Miniaturized low-loss ltcc millimeter wave bandpass filter

Abstract

This invention discloses a miniaturized, low-loss LTCC millimeter-wave bandpass filter, comprising a ceramic body and an external electrode. The external electrode is embedded outside the ceramic body. The ceramic body includes an LTCC ceramic dielectric substrate and an internal electrode embedded within the LTCC ceramic dielectric substrate. The internal electrode includes a top metal plate, a source terminal, a load terminal, a first resonator, a second resonator, a third resonator, a bottom metal plate, and grounding posts. The source terminal and the load terminal are symmetrically arranged and located below the top metal plate. The two ends of the two grounding posts are respectively connected to the top metal plate and the bottom metal plate. The first resonator and the third resonator are symmetrically arranged and located below the source terminal and the load terminal, respectively. One end of the first resonator and the third resonator are respectively connected to the two grounding posts. The second resonator is located above the bottom metal plate. This filter has a wide stopband suppression effect in the millimeter-wave band, effectively improving signal transmission efficiency.

Description

Technical Field

[0001] This invention relates to the field of LTCC filter technology, specifically to a miniaturized, low-loss LTCC millimeter-wave bandpass filter. Background Technology

[0002] With the rapid development of wireless communication technology, millimeter-wave communication technology has become a key technology in mobile communication and low-Earth orbit satellite communication due to its abundant spectrum resources and high data transmission rates. As a critical component of communication systems, filters face even more stringent requirements in millimeter-wave systems. High-reliability equipment demands that millimeter-wave filters possess characteristics such as high performance, small size, and lightweight design. Among these, small size and low loss are crucial performance indicators for millimeter-wave filters.

[0003] In the millimeter-wave band, distributed microstrip filters are easier to miniaturize compared to other structures. However, the microstrip filters currently used in communication systems are designed based on PCB (Printed Circuit Board) technology. Filters designed based on single-layer PCB technology result in a larger circuit area because the microstrip lines can only be designed on the same plane.

[0004] The performance of microstrip filters relies on the coupling between microstrip lines. Traditional filters designed using single-layer PCB technology adjust the coupling by changing the distance between adjacent transmission lines; however, the small spacing between these lines makes fabrication difficult. Furthermore, cross-coupling techniques can introduce more transmission zeros to improve passband and out-of-band performance. However, implementing cross-coupling in traditional single-layer PCB designs requires additional circuitry, leading to increased filter losses.

[0005] Filters designed using multilayer PCB technology can place the bandpass on different layers, and this stacking method can greatly reduce the filter size. A multilayer PCB-packaged bandpass filter proposed in "Yunbo Rao; Huizhen Jenny Qian; Jie Zhou; Yuandan Dong; XunLuo, Miniaturized 28-GHz packaged bandpass filter with high selectivity and wide stopband using multilayer PCB technology. IEEE Microwave and Wireless Components Letters, 32(2022)664-667" is beneficial for filter miniaturization. However, the PCB material used in this filter has high dielectric loss, and additional metal spacers are required when designing vias, which increases the filter's insertion loss and affects signal transmission efficiency. Furthermore, the additional via metal spacers on the front and rear sides of the filter facilitate connection with the internal electrode resonator, placing high demands on the manufacturing process. Additionally, the minimum linewidth of the internal electrode in this filter is 0.05mm, which requires high processing precision and limits the applicable packaging processes. Therefore, designing a bandpass filter in the millimeter-wave band that meets the requirements of miniaturization, has low loss characteristics, and is easy to manufacture remains a technical challenge. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by proposing a miniaturized, low-loss LTCC millimeter-wave bandpass filter to solve the technical problems of large chip size, high manufacturing difficulty, and high insertion loss in traditional bandpass filters.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0008] A miniaturized, low-loss LTCC millimeter-wave bandpass filter includes a ceramic body and an external electrode. The external electrode is embedded outside the ceramic body. The ceramic body includes an LTCC ceramic dielectric substrate and an internal electrode embedded within the LTCC ceramic dielectric substrate. The internal electrode includes a top metal plate, a source terminal, a load terminal, a first resonator, a second resonator, a third resonator, a bottom metal plate, and grounding posts. The source terminal and the load terminal are symmetrically arranged and located below the top metal plate. The source terminal and the load terminal are connected to the external electrode through an input feed metal plate and an output feed metal plate, respectively. The two ends of the two grounding posts are connected to the top metal plate and the bottom metal plate, respectively. The first resonator and the third resonator are symmetrically arranged and located below the source terminal and the load terminal, respectively. One end of the first resonator and the third resonator are connected to the two grounding posts, respectively. The second resonator is located above the bottom metal plate.

