CN113972456A - Three-order wide stop band 5G microstrip filter - Google Patents

Three-order wide stop band 5G microstrip filter Download PDF

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Publication number
CN113972456A
CN113972456A CN202111580060.1A CN202111580060A CN113972456A CN 113972456 A CN113972456 A CN 113972456A CN 202111580060 A CN202111580060 A CN 202111580060A CN 113972456 A CN113972456 A CN 113972456A
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filter
converter
resonator
novel composite
matrix
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CN113972456B (en
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刘望
何玉军
张宏泽
吴春华
陈新锋
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Nanjing Digitgate Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/203—Strip line filters
    • H01P1/20327—Electromagnetic interstage coupling
    • H01P1/20354—Non-comb or non-interdigital filters
    • H01P1/20381—Special shape resonators

Abstract

The invention discloses a three-order wide stop band 5G microstrip filter, which belongs to the technical field of communication and comprises a dielectric substrate, wherein the upper surface of the dielectric substrate is provided with a first novel composite resonator, a second novel composite resonator, a half-wavelength resonator, an input feeder, an output feeder, a first J converter and a second J converter, the half-wavelength resonator is arranged on a central axis of the dielectric substrate, one end of the first J converter is connected with the input feeder, the other end of the first J converter carries out tap feeding on the first novel composite resonator, the half-wavelength resonator carries out gap coupling feeding with the first J converter and the second J converter respectively, one end of the second J converter carries out tap feeding with the second novel composite resonator, and the other end of the second J converter is connected with the output feeder; the filter of the invention has two different resonators, and the stop band of the filter is widened by staggering the higher harmonics of the two different resonators, and the filter of the invention can cover a mobile low-frequency 5G frequency band.

Description

Three-order wide stop band 5G microstrip filter
Technical Field
The invention relates to the technical field of communication, in particular to a three-order wide stop band 5G microstrip filter.
Background
The filter plays a crucial role in the evolution of the radio communication system over the past generation as an important passive device in the radio frequency part. In recent years, attention has been paid to out-of-band rejection characteristics of filters, miniaturization of filters, wide stop-band rejection, and the like. A filter with good performance can lead signals in an operating frequency band to pass through without loss, and signals outside the operating frequency band are suppressed as much as possible. In the background of the rapid development of wireless communication, how to increase the out-of-band rejection characteristic of the filter to reduce interference to other frequency bands is also one of the important research points of the filter. Microstrip filters also have the advantages of simple fabrication process, short fabrication cycle, and low cost, and are often used as part of discrete devices in radio frequency circuits.
The existing filter mostly adopts several designs of the traditional cascade type band-pass filter as chapter 5 of reference [1] in the design of a coupling structure, namely, the traditional filter is coupled from a source to resonators, the resonators are coupled, and the final-order resonator is coupled with a load. This cascaded coupling structure generally becomes bulky as the order of the resonator increases, and has the disadvantage of lacking a transmission zero. Therefore, the special coupling structure is adopted, so that the size of the filter can be reduced to a certain extent, and the number of transmission zeros of the filter can be increased. Reference [2] proposes a novel coupling structure, which is used to design a filter by connecting the resonators to the terminals of a J-converter and coupling the resonators to the next stage. However, the dual-band resonator is similar to a three-half wavelength ladder impedance resonator, so that the overall size of the filter is large and the stop-band characteristic is not good.
Although the filter composed of the composite resonator in reference [3] has many transmission zeros, the composite resonator is a half-wavelength ladder impedance resonator which resonates to provide a resonance mode, and the high-frequency stop band of the filter is narrow due to the coupling mode of the J-converter cascade.
