High-Q-value and high-selectivity band-pass filter of dielectric integrated suspension line based on LTCC (Low Temperature Co-Fired Ceramic)

Abstract

The invention discloses a high-Q-value and high-selectivity band-pass filter based on an LTCC (Low Temperature Co-Fired Ceramic) dielectric integrated suspension line. According to the filter, a low-temperature co-fired ceramic process is combined with a dielectric integrated suspended line structure, and the dielectric and conductor loss is remarkably reduced and the quality factor is improved by constructing an air cavity in a multi-layer dielectric and adopting a resonator design with symmetrical upper and lower layers. Meanwhile, the U-shaped metal conductor transmission line is used for introducing cross coupling, transmission zero points are generated on the two sides of a passband, and therefore the filtering performance of high selectivity, low insertion loss, miniaturization and high reliability is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of band-pass filter, in particular to a high Q-value and high selectivity band-pass filter based on LTCC dielectric integrated suspended line BACKGROUND

[0002] Microwave filter is a key device in radio frequency front-end system such as wireless communication, radar and satellite communication, and its performance directly affects the channel selection, anti-interference ability and signal quality of the whole system, and plays a key role in wireless communication system. Insertion loss and out-of-band selectivity are the core indicators of the filter, which fundamentally depend on the quality factor (Q value) of the resonant structure. In order to achieve higher performance, traditional cavity filters or dielectric filters are used, the former has extremely high Q value and power capacity, but is bulky and difficult to integrate; the latter is small in size, but is limited in frequency stability and design flexibility. Although planar integrated circuit filters such as microstrip or stripline filters based on printed circuit board (PCB) technology have the advantages of small size, low cost and easy integration, the inherent conductor and dielectric loss of the planar structure leads to generally low Q value, which is difficult to meet the increasing demand for high performance.

[0003] Dielectric integrated suspended line circuit (SISL) has been successfully applied to the design of various filter structures because of its low loss and self-packaging characteristics, but currently the industry mainly relies on PCB technology to realize SISL filter, and this technology will expose its inherent limitations when pursuing higher performance, such as limited Q value improvement, insufficient structural precision, poor thermal performance and other problems. As a new electronic component integration and packaging technology, low temperature co-fired ceramic (LTCC) technology can exhibit higher quality factor, excellent thermal performance, outstanding size miniaturization and more reliable mechanical strength when processing filters, and is an ideal solution for high-performance filters. Therefore, how to combine LTCC and SISL to take advantage of each other and design a high Q-value and high selectivity filter is a problem we need to solve. SUMMARY

[0004] The purpose of the present application is to provide a high Q-value and high selectivity band-pass filter based on LTCC dielectric integrated suspended line to solve the problem that the filter cannot realize high Q value, high selectivity and self-packaging, etc.

[0005] The technical scheme adopted by the present application to achieve the purpose is: a high Q-value and high selectivity band-pass filter based on LTCC dielectric integrated suspended line, comprising five layers of dielectric substrates stacked from top to bottom, and upper and lower metal layers are arranged on the upper and lower surfaces of each dielectric substrate, respectively.

[0006] The second layer of dielectric substrate and the fourth layer of dielectric substrate are both provided with a rectangular cavity with the same structure in the middle position;

[0007] The upper and lower metal layers of the third layer of dielectric substrate are respectively provided with a notch corresponding to the rectangular cavity, and the upper and lower metal layers are respectively provided with an upper transmission line structure and a lower transmission line structure in the notch; the rectangular cavities of the second layer of dielectric substrate and the fourth layer of dielectric substrate form an air cavity for electromagnetic shielding.

[0008] A plurality of metalized through holes penetrating through the five layers of dielectric substrate are periodically distributed along the periphery of the rectangular cavity.

[0009] Preferably, the centers of the rectangular cavities of the second layer of dielectric substrate and the fourth layer of dielectric substrate coincide.

[0010] Preferably, the five layers of dielectric substrate are closely attached.

[0011] Preferably, the upper transmission line structure is located on the upper surface of the third layer of dielectric substrate and sequentially includes an input port, a first upper resonator, a second upper resonator, a third upper resonator, a fourth upper resonator, a fifth upper resonator, a sixth upper resonator, and an output port; the first to sixth upper resonators are all metal strips and are arranged in parallel; there is a gap between adjacent upper resonators.

[0012] The outer side of the first upper resonator is connected to the input port through a high-impedance line, and the outer side of the sixth upper resonator is connected to the output port through a high-impedance line; a U-shaped metal conductor transmission line is arranged between the second upper resonator and the fifth upper resonator for realizing cross-coupling between the second resonator and the fifth resonator, thereby introducing transmission zeros on both sides of the passband.

