CN204834812U - Cavity filter - Google Patents

Abstract

The utility model relates to a filter. The utility model discloses a cavity filter, which is composed of a closed cavity and resonant rods arranged transversely therein. One end of the resonant rod is open and the other end is connected with the cavity. There is a distance between the resonant rods. Signals are transmitted through spatial coupling, and a capacitive loading plate with an area larger than the cross-sectional area of the resonating rod is installed at the open end of the resonating rod, and the lateral dimension of the capacitive loading plate is less than or equal to the lateral dimension of the resonating rod. In the cavity filter of the utility model, the capacitive loading plate does not affect the arrangement of the resonant rods, greatly increases the flexibility of the cavity filter design, can reduce the distance between the resonant rods, and realizes the dense arrangement of the resonant rods, which is beneficial Increase the bandwidth of the filter. The further improved solution of the utility model can further optimize the structure of the cavity filter by adopting the wire cutting process, and improve the processing accuracy and reliability of the cavity filter. The utility model is particularly suitable for making high-order cavity filters.

Description

A cavity filter

technical field

The utility model relates to a filter, in particular to a cavity filter.

Background technique

The filter is an important part of the modern communication system. The important characteristic of the filter is to let the useful signal pass through the filter without attenuation, and the attenuation of the unwanted signal is the largest when passing through the filter. The cavity filter is a filter mainly used in the microwave frequency band. Its transmission theory is based on the strip transmission line, and the transmission characteristics are mainly determined by the structural parameters of the cavity filter. It has the characteristics of simple structure, excellent performance and convenient debugging.

Figures 1 to 5 show a schematic structural view of a 6th-order cavity filter, in which Figure 1 is a sectional view of the cavity filter, Figure 2 is a top view of Figure 1 with the cover plate 11 removed, Figure 3 is a perspective view of the resonant rod, and Figure 4 It is a structural schematic diagram of the resonant rod 20 and the capacitive loading plate 21, and FIG. 5 is an equivalent circuit diagram. The cavity filter is composed of a cavity and a resonant rod made of conductive material (usually a metal material, such as copper, aluminum, etc.), and the cavity is a regular hexahedron structure. For the convenience of processing, the cavity is generally composed of two parts, a rectangular box 10 and a cover plate 11, and a regular hexahedral structure is formed by welding and other processes, as shown in Figure 1. Six resonant rods are arranged in a row along the transverse central axis of the rectangular box 10. One end of the resonant rods is open and the other end is connected to the cavity. The distance between them is d1-d5, as shown in FIG. 1 . The spacing can be equal or not, and it can be set according to different needs. In a common cavity filter with a symmetrical structure, the spacing between the resonant rods is d1=d5, d2=d4, that is, the resonant rods are arranged symmetrically with the longitudinal central axis of the cavity, which can optimize the passband characteristics. In the cavity filter, signals are transmitted between the resonating rods through spatial coupling, the resonant frequency of the resonating rod is mainly determined by the length b and diameter a of the resonating rod 20, and the cavity structure size is related to other parameters of the filter. The equivalent circuit of this cavity filter is shown in Figure 5. The length of the resonant rod is approximately equal to 1/4 of the wavelength corresponding to the center frequency of the filter. The resonant rod 20 is equivalent to an inductance L, and its open end is equivalent to a capacitor C. A resonant rod is equivalent to an LC parallel resonant circuit, as shown in Figure 5. The larger the length b of the resonant rod 20 is, the larger the equivalent inductance L is, and the larger the diameter a of the resonant rod 20 is, the larger the equivalent capacitance C is. Each resonant rod transmits signals through parallel coupling to form a bandpass filter. The parallel coupling between the resonant rods is equivalent to capacitance Ct, and the first and last two resonant rods (resonant rod 1 and resonant rod 6) respectively constitute the input and output ports of the filter, and transmit signals through the connected signal lines. According to the LC resonance theory, when the useful signal passes through the filter, the LC generates parallel resonance, the impedance to the ground is the largest, and the signal is directly output from the other end; when the useless signal passes through the filter, the LC does not generate parallel resonance, the impedance to the ground is small, and the signal is large Partially to the ground, the signal attenuation is very large. In this way, the purpose of selecting useful signals and attenuating useless signals is achieved. Since the length of the resonant rod 20 is about 1/4 of the wavelength corresponding to the center frequency, it basically determines the size of the cavity filter. Therefore, when the operating frequency of the filter is low, the length b of each resonant rod becomes large, resulting in a larger volume of the entire filter. In order to solve this problem, there are many methods, among which capacitive loading is an important one. The so-called capacitive loading is to increase the capacitive effect at the open end of the resonant rod so that its length is less than 1/4 wavelength. At present, the commonly used method is to increase the area of the open circuit end of the resonant rod. According to the theory of parallel plate capacitors, the increase in the facing area increases the capacitance. According to the resonant frequency formula As the capacitance C increases, the inductance can be reduced, so the length of the resonant rod is reduced, thereby reducing the size of the filter. Usually, at the open-circuit end of the resonant rod 20, a capacitive loading plate 21 made of metal material with a diameter Φ larger than the diameter a of the resonant rod 20 is installed to increase the value of the resonant capacitor C, as shown in FIG. 4 . The problem brought about by this design scheme is that the presence of the capacitive loading plate 21 increases the distance between the resonant rods 20 , resulting in weakened coupling and reduced filter bandwidth, making it impossible to realize a broadband filter.

