A bandpass filter

Abstract

The application discloses a band-pass filter, and relates to the field of microwave technology.The band-pass filter comprises a first shielding layer, a resonant coupling layer and a second shielding layer which are sequentially arranged from top to bottom and are made of a low-temperature co-fired ceramic process.The resonant coupling layer comprises a first coupling line, a second coupling line, four resonators arranged from left to right and three couplers;one coupler is arranged between every two adjacent resonators;the first coupling line is located above the resonators at the leftmost end and the rightmost end;the second coupling line is located below the two resonators in the middle;the resonators and the couplers are connected with ground ports;the resonator at the leftmost end is connected with an input port;the resonator at the rightmost end is connected with an output port;the first shielding layer and the second shielding layer are connected with the ground ports.The application can make the relative bandwidth of the passband less than 10%, and improve the passband performance and the stopband suppression performance.

Description

Technical Field

[0001] This invention relates to the field of microwave technology, and in particular to a bandpass filter. Background Technology

[0002] With the continuous development of communication technology, wireless signals in space are becoming increasingly complex, and people have higher and higher requirements for the frequency selectivity of hardware. Narrowband bandpass filters can provide superior narrowband signals for radio frequency systems, and they are available in various designs and have a wide range of applications.

[0003] LTCC, or Low Temperature Co-fired Ceramic, is a thick-film process characterized by high stability, high quality factor, and high integration. Compared to other materials, ceramic materials exhibit high stability and a wide range of dielectric constant variations, making them suitable for the manufacture of microwave devices.

[0004] There are four common design approaches for narrowband filters: The first is the lumped element coupled resonator bandpass filter, which is derived from the low-pass prototype. It has many auxiliary design tools, a simple circuit, but is difficult to simulate in three dimensions. The second is the microstrip line bandpass filter, which achieves filtering function through capacitive or inductive coupling using a 1 / 2 wavelength resonator or a 1 / 4 wavelength resonator. The third is the waveguide bandpass filter, including parallel inductor waveguide coupled bandpass filters, pinhole diaphragm coupled waveguide resonator bandpass filters, and substrate integrated waveguide filters. The fourth is the stripline bandpass filter, including cross-shaped capacitive coupled stripline filters and combline bandpass filters.

[0005] Currently, the relative bandwidth of comb-line bandpass filters is around 15%, and both passband performance and stopband suppression performance need to be improved. Summary of the Invention

[0006] Based on this, embodiments of the present invention provide a bandpass filter that makes the relative bandwidth of the passband less than 10%, and improves the passband performance and stopband suppression performance.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] A bandpass filter includes: a first shielding layer, a resonant coupling layer, and a second shielding layer stacked sequentially from top to bottom; the first shielding layer, the resonant coupling layer, and the second shielding layer are all printed circuits made using a low-temperature co-fired ceramic process;

[0009] The resonant coupling layer includes: a first coupling line, a second coupling line, four resonators, and three couplers; the four resonators are arranged sequentially from left to right; a coupler is placed between every two adjacent resonators; the first coupling line is located above the leftmost and rightmost resonators; the second coupling line is located below the two middle resonators; all four resonators and three couplers are connected to a ground port; the leftmost resonator is connected to an input port; the rightmost resonator is connected to an output port; both the first and second shielding layers are connected to the ground port.

[0010] The first coupling line is used to couple the leftmost resonator and the rightmost resonator; the second coupling line is used to couple the two middle resonators; the coupler is used to couple two adjacent resonators.

[0011] Optionally, the bandpass filter further includes: an input layer, an output layer, and a ground layer; the input layer, the output layer, and the ground layer are all printed circuits made using a low-temperature co-fired ceramic process; the input layer and the output layer are arranged symmetrically on the left and right sides.

[0012] The input layer includes: two symmetrically arranged and interconnected input wireframes; one of the input wireframes is located above the first shielding layer, and the other input wireframe is located below the second shielding layer; the input wireframes are provided with input ports;

[0013] The output layer includes: two symmetrically arranged and interconnected output wireframes; one of the output wireframes is located above the first shielding layer, and the other output wireframe is located below the second shielding layer; the output wireframes are provided with output ports;

[0014] The grounding layer includes: a first grounding layer and a second grounding layer arranged symmetrically front to back;

[0015] The first grounding layer includes: two first grounding frames arranged symmetrically and connected to each other; one of the first grounding frames is located above the first shielding layer, and the other first grounding frame is located below the second shielding layer; the first grounding frames are arranged alternately with the input wireframe and the output wireframe respectively; the first grounding frame is provided with a first grounding port;

[0016] The second grounding layer includes: two second grounding frames arranged symmetrically and connected to each other; one of the second grounding frames is located above the first shielding layer, and the other second grounding frame is located below the second shielding layer; the second grounding frames are arranged alternately with the input wireframe and the output wireframe respectively; the second grounding frames are provided with second grounding ports; the grounding ports include the first grounding port and the second grounding port.

