CN108987864B

CN108987864B - Eighth-mode substrate integrated waveguide filter with fully adjustable center frequency and bandwidth

Info

Publication number: CN108987864B
Application number: CN201810596537.7A
Authority: CN
Inventors: 郭君; 游彬
Original assignee: Hangzhou Dianzi University
Current assignee: Hangzhou Dianzi University
Priority date: 2018-06-11
Filing date: 2018-06-11
Publication date: 2020-05-05
Anticipated expiration: 2038-06-11
Also published as: CN108987864A

Abstract

The invention relates to an eighth-mode substrate integrated waveguide filter with fully adjustable center frequency and bandwidth. The EMSIW filter is formed by a single-layer dielectric plate, and the tuning of the center frequency and the bandwidth is realized by loading a variable capacitance diode. The stub is loaded on the EMSIW cavity, the resonant frequency of the EMSIW cavity is reduced, and meanwhile, the frequency is tuned by loading the varactor diode at the tail end of the stub, so that the frequency tuning mode of the SIW structure is innovatively realized; the two EMSIW cavities are electrically coupled through the edge gap, the gap provides physical space for a loading element, and the inter-cavity coupling coefficient is tuned by loading a varactor in the edge gap, so that the bandwidth tuning of the SIW structure is realized. The EMSIW is introduced to meet the requirement of a modern radio frequency communication system on miniaturization, and the problem that the traditional cavity filter is difficult to adjust by externally loading a tuning element is solved.

Description

Eighth-mode substrate integrated waveguide filter with fully adjustable center frequency and bandwidth

Technical Field

The invention belongs to the technical field of electronic information, in particular to an eighth-mode substrate integrated waveguide (EMSIW) filter with fully adjustable center frequency and bandwidth, which is a radio frequency filter with fully adjustable center frequency and bandwidth and compact structure.

Background

In the era of rapid development of communication technology, the microwave device most widely applied to the radio frequency front end is a filter, and the filter can filter out interference signals outside a frequency band, so that the performance of a receiver is guaranteed. With the continuous development of the communication industry, the available spectrum resources become more and more scarce, and the available frequency bands become more and more crowded. The phenomenon just can highlight the important function of the filter, the capability of separating useful signals becomes more important under the large background of scarce frequency spectrum resources, the performance of the filter directly determines the quality of microwave signal processing of the radio frequency front end circuit, and the filter plays an immeasurable role in a wireless communication system.

In mobile communication, there are several different standards of the main stream communication system, such as CDMA2000, WCDMA, TDD-LTE, FDD-LTE, and future 5G standard. Generally, a wireless communication system requires a large number of filters, each having its own specifications and functions, and different filters are responsible for communication operations in different frequency bands. Therefore, if filters of different standards are used for frequency selection in each rf front end, the size and complexity of the whole communication system are greatly increased, and the cost is high. Although the multi-frequency structure can work at a plurality of frequency points, crosstalk between adjacent frequency bands is always an unsolved problem. From the viewpoint, if the adopted radio frequency filter can realize the reconstruction of the center frequency and the bandwidth, the crosstalk problem of the adjacent frequency bands and the coverage problem of the multiple frequency bands can be effectively solved. In addition, if one rf filter can meet the different requirements of the index at the same time, then the original number of large fixed non-tunable filters can be replaced by a very small number of reconfigurable rf filters. The sharp reduction of the number of filters not only can greatly reduce the volume and cost of the wireless communication system, but also can simplify the design process of the whole wireless communication system circuit.

In the past 10 years, the conventional cavity resonator has been still commonly used to design high performance filters due to its advantages of low loss, high power capacity, high performance and high stability. However, such cavity resonators also have their significant disadvantages, such as: large volume, fixed and unadjustable, etc. In today's environment requiring miniaturization of devices and improved spectrum utilization, the disadvantages of cavity resonators are significantly magnified. The conventional cavity resonator is not suitable for the design of the reconfigurable rf filter we propose.

