Miniaturized Microstrip Filters

Abstract

To provide a miniaturized microstrip filter with a low insertion loss, a low cost, and multiple zeros, in which a high impedance part and a low impedance part of a resonator are folded into an upper layer and a lower layer of the same substrate, respectively, to be connected through a metal via.SOLUTION: A single bandpass filter includes a dielectric substrate and a vertically folded stepped impedance resonator 2. The vertically folded stepped impedance resonator is located in a middle of the dielectric substrate, and coplanar waveguide transmission ports connected to the vertically folded stepped impedance resonator are disposed on both two sides of a lower surface of the dielectric substrate. The vertically folded stepped impedance resonator includes a folded low impedance line 6 and a high impedance line. The low impedance line is disposed on an upper surface of the dielectric substrate, the high impedance line is disposed on the lower surface of the dielectric substrate, and the two are connected through a metalized via 4 to form the small-size vertically folded stepped impedance resonator.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of radio frequency microwaves, and in particular to miniaturized microstrip filters. [Background technology]

[0002] As the division of wireless spectrum resources becomes finer and finer, the number of filters used in wireless systems is increasing, and the demand for improved performance is also increasing. Therefore, the realization of filters with low loss, strong and deep suppression, low cost, and high integration is expected. Microstrip filters are widely used filters, with the advantages of low cost, ease of planar integration, and high design flexibility.

[0003] Existing technologies for achieving compact filters mainly include the following steps: (1) bending resonators on the same plane; (2) forming a multilayer structure and stacking multiple resonators in multiple layers using vertical coupling methods, such as suspension substrate integrated microstrip line technology; (3) processing techniques using high-permittivity dielectric substrates, such as low-temperature co-fired ceramic technology; and (4) using multimode resonators to achieve the response effect of multiple resonators without increasing the number of resonators. However, while these miniaturization advantages are achieved, they also result in a deterioration in indicators such as cost, design simplicity, and vertical size. In addition to achieving miniaturization through changes to the filter structure itself, multipassband filters operating in multifrequency systems have reduced the number of filters used by expanding the operating frequency band. In filter design, in addition to ensuring passband performance, higher out-of-band suppression is also required, which is usually improved by creating out-of-band transmission zeros or increasing the filter order. Traditional filter designs generate a small number of zeros, usually no more than the filter order minus two. However, increasing the order of the filter also increases the loss, which often results in an insufficient number of out-of-band zeros, a narrow stopband, and insufficient suppression.Furthermore, although it is possible to extend the stopband by avoiding higher-order modes of each resonator, this method of design gradually reduces the design freedom as the order of the filter increases.

[0004] When designing compact, high-performance filters, stacking multiple dielectric substrates sacrifices vertical planarization requirements to reduce horizontal size and increase the number of substrates, resulting in increased manufacturing costs. Multilayer printed circuit boards often require pins for mounting, which reduces vertical positioning accuracy and potentially impacts filter performance. Bending resonators on the same layer limits size reduction and makes adjusting the coupling strength between resonators more difficult. Furthermore, when using multimode resonators, multiple modes interact and couple within the resonator, reducing the degree of freedom in adjustment. Meanwhile, other new processing technologies, such as low-temperature co-fired ceramic technology, are not as mature as printed circuit board technology and therefore require higher manufacturing costs, especially for multilayer designs, making cost a more prominent issue.

[0005] Increasing the filter order to improve out-of-band suppression results in a longer signal transmission path, greater loss within the passband, and an increased filter order, which leads to more complex design and larger filter size. Obtaining a wider stopband by avoiding higher-order mode resonance frequencies has several drawbacks. When increasing the filter order, it becomes more difficult to avoid higher-order modes so as not to generate high-order passbands. While changing the shape of the resonator is a common method for adjusting the frequency of higher-order modes, this can interfere with the fundamental frequency of the resonator and the coupling strength at the coupling position between the resonators, making overall adjustment more inconvenient. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to overcome the drawbacks of the prior art and provide a miniaturized microstrip filter with low insertion loss, low cost, and multiple zeros, thereby solving the problems of the prior art. [Means for solving the problem]

[0007] The object of the present invention is achieved by the following technical solution: A miniaturized microstrip filter, comprising a dielectric substrate and a vertical folded stepped impedance resonator, the vertical folded stepped impedance resonator being located at the center of the dielectric substrate, and a coplanar waveguide transmission port connected to the vertical folded stepped impedance resonator being disposed on each side of the lower surface of the dielectric substrate.

