CN110137643A - A kind of controllable big frequency of bandwidth is than coaxial cavity double frequency filter - Google Patents

Abstract

The invention discloses a bandwidth-controllable large-frequency-ratio coaxial cavity dual-frequency filter, comprising: a first coaxial cavity, a second coaxial cavity, an input port, an output port, a first rectangular metal coupling plate, a second Rectangular metal coupling sheet, the first step impedance pie slice loads the resonator, the second step impedance pie slice loads the resonator, the coupling window, and the entire filter structure is a symmetrical structure about the central plane of the coupling window. The invention not only realizes the cavity double-frequency filter with controllable center frequency, but also realizes the characteristic of large frequency ratio between the center frequencies of two passbands. At the same time, the bandwidth of the two passbands can be independently controlled within a certain range, and the small size, high power capacity, and simple design and processing are all beneficial effects of the filter, which can meet the design requirements of small dual-frequency communication systems , can be used in mobile communication, radar, satellite and other microwave electronic systems.

Description

A Coaxial Cavity Dual-band Filter with Controllable Bandwidth and Large Frequency Ratio

technical field

The invention relates to a cavity filter, in particular to a coaxial cavity dual-frequency filter with a large frequency ratio and controllable bandwidth.

Background technique

With the rapid development of wireless communications, spectrum resources are becoming increasingly scarce. In order to reduce communication costs and improve spectrum utilization, dual-frequency filters, as the most commonly used multi-frequency filters, have become a research hotspot because they can be compatible with two different standards of the key components of the dual-frequency communication system front-end. Due to the advantages of low insertion loss, high Q value (quality factor), high power capacity and high stability, coaxial cavity dual-frequency filters have been widely used in narrowband communications with high selectivity, especially in coaxial cavity Filter-based radio frequency filters are still one of the key equipment in mobile communication base stations, satellite communication systems and military communication systems.

In 2015, Chen Fuchang's research team proposed a method to design a coaxial dual-frequency filter using a dual-mode resonant cavity with step impedance at IEEE MWCL. In this filter, the coaxial inner conductor adopts a step impedance structure, and the resonant frequency of the third mode and the fundamental mode of the resonator is controlled by its electrical length and impedance ratio (the frequency ratio is 2), and a spiral feed structure and a hybrid Electromagnetic coupling structure, Figure 1 is the frequency response diagram of the filter. This method can increase the range of the passband center frequency ratio, but only the step impedance coaxial resonator can achieve a limited frequency ratio, and it is difficult to realize the independent control and adjustment of the two passband bandwidths. Therefore, the current difficulty in the research of cavity dual-band filters is: how to realize a cavity dual-band filter with a large frequency ratio while ensuring that the two passband bandwidths are controllable within a certain range.

The pie slice loading technology of step impedance is derived from the research of planar dual-frequency filter based on the inventor's previous work, and the double-mode resonance characteristic with a frequency ratio of more than 4 can be realized by using a short-circuit step impedance resonator (SLQSIR) loaded with stubs. The equivalent circuit analysis of the resonator shows that the resonant frequency of the third mode is determined by θ ₃ and θ _4. After determining the resonant frequency of the third mode, the resonant frequency of the fundamental mode can be independently determined by θ _op , so the two modes are independently controllable. However, it is difficult for the filters in the prior art to realize a large frequency ratio under the condition that both passband bandwidths are controllable within a certain range.

Contents of the invention

The technical problem to be solved by the present invention is to provide a dual-frequency broadband filter with a compact structure, small size, low cost, high Q value, high power capacity, and a large frequency ratio coaxial cavity. device.

