Microstrip Bandpass Filter

Abstract

The present invention provides a microstrip bandpass filter, comprising a ceramic substrate, a fifth-order resonator, a first feeder interface and a second feeder interface, each resonator is composed of a microstrip line, and the fifth-order resonator comprises a first resonator, a second resonator, a third resonator, a fourth resonator and a fifth resonator arranged in sequence along the length direction of the ceramic substrate, the first resonator, the second resonator, the third resonator and the fourth resonator are all comb-shaped structures, and the third resonator is composed of a half-wavelength U-shaped microstrip line. By making the third resonator in the middle composed of a half-wavelength U-shaped microstrip line, the influence of the parasitic inductance in the through hole on the microstrip line filter is reduced, thereby improving the effect of the filter's low-frequency upward warping and high-frequency downward warping, so that the low-frequency rectangular coefficient of the stopband is improved, and the fluctuation in the passband and the insertion loss at the high frequency are reduced. At the same time, the remaining four resonators are in a comb-shaped structure, and the structure is more compact, so as to reduce the volume of the filter.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular provides a microstrip line bandpass filter. Background Art

[0002] With the rapid development of wireless communication, the division between channels is becoming more and more detailed. Microwave filters, which separate useful and useless signals, have become important components in communication systems. The quality of their performance directly affects the quality of the entire communication system. At present, microwave filters have been widely used in many fields such as microwave communication, microwave guidance, navigation, telemetry, remote control, satellite communication, and military electronic countermeasures, and the requirements for microwave filters are getting higher and higher. The existing microstrip line filter types include hairpin type, comb type, interdigital type, parallel coupling type, etc. When the filter order is the same, the parallel coupling type filter is larger in size. The hairpin type microstrip line filter is an improved filter based on the parallel coupling type filter, and still has the disadvantage of large size. The comb line and interdigital filters have the advantage of small size, but due to the influence of the parasitic inductance of the grounding hole, they show the phenomenon of low-frequency upturn and high-frequency downturn. There are the disadvantages of poor low-frequency rectangular coefficient in the stop band, high insertion loss on the high-frequency side in the pass band, and large fluctuations in the band. Summary of the invention

[0003] The object of the present invention is to provide a microstrip line bandpass filter, aiming to solve the technical problems of the microstrip line bandpass filter in the prior art, such as large volume, high insertion loss and large intra-band fluctuation.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: providing a microstrip line bandpass filter, comprising a ceramic substrate, a fifth-order resonator arranged on the ceramic substrate, and a first feeder interface and a second feeder interface respectively arranged at two ends of the ceramic substrate, each of the resonators is composed of a microstrip line, and the fifth-order resonator comprises a first resonator, a second resonator, a third resonator, a fourth resonator and a fifth resonator arranged in sequence along the length direction of the ceramic substrate, one end of the first resonator is connected to the first feeder interface, one end of the fifth resonator is connected to the second feeder interface, the first resonator, the second resonator, the third resonator and the fourth resonator are all comb structures, and the third resonator is composed of a half-wavelength U-shaped microstrip line.

[0005] Furthermore, the third resonator includes a first section and a second section extending in the width direction of the ceramic substrate and a third section extending along the length direction of the ceramic substrate, the first section and the second section are located at two ends of the third section, and the first section and the second section are respectively connected to the two ends of the third section.

[0006] Furthermore, a connection between the first section and the third section and a connection between the first section and the second section are respectively provided with chamfers.

[0007] Further, the first resonator and the fifth resonator are symmetrically arranged with respect to the third resonator, and the second resonator and the fourth resonator are mirror-symmetrically arranged with respect to the third resonator.

[0008] Further, the first resonator includes a first section extending along the width direction of the ceramic substrate and a second section bent at one end of the first section toward the second resonator, one end of the first feeder interface is connected to the middle of the first section, and a free end of the first section is grounded;

[0009] The fifth resonator includes a third section extending along the width direction of the ceramic substrate and a fourth section bent at one end of the third section toward the fourth resonator, one end of the second feeder interface is connected to the middle of the third section, and the free end of the third section is grounded.

[0010] Furthermore, a first rounded corner is respectively provided at a connection point between the first section and the second section and at a connection point between the third section and the fourth section.

[0011] Furthermore, the ceramic substrate is provided with first through holes at positions corresponding to the free end of the first section and the free end of the third section, respectively, and the free end of the first section and the free end of the third section are connected to the ground through the corresponding first through holes.

