CN113972455B - Mechanically Adjustable Low Pass Filter - Google Patents

Abstract

The invention discloses a mechanically adjustable low-pass filter, which comprises a metal cavity, a sliding block, a PCB (printed circuit board) and a transmission device, wherein the metal cavity is provided with a first end and a second end; the PCB is arranged below the sliding block; the sliding block slides along the length direction of the PCB through a transmission device at one end of the cavity body; the PCB comprises a lower dielectric layer and a metal conducting strip layer attached to the upper surface of the dielectric layer; the upper metal conductive tape layer consists of a first input/output end, a second input/output end and a plurality of high-low impedance transmission lines; the sliding block is provided with a plurality of metal raised lines which respectively correspond to the high-low impedance transmission lines in the longitudinal position; the slide block is pushed to move to change the coverage area of the raised strips on the slide block and the low-impedance transmission lines and the high-impedance transmission lines of the low-pass filter, so that the equivalent capacitance inductance value is changed to achieve the purpose of adjusting the cut-off frequency of the low-pass filter. The invention has the advantages of large adjusting range, high adjusting resolution and simple adjusting mode.

Description

Mechanically Adjustable Low Pass Filter

technical field

The invention discloses a mechanically adjustable low-pass filter, which belongs to the technical field of basic electrical components.

Background technique

The filter is one of the key components in radar, communication and measurement systems. Its function is to allow a certain part of the frequency signal to pass smoothly, while the other part of the frequency signal is greatly suppressed. The performance of the device has a significant impact on the overall system performance. With the continuous development of mobile communication technology and the continuous emergence of wireless communication technologies such as WCDMA and WLANs, most of them are concentrated in the low frequency band of the radio frequency and microwave frequency bands, which makes the spectrum resources particularly crowded. The passband of the traditional microstrip filter cannot be adjusted flexibly, and has the disadvantage of fixed performance. In order to adapt to different frequency bands, the traditional method is to use multiple filters and use switches to switch frequency bands, but its disadvantage is also very obvious that more switches and filters are required. Therefore, the study of tunable filters provides a good solution to this problem. The filter is used in communication equipment, and its frequency and bandwidth are very flexible to the whole system through external control, and at the same time, the use of the number of filters is reduced, which is well adapted to the development requirements of wireless communication systems.

SUMMARY OF THE INVENTION

In view of the deficiencies of the above-mentioned background technology, the present invention provides a mechanically adjustable low-pass filter, which realizes a low-frequency adjustable filter with a large cut-off frequency adjustment range and flexible adjustment, and solves the problem of inconvenient adjustment of the existing low-frequency filter. technical problem. By pushing the slider to move, the invention changes the coverage area of the convex strip on the slider and the low-pass filter low-impedance transmission line and the high-impedance transmission line, thereby changing the value of the equivalent capacitance and inductance to adjust the cut-off frequency of the low-pass filter.

The present invention adopts following technical scheme for realizing above-mentioned purpose of invention:

A mechanically adjustable low-pass filter includes a metal cavity, a slider, a PCB board and a transmission device;

The metal cavity is in the shape of a cuboid, and is composed of a cavity cover plate and a cavity main body; the cavity main body includes a first cavity short side plate, a second cavity short side plate, two long side plates and a bottom plate; A through hole is provided on the short side plate of the second cavity;

The two long side plates of the cavity body are provided with symmetrical grooves for inserting the slider; the transmission device is composed of a screw rod and a high knurled nut, one end of the screw rod is fixedly connected with the slider, and the other end of the screw rod is connected from The through hole on the short side plate of the second cavity protrudes out of the metal cavity, the part of the screw extending out of the metal cavity has an external thread, and the external thread is matched with the internal thread of the high knurled nut; the slider passes through the cavity The transmission device at one end of the main body realizes sliding along the length direction of the PCB board; the PCB board is placed under the slider;

The connection between the two long side plates and the bottom plate of the cavity body is provided with stepped protrusions for setting and fixing the low-pass filter PCB board; the PCB board includes the lower dielectric layer and the upper surface of the dielectric layer. Metal conduction band layer; the upper metal conduction band layer is composed of a first input/output end, a second input/output end and a plurality of high and low impedance transmission lines; the high impedance transmission line and the low impedance line are at the first input/output end. The output end and the second input/output end are alternately arranged, the high-impedance transmission line is in a bent shape; the low-impedance transmission line is in the shape of a rectangular strip; a plurality of metal protrusions are arranged on the slider, so the The plurality of metal ridges correspond to a plurality of high- and low-impedance transmission lines in longitudinal positions respectively; the distance between the PCB board and the slider is greater than the thickness of the metal ridges; the vertical sliding of the slider is used to change the distance between the metal ridges and the transmission line. Overlay area to change the characteristic impedance and thus the cutoff frequency of the low-pass filter.

