Strip line filter

Abstract

The utility model provides a strip line filter. The strip line filter comprises a top-layer PCB, a middle-layer PCB and a bottom-layer PCB, micro-strip lines are laid on the bottom layer PCB and the middle layer PCB. The microstrip line of the bottom PCB comprises a bottom input straight-through line and a bottom output straight-through line which are located at the two ends of the bottom PCB in the length direction respectively and extend from the ends to the middle. The microstrip line of the middle-layer PCB comprises a middle input straight-through line and a middle output straight-through line which are located at the two ends of the middle-layer PCB in the length direction respectively and extend towards the middle from the positions away from the ends by a preset distance, and a pair of L-shaped coupling lines symmetrically arranged between the middle input straight-through line and the middle output straight-through line. The plurality of linear coupling lines are arranged between the L-shaped coupling lines in a staggered and spaced manner; and the L-shaped coupling line and the linear coupling line form a coupling part. According to the strip line filter, the environmental restriction of a microstrip filter is eliminated, the strip line filter has a high rectangular coefficient, and higher suppression degree is realized under the same volume.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of microwave components, and relates to filter technology, in particular to a stripline filter. BACKGROUND

[0002] A filter is one of main microwave devices, and is used for constituting a microwave assembly. Inside the microwave assembly, various types of radio frequency devices are connected in series mainly through microstrip lines. The filter is usually a microstrip filter directly processed by a PCB, so as to reduce the matching damage between the microstrip line and the filter. However, the conventional microstrip filter is limited by the surface characteristics of the microstrip line, has a small rectangular coefficient, and the suppression index is affected by the environment, so it is difficult to work in an ideal state and is difficult to meet the requirements of the microwave assembly. CONTENT OF THE UTILITY MODEL

[0003] In order to solve the above problems of the prior art, the application provides a stripline filter, which is formed by three layers of PCBs and microstrip lines on different layers, eliminates the environmental constraints of the microstrip filter, has a high rectangular coefficient, and realizes a higher suppression system under the same volume.

[0004] In order to achieve the above purpose, the utility model adopts the following technology:

[0005] A stripline filter comprises a top layer PCB, a middle layer PCB and a bottom layer PCB which are stacked from top to bottom in sequence.

[0006] The bottom layer PCB and the middle layer PCB are both provided with microstrip lines.

[0007] The microstrip lines on the bottom layer PCB include a bottom layer input straight-through line and a bottom layer output straight-through line which are respectively located at both ends of the length direction of the bottom layer PCB and extend from the ends to the middle.

[0008] The microstrip lines on the middle layer PCB include a middle layer input straight-through line and a middle layer output straight-through line which are respectively located at both ends of the length direction of the middle layer PCB and extend from a predetermined distance from the ends to the middle, a pair of L-shaped coupling lines symmetrically arranged between the middle layer input straight-through line and the middle layer output straight-through line, and a plurality of straight line type coupling lines staggered and arranged at intervals between the L-shaped coupling lines; the L-shaped coupling lines and the straight line type coupling lines constitute a coupling part.

[0009] The L-shaped coupling line includes a first segment parallel to the width direction of the middle layer PCB and a second segment perpendicularly connected to one end of the first segment, and the middle layer input straight-through line and the middle layer output straight-through line are perpendicularly orthogonally connected to the first segment of the corresponding L-shaped coupling line.

[0010] The intermediate input through line is connected with the bottom layer input through line through the first via hole penetrating from the intermediate layer PCB to the bottom layer PCB, and the intermediate output through line is connected with the bottom layer output through line through the second via hole penetrating from the intermediate layer PCB to the bottom layer PCB.

[0011] The top layer PCB, the intermediate layer PCB and the bottom layer PCB are all paved with ground copper areas, and the ground copper areas are provided with grounding via holes connecting the ground copper areas of the top layer PCB, the intermediate layer PCB and the bottom layer PCB.

[0012] The strip line filter of the utility model has the advantages of eliminating the environmental restriction of the microstrip filter, greatly improving the suppression index of the filter in performance, being convenient to install by adopting the SMT process when applied, and easily realizing batch production.

[0013] The strip line filter of the utility model eliminates the environmental restriction of the microstrip filter, greatly improves the suppression index of the filter in performance, is convenient to install by adopting the SMT process when applied, and easily realizes batch production. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a strip line filter exploded structure schematic diagram of the embodiment of the application.

[0015] Figure 2 It is an electromagnetic simulation plane prototype model of the embodiment of the application.

[0016] Figure 3 It is a simulation result parameter diagram of the electromagnetic simulation plane prototype model of the embodiment of the application.

[0017] Figure 4 It is an electromagnetic three-dimensional model schematic diagram of the embodiment of the application.

[0018] Figure 5 It is a simulation result parameter diagram of the electromagnetic three-dimensional model of the embodiment of the application.

[0019] Figure 6 It is a measured curve diagram of the strip line filter of the embodiment of the application after being installed on a test board.

