Microstrip line filter suitable for L wave band

Abstract

The microstrip line filter comprises a PCB substrate, a reference ground plane and a filter body, the reference ground plane is located on the bottom layer of the PCB substrate, and the filter body is located on the top layer of the PCB substrate. The filter body comprises an input matching unit, a first filtering unit, a second filtering unit, a third filtering unit, a fourth filtering unit, a fifth filtering unit and an output matching unit; the input matching unit and the output matching unit are impedance microstrip lines with the same shape, and the input matching unit and the output matching unit are symmetrically distributed on the PCB substrate with the third filtering unit as the center. The microstrip line filter designed by the utility model is small in size, high in precision, easy to process, low in cost, large in power capacity and easy to integrate into a circuit; the microstrip line filter is small in insertion loss, small in reflection coefficient and excellent in performance; the microstrip line filter provided by the utility model is high in out-of-band rejection, especially high in out-of-band rejection at a frequency doubling position.

Description

Technical Field

[0001] The invention belongs to the technical field of microstrip filters, and in particular relates to a microstrip line filter suitable for an L-band. Background Art

[0002] In recent years, the rapid development of wireless communications and the continuous emergence of wireless communication system applications have made the already stretched spectrum resources increasingly tight. In order to increase communication capacity and reduce signal crosstalk between adjacent channels, higher requirements have been placed on the clutter suppression capability and selectivity of filters. In addition, the high-density and highly integrated development of wireless communication systems has put forward new development requirements for the miniaturization and integration of filters.

[0003] Planar filters have the advantages of small size, easy processing through photolithography technology, compatibility with other planar circuit processes, low price and suitable for mass production, and can work in a wide frequency range by using different substrate materials. Although the planar structure has weaknesses such as large insertion loss and small power capacity, it is still the most widely used filter in radio frequency and microwave circuits. For this reason, the present invention proposes a microstrip line filter suitable for L band. Summary of the invention

[0004] The object of the present invention is to provide a microstrip line filter suitable for L band to solve the problems raised in the above background technology.

[0005] To achieve the above-mentioned object, the present invention provides the following technical solutions: a microstrip line filter suitable for L-band, comprising a PCB substrate, a reference ground plane, and a filter body, wherein the reference ground plane is located at the bottom layer of the PCB substrate, and the filter body is located at the top layer of the PCB substrate, and the filter body comprises an input matching unit, a first filtering unit, a second filtering unit, a third filtering unit, a fourth filtering unit, a fifth filtering unit, and an output matching unit; the input matching unit and the output matching unit are impedance microstrip lines of the same shape, and the input matching unit and the output matching unit are symmetrically distributed on the PCB substrate with the third filtering unit as the center;

[0006] The first filter unit and the second filter unit are step impedance resonator structures of the same shape, and the first filter unit and the second filter unit are symmetrically distributed on the PCB substrate with the third filter unit as the center;

[0007] The third filtering unit is distributed at the center of the PCB substrate, and the third filtering unit is composed of a fan-shaped microstrip line and a transmission line;

[0008] The fourth filter unit and the fifth filter unit have the same shape, and are symmetrically distributed on the PCB substrate with the third filter unit as the center.

[0009] Preferably, the step impedance resonator is two sections of straight microstrips or bent microstrips.

[0010] Preferably, the step impedance resonator is arranged on the same side or both sides of the transmission line.

[0011] Preferably, the radius of the fan-shaped microstrip line in the third filtering unit is 3.89 mm, and the central angle is 110°.

[0012] Preferably, the PCB substrate is composed of a base material, and the material of the base material includes but is not limited to FR4, RO4350B, epoxy board, glass fiber board or mixed pressure material.

[0013] Preferably, the material of the reference ground plane includes but is not limited to copper, gold, silver or an alloy; the copper coverage area of ​​the reference ground plane is larger than the area of ​​the filter body; the material of the filter body includes but is not limited to copper, gold, silver or an alloy.