In addition, reference [2]]And [3]In the volume of the filter, reference [2]]Is 1.16 lambdag×0.48λgReference document [3]Is 0.74 lambdag×0.52λg，（λgFor filteringGuided wave wavelength corresponding to the central frequency of the wave filter) are relatively large in volume; on the stop band of the filter, reference [2]]Stop band 3.27f 0|25dBAnd reference document [3]Stop band 0.5f 0|20dBAll are relatively narrow. (3.27f 0|20dBRepresents: from the operating frequencyf 0To 3.27 timesf 0Filter having a stop band rejection of 20dB in the frequency range of
[1] J. S. Hong and M. J. Lancaster, Microwave Filter for RF/Microwave Application [M]. New York, NY, USA: Wiley, 2001.
[2] R. Gómez-García, L. Yang, J.–M. Muñoz-Ferreras and D. Psychogiou, Selectivity-enhancement technique for stepped-impedance-resonator dual-passband filters [J]. IEEE Microwave Wireless Component Letters, 2019, vol. 29(7): 453-455.
[3] Z. Ma and Y. Kobayashi, Design and realization of bandpass filters using composite resonators to obtain transmission zeros [C]. 35th European Microwave Conference Proc., 2005: 1255-1258.
[4] R. J. Cameron, General coupling matrix synthesis methods for Chebyshev filtering functions [J]. IEEE Trans. Microwave Theory Tech., 1999, vol. 47(4): 433-442.
Some specific english explanations will be mentioned here:
a J converter: inverting the converter; frequency: frequency; amplitude: an amplitude;
normalized Frequency: normalizing the frequency; simulation, simulating an S parameter curve;
measurement: testing an S parameter curve; FBW: relative bandwidth;
s: a source; l: a load; r: a resonator is provided.
Disclosure of Invention
In view of the above problems, the present invention has the object of: a high-selectivity wide-stop-band microstrip filter is designed based on a novel composite resonator and a half-wavelength resonator.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a three-order wide stop band 5G microstrip filter comprises a dielectric substrate, wherein two novel composite resonators, a half-wavelength resonator, two J converters and a 50 omega feeder line are arranged on the upper surface of the dielectric substrate. The half-wavelength resonator is arranged on an axial line of the dielectric substrate, the first J converter is connected with a 50 omega input feeder line, the first novel composite resonator carries out tap feeding through a terminal of the first J converter, and the first J converter carries out gap coupling feeding with the half-wavelength resonator. And then, the half-wavelength resonator is in gap coupling with the second J converter, the terminal of the second J converter is in tap feed with the second novel composite resonator, and finally the second J converter is connected with a 50 omega output feeder line.
Preferably, the novel composite resonator is formed by connecting a short-circuit branch and an open-circuit branch in parallel, the short-circuit branch and the open-circuit branch are located on one side close to the feeder line, and the short-circuit branch is close to the J converter.
Preferably, the novel composite resonator is coupled with a feeder terminal tap through a J converter, the whole circuit is rotationally and symmetrically arranged along the central point of the dielectric substrate, and a transmission zero point (shown in figure 5) close to a passband is respectively generated at the symmetrical positions of the central frequency pointf z1Andf z2）。
preferably, the half-wavelength resonator provides only one resonant mode and does not produce a transmission zero. And the use of two different resonators facilitates achieving a wide stop-band rejection of the filter.
Preferably, a coupling topology of a third-order filter is formed: the input source feeds the novel composite resonator and the half-wavelength resonator respectively in a terminal tapping mode and a gap coupling mode of the J converter, the half-wavelength resonator outputs the load in the gap coupling mode, and meanwhile the load is connected with the other novel composite resonator in a tapping mode through the other J converter.
Preferably, the corresponding normalized coupling matrix is obtained by synthesis according to the coupling topological structure of the third-order filter.
Preferably, the corresponding normalized frequency response is calculated according to the normalized coupling matrix.
Preferably, the operating band of the microstrip filter is set to 2.515GHz-2.675GHz (mobile 5G band).
Preferably, the whole volume of the circuit is 0.53 lambdag×0.26λg（λgA guided wavelength corresponding to 2.6 GHz).
