CN114843727A

CN114843727A - Band-pass filter capable of controlling attenuation

Info

Publication number: CN114843727A
Application number: CN202210682444.2A
Authority: CN
Inventors: 李玉琨; 林磊; 陈建忠; 赵雨桐; 张佳丽
Original assignee: Fujian Huahai Sound Transmission Technology Co ltd
Current assignee: Fujian Huahai Sound Transmission Technology Co ltd
Priority date: 2022-06-16
Filing date: 2022-06-16
Publication date: 2022-08-02

Abstract

The invention belongs to the technical field of communication equipment components, and discloses a controllable attenuation band-pass filter, which comprises a dielectric layer; a metal layer is arranged on one side of the dielectric layer, and an input microstrip line, a plurality of resonators, a plurality of graphene nano-sheets and an output microstrip line are arranged on the other side of the dielectric layer; the resonators are arranged between the input microstrip line and the output microstrip line at intervals, an input coupling seam with a first preset width is reserved between the input microstrip line and the adjacent resonator, and a coupling line is arranged between the two adjacent resonators and is connected through the coupling line; the plurality of graphene nano sheets are respectively attached to the plurality of resonators; the input microstrip line, the resonators and the output microstrip line are all provided with a plurality of connecting holes, and the connecting holes penetrate through the dielectric layer to be connected with the metal layer. The attenuator and the filter are realized by one device, so that the cost is reduced, the integration level is good, the selectivity is good, the design structure is simple, and the attenuator and the filter have good application prospects in the development of communication systems.

Description

Band-pass filter capable of controlling attenuation

Technical Field

The invention belongs to the technical field of communication equipment components, and relates to a band-pass filter with controllable attenuation.

Background

In recent years, with the rapid development of fifth generation mobile communication, wireless local area network, satellite communication and the like, the utilization rate of wireless spectrum is higher and higher, and the requirements of miniaturization, high performance, low cost and high integration are put on a radio frequency microwave filter in a communication system. Due to the fact that the microstrip filter is small in size and easy to integrate, in addition to the fact that in recent years, the graphene material has good optical characteristics, the microstrip filter is easy to be well combined with the graphene material, and the microstrip filter based on the graphene becomes a research hotspot under the background. At present, a general filter only has a filtering function, after graphene is brushed, the filter can become an adjustable filter due to the characteristic that impedance can be changed after bias voltage is applied to the graphene, so that the filter has the function of an attenuator, and the graphene is concerned because of light weight, large surface area and excellent optical and electrical properties.

In recent years, a preparation method of large-scale graphene is remarkably developed, and application of the graphene in microwave and low terahertz ranges is promoted, such as a radio frequency graphene field effect transistor, a graphene antenna, a graphene microstrip attenuator and the like. The graphene nano sheet is composed of a small amount of graphene, is generally small in area and usually appears in the form of fragments, suspended matters or powder, provides a new solution for a microwave device, and is loaded to a proper position according to the resistance characteristic of the graphene to perform a coating elastic resistance behavior experiment so as to develop a microstrip adjustable device coated at the proper position.

At present, some people coat graphene in the gap of the microstrip line, and some people use the graphene to replace a metal plate to realize a microwave low-pass filter, and with the development of modern microwave devices, the microwave devices are more and more widely applied and more flexible. Therefore, the versatility and high integration of the device become more and more important, and the multifunction device can effectively reduce the circuit size and improve the adaptability in the application field. However, in the existing microstrip device, to implement two functions of filtering and attenuating, two devices, namely a filter and an attenuator, must be used simultaneously, and the common use of the filter and the attenuator may increase the size of the microwave circuit, and increase the difficulty and cost of circuit design.

Disclosure of Invention

The invention aims to overcome the defects that in the prior art, two devices, namely a filter and an attenuator, are required to be used simultaneously to realize two functions of filtering and attenuating in the existing microstrip device, and the common use of the filter and the attenuator can increase the size of a microwave circuit and improve the design difficulty and cost of the circuit, and provides a band-pass filter with controllable attenuation.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

a band-pass filter with controllable attenuation comprises a dielectric layer;

a metal layer is arranged on one side of the medium layer, and an input microstrip line, a plurality of resonators, a plurality of graphene nano sheets and an output microstrip line are arranged on the other side of the medium layer;

the resonators are arranged between the input microstrip line and the output microstrip line at intervals, an input coupling seam with a first preset width is reserved between the input microstrip line and the adjacent resonator, and a coupling line is arranged between the two adjacent resonators and is connected through the coupling line; the plurality of graphene nano sheets are respectively attached to the plurality of resonators;

the input microstrip line, the resonators and the output microstrip line are all provided with a plurality of connecting holes, and the connecting holes penetrate through the dielectric layer to be connected with the metal layer.

