Harmonic suppression interdigital filter

Abstract

The utility model discloses a harmonic suppression interdigital filter, which comprises a dielectric substrate, the upper surface and the lower surface of the dielectric substrate are metal layers, the dielectric substrate comprises a plurality of resonators, input / output ports and a grounding plane, the resonators are quarter-wavelength transmission lines, and the tail end of each resonator is provided with a metalized through hole to form the metalized through hole. The metalized through holes of the adjacent resonators are distributed at two opposite tail ends; the input port is a microstrip line with 50 ohm characteristic impedance and comprises an L-shaped or T-shaped demetalized groove; the upper surface of the dielectric substrate is provided with a plurality of resonators which are arranged in parallel, and every two resonators are arranged in opposite directions, so that an interdigital structure is formed. According to the utility model, out-of-band harmonic waves are suppressed without adding extra circuits, and the filter has the advantages of miniaturization, easy processing, large bandwidth and strong harmonic wave suppression.

Description

Technical Field

[0001] The utility model relates to the technical field of communication filters, in particular to a harmonic suppression interdigital filter. Background Art

[0002] With the development of society and the advancement of technology, communication frequency bands have become increasingly crowded. The scarcity of spectrum resources has resulted in very short frequency intervals between communication systems. This has put forward increasingly higher requirements on the suppression of microwave RF filters, requiring strong out-of-band suppression and harmonic suppression to reduce interference. In certain situations, large bandwidth is also required to meet high-speed communication needs.

[0003] Prior art 1:

[0004] A microstrip hairpin bandpass filter with parasitic suppression circuit, "Modern Electronic Technology" Vol. 41 No. 18. In order to solve the problem of parasitic passband near the passband of the hairpin bandpass filter, a low-pass filter is cascaded at the input end to improve the parasitic passband problem. According to the principle that the low-pass filter passes low frequencies and blocks high frequencies, the parasitic passband at high frequencies is suppressed, but there are the following defects:

[0005] 1. The low-pass filter occupies a large area of ​​the circuit board, increasing the size of the entire circuit, almost doubling the area of ​​the original band-pass filter, which is not conducive to miniaturization and increases material costs.

[0006] 2. The low-pass filter itself has a certain insertion loss. After the band-pass filter is cascaded with the low-pass filter, the insertion loss of the entire filter increases.

[0007] Prior Art 2

[0008] A microstrip bandpass filter with a parasitic passband suppression structure, publication number CN 201936973. Aiming at the problem of parasitic passband at the high end of the passband of the hairpin bandpass filter, the input transmission line is improved, and a U-shaped slot defect microstrip structure is introduced at the input end, but it has the following defects:

[0009] 1. In this structure, when the input / output port is thin, the U-shaped groove requires high processing precision and is difficult to process, which increases the cost.

[0010] 2. Judging from the transmission curve of this patent, the degree of suppression of the parasitic passband is not high and the suppression effect is not good.

[0011] 3. The passband insertion loss is large and the bandwidth is narrow. The filtering effect achieved by this structure is poor and its practicality as a filter is not high. Utility Model Content

[0012] The purpose of the utility model is to provide a harmonic suppression interdigital filter to solve the problems raised in the above background technology.

[0013] To achieve the above-mentioned object, the utility model provides the following technical solutions: a harmonic suppression interdigital filter, comprising a dielectric substrate, wherein the upper and lower surfaces of the dielectric substrate are metal layers, and the dielectric substrate comprises a plurality of resonators, an input / output port and a ground plane, wherein the resonator is a quarter-wavelength transmission line, and a metallized through hole is made at the end of each resonator to form a metallized through hole, and the metallized through holes of adjacent resonators are distributed at two opposite ends;

[0014] The upper surface of the dielectric substrate is provided with a plurality of resonators arranged in parallel, and every two resonators are placed in opposite directions to form an interdigital structure, and the number of resonators is determined according to design indicators.

[0015] Preferably, the metallized through hole electrically connects the resonator to the ground plane, and the number of metallized through holes on each resonator is 1 to 3, which can be selected according to the size and process restrictions. According to the manufacturing process requirements provided by the processing manufacturer, the parameters within the process requirements are selected for design. The resonator line width is narrow, so one hole is selected, and the line width is wide, so 2-3 holes can be selected according to actual conditions. The purpose is to ensure the quality of the metallized through hole, so as to form a good electrical connection. According to the process requirements provided by a manufacturer, the minimum aperture of the double-sided board is 0.3mm, and the minimum spacing between the hole edges of the vias is 0.254mm, so as to avoid the phenomenon of no copper in the hole due to the hole spacing being too close, resulting in the drill bit breaking and plugging during drilling. The patent has a line width of 1.4mm, and a hole with a diameter of 0.6mm is selected, which is sufficient to ensure the quality of the through-hole metallization, thereby ensuring a good electrical connection.

[0016] Preferably, the ground plane is a whole metal layer without any demetallization pattern.

[0017] Preferably, the input / output port is a microstrip line with a characteristic impedance of 50 ohms, including a demetallized slot to form an LC parallel resonant circuit, thereby generating a transmission zero point at the high end of the passband, thereby producing a harmonic suppression effect.