[0017] Optionally, each of the four resonators includes a second resonant frame, a first resonant frame, and a third resonant frame stacked sequentially from top to bottom; the first resonant frame is staggered with the second resonant frame and the third resonant frame.

[0018] Each of the three couplers includes a second coupling frame, a first coupling frame, and a third coupling frame stacked sequentially from top to bottom; the first coupling frame is staggered with the second coupling frame and the third coupling frame; the second coupling frame of the coupler is located between the second resonant frames of two adjacent resonators; the first coupling frame of the coupler is located between the first resonant frames of two adjacent resonators; and the third coupling frame of the coupler is located between the third resonant frames of two adjacent resonators.

[0019] The first coupling line includes a first coupling portion and a second coupling portion connected to the first coupling portion; the first coupling portion is located above the second coupling frame of the leftmost resonator, and the second coupling portion is located above the second coupling frame of the rightmost resonator.

[0020] The second coupling line includes a third coupling portion and a fourth coupling portion connected to the third coupling portion; the third coupling portion is located below the third coupling frame of one of the middle resonators, and the fourth coupling portion is located below the third coupling frame of the other middle resonator.

[0021] Optionally, the bandpass filter includes: an input connection line and an output connection line;

[0022] The leftmost resonator is connected to the input port on each of the input frames via the input connection line; the rightmost resonator is connected to the output port on each of the output frames via the output connection line.

[0023] Optionally, the bandpass filter further includes: an input tap and an output tap;

[0024] The leftmost resonator is connected to the input connection line via the input tap; the rightmost resonator is connected to the output connection line via the output tap.

[0025] Optionally, both the first shielding layer and the second shielding layer are defective structures.

[0026] Optionally, the input port, the output port, the first ground port, and the second ground port are all 50-ohm impedance ports.

[0027] Optionally, the linewidth of the first and third resonant frames of each resonator is 120 μm; the linewidth of the second resonant frame of each resonator is 100 μm; and the spacing between two adjacent resonators is 620 μm.

[0028] Optionally, the linewidth of each coupler is 100 μm; the line spacing between the coupler and the adjacent resonator is 310 μm;

[0029] The layer spacing between the first coupling portion of the first coupling line and the second coupling frame of the leftmost resonator is 200 μm; the layer spacing between the second coupling portion of the first coupling line and the second coupling frame of the rightmost resonator is 200 μm.

[0030] The layer spacing between the third coupling portion of the second coupling line and the third coupling frame of the middle resonator is 250 μm; the layer spacing between the fourth coupling portion of the second coupling line and the third coupling frame of the other middle resonator is 250 μm.

[0031] Optionally, the bandpass filter has dimensions of 3.2mm × 1.6mm × 0.94mm.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] This invention proposes a bandpass filter, comprising: a first shielding layer, a resonant coupling layer, and a second shielding layer, all stacked from top to bottom and manufactured using a low-temperature co-fired ceramic process; the resonant coupling layer includes: a first coupling line, a second coupling line, four resonators arranged from left to right, and three couplers; a coupler is placed between every two adjacent resonators; the first coupling line is located above the leftmost and rightmost resonators; the second coupling line is located below the two middle resonators. This invention, through the rational arrangement of the coupling structure between the resonators and couplers, the first coupling line, and the second coupling line, achieves a passband relative bandwidth of less than 10%, and improves both passband performance and stopband suppression performance. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1This is a front view of a bandpass filter provided in an embodiment of the present invention;

[0036] Figure 2 A side view of a bandpass filter provided in an embodiment of the present invention;

[0037] Figure 3 An internal view of a bandpass filter provided in an embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the test curve of a bandpass filter provided in an embodiment of the present invention.

