CN106910970B

CN106910970B - Cavity four-mode filter

Info

Publication number: CN106910970B
Application number: CN201710122276.0A
Authority: CN
Inventors: 褚庆昕; 钱璐
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2017-03-03
Filing date: 2017-03-03
Publication date: 2020-08-18
Anticipated expiration: 2037-03-03
Also published as: CN106910970A

Abstract

The invention discloses a cavity four-mode filter, which comprises a cavity resonator with four resonance modes, a first tuning pin, a second tuning pin, a third tuning pin, and an input port and an output port which are symmetrically arranged; the cavity resonator is a rectangular metal box, each inner side wall of the metal box is provided with a metal column, and each metal column is equivalent to a coaxial cavity resonator; the input port is formed by connecting an SMA joint with a feed probe and is arranged on the upper top surface of the metal box; the output port is formed by connecting an SMA joint with a feed probe and is arranged on the lower bottom surface of the metal box; the first tuning pin, the second tuning pin and the third tuning pin are respectively arranged on the upper top surface of the metal box. The invention realizes the single-cavity four-mode resonance characteristic through the interaction of the electric fields among the metal columns, has the advantages of small volume, high selectivity, large power capacity and easy control of bandwidth, and can meet the design requirements of miniaturization, low cost and good characteristic.

Description

Cavity four-mode filter

Technical Field

The invention relates to the technical field of high-frequency devices, in particular to a cavity four-mode filter.

Background

In recent years, as society is accelerated to enter an information era and the wireless communication industry is vigorously developed, a radio frequency front end circuit is widely applied to the fields of mobile communication, radar monitoring, navigation, remote sensing and the like as a cornerstone of the whole wireless communication system, so that the research on the radio frequency front end circuit is more and more important. The rf filter, as a key component of the rf front-end circuit, plays an important role in the whole wireless communication system, and the high-selectivity, small-volume, low-loss filter is a key device for implementing high-quality wireless communication.

In the past, in the aspect of improving the selectivity of the filter, a measure is often taken to improve the order of the filter. For a single-mode filter, the increase of the order tends to increase the size of the filter, which makes the design more difficult to miniaturize. The multimode resonator simultaneously comprises a plurality of modes, so that one multimode resonator is equivalent to the cascade connection of a plurality of single-mode resonators, and the increase of the volume can be avoided while the performance is improved. In addition, compared with a microstrip filter, the cavity filter has a significant advantage in the aspect of improving the power capacity of the filter. Therefore, the development of the multimode cavity filter is particularly urgent.

In 2015, Sai-Wai Wong et al published an article entitled "Triple-And quick-Mode Wideband filter Using Single waveguide in Single Metal Cavity" in IEEE Transaction On microwave theory And technologies, a top-level journal in the field, And designed a Single-Cavity three-Mode And four-Mode ultra-Wideband filter Using cylindrical waveguide cavities. The author designs a single-cavity three-mode and four-mode ultra-wideband filter by adding a metal cylinder inside a circular metal cavity and reducing the frequency of high-order modes TM01 and TM11 to be close to a degenerate TE mode.

In 2015, Xuguang Wang et al published an article entitled "Compact queue-Mode Bandpass Filter Using modified Coaxial Filter With Improved Filter-Factor" in the Top-level journal of the field, IEEE Transaction On microwave theory And technology, And designed a single-Cavity four-Mode Filter using rectangular Coaxial cavities. The authors have realized resonators with four high-Q resonant modes by magnetic field interaction between four coaxial columns within a rectangular cavity, and have designed a single-cavity four-mode filter.

Disclosure of Invention

The invention aims to overcome the defects and shortcomings of the prior art, and provides a novel cavity four-mode filter, which realizes the single-cavity four-mode resonance characteristic through the interaction of electric fields among metal columns, has the advantages of small volume, high selectivity, large power capacity and easy control of bandwidth, and can meet the design requirements of miniaturization, low cost and good characteristic.

