A miniaturized high-suppression LTCC columnar inductor bandpass filter

Abstract

The present invention discloses a miniaturized high-suppression LTCC columnar inductor bandpass filter, comprising a ceramic substrate, an external input electrode, an external output electrode, and an external grounding electrode; the ceramic substrate includes four parallel resonators, two grounding plates, five series-connected capacitors, and a source-load coupling capacitor. The present invention has the advantages of miniaturization, high proximal suppression, low cost, high batch consistency, and novel structure.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a miniaturized high-suppression LTCC columnar inductor bandpass filter. Background Art

[0002] With the continuous acceleration of the global information process, the communication industry has ushered in rapid development. The rapid development of the communication industry and the increasing market demand have put forward higher requirements for communication equipment. The high performance, high integration, high reliability and low cost of communication equipment have become the inevitable trend of its future development.

[0003] Since the Low Temperature Co-fired Ceramic (LTCC) technology was proposed in the 1980s, it has been widely used in the design and production of microwave passive devices. Compared with traditional thin film technology, the multi-layer structure of LTCC technology makes the module more integrated and smaller in size; high conductivity materials such as gold, silver, and copper are used as printed circuit paste to reduce module power loss. LTCC technology has the characteristics of high Q value and high reliability, and has been widely used in the production of miniaturized electronic devices.

[0004] Bandpass filters are indispensable components of communication equipment and are widely used in WLAN, DSTV, Bluetooth, satellite TV, PHS and cordless phones. At present, bandpass filters are mainly divided into two structures for realization: one is to realize it through the series connection of traditional low-pass filters and high-pass filters. This structure has the advantages of wide passband and small insertion loss, but it has difficulties in the design process, such as complex structure, many parasitic coupling phenomena, difficult debugging, and poor consistency of production batches. The second is to use the traditional bandpass filter structure. This structure has the advantages of high suppression and simple structure, but the actual designed product has a small passband width and large insertion loss.

[0005] Therefore, how to select a suitable structure, overcome the bottleneck of the existing bandpass filter structure, and realize LTCC bandpass filters with excellent electrical performance and high production batch consistency is a key issue currently faced by LTCC bandpass filter design. Summary of the invention

[0006] The present invention proposes a miniaturized high-suppression LTCC columnar inductor bandpass filter, which aims to solve the problems of difficult structural selection, low proximal suppression, poor consistency of production batches, and difficult debugging of existing bandpass filters. The filter greatly reduces the inductance and adopts a vertical in-line (VIC) capacitor structure to greatly increase the capacitance of the parallel resonant capacitor under the same area, so that the parallel resonance formed by the inductor and the resonant capacitor in parallel is large, and the designed bandpass filter has higher near-band suppression. At the same time, by introducing a source-load coupling capacitor, the near-end suppression of the passband is increased. The four parallel resonances inside the filter adopt a mirror-symmetrical structure, and a grounding layer is added to the top layer inside the ceramic substrate to optimize the internal layout, reduce the design difficulty, and greatly reduce the volume of the filter. The volume of the filter is only 3.2mm×2.5mm×1.5mm. The specific technical scheme of the present invention is as follows:

[0007] A miniaturized high-suppression LTCC inductor cylindrical bandpass filter, comprising a ceramic substrate, an external input electrode, an external output electrode, and an external grounding electrode; the external input electrode and the external output electrode are symmetrically printed on the left and right sides of the ceramic substrate; the external grounding electrode is symmetrically printed on the front and back sides of the ceramic substrate; the ceramic substrate includes four parallel resonances, two grounding plates, five series-connected capacitors and a source-load coupling capacitor C04; the two grounding plates include a first grounding plate SD1 and a second grounding plate SD2, wherein the second grounding plate SD2 adopts a defective ground structure including four circular defects; the five series-connected capacitors include an input capacitor C0, a first series capacitor C1, a second series capacitor C2, a third series capacitor C3, and an output capacitor C4;

[0008] The four parallel resonances are symmetrically distributed in the ceramic matrix in a field shape, including a first parallel resonance formed by a first inductor L1 and a first resonant capacitor C10 in parallel, a second parallel resonance formed by a second inductor L2 and a second resonant capacitor C20 in parallel, a third parallel resonance formed by a third inductor L3 and a third resonant capacitor C30 in parallel, and a fourth parallel resonance formed by a fourth inductor L4 and a fourth resonant capacitor C40 in parallel; the first parallel resonance and the second parallel resonance are connected via a first series capacitor C1, the second parallel resonance and the third parallel resonance are connected via a second series capacitor C2, and the third parallel resonance and the fourth parallel resonance are connected via a third series capacitor C3;

