Miniaturized band-pass filter based on LTCC

Abstract

The invention provides an LTCC (Low Temperature Co-Fired Ceramic)-based miniaturized band-pass filter, which relates to the technical field of microwave and millimeter wave circuits, adopts a multi-layer LTCC structure, integrates four VIC (Virtual Integrated Circuit) capacitors and one spiral inductor, and realizes high electrical integration. The design focuses on stabilizing frequency response and reducing material error influence; the whole manufacturing process of the filter comprises precise silk-screen printing and sintering processes, precise integration of elements is ensured, the filter has low insertion loss and a high Q value and is suitable for 5G communication and satellite communication application, the high-frequency signal processing performance is improved, and the size of the filter is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave and millimeter wave circuits, and in particular to a miniaturized bandpass filter based on LTCC. Background Art

[0002] In modern wireless communication systems, advances in signal processing technology play a vital role in improving communication quality, increasing frequency band utilization, and enhancing overall system performance. As a core component in signal processing, the precision of filter design and manufacturing directly impacts the performance of communication equipment. The growing demand for high-performance filters in fields such as 5G communications, radar, and satellite communications is placing higher demands on filter size, frequency response stability, and insertion loss.

[0003] Traditional filter designs often face challenges such as large size, difficulty in integration, and sensitivity to manufacturing errors. To overcome these limitations, low-temperature co-fired ceramic (LTCC) technology, due to its ability to co-sinter multiple layers of ceramic materials at relatively low temperatures, high dielectric constant, and excellent thermal matching, has become an ideal choice for miniaturized, high-performance filters. LTCC technology enables the high-level integration of passive components such as inductors and capacitors into a compact three-dimensional structure, thus achieving miniaturization and high performance of filters.

[0004] However, the design and manufacturing process of current LTCC filters is complex, involving precise multi-layer material stacking, screen printing, precise dimensional control, and rigorous sintering techniques. During this process, even slight variations in material thickness, dielectric constant, and geometric dimensions can significantly degrade filter performance. Furthermore, filters used in high-frequency applications require extremely high signal transmission characteristics, and any non-ideal coupling or reflection can severely impact system performance.

[0005] In view of this, this application is filed. Summary of the Invention

[0006] The present invention provides a miniaturized bandpass filter based on LTCC, which can at least partially improve the above problems.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A miniaturized bandpass filter based on LTCC, comprising: an LTCC substrate, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, an inductor L1, an input coupling feed line Lin, and an output coupling feed line Lout, integrated into the LTCC substrate by screen printing, and a first input port P1, a second output port P2, a first metal ground plate GND1, and a second metal ground plate GND2 mounted on the outer surface of the LTCC substrate; The input coupling feed line Lin and the output coupling feed line Lout are respectively arranged on both sides of the LTCC substrate, and the input coupling feed line Lin and the output coupling feed line Lout have the same size. One end of the input coupling feed line Lin and one end of the output coupling feed line Lout are respectively connected to the first input port P1 and the second output port P2. The other end of the input coupling feed line Lin is connected to the first capacitor C1, and the other end of the output coupling feed line Lout is connected to the second capacitor C2. The first input port P1 is connected to the first capacitor C1, and the second output port P2 is connected to the second capacitor C2. The first metal ground plate GND1 is connected to the inductor L1, and the second metal ground plate GND2 is connected to the third capacitor C3 and the fourth capacitor C4. The first capacitor C1 , the second capacitor C2 , the third capacitor C3 , and the fourth capacitor C4 are mirror-symmetrical, and the third capacitor C3 and the fourth capacitor C4 are perpendicular to the first capacitor C1 and the second capacitor C2 .