[0009] In the above technical solution, the first resonator and the third resonator are located below the source end and the load end, and are connected to the top metal sheet and the bottom metal sheet through metallized through holes without the need for additional pads. The two are mirror symmetrical and form horizontal electrical coupling, and the first resonator forms vertical electrical coupling with the load end.

[0010] The second resonator is located below the first and third resonators and forms a vertical magnetic coupling with the first and third resonators.

[0011] Preferably, both the first and third resonators are quarter-wavelength stepped impedance resonators. Quarter-wavelength resonators, due to their small size, allow for structural miniaturization, and their resonant modes consist only of odd-order modes, thus avoiding the excitation of second harmonics.

[0012] Preferably, the second resonator is a half-wavelength stepped impedance resonator. Half-wavelength resonators and quarter-wavelength resonators have different harmonic distributions, and the stopband suppression can be broadened by the mutual suppression of harmonics.

[0013] Preferably, the LTCC ceramic substrate has a dielectric constant of 7.5 and a loss tangent of 0.002. This LTCC ceramic with a medium dielectric constant reduces the filter size while ensuring low latency. The low loss tangent reduces the filter's insertion loss.

[0014] Preferably, the external electrode includes an input electrode, an output electrode, and a grounding electrode. The input electrode and the output electrode are arranged symmetrically on the left and right sides of the ceramic body, and the two grounding electrodes are arranged symmetrically on the front and rear sides of the ceramic body, so that no additional grounding pillars are needed on the front and rear sides.

[0015] Preferably, the source end is connected to the input electrode via an input feed metal plate, and the load end is connected to the output electrode via an output feed metal plate.

[0016] Preferably, the internal electrode further includes shielding units arranged symmetrically on both sides of the source end and the load end.

[0017] In the above technical solution, spurious signals are shielded by setting up a shielding unit, thereby improving the filtering effect of the filter.

[0018] Preferably, the shielding unit includes a shielding column and three shielding metal layers. The top of the shielding column is connected to a top metal sheet, and the bottom of the shielding column is connected to a bottom metal sheet. The three shielding metal layers are installed on the shielding column from top to bottom.

[0019] In the above technical solution, the three shielding metal layers are arranged in a symmetrical structure on both sides of the feed structure and the resonator, thereby forming a compact LTCC miniaturized filter structure.

[0020] Preferably, a grounding substrate is provided on the bottom side of the LTCC ceramic dielectric substrate.

[0021] In the above technical solution, the grounding substrate is set to adapt to the PCB board, making it more convenient to use.

[0022] Preferably, both the outer electrode and the inner electrode are made of silver.

[0023] This invention has the following characteristics and beneficial effects:

[0024] The above technical solution employs a three-dimensional multilayer structure to design stepped impedance microstrip lines, resulting in a smaller area and improved chip integration compared to bandpass filters implemented on single-layer PCBs. The coupled microstrip resonator and feed structure are located on different structural layers using vertical coupling, overcoming the technical challenge of high fabrication difficulty caused by the small spacing between coupled microstrip lines in planar coupling methods. More importantly, compared to filters designed using multilayer PCB processes, this millimeter-wave filter, based on LTCC technology, has lower dielectric loss due to the LTCC ceramic dielectric and reduces the need for additional vias and metal spacers during via design, significantly reducing insertion loss. Furthermore, the elimination of edge vias and metal spacers allows for flexible design of input / output and resonator termination lengths, avoiding connections to edge metal sheets and facilitating fabrication. In terms of manufacturing processes, the lower precision requirements for internal electrode linewidth allow the designed filter structure to be applied to different packaging processes. In addition, compared to PCB-based filters, LTCC-based filters exhibit better temperature stability and mechanical reliability, enabling stable operation in various environments. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0026] Figure 1 This is a schematic diagram of the outer surface structure of the LTCC millimeter-wave bandpass filter of the present invention;