[0013] The lower transmission line structure includes a first lower resonator, a second lower resonator, a third lower resonator, a fourth lower resonator, a fifth lower resonator, and a sixth lower resonator, which correspond one-to-one to the six upper resonators of the upper transmission line structure, are symmetrically distributed above and below, and are connected to each other through the metalized through holes to reduce conductor loss.

[0014] Preferably, one end of the first upper resonator, the second upper resonator, the fifth upper resonator, and the sixth upper resonator is connected to the upper surface metal layer of one long side of the notch of the upper metal layer of the third layer of dielectric substrate, and the other end is suspended; one end of the third upper resonator and the fourth upper resonator is connected to the upper surface metal layer of the other long side of the notch of the upper metal layer of the third layer of dielectric substrate, and the other end is suspended.

[0015] Preferably, the opening of the U-shaped metal conductor transmission line faces the third upper resonator and the fourth upper resonator, and does not contact the second upper resonator, the fifth upper resonator, and the upper surface metal layer of the third layer of dielectric substrate.

[0016] Preferably, the third dielectric substrate is provided with a channel for placing an input port or an output port at both ends of the upper and lower metal layers, and the channel is communicated with the notch of the same layer metal layer.

[0017] Preferably, a plurality of metalized through holes are provided along both sides of the channel and penetrate the five-layer dielectric substrate.

[0018] Preferably, the five-layer dielectric substrate is made of ceramic material, and the third layer dielectric substrate has the smallest thickness, and the second layer dielectric substrate and the fourth layer dielectric substrate have the largest thickness.

[0019] Preferably, the five-layer dielectric substrate is formed into a self-sealing structure by rivet pressing.

[0020] Compared with the prior art, the present application has the following advantages and beneficial results:

[0021] The present application uses LTCC ceramic material as the dielectric substrate, and at the same time, the rectangular cavities are arranged in the second layer and the fourth layer dielectric substrate to form air cavities, so that the electromagnetic field energy of the resonator is mainly distributed in the low-loss air, thereby greatly reducing the overall dielectric loss. The resonator uses double-layer wiring and utilizes metalized through holes for connection, effectively reducing the equivalent series resistance and the conductor loss of the filter, and improving the Q value of the filter.

[0022] The present application uses the upper and lower copper metal layers and the metalized through holes penetrating each layer to form a complete self-sealing shielding cavity, which strictly confines the electromagnetic energy inside the filter, avoiding energy radiation loss.

[0023] The present application sets a specific U-shaped metal conductor transmission line on the upper metal layer of the third dielectric substrate, and establishes a non-adjacent resonator cross-coupling path between the second upper resonator and the fifth upper resonator. By utilizing the multi-path transmission and destructive interference principle of signals, it can generate a transmission zero point on both sides of the filter passband. The two transmission zero points make the frequency response curve of the filter have an extremely steep roll-off rate near the cutoff frequency, thereby realizing high-intensity suppression of out-of-band interference signals and improving the out-of-band rejection of the filter, with high selectivity.

[0024] The present application applies the LTCC process to the dielectric integrated suspended line platform, uses ceramic material with lower loss tangent, reduces the dielectric loss of the filter, and at the same time realizes higher structural precision, more reliable mechanical stability and excellent thermal stability of the filter, which can enhance the anti-interference ability of the filter. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1This is a schematic diagram of the structure of a bandpass filter based on LTCC dielectric integrated suspension line provided in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the upper transmission line structure in the bandpass filter provided in an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the lower-layer transmission line structure in the bandpass filter provided in an embodiment of the present invention;

[0028] Figure 4 The figure shows the S-parameter simulation results of the bandpass filter provided in the embodiment of the present invention;

[0029] The diagram shows the following labels: 1. First dielectric substrate; 2. Second dielectric substrate; 3. Third dielectric substrate; 4. Fourth dielectric substrate; 5. Fifth dielectric substrate; 6-1. First upper resonator; 6-2. Second upper resonator; 6-3. Third upper resonator; 6-4. Fourth upper resonator; 6-5. Fifth upper resonator; 6-6. Sixth upper resonator; 6-7. Input port; 6-8. Output port; 6-9. U-shaped metal conductor transmission line; 6-10. First lower resonator; 6-11. Second lower resonator; 6-12. Third lower resonator; 6-13. Fourth lower resonator; 6-14. Fifth lower resonator; 6-15. Sixth lower resonator. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0031] like Figure 1 As shown, at least one embodiment provides a high-Q, high-selectivity bandpass filter based on LTCC dielectric integrated suspension lines, including a first dielectric substrate 1, a second dielectric substrate 2, a third dielectric substrate 3, a fourth dielectric substrate 4, and a fifth dielectric substrate 5 stacked from top to bottom; copper-clad metal layers are respectively arranged on the upper and lower surfaces of each dielectric substrate to form upper and lower metal layers, thereby forming a five-layer circuit board.