Compared with the prior art, the invention has the beneficial effects that:
1. a novel composite resonator is adopted, a normalized coupling matrix of the filter is obtained by constructing a coupling topological structure of the filter, and then normalized frequency response is obtained through calculation. The two novel composite resonators and the half-wavelength resonator are adopted to form the third-order band-pass filter, and the stop band of the filter is effectively widened;
2. on the stop band characteristic, because novel composite resonator belongs to quarter-wave resonator resonance, have natural advantage on the stop band and the filter uses two kinds of different syntonizers, can stagger the higher harmonic of two kinds of filters and make the stop band characteristic of filter 4.6f 0There is 20dB stop band rejection in the range.
Drawings
Fig. 1 is a schematic circuit diagram of a third-order wide stop-band microstrip filter according to an embodiment.
FIG. 2 is a schematic diagram illustrating the dimensions of a third-order wide stop-band microstrip filter according to an embodiment.
FIG. 3 is a schematic diagram of a third-order wide stop-band microstrip filter coupling topology according to an embodiment.
FIG. 4 is a diagram illustrating a normalized coupling matrix corresponding to the filter coupling topology according to an embodiment.
FIG. 5 is a diagram illustrating a normalized frequency response corresponding to the normalized coupling matrix in the example.
FIG. 6 is a schematic diagram of a third-order wide stop-band microstrip filter according to an embodiment.
FIG. 7 is a schematic diagram of an embodiment of a third-order wide stop-band microstrip filter with a variable short-circuit stub lengthfAnd influence on transmission zero is shown schematically.
FIG. 8 is a schematic diagram of an embodiment of a third-order wide stop-band microstrip filter with varying length of open-circuit brancheshTo transmissionThe null influence diagram.
FIG. 9 is a diagram illustrating simulation and test comparison of the narrow-band frequency response of the third-order wide-stop-band microstrip filter in the embodiment.
FIG. 10 is a diagram illustrating simulation and test comparison of the broadband frequency response of the third-order wide stop-band microstrip filter in the embodiment.
Detailed Description
The invention will be clearly and completely explained below with reference to the drawings and the specific embodiments.
The processing plate of the third-order wide stop band filter is an FR4 plate with the relative dielectric constant of 4.4 and the thickness of 1 mm. The upper surface of the dielectric plate is a microstrip line, the thickness of the copper-clad microstrip line is 0.035mm, and the lower surface of the dielectric plate is a copper-clad metal ground. Fig. 1 is a circuit detail diagram of a third-order wide stop-band microstrip filter. Fig. 1 shows a configuration of a novel composite resonator, a feeding mode of the novel composite resonator, and a coupling mode between a J-converter and a half-wavelength resonator. The method specifically comprises the following steps: the utility model provides a third-order wide stopband 5G microstrip filter, includes the dielectric substrate, the dielectric substrate upper surface is equipped with first novel composite resonator, the novel composite resonator of second, half wavelength resonator, input feeder, output feeder, first J converter and second J converter, half wavelength resonator sets up on the medium substrate axis, first J converter one end with input feeder connects, and the other end carries out the feed of taking a percentage to first novel composite resonator, half wavelength resonator respectively with first J converter and second J converter carry out the gap coupling feed, the one end of second J converter with the novel composite resonator of second carries out the feed of taking a percentage, the other end with output feeder connects.
Fig. 2 is a labeled schematic diagram of a third-order wide stop-band microstrip filter. Radius of grounding hole of short-circuit branchrIs 0.25 mm. The short-circuit branch is closer to the J converter, and the open-circuit branch is bent to realize miniaturization. The whole circuit is rotationally symmetrical about the center of the half-wavelength resonator.
Table 1: the specific dimensioning in fig. 2 is given in units: mm;
Figure 401684DEST_PATH_IMAGE001
fig. 3 shows a coupling topology of a third order wide stop band filter. S denotes a source and L denotes a load. The dotted line frame represents a novel composite resonator having a resonant frequency off 0Each with R1And R3And (4) showing. Wherein the nodes 2 and 5 represent short-circuit branches and have a resonant frequency off z1. Node 1 and node 4 represent open-circuit branches with a resonant frequency off z2. Half-wavelength resonator 3 (R)2) Shows that its resonant frequency isf 0. The solid line between the two nodes represents the tap feed mode and the dashed line represents the slot coupling mode.