[0009] The ceramic substrate is divided into six layers, wherein the first layer and the fifth layer are the first grounding layer SD1 and the second grounding layer SD2, wherein the second grounding layer SD2 is a defective ground structure including four circular defects, and both grounding layers are connected to the external grounding electrode of the ceramic substrate;

[0010] The input capacitor C0 is located in the second, third and fourth layers of the ceramic substrate, the second and fourth layers of the plate are connected through vias, and the third layer of the plate is connected to the external input electrode;

[0011] The first resonant capacitor C10 is located on the fourth and sixth layers of the ceramic substrate, and the fourth and sixth layer plates are connected through the circular defect of the fifth layer second grounding layer SD2 via a via column, and the fourth layer plate is connected to the lower plate of the input capacitor C0 through a transmission line; the first inductor L1 is located between the first layer and the second layer of the ceramic substrate, and the upper end is connected to the first grounding layer SD1, and the lower end is connected to the upper plate of the first resonant capacitor C10 through a via column;

[0012] The second resonant capacitor C20 is located on the fourth and sixth layers of the ceramic substrate, and the fourth and sixth layers of the plates are connected through the circular defect of the fifth layer second grounding layer SD2 via a via column; the second inductor L2 is located between the first and second layers of the ceramic substrate, the upper end is connected to the first grounding layer SD1, the lower end is connected to the upper plate of the second resonant capacitor C20 through a via column, and is connected to the upper plate of the first series capacitor C1 through a transmission line;

[0013] The output capacitor C4 is located on the second, third and fourth layers of the ceramic substrate, the second and fourth layers of the plate are connected through vias, and the third layer of the plate is connected to the external output electrode;

[0014] The fourth resonant capacitor C40 is located on the fourth and sixth layers of the ceramic substrate, and the fourth and sixth layer plates are connected through the circular defect of the fifth layer second ground layer SD2 through the via column, and the fourth layer plate is connected to the lower plate of the output capacitor C4 through the transmission line; the fourth inductor L4 is located between the first and second layers of the ceramic substrate, the upper end is connected to the first ground layer SD1, and the lower end is connected to the upper plate of the fourth resonant capacitor C40 through the via column;

[0015] The third resonant capacitor C30 is located on the fourth and sixth layers of the ceramic substrate, and the fourth and sixth layers of the plates are connected through the circular defect of the fifth layer and the second grounding layer SD2 via a via column; the third inductor L3 is located between the first and second layers of the ceramic substrate, the upper end is connected to the first grounding layer SD1, the lower end is connected to the upper plate of the third resonant capacitor C30 through a via column, and is connected to the upper plate of the third series capacitor C3 through a transmission line;

[0016] The second series capacitor C2 is located on the third layer of the ceramic substrate and is composed of two electrodes, which are respectively connected to the fourth-layer upper plates of the second resonant capacitor C20 and the third resonant capacitor C30 through via columns; the source-load coupling capacitor C04 is located on the third layer of the ceramic substrate and adopts a C-type structure to form a coupling with the upper plate of the first resonant capacitor C10 and the upper plate of the fourth resonant capacitor C40.

[0017] Furthermore, the first inductor L1, the second inductor L2, the third inductor L3, and the fourth inductor L4 are implemented by using a columnar metal hole column, and the size of the inductance is adjusted by adjusting the height and radius of the metal hole column;

[0018] The first resonant capacitor C10, the second resonant capacitor C20, the third resonant capacitor C30, the fourth resonant capacitor C40, the input capacitor C0, and the output capacitor C4 are implemented by vertical plug-in capacitor plates, and the capacitance value is adjusted by adjusting the distance between the plates and the area of ​​the plates facing each other;

[0019] The first series capacitor C1, the first series capacitor C2, the first series capacitor C3, the fourth series capacitor C4 and the source-load coupling capacitor C04 are implemented by a pair of flat capacitor plates, and the capacitance value is adjusted by adjusting the distance between the plates and the area facing the plates.

[0020] Furthermore, the structures of the first inductor L1, the second inductor L2, the first resonant capacitor C10, the second resonant capacitor C20 and the first series capacitor C1 are mirror-symmetrical to the structures of the third inductor L3, the fourth inductor L4, the third resonant capacitor C30 and the fourth resonant capacitor C40.

