A high steepness thin film filter based on interdigital structure

Abstract

The application provides a high steepness thin film filter based on an interdigital structure, which comprises a ceramic substrate, a metal ground layer below the ceramic substrate, and a circuit formed by nine terminal shorted interdigital resonators on the upper layer of the ceramic substrate, and a plurality of through ground vias are arranged around the substrate; each of the interdigital resonators comprises a short circuit end and an open circuit end, and the short circuit ends of the nine interdigital resonators are connected to each other. According to the scheme, the interdigital structure is formed based on the ceramic substrate, the structure is compact and small in size, and the terminal short circuit of the interdigital resonator can be realized through the plurality of through ground vias, compared with the method of etching a ground via at one end of a traditional interdigital resonator to realize the short circuit, the steepness of the filter is further improved.

Description

Technical Field

[0001] This invention relates to the field of radio frequency microwave filtering technology for wireless communication systems, specifically to a high steep-descent thin-film filter based on an interdigital structure. Background Technology

[0002] In modern wireless communication systems, radio frequency (RF) microwave filters are essential passive components, and their performance directly impacts the overall quality of the communication system. With the ever-increasing demand for communication bandwidth, RF microwave filters are rapidly evolving towards wider bandwidth, miniaturization, higher performance, and lower cost. Therefore, the development of novel, compact RF microwave filters with superior performance has attracted significant attention from researchers. In practical wireless communication environments, filters with high steepness are required, making them a practical necessity and a current hot topic in RF microwave filter design research. Consequently, existing technologies lack a compact, high-performance RF microwave filter with a high steepness. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a high steepness thin-film filter based on an interdigital structure, comprising a ceramic substrate, a metal grounding layer below the ceramic substrate, and a circuit formed by nine short-circuited interdigital resonators above the ceramic substrate. Multiple through-holes are provided around the substrate.

[0004] Each interfinite resonator includes a short-circuit terminal and an open-circuit terminal, and the short-circuit terminals of the nine interfinite resonators are interconnected.

[0005] Technical Effects: The high steepness thin-film filter based on interdigital structure provided by this invention has a compact structure and small size due to the interdigital structure formed on a ceramic substrate. In addition, the terminal short circuit of the interdigital resonator can be achieved through multiple through-holes, which further improves the steepness of the filter compared with the traditional method of etching a ground hole at one end of the interdigital resonator to achieve short circuit.

[0006] Furthermore, the aforementioned nine interdigital resonators include one left interdigital resonator, one right interdigital resonator, and seven intermediate interdigital resonators. The left interdigital resonator is connected to the first coplanar waveguide feed line, and the right interdigital resonator is connected to the second coplanar waveguide feed line.

[0007] Using this scheme, the first and second coplanar waveguide feed lines can serve as impedance change lines for connection to external circuits.

[0008] Furthermore, the open-circuit terminal of the left cross-finger resonator is connected to the first microstrip line, and the open-circuit terminal of the right cross-finger resonator is connected to the second microstrip line. The angle between the first microstrip line and the open-circuit terminal of the left cross-finger resonator is 90 degrees, and the angle between the second microstrip line and the open-circuit terminal of the right cross-finger resonator is 90 degrees.

[0009] Using this scheme, the open-circuit terminals of the left and right cross-finger resonators are each connected to a microstrip line at a 90-degree angle to them, which can be used to improve standing waves.

[0010] Furthermore, all nine interdigital resonators mentioned above are interdigital resonators with the same length and width, but the spacing between each pair of intermediate interdigital resonators is different.

[0011] Using this scheme, the operating frequency band of the filter can be adjusted by changing the length of the nine short-circuited interdigital resonators, the standing wave ratio of the filter can be adjusted by changing the spacing between the nine short-circuited interdigital resonators, and the bandwidth of the filter can be adjusted by changing the width of the nine short-circuited interdigital resonators and the spacing between the resonators. It has a high degree of design flexibility and can meet different needs.