[0008] The vertically folded stepped impedance resonator includes folded low-impedance lines and high-impedance lines, the low-impedance lines being disposed on the upper surface of a dielectric substrate and the high-impedance lines being disposed on the lower surface of the dielectric substrate, and the low-impedance lines and high-impedance lines being connected through metallized vias to form a compact vertically folded stepped impedance resonator. The low-impedance lines and high-impedance lines separate the positions of the strongest electric field distribution and the strongest magnetic field distribution in the vertically folded stepped impedance resonator into different layers, thereby realizing independent control of electric coupling and magnetic coupling.

[0009] Ground metal bodies are provided on both sides of the top surface and the bottom surface of the dielectric substrate, and a row of metallized vias is arranged in each of the ground metal bodies on both sides of the top surface, thereby surrounding the vertical folded stepped impedance resonator and connecting to the ground metal bodies on the bottom surface through the metallized vias.

[0010] Two low-impedance lines are provided on the upper surface of the dielectric substrate, and the two low-impedance lines are folded in a crisscross pattern; two high-impedance lines are provided on the lower surface of the dielectric substrate, and the two high-impedance lines are connected to the low-impedance lines through metallized vias, thereby forming two half-wavelength vertical folded stepped impedance resonators arranged in parallel; and the coplanar waveguide transmission ports arranged on both sides of the lower surface of the dielectric substrate are respectively connected to one and the other of the two high-impedance lines.

[0011] The two low-impedance lines in the two half-wavelength vertical folded stepped impedance resonators have different areas and generate two transmission zeros. The two half-wavelength vertical folded stepped impedance resonators are mixed-coupled to form a passband, and the strengths of the two pairs of mixed couplings formed are different, which generates two more transmission zeros.

[0012] Four low-impedance lines are provided on the upper surface of the dielectric substrate, and two high-impedance lines are provided on the lower surface of the dielectric substrate. The four low-impedance lines are connected to two high-impedance lines through metallized vias, and each high-impedance line is connected to a ground metal body through a ground branch, thereby forming four quarter-wavelength vertical folded stepped impedance resonators arranged in a square. The coplanar waveguide transmission ports provided on both sides of the lower surface of the dielectric substrate are respectively connected to one and the other of the two high-impedance lines.

[0013] Each pair of quarter-wavelength vertical folded stepped impedance resonators constitutes a passband path, and an electrical coupling is formed between the low-impedance lines in each pair of vertical folded stepped impedance resonators, and the coupling strength can be adjusted by adjusting the size of the gap between the two low-impedance lines.

[0014] There is mixed coupling between the two passband paths, and two transmission zeros are generated between the two passbands by controlling and adjusting the electrical coupling through the low-impedance line and controlling and adjusting the magnetic coupling through the ground branch, and by bringing the two ground branches close to each other, a source-load coupling is formed and more transmission zeros are generated. [Effects of the Invention]

[0015] The present invention has the following advantages: This vertically folded stepped-impedance resonator, a compact microstrip filter with low insertion loss, low cost, and multiple zeros, is constructed by folding the high- and low-resistance sections of the resonator onto the upper and lower layers of the same substrate and connecting them through metal vias. This allows for miniaturization and independent control of the resonator's electric and magnetic field coupling. The asymmetric design of the half-wave vertically folded stepped-impedance resonator creates two parallel-grounded series resonant circuits with different resonant frequencies, thereby generating two zeros and improving the stopband characteristics. At the same time, two additional zeros are generated by mixed coupling, enabling the filter to generate four transmission zeros with a low-order second-order response, achieving excellent stopband performance. Adding a ground branch to the asymmetric half-wave resonator creates a quarter-wave resonator, allowing for flexible adjustment of the frequencies and bandwidths of the two passbands using a structure similar to that of a single bandpass filter. This provides a compact microstrip filter with low insertion loss, low cost, and multiple zeros. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a top view of a single bandpass filter of the present invention. [Figure 2] FIG. 2 is a bottom view of the single bandpass filter of the present invention. [Figure 3] FIG. 1 is a front view of a single bandpass filter according to the present invention. [Figure 4] FIG. 2 is a top view of the dual bandpass filter of the present invention. [Figure 5] FIG. 2 is a bottom view of the dual bandpass filter of the present invention. [Figure 6] FIG. 1 is a front view of a dual bandpass filter according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] In order to clarify the objectives, technical solutions, and advantages of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described herein and illustrated in the drawings can be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the present application provided in conjunction with the drawings is not intended to limit the scope of the claimed application, but merely to represent selected embodiments of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without any creative work shall fall within the scope of protection of the present application. The present invention will be further described below with reference to the drawings.