[0021] Furthermore, the second series capacitor C2 and the third series capacitor C3 are centrally symmetrical in structure.

[0022] Furthermore, the ceramic body material is a ceramic material with a dielectric constant of 9.8 and a loss tangent of 0.003, and the external ground electrode, the external input electrode, and the external output electrode are printed with silver material.

[0023] Furthermore, the overall size of the filter is 3.2 mm×2.5 mm×1.5 mm.

[0024] Furthermore, the passband range of the filter is 2.21-2.41 GHz, the maximum insertion loss in the passband is 2 dB, the suppression in the low-end stopband 0-1.95 GHz is greater than 25 dB, a transmission zero is generated at 2.1 GHz, and the suppression reaches 30 dB; in the high-end stopband 2.60 GHz-3 GHz, the suppression is greater than 25 dB, a transmission zero is generated at 2.53 GHz, and the suppression reaches 29 dB.

[0025] The beneficial effects of the present invention are as follows:

[0026] (1) The innovative use of columnar inductors avoids the problems of large volume, parasitic coupling effects between layers, and uneven printing during actual LTCC process production of traditional multi-layer spiral inductors. At the same time, by using columnar inductors, the inductance can be greatly reduced and the resonance effect of parallel resonance can be enhanced.

[0027] (2) Introduce a two-layer grounding structure. The introduction of the top grounding layer allows the inductor to be directly grounded, avoiding redundant transmission lines and through-holes, reducing unnecessary parasitic coupling, and reducing the complexity of the design. The bottom grounding layer adopts a defective ground structure. Through four circular defects on the grounding layer, the parallel resonant capacitor realizes a vertical in-line (VIC) structure of plate-ground-plate, which greatly increases the capacitance per unit area. Combined with the small inductance of the columnar inductor, it greatly improves the resonance in a limited area, making the designed bandpass filter have higher near-band suppression.

[0028] (3) By introducing C-type source-load coupling capacitors, the near-end stopband suppression is increased, which greatly increases the space utilization. The designed bandpass filter has a suppression of 30dB at the low end 2.1GHz and a suppression of 29dB at the high end 2.53GHz, and has good electrical performance.

[0029] (4) The ceramic matrix adopts a mirror-symmetrical structure, and the four parallel resonances adopt a symmetrical layout, which makes the internal structure simpler and greatly reduces the amount of adjustment during the design process. At the same time, the four series-connected capacitors all adopt a common plate structure, which is directly coupled with the connected capacitors through a single-layer plate, reducing unnecessary plates and reducing the complexity of the model structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is an equivalent circuit schematic diagram of the LTCC bandpass filter of the present invention;

[0031] Figure 2 It is a schematic diagram of the external structure of the LTCC bandpass filter of the present invention;

[0032] Figure 3 It is a schematic diagram of the overall internal structure of the LTCC bandpass filter of the present invention;

[0033] Figure 4 It is a front view structural schematic diagram of the LTCC bandpass filter of the present invention;

[0034] Figure 5 It is a planar structural diagram of the first layer of the LTCC bandpass filter of the present invention;

[0035] Figure 6 The 3D structure diagram of the inductor column of the LTCC bandpass filter of the present invention;

[0036] Figure 7 It is a planar structural diagram of the second layer of the LTCC bandpass filter of the present invention;

[0037] Figure 8 It is a planar structural diagram of the third layer of the LTCC bandpass filter of the present invention;

[0038] Fig. 9 It is a planar structural diagram of the fourth layer of the LTCC bandpass filter of the present invention;

[0039] Fig.10 It is a planar structural diagram of the fifth layer of the LTCC bandpass filter of the present invention;

[0040] Fig.11 It is a planar structural diagram of the sixth layer of the LTCC bandpass filter of the present invention;

[0041] Fig.12 It is a diagram of the S11 simulation result of the LTCC bandpass filter of the present invention;

[0042] Fig.13 Graph showing the S21 simulation results of the LTCC bandpass filter of the present invention; DETAILED DESCRIPTION

[0043] In order to more clearly and in detail produce the technical implementation scheme of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and preferred embodiments. The specific embodiments described here are only used to explain the present invention and are not limited to the present invention.