The technical solution adopted by the present invention to solve the technical problem is to construct a dual-frequency filter with a large frequency ratio coaxial cavity with controllable bandwidth, including: a first coaxial cavity, a second coaxial cavity, an input port, an output port, The first rectangular metal coupling piece, the second rectangular metal coupling piece, the first step impedance pie piece loads the resonator, the second step impedance pie piece loads the resonator, and the coupling window; the bandwidth controllable large frequency ratio coaxial The cavity double-frequency filter is symmetrical about the central plane of the coupling window; the first coaxial cavity and the second coaxial cavity are hollow cubes; the input port sends the input signal to the first rectangular Metal coupling sheet; the output port receives the output signal transmitted by the second rectangular metal coupling sheet; the first rectangular metal coupling sheet and the second rectangular metal coupling sheet are large frequency with controllable bandwidth Compared with the feed structure of the coaxial cavity dual-frequency filter, it is used to control the Q value of the two passbands; the first step impedance pie slice loading resonator and the second step impedance pie slice loading resonator are the described The resonant structure of the bandwidth-controllable large-frequency-ratio coaxial cavity dual-frequency filter is used to generate the fundamental mode and the third-order mode forming two passbands; the coupling window is the bandwidth-controllable large-frequency-ratio coaxial cavity The coupling structure of the dual-band filter is used to control the K value of the two passbands.

In the bandwidth-controllable large-frequency-ratio coaxial-cavity dual-frequency filter of the present invention, the first rectangular metal coupling piece and the second rectangular metal coupling piece are respectively connected to the input The port is connected to the output port, the positions of the upper ends of the first rectangular metal coupling piece and the second rectangular metal coupling piece control the low-frequency passband Q value generated by the fundamental mode, and the first rectangular metal coupling piece and the The position of the lower end of the second rectangular metal coupling piece controls the Q value of the high-frequency passband generated by the third-order mode.

In the bandwidth-controllable large-frequency-ratio coaxial-cavity dual-band filter described in the present invention, the first step impedance pie-slice loaded resonator and the second step impedance pie-slice loaded resonator are composed of A thick metal solid cylinder, a loaded metal pie piece and a fine metal solid cylinder are connected in series, one end of the thick metal solid cylinder is an open end, and one end of the fine metal solid cylinder is welded to the first same The center of the bottom surface of the axial cavity and the second coaxial cavity.

In the bandwidth-controllable large frequency ratio coaxial cavity dual-frequency filter of the present invention, the coupling window includes an upper window, a middle window and a lower window, the upper window provides electrical coupling, and the lower window provides magnetic coupling, The middle window independently controls the electrical coupling between the metal pie pieces.

In the bandwidth controllable coaxial cavity dual frequency filter with large frequency ratio according to the present invention, the first coaxial cavity and the second coaxial cavity are both surrounded by six metal surfaces.

The filter of the invention not only realizes a cavity double-frequency filter with controllable center frequency, but also realizes a large frequency ratio characteristic between the center frequencies of two passbands. At the same time, the bandwidth of the two passbands can be independently controlled within a certain range, and the small size, high power capacity, and simple design and processing are all beneficial effects of the filter. In short, the filter can meet the requirements of small dual-band The design requirements of the communication system can be applied to microwave electronic systems such as mobile communication, radar, and satellite.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

Fig. 1 is the frequency response diagram of the dual-mode resonant cavity design coaxial dual-band filter using step impedance in the literature;

Fig. 2 is a 3-dimensional view of the structure of a coaxial cavity dual-frequency filter with a controllable bandwidth and a large frequency ratio proposed according to the present invention;

Fig. 3 is a side view of the structure of a coaxial cavity dual frequency filter with controllable bandwidth and large frequency ratio proposed according to the present invention;

Fig. 4 is the input end feed structure of the filter that the present invention proposes---rectangular metal coupling sheet;

Fig. 5 is the resonant structure of the filter that the present invention proposes---the first step impedance cake loads the resonator;

Fig. 6 is the coupling structure of the filter that the present invention proposes---three-window coupling window;

Fig. 7 is the changing diagram of the first two resonant modes of the pie slice loaded resonator with step impedance as the radius r of the pie slice is changed;

Fig. 8 is a change diagram of the frequency response of the filter proposed by the present invention as the length T1 of the lower end of the rectangular metal coupling piece changes;

FIG. 9 is a graph showing the simulation results of the transmission response of the filter proposed according to the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