[0027] Figure 2 This is the equivalent circuit diagram of the LTCC millimeter-wave bandpass filter of the present invention;

[0028] Figure 3 This is a three-dimensional schematic diagram of a miniaturized, low-loss LTCC millimeter-wave bandpass filter structure provided by the present invention;

[0029] Figure 4 This is a top view of the source and load terminals of the present invention;

[0030] Figure 5 This is a top view schematic diagram of resonator 1 and resonator 3 of the present invention;

[0031] Figure 6 This is a top view schematic diagram of the resonator 2 of the present invention;

[0032] Figure 7 This is a simulation result diagram of the S11 of the LTCC millimeter-wave bandpass filter of this invention;

[0033] Figure 8 This is a simulation result diagram of the S21 of the LTCC millimeter-wave bandpass filter of the present invention;

[0034] Figure 9 This is a three-dimensional schematic diagram of the LTCC millimeter-wave bandpass filter structure mounted on the PCB test board of the present invention;

[0035] Figure 10 This is a three-dimensional schematic diagram of the multilayer PCB test board of the present invention;

[0036] Figure 11 This is an S11 simulation result diagram of the LTCC millimeter-wave bandpass filter mounted on the PCB test board of the present invention;

[0037] Figure 12 This is the S21 simulation result diagram of the LTCC millimeter-wave bandpass filter mounted on the PCB test board of the present invention.

[0038] In the diagram, 1-ceramic body, 2-input electrode, 3-output electrode, 4-ground electrode;

[0039] 101-LTCC ceramic dielectric substrate, 102-top metal sheet, 103-input feed metal sheet, 104-output feed metal sheet, 105-source end, 106-load end, 107-first resonator, 108-third resonator, 109-second resonator, 110-bottom metal sheet, 111-grounding substrate, 112-shielding post, 113-grounding post. Detailed Implementation

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings.

[0042] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0043] To address the technical challenges of large chip size, high fabrication difficulty, and significant insertion loss in traditional bandpass filters, this application provides a miniaturized, low-loss LTCC (Low Temperature Co-fired Ceramic) millimeter-wave bandpass filter.

[0044] The miniaturized, low-loss LTCC millimeter-wave bandpass filter provided in this application embodiment can be applied to 5G millimeter-wave communication systems and low-Earth orbit communication satellite systems. Specifically, it can cover the n257 band (26.5GHz-29.5GHz) and n258 band (24.25GHz-27.5GHz) of FR2.

[0045] like Figure 1 , Figure 3 , Figure 9 and Figure 10 As shown, the present invention provides a miniaturized low-loss LTCC millimeter-wave bandpass filter, including an outer surface electrode, a multilayer LTCC filter structure, and a PCB test substrate.

[0046] like Figure 4 , Figure 5 , Figure 6As shown, the filter mainly consists of a source-load transmission line, two bent-down quarter-wavelength stepped impedance resonators, and one bent half-wavelength stepped impedance resonator. Through the bending of the resonators, the vertical multilayer stacking of the LTCC design, and the relatively large dielectric constant of the LTCC ceramic material, a compact structure that is easy to integrate is achieved.

[0047] like Figure 7 , Figure 8 , Figure 11 , Figure 12 As shown, the LTCC millimeter-wave filter has both extremely low insertion loss and high out-of-band rejection capability in the millimeter-wave band. The resonant frequency, bandwidth, zero point, and spurious position can all be flexibly adjusted to achieve filtering performance for different application scenarios.

[0048] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, but the embodiments of the present invention are not limited thereto.