[0018] As shown in FIGS. 1 to 3, one embodiment of the present invention relates to a miniaturized microstrip filter, which includes a dielectric substrate 8 and a vertical-folded stepped impedance resonator 2, the vertical-folded stepped impedance resonator 2 being located at the center of the dielectric substrate 8, and coplanar waveguide transmission ports 1 connected to the vertical-folded stepped impedance resonator 2 being located on both sides of the lower surface of the dielectric substrate 8, with the coplanar waveguide transmission port 1 located on the left side of the dielectric substrate 8 functioning as an input port and the coplanar waveguide transmission port 1 on the opposite side functioning as an output port.

[0019] Grounded metal bodies 3 are installed on both sides of the upper surface and the lower surface of the dielectric substrate 8, and a row of metallized vias 4 is arranged in each of the grounded metal bodies 3 on both sides of the upper surface, thereby surrounding the vertical folded stepped impedance resonator 2 and connecting it to the grounded metal bodies 3 on the lower surface through the metallized vias 4.

[0020] Here, the diameter of the metallized vias 4 is 0.12 mm, the via spacing is 0.5 mm, and the dielectric substrate 8 is a Rogers 5880 substrate, with a thickness of 0.508 mm, a dielectric constant of 2.2, and a loss tangent of 0.0009.

[0021] Furthermore, two low-impedance lines 6 are installed on the upper surface of the dielectric substrate 8, and the two low-impedance lines 6 are folded in a cross shape, and two high-impedance lines 7 are installed on the lower surface of the dielectric substrate 8, and the two high-impedance lines 7 are connected to the low-impedance lines 6 through metallized vias 4, thereby forming two half-wavelength vertically folded stepped impedance resonators 2 arranged in parallel, and the coplanar waveguide transmission ports 1 arranged on both sides of the lower surface of the dielectric substrate are respectively connected to one and the other of the two high-impedance lines 7.

[0022] In this embodiment, the stepped-impedance resonator is folded vertically, with the high-impedance line 7 and the low-impedance line 6 as the boundary. The two sections are distributed on the upper and lower layers of the same dielectric substrate 8, and then connected to the high-impedance line 7 and the low-impedance line 6 through a metalized via 4. This approach not only achieves compactness, but also separates the strongest electric field and strongest magnetic field in the resonator onto different layers, enabling independent control of the electrical and magnetic coupling between the resonators and enhancing design flexibility. Furthermore, the filter uses a half-wavelength vertically folded stepped-impedance resonator 2, which is equivalent to two parallel-grounded series LC circuits. Therefore, the resonator itself generates a transmission zero. Second, by asymmetrically processing a single resonator, the areas of the two low-impedance lines 6 of the resonator can be made different, resulting in two zeros. Based on the above resonator principle, two resonators are hybrid-coupled to form a passband. The feed structure uses a coplanar waveguide transmission port 1 to directly connect to the high-impedance line 7. This places the ground metal body 3 and the high-impedance line 7 on the same metal layer, maintaining the filter's single-layer substrate characteristics. The strengths of the two hybrid coupling pairs formed are different, creating two zeros. Based on the above design principle, a single, multi-zero, compact filter design is achieved. Furthermore, since the introduction of zeros does not increase the filter order, the benefit of low insertion loss is also achieved.