In order to achieve the purpose, the technical scheme provided by the invention is as follows: a cavity four-mode filter comprises a cavity resonator with four resonance modes, a first tuning pin, a second tuning pin, a third tuning pin, and an input port and an output port which are symmetrically arranged; the cavity resonator is a rectangular metal box, each inner side wall of the metal box is provided with a metal column, and each metal column is equivalent to a coaxial cavity resonator; the input port is formed by connecting an SMA joint with a feed probe and is arranged on the upper top surface of the metal box; the output port is formed by connecting an SMA joint with a feed probe and is arranged on the lower bottom surface of the metal box; the first tuning pin, the second tuning pin and the third tuning pin are respectively arranged on the upper top surface of the metal box.

The feed probe is a bent metal probe.

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

1. the invention utilizes the interaction of electric fields between the metal columns to form a novel cavity four-mode filter different from the traditional cavity filter.

2. The four resonance modes adopted by the invention have higher Q value, and the designed filter has higher selectivity and can meet various practical communication requirements.

3. The filter adopted by the invention is of a fully-closed metal structure, so that the power capacity is higher.

4. Because the filter is the metal cavity structure, easily processing is fit for batch industrial production, so the filter possesses simple structure, low in production cost's advantage.

Drawings

Fig. 1 is a top view of the cavity quad-mode filter of the present invention.

Fig. 2 is a front view of the cavity quad-mode filter according to the present invention.

Fig. 3 is a top view of the cavity resonator of the present invention with four metal posts.

Fig. 4 is a front view of the cavity resonator of the present invention with four metal posts.

Fig. 5a is an electric field distribution diagram of Mode1 in the cavity four-Mode resonator according to the present invention.

Fig. 5b is the electric field distribution diagram of Mode2 in the cavity four-Mode resonator according to the present invention.

Fig. 5c is the electric field distribution diagram of Mode3 in the cavity four-Mode resonator according to the present invention.

Fig. 5d is the electric field distribution diagram of Mode4 in the cavity four-Mode resonator according to the present invention.

FIG. 6a is a graph showing the Frequency curves of the modes of the resonator as a function of L in the HFSS (high Frequency Structure simulator) simulation.

FIG. 6b is a graph showing the Frequency curve of each mode of the resonator as a function of H in the HFSS (high Frequency Structure simulator) simulation.

FIG. 6c is a graph showing the Frequency curves of the modes of the resonator in the HFSS (high Frequency Structure simulator) simulation as a function of TH.

FIG. 6d is a graph showing the Frequency curves of the modes of the resonator as a function of CR in the HFSS (high Frequency Structure simulator) simulation.

FIG. 7a shows the insertion loss (| S) of the filter for variations in the height InputZ of the feed probe₂₁|) simulation result graph.

FIG. 7b shows the insertion loss (| S) of the filter for variations in the feed probe length InputXL₂₁|) simulation result graph.

FIG. 8a shows the insertion loss (| S) of the filter for a change in the length of the first tuning pin₂₁|) simulation result graph.

FIG. 8b shows the insertion loss (| S) of the filter for a change in the length of the second tuning pin₂₁|) simulation result graph.

FIG. 8c shows the insertion loss (| S) of the filter for a change in the length of the third tuning pin₂₁|) simulation result graph.

FIG. 9 shows the insertion loss (| S21|) and return loss (| S) of the cavity quad-mode filter according to the invention₁₁|) simulation result graph.

Detailed Description

The present invention will be further described with reference to the following specific examples.

The novel cavity four-mode filter has the core content that the cavity resonator with four resonance modes can ensure that the resonance frequency of the resonator is positioned in any frequency band by adjusting the structural size of the resonator, thereby changing the central frequency of the filter. The required filter can be further obtained by adding a port exciting structure, a coupling structure and a tuning structure on the basis of the resonator structure.

