LTCC-based dual-frequency band-pass filter

Abstract

The invention provides a dual-frequency band-pass filter based on LTCC (Low Temperature Co-Fired Ceramic), which relates to the technical field of microwave and millimeter wave circuits and systems and adopts a combined design of a U-shaped resonant structure and an E-shaped resonant structure. And efficient frequency band selection and bandwidth control are realized between the first resonator and the second resonator and between the third resonator and the fourth resonator. Due to the multi-point coupling design among the resonators, the filter can generate a plurality of transmission zero points, the out-of-band suppression effect is greatly improved, and it is ensured that noise and interference signals of the filter in the out-of-band frequency band are effectively suppressed; the adjustable function of the high-frequency-band center frequency of the dual-frequency band-pass filter can be achieved by adjusting the length and the width of the open-circuit branch line of the E-type resonator.

Description

Technical Field

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

[0002] Dual-bandpass filters are mainly used for the selective transmission of multi-band signals. Their initial development was to meet the needs of simultaneous processing of signals in different frequency bands in wireless communication equipment. However, with the improvement of frequency band utilization and signal quality requirements in modern communication systems, traditional filters have been unable to meet the requirements of high selectivity, low insertion loss, miniaturization and low cost in multi-band transmission. Therefore, in the fields of communication equipment, radar systems and satellite communications, the demand for high-performance dual-bandpass filters is increasing.

[0003] LTCC (Low Temperature Co-fired Ceramic) technology is widely used in the design and manufacture of high-frequency filters due to its excellent dielectric properties and high integration. The LTCC process allows passive components (such as inductors and capacitors) to be integrated into the ceramic substrate, thereby achieving miniaturization of the circuit and optimizing performance. However, the design of filters based on LTCC still faces some challenges, especially in the development of multi-band filters. However, despite the huge application potential of LTCC technology in high-frequency circuits, the design of dual-band bandpass filters based on LTCC still faces multiple technical difficulties. First, the complexity of dual-band filter design is mainly reflected in how to achieve precise tuning and bandwidth control of the two frequency bands. The resonator layout in the LTCC structure requires frequency selection through compact design in a limited space, which not only increases the difficulty of design, but also makes the electromagnetic coupling between different frequency bands more difficult to control. In order to ensure the effect of out-of-band signal suppression, the configuration of resonators and coupling elements in the LTCC substrate must be optimized to reduce interference with in-band transmission signals.

[0004] Secondly, although the high dielectric constant of LTCC can improve the performance of the filter, it is still necessary to overcome the problem of enhanced coupling effect caused by miniaturization design when realizing multi-band characteristics. Due to the narrow line spacing in the limited LTCC substrate space structure, the resonant structure is prone to performance deviation due to processing errors, thus affecting the bandwidth consistency and frequency stability of the dual-band filter. Especially for dual-band filters with complex structures, even small dimensional deviations during the manufacturing process may have a significant impact on the performance of the overall filter.

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

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

[0007] To achieve the above object, the present invention adopts the following technical solutions: A dual-frequency bandpass filter based on LTCC, comprising: a dielectric substrate, an input coupling feed line Lin printed on the upper surface of the dielectric substrate, an output coupling feed line Lout, a first resonator L1, a second resonator L2, a third resonator L3 and a fourth resonator L4, and a metal ground plate GND arranged at the bottom of the dielectric substrate; Among them, one end of the input coupling feed line Lin is configured at the first boundary of the dielectric substrate, one end of the output coupling feed line Lout is configured at the second boundary of the dielectric substrate, the other end of the input coupling feed line Lin and the other end of the output coupling feed line Lout are respectively connected to the first resonator L1 and the second resonator L2, the third resonator L3 is combined with the fourth resonator L4 to achieve magnetic coupling, the first resonator L1 is combined with the third resonator L3 to achieve electrical coupling, and the second resonator L2 is combined with the fourth resonator L4 to achieve electrical coupling.

