A suspended stripline high-pass filter based on alumina ceramic technology

Abstract

The present invention belongs to the technical field of microwave electronic components, and discloses a suspended stripline high-pass filter based on alumina ceramic technology, including an upper conductor, a lower conductor, a metal ground layer and a dielectric substrate; the suspended stripline high-pass filter based on alumina ceramic technology is successively the upper conductor, the lower conductor and the metal ground layer from top to bottom, and dielectric substrates are respectively arranged between the upper conductor, the lower conductor, the lower conductor and the metal ground layer. The present invention uses two layers of alumina ceramic substrates to realize the suspended stripline structure, which has no external radiation under ideal conditions, and realizes the miniaturization, light weight and low cost of its structure while achieving broadband low loss of the filter.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave electronic components, and particularly relates to a suspended stripline high-pass filter based on alumina ceramic technology. Background Art

[0002] Microwave filters are important components in microwave circuit systems and are also one of the microwave passive devices with the highest technical content. Their main function is to extract, separate, and suppress interference of signals. Microwave filters are widely used in fields such as wireless communication, navigation, and telemetry. A microwave high-pass filter is a microwave passive device that allows high-frequency signals to pass through and suppresses low-frequency signals. Since the filter structure at microwave frequencies generally has a periodic frequency response, there is no ideal high-pass filter response. Usually, a broadband band-pass filter in the microwave band can be used as a high-pass filter, that is, a pseudo-high-pass filter. Common pseudo-high-pass filters use microstrip or other open transmission line structures, but it is difficult for such pseudo-high-pass filters to achieve excellent high-Q values. The pseudo-high-pass filter using a traditional suspended line has a three-layer medium structure: an upper air layer, a dielectric layer, and a lower air layer. The conventional method for realizing a suspended stripline pseudo-high-pass filter is to print a conductor on a dielectric substrate, use a double-sided overlapping layout of metal patterns to realize the series capacitance of the high-pass filter, use a high-impedance line to ground to realize the parallel inductance, and then embed the dielectric substrate in a metal housing. The disadvantages of this structure are obvious: due to the metal cavity, a fastening structure generally needs to be designed, and it is difficult to achieve miniaturization of the volume. Taking a 6 - 18 GHz traditional suspended line high-pass filter as an example, its typical volume reaches 47 mm × 20 mm × 8.6 mm, which is difficult to meet the requirements of high-density integrated applications. The pseudo-high-pass filter realized by silicon-based MEMS technology has a small volume and good performance. However, its chip cost is high, the process is complex, and the cost performance is low. The pseudo-high-pass filter realized by IPD technology has a small volume, but the out-of-band rejection at the proximal end is difficult to meet the usage requirements in broadband communication systems. The rejection at 1 GHz away from the edge is within 10 dB (usually, the rejection at 1 GHz away from the sideband is required to be above 35 dBc), and the cost is also high.

[0003] Through the above analysis, the problems and defects existing in the prior art are as follows:

[0004] (1) It is difficult for a pseudo-high-pass filter using a microstrip or other open transmission line structure to achieve excellent high-Q values;

[0005] (2) The volume of a traditional suspended microstrip line pseudo-high-pass filter is large and it is difficult to meet the requirements of high-density integrated applications;

[0006] (3) The chip cost of a pseudo-high-pass filter using silicon-based MEMS technology is high, the process is complex, and the cost performance is low;

[0007] (4) The pseudo-high-pass filter implemented using the IPD process is small in size but difficult to meet the out-of-band rejection requirements and is costly. Summary of the Invention

[0008] In view of the above technical problems existing in the existing high-pass filters, the present invention proposes a non-traditional suspended stripline high-pass filter based on alumina ceramic technology, which realizes miniaturization, light weight, and low cost of its structure while achieving high out-of-band rejection with wideband and low loss of the filter.