Further, the plurality of high impedance transmission lines include a first high impedance transmission line and a second high impedance transmission line, and the plurality of low impedance transmission lines include a first low impedance transmission line, a second low impedance transmission line and a third low impedance transmission line;

the first input/output terminal, the first low-impedance transmission line, the first high-impedance transmission line, the second low-impedance transmission line, the second high-impedance transmission line, the third low-impedance transmission line and the second input/output terminal are connected in sequence; the The high-impedance transmission line and the low-impedance transmission line are arranged in parallel, the high-impedance transmission line includes a main transmission line and two corners, the two corners are connected to the low-impedance transmission line, and the corners are processed by chamfering; the first input/output end, the second input and output The ends are on the same horizontal line and symmetrical with respect to the central axis in the length direction of the PCB board, the central axis coincides with the central axis in the longitudinal direction of the second low-impedance transmission line, and the corresponding first low-impedance transmission line and the third low-impedance transmission line are symmetrical about the central axis, The first high-impedance transmission line and the second high-impedance transmission line are also symmetrical about the central axis.

Further, the first input/output end and the second input/output end are composed of a microstrip line and a suspension line; the microstrip line is 0.55mm long and 4mm wide; the suspension line is 14.97mm long , 6mm wide.

Further, the length of the low-impedance transmission line and the high-impedance transmission line are both less than a quarter of the working wavelength, and the width of the low-impedance transmission line is greater than the width of the high-impedance transmission line.

Further, the length of the first low-impedance transmission line is 47.59mm and the width is 8mm; the length of the second low-impedance transmission line is 47.59mm and the width is 20mm; the first high-impedance transmission line is divided into three sections with a width of 2.5mm, The overall length is 35mm.

Further, the plurality of metal protruding strips include: a first inductance adjustment metal strip, a second inductance adjustment metal strip, a first capacitance adjustment metal strip, a second capacitance adjustment metal strip and a third capacitance adjustment metal strip;

The first inductance adjustment metal strip and the second inductance adjustment metal strip correspond to the first high-impedance transmission line and the second high-impedance transmission line in longitudinal position and are symmetrical with respect to the central axis of the length direction of the slider; the first capacitance adjustment The metal strip and the third capacitance-adjusting metal strip correspond to the first low-impedance transmission line and the third low-impedance transmission line in longitudinal positions and are symmetrical with respect to a longitudinal center axis of the slider, which is the same as the second longitudinal center axis. The central axis of the capacitance adjustment metal strip in the length direction is coincident; the second capacitance adjustment metal strip corresponds to the longitudinal position of the second low-impedance transmission line;

The width of the first inductance adjustment metal strip and the second inductance adjustment metal strip is larger than the width of the first high impedance transmission line and the second high impedance transmission line; the width of the first capacitance adjustment metal strip and the third capacitance adjustment metal strip is the same as The widths of the first low-impedance transmission line and the third low-impedance transmission line are equal; the width of the second capacitance-adjusting metal strip is equal to the width of the second low-impedance transmission line.

When the slider is in the initial position, the first inductance adjustment metal strip and the second inductance adjustment metal strip completely cover the main transmission lines of the first high impedance transmission line and the second high impedance transmission line, respectively. The first capacitance adjustment metal strip and the second capacitance adjustment metal strip Neither the metal strip nor the third capacitance adjusting metal strip covers the first low-impedance transmission line, the second low-impedance transmission line and the third low-impedance transmission line;

After the slider starts to slide, the area of the first inductance adjustment metal strip and the second inductance adjustment metal strip covering the first high impedance transmission line and the second high impedance transmission line gradually decreases, and the first capacitance adjustment metal strip, the second capacitance adjustment metal strip and the The third capacitance-adjusting metal strip covers the first low-impedance transmission line, and the areas of the second low-impedance transmission line and the third low-impedance transmission line gradually increase.

