled by the coupling window width Ww and coupling window position W on the common sidewall. 12 Controlling the coupling between two FSIW-like rectangular cavities;

[0026] Preferably, the rectangular notch (2a) is used to adjust the second mode resonant frequency of the FSIW-like rectangular cavity, and the adjustment of the second mode resonant frequency is achieved by adjusting the width G of the rectangular notch (2a);

[0027] Preferably, the position T of the microstrip line (1a) IN The first window's broadband W IN and the length L of the groove line S It can control the external quality factors of the input and output ports;

[0028] Preferably, the microstrip line (1a) has a impedance of 50 ohms;

[0029] Preferably, the distance between the intermediate metal layer (2) and the top metal layer (1) and the bottom metal layer (3) is equal;

[0030] Preferably, the dielectric layer (4) is formed by stacking two dielectric substrates on top of each other, with the intermediate metal layer (2) located between the two dielectric substrates; more preferably, the dielectric substrate is a TanconicTLY-5 dielectric substrate with a relative permittivity of 2.2, a loss tangent of 0.0009, and a thickness of 0.508 mm.

[0031] More preferably, the first passband of the filter is set at 10 GHz and the second passband is set at 12 GHz.

[0032] In practical applications, the input and output ports can be further converted into other ports such as strip or coplanar waveguide through other adapter structures, but this is not within the scope of protection of this invention.

[0033] Specific working principle:

[0034] A microstrip line (1a) simultaneously excites multiple modes in a FSIW-like rectangular cavity. The first and second modes are used to construct the first and second passbands of a dual-band filter, respectively, while the third mode constitutes a parasitic passband closest to the filter's passband. Cross-coupling between the first and second modes can form a transmission zero, as can cross-coupling between the second and third modes.

[0035] Based on the electric field distribution of the first four modes of the FSIW-like rectangular cavity, it can be found that the first and third modes are mainly distributed in the FSIW-like rectangular cavity and the remaining intermediate metal layer (2) except for the rectangular notch, while the second mode is distributed throughout the entire FSIW-like rectangular cavity. Therefore, without changing the intermediate metal layer (2), changing the width of the rectangular notch (2a) in the FSIW-like rectangular cavity can change the resonant frequency (f2) of the second mode without changing the resonant frequencies (f1, f3) of the first and third modes. Setting W / L = At this point, f3 is furthest from f1, and their ratio reaches f3 / f1 = 1.784. Increasing the width G of the rectangular gap (2a) at this time can reduce f2 without changing f1 and f2. 3, Therefore, the dual-band filter can still have a wide stopband even with a small frequency ratio (f2 / f1). For example, when f2 / f1 = 1.2, the present invention can achieve f3 / f1 of 1.7, while when using a traditional SIW rectangular cavity, f3 / f1 is only 1.48.

[0036] The present invention has the following advantages:

[0037] (1) This invention extends the stopband bandwidth based on dual-band filtering;

[0038] (2) The center frequency of the second passband of the present invention can be adjusted independently, which simplifies the design;

[0039] (3) The present invention adopts a folded structure, which reduces the size of the filter while maintaining the shielding performance. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the overall structure of the filter of the present invention;

[0041] Figure 2(a) and (b) are respectively a top metal layer view and a schematic diagram of the middle metal layer of the filter of the present invention;

[0042] Figures 3 (a) and (b) are the left view of the FSIW-like rectangular cavity in the negative Y-axis direction (dielectric substrate length direction) and the right view of the FSIW-like rectangular cavity in the positive Y-axis direction after the common sidewall of the filter of the present invention is hidden;

[0043] Figure 4 The electric field amplitude distribution diagrams for the first three modes of the FSIW-like rectangular cavity;

[0044] Figure 5 The curves show the resonant frequencies of the first three modes in a FSIW-like rectangular cavity when the width G is changed.

[0045] Figure 6 A comparison of the f3 / f1 versus f2 / f1 curves for conventional SIW rectangular cavities and FSIW-like rectangular cavities;

[0046] Figures 7(a) and (b) show the response curves of the filter of the present invention in the 9-13 GHz band and the 13-18 GHz band, respectively, when the position of the second passband is adjusted.

[0047] The diagram is labeled as follows: Top metal layer 1, Middle metal layer 2, Bottom metal layer 3, Dielectric layer 4, First metallized via array 5, Second metallized via array 6, Third metallized via array 7, Microstrip line 1a, Groove line 1b, Rectangular metal patch 1c, Rectangular notch 2a. Detailed Implementation

[0048] The invention will now be further described with reference to the accompanying drawings.

[0049] like Figure 1 The high harmonic suppression ratio folded dual-band filter provided by the present invention includes a top metal layer 1, a middle metal layer 2, a bottom metal layer 3, a dielectric layer 4, a first metallized via array 5, a second metallized via array 6, and a third metallized via array 7.