[0012] Further, the second resonator includes a first fold extending along the width direction of the ceramic substrate and a second fold bent at one end of the first fold toward the first resonator, and a free end of the first fold is grounded;

[0013] The fourth resonator includes a third fold extending along the width direction of the ceramic substrate and a fourth fold bent at one end of the third fold toward the fifth resonator, and a free end of the third fold is grounded.

[0014] Furthermore, the ceramic substrate is provided with second through holes at positions corresponding to the free ends of the first fold and the third fold, respectively, and the free ends of the first fold and the third fold are connected to the ground through the corresponding second through holes.

[0015] Furthermore, the ceramic substrate is an alumina ceramic plate with a thickness of 0.235 mm.

[0016] The beneficial effects of the present invention are as follows: compared with the prior art, the microstrip bandpass filter of the present invention reduces the influence of the parasitic inductance in the through hole on the microstrip filter by virtue of the third resonator in the fifth-order microstrip filter being composed of a half-wavelength U-shaped microstrip line, thereby improving the low-frequency upwarping and high-frequency downwarping effects of the filter, thereby improving the low-frequency rectangular coefficient of the stopband, reducing the fluctuation in the passband and the insertion loss at the high frequency, and at the same time, the remaining four resonators are in a comb-like structure, which is more compact and can reduce the volume of the filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 A schematic diagram of the structure of a microstrip bandpass filter provided by an embodiment of the present invention;

[0019] Figure 2 A schematic diagram of simulation results of a microstrip bandpass filter provided by an embodiment of the present invention;

[0020] Figure 3 A schematic diagram comparing simulation results of a microstrip bandpass filter and a fifth-order interdigital filter provided in an embodiment of the present invention.

[0021] Among them, the main marks of the drawings in the figure are:

[0022] 10-microstrip bandpass filter; 11-first resonator; 12-second resonator; 13-third resonator; 14-fourth resonator; 15-fifth resonator; 16-first feeder interface; 17-second feeder interface; 18-first fillet; 19-second fillet; 111-first section; 112-second section; 121-first fold; 122-second fold; 131-first section; 132-second section; 133-third section; 134-chamfer; 141-third fold; 142-fourth fold; 151-third section; 152-fourth section;

[0023] 20 - first through hole; 21 - second through hole. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0026] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0027] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] See also Figure 1, the microstrip bandpass filter provided by the present invention is now described. The microstrip bandpass filter 10 includes a ceramic substrate (not shown), a fifth-order resonator, a first feeder interface 16 and a second feeder interface 17, the first feeder interface 16 is used to feed in or out an electromagnetic wave signal, and the second feeder interface 17 is used to feed in or out an electromagnetic wave signal, that is, the first feeder interface 16 and the second feeder interface 17 cooperate to form the electromagnetic wave signal output end and input end of the microstrip bandpass filter, the first feeder interface 16 and the second feeder interface 17 are respectively arranged on both sides of the ceramic substrate, and the fifth-order resonator is arranged on the ceramic substrate. Among them, each resonator is composed of a microstrip line, and the fifth-order resonator includes a first resonator 11, a second resonator 12, a third resonator 13, a fourth resonator 14 and a fifth resonator 15. The first resonator 11, the second resonator 12, the third resonator 13, the fourth resonator 14 and the fifth resonator 15 are arranged in sequence along the length direction of the ceramic substrate, one end of the first resonator 11 is connected to the first feeder interface 16, and one end of the fifth resonator 15 is connected to the second feeder interface 17, so that the signal of the electromagnetic board can flow into the first resonator 11, the second resonator 12, the third resonator 13, the fourth resonator 14 and the fifth resonator 15 through the first feeder interface 16, and then flow out through the second feeder interface 17, thereby realizing the electromagnetic wave. The clutter is filtered out to achieve the stability of signal transmission, wherein the width of each resonator microstrip line is the same to reduce the insertion loss in the passband, improve the stopband suppression, and have high reliability; specifically, the first resonator 11, the second resonator 12, the third resonator 13, and the fourth resonator 14 are all in a comb-like structure, which is more compact and can reduce the size of the resonator, so as to facilitate the miniaturization of the filter 10; the third resonator 13 is composed of a half-wavelength U-shaped microstrip line, so that the half-wavelength microstrip line does not need a grounding through hole, thereby reducing the influence of the parasitic inductance in the through hole on the microstrip line bandpass filter 10, thereby improving the low-frequency warping and high-frequency warping of the filter, so that the low-frequency rectangular coefficient of the stopband is improved, and the fluctuation in the passband and the insertion loss at high frequency are reduced. In addition, by providing a fifth-order resonator on the ceramic substrate, four of which are in a comb-like structure, the structure is more compact to reduce the size of the resonator, thereby facilitating the miniaturization of the filter 10.