Further, the length of the first inductance adjustment metal strip and the second inductance adjustment metal strip is 58.735mm, the width is 4.5mm, the length of the first capacitance adjustment metal strip and the third capacitance adjustment metal strip is 56.31mm, and the width is 8mm, the length of the second capacitor adjustment metal strip is 78.81mm, and the width is 20mm; the thickness of the plurality of metal strips is 7mm.

Further, there is a distance of 0.7mm between the PCB board and the metal strip on the slider; the distance between the middle of the PCB board and the bottom plate of the cavity body is 3.048mm; the dielectric constant of the lower dielectric board of the PCB board is 3.66 , the thickness is 0.254mm.

Further, the groove on the long side plate of the cavity main body is 10.302 mm away from the cavity bottom plate, and the groove width is 2 mm.

Further, the slider has a through hole for connecting with the screw rod, and the position of the through hole on the slider corresponds to the position of the through hole on the short side plate of the second cavity.

The present invention adopts the above-mentioned technical scheme, and has the following beneficial effects:

(1) The slider has a large degree of freedom of longitudinal sliding, and the accuracy of the cut-off frequency adjustment is less sensitive to the sliding distance.

(2) The cut-off frequency adjustment range is large, and the mechanically adjustable low-pass filter of the present invention can achieve a cut-off frequency adjustment range of 490 MHz on the basis of the cut-off frequency of 1 GHz.

(3) The slider can be controlled by the screw so that the capacitance and inductance can be increased or decreased at the same time. The adjustment range is wide and the return loss of the passband is maintained well during the entire adjustment process.

Description of drawings

FIG. 1 is a schematic structural diagram of a mechanically tunable low-pass filter of the present invention.

FIG. 2 is a schematic view of the front structure of the PCB board in FIG. 1 .

Figure 3 is a schematic diagram of the sliding block; Figure 3a shows the sliding block sliding 0mm, Figure 3b shows the sliding block sliding 10mm, and Figure 3c shows the sliding block sliding 30mm.

FIG. 4 is a schematic structural diagram of the slider in FIG. 1 .

Fig. 5 is the frequency response curve of S11 of the mechanically tunable low-pass filter of the present invention.

Fig. 6 is the frequency response curve of S21 of the mechanically adjustable low-pass filter of the present invention.

Description of the symbols in the figure: 1, cavity cover, 2, slider, 3, first short cavity side plate, 4, PCB board, 5, cavity body, 6, screw, 7, second short cavity side Plate, 8, High Knurled Nut, 9, First Input/Output Port, 10, Second Input/Output Port, 11, First Low Impedance Transmission Line, 12, First High Impedance Transmission Line, 13, Second Low Impedance Transmission Line , 14, the second high impedance transmission line, 15, the third low impedance transmission line, 16, the first inductance adjustment metal strip, 17, the second inductance adjustment metal strip, 18, the first capacitance adjustment metal strip, 19, the second capacitance adjustment Metal strip, 20, the third capacitor adjusting metal strip.

Detailed ways

The technical solutions of the invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, a mechanically adjustable low-pass filter disclosed in the present invention includes a metal cavity, a slider 2, a PCB board 4 and a transmission device;

The metal cavity is in the shape of a cuboid and consists of a cavity cover 1 and a cavity main body 5; the cavity main body 5 includes a first cavity short side plate 3, a second cavity short side plate 7, two long side plate and bottom plate; a through hole is provided on the short side plate 7 of the second cavity;

The two long side plates of the cavity body 5 are provided with symmetrical grooves for inserting the slider 2; the grooves on the long side plates of the cavity body 5 are 10.302 mm away from the cavity bottom plate, and the grooves The groove width is 2mm. The transmission device is composed of a screw 6 and a high knurled nut 8. One end of the screw 6 is fixedly connected with the slider 2, and the other end of the screw 6 extends out of the metal cavity from the through hole on the short side plate 7 of the second cavity. The part of the screw 6 extending out of the metal cavity has an external thread, and the external thread is matched with the internal thread of the high knurled nut 8; the slider 2 has a through hole for connecting with the screw 6, and the slider 2 is connected to the upper The positions of the holes correspond to the positions of the through holes on the short side plate 7 of the second cavity. The slider 2 slides along the length direction of the PCB board 4 through the transmission device at one end of the cavity body 5; the change of the position of the slider 2 can affect the change of the capacitance and inductance between the microstrip line on the PCB board 4 and the slider. , thereby changing the characteristic impedance to affect the cut-off frequency of the low-pass filter. At the same time, both sides of the PCB board 4 are fixed on the cavity body 5, and a cavity is formed between the middle part and the groove of the cavity body 5, that is, a suspended microstrip line structure. The PCB board 4 is placed under the slider 2; the connection between the two long side boards and the bottom plate of the cavity body 5 is provided with stepped protrusions for setting and fixing the low-pass filter PCB board 4;