[0049] Specifically, such as Figure 1 and Figure 2 As shown, it includes a ceramic body 1 and an external electrode. The external electrode is embedded on the outside of the ceramic body. The external electrode includes an input electrode 2, an output electrode 3 and a ground electrode 4. The input electrode 2 and the output electrode 3 are symmetrically arranged on the left and right sides of the ceramic body 1, and the two ground electrodes 4 are symmetrically arranged on the front and rear sides of the ceramic body 1.

[0050] In this embodiment, the overall external dimensions are 2.0mm × 1.2mm × 0.66mm. A ceramic material with a dielectric constant of 7.5 and a loss tangent of 0.002 is used as the green ceramic tape material, and metallic silver is used as the conductor material. The thickness of a single-layer green ceramic tape can be 72µm, and the thickness of the metallic conductor can be 10µm.

[0051] In a further embodiment, the ceramic body 1 includes an LTCC ceramic dielectric substrate 101 and an internal electrode embedded in the LTCC ceramic dielectric substrate 101. The internal electrode includes a top metal sheet 102, a source end 105, a load end 106, a first resonator 107, a third resonator 108, a second resonator 109, a bottom metal sheet 110, and a grounding post 113.

[0052] The source terminal 105 and the load terminal 106 are arranged symmetrically and located below the top metal sheet 102. The source terminal 105 and the load terminal 106 are connected to the external electrode through the input feed metal sheet 103 and the output feed metal sheet 104, respectively. Specifically, the source terminal 105 is connected to the input electrode 2 through the input feed metal sheet 103, and the load terminal 106 is connected to the output electrode 3 through the output feed metal sheet 104, thus forming a horizontal cross-coupling.

[0053] In this embodiment, as Figure 4 As shown, the source and load ends are coupled by a bent metal microstrip line and a bent metal microstrip line on the other side of the center of symmetry, and a transmission zero is introduced on the left and right sides of the passband.

[0054] In this embodiment, the source and load ends have the same structure, forming a U-shape after bending. The widths of the metal microstrip lines on both sides after bending are W1 = 0.07 mm and W2 = 0.08 mm, respectively; the heights of the metal microstrip lines on both sides are L1 = 0.46 mm and L3 = 0.52 mm, while the height of the metal microstrip line in the middle bend is L2 = 0.11 mm. The distance between the metal microstrip lines on both sides is S1 = 0.15 mm, and the distance between the source and load ends is S2 = 0.155 mm.

[0055] The two ends of the two grounding posts 113 are respectively connected to the top metal plate 102 and the bottom metal plate 110. The first resonator 107 and the third resonator 108 are arranged symmetrically and are located below the source end 105 and the load end 106, respectively. One end of the first resonator 107 and the third resonator 108 is connected to the two grounding posts 113, and the second resonator 109 is located above the bottom metal plate 110. The first resonator 107 and the third resonator 108 are both quarter-wavelength stepped impedance resonators. The second resonator 109 is a half-wavelength stepped impedance resonator.

[0056] Understandably, the first and third resonators are located below the source and load ends, and are connected to the top and bottom metal sheets through metallized vias, thus eliminating the need for additional spacers. The two are mirror-symmetrical and form a horizontal direct coupling.

[0057] The second resonator is located below the first and third resonators and is vertically directly coupled to the first and third resonators.

[0058] Specifically, such as Figure 5 As shown, in this embodiment, a quarter-wavelength first resonator 107 with one end grounded is directly coupled horizontally to a mirror-symmetrical third resonator 108.

[0059] In this embodiment, the first and third resonators have the same structure, forming a U-shape after bending. The widths of the metal microstrip lines on both sides after bending are W3 = 0.09 mm and W4 = 0.12 mm, respectively; the heights of the metal microstrip lines on both sides are L4 = 0.64 mm and L6 = 0.34 mm, respectively, while the height of the metal microstrip line in the middle bend is L4 = 0.64 mm. The distance between the metal microstrip lines on both sides is S3 = 0.0085 mm, and the distance between the first and third resonators is S4 = 0.16 mm.

