Thin film microstrip filter based on impedance compensation standing wave regulation and control

Abstract

The invention relates to a thin-film micro-strip filter based on impedance compensation standing wave regulation and control. The thin-film micro-strip filter comprises a substrate; the two coplanar waveguide feeder lines are laid on the upper layer of the substrate in a micro-strip form in a bilateral symmetry manner; the interdigital resonators are arranged on the upper layer of the substrate in a bilateral symmetry mode and located between the two coplanar waveguide feeder lines, and the two interdigital resonators located on the edge are connected with the two coplanar waveguide feeder lines in a 90-degree included angle mode; the two impedance compensation units are arranged on the upper layer of the substrate in a bilateral symmetry mode and are connected with the open-circuit terminals of the two interdigital resonators located on the edge in a 90-degree included angle mode. According to the invention, the two interdigital resonators located at the edge are connected with the coplanar waveguide feeder line forming the 90-degree included angle with the interdigital resonators, so that standing waves can be improved; meanwhile, the two impedance compensation units are used for realizing capacitance compensation of the circuit, so that the standing wave of the filter is improved, the steep drop degree of an upper sideband of the filter is good, the standing wave in a passband is good, and better filtering characteristics can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency microwave filtering of wireless communication systems, and in particular to a thin film microstrip filter based on impedance compensation standing wave control. Background Art

[0002] In modern wireless communication systems, RF microwave filters are essential passive components, and their performance is crucial to the overall quality of the communication system. With the growing demand for communication bandwidth, RF microwave filters are rapidly developing towards broadband, miniaturization, high performance, and low cost. Consequently, the development of new, compact RF microwave filters with superior performance has attracted significant attention from researchers. In practical wireless communication environments, filters must exhibit minimal return loss, which in turn requires minimal standing wave. Low return loss filters have become a practical requirement and a current research hotspot in RF microwave filter design. Summary of the Invention

[0003] The present invention provides a thin film microstrip filter based on impedance compensation standing wave control to solve at least one of the above technical problems.

[0004] The technical solution of the present invention to solve the above technical problems is as follows: a thin film microstrip filter based on impedance compensation standing wave control, comprising: substrate; Two coplanar waveguide feed lines are laid in a microstrip form and are symmetrically arranged on the upper layer of the substrate; A plurality of interdigital resonators, one terminal of which is short-circuited and the other terminal of which is open-circuited, are symmetrically arranged on the upper layer of the substrate and located between the two coplanar waveguide feed lines, and the two interdigital resonators located at the edge are respectively connected to the two coplanar waveguide feed lines at a 90-degree angle; Two impedance compensation units are symmetrically arranged on the upper layer of the substrate and are respectively connected to the open-circuit terminals of the two interdigital resonators located at the edges at an angle of 90 degrees.

[0005] On the basis of the above technical solution, the present invention can also be improved as follows.

[0006] Furthermore, the substrate is specifically an Al2O3 ceramic substrate.

[0007] Furthermore, a metal ground plane is provided on the lower layer of the substrate.

[0008] Furthermore, the two coplanar waveguide feeders have the same structure and both include: middle microstrip line; Two edge microstrip lines are symmetrically arranged on both sides of the middle microstrip line and connected to the metal ground plane through grounding vias; a first microstrip line connected to the middle microstrip line; The second microstrip line is connected to the first microstrip line at an angle of 90 degrees, and is also connected to the corresponding interdigital resonator located at the edge at an angle of 90 degrees.

[0009] Furthermore, the length of the interdigital resonator is 1 / 4 of the wavelength.

[0010] Furthermore, the number of the interdigital resonators is nine.

[0011] Furthermore, the impedance compensation unit includes a third microstrip line, and the third microstrip line is connected to the open-circuit terminal of the corresponding interdigital resonator located at the edge at an angle of 90 degrees.

[0012] Furthermore, the geometric lengths of the plurality of interdigital resonators are adjustable, and the operating frequency band of the filter can be adjusted by adjusting the geometric lengths of the plurality of interdigital resonators.

[0013] Furthermore, the positions of the two coplanar waveguide feed lines are adjustable, and the geometric dimensions of the two impedance compensation units are adjustable, and the filter standing wave is adjusted by adjusting the positions of the two coplanar waveguide feed lines and the geometric dimensions of the two impedance compensation units.

[0014] Furthermore, the geometric widths of the multiple interdigital resonators are adjustable, and the coupling spacing between two adjacent interdigital resonators is adjustable. By adjusting the geometric widths of the multiple interdigital resonators and the coupling spacing between two adjacent interdigital resonators, the filter bandwidth can be adjusted.