As shown in FIG. 2 , the PCB board 4 includes a lower dielectric layer and a metal conduction band layer attached to the upper surface of the dielectric layer; the upper metal conduction band layer consists of a first input/output end 9 and a second input/output end 10 and multiple high and low impedance transmission lines; the multiple high impedance transmission lines include a first high impedance transmission line 12 and a second high impedance transmission line 14, and the multiple low impedance transmission lines include a first low impedance transmission line 10, a second low impedance transmission line 13 and The third low-impedance transmission line 15; the high-impedance transmission line and the low-impedance line are alternately arranged between the first input/output terminal 9 and the second input/output terminal 10, the first input/output terminal Terminal 9, the first low impedance transmission line 11, the first high impedance transmission line 12, the second low impedance transmission line 13, the second high impedance transmission line 14, the third low impedance transmission line 15 and the second input/output terminal 10 are connected in sequence; the The high-impedance transmission line is bent; the low-impedance transmission line is in the shape of a rectangular strip; the high-impedance transmission line and the low-impedance transmission line are arranged in parallel, the high-impedance transmission line includes a main transmission line and two corners, and the two corners are connected with the low-impedance transmission line, The corners are chamfered; the first input/output end 9 and the second input and output end 10 are on the same horizontal line and are symmetrical about the central axis of the length direction of the PCB board 4, the central axis and the length direction of the second low-impedance transmission line 13. The central axis of the corresponding first low-impedance transmission line 11 and the third low-impedance transmission line 15 are symmetrical about the central axis, and the first high-impedance transmission line 12 and the second high-impedance transmission line 14 are also symmetrical about the central axis. The length of the low-impedance transmission line and the high-impedance transmission line are both less than a quarter of the working wavelength, and the width of the low-impedance transmission line is greater than the width of the high-impedance transmission line.

The slider 2 is provided with a plurality of metal ridges, and the plurality of metal ridges correspond to a plurality of high- and low-impedance transmission lines in longitudinal positions respectively. The distance between the PCB board 4 and the slider 2 is greater than the thickness of the metal ridges;

The plurality of metal protrusions include: a first inductance adjustment metal strip 16, a second inductance adjustment metal strip 17, a first capacitance adjustment metal strip 18, a second capacitance adjustment metal strip 19 and a third capacitance adjustment metal strip 20;

The first inductance adjustment metal strip 16 and the second inductance adjustment metal strip 17 correspond to the first high-impedance transmission line 12 and the second high-impedance transmission line 14 in longitudinal position and are symmetrical about the central axis of the length direction of the slider 2; The first capacitance-adjusting metal strip 18 and the third capacitance-adjusting metal strip 20 correspond to the first low-impedance transmission line 11 and the third low-impedance transmission line 15 in longitudinal positions and are symmetrical with respect to the central axis in the length direction of the slider 2 . The longitudinal center axis of the slider 2 coincides with the longitudinal center axis of the second capacitance adjustment metal strip 19; the second capacitance adjustment metal strip 19 corresponds to the second low impedance transmission line 13 in the longitudinal position; the first inductance adjustment The widths of the metal strips 16 and the second inductance adjustment metal strips 17 are larger than the widths of the first high impedance transmission line 12 and the second high impedance transmission line 14; the widths of the first capacitance adjustment metal strips 18 and the third capacitance adjustment metal strips 20 are equal to The widths of the first low-impedance transmission line 11 and the third low-impedance transmission line 15 are equal; the width of the second capacitance-adjusting metal strip 19 is equal to the width of the second low-impedance transmission line 13 .