From the coupling topology of fig. 3, the normalized coupling matrix of fig. 4 can be obtained by calculation.
Step 1: setting a target filter index: the return loss is 20dB, two transmission zeros are positioned at the positions of +/-3 j, and the normalized resonant frequency of the half-wavelength resonator and the novel composite resonator is 0;
step 2: obtaining a reflection coefficient polynomial according to the following formula
Figure 131874DEST_PATH_IMAGE002
And transmission coefficient polynomial
Figure 973928DEST_PATH_IMAGE003
：
Figure 185116DEST_PATH_IMAGE004
Figure 61805DEST_PATH_IMAGE005
（2）
Where N =3 represents the filter order, and RL is the predetermined reflection coefficient 20 dB. From the above formula
Figure 618688DEST_PATH_IMAGE006
Determining transmission zerosThe position of the point or points is,
Figure 229930DEST_PATH_IMAGE007
the position of the reflection zero point is determined. Wherein the content of the first and second substances,
Figure 491147DEST_PATH_IMAGE008
Figure 707495DEST_PATH_IMAGE010
Figure 435280DEST_PATH_IMAGE012
will be provided with
Figure 251926DEST_PATH_IMAGE013
By substitution of the formula
Figure 536408DEST_PATH_IMAGE014
Figure 728968DEST_PATH_IMAGE016
Figure 424391DEST_PATH_IMAGE018
Will be provided with
Figure 479066DEST_PATH_IMAGE019
= 3，
Figure 82086DEST_PATH_IMAGE020
= -3，
Figure 273027DEST_PATH_IMAGE021
Carry in = ∞ and recursively calculate polynomial
Figure 670510DEST_PATH_IMAGE022
And
Figure 212481DEST_PATH_IMAGE023
：
Figure 353612DEST_PATH_IMAGE024
Figure 679287DEST_PATH_IMAGE025
wherein
Figure 309989DEST_PATH_IMAGE026
=
Figure 808097DEST_PATH_IMAGE027
，
Figure 752920DEST_PATH_IMAGE028
Determined by the position of the preset transmission zero point,
Figure 839824DEST_PATH_IMAGE029
by
Figure 595422DEST_PATH_IMAGE030
And
Figure 174302DEST_PATH_IMAGE031
jointly determine that
Figure 657236DEST_PATH_IMAGE032
And
Figure 939925DEST_PATH_IMAGE033
substituted into the following formula and let s =
Figure 115692DEST_PATH_IMAGE034
：
Figure 853972DEST_PATH_IMAGE035
Figure 140596DEST_PATH_IMAGE036
Where m is a coupling matrix, I is a unit matrix (source reference 4), and values in the normalized coupling matrix can be integrated by substituting preset transmission zero positions and return loss into equations (11) and (12), and obtaining:
Figure 15143DEST_PATH_IMAGE037
Figure 33914DEST_PATH_IMAGE038
Figure 508758DEST_PATH_IMAGE039
Figure 349806DEST_PATH_IMAGE040
Figure 328126DEST_PATH_IMAGE041
and step 3: as shown in fig. 4, the matrix is a 7 x 7 matrix, S, L and the numbers 1-5 correspond to nodes in the coupled topology. M at diagonal line11 = m44=3 denotes that the open branch node generates a transmission zero m at the position of the normalized frequency 3 (at the high frequency of the pass band)22 = m55And =3 indicates that the position of the normalized frequency-3 (at the low frequency of the pass band) produces one transmission zero. When the open-circuit branch and the short-circuit branch are in parallel resonance, namely the novel composite resonator is in resonance, a transmission pole is generated at the normalized frequency 0 (passband). m is33=0 denotes a half-wavelength resonator R2Operating at normalized frequency 0(passband) creates a transmission pole.