[0029] For further information, see Figure 1As a specific implementation of the microstrip line bandpass filter provided by the present invention, the third resonator 13 includes a first section 131, a second section 132 and a third section 133, wherein the first section 131 and the third section 133 are both extended in the width direction of the ceramic substrate, and the third section 133 extends along the length direction of the ceramic substrate, the first section 131 and the third section 133 are located at both ends of the second section 132, and the lengths of the first section 131 and the third section 133 are equal, and the first section 131 and the second section 132 are respectively connected to both ends of the third section 133, and the first section 131 and the second section 132 are respectively perpendicular to the third section 133. Such a structure, by symmetrically arranging the first section 131 and the second section 132, and making the first section 131, the second section 132 and the third section 133 form a half-wavelength U-shaped structure, reduces the influence of the parasitic inductance in the grounding through hole on the ceramic base plate on the microstrip line bandpass filter 10, thereby improving the low-frequency upward warping and high-frequency downward warping of the filter, so that the low-frequency rectangular coefficient of the stop band is improved, and the fluctuation in the passband and the insertion loss at the high frequency are reduced.

[0030] For further information, see Figure 1 As a specific implementation of the microstrip line bandpass filter provided by the present invention, the connection between the first section 131 and the third section 133 and the connection between the second section 132 and the third section 133 are respectively provided with chamfers 134, and the first section 131 and the second section 132 are respectively perpendicular to the third section 133. In this way, the right-angle connection between the microstrip lines constituting the passband is connected by chamfers 134, which can make the electromagnetic field transition smooth, reduce electromagnetic radiation and reduce losses, thereby improving the performance of the filter.

[0031] For further information, see Figure 1 As a specific implementation of the microstrip line bandpass filter provided by the present invention, the first resonator 11 and the fifth resonator 15 are symmetrically arranged with respect to the third resonator 13, and the second resonator 12 and the fourth resonator 14 are mirror-symmetrically arranged with respect to the third resonator 13. It can be understood that the first resonator 11 and the fifth resonator 15 have exactly the same shape and size, and correspondingly, the second resonator 12 and the fourth resonator 14 have the same shape, which is not only convenient for processing and manufacturing, but also convenient for design, and can also ensure the symmetry of the resonators on both sides, reduce the insertion loss of the passband, and facilitate adjustment and determination of the range of the passband.

[0032] For further information, please also refer to Figure 1As a specific embodiment of the microstrip line bandpass filter provided by the present invention, the first resonator 11 includes a first section 111 and a second section 112, the first section 111 extends along the width direction of the ceramic substrate, and the second section 112 is bent at one end of the first section 111 toward the second resonator 12, wherein the first section 111 and the second section 112 are arranged perpendicular to each other, that is, the first section 111 and the second section 112 form an L-shaped microstrip line, one end of the first feeder interface 16 is connected to the middle of the first section 111, the free end of the first section 111 is grounded, and the length of the microstrip line constituting the first resonator 11 is a quarter wavelength, which will generate a transmission zero point in the passband. Correspondingly, the fifth resonator 15 includes a third fold 141 and a fourth fold 142, the third fold 141 extends along the width direction of the ceramic substrate, and the fourth fold 142 is bent at one end of the third fold 141 toward the fourth resonator 14, and the free end of the third section 151 is grounded, wherein the third fold 141 and the fourth fold 142 are perpendicular to each other, and the length of the microstrip line constituting the fifth resonator 15 is one-quarter wavelength, so that a transmission zero point is generated in the passband, that is, two transmission zero points are generated on both sides of the filter, so that the signals will cancel each other at some radio frequency points when transmitted in each path, so that the filter can obtain better filtering signals or harmonic suppression.