[0008] In summary, the LTCC-based dual-band pass filter adopts a combination design of a U-type resonant structure (L1, L2) and an E-type resonant structure (L3, L4), and realizes efficient frequency band selection and bandwidth control between the first resonator L1, the second resonator L2 and the third resonator L3, the fourth resonator L4 through electromagnetic coupling between the resonators. The multi-point coupling design between multiple resonators enables the filter to generate multiple transmission zeros, greatly improving the out-of-band suppression effect, ensuring that the noise and interference signals of the filter in the out-of-band frequency band are effectively suppressed; the adjustable function of the high-frequency center frequency of the dual-band pass filter can be realized by adjusting the length and width of the open branch line of the E-type resonator.

[0009] Compared with the prior art, the dual-bandpass filter based on LTCC has the following advantages: 1. An open-circuit branch line is loaded on the basis of two U-shaped microstrip lines to form an E-type resonator. The passband range of the dual-bandpass filter can be adjusted by changing the length of the loaded open-circuit branch line, and the bandwidth remains basically unchanged. 2. Using a high dielectric constant ( _r = 11.8) LTCC substrate, which greatly improves the filter's ability to achieve high-frequency operation in a small size, while reducing the generation of parasitic modes. 3. The multi-point coupling design between resonators enables the filter to generate multiple transmission zeros, greatly improving the out-of-band suppression effect and ensuring that the noise and interference signals of the filter in the out-of-band frequency band are effectively suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 1 is a schematic diagram of the overall structure of a dual-frequency bandpass filter based on LTCC provided in an embodiment of the present invention; Figure 2It is a microstrip line structure diagram of the upper surface of the LTCC dielectric substrate of the LTCC-based dual-frequency bandpass filter provided by an embodiment of the present invention; Figure 3 It is a microstrip line structure diagram of the upper surface of the LTCC dielectric substrate of the LTCC-based dual-frequency bandpass filter provided by an embodiment of the present invention; Figure 4 It is an S-curve diagram when the strip lines L33 and L43 of the LTCC-based dual-frequency bandpass filter provided by an embodiment of the present invention are 15.5 mm long and 0.54 mm wide; Figure 5 It is a diagram S11 showing the length variation when the strip lines L33 and L43 of the LTCC-based dual-frequency bandpass filter provided by an embodiment of the present invention are 0.54 mm wide; Figure 6 It is a diagram S21 showing the length variation when the strip lines L33 and L43 of the LTCC-based dual-frequency bandpass filter provided by an embodiment of the present invention are 0.54 mm wide; Figure 7 It is a graph S11 when the strip lines L33 and L43 of the LTCC-based dual-frequency bandpass filter provided by an embodiment of the present invention are 15.5 mm long and the width is changed; Figure 8 FIG. S21 is a diagram showing a change in width of the strip lines L33 and L43 of the LTCC-based dual-frequency bandpass filter provided in an embodiment of the present invention when the length is 15.5 mm. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0012] refer to Figures 1 to 8 As shown, the first embodiment of the present invention discloses a dual-frequency bandpass filter based on LTCC, which includes: a dielectric substrate 1, an input coupling feed line Lin printed on the upper surface of the dielectric substrate 1, an output coupling feed line Lout, a first resonator L1, a second resonator L2, a third resonator L3 and a fourth resonator L4, and a metal ground plate GND arranged at the bottom of the dielectric substrate 1; Among them, one end of the input coupling feed line Lin is configured at the first boundary of the dielectric substrate 1, one end of the output coupling feed line Lout is configured at the second boundary of the dielectric substrate 1, the other end of the input coupling feed line Lin and the other end of the output coupling feed line Lout are respectively connected to the first resonator L1 and the second resonator L2, the third resonator L3 is combined with the fourth resonator L4 to achieve magnetic coupling, the first resonator L1 is combined with the third resonator L3 to achieve electrical coupling, and the second resonator L2 is combined with the fourth resonator L4 to achieve electrical coupling.