When the slider 2 is in the initial position, the first inductance adjustment metal strip 16 and the second inductance adjustment metal strip 17 completely cover the main transmission lines of the first high impedance transmission line 12 and the second high impedance transmission line 14 respectively, and the first capacitance adjustment metal strip 18. Neither the second capacitance-adjusting metal strip 19 nor the third capacitance-adjusting metal strip 20 covers the first low-impedance transmission line 10 , the second low-impedance transmission line 13 and the third low-impedance transmission line 15 ;

After the slider 2 starts to slide, the area of the first inductance adjustment metal strip 16 and the second inductance adjustment metal strip 17 covering the first high impedance transmission line 12 and the second high impedance transmission line 14 gradually decreases, and the first capacitance adjustment metal strip 18 and the second high impedance transmission line 14 gradually decrease. The second capacitance adjustment metal strip 19 and the third capacitance adjustment metal strip 20 cover the first low impedance transmission line 10 , and the areas of the second low impedance transmission line 13 and the third low impedance transmission line 15 gradually increase.

As shown in FIG. 2 , the first input/output terminal 9 and the second input/output terminal 10 are composed of transmission lines with different widths at both ends. This is because both sides of the PCB board are in contact with the cavity, and the two sides and the middle part are in contact with the cavity. The distance of the main body is different and the width of the 50Ω line needs to be recalculated.

In this embodiment, a mechanically adjustable low-pass filter with a cut-off frequency adjustment range of 0.68-1GHz is designed, and there is a 0.7mm spacing between the PCB board 4 and the metal strip on the slider 2; the PCB board 4 The distance between the middle part and the bottom plate of the cavity body 5 is 3.048 mm; the dielectric constant of the lower dielectric plate of the PCB board 4 is 3.66 and the thickness is 0.254 mm.

The first input/output end 9 and the second input/output end 10 are composed of a microstrip line and a suspension line; the microstrip line is 0.55mm long and 4mm wide; the suspension line is 14.97mm long, The width is 6mm; the length of the first low-impedance transmission line 11 is 47.59mm and the width is 8mm; the length of the second low-impedance transmission line 13 is 47.59mm and the width is 20mm; the first high-impedance transmission line 12 is divided into three sections with a width of 2.5mm, total length is 35mm.

FIG. 3 is a schematic diagram of sliding of the slider, which are respectively 0mm, 10mm and 30mm of slider sliding.

Figure 4 shows the slider structure, with the locations of the inductor-capacitor adjustment metal strips respectively noted. The length of the first inductance adjustment metal strip 16 and the second inductance adjustment metal strip 17 is 58.735mm and the width is 4.5mm, the length of the first capacitance adjustment metal strip 18 and the third capacitance adjustment metal strip 20 is 56.31mm and the width is 8mm , the length of the second capacitor adjusting metal strip 19 is 78.81mm, the width is 20mm; the thickness of the plurality of metal strips is 7mm.

The |S ₁₁ | magnitude response of the filter, the reflection characteristic response. Fig. 5 is a schematic diagram of the |S ₁₁ | frequency response graph of the mechanically tunable low-pass filter of the present invention at 0.1-2 GHz, S is the sliding distance of the slider in the cavity, and its return loss can reach below -10dB, and the cut-off The frequency range is 0.62-1.11GHz, and the cutoff frequency can vary by 490MHz.

Filter's |S ₂₁ | magnitude response, transfer characteristic response. 6 is a schematic diagram of the frequency response graph of |S ₂₁ | of the mechanically tunable low-pass filter of the present invention at 0.1-2.0 GHz, S is the sliding distance of the slider in the cavity, the insertion loss is less than 0.2 dB, and the cut-off frequency is less than 0.2 dB. The range is 0.62-1.11GHz, and the cutoff frequency can vary by 490MHz.

It should be pointed out that this embodiment only adopts the form of a fifth-order filter, and the characteristic impedance of the transmission line is changed by using a slider above the suspension line, thereby changing the cutoff frequency of the filter.

The working principle of the present invention is as follows: when the slider slides, each metal protruding strip completely or partially covers a section of high-impedance line or low-impedance line on the PCB board, respectively. When the slider slides longitudinally, the ridges covering the high-impedance transmission line and the coverage area of the high-impedance transmission line decrease, so that the equivalent characteristic impedance of the high-impedance transmission line increases, that is, the equivalent inductance value increases; at the same time, the low-impedance transmission line is covered. The increase of the coverage area between the convex strip and the low-impedance transmission line reduces the equivalent impedance of the high-impedance transmission line, that is, the equivalent capacitance value increases. The simultaneous increase of the equivalent inductance and the equivalent capacitance reduces the cut-off frequency of the low-pass filter and maintains good pass-band and stop-band characteristics, so that the cut-off frequency of the low-pass filter is mechanically adjustable.

