CN110429362B

CN110429362B - Reconfigurable filter based on T-shaped resonator

Info

Publication number: CN110429362B
Application number: CN201910688525.1A
Authority: CN
Inventors: 贾式钰; 张友俊
Original assignee: Shanghai Maritime University
Current assignee: Shanghai Maritime University
Priority date: 2019-07-29
Filing date: 2019-07-29
Publication date: 2021-04-20
Anticipated expiration: 2039-07-29
Also published as: CN110429362A

Abstract

The invention discloses a reconfigurable filter based on a T-shaped resonator. The filter is characterized in that: the filter is composed of a T-shaped resonator and a microstrip line, so that the compactness of the structure is ensured; the filter comprises a primary transmission path and a secondary transmission path; the main transmission path of the filter is a T-shaped resonator, and an open-circuit branch is added at an input port and an output port respectively to ensure the performance of the main transmission path; the secondary transmission path of the filter comprises two grounding structures and two microstrip lines, wherein the microstrip lines are coupled through a gap, so that the good performance of the filter is ensured; the filter controls the secondary transmission path through the RF switch to realize filter reconstruction. The invention provides a novel topological structure of a reconfigurable filter, which is compact, meets the requirement of miniaturization, has low loss and has performance superior to filters with other structures.

Description

Reconfigurable filter based on T-shaped resonator

The technical field is as follows:

the invention relates to the field of microwave communication, in particular to a reconfigurable filter based on a T-shaped resonator, which has compact structure and simple manufacture and can be used for filtering in a microwave circuit.

Background art:

in modern wireless communication systems, a filter is used as a circuit or a device having selective effects on frequency and signals, and by controlling the frequency response, an allowed signal can almost completely pass through the filter, so that the interference of a noise signal can be effectively suppressed. Therefore, in a wireless communication system, the performance of the filter plays a crucial role, and the quality of the performance will have a great influence on the efficiency of the whole system. The main indexes for measuring the performance of the filter are central frequency, insertion loss, return loss, ripple coefficient, stop band attenuation and the like. Microwave filters have various classification modes: the filter can be divided into a flattest filter, a Chebyshev filter, an elliptic function filter and the like according to the characteristics of the frequency response of the filter; the filter can be divided into a low-pass filter, a high-pass filter, a band-stop filter and the like according to attenuation characteristics; the filter can be divided into a micro-strip filter, a strip line filter, a coaxial filter, a dielectric filter, a waveguide filter and the like according to the implementation form of the filter; from the perspective of energy sources, there are two categories, active and passive. Passive filters offer significant advantages over active devices, both in terms of ease of integration and noise immunity and transmission gain, which has led more experts and scholars to be involved in passive filter research. The passive microstrip filter is a planar structure, can control the working efficiency of a device by adjusting the dielectric constant of a medium, and has wide application in the microwave and radio frequency fields because of the simple structural characteristics and the advantages of small size, easy processing, easy integration with an active circuit, low cost and the like.

The filter is used as a frequency selection device of communication equipment, can inhibit the interference of useless signals outside a communication working frequency band, can also reduce the attenuation of the signals in the communication working frequency band, and the performance of the filter directly influences the communication quality of a microwave wireless communication system. Under the promotion of the high-speed development of modern communication technology, the requirements of system stability, reliability, integration degree and the like are more and more strict. The same wireless communication device needs to integrate multiple applications and communication modes corresponding to multiple different operating frequency bands and modes, and each frequency band needs to adopt different filters for selecting frequency bands. Therefore, the structure of the radio frequency front end becomes complex, the system performance is difficult to adjust, the problem of electromagnetic compatibility is more serious, the size of the system is increased, larger loss is caused, the research and development cost of the wireless communication system is increased, and the radio frequency front end is not suitable for large-scale application. At present, a wireless communication system is required to have the characteristics of miniaturization, high integration level, low loss and the like, so people hope to replace the traditional filter bank with a single reconfigurable filter, remove redundant radio frequency devices, save cost, simplify the structure of a radio frequency front end and reduce loss. In general, a reconfigurable filter means that the central operating frequency of the filter can be continuously adjusted within a certain frequency band range, and in recent research, the bandwidth, the order and the zero point of the filter are continuously adjusted.