[0013] Preferably, the dielectric substrate 1 uses a low temperature co-fired ceramic LTCC substrate.

[0014] Specifically, in this embodiment, the LTCC-based dual-frequency bandpass filter includes an LTCC substrate, an input / output coupling feed line Lin / Lout, four resonators, and a metal ground plate GND, wherein the magnetic coupling effect between the E-type resonant structures (L3, L4) and the electrical coupling effect of the E-type resonant structure (L3, L4) on the first resonator L1 and the second resonator L2 are utilized to realize a dual-frequency bandpass filter with adjustable center frequency.

[0015] Preferably, the relative dielectric constant of the low temperature co-fired ceramic (LTCC) substrate is in the range of 9.3 to 11.8, and the total thickness of the substrate is greater than or equal to 0.4 mm.

[0016] In this embodiment, the LTCC substrate has a relative dielectric constant of 11.8, a total thickness of 0.6 mm, and a number of process layers of 6. That is, the LTCC substrate uses RO4003 material with a relative dielectric constant of 11.8 and a thickness of 0.6 mm.

[0017] Preferably, the first resonator L1 is composed of three strip lines, namely, a first strip line L11 of the first resonator L1, a second strip line L12 of the first resonator L1 and a third strip line L13 of the first resonator L1, wherein the first strip line L11 of the first resonator L1 is connected to the input coupling feed line Lin, and a preset gap is left between the second strip line L12 of the first resonator L1 and the third strip line L13 of the first resonator L1 for printing the strip line of the third resonator L3, so as to realize electrical coupling between the first resonator L1 and the third resonator L3.

[0018] Preferably, the first resonator L1 and the second resonator L2 are spatially symmetrically integrated on both sides of the dielectric substrate 1, the first resonator L1 and the second resonator L2 are both U-shaped resonators, the first stripline L11 of the first resonator L1 is perpendicular to the second stripline L12 of the first resonator L1 and the third stripline L13 of the first resonator L1, the second stripline L12 of the first resonator L1 and the third stripline L13 of the first resonator L1 have the same size, the first stripline L21 of the second resonator L2 is perpendicular to the second stripline L22 of the second resonator L2 and the third stripline L23 of the second resonator L2, and the second stripline L22 of the second resonator L2 and the third stripline L23 of the second resonator L2 have the same size.

[0019] Preferably, the input coupling feed line Lin and the output coupling feed line Lout are made into microstrip lines by screen printing and integrated on the upper surface of the dielectric substrate 1, the left port of the input coupling feed line Lin is arranged at the first boundary of the dielectric substrate 1, the right port of the input coupling feed line Lin is connected to the first stripline L11 of the first resonator L1, the right port of the output coupling feed line Lout is arranged at the second boundary of the dielectric substrate 1, and the left port of the output coupling feed line Lout is connected to the first stripline L21 of the second resonator L2.

[0020] In this embodiment, the input coupling feed line Lin and the output coupling feed line Lout are made into microstrip lines by screen printing and integrated into the LTCC substrate. The left port of the input coupling feed line Lin is located at the boundary of the LTCC substrate, and the right port is connected to the strip line L11 of the first resonator L1; the right port of the output coupling feed line Lout is located at the boundary of the LTCC substrate, and the left port is connected to the strip line L21 of the second resonator L2. The first resonator L1 and the second resonator L2 are U-shaped resonators, and their strip lines L11 and L21 are perpendicular to the strip lines L12 and L13, L22 and L23 respectively, and L12 and L13 have the same size. One end of the input coupling feed line Lin and the output coupling feed line Lout are located at the boundary of the LTCC substrate, and the other end is connected to the first resonator L1 and the second resonator L2 respectively. The input coupling feed line Lin and the output coupling feed line Lout are located on both sides of the LTCC substrate and have the same size. The first resonator L1 and the second resonator L2 have the same size. One end of the first resonator L1 and the second resonator L2 are respectively connected to the input coupling feed line Lin and the output coupling feed line Lout to realize electrical coupling with the third resonator L3 and the fourth resonator L4.