After the normalized coupling matrix is obtained, the normalized external quality factor value can be calculated by equations (13) - (17).
Figure 130516DEST_PATH_IMAGE042
Figure 827076DEST_PATH_IMAGE043
After the normalized coupling matrix and the quality factor q are determined, the normalized frequency response of the filter can be obtained according to equations (3) - (5).
Figure 127608DEST_PATH_IMAGE044
Figure 976746DEST_PATH_IMAGE045
Wherein the content of the first and second substances,
Figure 196375DEST_PATH_IMAGE046
is a matrix
Figure 130964DEST_PATH_IMAGE047
Inverse matrix of
Figure 235186DEST_PATH_IMAGE048
The value corresponding to the ith row and the jth column in the matrix
Figure 922520DEST_PATH_IMAGE047
Can be calculated by the following formula:
Figure 532624DEST_PATH_IMAGE049
matrix array
Figure 514DEST_PATH_IMAGE050
Is a normalized coupling matrix.
Figure 718547DEST_PATH_IMAGE051
Is a 7 × 7 identity matrix except
Figure 463649DEST_PATH_IMAGE052
=
Figure 228343DEST_PATH_IMAGE053
And = 0. Matrix array
Figure 934262DEST_PATH_IMAGE054
Is a 7 x 7 all-zero matrix except
Figure 442603DEST_PATH_IMAGE055
=
Figure 42212DEST_PATH_IMAGE056
=1, Ω is the normalized frequency.
Fig. 5 is a normalized frequency response of a third order wide stop band filter. As can be seen from the response, the filter is a third-order bandpass filter, has three transmission poles, and has a transmission zero at + -3 positions of the passband symmetryf z1Andf z2the passband selectivity and out-of-band rejection of the filter are enhanced.
The operating frequency of the filter is set to the shifted 5G low band: 2.515GHz-2.675GHz, 20dB FBW is 6.17%. The actual external Q value can be calculated using the following equation:
Figure DEST_PATH_IMAGE057
Figure DEST_PATH_IMAGE058
FIG. 6 is a diagram of a third order wide stop band filter with an overall size of 0.53 λg×0.26λg（λgA guided wavelength corresponding to 2.6 GHz).
The relation between two transmission zeros of the filter in the actual microstrip circuit and parameters in the circuit structure is explored next. Fig. 7 is a graph for investigating the effect of the short-circuit stub length of the novel composite resonator on the transmission zero. It can be seen from the figure that the transmission zero point at low frequency is located when only the short circuit branch length (2.4 mm-3.4 mm) is changedf z1Transmission zero point varying from high frequency to low frequency and located at high frequencyf z2The position remains substantially unchanged. It can be concluded from this that the short-circuit stub length of the novel composite resonator influences the transmission zerof z1The position of (a).
Fig. 8 is a graph for investigating the effect of the open-circuit stub length of the novel composite resonator on the transmission zero. When the length of the open-circuit branch is changed from 8mm to 9mm and other size parameters are kept unchanged, the transmission zero pointf z1Remains substantially unchanged at the transmission zero point of high frequencyf z2Moving towards low frequencies. Thus transmission zero pointf z2Is mainly determined by the length of the open-circuit branch in the novel composite resonator.
Fig. 9 is a narrow-band frequency response of a third-order wide stop-band filter, where the solid line is the simulation curve and the dashed line is the test curve. From the figure it can be seen that: and the transmission zero points are arranged at the two sides of the passband and are approximately symmetrical relative to the center frequency, so that the out-of-band rejection and the passband selectivity of the filter are improved. The three transmission poles and the two approximately symmetrical transmission zeros of the simulation plot demonstrate the previously normalized frequency response. The test curve is approximately consistent with the simulation curve.