The above descriptions are only the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments. For those of ordinary skill in the art, without departing from the principles of the present invention, the Several improvements should also be considered within the scope of protection of the present invention.

Claims (8)

1. A mechanically adjustable low-pass filter, characterized in that it comprises a metal cavity, a slider (2), a PCB board (4) and a transmission device; The metal cavity is in the shape of a cuboid and is composed of a cavity cover plate (1) and a cavity main body (5); the cavity main body (5) includes a first cavity short side plate (3), a second cavity body a short side plate (7), two long side plates and a bottom plate; a through hole is provided on the short side plate (7) of the second cavity; The two long side plates of the cavity body (5) are provided with symmetrical grooves for inserting the slider (2); the transmission device is composed of a screw rod (6) and a high knurled nut (8). (6) One end is fixedly connected to the slider (2), the other end of the screw rod (6) protrudes from the through hole on the short side plate (7) of the second cavity to the outside of the metal cavity, and the screw rod (6) protrudes out of the metal cavity The external part has an external thread, and the external thread is matched with the internal thread of the high knurled nut (8); the slider (2) is realized along the length direction of the PCB board (4) through the transmission device at one end of the cavity body (5). sliding; the PCB board (4) is placed under the slider (2); Step-shaped protrusions are provided at the connection between the two long side plates and the bottom plate of the cavity body (5) for setting and fixing the low-pass filter PCB board (4); the PCB board (4) includes a lower dielectric layer and a metal conduction band layer attached to the upper surface of the dielectric layer; the upper metal conduction band layer consists of a first input/output end (9), a second input/output end (10) and a plurality of high and low impedance transmission lines; the high and low impedance transmission lines are composed of The impedance transmission line and the low-impedance line are alternately arranged between the first input/output end (9) and the second input/output end (10), and the high-impedance transmission line is bent; The impedance transmission line is in the shape of a rectangular strip; the slider (2) is provided with a plurality of metal protruding strips, and the plurality of metal protruding strips correspond to the longitudinal positions of the plurality of high and low impedance transmission lines respectively. 2) Change the coverage area of the metal ridges on the transmission line to change the characteristic impedance to change the cut-off frequency of the low-pass filter; the distance between the PCB board (4) and the slider (2) is greater than the thickness of the metal ridges; so The plurality of high-impedance transmission lines include a first high-impedance transmission line (12) and a second high-impedance transmission line (14), and the plurality of low-impedance transmission lines include a first low-impedance transmission line (11), a second low-impedance transmission line (13), and a second low-impedance transmission line (13). three low impedance transmission lines (15); the first input/output terminal (9), the first low impedance transmission line (11), the first high impedance transmission line (12), the second low impedance transmission line (13), the second high impedance transmission line (14), the third The low-impedance transmission line (15) and the second input/output end (10) are connected in sequence; the high-impedance transmission line and the low-impedance transmission line are arranged in parallel, the high-impedance transmission line includes a main transmission line and two corners, and the two corners are connected with the low-impedance transmission line , the corners are chamfered; the first input/output end (9), the second input and output end (10) are on the same horizontal line and are symmetrical about the central axis of the length direction of the PCB board (4), the central axis and the first The central axes of the two low-impedance transmission lines (13) in the longitudinal direction coincide, and the corresponding first low-impedance transmission line (11) and the third low-impedance transmission line (15) are symmetrical about the central axis, and the first high-impedance transmission line (12) and the second The high-impedance transmission line (14) is also symmetrical about the central axis; the plurality of metal ridges include; a first inductance adjustment metal strip (16), a second inductance adjustment metal strip (17), and a first capacitance adjustment metal strip (18) ), the second capacitance adjustment metal strip (19) and the third capacitance adjustment metal strip (20); The first inductance adjustment metal strip (16) and the second inductance adjustment metal strip (17) correspond to the first high impedance transmission line (12) and the second high impedance transmission line (14) in longitudinal position and are relative to the slider ( 2) The central axis in the length direction is symmetrical; the first