Utility model content

The technical problem to be solved by the utility model is to provide a cavity filter, which enhances the coupling between the resonant rods and realizes the broadband filtering effect.

The utility model solves the above-mentioned technical problem, and adopts the technical scheme that a cavity filter is composed of a closed cavity and resonant rods arranged horizontally in it, one end of the resonant rod is open and the other end is connected with the cavity , there is a distance between the resonant rods, and the signal is transmitted through space coupling. The open end of the resonant rod is installed with a capacitive loading plate with an area larger than the cross-sectional area of the resonating rod. size.

The technical solution of the utility model improves the shape of the capacitive loading plate. Under the condition of ensuring a sufficient area, the lateral dimension of the capacitive loading plate is limited within the transverse dimension of the resonant rod, and its edge does not exceed the lateral dimension of the resonant rod, so that The capacitive loading plate does not affect the spacing of the resonant rods, and the spacing between the resonant rods can be set as required, which increases the flexibility of filter design.

The lateral dimension of the capacitive loading plate=the lateral dimension of the resonant rod.

This technical solution makes full use of the lateral width of the resonant rod to design the area of the capacitive loading plate, which is beneficial to further optimize the spatial arrangement and shape of the filter.

Further, the capacitive loading plate is rectangular.

The rectangular capacitive loading plate is adopted, which has the characteristics of simple shape and easy processing. As long as the lateral width of the capacitive loading plate does not exceed the transverse dimension of the resonant rod, it will not affect the arrangement of the resonant rod, and its area size can be adjusted through its longitudinal dimension.

Further, the section of the resonant rod is rectangular.

The resonant rod with a rectangular structure is easy to process by wire cutting technology to ensure the dimensional accuracy of the resonant rod, which is of great significance to the cavity filter whose electrical parameters are determined by the structural size.

Furthermore, the resonant rod and the cavity are an integrated structure.

Due to the use of the resonant rod with a rectangular structure, it not only creates the conditions for improving the machining accuracy, but also lays the foundation for manufacturing the filter integrating the resonant rod and the cavity through the wire cutting process. The filter with this structure can be processed by precise wire cutting technology to make a filter with an integrated structure of the resonant rod and the cavity, which not only ensures the dimensional accuracy of the filter, but also compares with the existing technology that connects the resonant rod by screws. Product comparison adds to the stability and reliability of the filter structure.

The beneficial effect of the utility model is that the capacitive loading plate does not affect the arrangement of the resonant rods, greatly increases the flexibility of cavity filter design, can reduce the distance between the resonant rods, realizes the dense arrangement of the resonant rods, and is beneficial to improve The bandwidth of the filter. The further improved solution of the utility model can further optimize the structure of the cavity filter by adopting the wire cutting process, and improve the processing accuracy and reliability of the cavity filter.

Description of drawings

Fig. 1 is a sectional view of a prior art cavity filter;

Fig. 2 is a top view of Fig. 1 with the cover plate removed;

Fig. 3 is a perspective view of a prior art resonant rod;

Fig. 4 is a structural schematic diagram of a resonant rod and a capacitive loading plate;

Fig. 5 is an equivalent circuit diagram of the cavity filter shown in Fig. 1;

Fig. 6 is a sectional view of the cavity filter of Embodiment 1;

Figure 7 is a top view of Figure 6 with the cover plate removed;

Fig. 8 is a schematic structural diagram of a resonant rod and a capacitive loading plate in Embodiment 1;

Fig. 9 is a sectional view of the cavity filter of Embodiment 2;

Fig. 10 is a top view of Fig. 9 with the cover plate removed;

Fig. 11 is a perspective view of the resonance rod of Embodiment 2;

Fig. 12 is a schematic structural diagram of a resonant rod and a capacitive loading plate in Embodiment 2.