In order to realize a large frequency ratio cavity dual-frequency filter with controllable bandwidth, the present invention realizes a large frequency ratio coaxial dual-frequency filter with controllable bandwidth by adopting the pie slice loading technology of step impedance. The specific design principles are as follows :

1. Dual-band implementation principle

The structural diagram of the double frequency filter with a large frequency ratio cavity with controllable bandwidth proposed by the present invention is shown in Figure 2-3, Figure 4 is the feed structure, Figure 5 is the pie slice loaded resonator with step impedance, and Figure 6 is coupling structure. The first two modes of the resonator are loaded by the pie slice of the step impedance (the first resonance mode is the fundamental mode, and the second mode is the third mode) to achieve dual-frequency characteristics, because the pie slice loading point is open in the coaxial conductor Therefore, the size of the pie piece only affects the resonance frequency of the fundamental mode but not the resonance frequency of the third mode.

2. The realization principle of large frequency ratio.

The reason why the dual-frequency filter can achieve a large frequency ratio is that the resonant frequencies of the first two resonant modes of the step impedance pie slice loaded resonator have a large frequency ratio. The principle is: 1. The high impedance end of the step impedance resonator is at the short-circuit end, and the frequency ratio increases; 2. The pie piece loading structure is equivalent to a planar branch loading structure, and the frequency ratio can be further increased with the increase of its radius , as shown in Figure 7, as the radius r of the loaded pie piece increases, the resonant frequency of the fundamental mode of the resonator decreases continuously, while the resonant frequency of the third mode remains basically unchanged. Under the combined effect of these two structures, the dual-frequency filter proposed by the present invention has a large frequency ratio characteristic, and at the same time, the size of the loaded cake can independently control the center frequency of the low-frequency passband.

3. Implementation principle of bandwidth controllable

Not only the center frequencies of the two passbands of the dual-band filter are controllable, but also the bandwidth can be realized through the feed structure and the coupling structure. As shown in Figure 6, the feeding structure is realized by a rectangular metal coupling piece. Because the electric field distribution of the fundamental mode and the third-order mode are different, the electric field distribution of the fundamental mode is the strongest at the open end of the resonator, and the electric field is weaker near the pie piece, so the rectangular The position of the upper end of the metal coupling sheet mainly controls the Q value (Q1) of the low-frequency passband generated by the fundamental mode. The electric field distribution of the third mode is stronger near the cake, so the position of the lower end of the rectangular metal coupling piece mainly controls the high-frequency passband Q value (Q2) generated by the third mode. As shown in FIG. 8 , with the increase of the length T1 of the lower end of the rectangular metal coupling piece, Q1 in the low-frequency passband basically remains unchanged, while Q2 in the high-frequency passband changes greatly. Therefore, the Q value (Q2) of the high frequency passband can be independently controlled by T1. The K value of the two passbands is determined by the coupling window between the two resonators. As shown in Figure 7, the coupling window adopts a 3-window structure, in which the upper window provides electrical coupling, and the lower window provides magnetic coupling. Control the K value of the two passbands, and the middle window independently controls the electrical coupling between the pie slices. Since the electric field of the pie slice only affects the fundamental mode and not the third mode, the middle window can independently control the low frequency passband achieved by the fundamental mode K value. Therefore, when designing the K value, first realize the K value (K2) of the high-frequency passband through the electrical coupling and magnetic coupling of the upper and lower windows, and the size of the middle window is used to adjust the K value (K1) of the low-frequency passband.

The purpose of the present invention is to overcome the deficiency of the prior art—it is difficult to realize a cavity dual-frequency filter with a large frequency ratio under the condition that both passband bandwidths are controllable within a certain range. By adopting the pie slice loading technology of step impedance, a compact structure, small size, low cost, high Q value, high power capacity, bandwidth controllable and large frequency ratio coaxial cavity dual-band broadband filter are proposed. The filter can meet the design requirements of miniaturization and high power capacity, and can be applied to microwave electronic systems such as base stations, radars, and remote sensing in mobile communications. In order to achieve the above purpose, the technical solution provided by the present invention is: adopt the step impedance pie slice loading technology to realize the step impedance pie slice loading resonator, and use the rectangular metal coupling plate and the 3-window structure to realize the bandwidth controllable feed structures and coupled structures.