[0023] The working principle and process of this embodiment are as follows: a 50 ohm coplanar waveguide feed line is connected to the high-impedance line 7 of the vertical folded stepped impedance resonator 2 to excite it, and the two vertical folded stepped impedance resonators 2 form a mixed coupling via the low-impedance line 6 and the parallel-coupled lower high-impedance line 7, and finally transmit the signal to the output port through a symmetrical structure. Due to the structural characteristics of the half-wave vertical folded stepped impedance resonator 2 itself and the mixed coupling between the two resonators, four transmission zeros are introduced.

[0024] Here, the parameters of the single bandpass filter are shown in Table 1 below.

[0025] Table 1 shows the parameters of the single bandpass filter (unit: mm). [Table 1]

[0026] As shown in FIGS. 4 to 6, another embodiment of the present invention relates to a miniaturized microstrip filter, which includes a dielectric substrate 8 and a vertical-folded stepped impedance resonator 2, the vertical-folded stepped impedance resonator 2 being disposed at the center of the dielectric substrate 8, and coplanar waveguide transmission ports 1 connected to the vertical-folded stepped impedance resonator 2 are disposed on both sides of the underside of the dielectric substrate 8, with the coplanar waveguide transmission port 1 located on the left side of the dielectric substrate 8 functioning as an input port and the coplanar waveguide transmission port 1 on the opposite side functioning as an output port.

[0027] Grounded metal bodies 3 are installed on both sides of the upper surface and the lower surface of the dielectric substrate 8, and a row of metallized vias 4 is arranged in each of the grounded metal bodies 3 on both sides of the upper surface, thereby surrounding the vertical folded stepped impedance resonator 2 and connecting it to the grounded metal bodies 3 on the lower surface through the metallized vias 4.

[0028] Here, the diameter of the metallized vias 4 is 0.12 mm, the via spacing is 0.2 mm, and the dielectric substrate 8 is a Rogers 5880 substrate, with a thickness of 0.508 mm, a dielectric constant of 2.2, and a loss tangent of 0.0009.

[0029] Four low-impedance lines 6 are installed on the upper surface of the dielectric substrate 8, and two high-impedance lines 7 are installed on the lower surface of the dielectric substrate 8. The four low-impedance lines 6 are connected to two high-impedance lines 7 through metallized vias 4, and each high-impedance line 7 is connected to a ground metal body 3 through a ground branch 5, thereby forming four quarter-wavelength vertical folded stepped impedance resonators 2 arranged in a square. The coplanar waveguide transmission ports 1 installed on both sides of the lower surface of the dielectric substrate 8 are respectively connected to one and the other of the two high-impedance lines 7.

[0030] In this example, based on the single bandpass filter design described above, the high-impedance line 7 of the half-wavelength vertical folded stepped impedance resonator is grounded by a ground branch 5, resulting in four quarter-wavelength vertical folded stepped impedance resonators 2 with a similar structure. The two passband paths of the dual bandpass filter each consist of a pair of quarter-wavelength resonators. An electrical coupling is formed between the low-impedance lines 6 of each pair of vertical folded stepped impedance resonators 2, the strength of which can be controlled by adjusting the gap between them. Adjusting the size of different pairs of vertical folded stepped impedance resonators 2 allows the resonant frequency of the corresponding passband to be adjusted. A mixed coupling exists between the two paths, the electric and magnetic couplings of which are independently controlled by the low-impedance line 6 and the ground branch 5, respectively, resulting in two zeros between the two passbands. The two ground branches are located close to each other, forming a weak source-load coupling and introducing more transmission zeros. The feed structure is similar to that of the single bandpass filter, with the coplanar waveguide transmission port 1 directly connected to the high-impedance line 7 in both cases. The above analysis results in a low insertion loss, miniaturized dual bandpass filter similar to a single bandpass structure, which has four transmission zeros and a high degree of freedom in tuning the passband response.

[0031] The operating principle and process of this embodiment are as follows: A 50-ohm coplanar waveguide feed line is connected to the high-impedance line 7 through the coplanar waveguide transmission port 1, and the left-hand resonators of both paths are excited. Then, the parallel-arranged resonators of the same size are electrically coupled via the low-impedance line 6, and the output feed line is directly connected to output the signal, resulting in two passbands. The low-impedance line 6 and the ground branch 5 form a mixed coupling between the two paths, and the input and output feed lines form a weak magnetic coupling via the closely spaced ground branches 5, introducing four transmission zeros and improving the filter's stopband performance.