In the figure: 10 is a rectangular box; 11 is a cover plate; 20 is a resonant rod; 21 is a capacitive loading plate; a is the diameter of the resonant rod; b is the length of the resonant rod; C is the equivalent capacitance; L is the equivalent inductance; Ct is Coupling capacitance; d1~d5 is the distance between the resonant rods; Φ is the diameter of the capacitive loading plate; j is the transverse width of the resonant rod; k is the longitudinal length of the resonant rod; m is the transverse width of the capacitive loading plate; n is the longitudinal length of the capacitive loading plate .

Detailed ways

The technical solution of the utility model is described in detail below in conjunction with the accompanying drawings and embodiments.

Example 1

The structure of the cavity filter in this example is shown in Fig. 6 to Fig. 8, which consists of a closed cavity and resonant rods arranged horizontally in it. In this example, the cavity is composed of a rectangular box 10 made of metal copper and a cover plate 11. The resonant rod 20 is a cylindrical copper column, one end is open and the other end is connected with the cavity by screws, as shown in FIG. 6 . There is a distance between the resonant rods 20, and signals are transmitted through spatial coupling. A capacitive loading plate 21 is installed at the open circuit end of the resonating rod 20. The capacitive loading plate 21 is a rectangular capacitive loading plate, and its lateral dimension m is equal to the diameter a of the resonating rod 20, and its area is m×n greater than the cross-sectional area of the resonating rod π (a /2) ² . It can be seen from FIG. 7 that as long as the longitudinal dimension n of the capacitive loading plate 21 is not smaller than the diameter a of the resonating rod 20, the area of the capacitive loading plate can be ensured to be larger than the cross-sectional area of the resonating rod, and the length of the resonating rod 20 can be reduced. The area of the capacitive loading plate 21 can be adjusted by changing the longitudinal dimension n, so as to reduce the length of the resonant rod 20 and meet the requirements of different vibration frequencies. In this example, the capacitive loading plate will not affect the arrangement of the resonant rods, which can realize the close arrangement of the resonant rods, shorten the distance between the resonant rods, strengthen the coupling, and increase the bandwidth. Of course, the structure of the cavity filter in this example is also conducive to reducing the lateral size of the cavity, or realizing dense arrangement of resonant rods in a cavity with the same lateral size, and increasing the order of the filter.

Example 2

As shown in Figures 9 to 12, the structure of the cavity filter cavity of this example is the same as that of Example 1, and is also composed of a copper rectangular box 10 and a cover plate 11. The difference is that the section of the resonant rod 20 of this example is rectangular. , whose lateral dimension i is equal to the lateral dimension m of the capacitively loaded plate 21, as shown in FIG. 10 and FIG. 12 . The cavity filter of this example adopts the resonant rod 20 with a rectangular structure, which not only creates conditions for improving the machining accuracy, but also lays the foundation for manufacturing a filter integrating the resonant rod and the cavity through the wire cutting process. The cavity filter in this example can be processed by precise wire cutting technology to make a filter with an integrated structure of the resonant rod and the cavity, as shown in Figure 9, which can not only ensure the dimensional accuracy of the filter, but also increase the filter The stability and reliability of the device structure.

Claims (5)

1. A cavity filter, consisting of a closed cavity and resonant rods arranged transversely therein, one end of the resonant rod is open and the other end is connected to the cavity, there is a distance between the resonant rods, through space coupling For signal transmission, a capacitive loading plate with an area larger than the cross-sectional area of the resonating rod is installed at the open end of the resonating rod, and it is characterized in that the lateral dimension of the capacitive loading plate is less than or equal to the lateral dimension of the resonating rod. 2 . The cavity filter according to claim 1 , wherein the transverse dimension of the capacitive loading plate=the transverse dimension of the resonant rod. 3 . 3 . The cavity filter according to claim 1 , wherein the capacitive loading plate is rectangular. 4 . 4. A cavity filter according to claim 1, 2 or 3, characterized in that the section of the resonant rod is rectangular. 5 . The cavity filter according to claim 4 , wherein the resonant rod and the cavity are of an integrated structure. 5 .