[0032] Both the second and fourth dielectric substrates have a rectangular cavity with the same hollow structure in the middle, forming two closed air cavities that provide electromagnetic shielding.

[0033] The upper and lower metal layers of the third dielectric substrate each have notches. The upper metal layer notch is located directly below the rectangular cavity of the second dielectric substrate and has the same size and shape as the rectangular cavity. The lower metal layer notch is located directly above the rectangular cavity of the fourth dielectric substrate and has the same size and shape as the rectangular cavity. Upper and lower transmission line structures, i.e., dielectric integrated suspension lines, are respectively arranged within the notches of the upper and lower metal layers. The rectangular cavities of the second and fourth dielectric substrates constitute an air cavity for electromagnetic shielding. The third dielectric substrate separates the upper and lower air cavities.

[0034] The five-layer dielectric substrate has multiple periodically distributed metallized vias for grounding along the periphery of the rectangular cavity. The first and fifth dielectric substrates are used to encapsulate the entire structure. The five dielectric substrates and metal layers are pressed together using rivet holes to form a self-encapsulated dielectric integrated suspension line.

[0035] Furthermore, the centers of the rectangular cavities of the second and fourth dielectric substrates coincide.

[0036] Furthermore, such as Figure 2 As shown, the upper transmission line structure is located on the upper surface of the third dielectric substrate and includes, in sequence, an input port 6-7, a first upper resonator 6-1, a second upper resonator 6-2, a third upper resonator 6-3, a fourth upper resonator 6-4, a fifth upper resonator 6-5, a sixth upper resonator 6-6, and an output port 6-8; the first to sixth upper resonators are all made of metal strips and are arranged in parallel; there is a gap between adjacent upper resonators.

[0037] Input port 6-7 and output port 6-8 adopt a high-impedance line feeding structure. Specifically, the outer side of the first upper resonator 6-1 is connected to input port 6-7 through a high-impedance line, and the outer side of the sixth upper resonator 6-6 is connected to output port 6-8 through a high-impedance line.

[0038] The first upper-layer resonator 6-1, the second upper-layer resonator 6-2, the third upper-layer resonator 6-3, the fourth upper-layer resonator 6-4, the fifth upper-layer resonator 6-5, the sixth upper-layer resonator 6-6, and the symmetrically distributed first lower-layer resonators 6-10, second lower-layer resonators 6-11, third lower-layer resonators 6-12, fourth lower-layer resonators 6-13, fifth lower-layer resonators 6-14, and sixth lower-upper-layer resonators are quarter-wavelength resonators with short-circuited terminations. Each resonator is connected to the upper and lower layers via metallized vias (three metallized vias are used in this embodiment), effectively reducing conductor losses. The use of multiple metallized vias connecting the double-layer metal in the resonators keeps other undesirable modes away from the passband, improving the selectivity of the filter.

[0039] The U-shaped metal conductor transmission line 6-9 is arranged between the second upper layer resonator 6-2 and the fifth upper layer resonator 6-5, and is used to realize cross-coupling between the second resonator and the fifth resonator, thereby introducing transmission zero points on both sides of the passband and improving the selectivity of the filter.

[0040] As shown in Figure 3 The lower layer transmission line structure includes a first lower layer resonator 6-10, a second lower layer resonator 6-11, a third lower layer resonator 6-12, a fourth lower layer resonator 6-13, a fifth lower layer resonator 6-14, and a sixth lower layer resonator 6-15, which are respectively corresponding to the six upper layer resonators of the upper layer transmission line structure, are symmetrically distributed in an up-down manner, and are connected to each other through metallized vias to reduce conductor loss and construct six three-dimensional resonators.

[0041] Further, one end of the first upper layer resonator 6-1, the second upper layer resonator 6-2, the fifth upper layer resonator 6-5, and the sixth upper layer resonator 6-6 is connected to the upper surface metal layer of one long side of the upper layer metal layer of the third dielectric substrate 3; one end of the third upper layer resonator 6-3 and the fourth upper layer resonator 6-4 is connected to the upper surface metal layer of the other long side of the upper layer metal layer of the third dielectric substrate 3.

