CN110444840B - Double-frequency differential band-pass filter based on stub load resonator - Google Patents
Double-frequency differential band-pass filter based on stub load resonator Download PDFInfo
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Abstract
The invention provides a double-frequency differential band-pass filter based on a stub load resonator. The problems of high insertion loss, low selectivity and less flexible design of the filter are solved. Two opposite quasi-interdigital coupling branch load resonators, a step impedance microstrip line in three-line interdigital coupling with the quasi-interdigital coupling branch load resonators and U-shaped microstrip lines on two sides are printed in the middle of the upper surface of the dielectric substrate; two linear L-shaped stepped impedance slot lines which rotate 90 degrees anticlockwise are etched on the lower surface of the substrate. The structures are all centrosymmetric about the center point of the dielectric substrate. All the structures of the invention are designed to be symmetrical about the center of the central point of the substrate and have 90-degree bending of the stepped impedance gap line, so that the size of the filter is greatly reduced; the quasi-interdigital coupling and three-wire interdigital coupling structure reduces the insertion loss of the filter and forms three transmission zeros, thereby enhancing the selectivity of the filter; the branch node loaded in the center has two forms of open circuit and short circuit, the frequency is independently adjustable, different requirements are met, and the method is used for the radio frequency front end of a wireless communication system.
Description
Technical Field
The invention belongs to the technical field of microwave and radio frequency, mainly relates to the structure and design of a band-pass filter, and particularly relates to a double-frequency differential band-pass filter based on a branch load resonator, which can be applied to a radio frequency front end of a wireless communication system.
Background
In recent years, with the rapid development of wireless communication technology, a filter plays an increasingly important role as a key frequency selection device, and the performance of the filter directly affects the quality of the whole communication system. The microstrip band-pass filter has the advantages of small volume, light weight, capability of generating any transmission zero distribution, asymmetric suppression characteristic and the like, and is widely applied. Since the radio frequency and microwave communication frequency bands are very limited, it is increasingly necessary to expand the high frequency communication frequency band. In the newly proposed high-frequency passband, in order to be compatible with the traditional low-frequency communication band and the newly expanded high-frequency communication band, a dual-passband communication system is indispensable, for example, the current WIFI system is mostly dual-frequency of 2.4GHz and 5 GHz. As a core of the dual-band system, the dual-band filter plays a very important role in the communication system. The main approach for realizing the dual-passband filter by the traditional method is to cascade two single-passband filters, but the method occupies a large amount of space resources, so the filter directly generating two passbands is very popular. On the other hand, modern wireless systems are facing increasingly complex electromagnetic environments, which makes higher demands on the interference rejection capability of the filter. Differential circuits are widely used because of their excellent Common Mode (CM) interference resistance, which improves the dynamic range of the system. The differential structure is introduced into the double-frequency filter, so that not only is the miniaturization of the system realized, but also the good anti-interference performance is realized. Microstrip-slot line (MS) transition structures are widely used in differential passive devices due to their inherent CM interference immunity and independent Differential Mode (DM) response. In order to improve the performance of the dual-frequency differential band-pass filter, including insertion loss, out-of-band selectivity, common mode rejection and the like, the research on the differential dual-frequency band-pass filter is receiving more and more attention from many scholars at home and abroad. In 2015, Li Yang et al published a paper "Bananced Dual-Band Filter With Multiple Transmission Zeros Using double Short-Ended receiver Coupled Line" in IEEE TRANSACTION MICROWAVE THEORY AND TECHNINIQES periodical (VOL.63, NO.7, JULY 2015), AND proposed a Dual-Band differential Band-pass Filter based on a double-Ended Short-circuited Resonator, which realizes three Transmission Zeros, but the center frequencies of two pass-bands of the Filter cannot be independently adjusted, AND the designed overall size is larger. 2016 Nantong university Broussonetia et al invented a dual-band differential filter, with grant publication number CN 105762447B, which implemented a multi-layer board to achieve small size, but the structure was complex and the center frequencies of the two pass-bands of the filter did not have independent adjustability. In 2018, a study of "miniature Dual-band Differential Filter Using Dual-mode Dielectric Resonator" published by Jian-Xin Chen et al in the IEEE MICROWAVE AND WIRELESS COMPOSITE LETTERS journal (VOL.28, NO.8, AUGUST 2018) proposes a Dual-band Differential Filter based on a Dual-mode Dielectric Resonator, which can realize independent adjustment of frequency, but only one transmission zero point exists between two frequency bands, and the out-of-band selectivity of the Filter is not good enough.
In summary, based on the defects that the existing differential dual-band filter has a large structure size and large insertion loss, cannot independently adjust the frequency and bandwidth of two pass bands, has low selectivity and the like, the dual-band differential band-pass filter based on the minor-pitch load resonator, which has a compact structure, low insertion loss, high selectivity and capability of independently adjusting the center frequency, is designed, and has sufficient flexibility and practicability for increasingly complex communication systems.
Disclosure of Invention
The invention aims to provide a dual-frequency differential band-pass filter based on a stub load resonator, aiming at the defects of the prior art. The design flexibility and out-of-band selectivity of the dual-frequency differential filter are improved.
The invention relates to a dual-frequency differential band-pass filter based on a stub load resonator, which comprises a medium substrate, wherein two stub load microstrip resonators and two stepped impedance microstrip lines are printed on the upper surface of the medium substrate; the method is characterized in that:
the two E-shaped branch load resonators have opposite openings, a stepped impedance microstrip line is additionally arranged on the outer side of the E-shaped structure of the two E-shaped branch load resonators, and the molded surface on the outer side of the E-shaped structure is inserted into a groove at the tail end of a low impedance line in the stepped impedance microstrip line to form three-line interdigital coupling;
the step impedance microstrip line is connected with a rectangular high impedance microstrip line and a rectangular low impedance microstrip line, the tail end of the high impedance line is provided with a grounded metallized via hole,
the step impedance gap line comprises a linear step impedance gap line and an L-shaped step impedance gap line, and the L-shaped step impedance gap line rotates 90 degrees anticlockwise compared with the linear step impedance gap line; etching a linear stepped impedance slot line corresponding to the middle position of a linear microstrip bottom in the U-shaped microstrip line; the L-shaped stepped impedance slot line etching corresponds to the lower part of the high impedance line in the stepped impedance microstrip line;
the two branch load resonators, the two stepped impedance microstrip lines, the two U-shaped microstrip lines, the two linear type slot lines and the two L-shaped stepped impedance slot lines are all in central symmetry with respect to the central point of the dielectric substrate 1; the center-loaded branch of the branch load resonator is respectively provided with an open circuit and a short circuit, and can be used for independently adjusting the center frequencies of two frequency bands.