Emerging Substrate Integrated Waveguide (SIW) technology represents a very promising candidate for modern wireless communication systems, providing an attractive platform for microwave and millimeter wave applications due to its advantages of low cost, low power consumption, relatively high Q-value, high power handling capability, and high density integration. Compared with a cavity filter, the size of the advanced SIW filter is obviously reduced; the SIW filter has a lower insertion loss and an advantage of being suitable for a higher frequency band, compared to the microstrip line filter. The SIW technique provides a new technique option for reconfigurable rf filters. In addition, the SIW structure has its unique advantages in miniaturization of the filter. At present, half-mode (HMSIW), quarter-mode (QMSIW) and eighth-mode (mode) technologies have been developed based on the unique electromagnetic propagation characteristics of SIW. This miniaturization technique also maintains the same electromagnetic propagation characteristics as a full-mode SIW, reduces in size in half, and maintains good performance.

The reconfigurable radio frequency filter is the development direction of future radio frequency filters. The SIW architecture has many advantages and is gaining more and more attention and application in reconfigurable filter design. At present, no matter the radio frequency filter which can realize that the central frequency adjustable bandwidth can be preset, the bandwidth can be reconstructed, the central frequency can be fixed, or even the dual-passband frequency can be independently adjusted, a plurality of research results exist, but at present, the research results which can simultaneously realize that the central frequency and the bandwidth can be fully adjusted are relative or less, the central frequency and the bandwidth can realize the 'customized' of communication services of various systems, and the radio frequency filter is the ultimate design target of the adjustable filter. In today's increasingly crowded frequency spectrum, there are certain bandwidth requirements in many practical applications, and tuning filters with uncontrolled bandwidth are difficult to use. The research on the center frequency and bandwidth fully tunable filter with excellent performance has urgent need.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a band-pass filter with a compact structure and a fully adjustable center frequency and bandwidth of an eighth-mode substrate integrated waveguide (EMSIW) structure.

According to the invention, according to the magnetic symmetry of a Substrate Integrated Waveguide (SIW) cavity, the SIW cavity is cut along the center of the SIW cavity in a meter shape, one eighth of the SIW cavity is taken, and two EMSIW cavities form a coupling design filter. EMSIW possesses similar performance as SIW, but only one-eighth of its size, meeting the demand of modern wireless communication systems for miniaturization. The filter mainly comprises two EMSIW resonant cavities, a stub, an input and output feeder, a coupling gap and a variable capacitance diode for tuning the center frequency, the bandwidth and the external Q value.

The filter is mainly composed of a dielectric plate, and a top metal surface, an input/output feeder line and a variable capacitance diode are paved on the top layer of the dielectric plate; the bottom layer of the medium plate is paved with a bottom layer metal surface.

The top metal surface of the filter comprises a first metal surface and a second metal surface which have the same structure;

a row of first metal columns distributed periodically penetrates through the edge of the electric wall of the first metal surface, and simultaneously penetrates through the dielectric slab and the bottom metal surface; forming a first EMSIW structure by the first metal surface, the first metal pillar and the bottom metal surface;

a first stub line is arranged at the strongest position of an electric field of the first metal surface, the tail end of the first stub line is connected with the variable capacitance diode C1 and the first metal patch, a third metal column penetrates through the center of the first metal patch, and the third metal column penetrates through the dielectric plate and the bottom metal surface;

an input feeder is arranged on a virtual magnetic wall of the first EMSIW resonant cavity, and a varactor C2 is loaded in the middle of the input feeder;

the length of the first stub affects the resonant frequency of the first EMSIW cavity, the longer the first stub, the smaller the resonant frequency of the first EMSIW cavity;

varactor C1 is sized to adjust the center frequency; varactor C2 is sized to adjust the external Q value.

The shortest distance t1 between the input feed line and the electrical wall of the first metal plane affects the external Q value.