Optionally, at least three resonators are provided.

Optionally, the resonator is a quarter-wavelength step resonator.

Optionally, the graphene nano-sheets and the resonators are arranged in one-to-one correspondence, and are arranged on one side of the strongest position of the electric field of the resonators.

Optionally, the resonators are arranged in parallel, and the input microstrip line and the output microstrip line are symmetrically arranged with respect to the resonators.

Optionally, the graphene nanosheets are rectangular, and the length of the graphene nanosheets is the same as the width of the resonator.

Optionally, the graphene nanoplatelets are formed by mixing graphene nanoplatelets with an isopropanol solution, and then dropping the mixture into a preset position of the dielectric layer for precipitation until the isopropanol solution is completely vaporized.

Optionally, the connecting hole is a metal through hole, and the cross section of the connecting hole is circular, square, triangular, rhombic or trapezoidal.

Optionally, the width of the input coupling line is 0.15-0.25 mm.

Optionally, the device further comprises a bias voltage source; and the bias voltage source is connected with the plurality of graphene nano sheets and is used for providing bias voltage for the plurality of graphene nano sheets.

Compared with the prior art, the invention has the following beneficial effects:

the band-pass filter with controllable attenuation of the invention provides adjustable parameters through the graphene nano-sheet, further changes the impedance of a micro-strip resonance structure, ensures that the electric field intensity of the filter has good uniform attenuation effect by applying different bias voltages to the graphene nano-sheet so as to keep lower reflection loss, and the attenuation amplitude can be adjusted to be more than 10dB, further can change the resistance value of the graphene nano-sheet by controlling the bias voltage on the graphene nano-sheet, finally realizes that the passband gain attenuation of the filter is adjustable, combines the filter and the attenuation material together well, realizes the functions of an attenuator and the filter by using one device, further can effectively simplify the construction steps of a radio frequency system, reduces the cost and has good integration level, and simultaneously adopts a resonator and a mixed electromagnetic coupling structure based on a coupling line to form a resonant cavity, the graphene nanosheets are loaded around the resonant cavity, and the transmission zero points of the hybrid electromagnetic coupling filter are individually controllable, so that one or more transmission zero points can be generated on each side or the same side of the passband, and the band-pass filter with controllable attenuation has good selectivity, is simple in design structure and has good application prospect in the development of a communication system. In addition, the hybrid electromagnetic coupling filter and the graphene can be well transplanted to the design of other filters with non-microstrip structures, and the band-pass filter with controllable attenuation has wide application prospect and can be widely applied to base stations.

Drawings

FIG. 1 is a top view of a controlled attenuation bandpass filter according to an embodiment of the invention;

FIG. 2 is a bottom view of a controlled attenuation bandpass filter according to an embodiment of the invention;

FIG. 3 is an oblique view of a controlled attenuation bandpass filter according to an embodiment of the invention;

fig. 4 is a schematic diagram of a test graphene nanosheet loading position according to an embodiment of the present invention;

FIG. 5 is an exploded view of a controlled attenuation bandpass filter according to an embodiment of the invention;

FIG. 6 is a graph showing sizing of a controlled attenuation bandpass filter according to an embodiment of the present invention;

FIG. 7 is an equivalent circuit diagram of a controlled attenuation bandpass filter according to an embodiment of the invention;

FIG. 8 is a comparison graph of simulation and testing of a controlled attenuation bandpass filter S11 according to an embodiment of the present invention at different resistances;

FIG. 9 is a comparison graph of simulation and testing of the controlled attenuation bandpass filter S21 according to the present invention at different resistances;

FIG. 10 is a graph comparing simulation and testing of the phase response of the controlled attenuation bandpass filter S2 according to the present invention at different values;

fig. 11 is a graph showing simulation and test comparisons of the angle of the controlled attenuation bandpass filter S21 according to the embodiment of the invention at different resistances.