[0012] Furthermore, the first coplanar waveguide feed line and the second coplanar waveguide feed line have the same structure. The first coplanar waveguide feed line includes an input / output coplanar waveguide, a main coplanar waveguide feed line, a tapered coplanar waveguide for connecting the input / output coplanar waveguide and the main coplanar waveguide feed line, and a microstrip surface. The input / output coplanar waveguide includes a first intermediate microstrip line segment and a first edge slot line. The length of the first intermediate microstrip line segment is the same as the length of the first edge slot line. The main coplanar waveguide feed line includes a second intermediate microstrip line segment and a second edge slot line. The length of the second intermediate microstrip line segment is the same as the length of the second edge slot line. The tapered coplanar waveguide for connecting the input / output coplanar waveguide and the main coplanar waveguide feed line includes a third intermediate microstrip line segment and a third edge slot line. The width of the third intermediate microstrip line segment is tapered. There is an angle between the coplanar waveguide and the input / output coplanar waveguide. The microstrip surface is coupled to the left and right interdigital resonators.

[0013] By adopting this scheme, using the first coplanar waveguide feed line and the second coplanar waveguide feed line with the above structure, the circuit structure can be made more compact.

[0014] Furthermore, the angle between the gradient coplanar waveguide used to connect the input / output coplanar waveguide and the main coplanar waveguide feed line and the input / output coplanar waveguide is 120 degrees.

[0015] Using this scheme, a 120-degree angle can make the signal flow smoother, with less electromagnetic radiation and loss.

[0016] Furthermore, the circuit described above has a length of 8.13 mm, a width of 3.58 mm, and a ceramic substrate thickness of 0.381 mm. ， The thickness of the entire circuit is 0.389.

[0017] As can be seen from the above parameters, by adopting this scheme, the circuit structure in the filter is compact and the filter size is small.

[0018] Furthermore, the ceramic substrate mentioned above is an Al2O3 ceramic substrate.

[0019] Using this method, alumina ceramic materials exhibit good wear resistance, insulation at both room and high temperatures, thermal shock resistance, and chemical corrosion resistance.

[0020] Furthermore, the total number of the aforementioned interconnected grounding vias is 54.

[0021] Using this scheme, 54 grounding vias are selected, and the corresponding via grounding effect is better. Attached Figure Description

[0022] Figure 1 This is a three-dimensional structural schematic diagram of a high steep-gradient thin-film filter based on an interdigital structure according to the present invention;

[0023] Figure 2 This is a top view of a high-slope thin-film filter based on an interdigital structure according to the present invention;

[0024] Figure 3 The simulation results show the S-parameters (return loss S11 and insertion loss S21) of the high steepness thin film filter based on the interdigital structure in this invention.

[0025] Figure 4 This is a schematic diagram illustrating the effect of geometric length on frequency in this invention;

[0026] Figure 5 This is a schematic diagram illustrating the effect of the feeder position on the standing wave in this invention;

[0027] Figure 6 This is a schematic diagram illustrating the effect of the spacing between the nine short-circuited interdigital resonators in this invention on the standing wave ratio of the filter.

[0028] Figure 7 This is a schematic diagram illustrating the effect of the cross-finger resonator width w1 on the bandwidth in this invention;

[0029] Figure 8 This is a schematic diagram illustrating the effect of the interdigital resonator spacing S1 on the bandwidth in this invention;

[0030] Figure 9 This is a schematic diagram illustrating the effect of the number of vias on filter performance in this invention.

[0031] Appendix Figure 1-2 The structures represented by each label are listed below:

[0032] 1. First and second coplanar waveguide feeds; 2. Nine interdigital resonators with short-circuited terminals; 3. Multiple through-holes for grounding; 101. Input and output coplanar waveguides; 102. Main coplanar waveguide feed; 103. Gradiently tapered coplanar waveguide for connecting the input / output coplanar waveguides and the main coplanar waveguide feed; 104. Microstrip surface; 201. Left and right interdigital resonators; 202. Seven intermediate interdigital resonators. Detailed Implementation

[0033] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0034] It should be noted that when a part or component is considered to be "connected to," "located on," or "assembled" to another part or component, it can be directly mounted on the other part or component, or it may be located in an intermediate part or component. The terms "left," "right," "upper," "lower," and similar expressions used in this document are for illustrative purposes only.

[0035] In one specific implementation, such as Figure 1-2 As shown, a high steepness thin-film filter based on an interdigital structure includes a ceramic substrate, a metal ground layer below the ceramic substrate, and a circuit formed by nine short-circuited interdigital resonators 2 above the ceramic substrate. Multiple through-holes 3 are provided around the substrate.