[0033] For further information, see Figure 1 As a specific embodiment of the microstrip line bandpass filter provided by the present invention, the connection between the first section 111 and the second section 112 and the connection between the third section 151 and the fourth section 152 are respectively provided with a first fillet 18, that is, fillets are provided at the corners of each microstrip line, which can make the electromagnetic field transition smooth, reduce electromagnetic radiation and reduce losses, thereby improving the performance of the filter. Preferably, the ceramic substrate is provided with a first through hole 20 at the position corresponding to the free end of the first section 111 and the free end of the third section 151, and the free end of the first section 111 and the free end of the third section 151 are respectively connected to the ground through the corresponding first through hole 20. By providing the first through hole 20, the free end of the first end and the free end of the third section 151 are conveniently grounded. Preferably, the diameter of the first through hole 20 is 200um, and the through hole is filled with metal, which is convenient for processing and manufacturing.

[0034] For further information, see Figure 1As a specific embodiment of the microstrip bandpass filter provided by the present invention, the second resonator 12 includes a first fold 121 and a second fold 122, the first fold 121 extends along the width direction of the ceramic substrate, and the second fold 122 is bent at one end of the first fold 121 toward the first resonator 11, and the free end of the second section 112 is grounded, wherein the length of the microstrip line constituting the second resonator 12 is a quarter wavelength, which will generate a transmission zero point in the passband, so that the signals will cancel each other at some radio frequency points when transmitted in each path. Preferably, the first fold 121 and the second fold 122 are arranged perpendicular to each other, that is, the first fold 121 and the second fold 122 form an L-shaped microstrip line, and the second section 112 of the first resonator 11 and the second fold 122 of the second resonator 12 are parallel to each other and are respectively located on both sides of the ceramic substrate, so that parallel coupling between the two passbands is achieved. By staggering the bending parts of the two microstrip lines, the two microstrip lines are made more compact, so as to facilitate the miniaturization of the filter. Correspondingly, the fourth resonator 14 includes a third fold 141 and a fourth fold 142, wherein the third fold 141 extends along the width direction of the ceramic substrate, and the fourth fold 142 is bent at one end of the third fold 141 toward the fifth resonator 11, and the free end of the third fold 141 is grounded, wherein the length of the microstrip line constituting the fourth resonator 14 is one-quarter wavelength, which will generate a transmission zero point in the passband, so that the signals will cancel each other out at some radio frequency points when being transmitted in each path. Preferably, the third fold 141 and the fourth fold 142 are arranged perpendicular to each other, that is, the third fold 141 and the fourth fold 142 form an L-shaped microstrip line, and the fourth section 152 of the fifth resonator 15 and the fourth fold 142 of the fourth resonator 14 are parallel to each other and are respectively located on both sides of the ceramic substrate, thus realizing parallel coupling between the two passbands. By staggering the bending parts of the two microstrip lines, the two microstrip lines are made more compact, so as to facilitate the miniaturization of the filter.

[0035] For further information, see Figure 1 As a specific embodiment of the microstrip line bandpass filter provided by the present invention, second through holes 21 are respectively provided at the positions of the free ends of the first fold 121 and the third fold 141 of the ceramic substrate, and the free ends of the first fold 121 and the third fold 141 are respectively connected to the ground through the corresponding second through holes 21. By providing the through holes, the free ends of the first fold 121 and the third fold 141 can be grounded. Preferably, the through hole has a diameter of 200um, and the through hole is filled with metal, which is convenient for processing and manufacturing. In order to reduce the electromagnetic radiation and loss of the filter, a second fillet 19 is respectively provided at the connection between the first fold 121 and the second fold 122 and at the connection between the third fold 141 and the fourth fold 142.