[0015] The beneficial effects of the present invention are as follows: in a thin film microstrip filter based on impedance compensation standing wave control of the present invention, two interdigital resonators located at the edge are connected to a coplanar waveguide feeder at a 90-degree angle thereto, which can improve the standing wave; at the same time, the two impedance compensation units are used to realize capacitance compensation of the circuit, thereby improving the filter standing wave; the present invention can realize broadband filtering characteristics in the 4.0-7.0 GHz frequency band, the filter has good upper sideband steepness and good standing wave in the passband, and can realize better filtering characteristics; in addition, the operating frequency band of the filter can be adjusted by the geometric length of the multiple interdigital resonators, the filter standing wave can be adjusted by adjusting the positions of the two coplanar waveguide feeders and the geometric dimensions of the two impedance compensation units, and the filter bandwidth can be adjusted by adjusting the geometric width dimensions of the multiple interdigital resonators and the coupling spacing between two adjacent interdigital resonators, thereby having high design flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the three-dimensional structure of a thin film microstrip filter based on impedance compensation standing wave control according to the present invention; Figure 2 A top view of a thin film microstrip filter based on impedance compensation standing wave control according to the present invention; Figure 3 This is a simulation result diagram of the S parameters of a thin film microstrip filter based on impedance compensation standing wave control according to the present invention; Figure 4 This is a simulation result diagram comparing the S parameters of a thin-film microstrip filter based on impedance compensation standing wave control of the present invention with the S parameters of a traditional interdigital structure. DETAILED DESCRIPTION

[0017] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0018] like Figure 1 As shown, a thin film microstrip filter based on impedance compensation standing wave control includes: substrate1; Two coplanar waveguide feed lines 2 are laid in a microstrip form and are symmetrically laid on the upper layer of the substrate 1; Multiple interdigital resonators 3, one terminal of which is short-circuited and the other terminal of which is open-circuited, are symmetrically arranged on the upper layer of the substrate 1 and located between the two coplanar waveguide feed lines 2, and the two interdigital resonators 3 located at the edge are respectively connected to the two coplanar waveguide feed lines 2 at a 90-degree angle; Two impedance compensation units 4 are symmetrically arranged on the upper layer of the substrate 1 and are respectively connected to the open-circuit terminals of the two interdigital resonators 3 located at the edges at an angle of 90 degrees.

[0019] In the thin film microstrip filter based on impedance compensation standing wave control of the present invention, two coplanar waveguide feed lines 2 are respectively used to connect to the external circuit and play the role of impedance matching. Their characteristic impedance is a standard 50Ω; multiple interdigital resonators 3 are used to generate the filter passband characteristics, and two impedance compensation units 4 are used to realize the capacitance compensation of the circuit, thereby improving the filter standing wave.

[0020] In some embodiments, the substrate 1 is specifically an Al2O3 ceramic substrate, and a metal grounding surface is provided at the lower layer.

[0021] In this embodiment, the substrate 1 has a length W=6.97 mm, a width L=5.95 mm, and a thickness H=0.381 mm.

[0022] In some embodiments, as Figure 2 As shown, the two coplanar waveguide feed lines 2 have the same structure and both include: middle microstrip line 21; Two edge microstrip lines 22 are symmetrically arranged on both sides of the middle microstrip line and connected to the metal ground plane through grounding vias; A first microstrip line 23 connected to the middle microstrip line; The second microstrip line 24 is connected to the first microstrip line at an angle of 90 degrees, and is also connected to the corresponding interdigital resonator 3 located at the edge at an angle of 90 degrees.

[0023] Specifically, the corresponding interdigital resonator 3 located at the edge is connected to a second microstrip line 24 that is at an angle of 90 degrees thereto, so as to improve standing waves.

[0024] The length of the middle microstrip line 21 is L1 and the width is W1; the length of the edge microstrip line 22 is X1 and the width is Y1; the width of the edge slot line between the middle microstrip line 21 and the edge microstrip line 22 is g1, and its length is the same as the length of the middle microstrip line 21; the edge microstrip line 22 is connected to the metal ground surface through a grounding via, and the radius of the grounding via is R; the length of the first microstrip line 23 is L2 and the width is W2; the length of the second microstrip line 24 is L3 and the width is W3; the length of the first microstrip line 23 and the length of the second microstrip line 24 affect the standing wave of the filter.

[0025] In some embodiments, the length of the interdigital resonator 3 is 1 / 4 of the wavelength. The number of the interdigital resonators 3 is nine.