[0021] The third resonator L3 and the fourth resonator L4 are designed to have the same size. The third resonator L3 and the fourth resonator L4 are E-type resonators, specifically resonators loaded with open branch lines. The third resonator L3 is electrically coupled with the first resonator L1 on the left side and magnetically coupled with the fourth resonator L4 on the right side. The fourth resonator L4 is magnetically coupled with the third resonator L3 on the left side and electrically coupled with the second resonator L2 on the right side.

[0022] In this embodiment, the first resonator L1 and the second resonator L2 are integrated on the LTCC substrate by screen printing. The first resonator L1 is composed of three strip lines, a strip line L11 that is colinear with the input coupling feed line Lin and has the same size as the input coupling feed line Lin and is connected to the input coupling feed line Lin, and two strip lines L12 and L13 that are perpendicular to the strip line that is colinear with the input coupling feed line Lin and has the same size as the input coupling feed line Lin. A gap is left between the strip lines L12 and L13 for printing the strip line L31 of the third resonator L3, so as to realize the electrical coupling between the first resonator L1 and the third resonator L3. The second resonator L2 has the same structure and size as the first resonator L1, and is spatially symmetrically integrated with the first resonator L1 on both sides of the LTCC substrate.

[0023] Preferably, the third resonator L3 and the fourth resonator L4 are both E-type resonators, the second stripline L32 of the third resonator L3 is perpendicular to the first stripline L31 of the third resonator L3, the third stripline L33 of the third resonator L3, and the fourth stripline L34 of the third resonator L3, the first stripline L31 of the third resonator L3 and the fourth stripline L34 of the third resonator L3 have the same size, the second stripline L42 of the fourth resonator L4 is perpendicular to the first stripline L41 of the fourth resonator L4, the third stripline L43 of the fourth resonator L4, and the fourth stripline L44 of the fourth resonator L4, and the first stripline L41 of the fourth resonator L4 and the fourth stripline L44 of the fourth resonator L4 have the same size.

[0024] Preferably, the third resonator L3 and the fourth resonator L4 are made into microstrip lines by screen printing and integrated on the upper surface of the dielectric substrate 1 .

[0025] Preferably, the third resonator L3 is composed of four strip lines, namely a first strip line L31 of the third resonator L3, a second strip line L32 of the third resonator L3, a third strip line L33 of the third resonator L3 and a fourth strip line L34 of the third resonator L3, wherein the first strip line L31 located on the left side of the third resonator L3 is spatially perpendicular to the input coupling feed line Lin, and is arranged between the second strip line L22 of the second resonator L2 and the third strip line L23 of the second resonator L2, so as to realize electrical coupling of the third resonator L3 with the first resonator L1.

[0026] Preferably, the second stripline L32 located at the bottom of the third resonator L3 is vertically connected to the first stripline L31 of the third resonator L3, and is connected to the third stripline L33 of the third resonator L3 and the fourth stripline L34 of the third resonator L3, the third stripline L33 of the third resonator L3 is parallel to the first stripline L31 of the third resonator L3, the third stripline L33 of the third resonator L3 is longer than the first stripline L31 of the third resonator L3 and the fourth stripline L34 of the third resonator L3, the fourth stripline L34 located on the right side of the third resonator L3 is parallel to the first stripline L31 of the third resonator L3 and has the same size, and in space, the first stripline L31 of the third resonator L3 and the fourth stripline L34 of the third resonator L3 form a symmetrical structure with the third stripline L33 of the third resonator L3 as the symmetry axis.