[0008] In summary, the LTCC-based miniaturized bandpass filter adopts an LTCC multilayer structure and integrates multiple passive components such as 4 VIC capacitors and 1 spiral inductor on the multilayer structure, realizing the design of a miniaturized bandpass filter with a multilayer structure with a compact layout; not only the stability of the filter's filtering function is improved, but also the generation of parasitic modes is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 1 is a schematic diagram of the overall structure of a miniaturized bandpass filter based on LTCC provided by an embodiment of the present invention; Figure 2 This is a front view of the internal integrated passive device structure of the LTCC substrate provided by the first embodiment of the present invention; Figure 3 1 is a top view of the internal integrated passive device structure of the LTCC substrate provided by the first embodiment of the present invention; Figure 4 This is a front view of the overall structure of the internal integrated passive components of the LTCC substrate provided by the first embodiment of the present invention; Figure 5 This is an S-parameter curve diagram when the dielectric constant of the LTCC dielectric provided by an embodiment of the present invention is 9.1 and the length of Lc1 is 0.9 mm; Figure 6 This is an S11 diagram when the dielectric constant of the LTCC dielectric provided by an embodiment of the present invention is 9.1 and the length of Lc1 changes; Figure 7 This is a graph of S21 when the dielectric constant of the LTCC dielectric provided by an embodiment of the present invention is 9.1 and the length of Lc1 changes; Figure 8This is an S parameter curve diagram when the dielectric constant of the LTCC dielectric provided by an embodiment of the present invention is 9.1 and the length of Lc1 changes; Figure 9 This is an S11 diagram when the dielectric constant of the LTCC dielectric provided by an embodiment of the present invention is 9.0 and the length of Lc1 changes; Figure 10 This is a graph of S21 when the dielectric constant of the LTCC dielectric provided by an embodiment of the present invention is 9.0 and the length of Lc1 changes; Figure 11 This is an S parameter curve diagram when the dielectric constant of the LTCC medium provided by an embodiment of the present invention is 9.0 and the length of Lc1 changes. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0011] refer to Figures 1 to 11 As shown, the first embodiment of the present invention discloses a miniaturized bandpass filter based on LTCC, which includes: an LTCC substrate, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, an inductor L1, an input coupling feed line Lin and an output coupling feed line Lout integrated into the LTCC substrate by screen printing, and a first input port P1, a second output port P2, a first metal ground plate GND1, and a second metal ground plate GND2 mounted on the outer surface of the LTCC substrate; The input coupling feed line Lin and the output coupling feed line Lout are respectively arranged on both sides of the LTCC substrate, and the input coupling feed line Lin and the output coupling feed line Lout have the same size. One end of the input coupling feed line Lin and one end of the output coupling feed line Lout are respectively connected to the first input port P1 and the second output port P2. The other end of the input coupling feed line Lin is connected to the first capacitor C1, and the other end of the output coupling feed line Lout is connected to the second capacitor C2. The first input port P1 is connected to the first capacitor C1, and the second output port P2 is connected to the second capacitor C2. The first metal ground plate GND1 is connected to the inductor L1, and the second metal ground plate GND2 is connected to the third capacitor C3 and the fourth capacitor C4. The first capacitor C1 , the second capacitor C2 , the third capacitor C3 , and the fourth capacitor C4 are mirror-symmetrical, and the third capacitor C3 and the fourth capacitor C4 are perpendicular to the first capacitor C1 and the second capacitor C2 .

[0012] Specifically, in this embodiment, at high dielectric constant Multiple passive components are integrated into the LTCC substrate with _r = 11.8. Among them, the integrated first capacitor C1, second capacitor C2, third capacitor C3, fourth capacitor C4 and inductor L1 are small in size. This not only greatly improves the filter's ability to achieve high-frequency operation in a small size, but also ensures stable filtering within the filter's passband range when the process or external environment changes.

[0013] The input coupling feed line Lin and the output coupling feed line Lout in the LTCC-based miniaturized bandpass filter both have a 50Ω impedance line width, ensuring impedance matching at the feed port. The input coupling feed line Lin and the output coupling feed line Lout have a length (L_LINE), a width (W_LINE), and a thickness (H_L), respectively, and are located on the 14th layer of the LTCC substrate.