Compared with the prior art, the invention has the following advantages:
1. because the invention adopts the branch load resonator, the center frequency of two frequency bands of the filter can be independently adjusted by adjusting the branch loaded at the center of the microstrip resonator in the structure; different from most differential microstrip line-slot line transmission structures, the U-shaped microstrip line and the stepped impedance slot line are symmetrical about the center point of the dielectric slab, and the L-shaped stepped impedance slot line rotates 90 degrees anticlockwise compared with the linear stepped impedance slot line, so that the size of the filter is greatly reduced, and meanwhile, the good common mode rejection characteristic is kept.
2. The branch load resonator adopted by the invention has two forms, namely the terminal open-circuit branch and the terminal short-circuit branch, so that the flexibility and the convenience of design are enhanced, the filter can be conveniently suitable for different application requirements, and in addition, the size of the filter is further reduced due to the inherent characteristics of the short-circuit branch.
3. Because a pair of three-wire interdigital coupling linear gaps are etched in the stepped impedance microstrip line, and energy is transmitted between the stepped impedance microstrip line and the branch load microstrip resonator through three-wire interdigital coupling, the coupling between input and output is enhanced, and the insertion loss of the filter is reduced; compared with most of filters using a single resonator, the dual-band differential band-pass filter uses two resonators, one transmission zero is generated between the two resonators through quasi-interdigital coupling, the position of the transmission zero can be changed by adjusting the gap coupling between the stepped impedance microstrip line and the stub load resonator, the design flexibility and the out-of-band selectivity of the dual-band differential band-pass filter are remarkably improved, and meanwhile, higher common mode rejection is kept.
4. The invention has the characteristic of wide stop band, and enhances the selectivity of the filter.
Drawings
FIG. 1 is a schematic diagram of the overall structure of a dual-band differential filter based on open-circuited stub load resonators according to the present invention;
FIG. 2 is a schematic diagram of the overall structure of a dual-band differential filter based on short-circuited stub load resonators according to the present invention;
fig. 3 is a diagram of the position size of a U-shaped input/output microstrip line (the structure is completely the same in the two models);
FIG. 4 is a diagram of the position dimensions of an open-circuited stub load resonator and a stepped-impedance microstrip line;
FIG. 5 is a diagram showing the position dimensions of a short stub load resonator and a stepped impedance microstrip line;
FIG. 6 is a diagram showing the dimensions of the locations of structures on the lower surface of a dielectric substrate (the structures are identical in both models);
FIG. 7 is an S-parameter real-time diagram of the differential mode return loss and the differential mode insertion loss of the dual-frequency differential filter based on the open-circuited stub load resonator according to the present invention;
FIG. 8 is an S-parameter real-time diagram of the common-mode return loss and the common-mode insertion loss of the dual-band differential filter based on the open-circuited stub load resonator according to the present invention;
FIG. 9 is an S-parameter real-time graph of the differential mode return loss and the differential mode insertion loss of the dual-frequency differential filter based on the short-circuited stub load resonator according to the present invention;
fig. 10 is an S-parameter real-time diagram of the common-mode return loss and the common-mode insertion loss of the dual-band differential filter based on the short-circuited stub load resonator according to the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and the specific embodiments.
Example 1:
with the continuous development of the communication field, the communication system is more and more complex, and as an indispensable device in radio frequency transceiving, the filter becomes more and more important, and the performance of the filter is related to whether the whole communication system can normally operate. High frequency systems are particularly complex, which requires filters with greater interference rejection, and differential filters are available. In recent years, a plurality of differential filters are invented and proposed, but most of the differential filters cannot simultaneously meet the requirements of multiple frequency bands, low insertion loss, high selectivity and design flexibility.
The invention relates to a dual-frequency differential band-pass filter based on stub load resonators, which is shown in a figure 1 and a figure 2: the medium substrate comprises a medium substrate 1, wherein two branch load microstrip resonators 2 and two step impedance microstrip lines 3 are printed on the upper surface of the medium substrate 1, U-shaped microstrip lines 5 are printed on two sides of the two branch load microstrip resonators 2, a metal floor 6 is printed on the lower surface of the medium substrate 1, and step impedance slot lines are etched on the metal floor 6 and positioned on one side of the U-shaped microstrip lines 5.
The two E-shaped branch load resonators have opposite openings; a stepped impedance microstrip line 3 is additionally arranged on the outer side of the E-shaped structures of the two E-shaped branch load resonators, and the molded surface on the outer side of the E-shaped structure is inserted into a groove at the tail end of a low impedance line in the stepped impedance microstrip line 3 to form three-line interdigital coupling.
The stepped impedance microstrip line 3 of the invention is formed by connecting a rectangular high impedance microstrip line and a rectangular low impedance microstrip line, and the tail end of the high impedance line is provided with a grounding metallized through hole 4.
The stepped impedance gap line comprises a linear stepped impedance gap line 7 and an L-shaped stepped impedance gap line 8 which are etched and distributed on the lower surface of a dielectric substrate 1, namely a metal floor 6. The L-shaped stepped impedance slot line 8 is rotated 90 counterclockwise from the straight stepped impedance slot line 7. The wider rectangular slot in the linear stepped impedance slot line 7 is etched at the middle position below the bottom of the linear microstrip in the corresponding U-shaped microstrip line and along the inner side of the U-shaped microstrip line, or at the middle position corresponding to the bottom of the U-shaped microstrip line. The narrow rectangular slot in the linear stepped impedance slot line 7 is etched at the middle position corresponding to the lower part of the bottom of the linear microstrip in the U-shaped microstrip line and is along the outer side of the U-shaped microstrip line. The etching position of the narrower rectangular slot in the L-shaped stepped impedance slot line 8 corresponds to the lower part of the high impedance line in the stepped impedance microstrip line 3; the wider rectangular slot in the L-shaped stepped impedance slot line 8 is etched on the side below the stepped impedance microstrip line 3, and the long side of the rectangular slot is parallel to the long side of the low impedance line in the stepped impedance microstrip line 3.