[0018] Preferably, the demetallization slot is an L-shaped or T-shaped demetallization slot, the number of the demetallization slots is greater than or equal to 1, and a plurality of demetallization slots can be cascaded to form a plurality of transmission zeros, thereby achieving harmonic suppression in a wider frequency band.

[0019] Compared with the prior art, the beneficial effects of the utility model are:

[0020] 1. No additional circuit area is required. Only the input and output ports need to be structurally improved to achieve high harmonic suppression, save circuit area, and achieve miniaturization.

[0021] 2. The use of interdigital structure and demetallized slots can achieve both wide bandwidth and high harmonic suppression.

[0022] 3. The input / output port includes an L-shaped or T-shaped demetallized groove, which is easier to process and realize than the defective groove of the prior art 2, has lower processing accuracy requirements and lower costs. Moreover, it can be cascaded to suppress harmonics in a wider frequency band.

[0023] 4. The harmonic suppression effect is stronger, and the size of the demetallization slot can be flexibly adjusted to suppress harmonics at specific frequencies. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a common planar interdigital filter;

[0025] Figure 2 This is a simulation result diagram of a common planar interdigital filter;

[0026] Figure 3 It is a schematic diagram of the structure of the utility model;

[0027] Figure 4 It is the simulation result of the utility model;

[0028] Figure 5 Another implementation diagram of the input / output port of the utility model;

[0029] Figure 6 It is a cascade model diagram of two-stage demetallization tank;

[0030] Figure 7 This is the simulation result diagram of the input / output port;

[0031] Figure 8 The simulation result diagram of the cascade model of two-stage demetallization slots;

[0032] Fig. 9 The utility model is a method flow chart.

[0033] In the figure: 1. Resonator; 2. Metallized through hole; 3. Input / output port; 4. Ground plane; 5. Dielectric substrate; 6. Demetallized groove. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0035] See also Figure 1-9The utility model provides a technical solution: a harmonic suppression interdigital filter, including a 3-layer structure, the first and third layers are metal pattern layers, the second layer is a dielectric substrate 5, the first layer has 9 parallel resonators 1 and two input / output port lines 3, each resonator is electrically connected to a ground plane 4 through a metallized through hole 2, and every two resonators are placed in reverse to form an interdigital structure, and the coupling amount between the resonators is adjusted by changing the distance between the resonators or the length of the overlap. When the distance between the resonators is too close to reach the process limit, the coupling size is adjusted by adjusting the length of the overlap.

[0036] The width of the input / output port 3 is 50 ohm line width, and the length is designed according to the length of the inner conductor of the connector. The length needs to be greater than the length of the inner conductor of the connector. In addition to the length of the demetallized slot, a reserved length is required for the inner conductor to be welded to the input / output port 3. The input / output port 3 and the first-stage resonator 1 are modeled and simulated separately to obtain the delay value of the input port as the target delay value. The delay value is optimized by adjusting and optimizing the length of the input / output port 3 and the position of connection with the first-stage resonator 1, so that it approaches the target delay value, thereby determining the length of the input / output port 3 and the position of connection with the first-stage resonator 1.

[0037] The input / output port 3 includes an L-shaped or T-shaped demetallized slot 6. The working principle of the demetallized slot is as follows: after the input / output port 3 is demetallized, a thinner microstrip line and a thicker microstrip line are formed. The thicker microstrip line is equivalent to an inductor. The thinner microstrip line and the thicker microstrip line are coupled to each other through the demetallized slot and are equivalent to a capacitor. The inductor and the capacitor form a parallel resonant circuit, and the resonant frequency is:

[0038]

[0039] The L-shaped or T-shaped demetallized groove 6 is equivalent to an inductor and a capacitor parallel resonant circuit, thereby generating resonance at a specific frequency, so that a transmission zero point is generated in the transmission curve, and the signal of a specific frequency is suppressed, thereby suppressing harmonics. The resonant frequency of the parallel resonant circuit can be adjusted by adjusting the inductor or capacitor value. Specifically, the transmission zero point is moved to the frequency where harmonic suppression is required by adjusting the length or width of the demetallized groove.

[0040] Fig. 9 The method flow chart of the utility model is as follows:

[0041] S1: According to the index simulation, the filter without L-shaped demetallization slot is obtained. The transmission curve of the filter is as follows Figure 2 As shown, it can be seen that strong harmonics are generated at the high end of the passband.

[0042] S2: Simulate the input / output port with L-shaped demetallization slot Figure 7 From the S parameters shown, it can be seen that the transmission curve has a notch, which is used to suppress the harmonics of the filter.

[0043] S3: Adjust the length or width of the L-shaped demetallization groove so that the transmission zero point moves to the frequency where harmonic suppression is required, thereby determining the initial value of the size of the L-shaped demetallization groove.

[0044] S4: The initial value of the L-shaped slot size is brought into the entire filter model for simulation optimization. Specifically, the length or width of the L-shaped slot is optimized to obtain Figure 4 The transmission curve shown. Comparison of the transmission curves before and after the L-shaped demetallization groove Figure 2 and Figure 4 , and find the difference in harmonic suppression.