[0009] The present invention is implemented as follows. A suspended stripline high-pass filter based on alumina ceramic technology includes:

[0010] an upper conductor, a lower conductor, a dielectric substrate, and a metal ground layer;

[0011] The suspended stripline high-pass filter is sequentially an upper conductor, a lower conductor, and a metal ground layer from top to bottom, and dielectric substrates are respectively provided between the upper conductor and the lower conductor, and between the lower conductor and the metal ground layer.

[0012] Further, the high-impedance line is equivalent to an inductor, and the low-impedance line is equivalent to a capacitor.

[0013] Further, the first transmission line of the upper conductor is connected to the second transmission line of the upper conductor, and this second transmission line serves as a microstrip high-impedance shorting stub and is grounded through a metallized via.

[0014] Further, the first transmission line of the upper conductor is coupled to the third transmission line of the lower conductor and is equivalent to a series capacitor.

[0015] Further, the third transmission line of the lower conductor is side-connected to the fourth transmission line and the fifth transmission line of the lower conductor. The fourth transmission line is a high-impedance transmission line, and the fifth transmission line is a low-impedance transmission line. The fourth and fifth transmission lines together form a stepped-impedance resonator, which is used to be equivalent to a series resonance of an inductor and a capacitor.

[0016] Further, the third transmission line of the lower conductor is coupled to the sixth transmission line of the upper conductor and is equivalent to a series capacitor.

[0017] Further, the sixth transmission line of the upper conductor is side-connected to the seventh transmission line of the upper conductor. The seventh transmission line is connected to the eighth transmission line of the lower conductor through a metallized via. Among them, the seventh transmission line is a high-impedance line, and the eighth transmission line is a low-impedance line. They are connected through a metallized via to form a stepped-impedance resonator, which is equivalent to a series resonance of an inductor and a capacitor.

[0018] Further, symmetrically arranged at the center position of the sixth transmission line of the upper conductor are the same upper conductor transmission line and lower conductor transmission line of another layer, making the filter structure symmetric.

[0019] Furthermore, alumina ceramic dielectric substrates are respectively used between the upper conductor and the lower conductor, and between the lower conductor and the metal ground layer, with a dielectric constant of 9.8.

[0020] Furthermore, the lower conductor is provided with four pads, which are connected to the metal ground layer through metallized vias, making the connection between the upper and lower conductors firm.

[0021] Combined with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0022] First, in view of the technical problems existing in the above prior art and the difficulty of solving this problem, closely combining the technical solutions to be protected by the present invention and the results and data in the R & D process, etc., analyze in detail and profoundly how the technical solutions of the present invention solve the technical problems and the creative technical effects brought after solving the problems. The specific description is as follows:

[0023] The suspended stripline high-pass filter based on alumina ceramic process provided by the present invention uses two layers of alumina ceramic substrates to realize a non-traditional suspended stripline structure. Under the condition of achieving the same performance as similar products, it can achieve lower cost and smaller area.

[0024] The present invention adopts a non-traditional suspended stripline transmission structure. Compared with the traditional suspended stripline, the volume of the upper and lower air cavities is removed, the large inter-cavity crosstalk is eliminated, and the volume of the overall filter is reduced. It has the advantages of wide passband bandwidth, small volume, low insertion loss, low cost, etc. consistent with the traditional suspended stripline; at the same time, the double-layer alumina ceramic process is adopted to further reduce the filter area and cost.

[0025] Second, regarding the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are specifically described as follows:

[0026] The structure of the present invention is simple and compact, with a small area and easy to process. By using stepped impedance resonators, the size of the resonators is effectively reduced. It is not only more compact in structure and smaller in volume, realizing the miniaturization of the ultra-wideband filter, but also convenient for integration with peripheral circuits in the application of the suspended stripline filter.

[0027] The present invention has a high degree of integration. The present invention fixes the first stepped impedance resonators 14 and 15 and the third stepped impedance resonators 17 and 18 on the upper surface of the underground layer dielectric substrate 19. The upper conductor seventh transmission line 5 of the second resonator is fixed on the upper surface of the upper layer dielectric substrate 9 and is connected to the lower conductor eighth transmission line 15 fixed on the upper surface of the lower layer dielectric substrate 19 through the metallized via 6, with a high degree of integration.