[0027] In this embodiment, the third resonator L3 and the fourth resonator L4 are E-type resonators. The strip lines L32 and L42 are perpendicular to the strip lines L31, L33, L34, and L41, L43, L44, respectively. L31 and L34 have the same size, and L41 and L44 have the same size. Figure 2 and Figure 3 The overall structure of the filter is mirror-symmetric with respect to the axis AA′. The third resonator L3 and the fourth resonator L4 are integrated by screen printing. The E-type resonator is composed of 4 strip lines. The left strip line L31 is perpendicular to the input coupling feed line Lin in space and is located between the strip lines L22 and L23, so that the third resonator L3 forms an electric coupling structure with the first resonator L1; the bottom strip line L32 is perpendicular to the strip line L31 and is connected to L33 and L34; the open branch strip line L33 is parallel to the strip line L31 and is located in the middle of the third resonator L3. The open branch strip line L33 is longer than L31 and L34; the right strip line L34 is parallel to L31 and has the same size. In space, L34 and L31 form a symmetrical structure with L33 as the symmetry axis; the fourth resonator L4 has the same structure and size as the third resonator L3.

[0028] In this embodiment, the design steps of the LTCC-based dual-frequency bandpass filter are as follows: first, confirm the branch length of the resonator loaded with the open branch line according to the design requirements; the air gap width for realizing magnetic coupling between the third resonator L3 and the fourth resonator L4; confirm the electrical length of each resonator and the passband center frequency of the designed filter. Secondly, provide a low-temperature co-fired ceramic LTCC substrate with a dielectric constant of 11.8, a total thickness of the substrate of 0.6mm, and a number of process layers of 6 layers. Thirdly, integrate microstrip lines on the upper surface of the substrate by screen printing to form input coupling feed line Lin, output coupling feed line Lout and the first resonator L1, the second resonator L2, the third resonator L3, and the fourth resonator L4. Finally, a copper metal ground plane GND is mounted on the bottom surface of the LTCC substrate.

[0029] Specifically, in this embodiment, the structure of the upper surface of the LTCC substrate is as follows: Figure 2 As shown, the input coupling feed line Lin and the output coupling feed line Lout are both 50Ω impedance line widths to ensure impedance matching of the feeding port; the input coupling feed line Lin and the output coupling feed line Lout are 0.84mm long and 0.4845mm wide; the first resonator L1 strip line L11 is 0.74mm long and 0.2mm wide, colinear with the input coupling feed line Lin, the strip lines L12 and L13 are 9.05mm long and 0.20mm wide, perpendicular to the strip line L11, and a gap S1=0.48mm is left between the two lines; the third resonator L3 strip line L31 is 9.2mm long and 0.2mm wide m, located between the strip lines L12 and L13 to electrically couple the third resonator L3 with the first resonator L1, leaving a gap of 0.14mm with L12 and L13, the strip line L32 is 6.44mm long and 0.26mm wide, perpendicular to L31, L33, and L34, the strip line L33 is 15.5mm long and 0.54mm wide, the length and width of L33 and L43 can be changed during screen printing according to the application scenario requirements to achieve the purpose of adjusting the dual passband frequency, the strip line L34 has the same size as L31, and a gap S2=0.14mm is left between L34 and the strip line L41 of the fourth resonator L4.

[0030] The U-shaped resonator (L1, L2): The U-shaped resonator is composed of strip lines L11, L12 and L13, and L11 is colinear with the input coupling feeder. This structure helps to achieve effective transmission and coupling of the input signal. L12 and L13 are perpendicular to L11, forming a compact U-shaped structure. The combination of the distance from the input coupling feeder and the strip line size determines the resonant frequency of the first frequency band. L1 and L2 are the main resonators, corresponding to the low frequency band of the filter, and realize frequency selection with the third resonator L3 and the fourth resonator L4 through an electrical coupling mechanism.

[0031] The E-type resonator (L3, L4): The design of the E-type resonator enables it to simultaneously support signal transmission in two frequency bands with large differences. L3 is composed of strip lines L31, L32, L33 and L34, where L31 is located between L12 and L13, forming a strong electrical coupling. The length of L33 is adjustable, and the high-frequency band response of the filter can be adjusted by changing the design dimensions in the screen printing process. By adjusting the length of L33, the center frequency of the second frequency band can be changed while keeping other parameters unchanged, so that the filter can adapt to different high-frequency scenarios.