[0020] The drawing mark: 1-top layer PCB, 2-intermediate layer PCB, 3-bottom layer PCB, 4-bottom layer input through line, 5-bottom layer output through line, 6-intermediate input through line, 7-intermediate output through line, 8-first via hole, 9-second via hole, 10-grounding via hole, 11-L type coupling line, 12-straight line type coupling line, 13-input connecting part, 14-coupling part, 15-output connecting part. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the utility model clearer, the embodiments of the utility model will be described in detail below with reference to the drawings, but the embodiments described by the utility model are part of the embodiments of the utility model, rather than all the embodiments.

[0022] The embodiment of the application provides a strip line filter, as shown in the figure, which is prepared by using Rogers RO4003 substrate and comprises top layer PCB board 1, middle layer PCB board 2 and bottom layer PCB board 3 which are sequentially and vertically laminated. Figure 1 The bottom layer PCB board 3 is provided with microstrip pads.

[0023] The bottom layer PCB board 3 and the middle layer PCB board 2 are both provided with microstrip wires, and the microstrip wires are copper sheets.

[0024] The microstrip wire on the bottom layer PCB board 3 comprises bottom layer input through line 4 and bottom layer output through line 5 which are respectively located at both ends of the length direction of the bottom layer PCB board 3 and extend from the ends to the middle.

[0025] The microstrip wire on the middle layer PCB board 2 comprises middle layer input through line 6 and middle layer output through line 7 which are respectively located at both ends of the length direction of the middle layer PCB board 2 and extend from a predetermined distance from the ends to the middle, a pair of L-shaped coupling lines 11 which are symmetrically arranged between the middle layer input through line 6 and the middle layer output through line 7, and a plurality of straight line type coupling lines 12 which are staggered and arranged at intervals between the L-shaped coupling lines 11. The L-shaped coupling lines 11 and the straight line type coupling lines 12 constitute a coupling part 14.

[0026] The L-shaped coupling line 11 comprises a first segment which is parallel to the width direction of the middle layer PCB board 2 and a second segment which is vertically connected to one end of the first segment, and the middle layer input through line 6 and the middle layer output through line 7 are respectively vertically and orthogonally connected to the first segment of the corresponding L-shaped coupling line 11. Figure 1 As shown in the middle, the middle layer input through line 6 is vertically and orthogonally connected to the input connecting part 13 on the first segment of the L-shaped coupling line 11 on the left side, and the middle layer output through line 7 is vertically and orthogonally connected to the output connecting part 15 on the first segment of the L-shaped coupling line 11 on the right side.

[0027] The middle layer input through line 6 is connected to the bottom layer input through line 4 through the first via hole 8 which penetrates from the middle layer PCB board 2 to the bottom layer PCB board 3, and the middle layer output through line 7 is connected to the bottom layer output through line 5 through the second via hole 9 which penetrates from the middle layer PCB board 2 to the bottom layer PCB board 3. Specifically, the first via hole 8 and the second via hole 9 are metallized via holes.

[0028] The top layer PCB board 1, the middle layer PCB board 2 and the bottom layer PCB board 3 are all provided with a ground copper area, and the ground copper area is provided with a ground via 10 connecting the ground copper areas of the top layer PCB board 1, the middle layer PCB board 2 and the bottom layer PCB board 3. The ground via 10 is arranged on both sides of the length direction of the top layer PCB board 1, the middle layer PCB board 2 and the bottom layer PCB board 3. Specifically, the ground via 10 is a metallized via.

[0029] The ground copper area of the middle layer PCB board 2 is located at the periphery of the middle input straight line 6, the middle output straight line 7 and the coupling part 14. The middle input straight line 6 and the middle output straight line 7 are not connected with the ground copper area of the middle layer PCB board 2, and the other end of the first segment of the L-shaped coupling line 11 is connected with the ground copper area of the middle layer PCB board 2; each straight line type coupling line 12 is connected with the ground copper area of the middle layer PCB board 2 at only one end, wherein the different ends of adjacent straight line type coupling lines 12 are respectively connected with the ground copper areas of different side edges of the middle layer PCB board 2. The bottom layer input straight line 4 and the bottom layer output straight line 5 are not connected with the ground copper area of the bottom layer PCB board 3.

[0030] In order to verify the feasibility of the scheme of the present example, a filter covering a working frequency band of 10.5GHz-12.4GHz is selected to perform simulation design, and the design index requirements are as follows:

[0031] 1: working frequency: 10.5GHz-12.4GHz;

[0032] 2: input-output return loss: ≤-12dB;

[0033] 3: insertion loss: ≤3dB;

[0034] 4: in-band fluctuation: ≤1dB;

[0035] 5: suppression: ≥60dBc@4GHz-8GHz&15GHz-20GHz.

[0036] Firstly, the simulation software Genesye is used to perform preliminary modeling simulation, the original model is shown in Figure 2 , and the original model simulation result is shown in Figure 3 , wherein S11 is the return loss and S21 is the insertion loss. The lengths of each straight line and each coupling line to be designed are determined through preliminary simulation. It can be seen from the electronic plane original model that 13 orders need to be used in the original model to meet the requirements of high suppression and in-band fluctuation.