[0014] In short, the LTCC-based miniaturized bandpass filter not only achieves filter miniaturization but also maintains the high performance that the filter should have, and simplifies the production process and reduces production costs through multi-layer integration and surface-mounted ports and ground planes.

[0015] Preferably, the LTCC substrate is a low temperature co-fired ceramic dielectric substrate with a relative dielectric constant of 9.1, a total substrate thickness of 2.34 mm, 22 process layers, and a thickness of each process layer of the substrate being a preset constant H_LTCC.

[0016] In this embodiment, the relative dielectric constant of the LTCC substrate is 9.1, which helps achieve high-frequency operation in a smaller size while reducing the generation of parasitic modes. Furthermore, the high dielectric constant material can enhance the electric field strength of the capacitor, thereby achieving the desired capacitance value in a smaller volume.

[0017] Preferably, the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are all VIC capacitors composed of five layers of capacitor plates, the inductor L1 is a spiral inductor, the first input port P1 and the second output port P2 adopt a U-shaped structure, and the first metal ground plate GND1 and the second metal ground plate GND2 adopt a groove type.

[0018] In this embodiment, the dimensions and structure of the first capacitor C1, second capacitor C2, third capacitor C3, fourth capacitor C4, and inductor L1 integrated within the LTCC are determined based on design requirements, such as passband frequency and design volume. The spatial distances between the capacitors and inductors are also determined to prevent electromagnetic coupling from affecting the filter's performance. During the manufacturing process of this miniaturized LTCC-based bandpass filter, the filter's passband range and filtering performance remain essentially unchanged, unaffected by minor material errors, such as deviations in thickness, dielectric constant, and geometric dimensions.

[0019] Preferably, the first capacitor C1 includes a first electrode plate C11, a second electrode plate C12, a third electrode plate C13, a fourth electrode plate C14, a fifth electrode plate C15, a first through hole C1_TK1, a second through hole C1_TK2, and five lead-out strip structures corresponding to the first electrode plate C11, the second electrode plate C12, the third electrode plate C13, the fourth electrode plate C14, and the fifth electrode plate C15, respectively; Among them, the first layer of plate C11 is connected to the first input port P1 through the input coupling feed line Lin, the first layer of plate C11, the third layer of plate C13 and the fifth layer of plate C15 are combined with the first through hole C1_TK1 through the corresponding lead-out tape structure to form the first electrode of the first capacitor C1, and the second layer of plate C12 and the fourth layer of plate C14 are combined with the second through hole C1_TK2 through the corresponding lead-out tape structure to form the second electrode of the first capacitor C1.

[0020] Preferably, the second capacitor C2 includes a sixth plate C21, a seventh plate C22, an eighth plate C23, a ninth plate C24, a tenth plate C25, a third through hole C2_TK1, a fourth through hole C2_TK2, and five feeding strip lines corresponding to the sixth plate C21, the seventh plate C22, the eighth plate C23, the ninth plate C24, and the tenth plate C25, respectively; The sixth electrode plate C21 is connected to the second output port P2 through the output coupling feed line Lout, the sixth electrode plate C21, the eighth electrode plate C23 and the tenth electrode plate C25 are combined with the third through hole C2_TK1 through the corresponding lead-out strip structure to form the first electrode of the second capacitor C2, and the seventh electrode plate C22 and the ninth electrode plate C24 are combined with the fourth through hole C2_TK2 through the corresponding lead-out strip structure to form the second electrode of the second capacitor C2; The first capacitor C1 is connected to the second capacitor C2 via the first feed line C1_line led out of the fourth plate C14 and the second feed line C2_line led out of the ninth plate C24 of the second capacitor C2, so as to realize the series connection of the first capacitor C1 and the second capacitor C2.

[0021] Preferably, each electrode plate of the first capacitor C1 and the second capacitor C2 has the same size, a length equal to a preset constant Lc1, a width equal to a preset constant Wc1, and a thickness equal to a preset constant H_c.

[0022] In this embodiment, the first capacitor C1 and the second capacitor C2 have the same structure and size, and are both composed of five plates; the capacitor plates are made of silver inside the LTCC substrate through screen printing technology, and the plates are connected by silver through-holes.