[0044] Figure 1 FIG. 1 is an equivalent circuit schematic diagram of the LTCC bandpass filter of the present invention. Figure 1 As shown, the present invention adopts a traditional fourth-order bandpass filter structure, including a first resonance unit formed by capacitor C10 and inductor L1 in parallel, a second resonance unit formed by capacitor C20 and inductor L2 in parallel, a third resonance unit formed by capacitor C30 and inductor L3 in parallel, a fourth resonance unit formed by capacitor C40 and inductor L4 in parallel, and an input capacitor C0, an output capacitor C4 and three series capacitors C1, C2, and C3. The four resonance units are independent of each other and are connected to each other through three series-connected capacitors C1, C2, and C3. The first resonance unit and the fourth resonance unit are further connected to each other by introducing a source-load coupling capacitor C04 to increase the near-end suppression of the passband.

[0045] Figure 2 The external structure diagram of the LTCC bandpass filter of the present invention includes a ceramic substrate housing, an external input electrode, an external output electrode and an external grounding electrode. The overall external size of the present invention is 3.2mm×2.5mm×1.5mm, and a ceramic material with a dielectric constant of 9.8 and a loss tangent of 0.003 is used. The external input electrode, the external output electrode and the external grounding electrode are all printed on the ceramic substrate with silver material, and the external input electrode and the external output electrode are symmetrically printed in the middle of the left and right sides of the ceramic substrate; the external grounding electrode is divided into two parts, front and back, and is symmetrically printed on the front and back sides of the ceramic substrate.

[0046] Figure 3 and Figure 4 They are respectively the internal overall structure schematic diagram and the front view structure schematic diagram of the LTCC bandpass filter of the present invention. It can be clearly seen from the two figures that the internal overall structure is divided into six layers, among which the columnar inductor is between the first and second layers, and the internal overall structure adopts a vertical interconnection structure. The first and fifth layers are grounding plates, among which the second grounding plate SD2 of the fifth layer has four circular defects, which are symmetrically distributed in a field shape, and the radius of the four defect circles is 0.128mm. There are four inductors L1, L2, L3, and L4 between the first and second layers, all of which are cylinders with a radius of 0.08mm and a height of 1.16mm, among which L1 and L2 are mirror-symmetrical with L4 and L3 respectively. The upper ends of the four inductor columns are directly connected to the first grounding plate SD1, reducing unnecessary transmission lines and via columns, and avoiding unnecessary parasitic coupling phenomena. The lower end of L1 is connected to the fourth-layer upper plate of the first resonant capacitor C10 through a via column to form the first parallel resonance. The lower end of L2 is connected to the transmission line connected to the upper plate of the first series capacitor C1 and the upper plate of the second resonant capacitor C20 through a via column, forming a second parallel resonance. Similarly, the first resonant unit and the second resonant unit are mirror-symmetrical with the fourth resonant unit and the third resonant unit, respectively, and the overall structural layout is the same. Specifically, as for the resonant inductance of each resonant unit, as mentioned above, the four resonant units are symmetrical structures, so the first resonant capacitor C10 and the fourth resonant capacitor C40, the second resonant capacitor C20 and the third resonant capacitor C30 are of the same size, and only the structure of the first resonant capacitor C10 and the second resonant capacitor C20 is described here. The first resonant capacitor C10 and the second resonant capacitor C20 both adopt a vertical in-line (VIC) structure, and the fourth upper plate of the first resonant capacitor C10 and the sixth lower plate are connected through a through hole through the circular defect of the fifth second grounding layer SD2, and form a vertical in-line capacitor structure of plate-ground-plate with the second grounding layer SD2. Similarly, the fourth layer upper plate of the second resonant capacitor C20 is connected to the sixth layer lower plate through a through hole passing through the circular defect of the fifth layer second grounding layer SD2, forming a plate-ground-plate vertical plug-in capacitor structure with the second grounding layer SD2.