[0028] The present invention adopts the elliptic function filter synthesis method to obtain a lumped parameter model, and maps it to a specific physical structure through the LC lumped parameter model, solving the problem that the traditional mapping method for designing filters is not flexible enough and cannot generate transmission zeros at arbitrary positions, shortening the research and development cycle and improving the R & D efficiency.

[0029] The present invention has good expandable characteristics and high out-of-band rejection. The first step impedance resonator 54 of the lower conductor and the second step impedance resonator 55 of the lower conductor adopted by the present invention are divided into two parts. The high impedance line part is the fourth transmission line 14 of the lower conductor, the twelfth transmission line 17 of the lower conductor, and the low impedance line part is the fifth transmission line 13 of the lower conductor, the thirteenth transmission line 18 of the lower conductor, and they are all fixed on the upper surface of the lower dielectric substrate 19. The hybrid resonator 53 is divided into three parts. The low impedance line part is the eighth transmission line 15 of the lower conductor, the metallized via hole 6 connecting the upper conductor and the lower conductor, and the high impedance line is the seventh transmission line 5 of the upper conductor. Among them, the low impedance line part is connected to the high impedance line part fixed on the upper surface of the lower dielectric substrate 19 through the metallized via holes 6 at both ends of the upper dielectric substrate 9 to form a hybrid resonance. The out-of-band rejection characteristics can be significantly improved by increasing the filter order according to the actual index requirements. Compared with ordinary microstrip filters, the adjustability is very good.

[0030] Third, as the creative auxiliary evidence of the claims of the present invention, it is also reflected in the following important aspects:

[0031] The technical solution of the present invention fills the technical gaps at home and abroad in the industry:

[0032] The present invention for the first time uses a double-layer alumina ceramic thin film material as the dielectric substrate of a non-traditional suspended stripline to design a suspended stripline high-pass filter. This material has the advantages of heat resistance, low dielectric loss, low cost, strong mechanical properties, stable chemical properties, etc. The traditional suspended stripline structure has an upper air cavity, a dielectric layer, and a lower air cavity. Due to the need for a metal cavity, a fastening structure generally needs to be designed, so it is difficult to achieve miniaturization. The present invention overcomes the disadvantages of the traditional suspended stripline and realizes miniaturization. Its volume is only one-eighth of that of the traditional suspended microstrip structure. The pseudo high-pass filter fabricated by the silicon-based MEMS process can achieve miniaturization, but its manufacturing process requires photolithography, deposition, etching, doping, oxidation, diffusion, and implantation, etc. The process is complex, the mass production ability is weak, and the manufacturing cost is high. The present invention overcomes the disadvantages of the filter fabricated by the silicon-based MEMS process. Since the alumina ceramic substrate mainly uses alumina as the raw material, the content of alumina in nature is second only to alumina silicate and is very abundant. Moreover, this material has a high dielectric constant and a low loss tangent. While achieving miniaturization and high performance, it can also achieve low cost. The pseudo high-pass filter fabricated by the low-temperature co-fired ceramic (LTCC) process uses a multi-layer thick film process and can achieve miniaturization. However, its chip cost is also relatively high, the heat dissipation ability is weak, which affects the working stability, and the processing accuracy is low. The present invention overcomes the disadvantages of the LTCC process, with a mature process, low cost, and high processing accuracy. Description of the Drawings

[0033] Figure 1 is the circuit topology schematic diagram of the suspended stripline high-pass filter based on the alumina ceramic process provided by the embodiment of the present invention;

[0034] Figure 2 is the structural schematic diagram of the non-traditional suspended stripline used in the suspended stripline high-pass filter based on the alumina ceramic process provided by the embodiment of the present invention.

