A thin film microstrip filter

Abstract

The thin film microstrip filter comprises a long strip-shaped substrate and a resonator group arranged on the substrate, a line connecting the midpoints of the long sides of the substrate on both sides constitutes a center line, the resonator group comprises an even number of resonators symmetrically distributed along the center line, the resonators comprise at least an even number of folded resonators, all the folded resonators are symmetrically distributed along the center line and arranged close to the center line, the folded resonators are in H shape, the folded resonators comprise two first connecting ribs parallel to the center line and arranged at intervals, and a second connecting rib is arranged perpendicularly between the two first connecting ribs, the transmission zero point at the low end of the passband can be generated through the folded resonators, thereby enhancing the low-end out-of-band suppression and balancing the high-low end suppression index, the center frequency can be changed by adjusting the connecting position of the second connecting rib and the first connecting rib and the relative length of the first connecting rib and the second connecting rib, the adjustment mode is various, the limitation is small, and the application range is wider.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and more specifically to a thin-film microstrip filter. Background Technology

[0002] Microstrip filters are devices used to separate microwave signals of different frequencies. Their main function is to suppress unwanted signals, preventing them from passing through. With the rapid development of the modern microwave communication industry, miniaturized, lightweight, highly reliable, and high-frequency microwave devices are receiving increasing attention. As a result, thin-film processing technology has developed rapidly. Thin-film processing refers to the process of creating ultra-fine line patterns on ceramic substrates using processes such as evaporation, sputtering, patterning lithography, wet and dry etching, and electroplating to perform specific circuit functions.

[0003] Microstrip filters fabricated using thin-film technology are called thin-film microstrip filters. They have advantages such as fine lines, high precision, good heat dissipation, and high reliability, and are increasingly widely used in microwave circuit systems.

[0004] To reduce size and facilitate planar integration, traditional thin-film microstrip filters are mostly designed with interdigital structures. However, their out-of-band frequency response has the characteristics of high-end concavity and low-end convexity, resulting in poor out-of-band rejection at the low end of the passband. In practical applications, there is an increasing demand for similar high-end and low-end rejection performance. To solve this problem, thin-film microstrip filters have emerged that embed folded resonator pairs in the middle of traditional interdigital thin-film microstrip filters to generate transmission zeros at the low end of the passband, thereby improving the out-of-band rejection capability at the low end of the passband. For example, Chinese patent CN112467318A discloses such a microstrip bandpass filter. However, the resonator embedded in this scheme is a ring with an opening, and the center frequency can only be adjusted by changing the position of the opening. The adjustment methods are limited, the scope is narrow, and the application range is limited. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a thin-film microstrip filter that can enhance low-end out-of-band suppression and balance high and low-end suppression performance. This filter has multiple ways to adjust the center frequency, fewer limitations, and a wider range of applications.

[0006] To achieve the above objectives, the present invention provides a thin-film microstrip filter, comprising a long strip-shaped substrate and a resonator group disposed on the substrate. The line connecting the midpoints of the long sides of the substrate forms a center line. The resonator group comprises an even number of resonators symmetrically distributed along the center line. Each resonator comprises at least an even number of folded resonators. All the folded resonators are symmetrically distributed along the center line and disposed close to the center line. The folded resonators are H-shaped and include two first connecting ribs parallel to the center line and spaced apart, and a second connecting rib perpendicularly connected between the two first connecting ribs.

[0007] Preferably, the two first connecting ribs of the folded resonator are symmetrically distributed on both sides of the second connecting rib of the folded resonator.

[0008] More preferably, the folded resonator is provided with a grounding via, the grounding via is located at the end of the first connecting rib of the folded resonator away from the center line, the grounding via is a metallized via, and the grounding via is connected to and grounded to the back of the substrate.

[0009] More preferably, the distance between the second connecting rib and the grounding through hole is greater than or equal to half the length of the first connecting rib.

[0010] More preferably, when the center frequency is constant, the closer the second connecting rib is to the grounding through hole, the longer the length of the first connecting rib.

[0011] Preferably, the equivalent electrical length of the folded resonator is greater than or equal to half the wavelength.