[0060] like Figure 6 As shown, in this embodiment, the second resonator 109 is a half-wavelength SIR with open ends and bent. The coupling between the first resonator 107, the third resonator 108, and the second resonator 109 can generate a transmission zero on the left side of the passband. Combined with the transmission zeros generated on the left and right sides of the passband by the source and load couplings mentioned above, a total of two transmission zeros are introduced on the left side of the passband, and one transmission zero is introduced on the right side. The grounded quarter-wavelength SIR resonator and the half-wavelength SIR resonator have different harmonic distributions, and the stopband suppression can be broadened by mutual suppression of harmonics.

[0061] In this embodiment, the second resonator 109 has a W-shaped structure, and each bend is a 90-degree bend, forming a shape similar to a rectangular wave. The widths of the metal microstrip lines on both sides after the bend are W5 = 0.13 mm, W6 = 0.12 mm, and W7 = 0.13 mm, respectively; the heights of the metal microstrip lines are L7 = 0.14 mm, L8 = 0.26 mm, L9 = 0.17 mm, L10 = 0.40 mm, and L11 = 0.11 mm, respectively; and the distances between adjacent metal microstrip lines are S5 = 0.08 mm and S6 = 0.085 mm, respectively.

[0062] Furthermore, the internal electrode also includes shielding units arranged symmetrically on both sides of the source end 105 and the load end 106. The shielding unit includes a shielding post 112 and three shielding metal layers. The top end of the shielding post 112 is connected to the top metal sheet 102, and the bottom end of the shielding post is connected to the bottom metal sheet 110. The three shielding metal layers are installed on the shielding post 112 from top to bottom.

[0063] Specifically, the three-layer metal gasket shielding metal layers are parallel to the source and load ends of the first layer, the first and third resonators of the second layer, and the second resonator of the third layer, respectively. The shielding pillars are arranged in two rows, with the top of the first row of shielding pillars connected to the top metal plate and the bottom of the first row of shielding pillars connected to the second shielding metal layer. The top of the second row of shielding pillars is connected to the second shielding metal layer and the bottom of the second row of shielding pillars is connected to the bottom metal plate. This is used to connect the upper and lower grounding layers and also to avoid secondary harmonics generated by cavity resonance.

[0064] pass Figure 7 and Figure 8 The simulation results show that the miniaturized low-loss LTCC millimeter-wave bandpass filter provided in this embodiment can cover the 24.25-29.5GHz frequency band, with a minimum insertion loss of 0.71dB and a maximum insertion loss of 1.8dB in the passband, achieving extremely low insertion loss in the millimeter-wave band.

[0065] In a further embodiment, a grounding substrate 111 is provided on the bottom side of the LTCC ceramic dielectric substrate 101. The grounding substrate 111 facilitates the connection of an external PCB board.

[0066] Finally, to further illustrate the performance of the miniaturized, low-loss LTCC millimeter-wave bandpass filter provided in this embodiment, such as... Figure 9 The figure shows a three-dimensional schematic diagram of the LTCC millimeter-wave bandpass filter structure of the present invention mounted on a multilayer PCB test board.

[0067] Specifically, such as Figure 10 As shown, the multilayer PCB test board comprises three copper metal layers, one ground metal layer, three PCB dielectric layers, a grounded coplanar waveguide (GCPW) transmission line, and a ground via in the middle. The metal layers and transmission line are made of copper, which has excellent conductivity, low cost, and is not easily oxidized; both are 0.035 mm thick. PCB dielectric layers 1 and 3 are both made of Rogers RO3003, which has good high-frequency characteristics, a thickness of 0.127 mm, a dielectric constant of 3.0, and a loss tangent of 0.0013. PCB dielectric layer 2 is made of FR4, with a thickness of 0.537 mm, a dielectric constant of 4.4, and a loss tangent of 0.02. The ground via is located directly below the LTCC filter, arranged in an X-shape to suppress second harmonics generated by cavity resonance. The radii of the vias on both sides of the CPWG and the central ground via are all 0.3 mm. The two GCPW transmission lines have a characteristic impedance of 50 ohms, and the width of the middle transmission line is 0.24mm.