[0039] Symbol explanation:

[0040] Input port - P1, First ground port - P2, Output port - P3, Second ground port - P4, First input connection - Lin1, Second input connection - Lin2, Third input connection - Lin3, Input tap - T1, First output connection - Lout1, Second output connection - Lout2, Third output connection - Lout3, Output tap - T2, First resonator - R1, Second resonator - R2, Third resonator - R3, Fourth resonator - R4, First coupler - K1, Second coupler - K2, Third coupler - K3, First shielding layer - SD1, Second shielding layer - SD2, First coupling line - Z1, Second coupling line - U1, First resonant frame of the first resonator - R11, Second resonant frame of the first resonator - R12, Third resonant frame of the first resonator - R1 3. The first resonant frame of the second resonator - R21, the second resonant frame of the second resonator - R22, the third resonant frame of the second resonator - R23, the first resonant frame of the third resonator - R31, the second resonant frame of the third resonator - R32, the third resonant frame of the third resonator - R33, the first resonant frame of the fourth resonator - R41, the second resonant frame of the fourth resonator - R42, the third resonant frame of the fourth resonator - R43, the first coupling frame of the first coupler - K11, the second coupling frame of the first coupler - K12, the third coupling frame of the first coupler - K13, the first coupling frame of the second coupler - K21, the second coupling frame of the second coupler - K22, the third coupling frame of the second coupler - K23, the first coupling frame of the third coupler - K31, the second coupling frame of the third coupler - K32, the third coupling frame of the third coupler - K33. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Example 1

[0044] The bandpass filter provided in this embodiment of the invention is a combline bandpass filter. Please refer to [link / reference]. Figure 1 and Figure 2 The bandpass filter includes: a first shielding layer SD1, a resonant coupling layer, and a second shielding layer SD2 stacked sequentially from top to bottom; the first shielding layer SD1, the resonant coupling layer, and the second shielding layer SD2 are all printed circuits made using low-temperature co-fired ceramic (LTCC) process.

[0045] The resonant coupling layer includes: a first coupling line Z1, a second coupling line U1, four resonators, and three couplers. The four resonators are designated as first resonator R1, second resonator R2, third resonator R3, and fourth resonator R4. The three couplers are designated as first coupler K1, second coupler K2, and third coupler K3. The four resonators are arranged sequentially from left to right; a coupler is placed between every two adjacent resonators. The first coupling line Z1 is located above the leftmost resonator (i.e., the first resonator R1) and the rightmost resonator (i.e., the fourth resonator R4); the second coupling line U1 is located below the two middle resonators (i.e., the second resonator R2 and the third resonator R3); all four resonators and three couplers are connected to the ground port; the leftmost resonator (i.e., the first resonator R1) is connected to the input port P1; the rightmost resonator (i.e., the fourth resonator R4) is connected to the output port P3; the first shielding layer SD1 and the second shielding layer SD2 are both connected to the ground port.

[0046] The first coupling line Z1, also known as the Z-shaped coupling line, is used to couple the leftmost resonator (i.e., the first resonator R1) and the rightmost resonator (i.e., the fourth resonator R4). This coupling method is electrical coupling and can be called Z-shaped coupling.

[0047] The second coupling line U1, also known as the U-shaped coupling line, is used to couple the two resonators in the middle (i.e., the second resonator R2 and the third resonator R3). This coupling method is electrical coupling and can be called U-shaped coupling.

[0048] The coupler is used to couple two adjacent resonators together. This coupling method is magnetic coupling, which can be referred to as short-circuit stub coupling. Specifically, the first coupler K1 can adjust the magnetic coupling between the first resonator R1 and the second resonator R2; the second coupler K2 can adjust the magnetic coupling between the second resonator R2 and the third resonator R3; and the third coupler K3 can adjust the magnetic coupling between the third resonator R3 and the fourth resonator R4.

[0049] In one example, please see still Figure 1 and Figure 2 The bandpass filter further includes an input layer, an output layer, and a ground layer; the input layer, the output layer, and the ground layer are all printed circuits made using a low-temperature co-fired ceramic process; the input layer and the output layer are arranged symmetrically on the left and right.

[0050] The input layer includes two symmetrically arranged and interconnected input wireframes; one of the input wireframes is located above the first shielding layer SD1, and the other input wireframe is located below the second shielding layer SD2; the input wireframes are provided with an input port P1.