The two branch load resonators 2, the two step impedance microstrip lines, the two U-shaped microstrip lines 5, the two linear type gap lines 7 and the two L-shaped step impedance gap lines 8 are arranged symmetrically about the center point of the dielectric substrate 1. The center-loaded minor matters of the minor-load resonator 2 are respectively provided with an open circuit mode and a short circuit mode, and can be used for independently adjusting the center frequencies of two frequency bands.
Aiming at the problems of large size, high insertion loss, low selectivity and design flexibility of the existing filter, the invention provides a novel technical scheme based on a branch load filter
The idea of the invention is as follows: signals are input by the U-shaped microstrip line, and transmission of common-mode signals is inhibited through the conversion structure from the U-shaped microstrip line to the slot line, so that the anti-interference capability of the filter is enhanced; the slot line adopts a stepped impedance resonator, wherein the L-shaped stepped impedance slot line is rotated by 90 degrees anticlockwise compared with a straight stepped impedance slot line, the size of the filter is greatly reduced, and meanwhile, the good common mode rejection characteristic is kept. Differential mode signals are transmitted to the stepped impedance microstrip line through the stepped impedance slot line and are transmitted to the minor-pitch load resonator through three-wire interdigital coupling, the coupling between input and output is enhanced through the three-wire interdigital coupling mode, so that the filter has smaller insertion loss, and two transmission zeros can be generated near a differential mode passband; the invention adopts the branch load resonators, the center frequencies of two pass bands can be independently adjusted by adjusting the branches loaded at the centers of the microstrip resonators, the two branch load resonators generate a transmission zero point through quasi-interdigital coupling, and the position of the transmission zero point is adjustable. The branch load resonator has two forms, namely branch terminal open circuit and branch terminal short circuit, so that the flexibility and the convenience of design are enhanced, and the branch load resonator is convenient to adapt to different application requirements. In addition, the invention also has the characteristic of wide stop band. In conclusion, the invention obviously improves the design flexibility and out-of-band selectivity of the dual-frequency differential band-pass filter, and simultaneously keeps higher common-mode rejection.
Example 2:
the overall structure and the specific structure of the dual-frequency differential band-pass filter based on the stub load resonators are the same as those of embodiment 1, see fig. 1 and fig. 2, the two stub load resonators 2 which are symmetrical about the center of the dielectric substrate of the invention have opposite opening directions, see fig. 4 and fig. 5, that is, the two E-shaped stub load resonators 2 have opposite openings, and the coupling mode is quasi-interdigital coupling. The branches loaded in the microstrip resonator 2, which are either open-circuit branches or short-circuit branches, are all located at the right center of the C-shaped microstrip line formed by the E-shaped frame. The branch load microstrip resonator 2 comprises a C-shaped microstrip line folded into three sections and a branch loaded at the central position of the C-shaped microstrip line, the size of the microstrip resonator is reduced through folding, and multiband and flexible adjustment of the central frequency of the frequency band are achieved through the loaded branch. The two E-branch load resonators form a transmission zero point in a quasi-interdigital coupling mode and are symmetrical with respect to the center point of the dielectric substrate, and the two ends of the C-shaped microstrip line and the stepped impedance microstrip line 3 are coupled in an enhanced input and output mode through the three-wire interdigital coupling linear gap, so that two transmission zero points are additionally formed near the passband to improve out-of-band selectivity.
Referring to fig. 4, the total length of the folded half-wavelength resonator in the open-ended stub-loaded microstrip resonator 2 is Lr143.6mm, width Wr10.7mm, the length of the branch of the microstrip open circuit is Lr212mm, width Wr20.7mm, and a distance g coupled in parallel with the stepped impedance microstrip line 311.15mm, and a distance g for interdigital coupling with 3 three lines of the stepped impedance microstrip line2＝0.2mm。
Referring to fig. 5, the terminalThe total length of the folded half-wavelength resonator in the short-circuited stub-loaded microstrip resonator 2 is Lr142.4mm, width Wr10.8mm, the length of the microstrip short circuit branch is Lr24.3mm, width Wr20.8mm, radius r of the metallized via hole at the end of the short-circuit branch20.2mm, and a distance g coupled in parallel with the stepped impedance microstrip line 311.1mm, and a gap g for interdigital coupling with 3 three lines of the stepped impedance microstrip line2＝0.3mm。
Aiming at the problem that the central frequencies of two frequency bands of the existing differential double-frequency filter can not be independently adjusted mostly, the invention adopts the stub load resonator, and the central frequencies of the two frequency bands of the filter can be independently adjusted by adjusting the stub loaded at the center of the microstrip resonator in the structure; meanwhile, the branch load resonator has two forms, namely branch terminal open circuit and branch terminal short circuit, so that the flexibility and the convenience of design are enhanced, the branch load resonator is convenient to adapt to different application requirements, and the size of the filter is further reduced due to the inherent characteristics of the short-circuit branches. In addition, the dual-band differential band-pass filter uses two resonators, and a transmission zero is generated between the two resonators through quasi-interdigital coupling, so that the design flexibility and out-of-band selectivity of the dual-band differential band-pass filter are remarkably improved, and meanwhile, higher common mode rejection is kept.
Example 3:
the overall structure and the specific structure of the dual-frequency differential band-pass filter based on the stub load resonator are the same as those of the embodiment 1-2, referring to fig. 1, fig. 2, fig. 4 and fig. 5, the stepped impedance microstrip line 3 of the invention is formed by connecting a small rectangular high impedance microstrip line and a large rectangular low impedance microstrip line, the tail end of the high impedance microstrip line is grounded through a metalized via hole 4 and exceeds the waveguide wavelength of a quarter microstrip line of a bottom layer slot line, so that good transition of differential mode signals from the slot line to the microstrip line is realized. The two microstrip lines are parallel to the long side of the dielectric plate 1, and in order to realize smaller size, the two stepped impedance microstrip lines 3 are centrosymmetric with respect to the central point of the dielectric substrate.
Referring to fig. 4, when the stub loaded in the stub-loaded resonator 2 is open,high impedance microstrip line length L of stepped impedance microstrip line 331mm, width W30.8mm, low impedance microstrip line length L417mm, width W4Width W of a pair of three-line interdigital coupling linear slits etched in the inner part of 2.4mm5The radius r of the metalized via 4 at the end of the high-impedance microstrip line is 0.2mm, which is 0.65 mm.