Wherein: 1-input microstrip line; 2-inputting the coupling slot; 3-a first resonator; 4-connecting holes; 5-graphene nanoplatelets; 6-coupling slot between cavities; 7-a second resonator; 8-a third resonator; 9-coupled lines; 10-an output microstrip line; 11-a dielectric layer; 12-a metal layer; 13-first hybrid coupling structure equivalent circuit; 14-a second hybrid coupling structure equivalent circuit; 15-graphene nanosheet equivalent circuit; 16-quarter wavelength transmission line equivalent circuit.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention is described in further detail below with reference to the accompanying drawings:

referring to fig. 1 to 6, in an embodiment of the present invention, an attenuation-controllable bandpass filter is provided, and in particular, an attenuation-adjustable bandpass filter with high selectivity is provided, which can be used in a radio frequency front end of a wireless communication system, and can flexibly adjust an impedance value of a resonance device by using characteristics of a graphene material during filtering, and one device is used to implement functions of an attenuator and a filter, and has good selectivity.

Specifically, the band-pass filter with controllable attenuation comprises a dielectric layer 11; a metal layer 12 is arranged on one side of the dielectric layer 11, and an input microstrip line 1, a plurality of resonators, a plurality of graphene nanosheets 5 and an output microstrip line 10 are arranged on the other side of the dielectric layer; the resonators are arranged between an input microstrip line 1 and an output microstrip line 10 at intervals, an input coupling seam 2 with a first preset width is reserved between the input microstrip line 1 and an adjacent resonator, and a coupling line 9 is arranged between the two adjacent resonators and is connected through the coupling line 9; the plurality of graphene nano sheets 5 are respectively attached to the plurality of resonators; the input microstrip line 1, the resonators and the output microstrip line 10 are all provided with a plurality of connecting holes 4, and the connecting holes 4 penetrate through the dielectric layer 11 and are connected with the metal layer 12.

According to the attenuation-controllable band-pass filter, the graphene nano sheet 5 is used for providing adjustable parameters, so that the impedance of the microstrip resonance structure of the embodiment can be conveniently changed, different bias voltages are applied to the graphene nano sheet 5, the electric field intensity of the filter has a good uniform attenuation effect, the lower reflection loss is kept, and the attenuation amplitude can be adjusted to be more than 10 dB. The resistance value of the graphene nanosheet 5 can be changed by controlling the bias voltage on the graphene nanosheet 5, the pass band gain attenuation of the filter can be adjusted, the band-pass filter with controllable attenuation provided by the embodiment combines the filter and attenuation materials well, and then the construction steps of a radio frequency system can be effectively simplified, the cost is reduced, the integration level is good, and meanwhile, the band-pass filter has good selectivity, is simple in design structure, and has good application prospect in the development of a communication system.

The resonator and the hybrid electromagnetic coupling structure based on the coupling line 9 are adopted to form the resonant cavity, the graphene nanosheets 5 are loaded around the resonant cavity, and as the transmission zeros of the hybrid electromagnetic coupling filter are individually controllable, one or more transmission zeros can be generated on each side or the same side of the pass band. Meanwhile, the resonance frequency can flexibly control the transmission zero point to be positioned at the same side of the passband, namely the position of the transmission zero point can be controlled by controlling the frequency when the electric field energy is equal to the magnetic field energy, so that the situation that the signal amplitude of the needed frequency is basically unchanged because the signal amplitude of the needed frequency is not needed to be attenuated on the single side of the passband of the filter can be effectively improved, namely the single-side selectivity of the passband is better. Meanwhile, the coupling resonant frequency can flexibly control the transmission zero points to be positioned at two sides of the passband, so that the selectivity can be better by introducing the transmission zero points, namely the selectivity of the two sides of the passband is better, the amplitude of signals which do not need frequency at the two sides of the passband is effectively and rapidly attenuated by high selectivity, namely the out-of-band decline is faster, and a steeper transition band is provided.