[0026] Specifically, such as Figure 2 As shown, the nine interdigital resonators 3 are respectively a first interdigital resonator 31, a second interdigital resonator 32, a third interdigital resonator 33, a fourth interdigital resonator 34, a fifth interdigital resonator 35, a sixth interdigital resonator 36, a seventh interdigital resonator 37, an eighth interdigital resonator 38 and a ninth interdigital resonator 39; the first interdigital resonator 31 to the ninth interdigital resonator 39 are arranged in sequence from left to right, and the first interdigital resonator 31 and the ninth interdigital resonator 39 are two interdigital resonators located at the edge; the first interdigital resonator 31 is connected to the coplanar waveguide feeder 2 on the left at a 90-degree angle, and the ninth interdigital resonator 39 is connected to the coplanar waveguide feeder 2 on the right at a 90-degree angle; the open-circuit terminal of the first interdigital resonator 31 is connected to an impedance compensation unit 4 at a 90-degree angle, and the open-circuit terminal of the ninth interdigital resonator 39 is connected to another impedance compensation unit 4 at a 90-degree angle.

[0027] The nine interdigital resonators 3 all have a length of L5 and a width of W5; the coupling spacing between the first interdigital resonator 31 and the second interdigital resonator 32 is S1, the coupling spacing between the second interdigital resonator 32 and the third interdigital resonator 33 is S2, the coupling spacing between the third interdigital resonator 33 and the fourth interdigital resonator 34 is S3, the coupling spacing between the fourth interdigital resonator 34 and the fifth interdigital resonator 35 is S4, the coupling spacing between the fifth interdigital resonator 35 and the sixth interdigital resonator 36 is S4, the coupling spacing between the sixth interdigital resonator 36 and the seventh interdigital resonator 37 is S3, the coupling spacing between the seventh interdigital resonator 37 and the eighth interdigital resonator 38 is S2, and the coupling spacing between the eighth interdigital resonator 38 and the ninth interdigital resonator 39 is S1.

[0028] In some embodiments, the impedance compensation unit 4 includes a third microstrip line 41 , and the third microstrip line 41 is connected to the open-circuit terminal of the corresponding interdigital resonator 3 located at the edge at an angle of 90 degrees.

[0029] Specifically, the third microstrip line 41 is used to achieve capacitance compensation of the circuit to regulate the standing wave index, further improving the filter standing wave. Compared with the thin film microstrip filter of the same size structure and material without the impedance compensation unit 4, the standing wave of the present invention is significantly improved. The length of the third microstrip line 41 is L4 and the width is W4. The open-circuit terminals of the first interdigital resonator 31 and the ninth interdigital resonator 39 are connected to the third microstrip line 41 at a 90-degree angle. The length of the overall structure formed by the first interdigital resonator 31 and the third microstrip line 41 is L5+W4, and the length of the overall structure formed by the ninth interdigital resonator 39 and the other third microstrip line 41 is also L5+W4. The distance between the entire thin film microstrip filter based on impedance compensation standing wave control and the wide side edge of the substrate 1 is X2.

[0030] In this embodiment, the specific values ​​of the above geometric parameters are as follows: L1=0.78mm, L2=2.05, L3=0.4mm, L4=0.5mm, L5=5.15mm; W1=0.18mm, W2=0.18mm, W3=0.18mm, W4=0.4mm, W 5=0.45mm; S1=0.06mm, S2=0.11mm, S3=0.14mm, S4=0.15mm; X1=0.64mm, Y1=0.44mm; X2=0.2mm; R=0.15mm.

[0031] In the present invention, the geometric lengths of the multiple interdigital resonators 3 are adjustable, and by adjusting the geometric lengths of the multiple interdigital resonators 3, the operating frequency band of the filter can be adjusted. The positions of the two coplanar waveguide feeders 2 are adjustable, as are the geometric dimensions of the two impedance compensation units 4. By adjusting the positions of the two coplanar waveguide feeders 2 and the geometric dimensions of the two impedance compensation units 4, the standing wave of the filter can be adjusted. The geometric widths of the multiple interdigital resonators 3 are adjustable, and the coupling spacing between adjacent interdigital resonators 3 is adjustable. By adjusting the geometric widths of the multiple interdigital resonators 3 and the coupling spacing between adjacent interdigital resonators 3, the filter bandwidth can be adjusted.

[0032] Figure 3 The present invention provides simulation results of the S parameters (return loss S11 and insertion loss S21) of a thin-film microstrip filter based on impedance compensation standing wave control. The operating frequency band of the thin-film microstrip filter based on impedance compensation standing wave control is 4.0-7.0 GHz, the relative bandwidth is 55%, the return loss S11 in the passband is better than -18 dB, the return loss (i.e., standing wave) is good, and the insertion loss S21 is better than -0.7 dB; there are 8 transmission poles in the band; a transmission zero point is generated in the upper stopband, located at 7.52 GHz, reaching -44 dB; out-of-band suppression is better than -40 dB, and the upper sideband has a good steepness drop, reflecting good circuit performance.