[0014] Preferably, the fourth filter unit and the fifth filter unit improve the filter's suppression effect on DC and low frequency by adding vias that are short-circuited to the ground, and use quarter-wavelength lines to reduce insertion loss in the filter passband.

[0015] Compared with the prior art, the beneficial effects of the present invention are: the microstrip line filter designed by the present invention is small in size, high in precision, easy to process, low in cost, large in power capacity, and easy to integrate into a circuit; and the microstrip line filter of the present invention has a small insertion loss, a small reflection coefficient, and excellent performance; the microstrip line filter of the present invention has high out-of-band suppression, especially high out-of-band suppression at the double frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the overall structure of the microstrip line filter of the present invention.

[0017] Figure 2 It is a schematic diagram of the positions of the input matching unit and the output matching unit of the filter body of the present invention.

[0018] Figure 3 It is a schematic diagram of the positions of the first, second, fourth and fifth filter units on the filter body of the present invention.

[0019] Figure 4 It is a schematic diagram of the position of the third filter unit on the filter body of the present invention.

[0020] Figure 5 It is a structural schematic diagram of the first filtering unit and the second filtering unit of the present invention.

[0021] Figure 6 It is another structural schematic diagram of the first filtering unit and the second filtering unit of the present invention.

[0022] Figure 7 It is a structural schematic diagram of the fourth filtering unit and the fifth filtering unit of the present invention.

[0023] Figure 8 It is another structural schematic diagram of the fourth filtering unit and the fifth filtering unit of the present invention.

[0024] Fig. 9 It is the amplitude-frequency response diagram of the microstrip line filter of the present invention.

[0025] Wherein: 1. PCB substrate, 2. reference ground plane, 3. filter body, 31. input matching unit, 32. first filtering unit, 33. second filtering unit, 34. third filtering unit, 35. fourth filtering unit, 36. fifth filtering unit, 37. output matching unit. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] See also Figures 1 to 9 , provides a technical solution: a microstrip line filter suitable for L band, comprising a PCB substrate 1, a reference ground plane 2, and a filter body 3, wherein the reference ground plane 2 is located at the bottom layer of the PCB substrate 1, the filter body 3 is located at the top layer of the PCB substrate 1, and the filter body 3 comprises an input matching unit 31, a first filtering unit 32, a second filtering unit 33, a third filtering unit 34, a fourth filtering unit 35, a fifth filtering unit 36, and an output matching unit 37; the input matching unit 31 and the output matching unit 37 are of the same shape, and have a line width of 1.09 mm and a line length of 3 mm, and are 50Ω impedance microstrip lines, and the input matching unit 31 and the output matching unit 37 are symmetrically distributed on the PCB substrate 1 with the third filtering unit 34 as the center;

[0028] The first filter unit 32 and the second filter unit 33 are step impedance resonator structures of the same shape, the purpose of which is to increase the transmission zero point to improve the out-of-band suppression characteristics of the filter. The present invention adopts two transmission lines of different specifications, the first one has a line width of 0.35 mm and a line length of 5.35 mm; the second one has a line width of 1.89 mm and a line length of 8.98 mm; the first filter unit 32 and the second filter unit 33 are symmetrically distributed on the PCB substrate 1 with the third filter unit 34 as the center;

[0029] The third filtering unit 34 is distributed at the center of the PCB substrate 1, and the third filtering unit 34 is composed of a fan-shaped microstrip line and a transmission line; the radius of the fan-shaped microstrip line in the third filtering unit 34 is 3.89 mm, the central angle is 110°, the transmission line width is 0.6 mm, and the line length is 25 mm; the third filtering unit 34 is a deformation form of the traditional step impedance filter, the transmission line is a high impedance line, that is, the inductance is equivalent; the fan-shaped is a low impedance line, that is, the capacitance is equivalent; since the low impedance line used in the traditional step impedance filter is in a rectangular form, there will be a parasitic passband near 4 GHz, and the fan-shaped microstrip line in the present invention can effectively suppress this parasitic passband.