When the hybrid electromagnetic coupling structure resonates at a certain frequency, the impedance is infinite, so that energy is completely consumed, almost no output of an output port of the filter can generate a transmission zero point, the amplitude of a signal with required frequency is basically kept unchanged, the signal with the unnecessary frequency is quickly attenuated, the larger the amplitude attenuation of the side of the unnecessary signal at the junction of the required signal and the unnecessary signal is, the better the selectivity is, and the following formula is specifically referred to:

wherein f is _z1 And f _z2 Respectively representing the frequencies of the first and second transmission zeroes,

and

respectively, represent the electrical and magnetic coupling that exists between the first resonator 3 and the second resonator 7, respectively, and

and

then represent the electrical and magnetic coupling that exists between the second resonator 7 and the third resonator 8, respectively. Wherein the first transmission zero point f _z1 Is formed by an electrical coupling existing between the first resonator 3 and the second resonator 7

And magnetic coupling

Generated, and the second transmission zero f _z2 Is caused by the electrical coupling existing between the second resonator 7 and the third resonator 8

And magnetic coupling

As a result, the positions of the two transmission zeroes can be independently controlled.

In addition, the hybrid electromagnetic coupling filter and the graphene can be well transplanted to the design of other filters with non-microstrip structures, and the band-pass filter with controllable attenuation has wide application prospect and can be widely applied to base stations.

In one possible embodiment, at least three resonators are provided.

Specifically, the band-pass filter with controllable attenuation can flexibly select the order of the resonators and control the number of transmission zeros according to the requirement of design indexes to control the selectivity, the bandwidth requirement is wide, the number of the resonators is increased, the number of the transmission zeros is determined by the number of hybrid coupling, the position of the transmission zeros is determined by the strength of electric coupling magnetic coupling in the hybrid coupling, the electric coupling is mainly at the low end of a pass band, and the magnetic coupling is mainly at the high end of the pass band. The number and the position of the zero points are controlled by controlling the order number and the position of the resonator, so that the control filter has a good rectangular coefficient. By increasing the number of resonators, the hybrid coupling is increased, and the transmission zero point is increased. When the number of resonators of the filter is too small, the out-of-band decline is slow and not steep enough, the filter cannot be well adapted to the practical environment, a higher-order filter can provide a steeper transition band, a plurality of groups of hybrid coupling mechanisms are constructed, and a plurality of transmission zeros can be introduced at the same time, so that the passband selection characteristic of the filter is improved, but the corresponding increase of the order number can bring the cost increase and the volume increase, so that the appropriate order number can be selected according to the design index.

In one possible embodiment, the resonator is a quarter-wave stepped resonator.

Specifically, the resonator is formed of quarter-wavelength transmission lines, and the electrical coupling between the quarter-wavelength transmission lines is generated between the gaps of the coupled lower sections. The quarter-wavelength step resonator and the hybrid electromagnetic coupling structure based on the coupling line 9 are adopted, the graphene nanosheets 5 are loaded around the resonators, and the band-pass filter formed by the structure is compact in structure and excellent in performance. Meanwhile, the SIR has the maximum electric field fringe field density at the opening end, which is equivalent to a capacitor Cm, and on the other hand, the magnetic coupling is realized by a gap, namely an inter-cavity coupling slot 6, which connects two SIRs together and represents a coupling inductor which is equivalent to an inductor Lm, so that the hybrid electromagnetic coupling is equivalent to a parallel resonator consisting of Cm and Lm.

In one possible implementation, the graphene nano-sheets 5 are arranged in one-to-one correspondence with the resonators and are arranged on one side of the position where the electric field of the resonators is strongest.

In particular, the graphene nanosheets 5 have the advantages of light weight, large surface area, excellent optical and electrical properties and the like, and provide a new solution for microwave devices. The impedance value of the graphene nanoplatelets 5 loaded in the structure 5 around the resonator gradually changes, and as the impedance value increases, the input energy is gradually consumed, so that the signal amplitude of the passband is reduced, i.e. the device has good adjustable passband attenuation, i.e. the passband is the frequency range corresponding to the signal with the required frequency.

Experiments prove that different loading positions of the graphene nano-sheets 5, namely the graphene nano-sheets 5 are loaded on the left side, the right side, the upper side and the lower side or the upper side and the lower side of the resonator, and have different degrees of influence on an electric field and a magnetic field. Moreover, the graphene nano-sheets 5 with different shapes have different degrees of influence on the electric field and the magnetic field, specifically, the effect of attenuation is more obvious when the contact area is larger.