[0051] The output layer includes two symmetrically arranged and interconnected output wireframes; one of the output wireframes is located above the first shielding layer SD1, and the other output wireframe is located below the second shielding layer SD2; the output wireframes are provided with an output port P3.

[0052] The grounding layer includes: a first grounding layer and a second grounding layer arranged symmetrically front to back.

[0053] The first grounding layer includes: two first grounding frames arranged symmetrically and connected to each other; one of the first grounding frames is located above the first shielding layer SD1, and the other first grounding frame is located below the second shielding layer SD2; the first grounding frames are arranged alternately with the input wireframe and the output wireframe respectively; the first grounding frame is provided with a first grounding port P2.

[0054] The second grounding layer includes: two second grounding frames arranged symmetrically and connected to each other; one of the second grounding frames is located above the first shielding layer SD1, and the other second grounding frame is located below the second shielding layer SD2; the second grounding frames are arranged alternately with the input wireframe and the output wireframe respectively; the second grounding frame is provided with a second grounding port P4; the grounding port includes the first grounding port P2 and the second grounding port P4.

[0055] As an optional implementation, the input port P1, the first ground port P2, the output port P3, and the second ground port P4 are symmetrically arranged; the first coupling line Z1 is located above the first resonator R1 and the fourth resonator R4; the second coupling line U1 is located below the second resonator R2 and the third resonator R3; the first coupler K1 is located at the center of the first resonator R1 and the second resonator R2, the second coupler K2 is located at the center of the second resonator R2 and the third resonator R3, and the third coupler K3 is located at the center of the third resonator R3 and the fourth resonator R4, and is symmetrical with the first coupler K1, thus forming a stacked structure.

[0056] In another example, the bandpass filter includes an input connection line and an output connection line. The leftmost resonator (i.e., the first resonator R1) is connected to the input port P1 on each of the input frames via the input connection line; the rightmost resonator (i.e., the fourth resonator R4) is connected to the output port P3 on each of the output frames via the output connection line.

[0057] The input connection lines include: a first input connection line Lin1, a second input connection line Lin2, and a third input connection line Lin3. The output connection lines include: a first output connection line Lout1, a second output connection line Lout2, and a third output connection line Lout3. The first input connection line Lin1, the second input connection line Lin2, and the third input connection line Lin3 form an input signal shield; the first output connection line Lout1, the second output connection line Lout2, and the third output connection line Lout3 form an output signal shield.

[0058] As an optional implementation, the bandpass filter further includes an input tap T1 and an output tap T2. The leftmost resonator (i.e., the first resonator R1) is connected to the input connection line through the input tap T1; the rightmost resonator (i.e., the fourth resonator R4) is connected to the output connection line through the output tap T2.

[0059] In yet another example, the first shielding layer SD1 and the second shielding layer SD2 are printed inside the bandpass filter, and both are defective structures.

[0060] The input port P1, the output port P3, the first ground port P2, and the second ground port P4 are all 50-ohm impedance ports. The input port P1, the output port P3, the first ground port P2, and the second ground port P4 are all external electrode pins.

[0061] This embodiment of the bandpass filter addresses the issue of a relative bandwidth range of approximately 15% in combline bandpass filters by improving the coupling structure of the resonant device, thereby reducing the relative bandwidth of the passband to less than 10% and optimizing both passband performance and stopband suppression performance.

[0062] Example 2

[0063] This embodiment focuses on the structure of the resonator, coupler, first coupling line Z1 and second coupling line U1.

[0064] Each of the four resonators includes a second resonant frame, a first resonant frame, and a third resonant frame stacked sequentially from top to bottom; the first resonant frame is arranged alternately with the second resonant frame and the third resonant frame.

[0065] Each of the three couplers includes a second coupling frame, a first coupling frame, and a third coupling frame stacked sequentially from top to bottom; the first coupling frame is staggered with the second coupling frame and the third coupling frame; the second coupling frame of the coupler is located between the second resonant frames of two adjacent resonators; the first coupling frame of the coupler is located between the first resonant frames of two adjacent resonators; and the third coupling frame of the coupler is located between the third resonant frames of two adjacent resonators.

[0066] The first coupling line Z1 includes a first coupling part and a second coupling part connected to the first coupling part; the first coupling part is located above the second coupling frame of the leftmost resonator (i.e., the first resonator R1), and the second coupling part is located above the second coupling frame of the rightmost resonator (i.e., the fourth resonator R4).