[0032] Here, the parameters of the dual bandpass filter are shown in Table 2 below.

[0033] Table 2 shows the parameters of the dual bandpass filter (unit: mm). [Table 2]

[0034] It should be understood that the above is only a preferred embodiment of the present invention, and the present invention is not limited to the form disclosed herein, and other examples should not be considered as exclusive, and can be used in various other combinations, modifications, and improvements, and can be modified by the above teachings or the skills or knowledge of the relevant fields within the scope of the assumptions described herein. Furthermore, all modifications and changes made by those skilled in the art within the scope of the spirit and scope of the present invention are intended to be within the scope of protection of the appended claims of the present invention. [Explanation of symbols]

[0035] 1 coplanar waveguide transmission port 2 Vertically Folded Stepped Impedance Resonators 3 Grounded metal body 4 Metallized Vias 5 Ground Branch 6 Low impedance wire 7 High-impedance lines 8 Dielectric substrate

Claims

1. A miniaturized microstrip filter, comprising a dielectric substrate (8) and a vertically folded stepped impedance resonator (2), the vertically folded stepped impedance resonator (2) being located at the center of the dielectric substrate (8), and coplanar waveguide transmission ports (1) connected to the vertically folded stepped impedance resonator (2) being located on both sides of the lower surface of the dielectric substrate (8); The vertically folded stepped impedance resonator (2) includes folded low-impedance lines (6) and high-impedance lines (7), the low-impedance lines (6) being disposed on the upper surface of the dielectric substrate (8) and the high-impedance lines (7) being disposed on the lower surface of the dielectric substrate (8), and the low-impedance lines (6) and the high-impedance lines (7) being connected through metallized vias (4) to form a compact vertically folded stepped impedance resonator (2), and the low-impedance lines (6) and the high-impedance lines (7) are used to separate the strongest electric field distribution position and the strongest magnetic field distribution position in the vertically folded stepped impedance resonator (2) into different layers, thereby realizing independent control of electric coupling and magnetic coupling; A miniaturized microstrip filter characterized in that grounded metal bodies (3) are installed on both sides of the upper surface and on the lower surface of the dielectric substrate (8), a row of the metallized vias (4) is arranged in each of the grounded metal bodies (3) on both sides of the upper surface so as to surround the vertically folded stepped impedance resonator (2), and the grounded metal bodies (3) on both sides of the upper surface are connected to the grounded metal body (3) on the lower surface through the metallized vias (4).

2. 2. The miniaturized microstrip filter according to claim 1, wherein two low-impedance lines (6) are provided on the upper surface of the dielectric substrate (8), and a cross-shaped slit is formed between the two low-impedance lines (6); two high-impedance lines (7) are provided on the lower surface of the dielectric substrate (8), and the two high-impedance lines (7) are connected to the low-impedance lines (6) through the metallized vias (4), thereby forming two half-wavelength vertically folded stepped-impedance resonators (2) arranged in parallel; and the coplanar waveguide transmission ports (1) arranged on both sides of the lower surface of the dielectric substrate (8) are connected to one and the other of the two high-impedance lines (7), respectively.

3. Four low-impedance lines (6) are installed on the upper surface of the dielectric substrate (8), and two high-impedance lines (7) are installed on the lower surface of the dielectric substrate (8), and the four low-impedance lines (6) are connected to the two high-impedance lines (7) through the metallized vias (4), and each high-impedance line (7) is connected to a ground metal body (3) through a ground branch (5), thereby forming four quarter-wavelength vertically folded stepped impedance resonators (2) arranged in a square; 2. The miniaturized microstrip filter according to claim 1, wherein the coplanar waveguide transmission ports (1) installed on both sides of the lower surface of the dielectric substrate (8) are connected to one and the other of the two high-impedance lines (7), respectively.

4. 4. The miniaturized microstrip filter according to claim 3, wherein each pair of quarter-wavelength vertical folded stepped impedance resonators (2) constitutes a passband path, and an electrical coupling is formed between the low-impedance lines (6) in each pair of vertical folded stepped impedance resonators (2), and the coupling strength is adjusted by adjusting the size of the gap between two of the low-impedance lines (6).

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