Microstrip filters have become one of the important components of wireless communications because of their low loss, low cost, miniaturization and simplicity of manufacture. However, the circuit space is limited, and if a single filter element is switched by a switch, the filter element can be reconstructed into other types of filters, so that the utilization rate of the limited circuit space can be effectively improved. There are two main approaches currently used for filter reconstruction: firstly, the reconstruction of the filter is realized by adding adjustable elements, such as variable capacitors, resistors and the like, and adjusting the resistance and the capacitance of the capacitors; and secondly, by adding an RF switch, the reconfiguration of the circuit is realized, and the reconstruction of the filter is realized. The complexity of the circuit is increased by adding adjustable electronic devices, and errors due to soldering and other factors are increased, so that a method for reconstructing the filter through a Radio Frequency (RF) switch is receiving more and more attention. The band-stop filter is mainly used for suppressing an unnecessary frequency band, and the structure of a step impedance resonator is mainly adopted at present to increase the band-stop bandwidth of the filter. However, we have to consider the wide stop band characteristic and ensure the miniaturization of the filter, and we propose the T-type resonator structure. Compared with a step impedance resonator structure, the T-shaped resonator structure can change the impedance ratio of the T-shaped resonator structure more flexibly, so that the physical size of the filter is reduced, the characteristic of a wide stop band can be realized, and the T-shaped resonator structure can be suitable for the miniaturized reconfigurable filter designed by people.

From the prior literature, filters have been studied that mainly comprise: stepped Impedance Resonators (SIR), Defected Ground Structure (DGS) filters, hairpin-structure filters, and the like.

Disclosure of Invention

In order to meet the requirement of microwave technology development, the invention mainly aims to provide a reconfigurable filter based on a T-type resonator.

The invention provides a topological structure of a reconfigurable filter based on a T-shaped resonator. Since it is difficult or impossible to prove theoretically with maxwell's equations for practical situations, it can only be proven numerically. The method adopted in academia and engineering is to use commercial high-frequency electromagnetic simulation software to perform electromagnetic simulation for proving and optimizing.

There are many commercially available high frequency electromagnetic simulation software, and it is our intention that HFSS 13.0 and ADS2015 optimize the proposed low pass filter structure. And then the optimized structure is made into a sample, the sample is tested, and the topological structure of the filter is verified by an experimental method.

The invention relates to a reconfigurable filter based on a T-shaped resonator. Using the dielectric constant ε_r2.65, the material with the medium thickness h of 1mm is simulated and optimized. The actual size of the novel structure of the invention is 30.01mm 26.96mm, wherein the width of the feed line is 2.8 mm.

The reconfigurable filter based on the T-shaped resonator is provided with a pair of input signal ports and output signal ports which are respectively arranged on the left side and the right side of the filter structure, and the width of a feeder line is 2.8 mm. The reconfigurable filter based on the T-shaped resonator has a primary transmission path and a secondary transmission path, the secondary transmission path is controlled through the control of the RF switch, the circuit is recombined, and therefore the reconfigurable filter is reconstructed into a new filter structure.

The reconfigurable filter based on the T-shaped resonator. The main transmission path comprises a T-shaped resonator, two open-circuit branches are respectively added on two sides of the T-shaped resonator, wherein the horizontal length of the upper branch of the T-shaped resonator is 9.5mm, the width of the upper branch is 3.5mm, the distance between the upper branch and the lower branch is 4mm, and the width of the upper branch and the lower branch is 0.5mm, so that the compactness of the filter structure is ensured. This is the main body of the filter and the corresponding dimensions are optimized.

According to the reconfigurable filter based on the T-shaped resonator, the two open-circuit branches are additionally arranged at the input port and the output port, wherein the horizontal length of each open-circuit branch is 2.8mm, and the width of each open-circuit branch is 14.66mm, so that the bandwidth of a stop band is increased, the transmission zero point is increased, the good characteristic of the filter is realized, and the performance of the filter is better.