[0047] The input capacitor C0 and the output capacitor C4 also adopt a vertical plug-in (VIC) structure, and the two are mirror-symmetrical. Only the input capacitor C0 structure is described here. The fourth layer of the lower plate of the input capacitor C0 is connected to the upper plate of the first resonant capacitor through a transmission line; the second layer of the upper plate is connected to the lower plate through a through hole; the middle layer is the third layer of the input plate, which is connected to the external input electrode. The three layers of plates constitute a vertical plug-in structure of plate-input-plate, and the capacitance under the same unit area is larger. The first series capacitor C1 and the third series capacitor C3 are mirror-symmetrical, with the same structure size, and adopt a parallel plate structure. The third layer of the upper plate is connected to the lower end of the second inductor L2 and the third inductor L3 through a transmission line, and forms a parallel plate (MIM) capacitor with the first parallel resonant C10 and the fourth parallel resonant C40 fifth layer of the upper plate, avoiding the introduction of redundant plates. The two plates of the third layer of the second series capacitor C2 are connected to the second resonant capacitor C20 and the fourth layer of the upper plate of the third resonant capacitor through a through hole column. The lower plate of the third layer extends the upper plate of the third resonant capacitor C30, and the upper plate extends the upper plate of the second resonant capacitor C20. The two are coupled to each other to form a second series capacitor C2. The capacitor with this structure has a large capacitance and can independently control the capacitance of the two plates, which is convenient for debugging. The source-load coupling capacitor C04 is located on the third layer of the ceramic substrate and adopts a C-type structure to couple with the upper plate of the first resonant capacitor C10 and the upper plate of the fourth resonant capacitor C40 to form a capacitor.

[0048] The specific structure of the bandpass filter layers and inductors described above is as follows Figure 5-Figure 11 shown.

[0049] Figure 12-13 This is a simulation diagram of the S parameter results of the bandpass filter of the present invention. As shown in the figure, the passband range of the bandpass filter is 2.21-2.41GHz, the maximum insertion loss of the passband is 2dB, the suppression is greater than 25dB in the low-end stopband 0-1.95GHz, a transmission zero is generated at 2.1GHz, and the suppression reaches 30dB; the suppression is greater than 25dB in the high-end stopband 2.60GHz-3GHz, a transmission zero is generated at 2.53GHz, and the suppression reaches 29dB.

[0050] The invention has the advantages of novel and simple structure, high near-band suppression, convenient debugging, high consistency of production batches, etc., and is suitable for LTCC process batch production.

[0051] The above-described embodiment is a preferred embodiment of the present invention, and the present invention is not limited to the above-described implementation mode. Based on the embodiments of the present invention, any modification, equivalent replacement, and improvement made by ordinary technicians in this field based on the present invention without creative work should be included in the protection scope recorded in the claims.

Claims

1. A miniaturized high-suppression LTCC columnar inductor bandpass filter, comprising a ceramic substrate, an external input electrode, an external output electrode, and an external grounding electrode; the external input electrode and the external output electrode are symmetrically printed on the left and right sides of the ceramic substrate; the external grounding electrode is symmetrically printed on the front and back sides of the ceramic substrate; the ceramic substrate includes four parallel resonances, two grounding plates, five series-connected capacitors and a source-load coupling capacitor C04; the two grounding plates include a first grounding plate SD1 and a second grounding plate SD2, wherein the second grounding plate SD2 adopts a defective ground structure including four circular defects; the five series-connected capacitors include an input capacitor C0, a first series capacitor C1, a second series capacitor C2, a third series capacitor C3, and an output capacitor C4; The four parallel resonances are symmetrically distributed in the ceramic matrix in a field shape, including a first parallel resonance formed by a first inductor L1 and a first resonant capacitor C10 in parallel, a second parallel resonance formed by a second inductor L2 and a second resonant capacitor C20 in parallel, a third parallel resonance formed by a third inductor L3 and a third resonant capacitor C30 in parallel, and a fourth parallel resonance formed by a fourth inductor L4 and a fourth resonant capacitor C40 in parallel; the first parallel resonance and the second parallel resonance are connected via a first series capacitor C1, the second parallel resonance and the third parallel resonance are connected via a second series capacitor C2, and the third parallel resonance and the fourth parallel resonance are connected via a third series capacitor C3; The ceramic substrate is divided into six layers, wherein the first layer and the fifth layer are the first grounding layer SD1 and the second grounding layer SD2, wherein the second grounding layer SD2 is a defective ground structure including four circular defects, and both grounding layers are connected to the external grounding electrode of the ceramic substrate; The input capacitor C0 is located in the second, third and fourth layers of the ceramic substrate, the second and fourth layers of the plate are connected through vias, and the third layer of the plate is connected to the external input electrode; The first resonant capacitor C10 is located on the fourth and sixth layers of the ceramic substrate, and the fourth and sixth layer plates are connected through the circular defect of the fifth layer second grounding layer SD2 via a via column, and the fourth layer plate is connected to the lower plate of the input capacitor C0 through a transmission line; the first inductor L1 is located between the first layer and the second layer of the ceramic substrate, and the upper end is connected to the first grounding layer SD1, and the lower end is connected to the upper plate of the first resonant capacitor C10 through a via column; The second resonant capacitor C20 is located on the fourth and sixth layers of the ceramic substrate, and the fourth and sixth layers of the plates are connected through the circular defect of the fifth layer second grounding layer SD2 via a via column; the second inductor L2 is located between the first and second layers of the ceramic substrate, the upper end is connected to the first grounding layer SD1, the lower end is connected to the upper plate of the second resonant capacitor C20 through a via column, and is connected to the upper plate of the first series capacitor C1 through a transmission line; The output capacitor C4 is located on the second, third and fourth layers of the ceramic substrate, the second and fourth layers of the plate are connected through vias, and the third layer of the plate is connected to the external output electrode; The fourth resonant capacitor C40 is located on the fourth and sixth layers of the ceramic substrate, and the fourth and sixth layer plates are connected through the circular defect of the fifth layer second ground layer SD2 through the via column, and the fourth layer plate is connected to the lower plate of the output capacitor C4 through the transmission line; the fourth inductor L4 is located between the first and second layers of the ceramic substrate, the upper end is connected to the first ground layer SD1, and the lower end is connected to the upper plate of the fourth resonant capacitor C40 through the via column; The third resonant capacitor C30 is located on the fourth and sixth layers of the ceramic substrate, and the fourth and sixth layers of the plates are connected through the circular defect of the fifth layer and the second grounding layer SD2 via a via column; the third inductor L3 is located between the first and second layers of the ceramic substrate, the upper end is connected to the first grounding layer SD1, the lower end is connected to the upper plate of the third resonant capacitor C30 through a via column, and is connected to the upper plate of the third series capacitor C3 through a transmission line; The second series capacitor C2 is located on the third layer of the ceramic substrate and is composed of two plates, which are respectively connected to the fourth-layer upper plates of the second resonant capacitor C20 and the third resonant capacitor C30 through vias; the source-load coupling capacitor C04 is located on the third layer of the ceramic substrate and is coupled to the upper plates of the first resonant capacitor C10 and the fourth resonant capacitor C40 using a C-type structure; The structures of the first inductor L1, the second inductor L2, the first resonant capacitor C10, the second resonant capacitor C20 and the first series capacitor C1 are mirror-symmetrical to the structures of the third inductor L3, the fourth inductor L4, the third resonant capacitor C30 and the fourth resonant capacitor C40.