[0033] like Figure 4 As shown, when the filter structure parameters are set to the same, the standing wave return loss in the passband of the present invention is about 6 dB better than that of the traditional one without impedance compensation unit 4, and the standing wave performance is better.

[0034] The present invention can achieve broadband filtering characteristics in the 4.0-7.0 GHz frequency band, with good upper sideband steepness and good standing wave performance within the passband, thus achieving excellent filtering characteristics. The characteristic impedance of the input and output ports of the present invention is a standard 50Ω. The operating frequency band of the filter can be adjusted by adjusting the geometric length of the multiple interdigital resonators, the standing wave of the filter can be adjusted by adjusting the position of the two coplanar waveguide feeders and the geometric dimensions of the two impedance compensation units, and the filter bandwidth can be adjusted by adjusting the geometric width dimensions of the multiple interdigital resonators and the coupling spacing between adjacent interdigital resonators, thus providing high design flexibility. In addition, the overall dimensions of the entire circuit of the present invention are 6.97mm×5.95mm×0.389mm; the overall thickness of 0.389mm includes the thickness of the substrate 1 (0.381mm), the thickness of the metal ground plane provided on the lower layer of the substrate 1 (0.004mm), and the thickness of the gold layer provided on the upper layer of the substrate 1 (0.004mm), which is composed of the coplanar waveguide feeder 2, the interdigital resonator 3, and the impedance compensation unit 4. Compared with other microwave filters, the structure is more compact.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A thin film microstrip filter based on impedance compensation standing wave control, characterized in that: include: substrate; Two coplanar waveguide feed lines are laid in a microstrip form and are symmetrically arranged on the upper layer of the substrate; A plurality of interdigital resonators, one terminal of which is short-circuited and the other terminal of which is open-circuited, are symmetrically arranged on the upper layer of the substrate and located between the two coplanar waveguide feed lines, and the two interdigital resonators located at the edge are respectively connected to the two coplanar waveguide feed lines at a 90-degree angle; Two impedance compensation units are symmetrically arranged on the upper layer of the substrate and are respectively connected to the open-circuit terminals of the two interdigital resonators located at the edges at an angle of 90 degrees.

2. The thin film microstrip filter based on impedance compensation standing wave control according to claim 1, characterized in that: The substrate is specifically an Al2O3 ceramic substrate.

3. The thin film microstrip filter based on impedance compensation standing wave control according to claim 1, characterized in that: A metal ground plane is provided on the lower layer of the substrate.

4. The thin film microstrip filter based on impedance compensation standing wave control according to claim 3, characterized in that: The two coplanar waveguide feeders have the same structure and both include: middle microstrip line; Two edge microstrip lines are symmetrically arranged on both sides of the middle microstrip line and connected to the metal ground plane through grounding vias; a first microstrip line connected to the middle microstrip line; The second microstrip line is connected to the first microstrip line at an angle of 90 degrees, and is also connected to the corresponding interdigital resonator located at the edge at an angle of 90 degrees.

5. The thin film microstrip filter based on impedance compensation standing wave control according to claim 1, characterized in that: The length of the interdigital resonator is 1 / 4 of the wavelength.

6. The thin film microstrip filter based on impedance compensation standing wave control according to claim 1, characterized in that: The number of the interdigital resonators is nine.

7. The thin film microstrip filter based on impedance compensation standing wave control according to claim 1, characterized in that: The impedance compensation unit includes a third microstrip line, and the third microstrip line is connected to the open-circuit terminal of the corresponding interdigital resonator located at the edge at an angle of 90 degrees.

8. The thin film microstrip filter based on impedance compensation standing wave control according to claim 1, characterized in that: The geometric lengths of the plurality of interdigital resonators are adjustable, and the operating frequency band of the filter can be adjusted by adjusting the geometric lengths of the plurality of interdigital resonators.

9. The thin film microstrip filter based on impedance compensation standing wave control according to claim 1, characterized in that: The positions of the two coplanar waveguide feed lines are adjustable, and the geometric dimensions of the two impedance compensation units are adjustable. The filter standing wave is adjusted by adjusting the positions of the two coplanar waveguide feed lines and the geometric dimensions of the two impedance compensation units.

10. The thin film microstrip filter based on impedance compensation standing wave control according to claim 1, characterized in that: The geometric widths of the multiple interdigital resonators are adjustable, and the coupling spacing between two adjacent interdigital resonators is adjustable. The filter bandwidth can be adjusted by adjusting the geometric widths of the multiple interdigital resonators and the coupling spacing between two adjacent interdigital resonators.

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