[0035] Figure 3 is the three-dimensional schematic diagram of the suspended stripline high-pass filter based on the alumina ceramic process provided by the embodiment of the present invention;

[0036] Figure 4 is the top view of the suspended stripline high-pass filter based on the alumina ceramic process provided by the embodiment of the present invention;

[0037] Figure 5 is the second-layer schematic diagram of the suspended stripline high-pass filter based on the alumina ceramic process provided by the embodiment of the present invention;

[0038] Figure 6 is the first-layer schematic diagram of the suspended stripline high-pass filter based on the alumina ceramic process provided by the embodiment of the present invention;

[0039] Figure 7It is a three-dimensional explosion schematic diagram of a suspended stripline high-pass filter based on alumina ceramic technology provided by an embodiment of the present invention;

[0040] Figure 8 It is a simulation insertion loss and return loss diagram of a suspended stripline high-pass filter based on alumina ceramic technology provided by an embodiment of the present invention.

[0041] In the figure: 1a, radio frequency signal input (output) port; 1b, radio frequency signal output (input) port; 1, the first transmission line of the upper conductor; 2, the second transmission line of the upper conductor; 3, the metallized via hole from the upper conductor to the metal ground layer; 4, the sixth transmission line of the upper conductor; 5, the seventh transmission line of the upper conductor; 6, the metallized via hole connecting the upper conductor and the lower conductor; 7, the ninth transmission line of the upper conductor; 8, the tenth transmission line of the upper conductor; 9, the dielectric substrate between the upper conductor and the lower conductor; 10, the pad; 11, the metallized via hole connecting the pad to the metal ground layer; 12, the third transmission line of the lower conductor; 13, the fifth transmission line of the lower conductor; 14, the fourth transmission line of the lower conductor; 15, the eighth transmission line of the lower conductor; 16, the eleventh transmission line of the lower conductor; 17, the twelfth transmission line of the lower conductor; 18, the thirteenth transmission line of the lower conductor; 19, the dielectric substrate between the lower conductor and the metal ground layer; 51, the first high-impedance line; 52, the second high-impedance line; 53, the hybrid resonator; 54, the first stepped-impedance resonator of the lower conductor; 55, the second stepped-impedance resonator of the lower conductor; 100, the upper conductor; 101, the lower conductor; 102, the air-filled dielectric; 103, the bottom metal ground layer. Detailed implementation manners

[0042] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to 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.

[0043] This part is an explanatory embodiment that expands and explains the technical solutions of the claims in order to enable those skilled in the art to fully understand how the present invention is specifically implemented.

[0044] The suspended stripline high-pass filter based on alumina ceramic technology provided by the embodiments of the present invention includes a five-layer structure, which are, from top to bottom, an upper conductor, an intermediate dielectric substrate, a lower conductor, a lower dielectric substrate, and a bottom metal ground layer. The upper conductor is disposed on the upper surface of the intermediate dielectric substrate, and the lower conductor is disposed on the upper surface of the lower dielectric substrate and the lower surface of the intermediate dielectric substrate. The bottom metal ground layer is disposed on the lower surface of the lower dielectric substrate. In this embodiment, the dielectric substrate uses alumina ceramic material. The thickness of the intermediate dielectric substrate is 0.127 mm, the thickness of the lower dielectric substrate is 0.254 mm, the dielectric constant of the dielectric substrate is 9.8, the loss tangent is 0.002, the thickness of the upper conductor is 0.003 mm, and the thickness of the lower conductor is 0.01 mm.

[0045] As Figures 1 - 3 shown, the suspended stripline high-pass filter based on alumina ceramic technology adopts the design concept of elliptic function filter, combines Advanced Design system software to design and optimize lumped parameters, completes the design of the topological structure, and determines that the filter order is 9th order. Among them Figure 2 the non-traditional suspended line structure is, from top to bottom, an upper conductor 100, an intermediate dielectric substrate 9, a lower conductor 101, a lower dielectric substrate 19, a bottom metal ground layer 103, and an air layer filling medium 102 filled around the lower conductor. By using the non-traditional suspended stripline to simulate lumped elements, the high-pass filter with the non-traditional suspended stripline structure as shown in Figure 3 is obtained.