[0050] The first metallized via array 5 encloses two connected rectangles; the two connected rectangles share a common sidewall, and the common sidewall has a coupling window; the outer sidewalls of the two connected rectangles each have a first window and a second window; the coupling window has no metallized vias, the first window has a second metallized via array 6, and the second window has a third metallized via array 7;

[0051] The top metal layer 1 includes a microstrip line 1a and a rectangular metal patch 1c; one end of the microstrip line 1a is connected to one side of the rectangular metal patch 1c, and the other end serves as the input and output ports of the filter; a slot line 1b is opened on each side of the microstrip line 1a on the rectangular metal patch 1c; the microstrip line 1a and the two slot lines 1b all fall within the first window.

[0052] The bottom metal layer 3 and the top metal layer 1 have the same shape and are equal in size; with the geometric center of the dielectric layer 4 as the origin, the top metal layer 1 and the bottom metal layer 3 are centrally symmetrical.

[0053] The top metal layer 1, bottom metal layer 3, middle metal layer 2, dielectric layer 4 and first metallized via array 5 together construct two FSIW-like rectangular cavities, which are connected by a coupling window on a common sidewall.

[0054] The intermediate metal layer 2 is a metal patch with two rectangular notches 2a; the two rectangular notches 2a are located at the folds of the two FSIW-like rectangular cavities respectively;

[0055] Figures 2(a) and (b) are views of the top metal layer and a schematic diagram of the middle metal layer of the present invention. The high harmonic suppression ratio folded dual-band filter provided by the present invention consists of two identical FSIW-like rectangular cavities on the left and right. The length W, width L, and notch width G of the cavities determine the center frequencies of the first and second passbands of the filter. The width G of the rectangular notch 2a at the fold in the FSIW-like rectangular cavity serves to adjust the center frequency of the second passband. The coupling window position W at the common sidewall of the two resonant cavities... 12 Width W W It serves to adjust the coupling between cavities; the width of the feed windows (i.e., the first window and the second window) for the source and load is W. IN The position is T IN W IN T IN The coupling strength between the source and the load is jointly determined; two slot lines 1b are provided immediately adjacent to the connection between the microstrip line 1a and the rectangular metal sheet 1c, with a slot line length L. S Width W S Determines the enhancement of the power supply;

[0056] Table 1. Dimensions of filter parameters (unit: mm)

[0057]

[0058] Figures 3(a) and (b) are the left view of the cavity in the negative Y-axis direction and the right view of the cavity in the positive Y-axis direction after the common sidewall is hidden. It can be seen from the figures that the thickness of the upper and lower dielectric substrates is the same as H1. At the same time, the second metallized via array 6 connects the bottom metal layer and the middle metal layer of the cavity in the negative Y-axis direction and the top metal layer and the middle metal layer in the cavity in the positive Y-axis direction, respectively.

[0059] Figure 4 The figure shows the electric field distribution of the first three modes in the FSIW-like rectangular cavity. As can be seen from the figure, the second mode is distributed throughout the entire rectangular cavity, while the first and third modes are distributed in the middle metal layer of the FSIW-like rectangular cavity. Therefore, when the middle metal of the FSIW-like rectangular cavity remains unchanged, changing the width G of the rectangular notch 2a at the fold will not change the resonant frequencies of the first and third modes, but will change the resonant frequency of the second mode.

[0060] Figure 5 The curves showing the resonant frequencies of the first three modes of the FSIW-like rectangular cavity when the width G is changed are shown in the figure. As can be seen from the figure, when the width G of the rectangular notch increases, the resonant frequency of the second mode shifts to the lower frequency direction, while the resonant frequencies of the first and third modes remain basically unchanged.

[0061] Figure 6The graph compares the f3 / f1 ratios of a conventional SIW rectangular cavity and an FSIW-like rectangular cavity as a function of f2 / f1. As shown, when f2 / f1 is in the range of 1.1 to 1.3, the f3 of the FSIW-like rectangular cavity is higher than that of the conventional SIW rectangular cavity, especially when f2 / f1 is relatively small. Therefore, using an FSIW-like rectangular cavity to design a dual-band filter can achieve a wider stopband.