[0036] Each interfinite resonator includes a short-circuit terminal and an open-circuit terminal, and the short-circuit terminals of the nine interfinite resonators 2 are interconnected.

[0037] The high steepness thin-film filter based on interdigital structure provided by this invention has a compact structure and small size because it is based on an interdigital structure formed on a ceramic substrate. In addition, the terminal short circuit of the interdigital resonator can be achieved through multiple through-holes. Compared with the traditional method of etching a ground hole at one end of the interdigital resonator to achieve short circuit, the steepness of the filter is further improved.

[0038] Among them, such as Figure 1 As shown, the circuit described above is a single-layer structure and is symmetrical from left to right. The upper layer of the ceramic substrate is a microstrip structure, and the lower layer is a metal ground layer. Optionally, the ceramic substrate is an Al2O3 ceramic substrate. Alumina ceramic materials have good wear resistance, insulation at room temperature and high temperature, thermal shock resistance, and chemical corrosion resistance.

[0039] Optionally, the nine interdigital resonators 2 mentioned above include one left interdigital resonator, one right interdigital resonator, and seven intermediate interdigital resonators 202. The left interdigital resonator is connected to the first coplanar waveguide feed line, and the right interdigital resonator is connected to the second coplanar waveguide feed line.

[0040] Among them, such as Figure 1 As shown, the circuit mainly consists of two parts: the first part is a coplanar waveguide (CPW) feed line 1 for microstrip laying for connection with external circuits, including a first coplanar waveguide feed line and a second coplanar waveguide feed line; the second part is an interdigital resonator 2 with nine short-circuited terminals for generating the passband characteristics of the filter; fifty-four grounding vias 3 are etched on the ceramic substrate to realize the short-circuiting of the interdigital resonator terminals.

[0041] Optionally, the first coplanar waveguide feed line and the second coplanar waveguide feed line have the same structure. The first coplanar waveguide feed line includes an input / output coplanar waveguide 101, a main coplanar waveguide feed line 102, a tapered coplanar waveguide 103 for connecting the input / output coplanar waveguide and the main coplanar waveguide feed line, and a microstrip surface 104. The input / output coplanar waveguide 101 includes a first intermediate microstrip line segment and a first edge slot line. The length of the first intermediate microstrip line segment is the same as the length of the first edge slot line. The main coplanar waveguide feed line 102 includes a second intermediate microstrip line segment. The second intermediate microstrip line segment has the same length as the second edge slot line. The tapered coplanar waveguide 103 used to connect the input / output coplanar waveguide and the main coplanar waveguide feed line includes a third intermediate microstrip line segment and a third edge slot line. The width of the third intermediate microstrip line segment is tapered. The tapered coplanar waveguide 103 used to connect the input / output coplanar waveguide and the main coplanar waveguide feed line has an angle with the input / output coplanar waveguide 101. The microstrip surface 104 is coupled to the left and right interdigital resonators.

[0042] The use of the first and second coplanar waveguide feeders with the above-described structure allows for a more compact circuit structure. See details in [link to relevant documentation]. Figure 2The circuit structure diagram shown is as follows: 1 is a coplanar waveguide (first coplanar waveguide feed line), which includes an input / output coplanar waveguide 101, a main coplanar waveguide (CPW) feed line 102, a gradient coplanar waveguide 103 for connecting the input / output coplanar waveguide and the main coplanar waveguide feed line, and a microstrip surface 104. 101 is the input / output coplanar waveguide (CPW), and 101 includes a corresponding intermediate microstrip line (first intermediate microstrip line segment) with a length of l2 and a width of w2. The edge slot line (first edge slot line) of 101 has a width of s6 and a length equal to that of the intermediate microstrip line (first intermediate microstrip line segment). The lengths of the microstrip lines are the same. 102 is the main coplanar waveguide (CPW) feed line. The length of the middle microstrip line (second middle microstrip line segment) of 102 is l4, and the width is w4. The length of the edge slot line (second edge slot line) of 102 is the same as the length of the middle microstrip line (second middle microstrip line segment), and the width is the same as the width of the edge slot line of 101. 103 contains the corresponding middle microstrip line (third middle microstrip line segment) with a gradually changing width. The edge slot line (third edge slot line) of 103 forms a 120-degree angle with 101. 104 is the microstrip surface. Figure 2 The entire metal surface at the edge of the middle and top layers, microstrip surface 104 is used for grounding, and also for forming the CPW feed (first coplanar waveguide feed) together with 101, 102, and 103.