[0023] Specifically, the first plate C11 of the first capacitor C1 has a length of Lc1, a width of Wc1, and a thickness of H_c. It is located on the 14th layer of the LTCC substrate. A first feed strip line extending from the first plate C11 is connected to the input coupling feed line Lin and is connected to the third plate C13 and the fifth plate C15 via a first through-hole C1_TK1. The second plate C12 of the first capacitor C1 has a length of Lc1, a width of Wc1, and a thickness of H_c. It is located on the 13th layer of the LTCC substrate and is offset from C11 by 0.1 mm in the Y-axis direction. A feed strip line extending from the first plate C11 is connected to the fourth plate C14 via a second through-hole C1_TK2. The third plate C13 of the first capacitor C1 has a length of Lc1, a width of Wc1, and a thickness of H_c, and is located on the 12th layer of the LTCC substrate. The fourth plate C14 of the first capacitor C1 has a length of Lc1, a width of Wc1, and a thickness of H_c, and is located on the 11th layer of the LTCC substrate. The fifth plate C15 of the first capacitor C1 has a length of Lc1, a width of Wc1, and a thickness of H_c, and is located on the 10th layer of the LTCC substrate. The first feed strip line C1_line derived from the fourth plate C14 of the first capacitor C1 is connected to the second feed strip line C2_line derived from the ninth plate C24 of the second capacitor C2, thereby realizing the series connection of the first capacitor C1 and the second capacitor C2, and realizing the electrical connection of the first capacitor C1, the second capacitor C2, the third capacitor C3, the fourth capacitor C4, and the inductor L1 on the two long feed strip lines.

[0024] In this embodiment, since the structure and working principle of the second capacitor C2 are consistent with those of the first capacitor C1, they will not be described in detail.

[0025] Preferably, the third capacitor C3 includes an eleventh layer of plate C31, a twelfth layer of plate C32, a thirteenth layer of plate C33, a fourteenth layer of plate C34, a fifteenth layer of plate C35, a fifth through hole C3_TK1, a sixth through hole C3_TK2, and five lead-out strip structures corresponding to the eleventh layer of plate C31, the twelfth layer of plate C32, the thirteenth layer of plate C33, the fourteenth layer of plate C34, and the fifteenth layer of plate C35, respectively; Among them, the eleventh layer of plate C31, the thirteenth layer of plate C33 and the fifteenth layer of plate C35 are combined with the fifth through hole C3_TK1 through the corresponding lead-out tape structure to form the first pole of the third capacitor C3, the twelfth layer of plate C32 and the fourteenth layer of plate C34 are combined with the sixth through hole C3_TK2 through the corresponding lead-out tape structure to form the second pole of the third capacitor C3, the third capacitor C3 is connected to the first feed strip line C1_line through the third input coupling feed line C3_Lin led out from the eleventh layer of plate C31, and the third capacitor C3 is connected to the second metal ground plate GND2 through the third output coupling feed line C3_out led out from the fourteenth layer of plate C34.

[0026] Preferably, the fourth capacitor C4 includes a sixteenth layer of plate C41, a seventeenth layer of plate C42, an eighteenth layer of plate C43, a nineteenth layer of plate C44, a twentieth layer of plate C45, a seventh through hole C4_TK1, an eighth through hole C4_TK2, and five lead-out strip structures corresponding to the sixteenth layer of plate C41, the seventeenth layer of plate C42, the eighteenth layer of plate C43, the nineteenth layer of plate C44, and the twentieth layer of plate C45, respectively; Among them, the sixteenth layer of electrode plate C41, the eighteenth layer of electrode plate C43 and the twentieth layer of electrode plate C45 are combined with the seventh through hole C4_TK1 through the corresponding lead-out tape structure to form the first pole of the fourth capacitor C4, the seventeenth layer of electrode plate C42 and the nineteenth layer of electrode plate C44 are combined with the eighth through hole C4_TK2 through the corresponding lead-out tape structure to form the second pole of the fourth capacitor C4, the fourth capacitor C4 is connected to the first feed line C1_line through the fourth input coupling feed line C4_Lin led out from the sixteenth layer of electrode plate C41, the fourth capacitor C4 is connected to the second metal ground plate GND2 through the fourth output coupling feed line C4_out led out from the nineteenth layer of electrode plate C44, and the third capacitor C3 and the fourth capacitor C4 are perpendicular to the first feed line C1_line and the second feed line C2_line.