[0036] Specifically, in the filter, the first feeder interface 16 is connected to the first resonator 11 for feeding in or out an electromagnetic wave signal; the second feeder interface 17 is connected to the fifth resonator 15 for feeding in or out an electromagnetic wave signal; the first feeder interface 16 and the second feeder interface 17 have the same width; the first resonator 11, the second resonator 12 and the third resonator 13, the fourth resonator 14 and the fifth resonator 15 are located between the first feeder interface 16 and the second feeder interface 17, and the second resonator 12 is located between the first resonator 11 and the third resonator 13. Among the three resonators 13, the first resonator 11 is close to the first feeder interface 16, and the fifth resonator 15 is close to the second feeder interface 17; the fourth resonator 14 is between the third resonator 13 and the fifth resonator 15, and the third resonator 13 is between the second resonator 12 and the fourth resonator 14; the first resonator 11, the second resonator 12, the fourth resonator 14, and the fifth resonator 15 are all composed of a quarter-wavelength microstrip line, and the third resonator 13 is composed of a half-wavelength microstrip line, and the third resonator 13 has a U-shaped structure as a whole. The first resonator 11 is in an L-shaped structure as a whole, and is composed of a first section 111 and a second section 112, and the first section 111 and the second section 112 are perpendicular to each other. The second resonator 12 is in a mirror-symmetrical structure with the first resonator 11, and is composed of a third section 151 and a fourth section 152, and the third section 151 and the fourth section 152 are perpendicular to each other. The third resonator 13 is in a U-shaped structure as a whole, and is composed of a first section 131, a second section 132 and a third section 133, and the first section 131 and the second section 132 are parallel to each other and perpendicular to the two ends of the third section 133 respectively. The resonator 12 has an L-shaped structure as a whole, and is composed of a first fold 121 and a second fold 122, and the first fold 121 and the second fold 122 are perpendicular to each other. The fourth resonator 14 has a mirror-symmetrical structure with the second resonator 12, and is composed of a third fold 141 and a fourth fold 142, and the third fold 141 and the fourth fold 142 are perpendicular to each other. The first section 111, the second section 112, the first fold 121, the second fold 122, the first section 131, the second section 132, the third section 133, the third fold 141, the fourth fold 142, the third section 151 and the fourth section 152 have the same width.In this structure, the first feeder interface 16 feeds the first resonator 11, the second feeder interface 17 feeds the fifth resonator 15, the second resonator 12 is coupled to the first resonator 11 through the first fold 121, that is, the main coupling parts of the first resonator 11 and the second resonator 12 are the first section 111 and the first fold 121, the main coupling part of the second resonator 12 and the third resonator 13 is the part where the first fold 121 overlaps with the first section 131, and correspondingly, the fourth resonator 14 is coupled to the fifth resonator 15, and the fourth resonator 14 and the fifth resonator 15 are coupled to each other. The main coupling parts of the resonator 15 are the third fold 141 and the third section 151, and the main coupling parts of the third resonator 13 and the fourth resonator 14 are the parts where the second section 132 overlaps with the third fold 141. The first resonator 11, the second resonator 12, the fourth resonator 14 and the fifth resonator 15 are all composed of microstrip lines with a length slightly equal to one-quarter wavelength. Multiple transmission zeros are generated at the passband of the filter, so that the signals will cancel each other out at some radio frequency points when transmitted in each path, so that the filter can obtain better filtering signals or harmonic suppression.

[0037] For further information, please also refer to Figures 1 to 3 As a specific implementation of the microstrip bandpass filter provided by the present invention, the ceramic substrate is an alumina ceramic plate with a thickness of 0.235 mm, so that the ceramic base plate has sufficient supporting strength while the thickness of the ceramic base plate is as small as possible, that is, the height of the through hole is as small as possible, so as to reduce the volume of the filter and the in-band insertion loss, thereby reducing the influence of the parasitic inductance of the through hole on the filter.

[0038] The present invention provides a microstrip bandpass filter, which is manufactured by a photolithography and etching process. First, a through hole is made on a ceramic substrate, and a metal material such as copper or gold is used to fill the through hole. Then, a layer of metal film is plated on the upper and lower surfaces of the ceramic substrate respectively, and then each resonator, a first feeder interface 16 and a second feeder interface 17 are formed on the upper surface of the ceramic substrate by photolithography and etching.

[0039] For further information, please also refer to Figures 1 to 3As a specific embodiment of the microstrip line bandpass filter provided by the present invention, the width L0 of each microstrip line is equal, and L0 is 0.2mm, wherein the length L1 of the first section 111 and the third section 151 is 1.72mm, the length L2 of the second section 112 and the fourth section 152 is 0.29mm, the length L3 of the first fold 121 and the third fold 141 is 1.68mm, the length L4 of the second fold 122 and the fourth fold 142 is 0.27mm, wherein the length L5 of the first section 131 and the third section 133 is 1.82mm , the length L6 of the third section 133 is 0.6mm, the first feeder interface 16 has the same vertical height as the first feeder interface 16, the distance S1 between its center and the first through hole 20 is 0.33mm, the spacing between the first section 111 and the first fold 121 is equal to the spacing between the third section 151 and the third fold 141, the spacing S1 is 0.69mm, the spacing between the first fold 121 and the first section 131 is equal to the spacing between the second section 132 and the third fold 141, the spacing S2 is 0.48mm, and the dielectric plate used in the microstrip line is an alumina ceramic plate with a thickness of 0.254mm. To reduce the volume and in-band insertion loss. The diameter of the first through hole 20 and the second through hole 21 is 200um, and the through holes are filled with metal. The present invention uses the simulation software Advanced Design System (ADS) for simulation, Figure 2 The simulation result diagram of the microstrip bandpass filter 10 proposed by the present invention and Figure 3 The simulation result diagram of the microstrip bandpass filter 10 and the fifth-order interdigital filter proposed in the present invention is shown in FIG. Among them, the horizontal axis represents the signal frequency of the filter, and the vertical axis represents the amplitude, including the amplitude of the return loss S11 and the amplitude of the insertion loss S21. S11 represents the return loss curve at each frequency in the present invention, and S21 represents the insertion loss curve at each frequency in the present invention. Correspondingly, S10 represents the return loss curve at each frequency in the fifth-order interdigital filter, and S20 represents the insertion loss curve at each frequency in the fifth-order interdigital filter. Figure 2 and Figure 3 It can be seen that the filter of the present invention has a passband range of 12.2 GHz-12.8 GHz. The filter is greater than 55 dB at 1.7 GHz away from the passband. The in-band standing wave ratio is better than 1.2. It has good frequency selectivity, simple structure, convenient processing, compact size, and is convenient for PCB circuit integration.