The reconfigurable filter based on the T-shaped resonator realizes the adjustment of a secondary transmission path through an RF switch: reconstructing the open-circuit branch and the grounding structure into a dual-band-pass filter when the open-circuit branch is connected with the grounding structure; when the open-circuit branch is connected with the microstrip line structure, the wide stop band filter is reconstructed, wherein the width of the microstrip line is 2.8mm, and the horizontal length is 12.95 mm.

The novel reconfigurable filter based on the T-shaped resonator is characterized in that: a p-i-n diode is used as an RF switch, and a resistor, a capacitor and the like are introduced, so that the influence of direct current on a circuit is avoided.

In an embodiment of the invention, the parallel T-shaped branch, the open branch, the coupling line and the feed line are all made of copper foil.

From the prior literature, the low-pass filters that have been studied mainly comprise: stepped Impedance Resonators (SIR), Defected Ground Structure (DGS) filters, hairpin-structure filters, and the like.

The specific technical scheme of the invention is as follows:

a reconfigurable filter based on T-shaped resonators is provided, the dielectric constant of a microstrip substrate is 2.65, the dielectric thickness is 1mm, and the reconfigurable filter comprises 1T-shaped resonator, two open-circuit branches, a microstrip line, two grounding structures and a feeder line. The novel reconfigurable filter based on the T-shaped resonators is characterized in that the T-shaped resonators which are symmetrical about a central axis are arranged on the central axis; respectively arranging one microstrip line at the position 5mm above the open-circuit branch knot, wherein the two microstrip lines are symmetrical about the central axis; a grounding structure is respectively arranged between the two open-circuit branch knots and the central axis; two ends of the T-shaped resonator are respectively provided with an open-circuit branch knot, and protruding parts are arranged in the direction of the open-circuit branch knot and the horizontal microstrip line, which is connected and departs from the central axis, and are arranged as feeder lines which are used as input and output ports.

The reconfigurable filter based on the T-shaped resonator has the following specific dimensions:

the width of the feeder line of the two symmetrical input and output ports is 2.8mm, and the length of the feeder line is 2 mm; the horizontal side length of the open-circuit branch knot is 2.8mm, and the vertical height of the open-circuit branch knot is 14.66 mm; the length of the upper horizontal plane of the T-shaped branch is 9.5mm, and the distance between the upper horizontal plane and the lower horizontal plane is 3.5 mm; the distance between the T-shaped branch pitch and the horizontal microstrip line is 4mm, and the width of the microstrip line is 0.5 mm; the length of a microstrip line between the T-shaped branch and the open-circuit branch is 10mm, and the width of the microstrip line is 0.5 mm; the length of two microstrip lines above the branch knot of opening a way is 12.95mm, and the width is 2.8mm, and coupling distance between two microstrip lines is 1.26 mm.

The positive progress effects of the invention are as follows: the invention provides a novel reconfigurable filter topological structure, namely a reconfigurable filter based on a T-shaped resonator. The designed topological structure is processed into a real object and the real object is measured, and the result shows that the filter has better overall performance: wherein, the center frequency of the stop band of the band-elimination filter is 3.89GHz, and the relative bandwidth of-3 dB is 90.9% (2.12-5.65 GHz); the center frequency of a stop band of the broadband band-stop filter is 3.54GHz, the relative bandwidth of-3 dB is 137.85% (1.1-5.98GHz), wherein, the two microstrip lines at the upper side are coupled by adopting a gap, so that the insertion loss can be effectively reduced, and the transmission zero point is increased; the center frequencies of two pass bands of the dual-band-pass filter are respectively 1.53GHz and 6.89GHz, the relative bandwidths of-3 dB are respectively 17.6% (1.4-1.67GHz) and 1.16% (6.85-6.93GHz), a stop band smaller than-15 dB is arranged between the two pass bands, and the two pass bands are independently controllable. The reconfigurable filter has low insertion loss, high return loss and good performance. And the filter has simple structure and small size, and meets the design requirement of the low-pass filter.

Drawings

Fig. 1 is a schematic diagram of the geometry of the reconfigurable filter based on the T-type resonator.

Fig. 2 is a schematic diagram and a topological diagram of a T-type resonator of the present invention. (a) Is a schematic diagram, and (b) is a topological diagram.

FIG. 3 is a graph showing frequency response comparison of T-shaped resonators of the present invention adjusting different parameters. (a) Frequency response at w3 adjustment, (b) frequency response at l3 adjustment.