The present invention will be further described below in conjunction with specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, and are not intended to limit the present invention.

In order to clearly describe the present invention, Fig. 2-3 is the three-dimensional view and the side view of the present invention respectively, a kind of bandwidth controllable large frequency ratio coaxial cavity dual-band filter, comprising: a first coaxial cavity 1, a second coaxial cavity Shaft cavity 2, input port 3, output port 4, first rectangular metal coupling piece 5, second rectangular metal coupling piece 6, first step impedance pie slice loading resonator 7, second step impedance pie slice loading resonator 8. Coupling window 9.

Both the first coaxial cavity 1 and the second coaxial cavity 2 are hollow cubes surrounded by six metal surfaces, the first coaxial cavity 1 and the second coaxial cavity 2 have a metal surface coplanar as a coupling window 9, The input port 3 and the output port 4 are respectively opened on the input side of the first coaxial cavity 1 and the output side of the second coaxial cavity 2, and the first step impedance pie slice loads the resonator 7 and the second step impedance pie slice The loading resonator 8 is respectively welded at the center of the bottom surface of the first coaxial cavity 1 and the center of the bottom surface of the second coaxial cavity 2 .

Further, the input port 3 and the output port 4 are respectively connected to the first rectangular metal coupling piece 5 and the second rectangular metal coupling piece 6 through the interface inner conductor extension line. The position of the upper end of the rectangular metal coupling piece mainly controls the low-frequency passband Q value (Q1) generated by the fundamental mode, while the position of the lower end of the rectangular metal coupling piece mainly controls the high-frequency passband Q value (Q2) generated by the third-order mode, as shown in Figure 4 It is the feed structure for the input end of the filter—a rectangular metal coupling sheet 5b, which is connected to the input port 3 through the interface internal conductor extension line 5a.

Further, the first step impedance pie slice loaded resonator 7 and the second step impedance pie slice loaded resonator 8 are also symmetrical structures. Fig. 5 is the structural diagram of the first step impedance pie slice loading resonator, which is formed by a thick metal solid cylinder 7a, a loaded metal pie slice 7b, and a fine metal solid cylinder 7c connected in series, and the upper end of the thick metal solid cylinder 7a It is an open-circuit end, and the lower end of the thin metal solid cylinder is welded to the center of the bottom surface of the first coaxial cavity 1. Under the combined action of the two structures of step impedance and cake loading, not only the center frequencies of the two passbands are controllable, Moreover, the large frequency ratio characteristic of the dual-frequency filter is realized.

Further, the coupling window 9 is a three-window structure. Figure 7 is a structural diagram of a three-window coupling window. The upper window 8a provides electrical coupling, and the lower window 8c provides magnetic coupling. The upper and lower windows jointly control the K values of the two passbands, while the middle window 8b independently controls the electrical coupling between the pie slices. , since the electric field of the pie piece only affects the fundamental mode and does not affect the third-order mode, the middle window 8b can independently control the K value of the low-frequency passband realized by the fundamental mode, so when designing the K value, firstly through the electrical coupling and The magnetic coupling achieves the K value (K2) for the high frequency passband, while the medium window size is used to adjust the K value (K1) for the low frequency passband.

According to the above implementation manner, the size of the cavity in this embodiment is 12mm in length, 12mm in width and 40mm in height. The filter is made of metal, aluminum in this embodiment, and is plated with silver on the surface to reduce losses. The transmission response simulation results of the bandwidth-controllable large-frequency-ratio coaxial-cavity dual-frequency filter are shown in Fig. 9 . The low-frequency passband center frequency of the filter is 1.2GHz, the passband bandwidth is 30MHz, the high-frequency passband center frequency is 5.8GHz, the passband bandwidth is 60MHz, the center frequency ratio of the two passbands is 4.83, and the two passbands The in-band return loss S ₁₁ is lower than 20dB.