Referring to fig. 5, when the stub loaded in the stub-loaded resonator 2 is short-circuited, the high-impedance microstrip line length L of the stepped-impedance microstrip line 331mm, width W30.8mm, low impedance microstrip line length L416mm, width W4Width W of a pair of three-line interdigital coupling linear slits etched in the inner part of 2.4mm5Radius r of metallized via hole 4 at the end of high impedance microstrip line of 0.5mm1＝0.2mm。
In order to reduce the insertion loss of the filter and improve the out-of-band selectivity of the filter, three-wire interdigital coupling linear gaps are etched in the two stepped impedance microstrip lines respectively, and energy is transmitted between the stepped impedance microstrip lines and the branch load microstrip resonators through three-wire interdigital coupling, so that the coupling between input and output is enhanced, and the insertion loss of signals is reduced; in addition, the coupling mode can generate two transmission zeros near the differential-mode passband, and the positions of the transmission zeros can be changed by adjusting the slot coupling between the stepped impedance microstrip line and the stub load resonator, so that the out-of-band selectivity of the filter is improved.
Example 4:
the overall structure and specific structure of the dual-band differential band-pass filter based on the stub load resonator are the same as those of embodiments 1 to 3, and referring to fig. 6, the stepped impedance gap line of the present invention includes a linear stepped impedance gap line 7 connected to an L-shaped stepped impedance gap line 8, which are etched and laid out on the lower surface of the dielectric substrate 1, that is, on the metal floor 6. The L-shaped stepped impedance slot line 8 is rotated 90 counterclockwise from the straight stepped impedance slot line 7. The wider rectangular slot in the linear stepped impedance slot line 7 is etched at the middle position below the bottom of the linear microstrip in the corresponding U-shaped microstrip line and along the inner side of the U-shaped microstrip line, or is corresponding to the U-shaped microstrip lineAnd exceeds the quarter slot line wavelength at the bottom of the straight microstrip line of the U-shaped microstrip line 5. The narrow rectangular slot in the linear stepped impedance slot line 7 is etched at the middle position corresponding to the lower part of the bottom of the linear microstrip in the U-shaped microstrip line and is along the outer side of the U-shaped microstrip line. The etching position of the narrower rectangular slot in the L-shaped stepped impedance slot line 8 corresponds to the lower part of the high impedance line in the stepped impedance microstrip line 3; the wider rectangular slot in the L-shaped stepped impedance slot line 8 is etched on the side below the stepped impedance microstrip line 3, and the long side of the rectangular slot is parallel to the long side of the low impedance line in the stepped impedance microstrip line 3. The L-shaped stepped impedance slot line 8 exceeds the waveguide wavelength of a slot line of a quarter of the central position of the junction of the high-impedance microstrip line and the low-impedance microstrip line in the stepped impedance microstrip line 3. The two sections of stepped impedance gap lines and the U-shaped input microstrip line 5 on the medium substrate 1 right above form a conversion structure from the microstrip line to the gap line, and the conversion structure is used for transmitting differential mode signals and realizing inherent common mode signal suppression; the input/output linear stepped impedance gap line 7 and the L-shaped stepped impedance gap line 8 are both centrosymmetric about the central point of the dielectric substrate; l in linear type stepped impedance gap line 7s1＝9mm，Ls25.55mm, width Ws1＝5mm，Ws20.15 mm; l in L-shaped stepped impedance gap line 8s3＝9.85mm，Ls47mm, width Ws4＝3.3mm。
Different from most differential microstrip line-slot line transmission structures, the U-shaped microstrip line and the stepped impedance slot line are symmetrical about the center point of the dielectric slab, and the L-shaped stepped impedance slot line rotates 90 degrees anticlockwise compared with the linear stepped impedance slot line, so that the size of the filter is greatly reduced, and meanwhile, the good common mode rejection characteristic is kept.
Example 5:
the overall structure and specific structure of the dual-band differential band-pass filter based on the minor-length load resonator are the same as those of embodiments 1-4, and referring to fig. 3, a U-shaped microstrip line 5 of the present invention is formed by connecting a straight microstrip bottom and two mutually parallel straight microstrip arms, both the two U-shaped microstrip lines can be used as an input U-shaped microstrip line or an output U-shaped microstrip line, and are symmetrical with respect to the center point of a dielectric substrateThe linear microstrip arm in the U-shaped microstrip line 5 of the present invention is used for inputting differential mode signals and common mode signals simultaneously, and the impedance of the linear microstrip bottom and the impedance of the linear microstrip arm are both 50 Ω, so as to ensure good matching of the feed port. Length L of two microstrip arms of U-shaped input microstrip feed line 5112.4mm, line width W12.4mm, length L of the base of the microstrip215.2mm, width W2The distances from the boundary of the dielectric substrate are 4.8mm and 9.2mm respectively, which are 2.4 mm.
Most U-shaped microstrip line structures are symmetrical about a symmetry axis parallel to the side length of the dielectric plate, so that etched slot lines corresponding to the lower surface of the dielectric plate under the U-shaped microstrip lines and microstrip resonators on the upper surface of the dielectric plate are distributed along the straight line symmetry axis, the size of the filter is increased frequently. In addition, the impedance of the linear microstrip bottom and the impedance of the linear microstrip arm of the U-shaped microstrip line are both 50 omega, so that the matching of a feed port is better, and the filter has smaller insertion loss.
The invention aims to improve the design flexibility and out-of-band selectivity of the dual-frequency differential filter. The technical problems of single frequency band, high insertion loss, low selectivity, lack of design flexibility and the like of the conventional filter are successfully solved.
Two more detailed specific examples are given below to further illustrate the invention:
example 6:
the overall structure and specific structure of the dual-band differential band-pass filter based on the stub load resonators are the same as those of embodiments 1-5.
Referring to fig. 1, a dual-frequency differential band-pass filter based on an open-circuit stub load resonator comprises a dielectric substrate 1, wherein two open-circuit stub load microstrip resonators 2 which are centrosymmetric with respect to a central point of the dielectric substrate are printed on the upper surface of the dielectric substrate 1, two stepped impedance microstrip lines 3 which are coupled with the stub load resonators 2 through three-wire interdigital coupling are arranged, the tail ends of the two stepped impedance microstrip lines 3 are respectively provided with a metalized via hole 4 for grounding, U-shaped microstrip lines 5 are printed on two sides of the two stub load microstrip resonators 2, and input and output U-shaped microstrip lines are centrosymmetric with respect to the central point of the dielectric substrate; in this example, a metal floor 6 is printed on the lower surface of the dielectric substrate 1, and a straight stepped impedance slot line 7 and an L-shaped stepped impedance slot line 8 are etched on the metal floor 6 on the side corresponding to the U-shaped microstrip line 5. Wherein:
in this example, the dielectric substrate 1 was made of a rectangular F4BM-2 material having a relative dielectric constant of 2.2, a size of 53.7mm X34 mm, and a thickness of 0.8 mm.