Fig. 4 is a schematic circuit diagram and a size diagram of the reconfigurable filter based on the T-type resonator. (a) Schematic diagram, and (b) size diagram.

Fig. 5 is a schematic diagram of the reconfigurable filter based on the T-type resonator according to the present invention when two groups of switches are in an off state, and a comparison diagram of frequency response when different parameters are adjusted. (a) Schematic diagram (b) frequency response at w3 regulation, and (c) frequency response at l3 regulation.

Fig. 6 is a schematic diagram of the reconfigurable filters s1 and s1 'closed and s2 and s2' open based on the T-type resonators according to the present invention, and a comparison diagram of frequency responses when different parameters are adjusted. (a) Schematic, (b) frequency response at w3 regulation, and (c) frequency response at l3 regulation.

Fig. 7 is a schematic diagram of the reconfigurable filter s1, s1 'based on the T-type resonator of the invention when s2, s2' are open and when s is closed, and a comparison diagram of frequency response when different parameters are adjusted. (a) Schematic diagram, (b) two horizontal microstrip lines have gapless coupling contrast diagram.

Fig. 8 is a comparative graph of the S parameter simulation and actual measurement results of the reconfigurable filter based on the T-type resonator according to the present invention. (a) s1, s1', s2 and s2' are all open, and (b) s1 and s1 'are closed, and s2 and s2' are open, and (c) s1 and s1 'are open, and s2 and s2' are closed.

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further explained by combining the specific figures as follows:

fig. 1 is a schematic diagram of a geometrical structure of a reconfigurable filter based on a T-type resonator provided by the invention. The filter includes: the T-shaped resonator 1 ensures the compactness of the filter structure; two open-circuit branches 2 are respectively arranged at two ends of the T-shaped resonator structure; the grounding structures 3 are respectively arranged between the open circuit and the vertical central axis and are connected through an RF switch, and the reconstruction of the filter is realized at one side; a horizontal microstrip line 4 is respectively arranged above the open circuit and is connected with the open circuit branch section through an RF switch so as to realize the reconstruction of the filter, and the two microstrip lines are coupled through a gap; the direction of the open-circuit branch section connected with the horizontal microstrip line and departing from the central axis is provided with a protruding part which is set as a feeder line and used as an input port and an output port.

Fig. 2 is a schematic diagram and a topological diagram of a T-type resonator used in the present invention. FIG. 3 is a graph showing frequency response comparison of T-shaped resonators of the present invention adjusting different parameters. The invention adopts a T-shaped resonator structure, and the simulation parameters of the circuit are selected as follows: the simulation was carried out on a dielectric plate having an input impedance and an output impedance of 50 Ω, a relative dielectric constant of 2.65, and a thickness of 1mm, and (a) (b) is a change in frequency response when w3 and l3 were changed, respectively.

Fig. 4 is a circuit schematic and a size diagram of a reconfigurable filter based on T-type resonators. Wherein w1, l1, w2, l2, w3, l3 are the physical dimensions of the T resonator; w4 is the horizontal length of the open branch, l4 is the vertical length; w5 and l5 are respectively the width and the horizontal length of the microstrip line above the open-circuit branch, and the parameters are set as follows:

the width w of the feed line of the input port and the output port is 2.8mm, and the length l of the feed line is 2 mm; the horizontal side length w4 of the open-circuit branch is 2.8mm, and the vertical height l4 is 14.66 mm; the total length of the upper horizontal plane of the T-shaped branch is l 1-9.5 mm, and the distance between the upper horizontal plane and the lower horizontal plane is w 1-3.5 mm; the distance l2 between the T-shaped branch section and the horizontal microstrip line is 4mm, and the microstrip line width w2 is 0.5 mm; between T-shaped branch and open-circuit branchThe length l3 of the microstrip line is 10mm, and the width w3 is 0.5 mm; the length of two microstrip lines above the open branch is l5 ═ 12.95mm, the width is w5 ═ 2.8mm, and the coupling distance between the two microstrip lines is s ═ 1.26 mm. Selecting a dielectric constant epsilon_rThe material with the medium thickness h of 1mm is processed and manufactured into a material object with the medium thickness h of 2.65. The filter comprises a T-shaped resonator 1, an open-circuit branch 2, a grounding structure 3 and a coupled horizontal microstrip line structure 4, wherein the width of a left convex part and a right convex part of the open-circuit branch is 2.8mm, and the left convex part and the right convex part are feeder lines and correspond to the characteristic impedance of 50 ohms.