[0067] The second coupling line U1 includes a third coupling portion and a fourth coupling portion connected to the third coupling portion; the third coupling portion is located below the third coupling frame of one of the middle resonators, and the fourth coupling portion is located below the third coupling frame of another middle resonator.

[0068] For details, please see Figure 3 The first resonator R1 has three layers. The second resonant frame R12 in the first layer and the third resonant frame R13 in the third layer are connected to the second grounding port P4. The first resonant frame R11 in the second layer is connected to the first grounding port P2. The first resonant frame R11 in the second layer is connected to the input tap T1. The second resonant frame R12 in the first layer and the third resonant frame R13 in the third layer are coupled to the first resonant frame R11 in the second layer.

[0069] The second resonator R2 has three layers. The second resonant frame R22 in the first layer and the third resonant frame R23 in the third layer are connected to the second grounding port P4. The first resonant frame R21 in the second layer is connected to the first grounding port P2. The second resonant frame R22 in the first layer and the third resonant frame R23 in the third layer are coupled to the first resonant frame R21 in the second layer.

[0070] The third resonator R3 has three layers. The second resonant frame R32 in the first layer and the third resonant frame R33 in the third layer are connected to the second grounding port P4. The first resonant frame R31 in the second layer is connected to the first grounding port P2. The second resonant frame R32 in the first layer and the third resonant frame R33 in the third layer are coupled to the first resonant frame R31 in the second layer.

[0071] The fourth resonator R4 has three layers. The second resonant frame R42 in the first layer and the third resonant frame R43 in the third layer are connected to the second grounding port P4. The first resonant frame R41 in the second layer is connected to the first grounding port P2. The first resonant frame R41 in the second layer is connected to the output tap T2. The second resonant frame R42 in the first layer and the third resonant frame R43 in the third layer are coupled to the first resonant frame R41 in the second layer.

[0072] The first coupler K1 has three layers. The second coupling frame K12 in the first layer and the third coupling frame K13 in the third layer are connected to the second grounding port P4. The first coupling frame K11 in the second layer is connected to the first grounding port P2. The second coupler K2 also has three layers. The second coupling frame K22 in the first layer and the third coupling frame K23 in the third layer are connected to the second grounding port P4. The first coupling frame K21 in the second layer is connected to the first grounding port P2. The third coupler K3 also has three layers. The second coupling frame K32 in the first layer and the third coupling frame K33 in the third layer are connected to the second grounding port P4. The first coupling frame K31 in the second layer is connected to the first grounding port P2.

[0073] The bandpass filter of this embodiment has seven printed circuit layers, namely a three-layer printed circuit layer composed of a resonator and a coupler, a one-layer printed circuit layer composed of a first coupling line, a one-layer printed circuit layer composed of a second coupling line, and a two-layer printed circuit layer composed of a first shielding layer and a second shielding layer. The bandpass filter has the following connections: input port P1 is connected to the first input connection line Lin1, the second input connection line Lin2, and the third input connection line Lin3; first ground port P2 is connected to the first and third layers of the first resonator R1, the second resonator R2, the third resonator R3, the fourth resonator R4, the first coupler K1, the second coupler K2, and the third coupler K3; output port P3 is connected to the first output connection line Lout1, the second output connection line Lout2, and the third output connection line Lout3; second ground port P4 is connected to the second layer of the first resonator R1, the second resonator R2, the third resonator R3, the fourth resonator R4, the first coupler K1, the second coupler K2, and the third coupler K3; and first shielding layer SD1 and second shielding layer SD2 are connected to the first ground port P2 and the second ground port P4, respectively.

[0074] The first coupling line Z1 connects the first resonator R1 and the fourth resonator R4 via electrical coupling, and the second coupling line U1 connects the second resonator R2 and the third resonator R3 via electrical coupling.

[0075] This bandpass filter includes four 1 / 8 wavelength resonators, three frequency-modulated stubs, two coupling stubs, and two metal shielding layers. Each resonator consists of three short-circuited stubs, and the feed terminal is connected to the open-circuit port of the resonator via a stripline. This bandpass filter controls the bandwidth of the passband and suppresses higher harmonics by adjusting the position and size of the frequency-modulated stubs. Simultaneously, it introduces weak electrical coupling between the source and load, generating transmission zeros near the passband for better frequency selectivity. Implemented using LTCC technology, it offers advantages such as small component size, high-temperature resistance, low processing cost, good operational stability, good material consistency, and environmental friendliness, making it widely applicable in microwave base stations and the Internet of Things (IoT).