The bandwidth-controllable large-frequency-ratio coaxial-cavity dual-frequency filter of the embodiment of the present invention has two controllable center frequencies and bandwidth-controllable dual-passband characteristics, a large passband center frequency ratio, and a small The size can meet the design requirements of a small dual-frequency communication system, and it can be applied to microwave electronic systems such as mobile communication, radar, and remote sensing, and is worthy of promotion. The present invention includes but is not limited to the embodiments given above. Under the concept of the present invention, those skilled in the art can make different deformations and replacements without departing from the principle of the present invention, such as changing the coupling window into other shapes (double windows, four windows), change the coupling position of the feeder, change the cubic coaxial cavity to other shapes, use other metals for processing or electroplating, these deformations and replacements also belong to the protection scope of this patent.

Although the present invention is described through specific embodiments, those skilled in the art should understand that various changes and equivalent substitutions can be made to the present invention without departing from the scope of the present invention. In addition, various modifications may be made to the invention for a particular situation or material without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but should include all implementations falling within the scope of the appended claims.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (5)

1. A bandwidth controllable large frequency ratio coaxial cavity dual frequency filter is characterized in that it comprises: a first coaxial cavity, a second coaxial cavity, an input port, an output port, a first rectangular metal coupling sheet, The second rectangular metal coupling sheet, the first step impedance pie slice loads the resonator, the second step impedance pie slice loads the resonator, and the coupling window; the bandwidth-controllable large-frequency-ratio coaxial cavity dual-frequency filter is about all The central plane of the coupling window is symmetrical; the first coaxial cavity and the second coaxial cavity are hollow cubes; the input port sends the input signal to the first rectangular metal coupling piece; the output The port receives the output signal transmitted by the second rectangular metal coupling piece; the first rectangular metal coupling piece and the second rectangular metal coupling piece are dual-frequency filters for the bandwidth-controllable large frequency ratio coaxial cavity The feeding structure of the device is used to control the Q value of the two passbands; the first step impedance pie slice loading resonator and the second step impedance pie slice loading resonator are the large frequency ratio of the bandwidth controllable The resonant structure of the coaxial cavity dual-frequency filter is used to generate the fundamental mode and the third mode that form two passbands; the coupling window is the coupling structure of the coaxial cavity dual-frequency filter with a large frequency ratio and controllable bandwidth , used to control the K value of the two passbands. 2. The bandwidth-controllable large frequency ratio coaxial cavity dual-band filter according to claim 1, characterized in that, the first rectangular metal coupling piece and the second rectangular metal coupling piece are extended through the inner conductor of the interface Lines are respectively connected to the input port and the output port, the positions of the upper ends of the first rectangular metal coupling piece and the second rectangular metal coupling piece control the low-frequency passband Q value generated by the fundamental mode, and the first rectangular metal coupling piece The position of a rectangular metal coupling piece and the lower end of the second rectangular metal coupling piece controls the Q value of the high-frequency passband generated by the third-order mode. 3. The bandwidth controllable large frequency ratio coaxial cavity dual frequency filter according to claim 1, characterized in that, the first step impedance pie slice loads the resonator and the second step impedance pie slice The loaded resonator is composed of a thick metal solid cylinder, a loaded metal cake and a fine metal solid cylinder in series, one end of the thick metal solid cylinder is an open end, and one end of the thin metal solid cylinder is welded At the center of the bottom surfaces of the first coaxial cavity and the second coaxial cavity. 4. The large frequency ratio coaxial cavity dual frequency filter with controllable bandwidth according to claim 3 is characterized in that, the coupling window comprises an upper window, a middle window and a lower window, and the upper window provides electrical coupling, The lower window provides magnetic coupling, and the middle window independently controls the electrical coupling between the metal pie pieces. 5. The bandwidth-controllable large-frequency-ratio coaxial-cavity dual-band filter according to claim 1, characterized in that, the first coaxial cavity and the second coaxial cavity are surrounded by six metal surfaces .