Referring to fig. 3, in this example, the U-shaped microstrip line 5 is formed by connecting a straight microstrip bottom and two parallel straight microstrip arms, the two U-shaped microstrip lines are symmetric with respect to the center point of the dielectric substrate, the straight microstrip arm in the U-shaped microstrip line 5 is used for inputting a differential mode signal and a common mode signal simultaneously, and the impedances of the straight microstrip bottom and the straight microstrip arm are both 50 Ω, so as to ensure that the feed port is well matched. Length L of two microstrip arms of U-shaped input microstrip feed line 5112.4mm, line width W12.4mm, length L of the base of the microstrip215.2mm, width W2The distances from the boundary of the dielectric substrate are 4.8mm and 9.2mm respectively, which are 2.4 mm.
Referring to fig. 4, the open-circuit stub loaded microstrip resonator 2 in this example includes a C-shaped microstrip line folded into three sections and a stub with an open-circuit terminal loaded at the center of the C-shaped microstrip line, the size of the microstrip resonator is reduced by folding, and multiple frequency bands and the center frequency and bandwidth of the frequency bands can be flexibly adjusted by loading the stub. The opening directions of the two open-circuit branch load resonators are opposite, namely the directions are opposite, a transmission zero point is formed in a quasi-interdigital coupling mode and is symmetrical about the center of the center point of the dielectric substrate, the two ends of the C-shaped microstrip line and the stepped impedance microstrip line 3 are in input and output coupling enhancement through a three-wire interdigital coupling linear gap, and two transmission zero points are additionally formed near a passband so as to improve out-of-band selectivity; in this embodiment, the stepped impedance microstrip line 3 is formed by connecting a small rectangular high impedance microstrip line and a large rectangular low impedance microstrip line, and the tail end of the high impedance microstrip line is connected throughThe metalized via hole 4 is grounded and exceeds the waveguide wavelength of a quarter microstrip line of the bottom slot line, the two microstrip lines are both parallel to the long edge of the dielectric plate, and the high-impedance microstrip line is used for realizing the transition of differential mode signals from the slot line to the microstrip line; the total length of the folding type half-wavelength resonator in the branch load microstrip resonator 2 is Lr143.6mm, width Wr10.7mm, the length of the microstrip branch is Lr212mm, width Wr20.7mm, and a distance g coupled in parallel with the stepped impedance microstrip line 311.15mm, and a distance g for interdigital coupling with 3 three lines of the stepped impedance microstrip line20.2 mm; high impedance microstrip line length L of stepped impedance microstrip line 331mm, width W30.8mm, low impedance microstrip line length L417mm, width W4Width W of a pair of three-line interdigital coupling linear slits etched in the inner part of 2.4mm5The radius r of the metalized via 4 at the end of the high-impedance microstrip line is 0.2mm, which is 0.65 mm.
Referring to fig. 6, the linear stepped impedance slot line 7 in this example is formed by connecting a wider rectangular slot and a narrower slot; the L-shaped stepped impedance slot line 8 in the embodiment is composed of a section of narrow linear slot line and a section of wide slot line, the narrow slot line penetrates through the position right below the junction of the high-impedance microstrip line and the low-impedance microstrip line in the stepped impedance microstrip line 3 and exceeds the waveguide wavelength of the quarter slot line, and the two sections of stepped impedance slot lines and the U-shaped input microstrip line 5 on the medium substrate 1 right above form a conversion structure from the microstrip line to the slot line for transmitting differential mode signals and realizing the inherent common mode signal suppression; the input/output linear stepped impedance gap line and the L-shaped stepped impedance gap line are centrosymmetric about the central point of the dielectric substrate; l in linear type stepped impedance gap line 7s1＝9mm，Ls25.55mm, width Ws1＝5mm，Ws20.15 mm; l in L-shaped stepped impedance gap line 8s3＝9.85mm，Ls47mm, width Ws4＝3.3mm。
The invention adopts the mode of opening the terminals of the branches of the microstrip resonator, and can independently adjust the central frequencies of two frequency bands of the filter by adjusting the branches loaded at the center of the microstrip resonator, thereby enhancing the flexibility and the convenience of design. Different from most differential microstrip line-slot line transmission structures, the U-shaped microstrip line and the stepped impedance slot line are symmetrical about the center point of the dielectric slab, and the L-shaped stepped impedance slot line rotates 90 degrees anticlockwise compared with the linear stepped impedance slot line, so that the size of the filter is greatly reduced, and meanwhile, the good common mode rejection characteristic is kept.
Because a pair of three-wire interdigital coupling linear gaps are etched in the stepped impedance microstrip line, energy is transmitted between the stepped impedance microstrip line and the branch load microstrip resonator through three-wire interdigital coupling, the coupling between input and output is enhanced, and the insertion loss is smaller; compared with most of filters using a single resonator, the dual-band differential band-pass filter uses two resonators, one transmission zero is generated between the two resonators through quasi-interdigital coupling, the position of the transmission zero can be changed by adjusting the gap coupling between the stepped impedance microstrip line and the stub load resonator, the design flexibility and the out-of-band selectivity of the dual-band differential band-pass filter are remarkably improved, and meanwhile, higher common mode rejection is kept. In addition, the invention has the characteristic of wide stop band, and enhances the selectivity of the filter.
Example 7:
the overall structure and specific structure of the dual-band differential band-pass filter based on the stub load resonators are the same as those of embodiments 1-5.
Referring to fig. 2, a dual-band differential band-pass filter based on short-circuited stub load resonators includes a dielectric substrate 1, the upper surface of the dielectric substrate 1 is printed with two short-circuit branch load microstrip resonators 2 which are centrosymmetric with respect to the center point of the dielectric plate, the tail ends of the two short-circuit branches are grounded through a metalized via hole 9, the two stepped impedance microstrip lines 3 which are coupled with the short-circuit branch load resonators through three lines are interdigital, the tail ends of the two stepped impedance microstrip lines 3 are grounded through a metalized via hole 4, the two sides of the two branch load microstrip resonators 2 are printed with a U-shaped input microstrip line and a U-shaped output microstrip line 5 which are centrosymmetric with respect to the center point of the dielectric plate, the lower surface of the dielectric substrate 1 is printed with a metal floor 6 in the example, the metal floor 6 is positioned at one side of the U-shaped microstrip line 5, and a linear stepped impedance gap line 7 and an L-shaped stepped impedance gap line 8 which are connected with each other are etched. Wherein:
in this example, the dielectric substrate 1 was made of a rectangular F4BM-2 material having a relative dielectric constant of 2.2, a size of 51.7mm X34 mm, and a thickness of 0.8 mm.