[0027] Preferably, each electrode plate of the third capacitor C3 and the fourth capacitor C4 has the same size, a length equal to a preset constant Lc2, a width equal to a preset constant Wc2, and a thickness equal to a preset constant H_c.

[0028] In this embodiment, the third capacitor C3 and the fourth capacitor C4 have the same structure and are both composed of 5 plates. The capacitor plates are made of silver inside the LTCC substrate through screen printing technology, and the plates are connected through silver through-holes.

[0029] Specifically, the eleventh-layer plate C31 has a length of Lc2, a width of Wc2, and a thickness of H_c. It is located on the ninth layer of the LTCC substrate. The third capacitor C3 is connected to the first feed strip line C1_line via the third lead-out input coupling feed line C3_Lin extending from the eleventh-layer plate C31. This leads to the thirteenth-layer plate C33 and the fifteenth-layer plate C35 via the fifth through-hole C3_TK1. The twelfth-layer plate C32 has a length of Lc2, a width of Wc2, and a thickness of H_c. It is located on the eighth layer of the LTCC substrate and is offset from C31 by 0.1 mm in the Y-axis direction. A feed strip line extends from it, connecting to the fourteenth-layer plate C34 via the sixth through-hole C3_TK2. The thirteenth-layer electrode plate C33 is Lc2 long, Wc2 wide, and H_c thick, and is located on the 7th layer of the LTCC substrate. The fourteenth-layer electrode plate C34 is Lc2 long, Wc2 wide, and H_c thick, and is located on the 6th layer of the LTCC substrate. The fifteenth-layer electrode plate C35 is Lc2 long, Wc2 wide, and H_c thick, and is located on the 5th layer of the LTCC substrate. The third capacitor C3 is connected to the first feed strip line C1_line through the third lead-out input coupling feed line C3_Lin led out from the eleventh-layer electrode plate C31. The third capacitor C3 is connected to the second metal ground plate GND2 on the surface of the LTCC substrate through the third output coupling feed line C3_out led out from the fourteenth-layer electrode plate C34, thereby achieving grounding of the third capacitor C3. The overall structure of the third capacitor C3 and the fourth capacitor C4 is perpendicular to the first feed strip line C1_line and the second feed strip line C2_line.

[0030] In this embodiment, since the structure and working principle of the fourth capacitor C4 are consistent with those of the third capacitor C3, they will not be described in detail.

[0031] In this embodiment, the spacing between the first, second, third, fourth, and fifth plates C11, C12, C13, C14, and C15 in the Z-axis direction is H_LTCC+H_c, and the first, third, and fifth plates C11, C13, and C15 are offset by 0.1 mm relative to the spacing between the second and fourth plates C12 and C14 in the Y-axis direction. Since the spacing and offset between the five plates of the second, third, and fourth capacitors C2, C3, and C4 are the same as those of the first capacitor C1, they will not be further described.

[0032] Preferably, the inductor L1 includes multiple microstrip lines, a ninth through hole L1_TK1, a tenth through hole L1_TK2, and an eleventh through hole L1_TK3. The inductor L1 is connected to the first feeding strip line C1_line through the ninth through hole L1_TK1. The inductor L1 is connected to the first metal ground plate GND1 through the microstrip line.

[0033] In this embodiment, the miniaturized LTCC-based bandpass filter uses screen printing technology within the LTCC substrate to integrate inductor L1 using multiple microstrip lines (L11, L12, L13, L14, L15, L16, L17, L18, and L19) and silver vias (L1_TK1, L1_TK2, and L1_TK3) between the microstrip lines. The silver vias connect the microstrip lines, creating a spiral structure for inductor L1. Electrically, inductor L1 is located between third and fourth capacitors C3 and C4.