FIG. 10 is a wideband frequency response (1 GHz-12 GHz) for a third order wide stop band filter. Similarly, the solid line is a simulation curve, the dotted line is a test curve, and the simulation curve is well matched with the test curve. Because the filter adopts two different resonators and coupling modes, the stop band of the filter is expanded. As can be seen from FIG. 10, the simulation curve is at 4.6f 0There is 15dB stop band rejection in the range. Test curve at 4.6f 0There is a 20dB stop band rejection in the range.
The above is a detailed description of the preferred embodiments of the invention, but the invention is not limited to the examples. Those skilled in the art can make various equivalent changes or substitutions without departing from the spirit of the present invention, and such equivalent changes or substitutions are included in the scope defined by the claims of the present application.

Claims (11)

1. The utility model provides a three-order wide stop band 5G microstrip filter which characterized in that: the novel composite resonator comprises a dielectric substrate, wherein a first novel composite resonator, a second novel composite resonator, a half-wavelength resonator, an input feeder line, an output feeder line, a first J converter and a second J converter are arranged on the upper surface of the dielectric substrate, the half-wavelength resonator is arranged on an axial line of the dielectric substrate, one end of the first J converter is connected with the input feeder line, the other end of the first J converter is used for carrying out tap feeding on the first novel composite resonator, the half-wavelength resonator is respectively used for carrying out gap coupling feeding on the first J converter and the second J converter, one end of the second J converter is used for carrying out tap feeding on the second novel composite resonator, and the other end of the second J converter is connected with the output feeder line.
2. The three-order wide stop band 5G microstrip filter of claim 1, wherein: the first novel composite resonator, the first J converter, the second novel composite resonator and the second J converter are arranged in a rotational symmetry mode according to the center point of the dielectric substrate.
3. The three-order wide stop band 5G microstrip filter of claim 1, wherein: the novel composite resonator is formed by connecting a short circuit branch and an open circuit branch in parallel, the short circuit branch and the open circuit branch are located on one side close to the feeder line, the short circuit branch is close to the J converter, and the open circuit branch is bent to realize the miniaturization of the filter.
4. The three-order wide stop band 5G microstrip filter of claim 1, wherein: the new-type composite resonator belongs to quarter waveThe long resonator resonates, has natural advantage on the stop band, and the higher harmonics of the two filters can be staggered by using two different resonators in the filter, so that the actually measured stop band characteristic of the filter is 4.6f 0There is 20dB stop band rejection in the range.
5. The three-order wide stop band 5G microstrip filter of claim 1, wherein: forming a coupling topological structure of the microstrip filter according to the coupling relation between the novel composite resonator and the half-wavelength resonator, and obtaining a corresponding normalized coupling matrix and a normalized frequency response according to the coupling topological structure; the topological structure is as follows: the input source feeds the novel composite resonator and the half-wavelength resonator respectively in a terminal tapping mode and a gap coupling mode of the J converter, the half-wavelength resonator outputs the load in the gap coupling mode, and meanwhile the load is connected with the other novel composite resonator in a tapping mode through the other J converter.