Referring to fig. 3, in this example, the U-shaped microstrip line 5 is formed by connecting a straight microstrip bottom and two parallel straight microstrip arms, the two U-shaped microstrip lines are symmetric with respect to the center point of the dielectric substrate, the straight microstrip arm in the U-shaped microstrip line 5 is used for inputting a differential mode signal and a common mode signal simultaneously, and the impedances of the straight microstrip bottom and the straight microstrip arm are both 50 Ω, so as to ensure that the feed port is well matched. Length L of two microstrip arms of U-shaped input microstrip feed line 5112.4mm, line width W12.4mm, length L of the base of the microstrip215.2mm, width W2The distances from the boundary of the dielectric substrate are 4.8mm and 9.2mm respectively, which are 2.4 mm.
Referring to fig. 5, the stub loaded microstrip resonator 2 in this example includes a C-shaped microstrip line folded into three sections and a stub with a short-circuited end section loaded at the center of the C-shaped microstrip line, and the size of the microstrip resonator is reduced by folding, and a multiband is realized by loading the stub and the center frequency and the bandwidth of the frequency band are conveniently and flexibly adjusted. The opening directions of the two branch load resonators are opposite and are centrosymmetric about the center point of the dielectric substrate, and the two ends of the C-shaped microstrip line and the stepped impedance microstrip line 3 are coupled in an enhanced input and output mode through a three-line interdigital coupling linear gap, so that three transmission zeros are additionally formed near a passband to improve out-of-band selectivity; in this embodiment, the stepped impedance microstrip line 3 is formed by connecting a small rectangular high impedance microstrip line and a large rectangular low impedance microstrip line, the end of the high impedance microstrip line is grounded through a metalized via 4 and exceeds the waveguide wavelength of a quarter microstrip line of a bottom slot line, and the two microstrip lines are both connected with a dielectric plateThe long sides are parallel, and the high-impedance microstrip line is used for realizing the transition of differential mode signals from the slot line to the microstrip line; the total length of the folding type half-wavelength resonator in the branch load microstrip resonator 2 is Lr142.4mm, width Wr10.8mm, the length of the microstrip branch is Lr24.3mm, width Wr20.8mm, radius r of the metallized via hole at the end of the microstrip branch20.2mm, and a distance g coupled in parallel with the stepped impedance microstrip line 311.1mm, and a gap g for interdigital coupling with 3 three lines of the stepped impedance microstrip line20.3 mm; high impedance microstrip line length L of stepped impedance microstrip line 331mm, width W30.8mm, low impedance microstrip line length L416mm, width W4Width W of a pair of three-line interdigital coupling linear slits etched in the inner part of 2.4mm5Radius r of metallized via hole 4 at the end of high impedance microstrip line of 0.5mm1＝0.2mm。
Referring to fig. 6, the linear stepped impedance slot line 7 in this example is formed by connecting a wider rectangular slot and a narrower slot; the L-shaped stepped impedance slot line 8 in the embodiment is composed of a section of narrow linear slot line and a section of wide slot line, the narrow slot line penetrates through the position right below the junction of the high-impedance microstrip line and the low-impedance microstrip line in the stepped impedance microstrip line 3 and exceeds the waveguide wavelength of the quarter slot line, and the two sections of stepped impedance slot lines and the U-shaped input microstrip line 5 on the medium substrate 1 right above form a conversion structure from the microstrip line to the slot line for transmitting differential mode signals and realizing the inherent common mode signal suppression; the input/output linear stepped impedance gap line and the L-shaped stepped impedance gap line are centrosymmetric about the central point of the dielectric substrate; l in linear type stepped impedance gap line 7s1＝9mm，Ls25.55mm, width Ws1＝5mm，Ws20.15 mm; l in L-shaped stepped impedance gap line 8s3＝9.85mm，Ls47mm, width Ws4＝3.3mm。
The invention adopts the form of short circuit of the branch terminal of the microstrip resonator, and can independently adjust the center frequencies of two frequency bands of the filter by adjusting the branch loaded in the center of the microstrip resonator, thereby enhancing the flexibility and convenience of design. Different from most differential microstrip line-slot line transmission structures, the U-shaped microstrip line and the stepped impedance slot line are symmetrical about the center point of the dielectric slab, and the L-shaped stepped impedance slot line rotates 90 degrees anticlockwise compared with the linear stepped impedance slot line, so that the size of the filter is greatly reduced, and meanwhile, the good common mode rejection characteristic is kept. In addition, the short-circuit branch further reduces the size of the filter due to the inherent characteristics of the short-circuit branch.
Because a pair of three-wire interdigital coupling linear gaps are etched in the stepped impedance microstrip line, energy is transmitted between the stepped impedance microstrip line and the branch load microstrip resonator through three-wire interdigital coupling, the coupling between input and output is enhanced, and the insertion loss is smaller; compared with most of filters using a single resonator, the dual-band differential band-pass filter uses two resonators, one transmission zero is generated between the two resonators through quasi-interdigital coupling, the position of the transmission zero can be changed by adjusting the gap coupling between the stepped impedance microstrip line and the stub load resonator, the design flexibility and the out-of-band selectivity of the dual-band differential band-pass filter are remarkably improved, and meanwhile, higher common mode rejection is kept. The invention also has the characteristic of wide stop band, and enhances the selectivity of the filter.
The working principle of the invention is as follows: when signals are input by the U-shaped input microstrip line, microstrip differential mode signals excite an electric field of the first stepped impedance slot line below the U-shaped input microstrip line, and microstrip common mode signals cannot excite the electric field of the first stepped impedance slot line, so that only differential mode signals can pass through the linear stepped impedance slot line and are transmitted to the L-shaped stepped impedance slot line, the common mode signals are restrained, the differential mode signals are transmitted to the upper stepped impedance microstrip line through the transition structure from the stepped impedance slot line to the stepped impedance microstrip line, and are transmitted to the upper two open-circuit/branch-node loaded microstrip resonators in the middle through three-wire interdigital coupling, input and output coupling is enhanced, and therefore three transmission zeros are formed near a pass band and selectivity of the filter is improved.