[0062] Figures 7(a) and (b) show the response curves of the filter in the 9-13 GHz and 13-18 GHz frequency bands, respectively, when the position of the second passband is adjusted according to the technical solution of the present invention. As can be seen from the figures, as the width G of the rectangular notch 2a at the fold increases, the center frequency of the first passband of the filter remains at approximately 10 GHz, the center frequency of the second passband shifts significantly towards lower frequencies, while the parasitic passband remains at approximately 17.1 GHz. When G is 2.5 mm, the center frequency of the second passband is 12 GHz, and the relative bandwidth of the stopband is 0.425.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A wide-stopband, FSIW-like dual-band filter, comprising: Dielectric layer (4); The top metal layer (1) is located on the upper surface of the dielectric layer (4); The bottom metal layer (3) is located on the lower surface of the dielectric layer (4); An intermediate metal layer (2) is located within the dielectric layer (4); A first metallized via array (5) connecting the top metal layer (1), the middle metal layer (2), and the bottom metal layer (3); A second metallized via array (6) connecting the intermediate metal layer (2) and the bottom metal layer (3); A third metallized via array (7) connecting the top metal layer (1) and the middle metal layer (2); Its features are: The first metallized via array (5) encloses two connected rectangles; the two connected rectangles share a common sidewall, and the common sidewall has a coupling window; the outer sidewalls of the two connected rectangles each have a first window and a second window; the coupling window has no metallized vias, the first window has a second metallized via array (6), and the second window has a third metallized via array (7). The top metal layer (1) includes a microstrip line (1a) and a rectangular metal patch (1c); one end of the microstrip line (1a) is connected to one side of the rectangular metal patch (1c), and the other end serves as the input and output ports of the filter; a slot line (1b) is opened on each side of the microstrip line (1a) of the rectangular metal patch (1c); the microstrip line (1a) and the two slot lines (1b) all fall within the first window; The bottom metal layer (3) and the top metal layer (1) have the same shape and the same size; with the geometric center of the dielectric layer (4) as the origin, the top metal layer (1) and the bottom metal layer (3) are centrally symmetrical; The top metal layer (1), bottom metal layer (3), middle metal layer (2), dielectric layer (4) and first metallized via array (5) together construct two FSIW-like rectangular cavities, which are connected by a coupling window on a common sidewall. The intermediate metal layer (2) is a metal patch with two rectangular notches (2a); the two rectangular notches (2a) are located at the folds of the two FSIW-like rectangular cavities respectively.

2. The wide-stopband-like FSIW dual-band filter according to claim 1, characterized in that, The two FSIW-type rectangular cavities have the same size.

3. The wide-stopband-like FSIW dual-band filter according to claim 1, characterized in that, The coupling window width Ww and coupling window position W on the common sidewall 12 Controlling the coupling between two FSIW-like rectangular cavities.

4. The wide-stopband-like FSIW dual-band filter according to claim 1, characterized in that, The second-mode resonant frequency can be modulated by the width G of the rectangular notch (2a).

5. The wide-stopband-like FSIW dual-band filter according to claim 1, characterized in that, The intermediate metal layer (2) is equidistant from the top metal layer (1) and the bottom metal layer (3).

6. The wide-stopband-like FSIW dual-band filter according to claim 1, characterized in that, The dielectric layer (4) is formed by stacking two dielectric substrates on top of each other, with the intermediate metal layer (2) located between the two dielectric substrates; the dielectric substrate is a TanconicTLY-5 dielectric substrate with a relative permittivity of 2.2, a loss tangent of 0.0009, and a thickness of 0.508 mm.

7. The wide-stopband-like FSIW dual-band filter according to claim 1, characterized in that, The first passband of the filter is set at 10 GHz, and the second passband is set at 12 GHz.

8. The wide-stopband-like FSIW dual-band filter according to claim 1, characterized in that, The width G of the rectangular notch (2a) is greater than the thickness of the dielectric layer (4).

9. A wide-stopband-like FSIW dual-band filter according to claim 1, characterized in that, The microstrip line (1a) simultaneously excites multiple modes in a FSIW-like rectangular cavity; wherein, the first mode and the second mode are used to construct the first passband and the second passband of the dual-band filter, respectively, and the third mode constitutes the parasitic passband closest to the filter passband; the cross-coupling of the first mode and the second mode can form a transmission zero, and the cross-coupling of the second mode and the third mode can form another transmission zero. Based on the electric field distribution of the first four modes of the FSIW-like rectangular cavity, it was found that the first and third modes are distributed in the FSIW-like rectangular cavity and the rest of the intermediate metal layer (2) except for the rectangular notch; while the second mode is distributed in the entire FSIW-like rectangular cavity. Therefore, without changing the intermediate metal layer (2), changing the width of the rectangular notch (2a) in the FSIW-like rectangular cavity can change the resonant frequency f2 of the second mode without changing the resonant frequencies f1 and f3 of the first and third modes.

10. A wide-stopband-like FSIW dual-band filter according to claim 9, characterized in that, Set W / L= W and L represent the width and length of the rectangular cavity of the FSIW type, respectively. At this time, f3 is farthest from f1, and the ratio of the two reaches f3 / f1 = 1.

784. Increasing the width G of the rectangular notch (2a) can reduce f2 without changing f1 and f2. 3, Therefore, the dual-band filter still has a wide stopband even when the f2 / f1 ratio is small.

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