As shown in fig. 1, fig. 2, fig. 3, and fig. 4, the cavity four-mode filter provided in this embodiment includes a cavity resonator 1 having four resonance modes, a first tuning pin 4, a second tuning pin 5, a third tuning pin 6, and an input port 2 and an output port 3 that are symmetrically arranged; the cavity resonator 1 is a rectangular metal box, each inner side wall of the metal box is provided with a metal column 7, each metal column 7 is equivalent to a coaxial cavity resonator, and because the metal columns are relatively close to each other, electric fields among four coaxial cavities have interaction, so that four resonance modes with similar frequencies are formed; the input port is formed by connecting an SMA joint with a feed probe (specifically a bent metal probe), is arranged on the upper top surface of the metal box and is used for exciting an electric field in a required direction; the output port is formed by connecting an SMA joint with a feed probe (specifically a bent metal probe), is arranged on the lower bottom surface of the metal box and is used for exciting an electric field in a required direction; the first tuning pin 4, the second tuning pin 5 and the third tuning pin 6 are respectively arranged on the upper top surface of the metal box and used for adjusting the resonant frequency of each mode and the coupling between the resonant frequency and the third tuning pin.

Fig. 5a, 5b, 5c, and 5d sequentially show electric field distributions of

modes

1, 2, 3, and 4 in the cavity four-Mode filter. The two modes shown in fig. 5a and 5d have electric fields in the resonator in both horizontal and vertical directions. In the two modes shown in fig. 5b and 5c, only vertical or horizontal electric fields exist in the resonator, and the electric fields of the two modes are orthogonal to each other and form a pair of degenerate modes.

Referring to fig. 6a, 6b, 6c, and 6d, the frequency curve change of each mode of the resonator is obtained through HFSS simulation, and it can be known from the figure that the control of each mode frequency of the resonator can be realized by adjusting the structural parameters L, H, TH, and CR.

Referring to fig. 7a and 7b, the insertion loss (S) at different probe heights InputZ and different probe lengths InputXL is obtained by simulation₂₁) As a result of the simulation, the horizontal axis represents the signal frequency of the microstrip filter of the present invention, and the vertical axis represents the insertion loss (S) of the filter₂₁). From the figure it can be seen that both the probe height and probe length parameters effectively control the excitation intensity of each mode within the filter. With the increase of the height of the probe, the modes in the filter passband are gradually separated and more obvious; the excitation intensity of the modes within the filter pass-band increases significantly as the probe length increases.

Referring to fig. 8a, 8b, 8c, the insertion loss (| S) of the filter is shown with tuning pin changes₂₁|) simulation results, it can be found from the figure that the tuning pin can effectively adjust the frequency of each mode and the coupling between them.

Fig. 9 shows the insertion loss (| S21|) and the return of the cavity four-mode filter according to the present embodimentLoss (| S)₁₁|) simulation results, it can be found that the simulated filter has a center frequency of 2595MHz, | S₂₁The bandwidth range of |3dB is 2575MHz-2615MHz, within the range of 2580MHz-2609MHz (12%), its return loss exceeds 10dB, the performance is good.

The above-mentioned embodiments are merely preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, so that variations based on the shape and principle of the present invention should be covered within the scope of the present invention.

Claims

1. A cavity four-mode filter is characterized in that: the cavity resonator comprises four resonant modes, a first tuning pin, a second tuning pin, a third tuning pin, and an input port and an output port which are symmetrically arranged; the cavity resonator is a rectangular metal box, each inner side wall of the metal box is provided with a metal column, and each metal column is equivalent to a coaxial cavity resonator; the input port is formed by connecting an SMA joint with a feed probe and is arranged on the upper top surface of the metal box; the output port is formed by connecting an SMA joint with a feed probe and is arranged on the lower bottom surface of the metal box; the first tuning pin, the second tuning pin and the third tuning pin are respectively arranged on the upper top surface of the metal box.

2. The cavity four-mode filter according to claim 1, wherein: the feed probe is a bent metal probe.