[0034] Specifically, inductor L1 is spatially perpendicular to microstrip line L11. Inductor L1 is connected to the first feed strip line C1_line via the ninth through-hole L1_TK1, thereby electrically connecting inductor L1 to the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4. The inductor L1 forms a spiral structure via the tenth through-hole L1_TK2 and the eleventh through-hole L1_TK3, thereby electrically connecting inductor L1 between layers. Inductor L1 is connected to the first metal ground plane GND1 via microstrip line L19, thereby grounding inductor L1. The microstrip line length of inductor L1 is L_L1, width is W_L1, and thickness is H_L. The LTCC-based miniaturized bandpass filter can extend microstrip line L11 as needed to ensure that inductor L1 is connected to the first feed strip line C1_line via the ninth through-hole L1_TK1. Extending microstrip line L19 ensures that one end of inductor L1 is grounded.

[0035] Specifically, in this embodiment, the microstrip line L11 has a length of L_L1+0.25 mm, a width of W_L1, and a thickness of H_L, that is, the microstrip line L11 has a length of L_L1+0.25 mm, a width of W_L1, and a thickness of H_L; the microstrip lines L11, L12, and L13 are located on the 15th layer of the LTCC substrate, the microstrip lines L14, L15, and L16 are located on the 16th layer of the LTCC substrate, and the microstrip lines L17, L18, and L19 are located on the 17th layer of the LTCC substrate. The silver through-hole L1_TK1 penetrates the substrate and connects the 15th layer where the microstrip line L11 is located to the 11th layer where the first feed line C1_line is located. The silver through-hole L1_TK2 connects the microstrip lines L13 and L14, and the silver through-hole L1_TK3 connects the microstrip lines L16 and L17.

[0036] As can be seen from the above description, the electrical topology of the miniaturized LTCC-based bandpass filter in this embodiment is symmetrical. This symmetrical layout helps reduce electromagnetic coupling, thereby improving filter performance. A symmetrical structure generally provides better impedance matching and lower return loss.

[0037] In summary, the LTCC-based miniaturized bandpass filter exhibits excellent electromagnetic performance through the design of a specific VIC capacitor and spiral inductor structure, effectively improving the filter's performance in high-frequency applications. In particular, it stabilizes the frequency response and reduces the impact of minor material errors. This unique design maintains stable filtering within the filter's passband even when the integrated capacitor and inductor dimensions change due to process or external environment. The integrated capacitors and inductors are connected via silver vias, further reducing insertion loss and increasing Q, thereby improving signal processing capabilities and overall system performance.

[0038] Simply put, the LTCC-based miniaturized bandpass filter achieves a compact electrical structure through a microstrip design of spiral inductors and a multilayer plate configuration of VIC capacitors. This filter effectively addresses the frequency response deviation problem caused by minor material errors in the LTCC multilayer structure. While maintaining high-frequency performance and low insertion loss, it achieves miniaturization and high integration of the filter, while also enhancing electromagnetic compatibility and anti-interference capabilities. This structure not only saves space but also improves the overall integration of the filter, making it suitable for 5G communications, radar, and satellite communications equipment that require miniaturization and high performance.