6. The three-order wide stop band 5G microstrip filter of claim 5, wherein: the calculation method of the normalized coupling matrix comprises the following steps:
step 1: setting the return loss and two transmission zero positions of a target filter;
step 2: obtaining a reflection coefficient polynomial according to the following formula
Figure 250759DEST_PATH_IMAGE001
And transmission coefficient polynomial
Figure 980949DEST_PATH_IMAGE002
：
Figure 963949DEST_PATH_IMAGE003
Figure 687054DEST_PATH_IMAGE004
Wherein, N represents the order of the filter, and RL is a preset reflection coefficient; from the above formula
Figure 78590DEST_PATH_IMAGE005
The position of the transmission zero point is determined,
Figure 228948DEST_PATH_IMAGE006
determining the position of the reflection zero point; wherein the content of the first and second substances,
Figure 309031DEST_PATH_IMAGE007
Figure 976773DEST_PATH_IMAGE008
Figure 973548DEST_PATH_IMAGE009
will be provided with
Figure 278496DEST_PATH_IMAGE010
By substitution of the formula
Figure 501667DEST_PATH_IMAGE011
Will be provided with
Figure 566575DEST_PATH_IMAGE012
、
Figure 903009DEST_PATH_IMAGE013
And
Figure 660750DEST_PATH_IMAGE014
value ofThe above formula and calculating the polynomial U recursively3(w) and V3(w) a value; polynomial equation
Figure 682801DEST_PATH_IMAGE015
=
Figure 285821DEST_PATH_IMAGE016
And
Figure 7920DEST_PATH_IMAGE017
the value of (2) is converted into a corresponding value of a complex plane, and a corresponding reflection polynomial and a corresponding transmission polynomial can be calculated;
and step 3: constructing an all-zero 7 x 7 normalized coupling matrix, and using the values with coupling relation in the matrix according to the coupling relation between resonators in the coupling topological structure
Figure 670983DEST_PATH_IMAGE018
Representation, where i, j refers to the ith row and jth column in the matrix, S, L represents the source and load, respectively:
Figure 603167DEST_PATH_IMAGE019
among them, because of the reciprocal matrix, there are:
Figure 265004DEST_PATH_IMAGE020
because the coupling topology is symmetrical about the half-wavelength resonator, there are:
Figure 90878DEST_PATH_IMAGE021
the novel composite resonator is fed by a terminal tap of the J converter, and normalized transmission zero points generated by the open-circuit branch and the short-circuit branch are symmetrical about a Y axis, so that the novel composite resonator comprises the following components:
Figure 941153DEST_PATH_IMAGE022
and (4) calculating to obtain a complete normalized coupling matrix according to the polynomial obtained by calculation in the step (2) and the preset transmission zero position.
7. The three-order wide stop band 5G microstrip filter of claim 5, wherein: the calculation method of the normalized frequency response comprises the following steps:
Figure 95054DEST_PATH_IMAGE023
wherein the content of the first and second substances,
Figure 305456DEST_PATH_IMAGE024
is a matrix
Figure 235103DEST_PATH_IMAGE025
Inverse matrix of
Figure 505548DEST_PATH_IMAGE026
The value corresponding to the ith row and the jth column in the matrix
Figure 146745DEST_PATH_IMAGE025
Can be calculated by the following formula:
Figure 645990DEST_PATH_IMAGE027
matrix array
Figure 446456DEST_PATH_IMAGE028
Is a normalized coupling matrix; matrix array
Figure 28747DEST_PATH_IMAGE029
Is a 7 × 7 identity matrix except
Figure 265562DEST_PATH_IMAGE030
=
Figure 83345DEST_PATH_IMAGE031
= 0; matrix array
Figure 223471DEST_PATH_IMAGE032
Is a 7 x 7 all-zero matrix except
Figure 304559DEST_PATH_IMAGE033
=
Figure 294250DEST_PATH_IMAGE034
=1, Ω is the normalized frequency.
8. The three-order wide stop band 5G microstrip filter of claim 1, wherein: when the short-circuit branch and the open-circuit branch in the novel composite resonator resonate independently, a transmission zero point is generated at the low frequency and the high frequency of the passband of the filter respectively; when the short-circuit branch and the open-circuit branch in the novel composite resonator are in parallel resonance, a transmission pole can be generated in the pass band of the filter.
9. The three-order wide stop band 5G microstrip filter of claim 1, wherein: the dielectric substrate is an FR4 board with the relative dielectric constant of 4.4 and the thickness of 1 mm; the input feeder line and the output feeder line are 50 omega feeder lines.
10. The three-order wide stop band 5G microstrip filter of claim 1, wherein: the upper surface of the dielectric substrate is provided with microstrip line wiring, the thickness of copper coated by the microstrip line is 0.035mm, and the lower surface of the dielectric substrate is provided with a copper-coated metal ground.
11. The third-order wide stop-band 5G microstrip filter according to any of claims 1-10, wherein: the filter works at 2.515GHz-2.675GHz covering mobile 5G low frequency band.
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