The technical effects of the present invention will be further explained by combining the actual measurement results as follows:
example 8:
the overall structure and specific structure of the dual-band differential band-pass filter based on the stub load resonators are the same as those of embodiments 1 to 7.
The content of the measurement experiment is as follows:
the vector network analyzer N5230A is used for respectively carrying out measurement experiments one and two on the dual-frequency differential band-pass filter based on the open-circuit stub load resonator and the dual-frequency differential band-pass filter based on the short-circuit stub load resonator in the invention, and the experiment one tests the differential mode return loss of the dual-frequency differential band-pass filter
Sum and difference mode insertion loss
The experimental results are shown in fig. 7 and 8; experiment two tests the common mode return loss of the double-frequency differential band-pass filter
And common mode insertion loss
The experimental results are shown in fig. 9 and 10.
Measurement of experimental results and analysis:
FIG. 7 is an S-parameter real map of differential mode return loss and differential mode insertion loss of a dual-frequency differential filter based on open-circuited stub load resonators according to the present invention, where the differential mode return loss consumption
Indicating differential mode insertion loss
And (4) showing. The abscissa of fig. 7 is frequency in GHz; the ordinate is the S parameter in dB. The curve with solid square symbols in FIG. 7 is
The curve with the symbol of the open circle is
In the embodiment, the center frequencies of the two differential mode pass bands are respectively 2.50GHz and 3.60GHz, and the absolute bandwidths (relative bandwidths) are respectively 209.2MHz and 173.5MHz (8.68% and 4.99%); maximum differential mode return loss in first differential mode passband
35.4dB, minimum differential mode insertion loss
Is 2.05 dB; maximum differential mode return loss in the second differential mode passband
15.84dB, minimum differential mode insertion loss
Is 2.28 dB; the left side of the first differential-mode passband is provided with 1 transmission zero and is positioned at 1.8GHz, a transmission zero is arranged between the first differential-mode passband and the second differential-mode passband and is positioned at 2.67GHz, and the right side of the second differential-mode passband is provided with a transmission zero and is positioned at 3.76 GHz.
FIG. 8 is an S-parameter real-time diagram of the common-mode return loss and the common-mode insertion loss of the dual-frequency differential filter based on the open-circuited stub load resonator according to the present invention, wherein the common-mode return loss is consumed
Indicating common mode insertion loss
And (4) showing. The abscissa of fig. 8 is frequency in GHz; the ordinate is the S parameter in dB. The curve with solid square symbols in FIG. 8 is
The curve with the symbol of the open circle is
Common mode return loss in this embodiment
Less than or equal to 0.40dB in working frequency range and common mode insertion loss
Greater than or equal to 38.5dB, it can be seen from the data display of fig. 8 that the dual-band differential bandpass filter of the present invention effectively achieves significant common-mode rejection in the operating band.
Example 9:
the overall structure and the specific structure of the dual-frequency differential band-pass filter based on the stub load resonator are the same as those of the embodiments 1 to 7, and the content of the measurement experiment is the same as that of the embodiment 8.
Measurement of experimental results and analysis:
FIG. 9 is an S-parameter real map of differential mode return loss and differential mode insertion loss of a dual-frequency differential filter based on short-circuited stub load resonators according to the present invention, where differential mode return loss consumption
Indicating differential mode insertion loss
And (4) showing. The abscissa of fig. 9 is frequency in GHz; the ordinate is the S parameter in dB. The curve with solid square symbols in FIG. 9 is
The curve with the symbol of the open circle is
In the embodiment, the center frequencies of the two differential-mode pass bands are 1.94GHz and 2.55GHz respectively, and the absolute bandwidths (relative bandwidths) are 169.6MHz and 207.8MHz (8.93 percent and 8.31 percent) respectively; maximum differential mode return loss in first differential mode passband
20.15dB, minimum differential mode insertion loss
Is 2 dB; maximum differential mode return loss in the second differential mode passband
19.85dB, minimum differential mode insertion loss
1.92 dB; as can be seen from fig. 9, the filter has a small insertion loss, and the three transmission zeros significantly improve the out-of-band selectivity at the same time.
FIG. 10 is an S-parameter real-time diagram of the common-mode return loss and the common-mode insertion loss of the dual-frequency differential filter based on the short-circuited stub load resonator according to the present invention, wherein the common-mode return loss is consumed
Indicating common mode insertion loss
And (4) showing. The abscissa of fig. 10 is frequency in GHz; the ordinate is the S parameter in dB. The curve with solid square symbols in FIG. 10 is
The curve with the symbol of the open circle is
Common mode return loss in this embodiment
Less than or equal to 0.28dB in working frequency range and common mode insertion loss
Greater than or equal to 40dB, it can be seen from fig. 10 that the dual-frequency differential band-pass filter of the present invention achieves significant common mode rejection.
In short, the invention provides a dual-frequency differential band-pass filter based on a stub load resonator. The problems of high insertion loss, low selectivity and lack of flexible design of the existing filter are solved. Two branch load resonators which are in opposite directions at the center to form quasi-interdigital coupling, two stepped impedance microstrip lines which form three-line interdigital coupling with the branch load resonators, and U-shaped microstrip lines on two sides are printed on the upper surface of the dielectric substrate; two linear stepped impedance gap lines and two L-shaped stepped impedance gap lines which are rotated by 90 degrees counterclockwise compared with the linear stepped impedance gap lines are etched on the metal floor on the lower surface of the medium substrate. The circuit structures are all centrosymmetric about the center point of the dielectric substrate. All structures on the upper surface and the lower surface of the dielectric substrate are designed in a central symmetry mode about the central point of the dielectric substrate and are designed in a stepped impedance gap line bending mode by 90 degrees, and the size of a filter is greatly reduced; the quasi-interdigital coupling and three-wire interdigital coupling structure reduces the insertion loss of the filter and forms three transmission zeros, thereby enhancing the selectivity of the filter; the branch node loaded in the center has two forms of open circuit and short circuit, so that the method is convenient to adapt to different application requirements.