[0043] The microstrip surface 104 is coupled to the resonators at the left and right ends (left and right interdigital resonators) of the nine short-circuited interdigital resonators, with a coupling spacing of s5. Figure 2 In the diagram, 201 represents the left and right resonators of a nine-terminal short-circuited interdigital resonator. Each resonator has a length of p1 and a width of w1. Optionally, the open-circuit terminal of the left interdigital resonator is connected to a first microstrip line, and the open-circuit terminal of the right interdigital resonator is connected to a second microstrip line. The angle between the first microstrip line and the open-circuit terminal of the left interdigital resonator is 90 degrees, and the angle between the second microstrip line and the open-circuit terminal of the right interdigital resonator is also 90 degrees. Each of the open-circuit terminals of the left and right interdigital resonators is connected to a microstrip line at a 90-degree angle to it, which can be used to improve standing waves. The length of both the first and second microstrip lines is l3, and the width is w3. The coupling distances between the first and second microstrip lines and the microstrip surface 104 are x6, s7, and x9, respectively.

[0044] Optionally, all nine interdigital resonators mentioned above are interdigital resonators with the same length and width, and the spacing between each pair of intermediate interdigital resonators is different, namely s1, s2, s3, and s4.

[0045] The operating frequency band of the filter can be adjusted by changing the length of the nine short-circuited interdigital resonators, the standing wave ratio of the filter can be adjusted by changing the spacing between the nine short-circuited interdigital resonators, and the bandwidth of the filter can be adjusted by changing the width of the nine short-circuited interdigital resonators and the spacing between the resonators. It has a high degree of design flexibility and can meet different needs.

[0046] For details, please refer to Figure 2 The circuit diagram shown includes 7 interdigital resonators with the same length and width and short-circuited terminals, i.e., 7 intermediate interdigital resonators. The length of each interdigital resonator is p1 and the width is w1. The coupling spacings between the nine short-circuited interdigital resonators 2 are s1, s2, s3 and s4, respectively. Figure 2 In section 3, there are fifty-four identical grounding vias used to achieve short-circuiting of the interdigital resonator and improve the steepness of the upper sideband. Each via has a diameter of d1 and a height of H. The distance between the center of the via and the long edge of the ceramic substrate is x1, the distance between the center of the via and the edge of the microstrip surface 104 is x5, the distance between the center of the via and the short edge of the ceramic substrate is y3, and the distance between the center of the via and the edge groove of the first intermediate microstrip segment is x3.

[0047] Optionally, the circuit described above has a length of 8.13 mm, a width of 3.58 mm, a ceramic substrate thickness of 0.381 mm, and an overall circuit thickness of 0.389 mm. These parameters demonstrate that the circuit structure in the filter is compact, resulting in a small filter size.

[0048] To better understand the solution of the present invention, the following is in conjunction with... Figures 1 to 7 A more detailed description of the high steepness thin-film filter based on the interdigital structure described above is provided.

[0049] In this example, the high steepness thin-film filter based on the interdigital structure includes a ceramic substrate made of Al2O3 ceramic substrate with a thickness of 0.381 mm and a dielectric constant of 9.8; the next layer of the ceramic substrate is a metal ground layer with a thickness of 0.004 mm; the upper layer of the ceramic substrate includes a circuit formed by nine short-circuited interdigital resonators with a thickness of 0.004 mm; 54 through grounding vias are provided around the substrate; the overall circuit has a length of L = 8.13 mm and a width of W = 3.58 mm.