[0012] Preferably, the strength of the low-end parasitic zero point is negatively correlated with the mounting depth of the substrate within the mounting cavity.

[0013] Preferably, the substrate is an alumina ceramic substrate with a dielectric constant of 9.8.

[0014] Preferably, the resonator further includes an even number of ordinary resonators, all of which are symmetrically distributed along the center line, and are arranged in a straight line parallel to the center line, with the ordinary resonators located outside the folded resonator.

[0015] More preferably, the thin-film microstrip filter further includes an input port, which is connected to the outermost resonator of the resonator group via an impedance line with an impedance of 50 ohms.

[0016] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0017] The thin-film microstrip filter provided by this invention includes an elongated substrate and a resonator group disposed on the substrate. The line connecting the midpoints of the two long sides of the substrate forms a center line. By making the resonator group include an even number of resonators symmetrically distributed along the center line, and making the resonators include at least an even number of folded resonators, and making all folded resonators symmetrically distributed along the center line and disposed close to the center line, the folded resonators are H-shaped. Each folded resonator includes two first connecting ribs parallel to the center line and spaced apart, and a second connecting rib perpendicularly connected between the two first connecting ribs. This allows the folded resonators to generate a transmission zero at the low end of the passband, thereby enhancing the low-end out-of-band rejection and balancing the high and low-end rejection performance. Furthermore, the center frequency can be changed by adjusting the connection position between the second connecting rib and the first connecting rib, as well as the relative length of the first and second connecting ribs. This provides multiple adjustment methods, fewer limitations, and a wider range of applications. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a thin-film microstrip filter according to Embodiment 1 of the present invention.

[0019] Figure 2 yes Figure 1 The graph compares the electrical performance of a thin-film microstrip filter with that of a traditional interdigital thin-film microstrip filter. Point A indicates... Figure 1 The electrical performance curve of the thin-film microstrip filter is shown in Figure B, where B indicates the electrical performance curve of the traditional interdigital thin-film microstrip filter.

[0020] Figure 3 This is a schematic diagram of the structure of Embodiment 2 of the thin-film microstrip filter in this invention.

[0021] Figure 4 This is a schematic diagram of the structure of Embodiment 3 of the thin-film microstrip filter in this invention.

[0022] Wherein: 10. Substrate; 11. Center line; 20. Resonator group; 21. Folded resonator; 211. First connecting rib; 212. Second connecting rib; 22. Ordinary resonator; 23. Grounding via; 30. Impedance line; 40. Input port. Detailed Implementation

[0023] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] Example 1

[0025] like Figure 1As shown, the thin-film microstrip filter provided by this invention has a center frequency F0 = 9.75 GHz, a bandwidth of 1.5 GHz, and a suppression of F0 ± 1.75 GHz ≥ 40 dB. It includes a long strip-shaped substrate 10, a resonator group 20 disposed on the substrate 10, and an input port 40. The line connecting the midpoints of the long sides of the substrate 10 forms a center line 11. The resonator group 20 includes an even number of resonators symmetrically distributed along the center line 11. Specifically, these resonators include two folded resonators 21 symmetrically distributed along the center line 11, and four ordinary resonators symmetrically distributed along the center line 11. The folded resonator 21 is arranged in an H-shape and close to the center line 11. The ordinary resonator 22 is arranged in a straight line parallel to the center line 11 and is located outside the folded resonator 21. Each folded resonator 21 includes two first connecting ribs 211 that are parallel to the center line 11 and spaced apart, and a second connecting rib 212 that is vertically connected between the two first connecting ribs 211. All resonators are provided with grounding vias 23. The grounding vias 23 are metallized vias. The grounding vias 23 are connected to the back of the substrate 10 and grounded. The input port 40 is connected to the outermost resonator of the resonator group 20 through an impedance line 30 with an impedance of 50 ohms.

[0026] The advantage of this setup is that it can generate a transmission zero at the low end of the passband by folding the resonator, thereby enhancing the low-end out-of-band rejection and balancing the high and low-end rejection performance. It can also change the center frequency by adjusting the connection position of the second connecting rib and the first connecting rib, as well as the relative length of the first connecting rib and the second connecting rib. It has multiple adjustment methods, fewer limitations, and a wider range of applications.