Through experimental tests, the graphene nanosheets 5 are loaded at the positions where the electric field intensity is the largest, so that the attenuation of the passband energy of the filter is the largest, and the effect is the most obvious. The loaded graphene nanosheets 5 can be circular or polygonal, the impedance of the corresponding graphene nanosheets 5 is increased by controlling the bias voltage of the graphene nanosheets 5, the attenuation of an electric field is further increased, and therefore the adjustable attenuation is achieved.

When the dc bias voltage exceeds 4V, the graphene nanoplatelets 5 may overheat, and when the dc voltage reaches about 5V, the graphene nanoplatelets 5 may be broken down, so the voltage range is strictly controlled in the experiment or application process.

In a possible implementation manner, the plurality of resonators are arranged in parallel, the input microstrip line 1 and the output microstrip line 10 are symmetrically arranged about the plurality of resonators, the graphene nanosheet 5 is rectangular, and the length of the graphene nanosheet 5 is the same as the width of the resonators.

In one possible embodiment, the graphene nanoplatelets 5 are formed by mixing graphene nanoplates with an isopropanol solution, and then dropping the mixture into a predetermined position of the dielectric layer 11 for precipitation until the isopropanol solution is completely vaporized. Specifically, the graphene nanosheets 5 are prepared separately: graphene nanoplate XF022-1 produced by a commercial company was mixed with an isopropyl alcohol solution having a concentration of 2.5mg/mL to obtain a graphene nanoplate dispersion, and precipitated at a specific position of a filtration gap by a dropper and a custom mold, and when the isopropyl alcohol solution was completely vaporized, graphene nanoplate 5 was formed.

In a possible embodiment, the connection hole 4 is a metal through hole, and the cross-sectional shape is circular, square, triangular, diamond-shaped or trapezoidal. The connecting holes 4 can be selected to have different shapes according to different occasions, and mainly play roles in connection, fixation and heat dissipation.

In a possible embodiment, the width of the input coupling line 9 is 0.15-0.25 mm. In particular, the thicker the coupled line 9, the stronger the coupling, but mainly the position affects the coupling strength. Optionally, the coupling is smaller when the width of the coupling slot 6 is larger, and the electric coupling strength can be controlled by adjusting the width.

In one possible embodiment, the method further comprises a bias voltage source; the bias voltage source is connected with the plurality of graphene nano sheets 5 and is used for providing bias voltage for the plurality of graphene nano sheets 5.

In a possible implementation manner, the controllable attenuation band-pass filter includes a first resonator 3, a second resonator 7, and a third resonator 8, where the first resonator 3, the second resonator 7, and the third resonator 8 are quarter-wavelength stepped resonators and are arranged in parallel, the band-pass filter adopts a symmetric structure, input coupling is performed through an input coupling slit 2 between an input microstrip line 1 and the first resonator 3, the width of the input coupling slit 2 is 0.2, and the coupling weakening caused by the increase in width is determined according to an index. The dielectric layer 11 is a dielectric substrate of Rogers 4350. The connection hole 4 connects the upper and lower metal layers with the ground.

The first resonator 3 and the second resonator 7 are magnetically coupled in a cavity through a coupling slit 6 between the cavities, the electrical coupling between the first resonator and the second resonator is realized through an electrical coupling structure of a coupling line 9, the coupling line 9 is a thin microstrip line, the second resonator 7 and the third resonator 8 are also manufactured through a similar structure and idea, and it is worth mentioning that at least three resonators are arranged. The position of each resonator is determined by filter design indexes and a proposed topological structure, each resonator is loaded with the graphene nanosheets 5 at the position with the strongest electric field, the adjustable resistor formed by the three graphene nanosheets 5 is located at the position with the strongest electric field, and the graphene nanosheets 5 connected in parallel with the resonators gradually consume input energy, so that adjustable passband attenuation is realized. Specifically, the graphene nanosheets 5 are disposed on the right side of the first resonator 3, the second resonator 7 and the third resonator 8, and the vertical dimension of the graphene nanosheets is equal to the width of the resonant cavity, and the horizontal width of the graphene nanosheets is about 5 mm.