[0046] As Figure 1 , Figures 4 - 7As shown in the schematic diagram, a suspended stripline high-pass filter based on alumina ceramic technology is input through the first transmission line 1 of the upper conductor. The first high-impedance line 51 with a parallel microstrip shorting stub forms the first inductor L1. The first transmission line 1 of the upper conductor and the wide-side coupling of the third transmission line 12 of the lower conductor through the intermediate dielectric substrate 9 form the first capacitor C1. Further, the third transmission line 12 of the lower conductor is connected in parallel with the first stepped-impedance resonator 54 of the lower conductor, and the first stepped-impedance resonator of the lower conductor forms the second inductor L2 and the second capacitor C2. Further, the third transmission line 12 of the lower conductor and the wide-side coupling of the sixth transmission line 4 of the upper conductor through the intermediate dielectric substrate 9 form the third capacitor C3. Further, the sixth transmission line 4 of the upper conductor is connected in parallel with the hybrid resonator 53, which is composed of a section of the seventh transmission line 5 of the upper conductor connected to the eighth transmission line 15 of the lower conductor through the metallized vias 6 at both ends of the intermediate dielectric substrate 9, forming the third inductor L3 and the fourth capacitor C4. Further, the sixth transmission line 4 of the upper conductor and the wide-side coupling of the eleventh transmission line 16 of the lower conductor through the intermediate dielectric substrate 9 form the fifth capacitor C5. Further, the eleventh transmission line 16 of the lower conductor is connected in parallel with the second stepped-impedance resonator 55 of the lower conductor, and the second stepped-impedance resonator 55 of the lower conductor forms the fourth inductor L4 and the sixth capacitor C6. Further, the eleventh transmission line 16 of the lower conductor and the wide-side coupling of the ninth transmission line 7 of the upper conductor through the intermediate dielectric substrate 9 form the seventh capacitor C7. Further, the ninth transmission line 7 of the upper conductor is connected in parallel with the second high-impedance line 52 of the microstrip shorting stub to form the fifth inductor L5, and then outputs through the ninth transmission line 7 of the upper conductor. The main transmission path of the electromagnetic wave is mainly the first transmission line 1 of the upper conductor, the third transmission line 12 of the lower conductor, the sixth transmission line 4 of the upper conductor, the eleventh transmission line 16 of the lower conductor, and the ninth transmission line 7 of the upper conductor.

[0047] In order to prove the creativity and technical value of the technical solution of the present invention, this part is an application embodiment of the technical solution of the claim on a specific product or related technology.

[0048] The embodiment of the present invention can be applied to electromagnetic anti-interference technology, mainly in the occasion where the interference frequency is lower than the signal frequency. The present invention covers the C, X, and Ku bands, realizes ultra-wideband coverage, and has strong out-of-band suppression, and can effectively suppress the interference signals outside the passband of the filter. For example, there are narrowband interference signals with relatively high power such as 802.11a in the frequency band range of 5 GHz - 6 GHz. Due to the strong out-of-band suppression characteristics of the embodiment of the present invention, the embodiment of the present invention can be used to filter it well.

[0049] Some positive effects have been achieved during the research and development or use of the embodiments of the present invention, and it indeed has great advantages compared with the prior art. The following content will be described in combination with the data, charts, etc. of the test process.

[0050] The cut-off frequency of the suspended stripline high-pass filter based on alumina ceramic technology provided by the embodiments of the present invention is 6 GHz. The transmission line adopts a non-traditional suspended stripline structure, which has low loss, excellent temperature performance, and high-precision controllability in the process of production, achieving a higher Q value. At the same time, the embodiments of the present invention adopt a stepped impedance resonator to realize the series connection of capacitance and inductance and the alumina ceramic technology with a dielectric constant of 9.8, and the double-layer structure of the non-traditional suspended stripline makes the structure more compact, realizing miniaturization and low cost.