[0027] like Figure 2 As shown, this embodiment can not only generate transmission zeros at the low end of the passband, enhance low-end out-of-band suppression, and balance high and low-end suppression indicators, but also suppress parasitic passbands near the third harmonic by about 15dB.

[0028] Preferably, in the same folded resonator 21, the two first connecting ribs 211 of the folded resonator 21 are symmetrically distributed on both sides of the second connecting rib of the folded resonator 21; further, the grounding through hole 23 on the folded resonator 21 is located at the end of the first connecting rib 211 away from the center line 11 of the folded resonator 21; further, the distance between the second connecting rib 212 of the folded resonator 21 and the grounding through hole 23 is greater than or equal to half the length of the first connecting rib 21 of the folded resonator 21.

[0029] In this embodiment, the equivalent electrical length of the folded resonator 21 is greater than or equal to half the wavelength.

[0030] In this embodiment, the substrate 10 is an alumina ceramic substrate with a dielectric constant of 9.8 and a thickness of 0.254 mm. The strength of the low-end parasitic zero point is negatively correlated with the mounting depth of the substrate 10 in the mounting cavity.

[0031] Example 2

[0032] like Figure 3 As shown, Embodiment 2 is basically the same as Embodiment 1, except that in Embodiment 2, the second connecting rib 212 is closer to the grounding hole 23, and the first connecting rib 211 is longer. That is to say, when the center frequency is constant, the closer the second connecting rib 212 is to the grounding hole 23, the longer the first connecting rib 211 is.

[0033] Example 3

[0034] like Figure 4 As shown, Embodiment 3 is basically the same as Embodiment 1, except that in Embodiment 3, all resonators are folded resonators 21. The advantage of this arrangement is that it can minimize the width of the thin-film microstrip filter.

[0035] The above are merely specific embodiments of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A thin-film microstrip filter, comprising: The long strip-shaped substrate has a center line formed by connecting the midpoints of its two long sides. A resonator group disposed on a substrate, the resonator group comprising an even number of resonators symmetrically distributed along a center line, the resonator group comprising at least an even number of folded resonators, all of which are symmetrically distributed along the center line and disposed close to the center line. Its features are: The folded resonator is H-shaped and includes two first connecting ribs parallel to the center line and spaced apart, a second connecting rib perpendicularly connected between the two first connecting ribs, and a grounding via. The two first connecting ribs are symmetrically distributed on both sides of the second connecting rib. The grounding via is located at the end of the first connecting rib away from the center line of the folded resonator. The distance between the second connecting rib and the grounding via is greater than or equal to half the length of the first connecting rib. When the center frequency is constant, the closer the second connecting rib is to the grounding via, the longer the length of the first connecting rib. This thin-film microstrip filter can change the center frequency by adjusting the connection position between the second connecting rib and the first connecting rib, and can also suppress parasitic passbands near the third harmonic.

2. The thin-film microstrip filter according to claim 1, characterized in that: The grounding via is a metallized via, and the grounding via is connected to and grounded to the back of the substrate.

3. The thin-film microstrip filter according to claim 1, characterized in that: The equivalent electrical length of the folded resonator is greater than or equal to half the wavelength.

4. The thin-film microstrip filter according to claim 1, characterized in that: The strength of the low-end parasitic zero point is negatively correlated with the mounting depth of the substrate within the mounting cavity.

5. The thin-film microstrip filter according to claim 1, characterized in that: The substrate is an alumina ceramic substrate with a dielectric constant of 9.

8.

6. The thin-film microstrip filter according to claim 1, characterized in that: The resonator also includes an even number of ordinary resonators, all of which are symmetrically distributed along the center line. The ordinary resonators are arranged in a straight line parallel to the center line and are located outside the folded resonator.

7. The thin-film microstrip filter according to any one of claims 1 to 6, characterized in that: The thin-film microstrip filter also includes an input port, which is connected to the outermost resonator of the resonator group via an impedance line with an impedance of 50 ohms.

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