The switching of the three filter modes can be achieved by adjustment of the RF switch in the schematic diagram of fig. 4. Fig. 5 is a schematic diagram of the reconfigurable filters s1, s1', s2 and s2' based on the T-type resonators in an off state, and a frequency response comparison diagram when different parameters are adjusted. The term "a" is a schematic circuit diagram, the term "b" is a frequency response obtained when w3 is adjusted, and the term "c" is a frequency response obtained when l3 is adjusted. Fig. 6 is a schematic diagram of the reconfigurable filters s1 and s1 'closed and s2 and s2' open based on the T-type resonators according to the present invention, and a comparison diagram of frequency responses when different parameters are adjusted. The term "a" is a schematic circuit diagram, the term "b" is a frequency response obtained when w3 is adjusted, and the term "c" is a frequency response obtained when l3 is adjusted. Fig. 7 is a schematic diagram of the reconfigurable filter s1, s1 'based on the T-type resonator of the invention when s2, s2' are open and when s is closed, and a comparison diagram of frequency response when different parameters are adjusted. Wherein, (a) is a schematic diagram, and (b) is a comparison diagram of two horizontal microstrip lines with gapless coupling.

Fig. 8 is a comparative graph of the S parameter simulation and actual measurement results of the reconfigurable filter based on the T-type resonator according to the present invention. (a) A comparison graph of simulation and actual measurement results when s1, s1', s2 and s2' are both open, (b) a comparison graph of simulation and actual measurement results when s1 and s1 'are closed and s2 and s2' are open, and (c) a comparison graph of simulation and actual measurement results when s1 and s1 'are open and s2 and s2' are closed.

The reconfigurable filter based on the T-shaped resonator has the advantages of compact structure, good performance and the like.

The foregoing shows and describes the general principles, broad features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. The utility model provides a reconfigurable filter based on T type syntonizer, the dielectric constant of microstrip substrate is 2.65, and medium thickness is 1mm, includes 1T type syntonizer, two open circuit branches, coupling line, two ground structure and feeder, its characterized in that: the reconfigurable filter based on the T-shaped resonator is provided with a T-shaped resonator in the central axis; two open-circuit branches are respectively arranged at two ends of the resonator; the direction of the open-circuit branch section connected with the microstrip line and departing from the central axis is provided with a protruding part which is set as a feeder line and used as an input port and an output port; a grounding structure is respectively arranged on the open branch knot and the central line of the central axis, and the grounding structure is not connected with the whole structure; the upper sides of the open-circuit branches are respectively provided with a microstrip line which is not connected with the whole structure; the main transmission path is connected with the horizontal microstrip line above the open-circuit branch and the open-circuit branch is connected with the grounding structure through the RF diode serving as a switch.

2. A reconfigurable filter based on T-type resonators as claimed in claim 1, wherein: the width of the feeder of the input port and the output port is 2.8mm, and the length of the feeder is 2 mm; the horizontal side length of the open-circuit branch knot is 2.8mm, and the vertical height of the open-circuit branch knot is 14.66 mm; the length of the upper horizontal plane of the upper branch of the T-shaped resonator is 9.5mm, and the distance between the upper horizontal plane and the lower horizontal plane is 3.5 mm; the distance between the upper branch and the lower branch of the T-shaped resonator is 4mm, and the line width of the microstrip is 0.5 mm; the length of a lower branch of the T-shaped resonator is 10mm, and the width of the lower branch of the T-shaped resonator is 0.5 mm; the length of two microstrip lines above the branch knot of opening a way is 12.95mm, and the width is 2.8mm, and coupling distance between two microstrip lines is 1.26 mm.

3. A reconfigurable filter based on T-type resonators as claimed in claim 1, wherein: the T-shaped resonator, the open-circuit branch sections, the coupling lines and the feeder lines are all made of copper foils.