[0051] Use circuit simulation software to simulate the suspended stripline high-pass filter based on alumina ceramic technology provided by the embodiments of the present invention, and set the target center frequency to 12 GHz. Figure 8 The simulation results of its transmission coefficient and return loss are given. From Figure 8 it can be seen that its high-pass filtering effect is good and it has a very large bandwidth. The simulation result of its return loss shows that the return loss is less than -17 dB in the range of 6 GHz to 18 GHz. The simulation result of its transmission coefficient shows that the transmission coefficient S21 is greater than -3 dB in the range of 6 GHz to 8 GHz, and the transmission coefficient S21 is greater than -0.5 dB in the range of 8 GHz to 18 GHz. The size is only 6 mm × 4 mm × 0.394 mm.

[0052] The technical indicators obtained by simulation are as follows:

[0053] Frequency range: 6 GHz to 18 GHz

[0054] VSWR: <1.35:1

[0055] Out-of-band rejection: ≥28 dB @ 5.5 GHz;

[0056] ≥50 dB @ 5.5 GHz;

[0057] Insertion loss: ≤3 dB @ 6 GHz to 8 GHz;

[0058] ≤0.5 dB @ 8 GHz to 18 GHz.

[0059] In the description of the present invention, unless otherwise specified, "a plurality of" means two or more; the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation on the present invention. In addition, terms such as "first", "second", "third", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0060] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A suspended stripline high-pass filter based on alumina ceramic technology, characterized in that, Comprising: An upper conductor, a lower conductor, a metal ground layer, and a dielectric substrate; The suspension line high-pass filter based on the alumina ceramic process from top to bottom is an upper conductor, a lower conductor, and a metal ground layer in sequence, and dielectric substrates are respectively provided between the upper conductor and the lower conductor, and between the lower conductor and the metal ground layer; The third transmission line of the lower conductor is sequentially side-connected to the fourth transmission line and the fifth transmission line of the lower conductor. The fourth transmission line is a high-impedance transmission line, and the fifth transmission line is a low-impedance transmission line. The fourth and fifth transmission lines together form a stepped impedance resonator, which is used to equivalently represent the series resonance of an inductor and a capacitor; The sixth transmission line of the upper conductor is side-connected to the seventh transmission line of the upper conductor. The seventh transmission line is connected to the eighth transmission line of the lower conductor through a metallized via. The seventh transmission line is a high-impedance line, and the eighth transmission line is a low-impedance line. They are connected through a metallized via to form a stepped impedance resonator, which is equivalently represented as the series resonance of an inductor and a capacitor; Alumina ceramic dielectric substrates are respectively used between the upper conductor and the lower conductor, and between the lower conductor and the metal ground layer, and the dielectric constant is 9.

8.

2. The suspended stripline high-pass filter based on the alumina ceramic process according to claim 1, wherein The first transmission line of the upper conductor is connected to the second transmission line of the upper conductor. The second transmission line is used as a microstrip high-impedance short-circuit stub and is equivalently represented as a parallel inductor. The second transmission line is grounded through a via, and the inside of the via is metallized.

3. The suspension stripline high-pass filter based on alumina ceramic technology according to claim 1, characterized in that, The first transmission line of the upper conductor is coupled to the third transmission line of the lower conductor and is equivalently represented as a series capacitor.

4. The suspended stripline high-pass filter based on alumina ceramic technology according to claim 1, characterized in that, The third transmission line of the lower conductor is coupled to the sixth transmission line of the upper conductor and is equivalently represented as a series capacitor.

5. The suspended stripline high-pass filter based on alumina ceramic technology according to claim 2, wherein, Taking the central position of the sixth transmission line of the upper conductor as the symmetry point, the first transmission line of the upper conductor, the second transmission line of the upper conductor, the ninth transmission line of the upper conductor, and the tenth transmission line of the upper conductor are symmetrically arranged, and the third transmission line of the lower conductor, the fourth transmission line of the lower conductor, the fifth transmission line of the lower conductor, the eleventh transmission line of the lower conductor, the twelfth transmission line of the lower conductor, and the thirteenth transmission line of the lower conductor are symmetrically arranged to make the filter structure symmetric.

6. The suspended stripline high-pass filter based on alumina ceramic technology according to claim 1, wherein Four pads are provided on the lower conductor and are connected to the metal ground layer through metallized vias to firmly connect the upper and lower conductors.

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