[0039] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A miniaturized bandpass filter based on LTCC, characterized in that: include: An LTCC substrate, a first capacitor (C1), a second capacitor (C2), a third capacitor (C3), a fourth capacitor (C4), an inductor (L1), an input coupling feed line (Lin) and an output coupling feed line (Lout) integrated in the LTCC substrate by screen printing, and a first input port (P1), a second output port (P2), a first metal ground plate (GND1), and a second metal ground plate (GND2) mounted on the outer surface of the LTCC substrate; The input coupling feed line (Lin) and the output coupling feed line (Lout) are respectively arranged on both sides of the LTCC substrate, and the input coupling feed line (Lin) and the output coupling feed line (Lout) have the same size, one end of the input coupling feed line (Lin) and one end of the output coupling feed line (Lout) are respectively connected to the first input port (P1) and the second output port (P2), the other end of the input coupling feed line (Lin) is connected to the first capacitor (C1), the other end of the output coupling feed line (Lout) is connected to the second capacitor (C2), the first input port (P1) is connected to the first capacitor (C1), the second output port (P2) is connected to the second capacitor (C2), the first metal ground plate (GND1) is connected to the inductor (L1), and the second metal ground plate (GND2) is connected to the third capacitor (C3) and the fourth capacitor (C4); The first capacitor (C1), the second capacitor (C2), the third capacitor (C3), and the fourth capacitor (C4) are mirror-symmetrical, and the third capacitor (C3) and the fourth capacitor (C4) are perpendicular to the first capacitor (C1) and the second capacitor (C2).

2. The miniaturized bandpass filter based on LTCC according to claim 1, characterized in that: The LTCC substrate is a low temperature co-fired ceramic dielectric substrate, with a relative dielectric constant of 9.1, a total substrate thickness of 2.34 mm, 22 process layers, and a thickness of each process layer of the substrate being a preset constant H_LTCC.

3. The miniaturized bandpass filter based on LTCC according to claim 1, characterized in that: The first capacitor (C1), the second capacitor (C2), the third capacitor (C3), and the fourth capacitor (C4) are all VIC capacitors composed of five layers of capacitor plates, the inductor (L1) is a spiral inductor, the first input port (P1) and the second output port (P2) adopt a U-shaped structure, and the first metal ground plate (GND1) and the second metal ground plate (GND2) adopt a groove type.

4. The miniaturized bandpass filter based on LTCC according to claim 1, characterized in that: The first capacitor (C1) comprises a first layer of plates (C11), a second layer of plates (C12), a third layer of plates (C13), a fourth layer of plates (C14), a fifth layer of plates (C15), a first through hole (C1_TK1), a second through hole (C1_TK2), and five lead-out strip structures corresponding to the first layer of plates (C11), the second layer of plates (C12), the third layer of plates (C13), the fourth layer of plates (C14), and the fifth layer of plates (C15); The first layer of plates (C11) is connected to the first input port (P1) through an input coupling feed line (Lin); the first layer of plates (C11), the third layer of plates (C13) and the fifth layer of plates (C15) are combined with the first through hole (C1_TK1) through corresponding lead-out band structures to form the first pole of the first capacitor (C1); the second layer of plates (C12) and the fourth layer of plates (C14) are combined with the second through hole (C1_TK2) through corresponding lead-out band structures to form the second pole of the first capacitor (C1).

5. The miniaturized bandpass filter based on LTCC according to claim 4, characterized in that: The second capacitor (C2) comprises a sixth layer of plates (C21), a seventh layer of plates (C22), an eighth layer of plates (C23), a ninth layer of plates (C24), a tenth layer of plates (C25), a third through hole (C2_TK1), a fourth through hole (C2_TK2), and five feeding strip lines corresponding to the sixth layer of plates (C21), the seventh layer of plates (C22), the eighth layer of plates (C23), the ninth layer of plates (C24), and the tenth layer of plates (C25); The sixth electrode plate (C21) is connected to the second output port (P2) through an output coupling feed line (Lout); the sixth electrode plate (C21), the eighth electrode plate (C23) and the tenth electrode plate (C25) are combined with the third through hole (C2_TK1) through corresponding lead-out strip structures to form the first electrode of the second capacitor (C2); the seventh electrode plate (C22) and the ninth electrode plate (C24) are combined with the fourth through hole (C2_TK2) through corresponding lead-out strip structures to form the second electrode of the second capacitor (C2); The first capacitor (C1) is connected to a second feeder line (C2_line) derived from a ninth layer of the electrode plate (C24) of the second capacitor (C2) through a first feeder line (C1_line) derived from a fourth layer of the electrode plate (C14), so as to realize the series connection of the first capacitor (C1) and the second capacitor (C2).