The microstrip type filter is adopted in the embodiment, different guided wave structures can be selected according to different design indexes, and different shapes can be selected according to specific occasions for the outer contour shape of the filter. The graphene nanoplatelets 5 may be mixed with a solution selected according to different application scenarios, or may be coated in other shapes. The coupling line 9 can adjust the position of the structure in the resonance structure according to the filter indexes of different working frequencies and application scenarios. When the R value of the graphene nanosheet 5 is high, the graphene nanosheet 5 approaches an open circuit, the attenuation is small, the R value is reduced along with the increase of the bias voltage, the absorption of the graphene nanosheet 5 is more obvious, and the better attenuation is caused.

Referring again to fig. 6, in the present embodiment, L1 is 11.2mm, L2 is 12mm, L3 is 12mm, L4 is 13mm, L5 is 9.63mm, L6 is 6.2mm, W1 is 5.5mm, W2 is 1mm, W3 is 1.5mm, W4 is 5.2mm, W5 is 3mm, S1 is 0.105mm, S2 is 0.2mm, S3 is 0.17mm, S4 is 0.11mm, and D is 2 mm.

Referring to fig. 7, an equivalent circuit of the controllable attenuation band-pass filter is shown to facilitate understanding of the controllable attenuation band-pass filter. The left side of the first hybrid coupling structure equivalent circuit 13 forms a left transmission zero point, the right side of the second hybrid coupling structure equivalent circuit 14 forms a right transmission zero point, the graphene nanosheet equivalent circuit 15 is in a variable resistance form, and the capacitor C, the inductor L and the graphene nanosheet equivalent circuit 15 form a quarter-wavelength transmission line equivalent circuit 16.

The band-pass filter based on controllable attenuation is used for experiment and simulation, and the experiment and simulation conditions are that a laboratory hardware platform is adopted: the processor is an Intel i 75930 k CPU, the main frequency is 3.5GHz, and the memory is 16 GB. The software platform of the simulation experiment of the invention is as follows: windows 10 operating system and HFSS 18.0. Based on the above experiment, in order to realize practical application, a band pass filter with controllable attenuation of a third-order filter with adjustable attenuation is constructed, the center frequency of which is f0 ═ 1.36GHz, and the equal ripple bandwidth BW ═ 80 MHz.

Referring to fig. 8-10, the results of the simulation and testing of the controlled attenuation bandpass filter S11 at different resistances are shown, the results of the simulation and testing of the controlled attenuation bandpass filter S21 at different resistances and the results of the simulation and testing of the phase response of S21 at different resistances. In the figure, the solid line represents the measured value, the dotted line represents the simulation value, and Rs is the resistance value of the graphene nanoplatelets 5. It can be found that under different bias voltages, the attenuation amplitude of S21 can be adjusted to-1.64 to-11.13 dB, the reflection is less than-10 dB, and based on the phase response result of S21, the phase of the transmission coefficient is basically kept unchanged under different attenuation levels.

Referring to fig. 11, showing the electric field distribution of the quarter-wavelength SIR, which is convenient for analyzing the relationship between the loading position and the resonance strength, in order to study the specific influence of the graphene nano-sheet 5 on the electric field, the electric field distribution of the graphene nano-sheet 5 on the filter at different loading positions is simulated, and the graphene nano-sheet 5 generally corresponds to an adjustable lumped resistor R. The relationship between the analog value Rs of the graphene nanoplatelets 5 and the calculated resistance R may be expressed as Rs ≈ (L/W) × R, where L and W are the length and width of the graphene nanoplatelets 5, respectively.

The experimental content is that approximately 400 Ω graphene nanoplatelets 5 are loaded at the position where the electric field intensity is minimum, from the view of electric field distribution, the influence of the graphene nanoplatelets 5 on the electric field is small, and when the resistance value of the graphene nanoplatelets 5 becomes 100 Ω, the influence on the electric field is found to be almost unchanged, and the result shows that, under the condition that the electric field is weak, the graphene nanoplatelets 5 are loaded to a resonator, the influence on the amplitude attenuation of a filter is not large, and in the experimental process, the influence on the magnetic field distribution can also be seen when the graphene nanoplatelets 5 are loaded at the position, and it can also be seen that the total energy of the field can be weakened at the position, but the position where the attenuation influence on the field is maximum is not the position, and multiple experiments prove that the graphene nanoplatelets 5 are loaded at the position where the electric field is strongest.