[0076] Example 3

[0077] This embodiment focuses on the dimensions of each part of the bandpass filter.

[0078] In one example, the linewidth and spacing of the inner conductor (i.e., all conductor lines inside the device) are not less than 50 μm. The linewidth of the first and third resonant frames of each resonator is preferably 120 μm; the linewidth of the second resonant frame of each resonator is preferably 100 μm; and the spacing between two adjacent resonators is preferably 620 μm. The linewidth of each coupler is preferably 100 μm; and the spacing between the coupler and the adjacent resonator is preferably 310 μm.

[0079] In another example, the interlayer spacing of the inner conductors (i.e., all conductor lines inside the device) is not less than 15 μm, and the interlayer spacing between the resonator and the coupler is preferably 40 μm (i.e., the interlayer spacing between the three layers of the resonator is 40 μm, and the interlayer spacing between the three layers of the coupler is also 40 μm). The interlayer spacing between the first coupling portion of the first coupling line and the second coupling frame of the leftmost resonator (i.e., the first resonator) is preferably 200 μm; the interlayer spacing between the second coupling portion of the first coupling line and the second coupling frame of the rightmost resonator (i.e., the fourth resonator) is preferably 200 μm. The interlayer spacing between the third coupling portion of the second coupling line and the third coupling frame of one of the middle resonators is preferably 250 μm; the interlayer spacing between the fourth coupling portion of the second coupling line and the third coupling frame of another middle resonator is preferably 250 μm.

[0080] In yet another example, the bandpass filter employs a 7-layer printed circuit structure based on LTCC technology, with dimensions of 3.2mm × 1.6mm × 0.94mm.

[0081] Figure 4 The test curves for the bandpass filter are shown, with frequency on the horizontal axis and loss on the vertical axis. The curves show that the bandpass filter operates in the 7.1GHz–7.5GHz frequency band, with a relative bandwidth of 5.5%. The insertion loss is better than -1.65dB, the return loss at the input port is better than -19dB, the attenuation in the upper stopband range (DC–12GHz) is less than -30dB, and the attenuation in the lower stopband range (8.2GHz–17.5GHz) is less than -30dB. Therefore, the bandpass filter of this embodiment can achieve a passband relative bandwidth of less than 10% and improve both passband and stopband rejection performance.

[0082] Furthermore, the bandpass filter in this embodiment is designed using a combline structure; this bandpass filter can be combined in various ways to achieve more optimal solutions; this bandpass filter innovatively introduces short-circuit stubs (four resonators and three couplers) to tune the magnetic coupling between the resonators, effectively broadening the applicability of the combline filter.

[0083] The bandpass filter in this embodiment adopts a symmetrical design, resulting in a simple and symmetrical circuit structure that facilitates design and development. The microwave devices manufactured using LTCC technology exhibit excellent high-temperature resistance and can carry large currents. LTCC technology allows for the fabrication of dozens of substrate layers, embedding passive components internally, thus reducing interference from other assembled components and improving integration. While achieving narrowband frequency selectivity, the filter achieves small component size, simple structure, good stability, high reliability, high temperature resistance, and good material consistency. A defect-grounded shielding layer suppresses high-order harmonics of the signal. The circuit structure is simple, and by adjusting the combination of resonators and couplers, bandpass filters with various narrowband frequencies and stopband requirements can be implemented.