[0030] The fourth filter unit 35 and the fifth filter unit 36 ​​have the same shape, and are symmetrically distributed on the PCB substrate 1 with the third filter unit 34 as the center; the fourth filter unit 35 and the fifth filter unit 36 ​​improve the filter's suppression effect on DC and low frequencies by adding vias that are short-circuited to the ground, and use quarter-wavelength lines to reduce insertion loss in the filter passband.

[0031] In this embodiment, preferably, the step impedance resonator is two straight microstrips, such as Figure 6 As shown, it can also be a bent microstrip, such as Figure 5 shown.

[0032] In this embodiment, preferably, the step impedance resonator is arranged on the same side or both sides of the transmission line.

[0033] In this embodiment, preferably, the PCB substrate 1 is composed of a base material, and the material of the base material includes but is not limited to FR4, RO4350B, epoxy board, glass fiber board or mixed pressure material.

[0034] In this embodiment, preferably, the material of the reference ground plane 2 includes but is not limited to copper, gold, silver or an alloy; the copper-clad coverage area of ​​the reference ground plane 2 is larger than the area of ​​the filter body 3; the material of the filter body 3 includes but is not limited to copper, gold, silver or an alloy.

[0035] Although embodiments of the present invention have been shown and described (see the above detailed description for details), it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A microstrip line filter suitable for L-band, comprising a PCB substrate (1), a reference ground plane (2), and a filter body (3), wherein the reference ground plane (2) is located at the bottom layer of the PCB substrate (1), and the filter body (3) is located at the top layer of the PCB substrate (1), characterized in that: The filter body (3) comprises an input matching unit (31), a first filtering unit (32), a second filtering unit (33), a third filtering unit (34), a fourth filtering unit (35), a fifth filtering unit (36), and an output matching unit (37); the input matching unit (31) and the output matching unit (37) are impedance microstrip lines of the same shape, and the input matching unit (31) and the output matching unit (37) are symmetrically distributed on the PCB substrate (1) with the third filtering unit (34) as the center; The first filter unit (32) and the second filter unit (33) are step impedance resonator structures of the same shape, and the first filter unit (32) and the second filter unit (33) are symmetrically arranged on the PCB substrate (1) with the third filter unit (34) as the center; The third filtering unit (34) is distributed at the center of the PCB substrate (1), and the third filtering unit (34) is composed of a fan-shaped microstrip line and a transmission line; The fourth filter unit (35) and the fifth filter unit (36) have the same shape, and are symmetrically distributed on the PCB substrate (1) with the third filter unit (34) as the center.

2. The microstrip line filter suitable for L band according to claim 1, characterized in that: The step impedance resonator is two sections of straight microstrips or bent microstrips.

3. The microstrip line filter suitable for L band according to claim 2, characterized in that: The step impedance resonator is arranged on the same side or both sides of the transmission line.

4. The microstrip line filter suitable for L band according to claim 1, characterized in that: The radius of the fan-shaped microstrip line in the third filtering unit (34) is 3.89 mm, and the center angle is 110°.

5. The microstrip line filter suitable for L band according to claim 1, characterized in that: The PCB substrate (1) is composed of a base material, and the material of the base material includes but is not limited to FR4, RO4350B, epoxy board, glass fiber board or mixed pressure material.

6. The microstrip line filter suitable for L band according to claim 1, characterized in that: The material of the reference ground plane (2) includes, but is not limited to, copper, gold, silver or an alloy; the copper-clad coverage area of ​​the reference ground plane (2) is larger than the area of ​​the filter body (3); the material of the filter body (3) includes, but is not limited to, copper, gold, silver or an alloy.

7. The microstrip line filter suitable for L band according to claim 1, characterized in that: The fourth filter unit (35) and the fifth filter unit (36) improve the filter's suppression effect on direct current and low frequency by adding via holes that are short-circuited to the ground, and use a quarter-wavelength line to reduce the insertion loss in the filter passband.

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