[0068] Simulation results are as follows Figure 11 and Figure 12 As shown, the passband of the filter of this invention can cover 26.5GHz-29.5GHz, with an insertion loss as low as 0.69dB and as high as 1.16dB within the bandwidth. The lower stopband rejection is below -21dB, and the upper stopband rejection is below -17dB in the range of 31.98GHz-60GHz. This achieves extremely low-loss signal transmission within the millimeter-wave band while maintaining excellent out-of-band suppression, effectively improving signal transmission efficiency.

[0069] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments, including components, without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A miniaturized, low-loss LTCC millimeter-wave bandpass filter, characterized in that, The device includes a ceramic body (1) and an external electrode, the external electrode being embedded outside the ceramic body. The ceramic body (1) includes an LTCC ceramic dielectric substrate (101) and an internal electrode embedded within the LTCC ceramic dielectric substrate (101). The internal electrode includes a top metal plate (102), a source terminal (105), a load terminal (106), a first resonator (107), a third resonator (108), a second resonator (109), a bottom metal plate (110), and a grounding post (113). The source terminal (105) and the load terminal (106) are arranged symmetrically and located below the top metal plate (102). 5) and the load end (106) are connected to the external electrode through the input feed metal plate (103) and the output feed metal plate (104) respectively. The two ends of the two grounding posts (113) are connected to the top metal plate (102) and the bottom metal plate (110) respectively. The first resonator (107) and the third resonator (108) are arranged in a symmetrical structure and are located below the source end (105) and the load end (106) respectively. One end of the first resonator (107) and the third resonator (108) are connected to the two grounding posts (113) respectively. The second resonator (109) is located above the bottom metal plate (110).

2. The miniaturized low-loss LTCC millimeter-wave bandpass filter according to claim 1, characterized in that, The first resonator (107) and the third resonator (108) are both quarter-wavelength stepped impedance resonators.

3. The miniaturized low-loss LTCC millimeter-wave bandpass filter according to claim 1, characterized in that, The second resonator (109) is a half-wavelength stepped impedance resonator.

4. The miniaturized low-loss LTCC millimeter-wave bandpass filter according to claim 1, characterized in that, The dielectric constant of the LTCC ceramic dielectric substrate (101) is 7.5, and the loss tangent is 0.

002.

5. A miniaturized low-loss LTCC millimeter-wave bandpass filter according to claim 1, characterized in that, The external electrode includes an input electrode (2), an output electrode (3), and a ground electrode (4). The input electrode (2) and the output electrode (3) are arranged symmetrically on the left and right sides of the ceramic body (1), and the two ground electrodes (4) are arranged symmetrically on the front and rear sides of the ceramic body (1).

6. A miniaturized low-loss LTCC millimeter-wave bandpass filter according to claim 5, characterized in that, The source end (105) is connected to the input electrode (2) through the input feed metal plate (103), and the load end (106) is connected to the output electrode (3) through the output feed metal plate (104).

7. A miniaturized, low-loss LTCC millimeter-wave bandpass filter according to claim 1, characterized in that, The internal electrode also includes shielding units arranged symmetrically on both sides of the source end (105) and the load end (106).

8. A miniaturized low-loss LTCC millimeter-wave bandpass filter according to claim 7, characterized in that, The shielding unit includes several shielding columns (112) and three shielding metal layers. The top of the shielding column (112) is connected to the top metal plate (102), and the bottom of the shielding column (112) is connected to the bottom metal plate (110). The three shielding metal layers are installed on the shielding column (112) from top to bottom.

9. A miniaturized low-loss LTCC millimeter-wave bandpass filter according to claim 1, characterized in that, A grounding substrate (111) is provided on the bottom side of the LTCC ceramic dielectric substrate (101).

10. A miniaturized low-loss LTCC millimeter-wave bandpass filter according to claim 1, characterized in that, Both the outer and inner electrodes are made of silver.

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