[0084] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0085] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A bandpass filter, characterized in that, include: The first shielding layer, the resonant coupling layer, and the second shielding layer are stacked sequentially from top to bottom; The first shielding layer, the resonant coupling layer, and the second shielding layer are all printed circuits made using a low-temperature co-fired ceramic process; The resonant coupling layer includes: a first coupling line, a second coupling line, four resonators, and three couplers; the four resonators are arranged sequentially from left to right; a coupler is placed between every two adjacent resonators; the first coupling line is located above the leftmost and rightmost resonators; the second coupling line is located below the two middle resonators; all four resonators and three couplers are connected to a ground port; the leftmost resonator is connected to an input port; the rightmost resonator is connected to an output port; both the first and second shielding layers are connected to the ground port. The first coupling line is used to couple the leftmost resonator and the rightmost resonator; the second coupling line is used to couple the two middle resonators; the coupler is used to couple two adjacent resonators. Each of the four resonators includes a second resonant frame, a first resonant frame, and a third resonant frame stacked sequentially from top to bottom; the first resonant frame is staggered with the second resonant frame and the third resonant frame. Each of the three couplers includes a second coupling frame, a first coupling frame, and a third coupling frame stacked sequentially from top to bottom; the first coupling frame is staggered with the second coupling frame and the third coupling frame; the second coupling frame of the coupler is located between the second resonant frames of two adjacent resonators; the first coupling frame of the coupler is located between the first resonant frames of two adjacent resonators; and the third coupling frame of the coupler is located between the third resonant frames of two adjacent resonators. The first coupling line includes a first coupling portion and a second coupling portion connected to the first coupling portion; the first coupling portion is located above the second resonant frame of the leftmost resonator, and the second coupling portion is located above the second resonant frame of the rightmost resonator. The second coupling line includes a third coupling portion and a fourth coupling portion connected to the third coupling portion; the third coupling portion is located below the third resonant frame of one of the middle resonators, and the fourth coupling portion is located below the third resonant frame of the other middle resonator; The relative bandwidth of the passband of the bandpass filter is less than 10%.

2. A bandpass filter according to claim 1, characterized in that, Also includes: The circuit comprises an input layer, an output layer, and a ground layer; all three layers are printed circuits manufactured using a low-temperature co-fired ceramic process. The input layer and the output layer are arranged symmetrically on the left and right sides; The input layer includes: two symmetrically arranged and interconnected input wireframes; one of the input wireframes is located above the first shielding layer, and the other input wireframe is located below the second shielding layer; the input wireframes are provided with input ports; The output layer includes: two symmetrically arranged and interconnected output wireframes; one of the output wireframes is located above the first shielding layer, and the other output wireframe is located below the second shielding layer; the output wireframes are provided with output ports; The grounding layer includes: a first grounding layer and a second grounding layer arranged symmetrically front to back; The first grounding layer includes: two first grounding frames arranged symmetrically and connected to each other; one of the first grounding frames is located above the first shielding layer, and the other first grounding frame is located below the second shielding layer; the first grounding frames are arranged alternately with the input wireframe and the output wireframe respectively; the first grounding frame is provided with a first grounding port; The second grounding layer includes: two second grounding frames arranged symmetrically and connected to each other; one of the second grounding frames is located above the first shielding layer, and the other second grounding frame is located below the second shielding layer; the second grounding frames are arranged alternately with the input wireframe and the output wireframe respectively; the second grounding frames are provided with second grounding ports; the grounding ports include the first grounding port and the second grounding port.

3. A bandpass filter according to claim 2, characterized in that, include: Input and output cables; The leftmost resonator is connected to the input port on each of the input frames via the input connection line; the rightmost resonator is connected to the output port on each of the output frames via the output connection line.

4. A bandpass filter according to claim 3, characterized in that, It also includes: input taps and output taps; The leftmost resonator is connected to the input connection line via the input tap; the rightmost resonator is connected to the output connection line via the output tap.

5. A bandpass filter according to claim 1, characterized in that, Both the first shielding layer and the second shielding layer are defective structures.

6. A bandpass filter according to claim 2, characterized in that, The input port, the output port, the first ground port, and the second ground port are all 50-ohm impedance ports.

7. A bandpass filter according to claim 1, characterized in that, The linewidth of the first and third resonant frames of each resonator is 120 μm; the linewidth of the second resonant frame of each resonator is 100 μm; and the spacing between two adjacent resonators is 620 μm.

8. A bandpass filter according to claim 7, characterized in that, The linewidth of each coupler is 100 μm; the line spacing between each coupler and the adjacent resonator is 310 μm. The layer spacing between the first coupling portion of the first coupling line and the second resonant frame of the leftmost resonator is 200 μm; the layer spacing between the second coupling portion of the first coupling line and the second resonant frame of the rightmost resonator is 200 μm. The layer spacing between the third coupling part of the second coupling line and the third resonant frame of the middle resonator is 250μm; the layer spacing between the fourth coupling part of the second coupling line and the third resonant frame of the other middle resonator is 250μm.

9. A bandpass filter according to claim 8, characterized in that, The bandpass filter has dimensions of 3.2mm × 1.6mm × 0.94mm.

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