capacitance adjustment metal strip (18) and the third capacitance adjustment metal strip (20) are in the longitudinal direction with the first low impedance transmission line (11) and the third low impedance transmission line (15) Corresponding in position and symmetrical with respect to the central axis in the longitudinal direction of the slider (2), the central axis in the longitudinal direction of the sliding block (2) coincides with the central axis in the longitudinal direction of the second capacitor adjusting metal strip (19); the second capacitor adjusting the metal strip (19) corresponding to the longitudinal position of the second low impedance transmission line (13); The width of the first inductance adjustment metal strip (16) and the second inductance adjustment metal strip (17) is greater than the width of the first high impedance transmission line (12) and the second high impedance transmission line (14); the first capacitance adjustment The widths of the metal strip (18) and the third capacitance-adjusting metal strip (20) are equal to the widths of the first low-impedance transmission line (11) and the third low-impedance transmission line (15); the second capacitance-adjusting metal strip (19) The width is equal to the width of the second low impedance transmission line (13); When the slider (2) is in the initial position, the first inductance adjustment metal strip (16) and the second inductance adjustment metal strip (17) completely cover the first high impedance transmission line (12) and the second high impedance transmission line (14) respectively. the main transmission line, the first capacitance adjustment metal strip (18), the second capacitance adjustment metal strip (19) and the third capacitance adjustment metal strip (20) do not cover the first low impedance transmission line (11), the second low impedance transmission line (13) and a third low-impedance transmission line (15); After the slider (2) starts to slide, the area of the first inductance adjustment metal strip (16) and the second inductance adjustment metal strip (17) covering the first high impedance transmission line (12) and the second high impedance transmission line (14) gradually decreases , the first capacitance adjustment metal strip (18), the second capacitance adjustment metal strip (19) and the third capacitance adjustment metal strip (20) cover the first low impedance transmission line (11), the second low impedance transmission line (13) and the third capacitance adjustment metal strip (20). The areas of the three low-impedance transmission lines (15) gradually increase. 2. The mechanically adjustable low-pass filter according to claim 1, wherein the first input/output end (9) and the second input/output end (10) are composed of a section of microstrip line and a section of The suspension line is composed; the microstrip line is 0.55mm long and 4mm wide; the suspension line is 14.97mm long and 6mm wide. 3. The mechanically tunable low-pass filter according to claim 1, wherein the length of the low-impedance transmission line and the high-impedance transmission line are both less than a quarter of the operating wavelength, and the width of the low-impedance transmission line is greater than the high-impedance transmission line. The width of the transmission line. 4. The mechanically adjustable low-pass filter according to claim 3, characterized in that the first low-impedance transmission line (11) has a length of 47.59 mm and a width of 8 mm; the second low-impedance transmission line (13) The length is 47.59mm and the width is 20mm; the first high impedance transmission line (12) is divided into three sections, the width is 2.5mm and the total length is 35mm. 5. The mechanically adjustable low-pass filter according to claim 4, wherein the first inductance adjustment metal strip (16) and the second inductance adjustment metal strip (17) have a length of 58.735 mm and a width of 58.735 mm. The length of the first capacitor adjustment metal strip (18) and the third capacitor adjustment metal strip (20) is 56.31mm and the width is 8mm. The length of the second capacitor adjustment metal strip (19) is 78.81mm and the width is 20mm. ; The thickness of the plurality of metal strips is 7mm. 6. The mechanically adjustable low-pass filter according to claim 5, characterized in that, there is a distance of 0.7 mm between the PCB board (4) and the metal strip on the slider (2); the PCB board (4) 4) The distance between the middle part and the bottom plate of the cavity body (5) is 3.048mm; the dielectric constant of the lower dielectric plate of the PCB board (4) is 3.66 and the thickness is 0.254mm. 7 . The mechanically adjustable low-pass filter according to claim 1 , wherein the groove on the long side plate of the cavity main body ( 5 ) is 10.302 mm away from the cavity bottom plate, and the groove has a width of 10.302 mm. 8 . is 2mm. 8. The mechanically adjustable low-pass filter according to claim 1, characterized in that, the slider (2) has a through hole for connecting with the screw (6), and the slider (2) has a through hole on it. The position of the through hole corresponds to the position of the through hole on the short side plate (7) of the second cavity.

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