Claims (5)
1. A dual-frequency differential band-pass filter based on branch load resonators comprises a dielectric substrate (1), wherein two branch load microstrip resonators (2) and two step impedance microstrip lines (3) are printed on the upper surface of the dielectric substrate (1), U-shaped microstrip lines (5) are printed on two sides of the outer side of branch bearing sections of the two branch load microstrip resonators (2), the two U-shaped microstrip lines (5) are formed by connecting a linear microstrip bottom and two mutually parallel linear microstrip arms, a metal floor (6) is printed on the lower surface of the dielectric substrate (1), step impedance slot lines are etched on the metal floor (6), and the positions of the step impedance slot lines correspond to the positions of the U-shaped microstrip lines (5) on the upper surface of the dielectric substrate (1); the method is characterized in that:
the two branch load micro-strip resonators (2) are centered and are respectively a section of E-shaped branch load resonator, and the openings of the two E-shaped branch load resonators are opposite and penetrate through; two step impedance microstrip lines (3) are additionally arranged on the frames of the E-shaped structures of the two E-shaped branch load resonators, namely the frame profile on the outer side of the E-shaped structures is inserted into a groove formed by two long and thin high-impedance lines and two low-impedance lines in the step impedance microstrip lines (3) to form three-line interdigital coupling;
the step impedance microstrip line (3) is formed by connecting a rectangular high impedance microstrip line and a rectangular low impedance microstrip line, two long and thin rectangular high impedance microstrip lines are connected with one end of the rectangular low impedance microstrip line, the edges of the two long and thin rectangular high impedance microstrip lines are aligned, a groove inserted by an E-shaped structure outer side frame is formed between the two long and thin rectangular high impedance microstrip lines, and the other end of the low impedance microstrip line is connected with a high impedance microstrip line provided with a grounding metalized via hole (4);
the step impedance gap line comprises a linear step impedance gap line (7) and an L-shaped step impedance gap line (8), the linear step impedance gap line (7) and the L-shaped step impedance gap line (8) both comprise a rectangular gap line and a thin line-shaped gap line, the two thin line-shaped gap lines are intersected at 90 degrees, the long edges of the two rectangular gap lines are parallel to each other, and the step impedance gap line is formed integrally; the L-shaped stepped impedance gap line (8) is rotated 90 degrees anticlockwise in the direction of the extension line of the thin line-shaped gap line compared with the right end point of the thin line-shaped gap line in the straight stepped impedance gap line (7); etching a rectangular slot line in the linear stepped impedance slot line (7) to correspond to the inner side edge of the central position of the linear microstrip bottom in the U-shaped microstrip line, namely aligning a rectangular short edge of the rectangular slot line in the linear stepped impedance slot line (7) with the inner edge of the linear microstrip bottom of the U-shaped microstrip line, and enabling the central line of the rectangular short edge to correspond to the vertical central line of the linear microstrip bottom in the U-shaped microstrip line; etching a thin line-shaped gap line in the linear stepped impedance gap line (7) to a vertical center line corresponding to the bottom of the linear microstrip in the U-shaped microstrip line, and stopping at the intersection of the thin line-shaped gap line in the L-shaped stepped impedance gap line (8); the etching of the thin line-shaped slot line in the L-shaped stepped impedance slot line (8) corresponds to the edge of the high impedance line with the grounding via hole of the stepped impedance microstrip line (3), namely, the etching is aligned, and the width of the thin line-shaped slot line in the L-shaped stepped impedance slot line (8) is overlapped with the rectangular low impedance microstrip line in the stepped impedance microstrip line (3); a rectangular slot line in the L-shaped stepped impedance slot line (8) is positioned in the space above the low impedance microstrip line in the stepped impedance microstrip line (3), is parallel to two long and thin high impedance microstrip lines in the stepped impedance microstrip line (3) and is spaced apart from the long and thin high impedance microstrip lines, one short side of the rectangular slot line in the L-shaped stepped impedance slot line (8) is connected with a thin line-shaped slot line, and the thin line-shaped slot line in the L-shaped stepped impedance slot line (8) is stopped at the intersection with the thin line-shaped slot line in the linear stepped impedance slot line (7);
the two branch load resonators (2), the two step impedance microstrip lines, the two U-shaped microstrip lines (5), the two linear type gap lines (7) and the two L-shaped step impedance gap lines (8) are all in central symmetry around the central point of the dielectric substrate (1); the branch loaded at the center of the branch loaded microstrip resonator (2) is simultaneously provided with an open circuit or a short circuit, and can be used for independently adjusting the center frequencies of two frequency bands.
2. The dual-frequency differential band-pass filter based on the stub load resonators as claimed in claim 1, characterized in that the openings of the two E-type stub load microstrip resonators (2) are opposite, and the coupling mode is quasi-interdigital coupling.
3. The dual-frequency differential band-pass filter based on the stub load resonator as claimed in claim 1, wherein the stub load microstrip resonator (2) is an E-type stub load resonator, and the loaded stub, or the open stub or the short stub is located at the center of a C-type microstrip line formed by an E-type frame.
4. The dual-frequency differential band-pass filter based on stub load resonators as claimed in claim 1, wherein: rectangular slot lines in the linear type stepped impedance slot lines (7) exceed quarter slot line wavelengths at the bottoms of the linear micro-strips of the U-shaped micro-strip lines (5), thin slot lines in the L-shaped stepped impedance slot lines (8) penetrate through the positions right below the junctions of the high-impedance micro-strip lines and the low-impedance micro-strip lines in the stepped impedance micro-strip lines (3) and exceed quarter slot line waveguide wavelengths, and the two linear type stepped impedance slot lines (7), the two L-shaped stepped impedance slot lines (8) and the stepped impedance slot lines integrally formed by the two linear type stepped impedance slot lines are symmetrical about the center of a central point of the dielectric substrate.
5. The dual-frequency differential band-pass filter based on the stub load resonator as claimed in claim 1, wherein two U-shaped microstrip lines can be used as input or output microstrip lines, and are symmetric with respect to the center point of the dielectric substrate, and both the impedances of the straight microstrip bottom and the straight microstrip arm of the U-shaped microstrip lines are 50 Ω.
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| CN111769347B (en) * | 2020-07-31 | 2021-05-28 | 西安电子科技大学 | Differential ultra-wideband band-pass filter based on multimode slot line resonator |
| CN112350042B (en) * | 2020-11-20 | 2021-08-20 | 西安电子科技大学 | Single-ended to differential magic T with filtering characteristics |
| CN112768854B (en) * | 2020-12-29 | 2021-10-29 | 西安空间无线电技术研究所 | High-selectivity differential dual-passband microstrip filter based on stepped impedance resonator |
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