[0040] 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A microstrip bandpass filter, comprising a ceramic substrate, a fifth-order resonator arranged on the ceramic substrate, and a first feeder interface and a second feeder interface respectively arranged at two ends of the ceramic substrate, characterized in that: Each of the resonators is composed of a microstrip line, and the fifth-order resonator includes a first resonator, a second resonator, a third resonator, a fourth resonator and a fifth resonator which are sequentially arranged along the length direction of the ceramic substrate, one end of the first resonator is connected to the first feeder interface, one end of the fifth resonator is connected to the second feeder interface, the first resonator, the second resonator, the third resonator and the fourth resonator are all comb structures, and the third resonator is composed of a half-wavelength U-shaped microstrip line; The first resonator and the fifth resonator are symmetrically arranged with respect to the third resonator, and the second resonator and the fourth resonator are mirror-symmetrically arranged with respect to the third resonator; The first resonator comprises a first section extending along the width direction of the ceramic substrate and a second section bent at one end of the first section toward the second resonator, wherein the first section and the second section are arranged perpendicular to each other, one end of the first feeder interface is connected to the middle of the first section, the free end of the first section is grounded, and the length of the microstrip line constituting the first resonator is a quarter wavelength; The fifth resonator includes a third section extending along the width direction of the ceramic substrate and a fourth section bent at one end of the third section toward the fourth resonator, wherein the third section and the fourth section are perpendicular to each other, one end of the second feed line interface is connected to the middle part of the third section, the free end of the third section is grounded, and the length of the microstrip line constituting the fifth resonator is one quarter of a wavelength.

2. The microstrip line bandpass filter according to claim 1, characterized in that: The third resonator includes a first section and a second section extending in the width direction of the ceramic substrate and a third section extending along the length direction of the ceramic substrate. The first section and the second section are located at two ends of the third section, and the first section and the second section are respectively connected to the two ends of the third section.

3. The microstrip line bandpass filter according to claim 2, characterized in that: A connection between the first section and the third section and a connection between the first section and the second section are respectively provided with chamfers.

4. The microstrip line bandpass filter according to claim 1, characterized in that: A first rounded corner is respectively provided at a connection point between the first section and the second section and at a connection point between the third section and the fourth section.

5. The microstrip line bandpass filter according to claim 1, characterized in that: The ceramic substrate is provided with first through holes at positions corresponding to the free end of the first section and the free end of the third section, respectively. The free end of the first section and the free end of the third section are connected to the ground through the corresponding first through holes.

6. The microstrip line bandpass filter according to claim 1, characterized in that: The second resonator includes a first fold extending along the width direction of the ceramic substrate and a second fold bent at one end of the first fold toward the first resonator, and a free end of the first fold is grounded; The fourth resonator includes a third fold extending along the width direction of the ceramic substrate and a fourth fold bent at one end of the third fold toward the fifth resonator, and a free end of the third fold is grounded.

7. The microstrip line bandpass filter according to claim 6, characterized in that: The ceramic substrate is provided with second through holes at positions corresponding to the free ends of the first fold and the third fold, respectively. The free ends of the first fold and the third fold are connected to the ground through the corresponding second through holes.

8. The microstrip line bandpass filter according to any one of claims 1 to 7, characterized in that: The ceramic substrate is an alumina ceramic plate with a thickness of 0.235 mm.

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