[0042] The first upper layer resonator 6-1 and the sixth upper layer resonator 6-6 are equal in length and width, the second upper layer resonator 6-2 and the fifth upper layer resonator 6-5 are equal in length and width, and the third upper layer resonator 6-3 and the fourth upper layer resonator 6-4 are equal in length and width. The length of the first upper layer resonator 6-1 is greater than that of the second upper layer resonator 6-2.

[0043] Further, the opening of the U-shaped metal conductor transmission line 6-9 faces the third upper layer resonator 6-3 and the fourth upper layer resonator 6-4, and does not contact the second upper layer resonator 6-2, the fifth upper layer resonator 6-5, and the upper surface metal layer of the third dielectric substrate 3.

[0044] Further, the third dielectric substrate 3 is provided with a channel at both ends of the upper and lower metal layers for placing the input port 6-7 or the output port 6-8, the channel is in communication with the metal layer gap of the same layer, and is in communication with the upper and lower air cavities, respectively. The first dielectric substrate 1 and the second dielectric substrate 2 are provided with a gap at both ends, but there is still a certain distance between the metallized vias and the edges of the rectangular cavity.

[0045] Further, a plurality of metallized vias are arranged periodically along the two sides of the channel and penetrate through the five layers of dielectric substrates.

[0046] Further, the five-layer dielectric substrates are all selected from ceramic materials with a dielectric constant of 9.8 and a loss tangent of 0.001, wherein the third layer dielectric substrate has the smallest thickness, and the second layer dielectric substrate and the fourth layer dielectric substrate have the largest thickness. Specifically, the third layer dielectric substrate has a thickness of 0.2478 mm, the first layer dielectric substrate and the fifth layer dielectric substrate have a thickness of 0.6018 mm, and the second layer dielectric substrate and the fourth layer dielectric substrate have a thickness of 1.8054 mm. The second layer dielectric substrate and the fourth layer dielectric substrate form a larger cavity, so that more electromagnetic energy is distributed in the air, and the dielectric loss of the circuit can be greatly reduced.

[0047] Further, the five-layer dielectric substrates are closely attached and are formed into a self-packaging structure through rivet pressing.

[0048] The band-pass filter based on the dielectric integrated suspended line platform forms a cavity through the pressing of the five-layer dielectric substrates, and is self-pressed, so that self-packaging is achieved, a heavy metal shielding box is not needed, the size of the filter can be greatly reduced, batch production is facilitated, and production cost is greatly reduced. In addition, based on the advantages of the dielectric integrated suspended line platform itself, a rectangular cavity is formed by digging out the second layer dielectric substrate and the fourth layer dielectric substrate, and the rectangular cavity is surrounded by a metalized via, so that most of the electromagnetic field is bound in the air, which can achieve good electromagnetic shielding effect and reduce radiation loss.

[0049] In the present application, the dielectric integrated suspended line filter is produced and processed by using the LTCC process, so that higher structural precision, more reliable mechanical stability and excellent thermal stability are achieved, and the anti-interference ability of the filter can be enhanced.

[0050] The principle of the band-pass filter of the present application is mainly as follows:

[0051] When the signal is excited on the upper-layer transmission line structure of the third layer dielectric substrate 3, the electromagnetic field generated thereby is expanded upward and downward, and is preferentially squeezed and constrained in the low-loss air cavity. Since the dielectric loss of air is much lower than that of any solid medium, this greatly reduces the dielectric loss of the resonant unit from the physical structure, which is the primary condition for obtaining high no-load Q value.

[0052] Each resonator adopts a three-dimensional structure arranged symmetrically upward and downward and connected through a metalized via, which is equivalent to widening the current path of the resonator and increasing the effective cross-sectional area of the conductor. According to the resistance formula, this directly reduces the equivalent series resistance of the resonator, thereby significantly reducing the conductor loss.

[0053] The whole structure is formed by upper and lower metal layers and the metalized through-hole wall, which forms a closed shielding cavity.

[0054] In addition, the input signal is fed from the input port to the first resonator, and then the subsequent resonators are excited in turn through the main coupling path, and finally output from the sixth resonator. The strength of these couplings determines the center frequency and bandwidth of the filter passband.

[0055] The signal has two paths to the output end: one is the conventional path through the main coupling path; the other is the cross-coupling path realized by the U-shaped metal conductor transmission line. At a specific frequency point outside the passband, the signals of the two paths are in opposite phase and equal in amplitude, and destructive interference occurs at the output port, resulting in no signal output, which is manifested as a transmission zero point on the frequency response curve. By accurately setting the structure and position of the U-shaped metal conductor transmission line, one transmission zero point can be introduced on each side of the passband. The two zero points greatly improve the out-of-band rejection capability and roll-off speed of the filter near the cutoff frequency, achieving high selectivity.