The second EMSIW structure is the same as the first EMSIW structure, a gap is reserved between the two EMSIW resonant cavities, and the two EMSIW structures are arranged in a central symmetry mode and are electrically coupled. A varactor C5 connected with the two EMSIW resonant cavities is loaded in the gap;

the second EMSIW structure is specifically composed of a second metal face, a second metal pillar, and an underlying metal face. A row of second metal columns distributed periodically penetrates through the electric wall of the second metal surface, and simultaneously penetrates through the dielectric plate and the bottom metal surface;

a second stub is arranged at the strongest position of the electric field of the second metal surface, the tail end of the second stub is connected with the variable capacitance diode C3 and the second metal patch, a fourth metal column penetrates through the center of the second metal patch, and the fourth metal column penetrates through the dielectric slab and the bottom metal surface;

an output feeder is arranged on a virtual magnetic wall of the second EMSIW resonant cavity, and a varactor C4 is loaded in the middle of the output feeder;

the length of the second stub affects the resonant frequency of the second EMSIW cavity, the longer the second stub, the smaller the resonant frequency of the second EMSIW cavity;

varactor C3 is sized to adjust the center frequency and varactor C4 is sized to adjust the external Q value.

Varactor C5 is sized to adjust the coupling coefficient between the two EMSIW resonators.

The shortest distance t3 between the output feed line and the electrical wall of the second metal plane affects the external Q value.

The filter adopts a PCB technology.

The two EMSIW cavities of the band-pass filter are the same, the variable capacitance diodes C1 and C3 for adjusting the central frequency can be controlled by the same voltage, and the central frequency of the band-pass filter can be adjusted by applying voltages to the variable capacitance diodes C1 and C3; by applying voltage to the varactor C5, the coupling coefficient of the filter can be adjusted, and the bandwidth of the filter can be changed; the varactors C2 and C4 used to adjust the external coupling can be controlled with the same voltage, and the external Q value of the filter can be adjusted by applying voltages to the varactors C2 and C4.

The invention creatively designs the adjustable filter by utilizing the EMSIW structure, solves the problem that the cavity filter is difficult to load a tuning element to realize center frequency and bandwidth tuning, introduces the EMSIW structure and greatly realizes the miniaturization of the filter. According to the invention, the short stub and the variable capacitance diode are loaded in the EMSIW cavity, so that the frequency tuning mode of the SIW structure is innovatively realized; the two EMSIW cavities are electrically coupled through edges, and a coupling coefficient between the varactor tuning cavities is loaded between coupling gaps of the EMSIW cavities, so that a bandwidth tuning mode of the SIW structure is innovatively realized; meanwhile, the tuning of the external Q value of the filter can be realized by loading the variable capacitance diode on the input and output feeder.

Compared with the unloaded stub, the loaded stub at the strongest position of the electric field of the EMSIW cavity can obviously reduce the resonant frequency and further realize the miniaturization of the filter.

The filter has compact structure, provides a new idea for miniaturization of the adjustable cavity filter, and has novel center frequency and bandwidth tuning modes, large bandwidth tuning range, fewer tuning elements and lower manufacturing process requirement.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIGS. 2(a), (b) are schematic top and bottom views, respectively, of the present invention;

fig. 3(a) and (b) are simulation diagrams of S parameters tuned by the tunable filter at each frequency point bandwidth;

wherein 1 is a first triangular metal surface, 2 is a second triangular metal surface, 3 is an input feeder, 4 is an output feeder, 5 is a first stub, 6 is a second stub, 7 is a first metal patch, 8 is a second metal patch, 9 is a first metal column, 10 is a second metal column, 11 is a third metal column, 12 is a fourth metal column, 13 is a bottom metal surface, d is the diameter of the metal column, P is the distance between adjacent metal columns, and h is the thickness of the dielectric plate.

Detailed Description

The invention will be further explained with reference to the drawings

As shown in FIGS. 1 and 2, the EMSIW tunable filter of the invention is composed of a piece of Rogers with a thickness h and a dielectric constant of 10.2

6010 the dielectric plate comprises a top layer mainly including a first and a second triangular metal surfaces 1 and 2, an input/