[0045] The dielectric substrate material in the embodiment is Rogers 5880 plate, with a relative dielectric constant of 2.2, a thickness of 0.508mm, a thickness of the first three metal layers of 1oz, and an operating frequency band of 10.7-12.7GHz. The width and length of the resonator are calculated based on the relative dielectric constant, the thickness of the plate, and the operating frequency. The width of the input and output ports is 1.4mm, the width of the resonator is also 1.4mm for a 50-ohm line width, and the length of the resonator is about 4.3mm, which is a quarter wavelength. During the specific simulation, the filtering effect is achieved by adjusting the length of each resonator and the coupling of the resonators. The length or width of the demetallized groove is adjusted so that the transmission zero point moves to the frequency where harmonic suppression is required to obtain an L-shaped demetallized groove with a long side length of 1.4mm, a short side length of 0.7mm, and a demetallized groove width of 0.3mm. By optimizing the parameters of the entire filter, a transmission curve with a harmonic suppression effect is finally obtained.

[0046] Figure 2 For ordinary filter Figure 1 From the transmission curve, it can be seen that strong harmonics are generated at the high end of the out-of-band, and the suppression degree of the worst frequency point is -13dB. If it is not suppressed, it will affect the spurious of the system and thus affect the sensitivity of the system. Therefore, harmonic suppression is very important. Figure 4 This is the simulation curve of the embodiment of the utility model. The harmonic suppression in the frequency band that needs to be suppressed at the high end of the out-of-band can reach about 74dB, and the suppression effect is very obvious. Figure 2 and Figure 4 It can be seen that the difference in harmonic suppression before and after the L-shaped demetallized groove can reach about 60dBc, and the harmonic suppression effect is significant. By adjusting the length and width of the demetallized groove 6, an interdigital filter with high harmonic suppression is achieved.

[0047] Another implementation of input / output port 3 is as follows Figure 5 As shown, the T-shaped demetallized slot can also achieve good harmonic suppression effect.

[0048] Demetallized slots can also be cascaded to achieve multiple transmission zeros, thereby achieving harmonic suppression in a wider frequency band. Figure 6 The figure shows a model of two cascaded demetallized slots. The two demetallized slots are equivalent to two LC parallel resonant tanks, which produce two transmission zeros. Figure 8 The simulation results of the model with two demetallized slots cascaded show that two zeros are realized between 18 GHz and 20 GHz, and the positions of the two zeros can be flexibly controlled separately. The closer the two zeros are, the narrower the bandwidth of harmonic suppression is, and vice versa. Theoretically, N demetallized slots 6 can be cascaded to achieve N transmission zeros. Although increasing the number of cascades can achieve wider harmonic suppression, the size will increase. Therefore, a compromise design is required in terms of size and performance.

[0049] The utility model can suppress harmonics at a specific frequency without adding a new circuit, thus realizing miniaturization; the L-shaped or T-shaped demetallized groove is simple to process, easy to realize, and has low requirements on processing conditions; it can simultaneously meet the requirements of large bandwidth and high harmonic suppression; the L-shaped or T-shaped demetallized groove can be cascaded to realize multiple transmission zero points, and the transmission zero point is controllable, thereby suppressing harmonics in a certain frequency band; the L-shaped or T-shaped demetallized groove is used to form a notch structure, control the transmission zero point position, and realize the harmonic suppression requirement.

[0050] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in the field. Although the embodiments of the utility model have been shown and described, it is understandable to those of ordinary skill in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principle and spirit of the utility model. The scope of the utility model is defined by the attached claims and their equivalents.

Claims

1. A harmonic suppression interdigital filter, characterized in that: The invention comprises a dielectric substrate (5), the upper and lower surfaces of the dielectric substrate (5) being metal layers, comprising a plurality of resonators (1), an input / output port (3) and a ground plane (4), the resonator (1) being a quarter-wavelength transmission line, a metallized through hole being manufactured at the end of each resonator (1) to form a metallized through hole (2), and the metallized through holes of adjacent resonators (1) being distributed at two opposite ends; The upper surface of the dielectric substrate (5) is provided with a plurality of resonators (1) arranged in parallel, and every two resonators are placed in opposite directions, thereby forming an interdigital structure.

2. The harmonic suppression interdigital filter according to claim 1, characterized in that: The metallized through holes (2) electrically connect the resonator (1) to the ground plane (4), and the number of the metallized through holes (2) on each resonator (1) is 1 to 3.

3. The harmonic suppression interdigital filter according to claim 1, characterized in that: The ground plane (4) is a whole metal layer.

4. The harmonic suppression interdigital filter according to claim 1, characterized in that: The input / output port (3) is a microstrip line with a characteristic impedance of 50 ohms, comprising a demetallized slot (6) to form an LC parallel resonant circuit.

5. The harmonic suppression interdigital filter according to claim 4, characterized in that: The demetallization groove (6) is an L-shaped or T-shaped demetallization groove, and the number of the demetallization grooves (6) is greater than or equal to one.

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