[0056] Since the dielectric substrate adopts LTCC material, its excellent thermal stability ensures that the filter performance remains stable at different temperatures, and its high mechanical strength makes the self-packaging structure firm and reliable, without the need for an additional metal shell, truly realizing the integration of miniaturization, light weight and high reliability.

[0057] Figure 4 The S parameter simulation result diagram of the LTCC band-pass filter of the present application can be seen from the simulation result that the present application can realize lower insertion loss and higher out-of-band rejection capability, the passband range of the filter is 6.5-7.08GHz, the minimum insertion loss of the passband is 0.67dB, the maximum insertion loss of the passband is 1.68dB, the low resistance band 3-6.43GHz is suppressed by more than 30dB, and 7.20-11GHz is more than 30dB.

Claims

1. A high-Q, high-selectivity bandpass filter based on LTCC dielectric integrated suspension line, characterized in that... It includes five dielectric substrates stacked from top to bottom, with upper and lower metal layers respectively arranged on the upper and lower surfaces of each dielectric substrate. A rectangular cavity with the same structure is provided in the middle of both the second and fourth dielectric substrates; The upper and lower metal layers of the third dielectric substrate have notches corresponding to the rectangular cavity, and the upper transmission line structure and the lower transmission line structure are respectively arranged in the notches of the upper and lower metal layers; the rectangular cavities of the second and fourth dielectric substrates constitute an air cavity for electromagnetic shielding. Multiple metallized vias penetrating the five-layer dielectric substrate are periodically distributed along the periphery of the rectangular cavity.

2. The bandpass filter according to claim 1, characterized in that, The centers of the rectangular cavities of the second and fourth dielectric substrates coincide.

3. The bandpass filter according to claim 1, characterized in that, The five-layer dielectric substrate is tightly bonded together.

4. The bandpass filter according to claim 1, characterized in that, The upper transmission line structure is located on the upper surface of the third dielectric substrate and includes, in sequence, an input port, a first upper resonator, a second upper resonator, a third upper resonator, a fourth upper resonator, a fifth upper resonator, a sixth upper resonator, and an output port; the first to sixth upper resonators are all made of metal strips and are arranged in parallel; there is a gap between adjacent upper resonators; The outer side of the first upper-layer resonator is connected to the input port via a high-impedance line, and the outer side of the sixth upper-layer resonator is connected to the output port via a high-impedance line. A U-shaped metal conductor transmission line is provided between the second and fifth upper-layer resonators to achieve cross-coupling between the second and fifth resonators, thereby introducing transmission zeros on both sides of the passband. The lower-level transmission line structure includes a first lower-level resonator, a second lower-level resonator, a third lower-level resonator, a fourth lower-level resonator, a fifth lower-level resonator, and a sixth lower-level resonator, which correspond one-to-one with the six upper-level resonators of the upper-level transmission line structure. They are symmetrically distributed vertically and interconnected through metallized vias to reduce conductor loss.

5. The bandpass filter according to claim 4, characterized in that, One end of the first, second, fifth, and sixth upper-layer resonators is connected to the upper surface metal layer of one long side of the notch in the upper metal layer of the third dielectric substrate, and the other end is suspended; one end of the third and fourth upper-layer resonators is connected to the upper surface metal layer of the other long side of the notch in the upper metal layer of the third dielectric substrate, and the other end is suspended.

6. The bandpass filter according to claim 4, characterized in that, The opening of the U-shaped metal conductor transmission line faces the third and fourth upper resonators, and does not contact the second, fifth, or upper surface metal layer of the third dielectric substrate.

7. The bandpass filter according to claim 4, characterized in that, The third dielectric substrate has a channel at both ends of the upper and lower metal layers for placing an input port or an output port, and the channel is connected to a notch in the same metal layer.

8. The bandpass filter according to claim 7, characterized in that, Multiple metallized vias are periodically distributed along both sides of the channel and penetrate the five-layer dielectric substrate.

9. The bandpass filter according to claim 1, characterized in that, All five dielectric substrates are made of ceramic material, with the third dielectric substrate having the smallest thickness and the second and fourth dielectric substrates having the largest thickness.

10. The bandpass filter according to claim 1, characterized in that, The five-layer dielectric substrate is formed into a self-encapsulating structure by riveting.

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