[0037] According to the Figure 2 original model, the structure is optimized, a design scheme of 13 orders is adopted, and the characteristics of the stripline are used to design the stripline filter according to the scheme of the present example. According to this design scheme, an electromagnetic three-dimensional model is established by using the HFSS simulation software, as shown inFigure 4 As shown, the sky-blue area represents the Rogers RO4003 substrate, and the yellow section in the middle is the designed microstrip line circuit. After completing the 3D model, the corresponding performance requirements were loaded into the HFSS simulation requirements for simulation. The simulation results are as follows. Figure 5 As shown.

[0038] from Figure 5 The following data can be obtained: Within the operating bandwidth of 10.5GHz-12.4GHz, the maximum loss is 1.5dB and the minimum loss is 1.28dB, meeting the requirement of ≤3dB loss; the in-band ripple is 0.22dB, which is the difference between the maximum and minimum losses, meeting the requirement of ≤1dB loss; the input and output return loss is ≤-18dB, meeting the requirement of ≤-12dB loss; the suppression of frequencies below 8GHz is 82.88dB, which is >80dBc after removing the loss; the suppression of frequencies above 15GHz is 78.82dB, which is >75dBc after removing the loss, meeting the requirement of ≥60dBc suppression.

[0039] The physical prototype was fabricated according to the design model. The three-layer PCB board is 15.5mm long, 4.8mm wide, and 1.0mm thick. After fabrication, the stripline filter was mounted on a test fixture using surface mount technology for testing. The test results are as follows. Figure 6 As shown, the processed stripline filter can achieve a suppression of less than 60dBc. Although the loss, in-band waveguide, and standing wave ratios are somewhat different from the design values, this is due to the poor performance of the testing fixture. The actual performance meets the design requirements.

[0040] The above description is only a preferred embodiment of this application and is not intended to limit this application. Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application.

Claims

1. A stripline filter, characterized by, The top layer PCB board (1), the middle layer PCB board (2) and the bottom layer PCB board (3) are sequentially stacked from top to bottom. The bottom layer PCB board (3) and the middle layer PCB board (2) are both provided with microstrip lines. The microstrip lines on the bottom layer PCB board (3) include a bottom layer input straight-through line (4) and a bottom layer output straight-through line (5) respectively located at the two ends of the length direction of the bottom layer PCB board (3) and extending from the ends to the middle. The microstrip lines on the middle layer PCB board (2) include a middle layer input straight-through line (6) and a middle layer output straight-through line (7) respectively located at the two ends of the length direction of the middle layer PCB board (2) and extending from the ends to the middle, a pair of L-shaped coupling lines (11) symmetrically arranged between the middle layer input straight-through line (6) and the middle layer output straight-through line (7), and a plurality of straight-line coupling lines (12) staggered and arranged between the L-shaped coupling lines (11). The L-shaped coupling line (11) includes a first segment parallel to the width direction of the middle layer PCB board (2) and a second segment perpendicularly connected to one end of the first segment, and the middle layer input straight-through line (6) and the middle layer output straight-through line (7) are perpendicularly and orthogonally connected to the first segment of the corresponding L-shaped coupling line (11). The middle layer input straight-through line (6) is connected to the bottom layer input straight-through line (4) through a first via hole (8) penetrating from the middle layer PCB board (2) to the bottom layer PCB board (3), and the middle layer output straight-through line (7) is connected to the bottom layer output straight-through line (5) through a second via hole (9) penetrating from the middle layer PCB board (2) to the bottom layer PCB board (3).

2. The stripline filter of claim 1, wherein, The top layer PCB board (1), the middle layer PCB board (2) and the bottom layer PCB board (3) are all provided with ground copper areas, and the ground copper areas are provided with a grounding via hole (10) connecting the ground copper areas of the top layer PCB board (1), the middle layer PCB board (2) and the bottom layer PCB board (3).

3. The stripline filter of claim 1, wherein, The microstrip lines are copper sheets.

4. The stripline filter of claim 1, wherein, The L-shaped coupling line (11) and the straight-line coupling line (12) form a coupling part (14).

5. The stripline filter of claim 2, wherein, The ground copper area of the middle layer PCB board (2) is located at the periphery of the middle layer input straight-through line (6), the middle layer output straight-through line (7) and the coupling part (14).

6. The stripline filter of claim 5, wherein, The middle layer input straight-through line (6) and the middle layer output straight-through line (7) are not connected to the ground copper area of the middle layer PCB board (2), and the other end of the first segment of the L-shaped coupling line (11) is connected to the ground copper area of the middle layer PCB board (2); each straight-line coupling line (12) is connected to the ground copper area of the middle layer PCB board (2) at only one end, and different ends of adjacent straight-line coupling lines (12) are respectively connected to the ground copper areas of different side edges of the middle layer PCB board (2).

7. The stripline filter of claim 2, wherein, The bottom layer input straight-through line (4) and the bottom layer output straight-through line (5) are not connected to the ground copper area of the bottom layer PCB board (3).

8. The stripline filter of claim 1, wherein, The top layer PCB board (1), the middle layer PCB board (2) and the bottom layer PCB board (3) adopt Rogers RO4003 substrates.

9. The stripline filter of claim 1, wherein, The microstrip lines are coated with a solder mask material.

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