[0032] In summary, the dual-band bandpass filter based on LTCC realizes the design of dual-band bandpass filter through the combination of U-type and E-type resonators, with precise electrical coupling mechanism and adjustable stripline. This filter can not only meet the needs of modern wireless communication systems for multi-band signal processing, but also effectively reduce insertion loss and enhance the out-of-band selectivity and common-mode rejection performance of the filter through structural optimization and impedance matching technology.

[0033] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A dual-frequency bandpass filter based on LTCC, characterized in that: include: A dielectric substrate, an input coupling feed line, an output coupling feed line, a first resonator, a second resonator, a third resonator and a fourth resonator printed on the upper surface of the dielectric substrate, and a metal ground plate disposed at the bottom of the dielectric substrate; One end of the input coupling feeder is configured at a first boundary of the dielectric substrate, one end of the output coupling feeder is configured at a second boundary of the dielectric substrate, the other end of the input coupling feeder and the other end of the output coupling feeder are connected to the first resonator and the second resonator respectively, the third resonator is combined with the fourth resonator to achieve magnetic coupling, the first resonator is combined with the third resonator to achieve electrical coupling, and the second resonator is combined with the fourth resonator to achieve electrical coupling.

2. The LTCC-based dual-frequency bandpass filter according to claim 1, characterized in that: The dielectric substrate uses a low temperature co-fired ceramic LTCC substrate.

3. The LTCC-based dual-frequency bandpass filter according to claim 1, characterized in that: The first resonator and the second resonator are symmetrically integrated on two sides of the dielectric substrate, and both the first resonator and the second resonator are U-shaped resonators.

4. The LTCC-based dual-frequency bandpass filter according to claim 1, characterized in that: The first strip line of the first resonator is connected to the input coupling feed line, and a preset gap is left between the second strip line of the first resonator and the third strip line of the first resonator for printing the strip line of the third resonator to achieve electrical coupling between the first resonator and the third resonator.

5. The LTCC-based dual-frequency bandpass filter according to claim 1, characterized in that: The first stripline of the second resonator is connected to the output coupling feed line, and a preset gap is left between the second stripline of the second resonator and the third stripline of the second resonator for printing the stripline of the fourth resonator to achieve electrical coupling between the second resonator and the fourth resonator.

6. The LTCC-based dual-frequency bandpass filter according to claim 1, characterized in that: The input coupling feed line and the output coupling feed line are microstrip lines with a characteristic impedance of 50 ohms.

7. The LTCC-based dual-frequency bandpass filter according to claim 1, characterized in that: The third resonator and the fourth resonator are both E-type resonators.

8. The LTCC-based dual-frequency bandpass filter according to claim 7, characterized in that: The first strip line on the left side of the third resonator is vertical to the input coupling feed line in space and is printed between the second strip line and the third strip line of the first resonator to achieve electrical coupling between the third resonator and the first resonator, and the fourth microstrip line on the right side of the third resonator achieves magnetic coupling with the fourth microstrip line on the left side of the fourth resonator.

9. The LTCC-based dual-frequency bandpass filter according to claim 7, characterized in that: The first strip line on the right side of the fourth resonator is vertical to the output coupling feed line in space and is printed between the second strip line and the third strip line of the second resonator to achieve electrical coupling between the third resonator and the second resonator, and the fourth microstrip line on the left side of the fourth resonator achieves magnetic coupling with the fourth microstrip line on the left side of the third resonator.

10. The LTCC-based dual-frequency bandpass filter according to claim 1, characterized in that: The input coupling feed line, the output coupling feed line, the first resonator, the second resonator, the third resonator and the fourth resonator are mirror-symmetric about the axis AA′.

Images