6. The miniaturized bandpass filter based on LTCC according to claim 1, characterized in that: Each electrode plate of the first capacitor (C1) and the second capacitor (C2) has the same size, a length of a preset constant Lc1, a width of a preset constant Wc1, and a thickness of a preset constant H_c.

7. The miniaturized bandpass filter based on LTCC according to claim 5, characterized in that: The third capacitor (C3) includes an eleventh layer of plates (C31), a twelfth layer of plates (C32), a thirteenth layer of plates (C33), a fourteenth layer of plates (C34), a fifteenth layer of plates (C35), a fifth through hole (C3_TK1), a sixth through hole (C3_TK2), and five lead-out strip structures corresponding to the eleventh layer of plates (C31), the twelfth layer of plates (C32), the thirteenth layer of plates (C33), the fourteenth layer of plates (C34), and the fifteenth layer of plates (C35); The eleventh layer of plates (C31), the thirteenth layer of plates (C33) and the fifteenth layer of plates (C35) are combined with the fifth through hole (C3_TK1) through the corresponding lead-out strip structure to form the first pole of the third capacitor (C3); the twelfth layer of plates (C32) and the fourteenth layer of plates (C34) are combined with the sixth through hole (C3_TK2) through the corresponding lead-out strip structure to form the second pole of the third capacitor (C3); the third capacitor (C3) is connected to the first feed strip line (C1_line) through the third input coupling feed line (C3_Lin) derived from the eleventh layer of plates (C31); and the third capacitor (C3) is connected to the second metal ground plate (GND2) through the third output coupling feed line (C3_out) derived from the fourteenth layer of plates (C34).

8. The LTCC-based miniaturized bandpass filter according to claim 7, characterized in that: The fourth capacitor (C4) includes a sixteenth layer of plates (C41), a seventeenth layer of plates (C42), an eighteenth layer of plates (C43), a nineteenth layer of plates (C44), a twentieth layer of plates (C45), a seventh through hole (C4_TK1), an eighth through hole (C4_TK2), and five lead-out strip structures corresponding to the sixteenth layer of plates (C41), the seventeenth layer of plates (C42), the eighteenth layer of plates (C43), the nineteenth layer of plates (C44), and the twentieth layer of plates (C45); The sixteenth layer of plates (C41), the eighteenth layer of plates (C43) and the twentieth layer of plates (C45) are combined with the seventh through hole (C4_TK1) through the corresponding lead-out strip structure to form the first pole of the fourth capacitor (C4); the seventeenth layer of plates (C42) and the nineteenth layer of plates (C44) are combined with the eighth through hole (C4_TK2) through the corresponding lead-out strip structure to form the second pole of the fourth capacitor (C4); the fourth capacitor (C4) is connected to the first feed strip line (C1_line) through the fourth input coupling feed line (C4_Lin) led out from the sixteenth layer of plates (C41); the fourth capacitor (C4) is connected to the second metal ground plane (GND2) through the fourth output coupling feed line (C4_out) led out from the nineteenth layer of plates (C44); and the third capacitor (C3) and the fourth capacitor (C4) are perpendicular to the first feed strip line (C1_line) and the second feed strip line (C2_line).

9. The miniaturized bandpass filter based on LTCC according to claim 8, characterized in that: Each electrode plate of the third capacitor (C3) and the fourth capacitor (C4) has the same size, a length of a preset constant Lc2, a width of a preset constant Wc2, and a thickness of a preset constant H_c.

10. The miniaturized bandpass filter based on LTCC according to claim 5, characterized in that: The inductor (L1) comprises a plurality of microstrip lines, a ninth through hole (L1_TK1), a tenth through hole (L1_TK2), and an eleventh through hole (L1_TK3); the inductor (L1) is connected to a first feeding strip line (C1_line) through the ninth through hole (L1_TK1); and the inductor (L1) is connected to the first metal ground plate (GND1) through the microstrip line.

Images