output feeder line

3 and 4, a first and a

second stub lines

5 and 6, a first and a

second metal patches

7 and 8, and a varactor diode C1-C5. A row of a plurality of first metal columns 9 distributed periodically penetrates through the edge of a first right-angle side 14 of a first triangular metal surface 1, meanwhile, the first metal columns 9 penetrate through a dielectric plate and a bottom metal surface, the first triangular metal surface 1, the first metal columns 9 and the bottom metal surface 13 form a first EMSIW structure, the tail end of a second right-angle side 15 of the first triangular metal surface 1 is connected with a section of first stub 5, the length of the first stub 5 can influence the resonant frequency of the first EMSIW cavity, the longer the first stub 5 is, the lower the resonant frequency of the first EMSIW cavity is, the tail end of the first stub 5 is connected with a variable-capacitance diode C1 and a first metal patch 7, the center of the first metal patch 7 penetrates through a third metal column 11, the third metal column 11 penetrates through the dielectric plate and the bottom metal surface 13, the size of the variable-capacitance diode C1 is adjusted to adjust the resonant frequency of the first EMSIW cavity, the center frequency can be adjusted electrically, the input feeder line 3 is placed on one side of the second right-angle side 15, the external Q value can be adjusted by the shortest distance t1 between the input feeder line 3 and the first right-angle side 14 of the first triangular metal surface 1, the variable capacitance diode C2 is loaded in the middle of the input feeder line 3, and the variable capacitance diode C2 is adjusted to tune the external Q value, so that the external Q value can be adjusted electrically; a row of a plurality of second metal columns 10 distributed periodically penetrates through the edge of a first right-angle side 16 of a second triangular metal surface 2, meanwhile, the second metal columns 10 penetrate through a dielectric plate and a bottom metal surface 13, the second triangular metal surface 2, the second metal columns 10 and the bottom metal surface 13 form a second EMSIW structure, the tail end of a second right-angle side 17 of the second triangular metal surface 2 is connected with a section of second stub 6, the length of the second stub 6 can influence the resonance frequency of a second EMSIW cavity, the longer the second stub 6 is, the lower the resonance frequency of the second EMSIW cavity is, the tail end of the second stub 6 is connected with a varactor C3 and a second metal patch 8, the center of the second metal patch 8 penetrates through a fourth metal column 12, the fourth metal column 12 penetrates through the dielectric plate and the bottom metal surface 13, and the size of the varactor C3 is adjusted to adjust the resonance frequency of the second EMSIW cavity, the center frequency is electrically adjustable, the output feeder is placed on one side of the second right-angle side 17, the external Q value can be adjusted by the shortest distance t3 between the output feeder 4 and the first right-angle side 16 of the second triangular metal surface 2, the variable capacitance diode C4 is loaded in the middle of the output feeder 4, and the variable capacitance diode C4 is adjusted to tune the external Q value, so that the external Q value is electrically adjustable.

As shown in fig. 1 and 2, the first and second triangular metal surfaces 1 and 2 are oppositely disposed with a gap g along the hypotenuse, the size of the gap g affecting the coupling coefficient of the filter, and the gap g providing a physical space for the loading element. The varactor C5 is loaded in the middle of the hypotenuses of the first and second triangular metal surfaces 1 and 2, and the varactor C5 is adjusted to tune the coupling coefficient of the filter, thereby realizing the electrical adjustability of the coupling coefficient.

Table 1 shows specific values of the structural parameters of the filter.

Table 1 filter structure design parameters, units: millimeter

W1/W2/W3

L1/L2/L3/L4

t1/t2/t3/t4

P

d

g

h

0.58/1.5/0.5

7.4/8.7/1.2/2

3.5/5.35/3.5/5.35

0.8

0.6

1.4

0.635

The filter can realize the frequency selection tuning range of the central frequency from 2.17GHz to 2.72GHz by adjusting the applied voltage of the variable capacitance diodes C1 and C3, and can realize the bandwidth tuning of each frequency point in the central frequency tuning range by adjusting the applied voltage of the variable capacitance diodes C2, C4 and C5, the processed filter measures the 3dB bandwidth tuning of 140MHz to 208MHz at 2.17GHz, the 3dB bandwidth tuning of 231MHz to 355MHz at 2.45GHz and the 3dB bandwidth tuning of 314MHz to 435MHz at 2.72GHz by using a network vector analyzer.

As can be seen in FIG. 3, the tunable broadband-tunable-core-band antenna of the invention has the advantages of better realization of tunable bandwidth and center frequency, wider center frequency and bandwidth tuning range, insertion loss (S21) of 1.59-4dB, return loss (S11) of more than 10dB and better tunable performance in the whole tuning range.