[0050] Each interfinite resonator includes a short-circuited end and an open-circuited end. The short-circuited ends of the nine interfinite resonators are interconnected. The nine short-circuited interfinite resonators are used to generate the passband characteristics of the filter. Fifty-four grounding vias running through the upper and lower layers realize the short-circuiting of the interfinite resonators. The resonators at the left and right ends of the nine short-circuited interfinite resonators (left and right interfinite resonators) are connected to the input and output coplanar waveguide (CPW) feed lines, respectively. That is, the left interfinite resonator is connected to the first coplanar waveguide feed line, and the right interfinite resonator is connected to the second coplanar waveguide feed line. The nine short-circuited interfinite resonators are all short-circuited at one end and open-circuited at the other end, with a length of 1 / 4 of the wavelength corresponding to the center frequency: wavelength = wave velocity / center frequency. As the wavelength decreases, the center frequency increases.

[0051] The open-circuit terminal of the left cross-finger resonator is connected to the first microstrip line, and the open-circuit terminal of the right cross-finger resonator is connected to the second microstrip line. The angle between the first microstrip line and the open-circuit terminal of the left cross-finger resonator is 90 degrees, and the angle between the second microstrip line and the open-circuit terminal of the right cross-finger resonator is 90 degrees. The short-circuit terminals of the nine short-circuited cross-finger resonators are interconnected to improve the steepness of the filter.

[0052] For details, please refer to Figure 2 202 consists of seven interdigital resonators with the same length and width, all with short-circuited terminals, i.e., seven intermediate interdigital resonators. Each interdigital resonator has a length of p1 and a width of w1. The coupling spacings between the nine short-circuited interdigital resonators 2 are s1, s2, s3, and s4, respectively. Figure 2 In section 3, there are fifty-four identical grounding vias used to achieve short-circuiting of the interdigital resonator and improve the steepness of the upper sideband. Each via has a diameter of d1 and a height of H. The distance between the center of the via and the long edge of the ceramic substrate is x1, the distance between the center of the via and the edge of the microstrip surface 104 is x5, the distance between the center of the via and the short edge of the ceramic substrate is y3, and the distance between the center of the via and the edge groove of the first intermediate microstrip segment is x3.

[0053] In conventional interdigital structures, short-circuiting at the termination is achieved by drilling a grounding via at one end of the interdigital microstrip line, thus grounding that end of the interdigital microstrip line. This solution involves drilling 54 grounding vias at the edge of the substrate with a coplanar waveguide (CPW) feed line laid with microstrip, grounding the CPW edge microstrip, and alternately connecting one end of the interdigital microstrip line to the edge microstrip of the CPW feed line, thereby grounding one end of the interdigital microstrip line.

[0054] 1 is a coplanar waveguide (first coplanar waveguide feed line), comprising an input / output coplanar waveguide 101, a main coplanar waveguide (CPW) feed line 102, a graded coplanar waveguide 103 connecting the input / output coplanar waveguide and the main coplanar waveguide feed line, and a microstrip surface 104. 101 is the input / output coplanar waveguide (CPW), comprising a corresponding intermediate microstrip line (first intermediate microstrip segment) with a length of l2 and a width of w2, and an edge slot line (first edge slot line) with a width of s6 and a length equal to that of the intermediate microstrip line (first intermediate microstrip segment). 102 is the main coplanar waveguide (CPW). The CPW feed line 102 includes the middle microstrip line (second middle microstrip segment) of 102 with a length of l4 and a width of w4. The edge slot line (second edge slot line) of 102 has the same length as the middle microstrip line (second middle microstrip segment) and the same width as the edge slot line of 101. 103 includes the middle microstrip line (third middle microstrip segment) corresponding to 103 with a gradually changing width. The edge slot line (third edge slot line) of 103 forms a 120-degree angle with 101. 104 is a microstrip surface used to form the CPW feed line (first coplanar waveguide feed line) together with 101, 102 and 103.

[0055] The microstrip surface 104 is coupled to the resonators at the left and right ends (left and right interdigital resonators) of the nine short-circuited interdigital resonators, with a coupling spacing of s5. Figure 2 In the diagram, 201 represents the left and right resonators of a nine-terminal short-circuited interdigital resonator. Each resonator has a length of p1 and a width of w1. Optionally, the open-circuit terminal of the left interdigital resonator is connected to a first microstrip line, and the open-circuit terminal of the right interdigital resonator is connected to a second microstrip line. The angle between the first microstrip line and the open-circuit terminal of the left interdigital resonator is 90 degrees, and the angle between the second microstrip line and the open-circuit terminal of the right interdigital resonator is also 90 degrees. Each of the open-circuit terminals of the left and right interdigital resonators is connected to a microstrip line at a 90-degree angle to it, which can be used to improve standing waves. The length of both the first and second microstrip lines is l3, and the width is w3. The coupling distances between the first and second microstrip lines and the microstrip surface 104 are x6, s7, and x9, respectively.