Before the design of the band-pass filter with controllable attenuation, a direct-current voltage source is used for supplying power to the microstrip line and the graphene nanosheets 5. The multimeter measures the direct current resistance at bias current and studies the change of resistance with the change of voltage, i.e. when the bias voltage is 0, the resistance of the graphene nanosheet 5 is 402 Ω, and the resistance decreases linearly with the increase of voltage. When the direct-current voltage exceeds 4V, the graphene nanosheet 5 is overheated, when the voltage exceeds about 5V, the graphene nanosheet 5 is broken down, and tests on the microstrip line and the graphene nanosheet 5 prove that the resistance of the graphene nanosheet 5 can be adjusted.

The invention relates to a band-pass filter with controllable attenuation, in particular to a high-selectivity band-pass filter based on graphene nano-sheet controllable attenuation. By applying different bias voltages to the graphene nanosheets 5 to keep the reflection loss low, the attenuation amplitude can be adjusted to above 10 dB. Experiments prove that the resistance value of the graphene nanosheet 5 can be changed by controlling the bias voltage on the graphene nanosheet 5, and the adjustable attenuation is realized in the resonant structure. The graphene material has a good attenuation effect on the electric field intensity, the quarter-wavelength step resonator and the hybrid electromagnetic coupling structure are adopted, the graphene nanosheets 5 are loaded around the resonators, the model formed by the structure is compact in structure and excellent in performance, and one or more transmission zeros can be generated on each side or the same side of the passband as the transmission zeros of the hybrid electromagnetic coupling filter are individually controllable.

The filter in the embodiment consists of a coupling line, quarter-wavelength step impedance, mixed electromagnetic coupling and graphene, a micro-strip circuit is manufactured on a dielectric layer 11, and a connecting hole 4 is controlled to be a proper value and is connected with an upper metal layer, a lower metal layer and the ground; the three graphene nano sheets 5 are loaded at the strongest part of the electric field as an adjustable resistor, and the graphene nano sheets 5 connected with the resonator in parallel gradually consume input energy, so that adjustable passband attenuation is realized. The invention combines the functions of the filter and the attenuator well, has good selectivity, has simple design structure, is beneficial to simplifying the construction steps of a radio frequency system, reduces the cost, can be transplanted to the design of other filters well, and has good application prospect in the development of a communication system.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A band-pass filter with controllable attenuation is characterized by comprising a dielectric layer;

a metal layer is arranged on one side of the dielectric layer, and an input microstrip line, a plurality of resonators, a plurality of graphene nano-sheets and an output microstrip line are arranged on the other side of the dielectric layer;

2. A controlled attenuation bandpass filter according to claim 1, characterized in that the resonators are provided in at least three.

3. A controlled attenuation bandpass filter according to claim 1 or 2, wherein the resonators are quarter-wave step resonators.

4. The controlled attenuation bandpass filter of claim 3, wherein the graphene nanoplatelets are arranged in one-to-one correspondence with the resonators and are located on one side of the location where the electric field of the resonators is strongest.

5. A controlled attenuation bandpass filter according to claim 3, wherein the resonators are arranged in parallel, and the input microstrip line and the output microstrip line are arranged symmetrically with respect to the resonators.

6. A controlled attenuation bandpass filter according to claim 3, wherein the graphene nanoplatelets are rectangular and have a length equal to the width of the resonator.

7. The controlled attenuation bandpass filter according to claim 1, wherein the graphene nanoplatelets are formed by mixing graphene nanoplates with an isopropanol solution, and then dropping the mixture into a predetermined position of the dielectric layer for precipitation until the isopropanol solution is completely vaporized.

8. A controlled attenuation bandpass filter according to claim 1, wherein the connection holes are metal through holes and have a cross-sectional shape of a circle, square, triangle, diamond or trapezoid.

9. A controlled attenuation bandpass filter according to claim 1, wherein the width of the input coupling line is 0.15-0.25 mm.

10. The controlled attenuation bandpass filter of claim 1, further comprising a bias voltage source; and the bias voltage source is connected with the plurality of graphene nano sheets and is used for providing bias voltage for the plurality of graphene nano sheets.