The invention innovatively designs the adjustable filter by utilizing the EMSIW structure, realizes the full tuning of the center frequency and the bandwidth of the filter, and solves the problem that the cavity filter is difficult to load a tuning element to realize the tuning of the center frequency and the bandwidth. The EMSIW loading stub structure is introduced, so that the miniaturization of the filter is greatly realized, the tunable filter disclosed by the invention needs few tuning elements, and the manufacturing process requirement is lower.

Claims

1. The integrated waveguide filter of the one-eighth mode substrate with fully adjustable center frequency and bandwidth is characterized by mainly comprising a dielectric slab, two EMSIW resonant cavities, a top metal surface, an input/output feeder line and a variable capacitance diode, wherein the top metal surface, the input/output feeder line and the variable capacitance diode are laid on the top layer of the dielectric slab; a bottom metal surface laid on the bottom layer of the dielectric slab;

the top metal surface comprises a first metal surface and a second metal surface which have the same structure;

a row of first metal columns distributed periodically penetrates through the edge of the electric wall of the first metal surface, and simultaneously penetrates through the dielectric slab and the bottom metal surface; a first EMSIW resonant cavity structure is formed by the first metal surface, the first metal column and the bottom metal surface;

a first stub line is arranged at the strongest position of an electric field of the first metal surface, the tail end of the first stub line is connected with the variable capacitance diode C1 and the first metal patch, the center of the first metal patch penetrates through a third metal column, and meanwhile, the third metal column penetrates through the dielectric slab and the bottom metal surface;

an input feeder is arranged on a virtual magnetic wall of the first EMSIW resonant cavity, and a variable capacitance diode C2 is loaded in the middle of the input feeder;

the structure of the second EMSIW resonant cavity is the same as that of the first EMSIW resonant cavity, a gap is reserved between the two EMSIW resonant cavities, and the two EMSIW structures are electrically coupled; a varactor C5 connected with the two EMSIW resonant cavities is loaded in the gap;

the second EMSIW resonant cavity structure is specifically composed of a second metal surface, a second metal column and a bottom metal surface; a row of second metal columns distributed periodically penetrates through the electric wall of the second metal surface, and simultaneously penetrates through the dielectric plate and the bottom metal surface;

a second stub is arranged at the strongest position of the electric field of the second metal surface, the tail end of the second stub is connected with the variable capacitance diode C3 and the second metal patch, the center of the second metal patch penetrates through a fourth metal column, and the fourth metal column penetrates through the dielectric plate and the bottom metal surface;

and an output feeder is arranged on a virtual magnetic wall of the second EMSIW resonant cavity, and a varactor C4 is loaded in the middle of the output feeder.

2. The eighth mode substrate integrated waveguide filter having a fully tunable center frequency and bandwidth of claim 1, wherein the length of the first stub affects the resonant frequency of the first EMSIW cavity.

3. The fully tunable center frequency and bandwidth eighth-mode substrate integrated waveguide filter of claim 1, wherein varactor C1 is sized to tune the center frequency; varactor C2 is sized to adjust the external Q value.

4. The eighth mode substrate integrated waveguide filter having fully tunable center frequency and bandwidth of claim 1, wherein the shortest distance t1 between the input feed line and the electrical wall of the first metal plane affects the external Q value.

5. The eighth mode substrate integrated waveguide filter having a fully tunable center frequency and bandwidth of claim 1, wherein the length of the second stub affects the resonant frequency of the second EMSIW cavity.

6. The fully tunable center frequency and bandwidth eighth-mode substrate integrated waveguide filter of claim 1, wherein varactor C3 is sized for center frequency tuning and varactor C4 is sized for external Q tuning.

7. The eighth-mode substrate integrated waveguide filter with fully tunable center frequency and bandwidth of claim 1, wherein the varactor C5 is sized to adjust the coupling coefficient between two EMSIW resonators.

8. The eighth mode substrate integrated waveguide filter having fully tunable center frequency and bandwidth of claim 1, wherein the shortest distance t3 between the output feed line and the electrical wall of the second metal plane affects the external Q value.

9. The eighth mode substrate integrated waveguide filter with fully tunable center frequency and bandwidth of claim 1, wherein the filter is fabricated using PCB technology.