2. The miniaturized high-suppression LTCC columnar inductor bandpass filter according to claim 1, characterized in that: The first inductor L1, the second inductor L2, the third inductor L3, and the fourth inductor L4 are implemented by using columnar metal hole columns, and the size of the inductance is adjusted by adjusting the height and radius of the metal hole columns; The first resonant capacitor C10, the second resonant capacitor C20, the third resonant capacitor C30, the fourth resonant capacitor C40, the input capacitor C0, and the output capacitor C4 are implemented by vertical plug-in capacitor plates, and the capacitance value is adjusted by adjusting the distance between the plates and the area of ​​the plates facing each other; The first series capacitor C1, the first series capacitor C2, the first series capacitor C3, the fourth series capacitor C4 and the source-load coupling capacitor C04 are implemented by a pair of flat capacitor plates, and the capacitance value is adjusted by adjusting the distance between the plates and the area facing the plates.

3. The miniaturized high-suppression LTCC columnar inductor bandpass filter according to claim 1, characterized in that: The second series capacitor C2 and the third series capacitor C3 are centrally symmetrical in structure.

4. The miniaturized high-suppression LTCC columnar inductor bandpass filter according to claim 1, characterized in that: The ceramic body material is a ceramic material with a dielectric constant of 9.8 and a loss tangent of 0.003, and the external ground electrode, the external input electrode, and the external output electrode are printed with silver material.

5. The miniaturized high-suppression LTCC columnar inductor bandpass filter according to claim 1, characterized in that: The overall size of the filter is 3.2mm×2.5mm×1.5mm.

6. The miniaturized high-suppression LTCC columnar inductor bandpass filter according to claim 1, characterized in that: The passband range of the filter is 2.21-2.41GHz, the maximum insertion loss in the passband is 2dB, the suppression in the low-end stopband 0-1.95GHz is greater than 25dB, a transmission zero is generated at 2.1GHz, and the suppression reaches 30dB; in the high-end stopband 2.60GHz-3GHz, the suppression is greater than 25dB, a transmission zero is generated at 2.53GHz, and the suppression reaches 29dB.

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