[0056] In this example, the specific values ​​of the above geometric parameters are as follows: w1 = 0.55mm, w2 = 0.12mm, w3 = 0.13mm, w4 = 0.4mm; l1 = 1.0mm, l2 = 0.5mm, l3 = 0.48mm, l4 = 0.3mm; s1 = 0.08mm, s2 = 0.15mm, s3 = 0.18mm, s4 = 0.18mm, s5 = 0.08mm, s6 = 0.05mm, s7 = 0.05mm; p1 = 2.55mm, p2 = 1mm; x1 = 0.1mm, x3 = 0.25mm, x5 = 0.35mm, x6 = 0.13mm, x9 = 0.25mm; y3 = 0.05mm; d1 = 0.25mm; H = 0.389.

[0057] Based on the filter in this example, see [link to relevant documentation]. Figure 3 The return loss S shown 11 and insertion loss S 21 Simulation results, such as Figure 3 As shown, the horizontal axis represents frequency in GHz, and the vertical axis represents S-parameters (loss). The filter operates in the 8.0-12.5 GHz frequency band with a relative bandwidth of 45%. The passband return loss S11 is better than -15 dB, and the insertion loss S21 is better than -0.6 dB. It has nine transmission poles within the passband. A transmission zero is generated in the upper stopband at 13.3 GHz, reaching -48 dB. The out-of-band rejection is better than -40 dB, and the upper sideband sag is good, demonstrating excellent circuit performance. This invention designs a high-sag thin-film filter based on an interdigital structure, applicable to the 8.0-12.5 GHz frequency band with a fractional bandwidth of 45%, falling within the broadband range. It has a center insertion loss of 0.6 dB, indicating low loss, and a good upper sideband sag.

[0058] In summary, the significant advantages of the solution proposed in this invention are: it can achieve broadband filtering characteristics in the 8.0-12.5GHz frequency band, with a good upper sideband sag, resulting in excellent filtering performance. Furthermore, the characteristic impedance of both the input and output ports of the circuit is a standard 50Ω. The operating frequency band of the filter can be adjusted by the geometric length of the nine short-circuited interdigital resonators. The geometric length of the interdigital resonators is 1 / 4 of the wavelength corresponding to the center frequency. Since wavelength = wave velocity / center frequency, with a fixed wave velocity, increasing the geometric length increases the wavelength and decreases the frequency. Therefore, the operating frequency band of the filter can be adjusted based on the geometric length.

[0059] The standing wave ratio (SWR) of the filter can be adjusted by changing the spacing between the nine short-circuited interdigital resonators and the positions of the input and output feed lines. The bandwidth of the filter can also be adjusted by changing the geometric width of the nine short-circuited interdigital resonators and the spacing between them, offering high design flexibility. The overall circuit dimensions are 8.13mm × 3.58mm × 0.389mm, making it more compact than other microwave filters. With the same filter structure parameters, this invention exhibits better upper sideband steepness performance than traditional filter structures.

[0060] As an example, see Appendix Figure 4 To be continued Figure 9 , Figure 4 The effect of geometric length on frequency is shown. Figure 4 The horizontal axis represents frequency, and the vertical axis represents S21 (insertion loss). Figure 4 It is known that as the geometric length of the interdigital resonator increases, the frequency decreases. Therefore, the operating frequency of the filter can be adjusted by regulating the geometric length of the interdigital structure. Figure 5 This illustrates the effect of feeder position on standing wave ratio. Figure 5 The horizontal axis represents frequency, and the vertical axis represents VSWR (standing wave ratio). Figure 5 It can be seen that the standing wave ratio of the filter can be adjusted by adjusting the position of the input and output feed lines, and the standing wave ratio is better when the feed line position is 1. Figure 6 This illustrates the effect of the interdigital resonator spacing S1 on the standing wave. Figure 6 The horizontal axis represents frequency, and the vertical axis represents VSWR (standing wave ratio). Figure 6 It can be seen that the standing wave ratio of the filter can be adjusted by adjusting the spacing between the nine short-circuited interdigital resonators, and the standing wave ratio is better when the spacing is 0.08. Figure 7 This illustrates the effect of the interdigital resonator width w1 on the bandwidth. Figure 7 The horizontal axis represents frequency, and the vertical axis represents S21 (insertion loss). Figure 7 It can be seen that the bandwidth of the filter can be adjusted by adjusting the width of the interdigital resonator with nine short-circuited terminals. Figure 8 This illustrates the effect of the interdigital resonator spacing S1 on the bandwidth. Figure 8 The horizontal axis represents frequency, and the vertical axis represents S21 (insertion loss), derived from... Figure 8 It can be seen that as the spacing between the nine short-circuited interdigital resonators increases, the lower stopband curve shrinks towards the inside of the passband, resulting in a decrease in bandwidth. Therefore, it can be concluded that increasing the resonator spacing reduces the bandwidth. Figure 9 This illustrates the impact of the number of vias on filter performance. Figure 9 The horizontal axis represents frequency, and the vertical axis represents S-parameters, derived from... Figure 9 It can be seen that when the number of through holes is 54, the steepness of the upper stopband is better.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the description above. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, using the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. An interdigital structure based high roll-off thin film filter, characterized by, The application relates to a ceramic substrate, a lower layer of which is a metal ground layer, an upper layer of which comprises a circuit formed by nine terminal short-circuit interdigital resonators, and a plurality of through ground vias arranged around the ceramic substrate. For each of the interdigital resonators, the interdigital resonator comprises a short-circuit end and an open-circuit end, and the short-circuit ends of the nine interdigital resonators are connected to each other. The nine interdigital resonators comprise one left interdigital resonator, one right interdigital resonator and seven intermediate interdigital resonators, the left interdigital resonator is connected to a first coplanar waveguide feed line, and the right interdigital resonator is connected to a second coplanar waveguide feed line. The first coplanar waveguide feed line and the second coplanar waveguide feed line have the same structure, the first coplanar waveguide feed line comprises an input-output end coplanar waveguide, a main coplanar waveguide feed line, a tapered coplanar waveguide for connecting the input-output end coplanar waveguide and the main coplanar waveguide feed line and a microstrip surface, the input-output end coplanar waveguide comprises a first intermediate microstrip line segment and a first edge slot line, the length of the first intermediate microstrip line segment is the same as the length of the first edge slot line, the main coplanar waveguide feed line comprises a second intermediate microstrip line segment and a second edge slot line, the length of the second intermediate microstrip line segment is the same as the length of the second edge slot line, the tapered coplanar waveguide for connecting the input-output end coplanar waveguide and the main coplanar waveguide feed line comprises a third intermediate microstrip line segment and a third edge slot line, the width of the third intermediate microstrip line segment is tapered, there is an included angle between the coplanar waveguide and the input-output end coplanar waveguide, and the microstrip surface is coupled to the left interdigital resonator and the right interdigital resonator. The open-circuit end of the left interdigital resonator is connected to a first microstrip line, the open-circuit end of the right interdigital resonator is connected to a second microstrip line, the included angle between the first microstrip line and the open-circuit end of the left interdigital resonator is 90 degrees, and the included angle between the second microstrip line and the open-circuit end of the right interdigital resonator is 90 degrees. The nine interdigital resonators are all interdigital resonators with the same length and the same width, and the spacing between every two intermediate interdigital resonators is different.

2. The filter of claim 1, wherein, The included angle between the tapered coplanar waveguide for connecting the input-output end coplanar waveguide and the main coplanar waveguide feed line and the input-output end coplanar waveguide is 120 degrees.

3. The filter of claim 1, wherein, The length of the circuit is 8.13 mm, the width of the circuit is 3.58 mm, the thickness of the ceramic substrate is 0.381 mm, and the overall thickness of the circuit is 0.389 mm.

4. The filter according to any one of claims 1 to 3, characterized in that, The ceramic substrate is an Al2O3 ceramic substrate.

5. The filter according to any one of claims 1 to 3, characterized in that, The total number of the plurality of through ground vias is 54.

6. The filter of any one of claims 1 to 3, wherein, ​

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